Raptors - a Field Guide to Surveys and Monitoring (Second Edition 2009)

“People studying raptors should find this book indispensable…”

Professor Ian Newton FRS

Raptors

a Field Guide for Surveys and Monitoring

a Field Guide FOR Surveys and Monitoring

Written and edited by a team from the Scottish Raptor Monitoring Group, the book draws on the knowledge and experience of more than 300 raptor specialists, in particular members of the Raptor Study Groups. It has been funded by Scottish Natural Heritage, with assistance from the other Statutory Nature Conservation Agencies in Britain and Ireland and from voluntary conservation bodies concerned with birds of prey. There are growing demands for high quality information on the numbers, distribution and population trends of these fascinating birds. This book aims to promote best practice for fieldwork, and should provide an excellent starting point for anyone beginning a raptor study.

raptors

This is the second edition of the highly successful field guide to methods for surveying and monitoring raptors. Incorporating new information and feedback from raptor experts on the first edition, the book covers all birds of prey (diurnal raptors and owls) which occur regularly in Britain and Ireland. Photographic guides to raptor feathers and the growth of raptor chicks are important additions, which fieldworkers will find invaluable.

Jon Hardey Humphrey Crick Chris Wernham Helen Riley Brian Etheridge Des Thompson

Price £18.99

Jon Hardey Humphrey Crick Chris Wernham Helen Riley Brian Etheridge Des Thompson

Raptors:

a field guide for surveys and monitoring Second edition

Jon Hardey Humphrey Crick Chris Wernham Helen Riley Brian Etheridge Des Thompson

THE STATIONERY OFFICE: EDINBURGH

This book is dedicated to the memory of: Derek Ratcliffe (1929 – 2005) Pioneer of systematic surveys of raptors, Derek was a good friend and mentor to many people who have studied these birds. Through his work on pesticides and protected areas, Derek was a leader of the statutory nature conservation movement in Britain during the 1970s and 1980s. He published classic books on the peregrine, the raven and upland birds. © Scottish Natural Heritage 2009 First published in 2006 by The Stationery Office Limited 20 Rutland Square, Edinburgh EH1 2BW Reprinted March 2007 Reprinted September 2007 Second edition September 2009 Applications for reproduction should be made to Scottish Natural Heritage, Great Glen House, Leachkin Road, Inverness IV3 8NW British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library ISBN 978 0 11 497345 2

“This excellent manual will facilitate the standardisation of research techniques and ensure that the collection of data meets the highest possible standards – not just in Britain and Ireland, but across Europe, where the subject matter is equally relevant.”

Ibis, July 2007 “The publishers deserve to be congratulated on creating a thoroughly useful publication...if you’d like to see more raptors and understand their lifestyles, you should buy it.”

Birdwatch, July 2007

The cover image of a white-tailed eagle in flight captures the energy, power and grace of a raptor. The ongoing reintroduction of this species to Britain is a significant conservation success story that relies heavily on robust survey and monitoring work, and cooperation between countries. Photo: Laurie Campbell.

We are delighted to be able to reproduce two paintings by the late Donald Watson, taken from his book, The Hen Harrier, published in 1977. These comprise a male and female hen harrier in forest breeding habitat (frontispiece) and a pair about to engage in a food pass (the CD cover and label). Donald inspired people through his evocative landscape paintings and bird illustrations, and his writing. The paintings are reproduced with kind permission of T & A D Poyser, A&C Black and the Watson family.

Contents Foreword by Ian Newton Preface Acknowledgements The authors Editorial note

ix x xi xiii xiv

Part 1 Introduction 1. Introduction

1.1

1.2

1

2

Why monitor raptors? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 The development of raptor monitoring in Britain and Ireland . . . . . . . . . . . 2

1.2.1 Raptor Study Groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.2.2 The UK Raptor Working Group . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.2.3 The Scottish Raptor Monitoring Scheme . . . . . . . . . . . . . . . . . . . . . 5

1.3

International perspectives on raptor monitoring . . . . . . . . . . . . . . . . . . . . 6

1.4

The status of raptors in Britain and Ireland . . . . . . . . . . . . . . . . . . . . . . . . 6

1.5

A survey and monitoring guide for raptors . . . . . . . . . . . . . . . . . . . . . . . . 7

2. Survey, surveillance and monitoring

10

2.1

Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

2.2

Choice of survey methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2.2.1 Counts of occupied home ranges and active nests . . . . . . . . . . . . . 11

2.2.2 Alternative survey methods: transects and point counts . . . . . . . . . 12

Surveys and monitoring in Britain and Ireland . . . . . . . . . . . . . . . . . . . . . 14

2.3

3. Population estimates

16

3.1

Population sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

3.2

Breeding birds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

3.2.1 Occupied sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

3.2.2 Territorial pairs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

3.2.3 Breeding pairs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Non-breeding birds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17

3.3

4. Breeding season parameters

19

4.1

Home range and territory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

4.2

Nest sites, nesting ranges and alternatives . . . . . . . . . . . . . . . . . . . . . . . . 19 Raptors: a field guide for surveys and monitoring

v

4.3

Nests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

4.4

Occupancy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

4.5

Proof of breeding, breeding success and fledging . . . . . . . . . . . . . . . . . . 21

4.6

Productivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

4.7 Breeding failure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

4.7.1 Natural reasons for non-breeding or failure . . . . . . . . . . . . . . . . . 22

4.7.2 Persecution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

5. Identification and breeding behaviour of raptors

5.1

5.2

24

Identification of raptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Identifying raptor signs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

5.2.1 Kills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

5.2.2 Pellets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

5.2.3 Droppings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

5.2.4 Feathers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Breeding behaviour of raptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

5.3

5.3.1 Display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26

5.3.2 Egg laying and incubation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

5.3.3 Hunting and feeding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

5.3.4 Interpretation of behaviour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Vocalisations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

5.4

6. Additional techniques for studying raptors

29

6.1

Ringing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

6.2

Wing-tagging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

6.3

Remote tracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

6.3.1 Radio-tracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

6.3.2 Satellite tracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

6.3.3 PIT tags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

6.4

Biological and chemical ‘markers’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

6.4.1 Genetic markers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

6.4.2 Chemical markers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Nomograms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

6.5

6.5.1 Egg density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

6.5.2 Chick growth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

Nest boxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

6.6

7. Good practice for fieldwork

7.1

39

Legal considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 7.1.1 Licences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

7.1.2 Access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Minimising disturbance and good field craft . . . . . . . . . . . . . . . . . . . . . . 44

7.2

vi Raptors: a field guide for surveys and monitoring

7.3 Weather . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

7.4 Time of day . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

7.5 Frequency of site visits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

7.6 Observer effort . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

7.7 Recording observations and site features . . . . . . . . . . . . . . . . . . . . . . . . . 46

7.7.1 Recording sightings of birds, nests or other signs . . . . . . . . . . . . . 47

7.7.2 Recording details of survey visits . . . . . . . . . . . . . . . . . . . . . . . . . .49

7.8 Handling and measuring eggs and young . . . . . . . . . . . . . . . . . . . . . . . . 50

7.8.1 Wing length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

7.8.2 Tarsus (leg) length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

7.8.3 Tarsus width and depth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

7.8.4 Foot span and hind claw . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

7.8.5 Bill (culmen) and total head length . . . . . . . . . . . . . . . . . . . . . . . . 54

7.8.6 Mass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

7.8.7 Measuring and weighing eggs . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

7.8.8 Other measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

7.9 Wildlife crime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

7.9.1 Site confidentiality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

7.10 Health and safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

7.10.1 Diseases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

7.10.2 Health and safety legislation and responsibilities . . . . . . . . . . . . 62

Part 2 Species Accounts

65

Introduction to species accounts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

Honey-buzzard (European honey buzzard) Pernis apivorus . . . . . . . . . . . . . . . . . 70

Red kite Milvus milvus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

White-tailed eagle Haliaeetus albicilla . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85

Marsh harrier (western marsh harrier) Circus aeruginosus . . . . . . . . . . . . . . . . . . 92

Hen harrier (northern harrier) Circus cyaneus . . . . . . . . . . . . . . . . . . . . . . . . . . 100

Montagu’s harrier Circus pygargus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110

Goshawk (northern goshawk) Accipiter gentilis . . . . . . . . . . . . . . . . . . . . . . . . 117

Sparrowhawk (Eurasian sparrowhawk) Accipiter nisus . . . . . . . . . . . . . . . . . . . 127

Buzzard (common buzzard) Buteo buteo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136

Golden eagle Aquila chrysaetos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143

Osprey (western osprey) Pandion haliaetus . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150

Kestrel (common kestrel) Falco tinnunculus . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157

Merlin Falco columbarius . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165

Hobby (Eurasian hobby) Falco subbuteo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176

Peregrine (peregrine falcon) Falco peregrinus . . . . . . . . . . . . . . . . . . . . . . . . . . 184

Barn owl (western barn owl) Tyto alba . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191

Snowy owl Bubo scandiacus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .199

Little owl Athene noctua . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204 Raptors: a field guide for surveys and monitoring

vii

Tawny owl Strix aluco . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209

Long-eared owl Asio otus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .217

Short-eared owl Asio flammeus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223

Raven (northern raven) Corvus corax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232

Species occurring irregularly in Britain and Ireland . . . . . . . . . . . . . . . . . . . . . . 239

Black kite Milvus migrans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239 Pallid harrier Circus macrourus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239 Rough-legged buzzard Buteo lagopus . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239 Gyr falcon (gyrfalcon) Falco rusticolus . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240 Eagle owl (Eurasian eagle-owl) Bubo bubo . . . . . . . . . . . . . . . . . . . . . . . . 240

Part 3 Feathers

243

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244

Wing and tail feathers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244

Feather morphology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244

Moult . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245

Introduction to the feather plates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247

Identification of species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247

Plates 1–57 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250–278

Part 4 The development of raptor chicks

281

Plates 58–80 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283–292

Appendices

294

1 Status and trends of raptors in Britain and Ireland . . . . . . . . . . . . . . . . . . . . 294

2 Contacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294

3 Examples of raptor recording forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305

4 Scientific names of species mentioned in the text . . . . . . . . . . . . . . . . . . . . . 321

Glossary References Index

323 329 363

In addition to illustrations at the beginning of each species account, the following illustrations are embedded in the text: short-eared owl (page 1), white-tailed eagle (9), honey-buzzards (15), kestrel (18), hen harrier (23), sparrowhawk (38), goshawk (65), marsh harrier (243), tawny owl (275) and peregrine chicks (281).

viii Raptors: a field guide for surveys and monitoring

Foreword It is a pleasure to write a foreword for this second edition so soon after the first edition was published and then reprinted. The demand for this book is a measure of its value to raptor researchers.

Birds of prey have, from time immemorial, fired the human imagination. Over the ages they have been symbolised, even deified. But in 19th century Britain, they were ruthlessly destroyed in the interests of game management, and in the middle of the 20th century some species suffered further massive declines following the introduction of organochlorine pesticides in agriculture. In recent years, however, with increased legal protection, reduced use of organochlorines, and active conservation management, some raptor species have recovered from low population levels. Nevertheless, given the complex range of factors currently influencing raptors, including changes in land management and climate, continuing persecution and declining prey populations, there is a great need for accurate information on numbers, distributions and population changes of these spectacular birds.

Many raptors are elusive, and for birdwatchers, catching fleeting glimpses of the birds themselves, or finding their pellets, plucked prey remains or moulted feathers, has long added to the excitement of days in the field. For scientists, raptors provide the challenge of understanding variation in numbers – either from region to region or from year to year – and the complexities of relationships between predators, prey and habitat.

This book provides in-depth descriptions of field techniques for breeding season surveys of all the diurnal and nocturnal birds of prey which nest regularly in the British Isles. It is based on the collective knowledge and experience of scores of raptor enthusiasts who have learned their field craft over many years. Since the early 1980s, the Raptor Study Groups, now with a membership of more than 300 volunteer specialists organised into regional groups, have played a vital role in collecting data on raptors in Britain and Ireland. These groups have also provided a forum for the exchange of information and ideas about survey techniques, and have been key to the development of national surveys of a growing number of species. It is pleasing to know that so much of that experience is reflected in this book.

As well as this remarkable wealth of personal field experience, the book draws on published and unpublished data and information, and identifies gaps in knowledge. Written and edited by a team of ecologists and raptor specialists, the book is aimed at people with an interest in surveying and monitoring raptors for scientific and conservation purposes. I believe this manual will interest both seasoned as well as less-experienced raptor fieldworkers, and should be invaluable to raptor enthusiasts throughout Europe and beyond.

The present state of our knowledge of these birds is a credit to the many dedicated fieldworkers who have accumulated the necessary information through years of hard physical effort and painstaking observation. People studying raptors should find this book indispensable, and might wish to reflect on the fact that the equivalent of many lifetimes of field experience have been tapped for its production.

Professor Ian Newton OBE, FRS, FRSE Monks Wood July 2009 Raptors: a field guide for surveys and monitoring 

ix

Preface ‘If I were to give my own ideas free play, I would arrive at a present population for the birds of prey in Europe amounting to 1% of the number still to be found in Europe 150 years ago’.

With this quote attributed to Professor Karel Voous in 1965, Maarten Bijleveld began his book on Birds of Prey in Europe (1974). More than forty years on, populations of some species have increased and the percentage is now higher, perhaps nearer 5%. Indeed, if we fast forward to the publication of Birdlife International’s (2004) Birds in Europe: population estimates, trends and conservation status, we find global statistics and detailed population estimates for raptors in more than 40 European countries. Clearly, there has been a sustained and intensive effort to survey and monitor birds of prey, and steadily our knowledge of these birds and the factors influencing them has improved (e.g. Brown 1976; Newton, 1979; Thompson et al., 2003; Whitfield et al., 2008a).

Raptors: a field guide for surveys and monitoring is borne out of our wish to provide robust estimates of population sizes and early means of detecting changes in raptor populations.

We are delighted that the first edition was so well received. While it is only three years since the book was first published, it has already been reprinted several times. Rather than reprint again, we have seized the opportunity to revise the book in order to incorporate feedback from surveyors, correspondents and book reviewers. For this second edition the text has been substantially revised and updated, and significantly we have added major photographic guides to the identification of raptor feathers and the development of raptor chicks. The accompanying CD of raptor calls was well received in the first edition, and we retain it here.

The guide is for fieldworkers - naturalists, scientists, birdwatchers, ecological contractors, land managers and landowners – to help people record, interpret and report the results of field observations. We are anxious to continue receiving feedback. In future editions we will seek to include more information on assessments of the condition of nestlings, the behaviour and range use of raptors in the non-breeding season, methods for monitoring the numbers and movements of juvenile and non-breeding birds, and molecular techniques for population sampling.

No field guide, no matter how detailed, can ever be a substitute for knowledge and skills developed in the field over time. We strongly advise anyone beginning a study of a raptor to seek advice and guidance from someone with direct experience of the bird. In Britain and Ireland, members of Raptor Study Groups can offer this knowledge and experience for a range of raptor species, and some may be able to provide opportunities to participate in fieldwork alongside an experienced mentor.

Above all else, we urge you to watch birds of prey and enjoy the experience. These birds collectively provide one of the best barometers of the health of our environment, and for millions of people symbolise the majesty, wildness, power, grace and freedom of nature.

x Raptors: a field guide for surveys and monitoring

Acknowledgements More than one hundred people have contributed directly to this field guide. We thank the following for contributions, comments, suggestions and observations: Arjun Amar, Beatrice Arroyo, Graham Austin, Harry Bell, Stuart Benn, Rob Bijlsma, Gill Billsborough, Jez Blackburn, Jon Brain, Roger Broad, Keith Brockie, Terry Burke, John Burlison, Nigel Buxton, Ingvar Byrkjedal, John Calladine, Duncan Cameron, Ian Carter, Paul Castle, Anthony Chapman, John Chapman, Jacquie Clark, the late Roger Clarke, Liz Coiffait, Ian Collins, Brian Cosnette, Jim Craib, Tony Cross, Peter Cush, Peter Davies, Martin Davison, Cliff Dawson, Roy Dennis, Dave Dick, R.C. Dickson, Andrew Dixon, Ron Downing, Steve Downing, Eddie Duthie, Mark Eaton, Simon Elliot, Ian Enlander, Richard Evans, Alan Fielding, Klaus Dietrich Fiuczynski, Francesco Germi, Paul Gill, Ricky Gladwell, Phil Glennie, Alex Goldau, Peter Gordon, Justin Grant, Mark Grantham, Jeremy Greenwood, Mike Gregory, Ray Hawley, Paul Haworth, the late Roger Hayward, Alan Heavisides, Björn Helander, Mark Holling, Hugh Insley, David Jardine, David Johnson, John Atle Kålås, Robert Kenward, Mick Lacey, Roy Leigh, Jerry Lewis, John Lusby, Liz McDonald, John Mackay, Mike Madders, Garry Marchant, Mike Marchant, Mick Marquiss, John Massie, Wendy Mattingley, Eric Meek, Anthony Messenger, John Milburne, Jane Milloy, Neil Morrison, Steve Moyes, Graham Neville, Ian Newton, Mike Nicol, David Norriss, Aonghus O Domhnaill, Duncan Orr-Ewing, Lorcán Ó Toole, Sandy Payne, Steve Petty, Dave Pierce, Ian Poxton, Colvyn Quaggin, David Ramsden, David Raw, Graham Rebecca, Steve Redpath, Chris Redfern, Gordon Riddle, Steve Roberts, Paul Robertson, Chris Rollie, Martin Roome, Ben Ross, Marc Ruddock, Geoff Sample, Andrew Sandeman, Don Scott, Richard Selman, Chris Sharpe, Geoff Shaw, Geoff Sheppard, Mike Shrubb, Innes Sim, George D. Smith, Andrew Stevenson, Alan Stewart, Patrick Stirling-Aird, Peter Sunde, Bob Swann, Larry Toale, Mike Toms, John Underhill-Day, Dave Walker, Chris Watson, Graeme Watson, the late Jeff Watson, Jim Wells, Sian Whitehead, Phil Whitfield, Derek Whitton, Andy Wilson and John Young. Many of these people have worked with us in drafting texts for the species accounts.

We are delighted to be able to include a section on feather identification and we thank Marian Cie´slak and Bolesław Dul for permission to reproduce material from, Feathers: identification for bird conservation, from the Natura Publishing House (2006), and Marian Cie´slak for supplying excellent photographs of raptor feathers. Brian Cosnette, Eddie Duthie, Ron Downing, Mike Groves, Mark Hamblin, R.B.M. Hendreicks, David Jardine, Lorcán Ó Toole and an anonymous photographer kindly provided photographs to illustrate the arrangement of raptor feathers and the development of raptor chicks. We thank Lorna Hardey, Jane Milloy, and Steve Roberts for their vignettes and the Royal Society for the Protection of Birds (RSPB) for donating illustrations by John Busby, Mike Langman and Dan Powell. We are grateful to Rob Bijlsma for permission to use data from his 1997 and 1999 publications (see reference list) to produce growth curves for nestlings of a number of raptor species, and to the authors and publishers credited throughout the book for granting us permission to reproduce figures.

We thank Nial Smith for the concept for the new cover design and Laurie Campbell for the cover photograph.

Geoff Sample has produced an excellent compilation of raptor calls to accompany the book; we thank Cheryl Tipp and Stuart Reading for help in sourcing calls, and the British Library Sound Archive, the BBC Natural History Library and the sound recordists listed on the CD cover for permission to reproduce recordings.

We thank Professor Ian Newton for writing the Foreword, and for his encouragement of raptor fieldworkers; his passion for fieldwork and lucid writing is inspirational. We are grateful to Raptors: a field guide for surveys and monitoring

xi

our colleagues for their support, and in particular we would like to mention those who have worked closely with us within the Scottish Raptor Monitoring Group: Colin Galbraith, Nigel Buxton, Rhys Bullman, David Stroud, Patrick Stirling-Aird, Wendy Mattingley, Alan Heavisides, Jeremy Greenwood, Duncan Orr-Ewing, Jeremy Wilson, Arjun Amar, Mark Holling, Malcolm Ogilvie and Gordon Riddle. The publisher, TSO Scotland, has been meticulous as ever, and it is a pleasure to record our thanks to Ron Wilson, Shona Struthers, Karen Pope, Jane McNair, CĂŠcile Hascoet, Jon Dalrymple and colleagues for all their work. We appreciate the help with editing provided by Jo Newman, Maureen Scott, Joyce Garland, Marion Whitelaw and Lulu Stader, and additional support from Marian Brown, Maureen Macdonald, Catriona Hendrie and Ed Mackey.

We are most grateful to the following for financial contributions to the book: Scottish Natural Heritage; the British Trust for Ornithology; the Countryside Council for Wales; the Department of Agriculture, Fisheries and Forestry, Isle of Man; Natural England; the Northern Ireland Environment Agency; and RSPB (Scotland).

Finally, we must end on a note of sadness, for we really had hoped that Roger Clarke, Roger Hayward, Mike Madders, Derek Ratcliffe, Simon Thirgood, Jeff Watson and Donald Watson would still be with us to enjoy watching raptors. They were close friends and exceptional naturalists.

Des Thompson, Helen Riley, Chris Wernham, Humphrey Crick, Jon Hardey and Brian Etheridge September 2009

xii  Raptors: a field guide for surveys and monitoring

The authors Jon Hardey is Chairman of the North East Scotland Raptor Study Group, and a recognised expert on survey and monitoring of peregrines and moorland raptors. He works as a consultant ecologist with both developers and conservation organisations. Recent work has included environmental assessments of bird and mammal populations, habitat surveys for wind farms and other developments, research on peregrines, hen harriers and common gulls for Scottish Natural Heritage (SNH), and baseline surveys of montane breeding bird assemblages in the eastern Grampians. He is currently researching the breeding performance of peregrines in northeast Scotland at Aberdeen University.

Dr Humphrey Crick is a member of the Chief Scientist’s team at Natural England, working as a specialist on climate change. Previously he spent many years at the British Trust for Ornithology (BTO) where he led the raptor research programme, analysing Nest Record Cards and leading national surveys of peregrine in 1991 and 2002, and barn owl in 1995-97. He was a member of the Rare Breeding Birds Panel from 1995-2008 and worked hard to develop coordinated raptor monitoring in the UK, including the Scottish Raptor Monitoring Scheme.

Dr Chris Wernham is Head of the BTO, Scotland. With a background in population ecology, she was formerly the Senior Population Biologist for ringing-based research at the BTO, and the lead editor of its Migration Atlas project. In her current position, she has a remit to develop the BTO’s monitoring of birds in Scotland, both in terms of the design and support of scientific programmes, and also the continued recruitment of volunteer surveyors. She is the BTO’s principal representative on the Scottish Raptor Monitoring Group and has a keen interest in raptors and upland birds.

Dr Helen Riley has been involved in a wide range of national and international bird conservation issues while working with the Nature Conservancy Council (NCC), the Joint Nature Conservation Committee (JNCC), SNH and the Secretariat for the international Agreement on the Conservation of Albatrosses and Petrels. She has experience of field surveys of a range of bird species and has been closely involved with the development of the Scottish Raptor Monitoring Scheme and programmes of research on upland raptors in Scotland. She now works as an ecological consultant.

Brian Etheridge has studied breeding raptors in the Highlands for the past 30 years and, with the exception of snowy owl, has visited the nests of all of the raptor species listed in this book. His long-term studies in the past have involved sparrowhawks and buzzards, with honey-buzzards, red kites and hen harriers his current passion. Brian is employed as Raptor Monitoring Officer for the Scottish Raptor Monitoring Scheme and by RSPB Scotland as Red Kite Project Officer, based in their Inverness office.

Professor Des Thompson was founder chair of the Scottish Raptor Monitoring Scheme and is a Policy and Advice Manager in SNH. This is his twelfth book; others include the team efforts, Birds of Prey in a Changing Environment (2003), Alpine Biodiversity in Europe (2003), and The Nature of the Cairngorms: diversity in a changing environment (2006). As chair of the JNCC Uplands Lead Coordination Network, he has had particular responsibility for developing UK guidance on habitat monitoring under the EC Birds and Habitats directives.

A longstanding friend and colleague of the late Derek Ratcliffe, he enjoys watching raptors, though confesses to a particular affection for waders.

Raptors: a field guide for surveys and monitoring

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Editorial note The taxonomy of bird species referred to in this book follows that used by the British Ornithologists’ Union (BOU) for the latest published version of the British list (Dudley et al., 2006). Raptor species names follow the vernacular British names recommended by the BOU (www.bou.org.uk/recbrlstbni.html). Noting that the BOU has adopted the International Ornithological Congress’ (IOC) recommendations for English bird names at the international level, we give IOC names for individual species, where different to the vernacular name, in brackets in the contents list and after the first mention in each species account; The IOC names are taken from Gill et al. (2009). Vernacular and IOC bird names are also included in Appendix 4.

All website addresses cited in this book have been checked and are correct at the time of publication. As a matter of principle, however, such addresses are given for information only and are not viewed as a formal source of published information.

xiv Raptors: a field guide for surveys and monitoring

Part 1

Introduction Raptors: a field guide for surveys and monitoring 

1

1. INTRODUCTION ‘The results, which became available by the end of 1962, were totally unexpected, showing that the peregrine population was declining at a headlong rate and was already reduced to a low level in the southern half of Britain.’

Derek Ratcliffe (1980). The Peregrine Falcon. Poyser, Calton.

1.1 Why Monitor Raptors?

The description of field methods for use in surveys and monitoring of raptor populations is the focus of this book. Surveys involve the collection of data on numbers, distribution and breeding success. By drawing these data together, over years and indeed decades, we can monitor changes over time. If we can draw on information relating to the population ecology of raptors as well as environmental data, we can begin to identify the causes of change.

Raptor conservation is the primary purpose of such monitoring, with the aim of identifying species which may be in need of conservation action and to help support the legal obligations of governments.

National and international laws to protect wildlife and habitats require assessments of the conservation status of birds of prey (as well as other animal and plant species). Such monitoring has historically focused on rare or threatened species, but there are increasing moves to expand monitoring to commoner species, for example as indicators of environmental quality and biodiversity (e.g. Anon, 2007; Gregory et al., 2003).

Besides conservation, there are other good reasons to monitor raptors (Movalli et al., 2008). As top predators, raptors are often the first species to be affected by a range of environmental pressures, such as changes in habitat availability or quality, prey populations, pollutants and human disturbance. Raptors can provide a cost-effective and sensitive means of detecting environmental change, as was so successfully demonstrated through pioneering research on the response of birds of prey to organochlorines in the environment (a matter we return to below). Today, the UK Predatory Bird Monitoring Scheme continues to monitor the concentrations of pesticides in some species of birds of prey (Walker et al., 2008). The scheme aims to identify and quantify chemical threats to vertebrate wildlife so that mitigation measures can be employed, and to assess the success of such measures.

Illegally shot or poisoned raptors are largely the product of perceived competition for resources (such as gamebirds and livestock) between some people and birds of prey (e.g. Newton, 1979; Anon., 2002; Marquiss et al., 2003). The Royal Society for the Protection of Birds (RSPB) has a long-established monitoring programme for wildlife persecution incidents and results are published annually (e.g. RSPB, 2007a & b). In Scotland, the RSPB is now working with the Scottish Rural Property and Business Association (SRPBA) to develop a database of persecution incidents for raptors and other wildlife. Monitoring of persecution provides information on the success of measures to resolve conflicts between people and wildlife (e.g. Galbraith et al., 2003; Redpath et al., 2004). In the UK, the broad pattern in lowland areas is of increased tolerance or active support for birds of prey, but in some upland areas raptor numbers are still depressed or some species entirely absent because of continuing illegal persecution (RSPB, 2007b; Natural England, 2008; Whitfield et al., 2008a).

2 Raptors: a field guide for surveys and monitoring

1.2 The development of raptor monitoring in Britain and Ireland The first peregrine survey of Great Britain, organised by Derek Ratcliffe for the British Trust for Ornithology (BTO) in 1961 and 1962, marked the advent of systematic monitoring of birds of prey in Britain. It revealed a huge decline in peregrine numbers and led to the discovery of the toxic effects of organochlorine pesticides (Ratcliffe, 1963, 1970, 1993). The work proved, to both statutory (government) and voluntary conservation bodies, the value of mass participation surveys by a partnership of professional and volunteer ornithologists.

It also demonstrated the value of collaboration and cooperation between the hitherto rather independent raptor enthusiasts who were gathering large amounts of invaluable information throughout Britain. The bigger picture that emerged from the consolidation of their efforts was vital in demonstrating to government and the agrochemical industries the harmful environmental effects of organochlorine pesticides. This work led to the phased withdrawal of these compounds, and the recovery of the peregrine – a totemic conservation success story (Crick & Ratcliffe, 1995; Ratcliffe, 2003).

Early studies of other raptors, such as sparrowhawk, kestrel, barn owl and golden eagle, also showed the detrimental effects of persistent pollutants (Prestt, 1965). In 1963, the Institute for Terrestrial Ecology (ITE; now the Centre for Ecology & Hydrology, CEH) began a long-term programme of pollutant monitoring in raptors. This work, which continues today, depends upon the submission of carcasses from birdwatchers around the country (Cooke et al., 1982; Shore et al., 2002). The burgeoning interest in raptors and their population dynamics was spurred by the production of two important reviews. The first was the New Naturalist volume on Birds of Prey, by Leslie Brown (1976). Building on his lifetime involvement with raptors and raptor workers around the world, Brown described the natural history of British raptors, and revealed many gaps in knowledge. The second key publication was Ian Newton’s (1979) Population Ecology of Raptors, a ground-breaking review of factors affecting the abundance, distribution, survival and productivity of these birds, which set the scene for many subsequent population studies of birds of prey.

Many long-term studies of raptors were begun by ITE/CEH staff, notably of sparrowhawk (Newton, 1986) kestrel (Village, 1990), peregrine (Mearns & Newton, 1988), hen harrier (Picozzi, 1978) and buzzard (Picozzi & Weir, 1974). The RSPB began important studies of raptors in Scotland, notably of the osprey (Dennis, 1983, 1987), golden eagle (Dennis et al., 1984) and hen harrier (Bibby & Etheridge, 1993), and in Wales, on merlin (Bibby, 1986; Bibby & Nattrass, 1986). Staff in the Nature Conservancy Council (and its successor government agencies) made detailed studies of the peregrine (Ratcliffe, 1980, 1993), golden eagle (Watson, 1997), the white-tailed eagle (Love, 1983) and the red kite (Carter & Grice, 2000).

Increasingly, these studies have become collaborative, involving substantial cooperation between professional and volunteer bird watchers, giving rise to important books, research papers and reports.

1.2.1 Raptor Study Groups Studies of raptors in Britain and Ireland have long depended on the efforts of committed and enthusiastic individuals, giving unstintingly of their time and energy. In the 1980s, raptor fieldworkers began to form regional Raptor Study Groups. The impetus for the formation of the first groups, which took place in Scotland, was the coordination of surveys of golden eagle and peregrine, with the primary aim to avoid increased disturbance through multiple visits to the same raptor sites. Instead, sites were allocated to individuals, thereby keeping disturbance to a minimum, but also increasing the total coverage. As well as coordinating Raptors: a field guide for surveys and monitoring

3

survey coverage, the Raptor Study Groups provided a forum for the exchange of information and ideas about techniques, and they began to collect and collate valuable long-term datasets.

This led to the annual reporting of results, for example in the Raptor Round-up, published by the Scottish Ornithologists’ Club (SOC). The Raptor Study Groups, which have now expanded into England, Wales, Northern Ireland and the Republic of Ireland, have been key to the development of a programme of national surveys for a range of raptor species, achieving a remarkably high level of coverage.

Many of the long-term studies of raptors have also benefited from the wealth of expertise and experience existing within the Raptor Study Groups. Given the widely dispersed nature of raptors, it would have been impossible to cover the ground without voluntary help, and many of the enthusiasts were ringers who were able to add vital information on survival rates and movements of raptors (c. 1,000 adult raptors and 6,000 raptor chicks are ringed annually in Britain and Ireland; see raptor species accounts in Wernham et al., 2002). Volunteer birdwatchers also contribute valuable information to monitoring schemes, such as the Nest Record Scheme run by the BTO (c. 2,000 raptor records received annually, Crick et al., 2003) and the breeding and wintering bird atlases (Sharrock, 1976; Lack, 1986; Gibbons et al., 1993).

With the exception of the Isle of Man, all of the areas covered by this field guide fall within the European Union. As a result of obligations under the 1979 Birds Directive (79/409/EEC), the first environmental legislation passed by the European Commission, the Statutory Nature Conservation Agencies in Britain and Ireland embarked on a programme of work to classify Special Protection Areas (SPAs) for birds (Way et al., 1993; Stroud et al., 2001). Identifying a network of important conservation areas for raptors was a challenging task and, here, information collected by the Raptor Study Groups proved essential (both in identifying statutory sites and supporting the conservation of populations in the wider countryside). As the British stronghold for most of the upland raptors, Scotland has classified a large number of SPAs for these birds. Sensitivities surrounding the selection of sites for controversial species, such as the hen harrier, have meant that Scottish Natural Heritage (SNH) has had to present very detailed scientific cases to support the boundaries of proposed SPAs. Detailed discussions between the Statutory Nature Conservation Agencies and the Raptor Study Groups arose from this work, and in combination with the report of the UK Raptor Working Group, consolidated a cooperative approach to fieldwork and data analyses.

1.2.2 The UK Raptor Working Group The recovery of some birds of prey populations and perceived conflicts, especially with gamebird and racing pigeon interests, led to the formation of the UK Raptor Working Group in the late 1990s (Anon., 2000). The group was jointly chaired by the (then) Department of the Environment, Transport and the Regions (DETR) and the Joint Nature Conservation Committee (JNCC), and had a wide-ranging membership, including Government Environment Departments, the Statutory Country Conservation Agencies (represented by the JNCC), representative bodies for sporting, landowning and pigeon-racing interests and voluntary conservation bodies with expert knowledge. The Raptor Study Groups were also represented, in recognition of their significant contribution to the monitoring and conservation of birds of prey.

A key element of the UK Raptor Working Group’s report (Anon., 2000) was a consideration of the abundance, distribution and population trends of raptors. The Group was impressed by the quantity and quality of available data on raptors, and recognised the essential contribution of volunteer raptor fieldworkers in gathering the data. Nevertheless, taking account of the controversies associated with raptors and the need for very precise information on their

4 Raptors: a field guide for surveys and monitoring

status, the Group’s recommendations included several that related to enhancements to the monitoring of the UK’s raptor populations.

To mark the publication of the UK Raptor Working Group’s report, a conference was held to draw together research on birds of prey in Britain and other parts of Europe. The organisers, SNH, the JNCC and the British Ornithologists’ Union, intended that the event would be a milestone. It was, and the ensuing publication (Thompson et al., 2003) demonstrated an impressive range and depth of studies, with many benefiting from the synergies of volunteerprofessional collaboration.

1.2.3 The Scottish Raptor Monitoring Scheme Some of the key recommendations in the final report of the UK Raptor Working Group concerned the development of improved monitoring and reporting on raptor populations.

SNH supported this in part because it needed detailed and accurate data on the location of raptor sightings and breeding attempts in order to designate, manage and monitor of Sites of Special Scientific Interest (SSSIs) and SPAs for birds of prey. SNH drew together the major contributors to raptor monitoring in Scotland to forge an agreement to form the Scottish Raptor Monitoring Scheme (SRMS; Anon., 2002; Wernham et al., 2008). The parties to the agreement were SNH, JNCC, the Scottish Raptor Study Groups (SRSG), BTO Scotland, the Rare Breeding Birds Panel (RBBP), RSPB Scotland, and the SOC. The formation of this Scottish Raptor Monitoring Group (SRMG) has been a significant step in the development of raptor monitoring, and provides a model for similar developments in other countries. The SRMS covers diurnal birds of prey and owls, as well as the raven because of its ecological similarity to raptors (Ratcliffe, 1997). The Scheme is working to three broad objectives, to: a) promote better cooperation between the various bodies responsible for gathering information on Scottish raptors; b) provide robust information on Scottish raptor populations, in order to determine trends in numbers, range, survival and productivity, and to understand the causes of population changes; and c) maintain high and uniform standards for the collection, collation, auditing and analysis of data, and reporting of information.

A Raptor Monitoring Officer is employed by the SRMG, responsible for liaising with the SRSG and other organisations and individuals involved in raptor survey in Scotland, with the aim of collecting and collating raptor data on an annual basis. During the first five years of the SRMS, 2003 – 2007, about 3,700 records have been submitted annually, covering 19 species which breed regularly in Scotland. Summaries of these data have been published so far in four annual reports (Etheridge, 2005; Etheridge et al., 2006, 2007, 2008). With five years of data available from 2007, reporting will be developed to provide quantitative trends in occupancy rates and productivity (Wernham et al., 2008). A list of the variables which contributors are asked to provide, and which are included in the SRMS reporting spreadsheet, is included in Appendix 3.

The Scheme has also made scientific input to research on factors limiting the golden eagle population in Scotland (Whitfield et al., 2008a) and is developing similar ‘Raptor Conservation Frameworks’ for peregrine (Humphreys et al., 2006) and hen harrier (Whitfield et al., 2006a).

Over the next five years the SRMS aims to better define existing coverage for all raptor species and enhance coverage for species which may be under-recorded (such as honey-buzzard) as Raptors: a field guide for surveys and monitoring

5

well as widespread species (Wernham et al., 2008). For some species, future aims will be met by developing links with other sources of raptor data, such as the Breeding Bird Survey.

This field guide, now in its second edition, originated from the SRMG, with the aim of setting down the standardised field survey methods which have been adopted for individual species over the last 50 or so years, and so that these methods can be consolidated by existing raptor workers and adopted by new fieldworkers.

1.3 International perspectives on raptor monitoring An extensive review of international monitoring of raptors is outside the scope of this book but two issues are worthy of note. The European Union has adopted an action plan, under the Biodiversity Convention, to meet commitments to significantly reduce the rate of biodiversity loss (EC, 2006). As sentinels of wider environmental health, monitoring of raptors is a key means of contributing to assessments of the success of this action plan (Movalli et al., 2008).

To this end, Kovács et al. (2008) provide a summary of current monitoring of raptor status and trends in Europe and consider how improvements could be made in terms of pan-European coordination of national initiatives to monitor the status and trends of raptors.

The governments of the United Kingdom and the United Arab Emirates have jointly led the development of an international agreement to help conserve migratory birds of prey and owls in the Africa-Eurasian region. This followed resolutions by the World Working Group on Birds of Prey and Owls, held in Budapest in 2003, and the Convention on Migratory Species in Nairobi in 2005, calling for action to tackle the threats faced by these birds. A study commissioned by the UK Government found that more than 50% of migratory raptors in the African-Eurasian region had an unfavourable conservation status, and many were considered to be undergoing rapid or long-term declines (Goriup & Tucker, 2005; Tucker & Goruip, 2005). After two international meetings (in Scotland and the United Arab Emirates) to explore options for international cooperation and to negotiate an agreement, a ‘Memorandum of Understanding (MOU) on the conservation of Migratory Birds of Prey in Africa and Eurasia’ entered into effect on 1 November 2008 (www.cms.int/species/raptors/index.htm).

Signatories to the MOU agree to adopt, implement and enforce measures to conserve birds of prey and their habitat. The MOU includes an action plan with the general aim of ensuring that all migratory birds of prey (diurnal raptors and owls) in the African-Eurasian region are maintained in, or returned to, favourable conservation status. This includes requirements to monitor populations of migratory raptors to establish reliable population trends.

These recent international developments mean it is all the more important to promote standardised and systematic methods for surveying and monitoring birds of prey.

1.4 The status of raptors in Britain and Ireland Many species of raptor in Britain and Ireland are recovering from low population levels in the first half of the 20th century, or earlier, in many cases because of a combination of human persecution and land use change (Newton, 1979; Thompson et al., 2003). Some species had been lost altogether, and their reintroductions to Britain and Ireland have been conservation ‘causes célèbres’. The white-tailed eagle, which became extinct in Britain in 1918, is now successfully re-established in the west of Scotland, following the release of a total of 140 young birds from Norway between 1975 and 1998 (Bainbridge et al., 2003); with a total of 36 territorial pairs recorded in 2006 (Etheridge et al., 2008). The red kite is another success story, with self-sustaining populations now established in many parts of Britain following reintroductions into Scotland and England, and the recovery of the once relict Welsh population

6 Raptors: a field guide for surveys and monitoring

(Carter et al., 2003). Ireland (including Northern Ireland and the Republic of Ireland) has the most restricted raptor assemblage of any region in Europe, having lost at least eight breeding species historically. In an effort to redress some of the losses, the Irish Raptor Study Group has been a major force behind the current reintroduction projects for golden eagles, white-tailed eagles and red kites in Ireland (www.goldeneagle.ie).

Populations of these birds, as well as the osprey, which famously returned to breed regularly in Scotland in 1954 (Dennis & McPhie, 2003), have been monitored annually since reintroduction or re-establishment. This work has concentrated on recording numbers, distribution, and productivity, providing an invaluable source of information on population growth.

The most recent estimates of breeding populations of raptors in the different countries of Britain and Ireland are given in Appendix 1 (Table A.1). Recent reviews by the UK Raptor Working Group (Anon., 2000), and Greenwood et al. (2003) have demonstrated the international importance of some of the raptor populations in Britain and Ireland, which together hold 5% or more of the European populations of hen harrier, sparrowhawk, golden eagle, kestrel, merlin, hobby, peregrine and short-eared owl (Appendix 1, Table A.2).

Current monitoring of raptors in Britain and Ireland involves a combination of professional fieldworkers, members of the Raptor Study Groups and other volunteer fieldworkers. Periodic national surveys are carried out for scarcer species such as hen harrier, golden eagle, merlin and peregrine. For these and some of the more abundant species, such as buzzard, sparrowhawk and kestrel, annual monitoring is also carried out by members of the Raptor Study Groups in their local areas, the total coverage for individual species varying with the number of raptor workers who choose to study that species. Other schemes also provide information on raptors. For example, the BTO/JNCC/RSPB Breeding Bird Survey (BBS; Risely et al., 2008) provides annual monitoring of population trends for some of the more abundant raptors (sparrowhawk, kestrel, buzzard and, less precisely, hobby).

1.5  A survey and monitoring guide for raptors In writing this field guide, we have sought to tap the expertise of voluntary and professional raptor workers, much of which was previously unpublished. Originally, it was intended to cover Scotland only, but in response to interest expressed by raptor workers further afield, the scope was expanded to cover Britain, Ireland and the Isle of Man. The resulting book has drawn on the great depth of experience which is found within the raptor fieldworker community throughout this area (and also some European experts), but in particular the members of the SRSG. More than one hundred experienced fieldworkers have contributed to drafts of the text.

Following a detailed introduction, species-specific sections give accounts of field methods for survey and monitoring. The introductory sections which follow consider briefly the definitions of survey and monitoring, and the selection of appropriate survey methods. Estimating the size of raptor breeding populations is especially important, and so is described in some detail. Standard definitions and guidance on measurement in the field are provided for count units, breeding success, productivity and breeding failure. A range of further techniques is described, including ringing and other forms of individual marking, remote tracking, and biological and chemical markers. General guidance is provided on the identification of raptors, including the signs which can reveal their presence (e.g. pellets, feathers, plucks and kills), and the types of behaviour (such as territorial displays and courtship feeding) that may aid the interpretation of field observations.

Good practices for fieldwork are described, ranging from taking chick measurements for the Raptors: a field guide for surveys and monitoring 

7

purposes of estimating age, to advice on recording observations and minimising disturbance.

In addition, information is provided on wildlife legislation and requirements for licences to visit nests and ring birds, accessing land for the purposes of survey work, and health and safety.

Throughout, details of further reference material are provided.

The species accounts give detailed guidance on field survey methods for 22 species of raptor (including the raven) that breed regularly in Britain and Ireland; shorter accounts are provided for five species that occur less regularly. The species covered include diurnal birds of prey (of taxonomic orders Falconiformes and Accipitriformes), owls (order Strigiformes), as well as the raven (order Passeriformes, family Corvidae). The accounts are based on the knowledge of experts on each of the species, acquired over many years of fieldwork, as well as the scientific literature. We hope that each account will form a useful starting point for anyone seeking to study that species.

Two final sections, new to the second edition, provide colour plates illustrating the wing and tail feathers for 23 species of raptor which occur in Britain and Ireland, and the growth of raptor chicks for six species. The feather plates are accompanied by an introduction to feathers and in particular their use in bird identification and raptor surveys. The plates of raptor chicks at different stages of development provide an illustration of the appearance of the nestlings of a range of species at different growth stages.

As a supplement to the species accounts, a CD of raptor calls is provided. This includes examples of the calls that are most relevant to fieldworkers carrying out raptor surveys, to aid in the identification of species and/or the interpretation of behaviour.

8  Raptors: a field guide for surveys and monitoring

Raptors: a field guide for surveys and monitoring 

9

2. SURVEY, SURVEILLANCE AND MONITORING 2.1 Definitions An ornithological survey involves making systematic observations of the numbers or distribution of a species or assemblage in an area. The aim may be to count the number of individuals or nests of a single bird species, or to record the presence or absence of one or more species in order to assess their distribution. Surveillance entails making such surveys at intervals of time, using comparable methods so that any changes taking place can be identified. Monitoring is the collection and analysis of repeated observations or measurements to evaluate change with respect to defined targets or the degree of deviation from an expected norm (Helawell, 1991; Elzinga et al., 2001). In the context of raptor monitoring, the ‘expected norm’ can be a previous estimate of the species’ population in the area that is being monitored.

A standard or target for monitoring may be that the population estimate remains within a given range of the previous estimate (e.g. within 25%). If a population declines below this limit then an ‘alert’ may be triggered and conservation-related actions initiated, for example research to investigate the cause of the decline. Thus, whereas surveys and surveillance are to a large extent open-ended, a monitoring programme requires a standard to be defined in advance (Hill et al., 2005). Monitoring leads to an investigation of the causes of population change, and the identification and implementation of management actions to address adverse trends (see Furness & Greenwood, 1993; Greenwood, 2000).

For wildlife monitoring, there are at least five particularly valuable elements which can be built into any programme:– 1. A large number of study plots is required to ensure that the results are generally applicable to the population that is being monitored. Data from a small number of study plots may be biased if the sample contains some atypical sites (see Section 3.1 on population sampling). Inclusion of many sites also allows for the analysis of population data and environmental variables in different locations.

2. Habitat information, gathered concurrently with the population information in a standardised manner, can be used to investigate relationships between distribution, population changes and environmental variables. Habitat information can also be obtained from maps, aerial photographs and satellite imagery, but that gathered along with observations of birds and/or nests is generally of a finer scale. Some habitat variables, such as vegetation height in the vicinity of the nests of a ground-nesting species, or the particular tree species used by a tree-nesting raptor, are more or less impossible to obtain from remotely mapped habitat data.

3. Annual monitoring is useful in allowing long-term trends to be distinguished from shortterm fluctuations, such as those which may result from adverse weather conditions. It also allows the investigation of correlations between populations and environmental variables over time.

4. Inclusion of several species in a monitoring programme allows comparisons of population change between species with differing ecologies. Including commoner species can ensure that sample sizes are large enough to detect significant widespread changes.

5. Monitoring all demographic processes (rates of reproduction, survival/mortality, and movement: immigration/emigration/dispersal) provides more insight than the surveillance of numbers alone (Baillie, 1991). The aim is to identify the parts of the life cycle of a species that are driving population changes. Further research can then be targeted more effectively towards investigating the factors behind the change. For example, if breeding

10 Raptors: a field guide for surveys and monitoring

numbers are falling and breeding success is shown to decline but no changes in survival (or mortality) rates are observed, then it is likely that the population decrease is being driven largely by the declining breeding success, and therefore factors that influence breeding success might be the focus of subsequent further investigations. If, conversely, it is the survival rates of adult birds that are falling, and driving the population decrease, then subsequent research may need to focus on different limiting factors, perhaps operating outside the breeding season (e.g. possibly in a remote wintering area).

An example of the insights that can be gained from demographic studies is provided by research on golden eagles in Scotland (Whitfield et al., 2003, 2004a & b, 2006b, 2008a).

Although numbers have remained stable overall since the first national survey in 1982 (Dennis et al., 1984; Green, 1996; Eaton et al., 2007), there have been declines in some areas and increases in others. Population modelling has indicated that persecution is responsible for an estimated 3-5% annual mortality in golden eagles, and in the absence of this mortality the Scottish population would increase (Whitfield et al., 2004b). Persecution (assessed by the incidence of records of the use of illegal poison) was found to be most common on grouse moors in eastern and central Scotland (Whitfield et al., 2003), and was associated with a reduction in the age of first breeding of golden eagles, territory vacancies, and the use of territories by non-breeding immatures. By reducing adult survival and creating vacant territories, persecution is thought to create ‘ecological traps’, attracting mobile immature eagles to areas of apparently suitable habitat where they in turn fall victim to illegal poisoning (Whitfield et al., 2004a).

Although the routine monitoring of numbers and demographic rates will rarely provide a full understanding of any adverse changes, it is important in identifying the investigations required to determine the causes of such changes. The survey techniques described in this book are designed to provide information on the size of raptor breeding populations and also (depending on the number and timing of visits, the accessibility of nests, and the sensitivity of a different species to disturbance) breeding success. Techniques for measuring survival, mortality, dispersal and immigration/emigration rates of raptors normally involve the monitoring of marked individuals (e.g. Summers et al., 2003) or the analysis of genetic or chemical markers from tissues such as feathers or blood samples. Such techniques are considered further in Section 6.

2.2 Choice of survey methods Birds of prey are generally found at low densities over extensive areas, and this influences the survey methods that are most appropriate for monitoring. In addition to the information and references given below, comprehensive sources of further information on survey techniques are provided by Fuller & Mosher (1987) and Bird & Bildstein (2007), which deal specifically with raptors; and Bibby et al. (2000) and Sutherland et al. (2004), which describe census techniques for birds.

2.2.1 Counts of occupied home ranges and active nests To date, surveys of breeding birds of prey in Britain and Ireland have focused largely on the detection of occupied home ranges and the location of active nests within a defined study area – an extensive survey method that has been described as a form of territory mapping (Bibby et al., 2000; Hill et al., 2005). Observers usually work on foot and attempt to cover the survey area evenly, so that all parts are observed. However, as raptors can range over very large areas, surveyors may focus on parts of a study area where the target species has been recorded breeding in the past. Surveys aim to locate all occupied home ranges and active nests within the study area. Fieldworkers tend to focus on one species because of the Raptors: a field guide for surveys and monitoring

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large size of home ranges, requirements for intensive observation, and differences in habitat preference, detectability and behaviour between raptor species. Recommendations for this type of survey form the main part of the accounts for each species in this field guide.

If a species is relatively rare or easy to locate, it may be possible to survey the entire breeding population. During the survey, all potential home ranges should be visited and occupancy established by applying a set of rigorous criteria (e.g. Marquiss et al., 1978; Newton et al., 1986; Watson et al., 1989). This approach has been used for golden eagles in Scotland (Green, 1996; Eaton et al., 2007).

For species that are more abundant, foot-searches to locate occupied home ranges and nests can also be used in population sampling surveys, for example for merlin in Britain (Rebecca & Bainbridge, 1998), and hen harrier in the UK and Isle of Man (Sim et al., 2001, 2007). These surveys allow the size of the entire breeding population to be estimated from coverage of a sample of areas within the breeding range, and statistical confidence limits to be placed on the estimates.

2.2.2 Alternative survey methods: transects and point counts These standardised counts offer an alternative approach to surveys that aim to detect all occupied ranges and nests within a survey area. Although not complete enough to measure or estimate absolute population size, such counts can provide a reliable ‘index’ of the changes in numbers of a species between years. The main approaches are described briefly below, and are highlighted in the individual species accounts for those species for which they might prove particularly appropriate in enhancing existing monitoring effort. These can be used to assess changes in the relative abundance of birds of prey in winter as well as during the breeding season, and can also give information on the habitats used for foraging.

Road Surveys Large scale transects can be made from motor vehicles (Millsap & LeFranc, 1988; Viñuela, 1997; Resources Inventory Committee, 2001; Leitao et al., 2001; Boano & Toffoli, 2002).

Road surveys are most appropriate for surveying large and obvious species in open habitats.

The observer notes all birds of prey seen in a known distance travelled over a recorded time.

The detectability of birds will vary with a number of factors, notably the species (size and behaviour), habitat, season, time of day and weather. Surveys might be designed either to coincide with the period of maximum detectability (if known or established by intensive observational study) or to be carried out over periods when detectability is less than maximal but relatively constant, so that the same methods can be repeated from one year to the next, providing a reliable index of change (but no indication of absolute numbers). Observations should be recorded on a map and each record should include the time of the observation and approximate distance and direction from the vehicle. Weather conditions should always be recorded. Road surveys have the advantage of covering large areas in search of widely dispersed species. Continuous surveys from vehicles are obviously not appropriate on busy roads, although approaches based on stopping and making observations from fixed vantage points along the survey route might still be suitable. Road surveys at night using spotlights have been used to survey grassland owls in California (Condon et al., 2005).

Transect surveys on foot These generally produce a lower encounter rate with raptors than road surveys, but have the advantage of allowing access to areas remote from roads. Observers should walk along a chosen route of predetermined length. Randomly selected routes are always preferable

12 Raptors: a field guide for surveys and monitoring

but, at the least, they should be representative of appropriate habitat(s) for the species under study. Observers should record the position of each bird of prey seen or heard and its approximate distance and direction from the transect line. The time taken to cover the route should also be recorded. In rugged terrain the survey technique may have to be modified (Dawson, 1981), and watches of a fixed duration (stand-watches) from vantage points may be more effective. In closed habitats, the fieldworker should stop at regular intervals and listen for raptors (Resources Inventory Committee, 2001).

Vantage point surveys (stand-watches) For these, fieldworkers should position themselves on appropriately selected vantage points and record all raptors observed and heard (Resources Inventory Committee, 2001). Vantage point surveys can be a useful supplement to other survey methods, including the detection of occupied home ranges and nests within a discrete study area. Vantage point surveys are therefore often recommended in the species accounts in this field guide, but only at certain stages of the annual cycle, for example, to detect territorial raptors early in the breeding season (e.g. for short-eared owl), and/or to locate nests (e.g. hen harrier). These surveys may also be used to count numbers of individual raptors entering or leaving a winter roost (e.g. red kite); for monitoring the abundance and flightlines of foraging raptors in an area (e.g. environmental impact assessments for windfarms: Whitfield et al., 2005; Madders & Whitfield, 2006; Band et al., 2007); or for counting the numbers of migratory raptors passing a given location. Vantage point surveys can be combined with transect surveys to provide a combined means of monitoring changes in raptor numbers over time (for further details of the general use of such ‘point counts’ in this context see Bibby et al., 2000).

Call playbacks These rely on responses by wild birds to the playback of recorded calls, and have considerable potential for surveying nocturnal birds of prey and woodland raptors (Forsman et al., 1977; Mosher et al., 1990; Redpath, 1994; Mosher & Fuller, 1996; Stewart et al., 1996; Bosakowski & Smith, 1998; Gosse & Montevecchi, 2001; Freeman et al., 2006). The observer should broadcast an amplified call from equally spaced points within the survey area, and then, using a compass, plot the direction of calls made in response. Such surveys should always be repeated more than once at any given location, avoiding adverse weather as this can affect both the audibility of calls and bird behaviour. Some species respond more than others, and within a species response rates can be influenced by age and sex, time of year and lunar cycle (Fuller & Mosher, 1987). If the aim of such surveys is to produce an estimate of absolute population size, then validation work to assess the proportion of birds which respond, and variation in the response rate, should be carried out. Of the raptors which occur in Britain and Ireland, this technique is considered to be particularly appropriate for tawny owl and goshawk, and further information is provided in the accounts for these species.

Aerial surveys Such surveys cover extensive areas, and have been used effectively for some of the larger raptors such as osprey (Henny et al., 1977), golden eagle (Boeker, 1974; McIntyre & Adams, 1999), bald eagle (Grier et al., 1981) and peregrine (White, 1975), including combined surveys of several species. Productivity can often be measured if the surveys are made when there are well-grown young in the nest. Surveys for large, conspicuous nests can also be conducted in winter, reducing disturbance during the breeding season (Resources Inventory Committee, 2001). The observers fly along set transects or grids, the optimal spacing of which depends on the spatial dispersion of the species (Krebs, 1999) and record observations of the target species. Surveys should be carried out at a minimum of 50 m above nest height, Raptors: a field guide for surveys and monitoring 

13

at a speed of 30–130 km per hour (Elliot et al., 1998; Bowman & Schempf, 1999). Ultralights (Looman et al., 1985) have been shown to be more cost-effective than helicopters or light planes in some circumstances.

2.3 Surveys and monitoring in Britain and Ireland In the UK, a regular programme of national surveys for scarce bird species has been established under the auspices of the Statutory Country Conservation Agencies and RSPB Annual Breeding Bird Scheme (SCARABBS). The SCARABBS programme currently includes several raptor species (including red kite, white-tailed eagle, osprey, marsh harrier, hen harrier, golden eagle, merlin, peregrine and barn owl), producing periodic estimates of the UK breeding population (e.g. Crick & Ratcliffe, 1995; Rebecca & Bainbridge, 1998; Wotton et al., 2002; Eaton et al., 2007; Sim et al., 2007). The general aim is to repeat national surveys of individual species every ten years, although, depending on their status, some species are surveyed more frequently and some less (e.g. due to concerns about the impact of illegal persecution in some areas of the UK, national surveys of hen harriers are carried out at 6 year intervals). Surveys are designed to be adapted to the particular habits and habitats of the species concerned. Thus, surveys of species such as merlin and hen harrier concentrate on known areas of population concentration but include elements of randomised survey-square selection to assess population status elsewhere, so that population change can be monitored and population size can be estimated in a repeatable manner.

The Rare Breeding Birds Panel (RBBP) plays a key role in the monitoring of the rarer UK raptors (honey-buzzard, red kite, white-tailed eagle, all harriers, northern goshawk, golden eagle, osprey, merlin, hobby and peregrine; Holling & RBBP, 2008). Since 1972, the Panel has collated information on the abundance and breeding performance of rare birds (generally those with populations of less than 300 pairs) as well as those listed on Schedule 1 of the Wildlife and Countryside Act 1981. The data are provided by Local Bird Recorders, Statutory Country Conservation Agencies, voluntary conservation bodies (especially RSPB and BTO) and by groups or individual volunteers, especially the Raptor Study Groups. A Rare Breeding Birds Panel has recently been established in the Republic of Ireland.

The Hawk and Owl Trust is primarily involved in raptor conservation measures in Britain and Ireland, but also undertakes some national survey and monitoring work, for example the national barn owl survey in 1982–85 (Shawyer, 1987), and, in collaboration with the BTO and Chris Rollie (for Scotland), the long-running hen harrier winter roost survey, begun in 1983 (Clarke & Watson, 1990, 1997).

Annual information on the relative abundance of some birds of prey in the UK is provided by the BTO/JNCC/RSPB Breeding Bird Survey (BBS), in which breeding bird populations are monitored in randomly selected 1 km squares across the UK (Risely et al., 2008; see www.bto.org/bbs).

Standardised transect counts are carried out each year in each square, providing reliable, unbiased information on population changes for the more common birds of prey, particularly for sparrowhawk, buzzard and kestrel. The BBS also provides information on changes in the abundance of important prey for raptors, such as meadow pipit, which can be used to help interpret changes in the numbers and breeding performance of raptors. In the Republic of Ireland, the Countryside Bird Survey (CBS), run by BirdWatch Ireland (www.birdwatchireland.ie), follows the same methods as BBS and is thus complementary.

Another key monitoring scheme for raptors in the UK is the BTO’s Nest Record Scheme, undertaken as part of the partnership between the BTO and the JNCC (on behalf of the UK

14 Raptors: a field guide for surveys and monitoring

Statutory Country Conservation Agencies, Crick et al., 2003). A network of 550–600 volunteer nest recorders and recording groups submit a total of approximately 30,000 records to the Nest Record Scheme each year. Each Nest Record Card (NRC) details the history of a single breeding attempt at an individual nest. Observers record species, county, year, place name, six figure grid reference, altitude, habitat and nest site details, dates of each visit, numbers of eggs or young, standardised codes to describe the development stage of nests, eggs, young, activity of the parents and the outcome of the nest (giving the cause of any failure if known).

Annual reports are published in BTO News (e.g. Leech & Barimore, 2008). A development of nest recording towards relative abundance monitoring is demonstrated by the BTO’s Barn Owl Monitoring Programme, started in 2000 (Leech et al., 2005). This monitors breeding performance and nest site occupancy as an index of relative abundance.

Substantial numbers of NRCs are received each year for many of the raptors breeding in the UK, including buzzard, kestrel, sparrowhawk, merlin, peregrine and the raven. The data made an important contribution to Brown’s (1976) review of British raptors, and have been used by authors of species monographs (e.g. Bunn et al., 1982 on barn owl; Clarke, 1996 on Montagu’s harrier; Scott, 1997 on long-eared owl). NRC data have also been used in studies of the effects of organochlorine pesticides and rodenticides (e.g. Cramp, 1963; Henderson et al., 1993; Newton, 1973, 1974) as well as in general analyses of raptor breeding biology and population dynamics (e.g. Crick, 1993 on merlin; Fiuczynski & Nethersole-Thompson, 1980 on hobby; Garner & Milne, 1997 on long-eared owl; Glue & Scott, 1980 on little owl; Grant et al., 1994 on barn owl; O’Connor, 1982 on kestrel; Percival, 1990 on barn and tawny owls; Tubbs, 1972 on buzzard) and investigating changes in laying dates of upland birds (including raptors) over time (Moss et al., 2005).

As described in Section 1.2.3, the Scottish Raptor Monitoring Scheme has recently begun to publish annual reports of raptor monitoring in Scotland (Etheridge, 2005; Etheridge et al., 2006, 2007, 2008).

Raptors: a field guide for surveys and monitoring

15

3. POPULATION ESTIMATES 3.1 Population sampling Raptor populations may be surveyed by covering the whole population (for species which are rare or relatively easy to locate) or by sampling a representative portion. In the latter case, extrapolations are made from the numbers recorded in sample areas to give an estimate for the size of the whole population. Ideally, a sampling strategy involves the randomised selection of defined areas for fieldwork. This avoids any bias arising from surveying only the ‘best’ areas (e.g. where birds may be most abundant) or the most accessible habitats or locations (such as those close to where most surveyors live). The sampling may need to be ‘stratified’ by habitat or region to ensure good coverage of all habitats and geographical areas. This involves randomised selection of study areas within specified habitats or regions. It is not always possible to achieve completely randomised samples in a survey design because of the need to incorporate established survey plots, for which valuable long-term survey data are available. Other issues such as the remoteness of some parts of a species’ range may also affect the feasibility of randomised sampling.

All study plots, whether randomly selected or selected by fieldworkers, have strictly defined boundaries within which fieldworkers attempt to survey the complete breeding population.

This allows the determination of trends through time without potential bias due to variation in observer effort. It also allows for the description or characterisation of plots, in terms of location, area and habitat(s) present, and of course, provides a basis for repeat visits in the future.

Studies based on non-randomised study plots need to be supplemented, at least periodically, with additional randomised surveys that aim to assess whether the breeding range of the population has changed (either contracted or expanded). This allows reassessment of the representativeness of the long-term study plots.

Birds of prey do not nest randomly but rather select locations that provide both secure nest sites and suitable foraging habitat. Knowledge of the requirements for individual species allows the areas to be surveyed within a given study plot to be delimited to some extent (e.g. woodland areas may be omitted from surveys for species which range over open country).

Experienced raptor fieldworkers (such as those from the Raptor Study Groups) often work the same areas over many years, accumulating detailed knowledge of the habitats used by birds of prey within their chosen study plot.

3.2 Breeding birds The survey methods that are the focus of this field guide involve the location of birds that are potentially breeding (occupied sites), and their nests (or other evidence of breeding) if they breed. The aims are to measure both the size of the breeding population and breeding performance or success. The latter is a key population parameter, as it determines potential overall productivity of fledged young. The accounts within this book suggest the minimum number and the timing of visits that are likely to be required to fulfil these aims effectively for each species. In general, one or more visits are required early in the breeding season to establish occupancy, and a minimum of one or two subsequent visits to establish breeding success or confirm that a site is not occupied or that breeding has not taken place.

The results of raptor surveys are generally reported as counts of numbers of ‘occupied’ sites or ranges, ‘territorial pairs’ or ‘breeding pairs’. Unfortunately there is no universally accepted definition of any of these terms but the following descriptions cover most of the current usage.

16 Raptors: a field guide for surveys and monitoring

3.2.1 Occupied sites Occupied sites or home ranges are those where a single bird or a pair of birds of the target species is recorded during the breeding season (usually sightings on more than one occasion) or where there is strong evidence from signs (e.g. moulted feathers, pellets, plucks) that birds are present. As well as those occupied by breeding pairs, occupied sites may include areas occupied by non-breeding pairs or single birds unable to secure a mate; hence numbers of occupied sites do not necessarily equate to the number of birds (or pairs) that breed or are capable of breeding in any given year.

3.2.2 Territorial pairs A territorial pair (or a single bird) is one that defends a territory against intrusions by other raptors of the same species and/or against potential predators. Defence of a territory during the breeding season can provide evidence of intention to breed.

3.2.3 Breeding pairs The results of surveys presented as numbers of ‘breeding pairs’ often refer to an estimate of the numbers of pairs that are capable of breeding in any given year, rather than pairs that are actually confirmed as laying eggs in that year. Criteria for identifying breeding pairs may be variously defined to include pairs that defend a nesting territory in the spring (equivalent to territorial pairs as described above); pairs that display or where a male is seen to provide food to a female; pairs that repair or build a nest or prepare a nest scrape; pairs (or a single bird) observed sitting on a nest; or pairs that lay at least one egg. Depending on the intensity of survey, reported figures for ‘breeding pairs’ may include sites that are known to be occupied by pairs of birds (some but not all of which are confirmed to lay eggs in that year) and also a correction to include some home ranges where only single birds were seen but whose partners may have been missed during the survey (e.g. Banks et al., 2003 for peregrine; Eaton et al., 2007 for golden eagle). Some birds of prey do not always breed as monogamous pairs, for example harriers that may be polygynous (one male mated to two or more females). For such species, breeding populations may be reported in terms of the number of breeding females.

Because of the lack of standard criteria for identifying the count units for breeding birds of prey, it is important that the criteria used to derive population estimates in a particular study are clearly recorded with the stored data and are included with any data reported to monitoring schemes or written up for reports and scientific papers. The species accounts in this field guide describe the observational criteria that can be used to assess the presence of occupied sites and breeding pairs for each raptor species. Fieldworkers are also encouraged to consult books and scientific papers reporting survey results for their target species (many of which are referenced in the species accounts) to see how breeding numbers have been reported elsewhere.

3.3 Non-breeding birds Non-breeding birds include some that occupy home ranges but fail to lay eggs, and some that do not occupy home ranges at all. Individual birds falling into the first category will be recorded during surveys for occupied sites. Birds are generally recorded as non-breeders if a single bird only is recorded at a given locality in a particular year, or a pair of birds is recorded but no evidence of laying is found. In both situations there is generally some uncertainty attached to defining the number of non-breeding individuals unless very frequent visits are made. The second bird of a non-breeding pair may not be seen during the small number of visits that are generally made, due to a lesser attachment to the nest site, and it can be Raptors: a field guide for surveys and monitoring

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difficult to separate pairs that do not lay from those that do lay but fail soon after laying.

These problems are exacerbated still further for species that are relatively more cryptic in behaviour or the nests of which are difficult to observe directly (such as the nocturnal owls).

Non-breeding individuals that do not occupy home ranges at all are monitored only rarely because of the difficulty in making systematic observations of this component of the population. This is unfortunate because ‘floating’ populations of non-breeding birds may be important in buffering breeding populations of many raptor species from short-term fluctuations (Kenward et al., 2000; Whitfield et al., 2004a & b). Such individuals can take up occupation of home ranges if they become available, or if favourable changes in the environment render conditions suitable for more individuals to breed. The cryptic and often wide-ranging behaviour of these non-breeding birds, a high proportion of which are likely to be immatures, makes designing surveys to include them, and differentiate them from birds that occupy home ranges, almost impossible for most species. The non-breeding component of the population reaches a maximum in mid- to late summer, when newly fledged young disperse. Numbers then fall, due to mortality and emigration, through the autumn and winter. The numbers of non-breeders in a raptor population at any given point in time can only be inferred precisely with a detailed knowledge of the demography of the population (age-specific survival rates, reproductive rates, age structure and the proportions of breeding birds of different ages) and movements (immigration, emigration/dispersal and migratory movements). At present, the quality of information available on the demography and movements of most raptor species breeding in Britain and Ireland means that it is generally difficult to estimate numbers of non-breeders with any degree of precision.

18  Raptors: a field guide for surveys and monitoring

4. BREEDING SEASON PARAMETERS A number of different but related terms are commonly used when discussing the survey and monitoring of birds of prey. In order to ensure that any data collected are both compatible and comparable, it is essential that the definitions of some of the most frequently used terms are agreed. Definitions of some of the most important terms used in the species accounts in this book are given below.

4.1 Home range and territory During the breeding season, the ‘home range’ constitutes the immediate area around the nest site and the area over which a raptor or pair of raptors forage (Newton, 1979). A ‘territory’ or ‘nesting territory’ is an area which is defended by the resident bird(s) against conspecifics. Some birds of prey, such as golden eagles and tawny owls, defend more-or-less the entire home range; others, such as goshawks and kestrels, defend only part of the home range, around the nest site, and have extensive home ranges for hunting which overlap with those of neighbouring pairs; species such as marsh harriers, which can nest in loose colonies, may sometimes occupy very small nesting territories (further details in species accounts).

For species that defend territories during the breeding season, observations of individuals behaving territorially (e.g. displays, aggressive behaviour towards conspecifics or potential predators) can be used to confirm occupancy. Where information is available, the species accounts in this book state whether or not exclusive home ranges or nesting territories are defended during the breeding season.

4.2 Nest sites, nesting ranges and alternatives The nest and its immediate surrounds (e.g. the ledge on which it is placed) are referred to as the ‘nest site’. A pair of raptors may use the same nest site in successive years, as is nearly always the case with established pairs of ospreys (Poole, 1989), or move to a new, alternative nest site.

Alternative nest sites may occur in close proximity, for example, a group of sparrowhawk nests in a wood, or they may be several kilometres apart, such as golden eagle nests on different cliffs within a home range. Some species, such as peregrine or goshawk, may have home ranges containing a number of different and widely separated areas with groups of closely spaced alternative nests. The term ‘nesting range’ is used in this book to refer to the area containing all the alternative nests thought to occur within the home range of a given pair of raptors (Fuller et al., 1985). For some species, nesting ranges may be similar in size to nesting territories; for others the nesting territory may be smaller than the nesting range, if alternative nests are widely spaced and only a small area around an active nest is defended in any one breeding season. Nesting ranges may be recognisable, within and outside the breeding season, by the presence of old and current nests and accumulations of faeces, pellets and prey remains close to favoured eating and roosting perches. Known nesting ranges within a study area can form the initial target areas for survey in a subsequent year. Where evidence of nesting ranges persists outside the breeding season, their locations can be recognised during visits at any time of year and used to identify areas to begin fieldwork in a new study area the following spring.

Further information on this is provided in the species accounts.

Evidence for the use by a pair of raptors of alternative nest sites is based on long-term data that show that only one nest site or nesting range in a given locality is occupied in any one year, and/or from the trapping of the same ringed breeding birds on different cliffs (e.g.

Ratcliffe, 1993; Watson, 1997). The degree to which such alternatives are used may be, at least in part, due to the availability of suitable nest sites within the home range of any given pair. The alternatives used by adjacent pairs may overlap if the same nest site is used in Raptors: a field guide for surveys and monitoring

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different years by different pairs of birds. For example, this occurred in southwest Scotland during the 1980s as the peregrine population increased (Ratcliffe, 1993). Conversely, when a population declines, a pair of birds may begin to utilise former nest sites of an adjacent pair that is no longer present.

The attraction of individual nest sites to successive pairs of many species of raptor is well documented. Peregrine cliffs known to falconers between the 16th and 19th centuries were still in use in the 1930s (Ferguson-Lees, 1951; Ratcliffe, 1993). Some osprey nests in the United States have been in continuous occupation for up to 45 years (Bent, 1938). Cliff ledges and, to a lesser extent, trees might be expected to provide stable places for nests in the long term. For raptor species breeding in less stable habitats, occupation of nesting ranges can also persist over long periods. Merlins breed in tall heather and particular nesting sites may become unsuitable as the heather becomes senescent or is managed by burning. Wright’s (1997) study of breeding merlins showed that, over 12 years, there was a clear preference for certain specific nesting localities, indicating that despite habitat change, pairs will continue to breed in the same general area as long as there are suitable stands of heather. Extreme habitat change can, however, cause desertion of nesting ranges. For example, afforestation can lead to the loss of breeding pairs of golden eagle (Marquiss et al., 1985; Whitfield et al., 2001).

4.3 Nests The nests of the raptor species considered in this book vary from nothing more than a scrape on the ground or a nesting ledge (e.g. ground-nesting merlins and peregrines), through modest nest structures (e.g. hen harrier), to very large or elaborate nests, many of which persist for many years (e.g. golden and white-tailed eagles and the raven). Some raptors utilise the nests of other tree-nesting species, such as crows, for breeding. Of these, some may not add any further material to existing nests (e.g. hobby), while other species, such as buzzard, may add substantial amounts of new material. A further suite of species, including several of the owls and the kestrel, regularly nest in holes, and may also use nest boxes for breeding (see Section 6.6). Guidance on recognising the nests of each species and potential confusion with other species is provided in the species accounts.

4.4 Occupancy A home range, territory or nesting range is generally recorded as occupied if a single bird or pair of birds is observed during the breeding season, or if there is strong evidence from signs that birds of the target species are present. During a single field visit prior to laying, during laying or during incubation, it is often difficult to establish if a pair of birds or a single bird is present. Two or more visits early in the season to check for occupancy are preferable if at all possible and sightings of bird(s) on more than one occasion provide stronger evidence than a single sighting. Supporting evidence for occupation includes new nests being built or fresh material added to old nests, freshly used nests or scrapes, the presence of droppings, fresh pellets, moulted feathers and prey remains such as plucks.

Care must be taken in interpreting evidence of occupation and only recent signs and those that can be attributed to a specific species with certainty should be used. The acceptable criteria for confirming occupation vary between species due to differences in their breeding behaviour and breeding habitat and useful criteria are described in the individual species accounts. It is important to visit nesting ranges early in the breeding season when assessing occupancy because birds that do not lay, or fail after laying, may move away from the nesting area. If a fieldworker builds up knowledge of the pairs breeding in a given study area, then sites with a history of breeding failure can be prioritised for visiting early in the field season in subsequent years.

20 Raptors: a field guide for surveys and monitoring

4.5 Proof of breeding, breeding success and fledging Breeding is established if it can be ascertained that eggs have been laid and/or, depending on the species, if behaviours that indicate that breeding is ongoing (e.g. a food pass) are observed. It can be difficult to distinguish failure soon after laying from non-breeding unless a nest site has been located and the presence of eggs confirmed (bearing in mind that close approaches to nests during the laying period should be avoided as birds may be very sensitive to disturbance at this time).

Breeding is termed ‘successful’ if (at least one) young fledge. The definition of fledging varies in the literature but in this book the term is used to refer to the acquisition of the ability to fly by raptor chicks. One or both parents typically continue to feed raptor fledgings for a period of time after they have begun to fly, while the young develop hunting skills. For survey and monitoring purposes, a fledgling raptor, owl or raven should meet the following criteria: • a young bird that has left the nest but is still dependent on its parents for food (Middleton & Prigoda, 2001); • capable of flight; and • fully feathered.

Evidence for successful fledging can be obtained by direct observation of fledged young during nest visits at the appropriate time. If fledging is missed, for example because of uncertainty about the likely date when young will be ready to leave a nest, evidence for sucessful fledging can be obtained by examining the nests of some raptor species. Supporting evidence for successful fledging includes large accumulations of droppings and the remains of kills in or close to the nest. Down and droppings may also accumulate where fledged young sit regularly after leaving the nest. For example, young sparrowhawks that fledge successfully often leave down in the clefts of branches onto which they move. Similarly, the fledged young of ground-nesting species, such as merlin, will often leave distinctive trails of down that lead away from the nest into the surrounding vegetation (although care is required with interpretation as merlin chicks may also leave the nest before they fledge, see Section 3.3.2 of species account). With experience, recognition of a combination of signs can be used to conclude that successful fledging of young has occurred.

It is often difficult to count young accurately once fledged because they may disperse from the immediate area of the nest and from each other. The minimum number should be recorded if there is any doubt, based on birds seen at the same time or sightings that are considered to involve different fledglings. In such cases, the observer should indicate that more young are possibly present by adding a '+' after the recorded number. The accounts for individual species give guidance on the most suitable times and circumstances for counting fledged young as accurately as possible.

Counts of large feathered young in the nest with little or no down are often given as an estimate of the number of fledged young. Such young are generally capable of leaving the nest and care should be taken on approach in case they fledge prematurely (see Section 7.8 for further guidance). It is preferable to carry out a subsequent visit to the nest to establish whether all the young fledge successfully, but if this is not possible the previous count can be used as an estimate of productivity for many species. Counts of fledged young can be particularly difficult for owls which tend to show extreme asynchrony in hatching so that chicks, especially in large broods, may be at a wide range of ages. In addition, the young of some owl species may leave the nest one to two weeks before they can fly and hide in Raptors: a field guide for surveys and monitoring

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surrounding vegetation. Further guidance on methods for counting fledged young is provided in individual species accounts.

The age of the young should be recorded or estimated at each visit when counts are made, as this provides data that can be used to monitor breeding success even when the timing of visits does not allow fledging to be established for certain. A mathematical modelling technique, the ‘Mayfield method’, can be used to make an estimate of the number of fledged young, based on knowledge of average losses during consecutive stages of chick rearing (Mayfield, 1961, 1975; Dow, 1978; Johnson, 1979; Bart & Robson, 1982; Steenhof, 1987; Crick et al., 2003).

4.6 Productivity Productivity may be measured or reported in one of three ways: (i) as the average number of young fledged per occupied home range; (ii) the average number of young fledged per breeding pair, territorial pair or female laying eggs; or (iii) the average number of young fledged per successful pair or female. Ideally, data should be collected to allow reporting of all of these measures but often only (ii) and (iii), or (iii) alone are achievable because it is not possible to follow all pairs in a given study area closely enough to record outcomes, and particularly to record pairs that do not lay or fail early in the breeding cycle. Productivity is normally reported on an annual basis for a study population. Whichever method of measuring productivity is reported, the method of calculation and underpinning survey methodology and coverage must be clearly stated.

One aim of measuring productivity is to estimate the average number of young produced per adult female, adult pair or adult bird in a population, which can be used to model the potential future growth of a population and predict whether it is likely to increase or decrease.

With respect to this, it is important to note that there are biases inherent in measurement; for example, if a population contains adult birds which do not attempt to breed and do not hold territories, as is the case with many raptor populations (see Section 3.3 above), measures (i), (ii) and (iii) above will all over-estimate productivity relative to the total numbers of adults in the population (e.g. Newton, 1979; Thomson et al., 2001; Green, 2004).

4.7 Breeding failure Strictly speaking, breeding failure occurs if eggs are laid but no young eventually fledge. In practice, however, for birds of prey it can be difficult to distinguish birds that fail soon after laying from non-breeders that do not lay at all. It is also often difficult to establish the cause of individual cases of nest failure but recording information that may provide clues to this is very useful for interpreting survey and monitoring results. It is important, however, that observers record only what they see, and that assumptions are not made about the causes of failure.

4.7.1 Natural reasons for non-breeding or failure Failure to lay eggs at all, or to complete a clutch, may occur when one or both members of a pair are in poor condition, or immature. Adverse weather, such as heavy snowfall, or a poor food supply, can also prevent laying or clutch completion. Failure during incubation can occur as a result of eggs being deserted or taken by predators. Clutches may be deserted following the death of one of the adults, due to lack of food, harassment by other birds or because of bad weather. Care should be exercised in recording the cause of failure because predation by corvids, gulls or mammalian predators may occur after a clutch has been deserted for other reasons. Nests targeted by predators will often contain eggshells or predator faeces. Some clutches or individual eggs within a clutch may be infertile and may be incubated beyond their full term. This can be caused by chemical pollutants affecting the reproductive behaviour

22 Raptors: a field guide for surveys and monitoring

and fertility of the adults but can also occur naturally. Some young may die before fledging for similar reasons to those leading to clutch desertion. If the young have disappeared from a nest before their predicted fledging date, evidence for hatching can often be found at the nest, including droppings and down/feathers, but establishing any cause of disappearance is often very difficult.

4.7.2  Persecution If human interference is suspected to be the cause of nesting failure, it is important to record accurately any observations that provide supporting evidence (see Section 7.9).

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5. IDENTIFICATION AND BREEDING BEHAVIOUR OF RAPTORS 5.1 Identification of raptors To survey raptors (or any birds) successfully, fieldworkers must be able to identify their subjects accurately to species and also to determine their age and sex (Clark, 2007) where this is possible in the field. As well as visual identification, this will require knowledge of calls, especially for woodland and nocturnal species (see Section 5.4 below). There are a number of specialist field guides for raptor identification. Forsman’s (1999) Handbook of Field Identification for the Raptors of Europe and the Middle East and Clark & Schmitt’s (1999) Field Guide to the Raptors of Europe, the Middle East and North Africa both provide comprehensive guides to the identification of birds of prey. In addition, Flight Identification of European Raptors by Porter et al. (1981) is a very useful guide for flying birds and Collins Birds of Prey (Gensbol & Thiede, 2008) provides detailed guidance on identification of European species. For owls, König & Wieck (2008) describes all known species worldwide. Many general bird field guides are also useful for the identification of all of the species in this book, for example, the Collins Bird Guide for Britain and Europe (Svensson et al., 1999), and Birds of Europe with North Africa and the Middle East (Jonsson, 1992); both have clear illustrations showing the variation in plumage, including immature phases, found in European raptors. Species monographs (many of which are referred to in the individual accounts in this book) and Birds of the Western Palaearctic (Cramp & Simmons, 1980, for diurnal birds of prey; Cramp, 1985, for the owls; Cramp & Perrins, 1994, for raven) are further important sources of reference. BWPi (2006), a DVD version of the Birds of the Western Palearctic, includes video footage of many species. Fieldworkers are advised to refer to more than one text, particularly if there is some doubt over identification. Clark (2007) provides useful advice on the field identification of raptors, including ageing and sexing.

If an unfamiliar raptor is seen it may be an ‘escaped’ captive bird, either an exotic species from another country or, possibly, a hybrid between closely related species. Many of the exotic raptors used in falconry come from North America, and Sibley (2000), or Ferguson‑Lees & Christie, (2001, 2005), can assist in the identification of these escapees. Hybrid birds are more difficult. Fieldworkers should note the plumage details and size of any aberrant birds before speculating on their origins. Any suspected falconry escape should also be checked for jesses (trailing straps) on the legs. If any such exotic or hybrid birds are thought to be breeding in Britain, Ireland or the Isle of Man, the appropriate Statutory Nature Conservation Agency should be informed as well as the Local Bird Recorder who will pass information to the Rare Birds Breeding Panel (contact details in Appendix 2).

5.2 Identifying raptor signs A range of different signs can indicate the likely presence of raptors in an area, although, on their own, signs do not generally allow occupancy to be established definitively. The main signs referred to throughout this guide are the remains of kills, pellets, droppings and feathers. Brown et al.’s (2003) guide to the Tracks and Signs of the Birds of Britain and Europe is a good overall source of reference for identifying signs left by birds of prey.

5.2.1 Kills Raptors pluck bird prey and their sharp beaks often leave a hole or broken section of feather quill, whereas small carnivorous mammals, such as weasels, will bite completely through the quill, and larger ones, like red foxes, pull the feathers out in mouthfuls so that the feather plumes are also damaged. Most birds of prey also decapitate their prey and it is possible to see

24 Raptors: a field guide for surveys and monitoring

V-shaped notches cut out of bones, such as the breast-bone, where the beak has bitten. Often all that remains are the head, wings, legs and some body bones. The location, habitat and prey type is often of more use in indicating the likely species of raptor involved than the plucking style. For example, merlins will pluck their prey on prominent stones or fences in moorland, while sparrowhawk plucking stumps will often be found deep inside woodland. Buzzards that eat small mammals and rabbits usually turn the carcases ‘inside-out’ and the skin and fur of larger prey may be shredded. Mammalian predators tend to leave carcases with crushed bones and teeth, as opposed to beak, marks (Brown et al., 2003).

5.2.2 Pellets These are the regurgitated remains of indigestible parts of prey, such as bones, fur and feathers. Most raptors produce these as do other carnivorous bird species, such as grey heron, kingfisher, corvids and gulls. Mammalian carnivore droppings can look similar to raptor pellets, especially those of the red fox, but such droppings are generally found singly, show twisting along the long axis and have a distinct smell. Raptor pellets are often found in groups under a roosting branch, near a plucking post or in buildings. Brown et al. (2003) provide a good guide to identifying and analysing pellets and there is a range of guides that describe how to identify the prey remains found in them (e.g. Yalden, 2003; Thomas & Shields, 2008). Like kills, the locations and habitats in which pellets are found often provide a good indication of the species involved but firm identification may not be possible because pellets can vary in form within a species, and overlap in size and type with those of other species. The species accounts provide further guidance on the recognition of pellets and potential confusion with other raptor species.

Pellets that are collected should be placed individually in polythene bags and labelled with the date and location found as well as any other relevant information. As soon as possible afterwards they should be dried slowly, microwaved for a few minutes or frozen to prevent decomposition.

5.2.3 Droppings Raptors often excrete faeces by lifting the tail and squirting them out as a jet. Droppings are generally most useful for helping to locate the nest sites of raptors on places such as cliffs, through the presence of obvious white splashing. Cliffs may also show patches of bright green, where algae have benefited from the fertilising effect of the regular emission of droppings. Droppings may also be useful for assessing whether a nest hole or building used for nesting or roosting by owls is occupied (e.g. see the species account for barn owl), and even, for red kite, to give an indication of hatching and the rough age of young, based on the spread of ‘whitewash’ under a nest. Droppings alone will not be species-specific enough to allow occupancy to be established in most cases, or to distinguish between a nesting or roosting site, without additional information or evidence.

5.2.4 Feathers Moulted feathers found at a raptor roost or nest site, or in the vicinity of signs such as pellets or plucks, should be collected because these can be used both to identify the species and potentially also individual birds, as feather patterning can be unique to a particular individual.

The latter has been observed for sparrowhawks (Newton, 1986) and barn owls (Taylor, 1994) for example. Moulted feathers can also be used to detect pollutants (Odjsö et al., 2004; Dauwe et al., 2005) and to establish genetic relationships within raptor populations (Rudnick et al., 2005; see also Section 6.4 below). Feathers from plucked prey and pellets can also give clues to the raptor species involved.

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Feathers should be collected in paper envelopes (polythene bags should be avoided as they create dampness that will cause the feather to deteriorate rapidly) and clearly labelled with the date and location of finding. Notes should also be made of any clues as to their origin; for example a single feather with a smooth shaft and only trace amounts of skin is likely to be moulted; several feathers together associated with fragments of skin or body may indicate predation (Cie´slak & Dul 2006). Wet feathers should be dried as soon as possible after collection. Dirt or stains on feathers can be removed gently with warm water and a little washing up liquid or shampoo. Feathers should then be rinsed in clean water and allowed to drip dry. Paper bags or other ‘breathable’ containers are recommended for long-term storage, rather than plastic bags (Brown et al., 2003).

Further guidance on feather identification and photographic plates showing the wing and tail feathers of most of the raptor species featured in this book, are included in Section 3 below. These photographs have been very kindly supplied by Marian Cie´slak, co-author of the excellent field guide, Feathers: Identification for Bird Conservation, from the Natura Publishing House (Cie´slak & Dul, 2006).

5.3 Breeding behaviour of raptors An understanding and recognition of the behaviour of birds of prey is important in assessing the relevance of observations to survey and monitoring. Sightings of adult birds away from a nest site indicate the presence of birds in an area but may not provide clues to their breeding status. Some types of behaviour, however, provide valuable evidence to help assess the breeding status of birds. Some of the main types of behaviour that can be used in this context are described briefly below. Further details of behavioural information of specific value for survey and monitoring purposes is provided in the individual species accounts.

5.3.1 Display Many species of birds of prey breeding in Britain and Ireland perform some kind of territorial or nuptial display, which can make them easier to detect at certain times of year. The main types of display used are: (i) perching-and-calling; (ii) soaring-and-calling; and (iii) mutual aerial display (Brown, 1976; Hammond & Pearson, 1993). The exact form that such displays take varies between raptor groups and between the habitats used for breeding. Generally, species that breed in woodland are more vocal than those that breed in open habitats. Perching-andcalling is used by many such species, and is the principle display used by nocturnal owls. It is also an important part of nuptial display for many diurnal forest raptors, such as goshawk and buzzard. The most widespread and frequent type of aerial display is soaring-and-calling.

Raptors favour bright mornings with light to moderate winds for this type of behaviour, which may include undulating and swooping flights, and spectacular dives. Buzzards and sparrowhawks will do this above the woodland in which they nest. Elaborate versions of some such displays in birds of prey are known as ‘sky-dancing’ (e.g. hen harrier and osprey).

Both birds of a pair may participate in mutual aerial displays, which often involve the most spectacular flight manoeuvres; these may include the two birds of a pair chasing each other in flight-play (e.g. in peregrines) and mock-fighting where talons meet and the birds may spin downwards, locked together, for several hundred feet (e.g. white-tailed eagles).

Many displays are seen prior to the breeding season, particularly in species that are largely sedentary, for example golden eagles display on fine days in winter and early spring. Some displays, such as the descent flights of male harriers, probably only occur late on in the display season, when sexual ‘excitement’ reaches a peak. Males of many species may continue to display above or near to the nest once eggs are laid and when there are small young but, generally,

26 Raptors: a field guide for surveys and monitoring

display is inhibited somewhat once the male is required to feed a growing brood. Some raptors, such as hen harrier and merlin, may display if breeding failure occurs. Species that occupy their home range year round, such as golden eagles and most peregrines in Britain, may also display ‘out-of-season’ if eggs are not laid or breeding failure occurs.

The displays of raptors provide clear evidence of the presence of individuals with intention to breed, and for many species give strong evidence for occupation of a home range. Birds may cover large areas of habitat, however, so that display flights may not reveal the location of the nest site. For species which display over very large areas or have the potential to move large distances to breed (e.g. goshawk), display flights may not be a useful indicator of occupancy.

Advice on the use of display along with other criteria for establishing occupancy is provided in the individual species accounts.

5.3.2 Egg laying and incubation Egg laying is generally a sensitive time for raptors, and care should be taken to avoid disturbing birds when they are laying as they may abandon a breeding attempt. As laying approaches, many species line the nest site with some soft fresh material (e.g. leaves, moss, rushes). Eggs are generally laid at intervals of more than one day. The female often begins to incubate before the clutch is complete (e.g. with the first egg in larger species, such as golden eagle and osprey, or after several eggs have been laid in smaller species). In most species, the female does the bulk of the incubation and may be fed by the male at the nest (see 5.3.3 below). In diurnal species in which the male assists with incubation, he generally does this only during daylight hours.

For species that nest in open habitats, such as on cliffs, careful observations of the nest site from a safe distance can often reveal birds either laying or incubating. Laying birds may visit the nest for a brief period only, especially when laying the first eggs. Incubating birds will remain on the nest for extended periods and can often be seen turning the eggs as they settle down. Observations of males bringing food to females (see Section 5.3.3 below) and/ or incubation change-overs can also indicate the location of a nest site. However these occur very infrequently in most species, such that extended periods of watching are likely to be required to observe them. Where available, information on change-over times is provided in the species accounts.

5.3.3 Hunting and feeding Fieldworkers should observe hunting birds of prey carefully, as those that are breeding are likely to return to the nest or its vicinity with prey. Any bird carrying prey should be watched: if the bird flies out of sight, a compass bearing of the direction of flight will often give the appropriate direction in which to search for a nest. Birds delivering prey to the nest may be adults of either sex provisioning young. In addition, males of many raptor species deliver food to females at or near the nest during the courtship/prelaying period, incubation, and while small chicks are being brooded. Food may be presented to the female at the nest or a nearby perch (e.g. sparrowhawk). Some species exhibit spectacular aerial food passes (e.g. most harriers and the peregrine). Watching birds after a food pass can provide a clear indication of the location of a nest. During incubation a male may slip on to the nest to incubate or cover the eggs while the female feeds; and once the chicks have hatched the female may carry prey directly to the nest after a food pass.

The frequency with which food is brought to an incubating female raptor or to young is important in determining the minimum length of time for which it is necessary to watch an area to establish if breeding birds are present. The frequency of food delivery will depend on Raptors: a field guide for surveys and monitoring

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the stage of breeding and the type of prey: an incubating female will require less food than a brood of young; the food requirements of young will vary with age; and species that feed on and can carry large prey (e.g. golden eagle, peregrine) will generally visit less frequently than those feeding on very small prey (e.g. hobby, honey-buzzard). In addition, for a given species, small prey will usually be delivered to a nest more frequently than large prey (e.g. hobbies may deliver insects to nestlings at intervals of a few minutes, whereas bird prey may be delivered at intervals of several hours; see Section 2.6 of species account). Details of feeding rates are provided in the individual species accounts where information has been found.

5.3.4 Interpretation of behaviour It is useful for any fieldworker planning survey or monitoring work on a particular raptor species to find out as much as possible about the breeding behaviour of that species before fieldwork begins. Descriptions and an indication of the importance of the species-specific displays are given briefly in the individual species accounts in this book, but it is recommended that further information is sought from other sources (e.g. Cramp & Simmons, 1980; Cramp, 1985; Cramp & Perrins, 1994; and individual species monographs, referenced in the species accounts). Ideally, fieldworkers should be aware of any behaviours of a species that can be linked unambiguously to establishing occupancy, laying, the presence of young and so on.

However, not all behaviour may be interpreted so clearly, which means that careful recording of all behaviour by raptors observed should be carried out for future reference in making decisions about breeding status.

5.4 Vocalisations A knowledge of raptor calls can be vital for identifying species, establishing the occupation of a nesting range, determining the stage of breeding and in establishing breeding success.

The use of calls for detecting occupation by nocturnal owls and woodland raptors (e.g. goshawk) is described in the individual species accounts. For owls or raptors living in more open habitats, where visual observations play a more important part in surveying, calls can still have an important function. Territorial, courtship, or alarm calls can reveal the presence of birds before they are seen.

The use of the repertoire of calls often varies through the breeding cycle. Courtship calls indicate that the birds have not laid or have just started laying. As incubation progresses, both birds of a pair may call as food is brought to the female. These calls can help fieldworkers to locate the nest. After hatching, young often beg for food or call as they are fed. The calls of young can be used to locate nests and confirm breeding success and are particularly useful in the case of owls and woodland raptors. Some raptors can also be sexed due to differences in calls between males and females.

Any fieldworker intending to carry out survey work on a given raptor species is urged to familiarise themselves with appropriate calls, which can be an important aid to field surveys.

The CD of raptor calls that accompanies this field guide contains examples of key calls of most of the regularly occurring raptor species in Britain and Ireland. These are calls that can be used to identify species or interpret behaviour. Further information on the specific calls of raptors, owls and the raven can be found in species monographs (cited in the individual species accounts), in species accounts of Cramp & Simmons (1980), Cramp (1985), Cramp & Perrins (1994) and BWPi (2006; includes recordings of calls for individual species); as well as compilations of bird calls.

28 Raptors: a field guide for surveys and monitoring

6. ADDITIONAL TECHNIQUES FOR STUDYING RAPTORS 6.1 Ringing Conventional ringing involves placing an unobtrusive, light-weight, metal ring on a bird’s leg.

A unique number is engraved on each ring, together with a return address. If a ringed bird is caught subsequently, or found dead, it can then be reported and the recovery details linked with the original details, to show, for example, how far it has travelled and how long it has lived. A range of ring sizes is available for different species (and sometimes for the two sexes within a species where males and females differ considerably in size), to ensure that rings fit correctly and cause the birds no harm or inconvenience. The British and Irish Ringing Scheme is run by the BTO. All ringers require specific training and an appropriate licence to catch birds for the purposes of ringing (see Section 7.1.1 of this book and Chapter 3 in Redfern & Clark, 2001).

Further information on training to become a ringer, and details of how to report a ringed bird, can be obtained from the Ringing Unit at the BTO (Contact details in Appendix 2).

In Britain and Ireland, records from ringed birds have proved invaluable, both for providing information on movements and migration (Wernham et al., 2002), and contributing to all aspects of integrated population monitoring (potentially providing information on survival rates, productivity and population size; Baillie et al., 1999; Clark & Wernham, 2002). Ringing has provided the data on which much original knowledge of the seasonal movements of British and Irish birds of prey has been based (e.g. Mead, 1973, 1993; Bunn et al., 1982; Newton, 1986; Heavisides, 1987; Percival, 1990; Watson, 1997; Evans et al., 1999) and has contributed much additional information on their local movements, site fidelity and demography (e.g. Snow, 1968; Newton, 1975; Mearns & Newton, 1984; Kenward et al., 2000).

Many raptor species ringed in Britain and Ireland have relatively higher return rates (in terms of the number of rings reported for a given number of birds ringed) than some other bird groups, so that ‘background’ ringing over time provides useful broad-scale information, particularly on the movements of each species and how these change through time (Wernham et al., 2002).

It can also provide broad-scale information on survival rates. Some specific methodological problems with obtaining survival rates from ringing data exist, however, because most birds of prey are ringed as chicks in the nest (see Crick et al., 1990 for a review of the use of ring recoveries of raptors for estimating their survival rates). In general for raptors, records from conventional ringing can be used most satisfactorily to estimate survival rates if supplementary information from studies of marked adults (such as wing-tagging projects, Section 6.2) is available for analysis in unison.

The return of information per bird handled during conventional ringing is much lower than for some other marking methods (Sections 6.2 and 6.3 below). Other methods, however, with the exception of wing-tagging, are much more expensive, meaning that studies can generally only afford to mark a smaller number of individuals; and these may be less representative of the population as a whole than the larger numbers that can be followed via ringing.

Other marking methods may also influence the behaviour of some species, whereas there is generally no evidence of any influence of ringing on behaviour. Equally, there are various biases associated with ringing records (Wernham & Siriwardena, 2002), such as geographical differences in the chances of dead ringed birds being reported, and variation in reporting rates with recovery method (e.g. birds that are killed deliberately might be less likely to be reported; young birds might be more prone to being killed and so on). For these reasons, conventional ringing and the alternative marking methods for raptors (discussed in Sections 6.2 and 6.3 Raptors: a field guide for surveys and monitoring

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below) should be seen as complementary, and efforts should be made to compare results from different methods whenever possible.

Most ringing of birds of prey involves young in the nest because of the obvious difficulties of catching adult birds. Any such ringing requires consideration for the safety of the fieldworker and the birds. Any ringer planning to ring birds of prey should consult Section 9.3.5 of the Ringers’ Manual (Redfern & Clark, 2001), which provides information on suitable ages at which young birds of prey should be ringed. Further relevant information on health and safety is provided in Section 7.10 and in the individual species accounts.

6.2  Wing-tagging Wing or patagial tags are usually made from flexible coloured PVC fabric. They are attached to the bird through the patagium (a flap of skin on the leading edge of the wing), with either nylon or stainless steel pins and washers. Symbols, letters and/or numbers can be painted onto the tags to enable identification of individual birds (see Section 10.3.3 in Redfern & Clark, 2001). Great care must be taken in attaching wing markers and specific training and licensing are required (see Section 7.1.1 below and Chapter 10 of Redfern & Clark, 2001) Advice on making wing tags can be obtained from the BTO Ringing Unit or the SRMG Raptor Monitoring Officer (Appendix 2).

Wing tags have been used on a variety of species, particularly on diurnal birds of prey. Birds tagged as chicks in the nest appear to accept the tags as though they are additional feathers.

Wing tags are best suited to species that have a slower mode of flight, such as kites, harriers, eagles and buzzards. They are less suitable for species with rapid wing beats or pursuit hunters, such as falcons and sparrowhawks. As wing tags can be observed and any numbers or letters read at a much greater distance than conventional rings, and without re-capture of birds, they have the advantage of generating multiple sightings of the same individual for as long as they are attached. Because they are conspicuous, tags can also substantially increase the likelihood of a dead bird being found and reported. Depending on the method of attachment and skill of the person doing the fitting, wing tags can last at least 10 years on long-lived species, such as red kites.

Tags have been used successfully in Britain on hen harriers (Etheridge et al., 1997; Summers et al., 2003), marsh harriers, red kites (Evans et al., 1997) and white-tailed eagles. Provided sufficient effort is spent searching for marked birds, wing-tagging can be an extremely useful technique for gaining information on the movements, site and mate fidelity, individual breeding performance and survival of diurnal birds of prey. It should not, however, be undertaken without careful consideration for the species involved, the size of the tag used, and the skill and experience of those undertaking the study.

Wing tags may have negative effects on some bird species, including: impairment of flight behaviour; weight loss; a reluctance to migrate; initial discomfort followed by frequent preening or constant annoyance; skin abrasion and feather wear; entanglement and increased mortality; alteration of social behaviour; increased conspicuousness and risk of predation; and reduced breeding success (Varland et al., 2007; Calvo & Furness, 1992). Although minor skin abrasion and feather wear may occur, the available data suggests that correctly fitted wing tags have negligible effects on breeding behaviour and reproductive success of raptors and ravens (Kochert et al., 1983; Smallwood & Natale, 1998; Varland et al., 2007). It is possible that birds tagged as adults may be less tolerant of wing tags than those marked as nestlings, although it may be difficult to distinguish the affects of tags from the stress associated with

30  Raptors: a field guide for surveys and monitoring

the capture of adult birds for marking. The latter has certainly been implicated as a cause for concern for golden eagles studied in Scotland (Gregory et al., 2003). In a North American study, however, no apparent affects of capture and tagging of adult golden eagles on behaviour or breeding success were reported (Phillips et al., 1991). Golden eagles released under the Irish reintroduction project are tagged as pulli, using tags with a rounded bottom edge to reduce wind drag and flapping. Survival of tagged birds (wing- and radio-tagged) has been high and no negative effects of wing-tagging have been identified to date. Birds will continue to be monitored closely so that any effects of wing-tagging on survival or productivity can be assessed (Lorcán Ó Toole, pers. comm.).

In Britain and Ireland, sightings of wing-tagged raptors should be reported to the Ringing Unit at the BTO (contact details in Appendix 2). Where contact details are known or can be obtained, sightings should also be reported as soon as possible to individual project workers or species coordinators, as this can provide an opportunity for researchers to follow-up sightings and obtain additional information.

6.3 Remote tracking A large range of devices are available for tracking individual birds remotely at distances of a few centimetres or kilometres to a global scale, including radio-transmitters, logging devices and other electronic tags. Remote tracking devices have a clear advantage over ringing and wing-tagging in many applications because they do not rely on cold searching by the observers or on reports from members of the public, and are therefore less subject to spatial biases. However, most such techniques are considerably more expensive than ringing or wing-tagging (by orders of magnitude), meaning that smaller samples of birds are generally followed. Reviews of the range of devices available, and the effects that they may have on birds, are provided by Calvo & Furness (1992), Gauthier-Clerc & Le Maho (2001), Marchant (2002), and Wernham & Baillie (2002). The use of any such devices in Britain and Ireland requires specific licensing permission (see Section 7.1.1 and Chapter 10 of Redfern & Clark, 2001), including stipulations to report on any observed effects on the study species. Some general guidelines for use of these devices, including acceptable weights and methods of attachment, are given in Section 10.4 of Redfern & Clark (2001).

In the context of the survey and monitoring of the raptors that are the focus of this book, there is great potential for remote tracking studies to increase knowledge of the ranging behaviour and daily activity patterns of a number of species, particularly if the costs of the techniques decrease in future so that larger samples of birds can be tagged.

6.3.1 Radio-tracking Radio tags are light, low-power, very high frequency (VHF) transmitters that are designed to be tracked either manually or from an Automatic Radio Tracking Station (ARTS). The heavier types of tag (6–100 g) powered by 3.5V lithium thionyl-chloride batteries are a suitable size for use on most birds of prey in Britain and Ireland. They currently have life spans of four months to six years and potential ranges of up to several kilometres, depending on the exact tag specification and battery size, bird behaviour, terrain and tracking location. Ranges may be increased considerably by tracking from raised locations or from the air; for example signals from soaring radio-tagged eagles released under the Irish reintroduction project have been recorded at up to 25 km, when tracking from a mountain top (Lorcán Ó Toole, pers. comm.). In conjunction with suitable tags, ARTS stations can record the presence or absence of tags within a range of up to about 1 km for birds on the ground (Redfern & Clark, 2001).

Radio tags are generally custom-built by specialist manufacturers who ensure that they work Raptors: a field guide for surveys and monitoring

31

on appropriate frequencies for Britain and Ireland and that they comply with the relevant EU Directives (see Appendix 1 of Redfern & Clark, 2001 for contact details of manufacturers).

These companies can also supply the receiving equipment and directional antennae needed for conventional hand-held tracking. Anyone planning a radio-tracking study is advised to consult with more than one company over equipment specification and prices, and it may also be worth seeking independent advice from radio engineers.

The limited detection range in conventional radio-tracking means that the technique is most useful for intensive work on local movements. The technique has been widely applied to raptor species to investigate post-fledging behaviour, dispersal of juveniles/immatures and ranging behaviour (e.g. Arroyo et al., 2005, 2006 for hen harriers; Grant & McGrady, 1999 for golden eagle; Tyack et al., 1998; Walls & Kenward, 1995, 1998; Walls et al., 1999; Kenward et al., 2001a for buzzard; Petty & Thirgood, 1989 for tawny owl), mortality and breeding success (e.g. Kenward et al., 1999 for goshawk) and for various more applied studies, such as the predation of pheasants by buzzards (Kenward et al., 2001b).

Further useful technical information, including advice on study design and analytical methods as well as case studies, can be found in Priede & Swift (1992), Kenward (2001, 2004), Millspaugh & Marzluff (2001) and Walls & Kenward (2007).

6.3.2 Satellite tracking Whereas radio tags generally have to be tracked manually and have very limited range, satellite systems allow the remote tracking of birds anywhere in the world. Satellite telemetry has revolutionised the study of raptor migration and aspects of life history such as the movements of immature birds before they settle on breeding territories (Meyburg & Fuller, 2007). The main limitations of satellite tags currently are their size, weight and cost. Two types of tag are available. Platform terminal transmitters (PTTs) transmit to satellites (e.g. ARGOS), which then transmit the position data back to ground stations. The smallest tags available currently weigh about 20 g, have a battery life of several weeks to several months, depending on how often they transmit, and can be programmed to transmit at regular intervals and to vary the interval several times during the battery life. The larger the tag, the longer the battery life, or the greater the transmission power, and, hence, the accuracy of locations. PTTs provide locations to a maximum accuracy of a few kilometres, or a few tens of kilometres in the case of smaller models (although for transmitters attached to animals the precision of locations may be lower than suggested by manufacturers; Meyburg & Fuller, 2007). Solar-powered PTTs are also available, allowing the tags to transmit indefinitely, but they are heavier than battery-powered tags of a similar specification.

Global positioning system (GPS) tags calculate their positions using satellite transmissions (e.g.

US NAVISTAR system). They can either store data on board to be accessed upon retrieval, or transmit data back to ground via satellites (which requires a heavier tag). They are currently larger and more expensive than PTTs (minimum c. 35 g) but can be accurate to within 5–10m.

The current expense of satellite tracking means that it is most likely to be used in studies of the long-distance movements of relatively small numbers of individuals, rather than in survey and monitoring of larger samples of birds of prey. Following recent pioneering work on lesser spotted eagle (Meyburg et al., 1995, 2001), golden eagle (Brodeur et al., 1996) osprey (Kjellen et al., 1997, 2001; Hake et al., 2001; Thorup et al., 2003), Swainson’s hawks and peregrines (Fuller et al., 1998), there is now a growing number of published studies showing the utility of the technique for migration studies on a range of species (e.g. honey-buzzards, Hake et al., 2003; Thorup et al., 2003). Recent studies of ospreys, honey-buzzards, and marsh harriers have also been carried out in Britain and Ireland (see www.roydennis.org).

32 Raptors: a field guide for surveys and monitoring

6.3.3 PIT tags Passive integrated transponder (PIT) tags are very small rods (minimum size c. 12 x 2 mm, weight c. 0.06–0.08 g) that are used to identify individual animals, particularly domestic pets (Gauthier-Clerc & Le Maho, 2001; Redfern & Clark, 2001). Each tag is programmed with a unique number (like a barcode) which can be displayed by a special reading device which energises the tag with radio waves. For use on domestic animals, such tags are usually injected just under the skin but they can be used equally effectively on wild birds by gluing them to feathers (temporary) or rings (more permanent). The tags and readers are relatively cheap and they last a long time because they do not require internal battery power. The main limitation of the technique, currently, is the very low detection distance (ranging from only a few centimetres for the very small tags up to a maximum of c. 1 m). This restricts the use of PIT tags to situations where birds must pass very close to the reader antenna, such as recording incubation durations and feeding rates at nest sites with restricted access routes (e.g. Becker & Wendeln, 1997; Becker et al., 2001 working on terns). Although PIT tags in their current form are unlikely to be of use in studies of the ranging behaviour of raptors, such tags may be valuable for studies of nesting behaviour (in boxes or in situations where a suitable antenna can circle the nest). PIT tags are being used in an ongoing study of the population dynamics of peregrines in Scotland, the aim being to investigate mortality, recruitment and turnover by capturing and re-capturing birds at nest sites. The tags are attached to blank rings which are fitted on one leg of a bird captured as an adult or nestling (the other leg being fitted with a conventional BTO ring). These tags can be read automatically by a battery powered reader placed in a nest, so that birds can be re-captured electronically over successive years. To fit the tags, no special training is required beyond that for ringing; tags are made available free to ringers and tag readers are available on loan (Smith & McGrady, 2008; Smith, 2009).

6.4 Biological and chemical ‘markers’ In the last few decades, techniques for analysing genetic material and also chemical ‘markers’ found in body tissues, such as stable isotopes of some common elements, have advanced markedly. Whilst most techniques are becoming cheaper as available technology and the number of applications increases, they still require either specialist laboratory setups or funding to commission analyses from commercial companies, generally necessitating collaboration with those with appropriate expertise. For birds of prey, as with other groups of organisms, these techniques are likely to be used most effectively to answer the types of questions outlined below if the results are interpreted together with those from other broad-scale ecological and demographic work, such as the wide-scale survey and monitoring research that forms the focus of this field guide.

6.4.1 Genetic markers Modern genetic techniques now play a significant part in conservation research in general, allowing relationships between individuals, populations and species to be delineated. Details of analytical procedures and the growing range of genetic markers that can be used are outside the scope of this manual but several useful reviews are available (e.g. Haig, 1998; Parker et al., 1998; Parkin, 2003). The extraction and amplification of high-quality DNA from previously unusable tissue types, particularly moulted feathers, is now possible (e.g. Leeton et al., 1993; Eguchi & Eguchi, 2000; Rudnick et al., 2005). This means that suitable samples for some applications can now be collected non-invasively without the need for complex training procedures (e.g. for blood sampling) or a specific licence (see Section 7.1.1).

There are a number of areas where genetic analyses might contribute valuable information to survey and monitoring work on birds of prey. Although many species of raptor can be Raptors: a field guide for surveys and monitoring

33

sexed in the field visually, this is often not true of juveniles or young in the nest, although it is often necessary to sex young in order to estimate age with accuracy (see details in each species account). A sex-linked gene that is present in most birds, including raptors, has been identified (Griffiths et al., 1998), which means that most birds can be sexed relatively easily in the laboratory from a tissue sample collected in the field. There is thus much scope for deriving or improving the sex-specific growth curves for young of a range of species. The similarity in genetics between individual birds in a population can be used to calculate dispersal rates: if genetic relatedness is high then dispersal is low and vice versa. DNA fingerprinting involves the determination of genes at a sufficient number of loci to identify individual birds and determine parentage (e.g. Burke & Bruford, 1987; Warkentin et al., 1994; Gavin et al., 1998; Müller et al., 2001). It has been used successfully in criminal investigations to prove that raptors that have been passed-off as captive-bred have not come from the parentage claimed (Wetton & Parkin, 1997). DNA fingerprinting has potential to be a powerful technique for population monitoring as it can be used to determine the identities of individuals using home ranges or nest sites from one year to the next, to measure site fidelity and population turnover. Current research into golden eagle population dynamics in Scotland is using moulted feathers and mouth-swabs of nestlings as sources of DNA. The aims of the project include investigation of the site fidelity of breeding adults and estimation of adult survival rates (Tingay et al., 2008).

Further applications of specific genetic techniques with relevance to populations of birds of prey include assessments of genetic diversity, population viability, inbreeding, effective population size and identifying the founders of new populations. Further details and examples are provided in Haig (1998) and Parker et al. (1998). Other applications involve the identification of populationor race-specific genetic markers to investigate migration patterns, habitat requirements, and dispersal/metapopulation structure. For example, population-specific markers have been developed for differentiating neotropical peregrine populations and for establishing the breeding origins of individuals that mix on migration (Longmire et al., 1988, 1991). Broader genetic markers have been investigated recently for their utility in tracking shorebird movements (Haig et al., 1997). Such techniques, if developed for birds of prey, could assist in determining, for example, the breeding origins and composition of wintering populations for species where it is known (e.g. from ring recovery information) that a proportion of the wintering population originates from outside the geographical area of interest (e.g. for sparrowhawks in Britain).

6.4.2 Chemical markers A growing number of studies have used stable isotope ratios (see Hobson, 1999, 2007, for recent reviews) and other chemical components of body tissues in ecological research.

Isotopes are forms of an element that differ in atomic mass due to different numbers of neutrons in the nucleus. Stable (‘heavy’ and non-radioactive) isotopes of several chemical elements that are abundant in the environment (e.g. carbon, nitrogen, hydrogen, oxygen, sulphur, strontium and lead) have distributions that vary spatially in a predictable manner, such as across broad geographical areas in line with rainfall patterns or major pollution sources, or between different habitats. For example, in general terms the ratio of deuterium (²H) to normal hydrogen (¹H) in growing-season rainfall varies in a graded manner across continents (Hobson, 1999, 2003; Hobson et al., 2004), and relative ratios become incorporated in plant growth and the tissues of animals further up the food chain. The content of carbon (¹³C) in animal tissues varies with the proportion of plants with different photosynthetic pathways (C3 versus C4 or CAM plants) at the base of the food chain, and hence broadly with latitude and major habitat biomes, and marine food sources are markedly higher in the ¹³C isotope than terrestrial sources. The strontium (87Sr) isotope content varies in terrestrial systems with rock type (see e.g. Chamberlain et al., 1997;

34 Raptors: a field guide for surveys and monitoring

Graustein, 1998, for reviews). In any research using stable isotopes, the body tissues to be sampled must be selected carefully, with consideration for the turnover times of the isotopes in question. The isotope ‘signature’ will reflect the diet on a timescale varying from that over the most recent few days to weeks in metabolically active tissues, such as blood, to that integrated over the entire growth period of an individual in bone or collagen. Tissues made of keratinous material, such as feathers and claws, are inert once formed, so that the composition of their isotope ratios will reflect the geographical location or diet during the time of formation. Because they can be obtained non-invasively, the latter tissue types are favoured in ecological research but their use requires knowledge of the stage in the annual cycle when growth has taken place.

Stable isotope techniques could be of increasing value in a number of areas of research on birds of prey. For example, differences in ‘signatures’ from marine and terrestrial sources could be exploited to look at the proportion of the diet of species that forage in both these habitats (e.g. white-tailed eagles and the proportion of their diet that comes from marine sources, such as marine fish and seabirds, versus terrestrial sources, including domestic animals; see Bearhop et al., 1999 for an example of research on cormorants). Ratios of appropriate isotopes could also be used, alternatively or in complementary research to that using genetic approaches, to assess the wintering areas of migrant raptors, migratory divides, or the breeding origins and population composition of those wintering in a given geographical area (Hobson, 2005), assuming that there is sufficient knowledge of the growth patterns of the selected tissues (e.g. the moult cycle if feathers are to be used). Studies using stable isotopes to answer these types of questions, and thus knowledge of the approaches that are likely to be successful, are increasing (e.g. Alisauskas & Hobson, 1993; Chamberlain et al., 1997; Rubenstein et al., 2002; Evans et al., 2003; Hobson, 2005; Lott & Smith, 2006). Other chemical signatures might also play a useful part in such studies for some species of bird of prey (e.g. see Parrish et al., 1983 for the use of trace elements to pinpoint peregrine wintering areas).

6.5 Nomograms This section describes methods for developing nomograms (graphical plots) of egg density and components of chick growth. These nomograms can be used to predict the hatching date of eggs from measurements of egg density, and the age and/or growth stage of nestlings from weight and/or body measurements. Nomograms can allow raptor fieldworkers to use egg or chick measurements, taken during a single nest visit, to estimate hatching or fledging dates and identify the best times for subsequent visits to the nest, for example to ring chicks.

This avoids the need for interim visits, which might cause unnecessary disturbance or might be prohibitive in terms of the time available. The calculation of age-specific survival rates of eggs or young (Mayfield, 1961, 1975; Dow, 1978; Johnston, 1979; Bart & Robson, 1982; Steenhof, 1987; Crick, 1993) also relies on the ability to age eggs and/or chicks accurately.

6.5.1 Egg density During incubation, all eggs lose approximately 16% of their initial mass (Rahn & Ar, 1974; Hoyt, 1979). This loss, which under natural conditions occurs at a roughly constant daily rate, can be attributed almost exclusively to the loss of water vapour from the developing embryo (Rahn & Ar, 1974). A consequence is that the density of an egg decreases as the incubation period progresses (Hoyt, 1979; Furness & Furness, 1981); hence, measurements of egg density can be used to estimate the time left to hatching from a standard curve.

Egg density is calculated by dividing the mass of an egg by its volume, described by the following equation: Raptors: a field guide for surveys and monitoring

35

Egg density =

W

Kv LB2

(i)

where L is egg length, B is egg breadth at the widest point, W is egg mass (see Section 7.8.7 for guidance on measuring eggs), and Kv is the volume constant. It is suggested that egg dimensions are measured in millimetres and mass in grams, but other units can be used as long as they are consistent. The volume constant Kv has been measured as 0.51 based on the eggs of 115 species of bird (Hoyt, 1979). It is a function of egg shape but, as there is as much intraspecific as interspecific variability in Kv, this value is considered to be applicable to all but a few species in which the eggs are very pointed.

To create a nomogram, the densities of appropriate samples of eggs of known age need to be measured for each species. In general, measurements should be made on nests in natural situations (not those of captive birds). Such measurements are ideally made daily but could be undertaken at 3–4 day intervals. If eggs are marked then, once the length and breadth of each has been measured, the observer only needs to weigh the eggs on subsequent visits. The fieldwork required to create such a nomogram is intensive. It requires an appropriate licence to handle eggs (Section 7.1.1) and visits need to be planned carefully, and appropriately accessible sites selected, so as to minimise potential disturbance. Such an approach should not be attempted for species that are particularly sensitive to disturbance during laying and incubation.

Once field data have been collected, a graphical plot of egg density against time (e.g. days to hatching) can be produced and used to estimate the hatching date of any egg for which the density is measured. Published examples of such curves are not generally available for raptors in the UK. Examples of nomograms for barn owl and tawny owl, derived by Percival (1990, 1992) from samples of natural nests, are included in the accounts for these species.

Addled or infertile eggs do not lose water as fast as developing eggs (Furness & Furness, 1981) and thus their age cannot be estimated from a calibration curve. Recorders should be able to detect this because such eggs will have a greater density and, as a consequence, will appear to have been laid more recently than the rest of the clutch. During repeat visits, the change in the density will be proportionally less than for eggs showing normal development.

If eggs can be numbered in order of laying, then the presence of addled or infertile eggs is easier to detect.

6.5.2 Chick growth For the purposes of survey and monitoring, it is often important to establish the age of individual chicks. It is generally impractical and undesirable for nest visits to be made on a daily basis around the time of hatching, which would allow precise ageing to be carried out. Instead, it is usually necessary to estimate the age of chicks. As the age of a chick increases, there are associated increases in its weight and various aspects of body size. Where these follow a predictable pattern, it is possible to calculate the age of the chick from a measurement taken in the field on any given date.

Measurements of a given parameter (e.g. weight) against age, from appropriate samples of individuals of known age, can be fitted to a growth curve of known form, typically using either a Logistic, von Bertalanffy or Gompertz equation (Ricklefs, 1968, 1973; Brown & Rothery, 1993; Barkowska et al., 1995 — these all belong to the ‘Richards’ family of growth models, Richards, 1959). The Logistic equation most frequently provides the best fit for avian data;

36 Raptors: a field guide for surveys and monitoring

for example, this has been demonstrated for the barn owl age/weight relationship (O’Connor, 1984; Wilson et al., 1987).

The different measures that have been used as predictors of chick age vary in their usefulness during different stages of chick growth. For many species, structural measurements (e.g. wing length, tarsus, head and bill length) are better predictors of age than body mass because weight change is generally more influenced by short-term fluctuations in food supply.

Therefore, chicks of the same age can show quite large variation in mass. Head and bill length can be a useful measurement for determining the age of young raptor chicks but this tends to reach a maximum at about two-thirds of the way through chick development in the nest.

Wing length is useful for all but the early stages of chick development (once the feathers have emerged from their sheaths or ‘pins’).

In order for such information to be used to produce reliable estimates of age, measurements need to be taken on representative samples of chicks of known age and in the wild rather than in captivity. A growth curve can then be produced and used to read off the age of any chick for which a size measurement is taken in the field. As raptors are often sexually dimorphic in size (females being larger), separate curves may be required for male and female chicks, which relies on the identification of suitable criteria for sexing chicks.

Where data are available, growth curves are provided in the species accounts in this field guide, as a starting point for ageing and sexing young. When using these growth curves to estimate the age and/or sex of raptor chicks, fieldworkers should bear in mind that some broods contain a ‘runt’ which is considerably smaller than its siblings; if they survive, runts and undernourished chicks may fledge to be much smaller than average. Most of the available growth curves are based on small samples and/or data for one particular population of a species and may not apply to that species elsewhere, for example the white-tailed eagle species account (Section 3.5) describes differences in chick growth between different populations of this species in Sweden. For most species it is likely that collection of further data is required to ensure that growth curves are robust enough for general use for raptor fieldwork in Britain and Ireland. Fieldworkers undertaking intensive studies of particular species (and who are in possession of appropriate licences, Section 7.1.1) are encouraged to collect measurements of chicks to add to the limited body of data currently available for ageing and sexing. Guidance on standard methods for taking bird measurements is provided in Section 7.8.

6.6 Nest boxes Artificial nest platforms or boxes can be a valuable conservation and monitoring tool for many raptor species. Nest boxes are widely used for hole-nesting species, to encourage nesting in an area where natural nest sites are in short supply, and to facilitate access to nests for monitoring purposes. Information on nest box construction is widely available (e.g. du Feu, 2003) and the BTO Nest Record Scheme receives the majority of barn owl, tawny owl, little owl and kestrel records from nest box sites. For these species, long-term studies would be largely impractical without the use of nest boxes. Examples of important nest box studies include Southern’s (1970) seminal research on tawny owls in Wytham Wood in Oxfordshire, Village’s (1990) population research on kestrels, Taylor’s (1994) work on barn owls and Petty’s (1992) research on tawny owls in Kielder Forest.

Artificial nest platforms are more rarely used in the UK, although they have been used extensively elsewhere, for example to provide nest sites for ospreys in the United States (Poole, 1989). Nesting baskets have been used to provide a more stable artificial ‘corvid-like’ nest for Raptors: a field guide for surveys and monitoring

37

species such as long-eared owls (Garner & Milne, 1997) and merlins nesting in trees (Rebecca et al., 1991), and artificial ledges have been created to facilitate peregrine nesting in sites where natural ledges are unsafe or vulnerable to predation.

The use of nest boxes may affect the population under study. Newton (1998) provides several examples of increases in the population density of raptors, such as little owl, barn owl and kestrel, following the provision of nest boxes. This can result in increased competition for resources such as food. Nest boxes can also attract species into an area where there are no naturally suitable nest sites (Dewar & Shawyer, 1996), or may be used in preference to natural sites. For example, Petty (1992) found that 83% of his study population of tawny owls switched to boxes in their first year and that none of the previous natural sites, including ground nests, were used after four years. This switch is likely to have reduced the vulnerability of the nesting birds to predation from species such as red fox, pine marten and goshawk (Petty & Thomas, 2003). In addition, nest boxes are likely to be better insulated against poor weather conditions. Thus, researchers should be aware that nest boxes may improve nesting success through the provision of safer and better insulated nesting sites, but may also have detrimental influences on the study populations, through increased breeding density and competition for resources such as food. Studies based largely on birds using nest boxes may therefore provide results that are not representative of the wider breeding population that does not use boxes.

38  Raptors: a field guide for surveys and monitoring

7. GOOD PRACTICE FOR FIELDWORK 7.1 Legal considerations 7.1.1 Licences Wild birds, their nests and eggs are protected throughout Britain and Ireland. Fieldworkers who intend to handle eggs, or capture and handle and/or ring raptors or their chicks, will need to apply for a ringing permit and/or additional licences. In addition, for some specially protected species, a licence is required to closely approach the nest.

A summary of legislation to protect wild birds and current licensing arrangements – the detail of which varies between different parts of Britain and Ireland – is provided below. Licensing arrangements may change over time. Fieldworkers are therefore advised to consult the licensing section of the appropriate Statutory Country Conservation Agency, or the BTO Ringing Unit, before starting work (contacts in Appendix 2).

Permits and licences, or copies of them, should be carried by fieldworkers during survey work.

Such permits or licences do not give a fieldworker right of access to land.

Legislation to protect wild birds In England, Wales and Scotland, the Wildlife and Countryside Act 1981 (as amended by subsequent legislation, see below) makes it illegal to: intentionally kill, injure or take (i.e. capture) any wild bird (with the exception, in season, of certain game birds and waterfowl); take, damage or destroy the nest of a wild bird while it is in use or being built; or take or destroy eggs. Special penalties for these offences apply for some scarcer species, listed on Schedule 1 of the Act. In addition, for Schedule 1 species, which include many of the raptors dealt with in this book (see species accounts for details) there are additional offences relating to disturbance whilst a bird is building its nest, or in, on, or near a nest with eggs or young; and for disturbance of dependent young.

The Nature Conservation (Scotland) Act 2004 makes some amendments to the Wildlife and Countryside Act as it applies in Scotland. The protection afforded to wild birds, their nests, and eggs and protection against disturbance of Schedule 1 species at the nest and their dependent young, is extended to include ‘reckless’ as well as intentional acts. A person is ‘reckless’ if he or she foresaw there was a risk of disturbance and took that risk, or gave no thought to whether there was a risk or not and failed to consider an obvious risk. Some new offences are added, including that of obstructing or preventing a wild bird from using its nest. There are also two new Schedules (1A and A1) for bird species that are protected from harassment and whose nests are given year-round protection. At present a single species, the white-tailed eagle, is listed on both schedules, although the Act gives Ministers powers to add species to these lists in the future.

The Countryside and Rights of Way Act 2000 makes some amendments to species protection provisions in England and Wales, including the creation of a new offence of recklessly disturbing Schedule 1 birds or their dependent young at a nest site. In addition, the Natural Environment and Rural Communities Act 2006 gives year-round protection to the nests of golden eagle, white-tailed eagle and osprey (listed on Schedule ZA1).

In the Isle of Man, the Wildlife Act 1990 provides similar protection for wild birds to that described for the Wildlife and Countryside Act. Schedule 1 (specially protected birds) was Raptors: a field guide for surveys and monitoring

39

updated by the Wildlife Act 1990 (Variation of Schedules) Order 2004 and includes all birds of prey and owls but not the raven. The concept of ‘reckless’ disturbance is not included in this Act, although aspects of the legislation are under review and may be updated in the near future.

The Wildlife (Northern Ireland) Order 1985 also performs a similar function to the Wildlife and Countryside Act 1981, making it illegal in Northern Ireland to intentionally kill, injure, or take any wild bird or their eggs or nests. As in Britain, special penalties are available for offences related to birds listed on Schedule 1, for which there are additional offences of disturbing birds at their nests, or their dependent young.

The protection of birds in the Republic of Ireland is covered by the Wildlife Act 1976 which has been amended by the Wildlife (Amendment) Act 2000. Protected wild birds include all birds of prey and owls. It is an offence to hunt wild birds (other than a species for which an open season is specified in an order under section 24 of the Act), to injure them, to wilfully take, remove or destroy eggs and nests or to wilfully disturb birds near to a nest.

Permits and licences for nest visits and ringing chicks All applications for licences or permits to undertake surveys involving visits to raptor nests will need to be made either to the Statutory Country Conservation Agency covering the area where fieldwork takes place, or to the BTO. Contact details for these Agencies and the BTO Ringing Unit are given in Appendix 2.

The Statutory Country Conservation Agencies in Britain and Ireland grant licences to disturb or take wild bird species for: scientific purposes; for ringing or marking, or examining any ring or mark; for photography; and for the purposes of conservation. In this context, ‘take’ refers to the temporary capture, possession or control of any live wild bird, or anything derived from such a bird, including, for example, eggs.

In England, Wales and Scotland, the Statutory Country Conservation Agencies have licensed the BTO to issue permits that allow trained ringers to take and ring wild birds using certain methods. Fieldworkers who wish to ring, mark or capture, or to examine rings or marks of nonSchedule I raptors in Britain, need only apply to the BTO for a ringing permit. The applicant will need to go through a period of training and assessment appropriate for the type of permit required (contact the Ringing Unit at BTO for further information). If a fieldworker intends to visit the nests of non-Schedule 1 raptors to inspect the contents and measure eggs or chicks, but the chicks will not be ringed, then licence applications should be made to the Statutory Country Agency, or to BTO if records will be submitted to the Nest Record Scheme.

For Schedule 1 birds, licences are required to cover disturbance of birds while they are building a nest or are in, on or near a nest containing eggs or young; or disturbance of the dependent young.

Ringing permits do not cover disturbance to Schedule 1 species (although they do cover the actual ringing of these species), so any fieldworker intending to ring, handle, or closely approach the nest sites of Schedule 1 raptors must apply for a separate licence. In England, Scotland and Wales, applications for ringing, marking or handling Schedule 1 raptors, their eggs or their young should be made to the Ringing Unit at the BTO. The BTO issues permits allowing the disturbance of Schedule 1 birds to suitable applicants from England directly, whilst applications from Scotland and Wales are routed to the appropriate Statutory Country Conservation Agency for issue.

All applications for Schedule 1 licences in England, Scotland and Wales that do not involve handling birds, their eggs or their young should be made direct to the Statutory Country

40 Raptors: a field guide for surveys and monitoring

Conservation Agency rather than the BTO. The exception is members of the BTO’s Nest Record Scheme, who should apply to the BTO for a Schedule 1 licence even if birds or eggs are not being handled.

Applicants for Schedule 1 licences will be asked: to indicate the species and geographical area they will cover; to describe in some detail the work to be carried out; and (for new applicants) provide the names and addresses of two referees who are familiar with their work and able to advise on their suitability to receive a licence. Such a licence may permit the licence-holder to be accompanied by others, for example in circumstances where additional people are required for health and safety reasons, although their presence may cause additional disturbance.

A licence can also include accredited agents who can operate independently of the lead name on the licence. In such cases, licence applicants are asked to provide the names of any assistants who will be working with them.

BTO ringing permits are valid in Northern Ireland, so fieldworkers wishing to ring raptors in Northern Ireland should apply to the BTO as described for England, Scotland and Wales.

Separate licences are required to ring or otherwise disturb species on Schedule 1 of the Wildlife (Northern Ireland) Order 1985 and applications for such licences should be made to the Northern Ireland Environment Agency (NIEA).

In the Republic of Ireland, under the Wildlife Act 1976 (as amended), licences are required to take wild birds for ringing or other marking purposes, and a special licence is required to ring at or visit the immediate vicinity of the nests of sensitive species listed on Schedule II of licences issued under Section 32 of the Act (as amended). Applications for both types of licence should be made to National Parks and Wildlife Service (NPWS).

In the Isle of Man, under the terms of the Wildlife Act 1990 and its Variation of Schedules Order 2004, a licence is required to ring birds or disturb Schedule 1 species at the nest.

Applications for both types of licence should be made to the Wildlife and Conservation Office of the Department of Agriculture, Fisheries and Forestry (DAFF). Applicants will be required to demonstrate that they have adequate training or supervision. A BTO permit will also be required for the supply of BTO rings.

Photography Licenses to ring, take or disturb the nest contents of a wild bird do not cover photography.

Provided that care is taken to cause no significant additional disturbance, however, this does not preclude the taking of quick, opportunistic photographs to record something interesting that has been found. Fieldworkers whose specific aim is to photograph raptors at nests will require a photographic licence from the appropriate Statutory Country Conservation Agency and should contact the Agency for details of requirements for licence applications.

Licences for wing-tagging and remote tracking In England, Scotland and Wales, anyone wishing to capture raptors for the purpose of fitting non-conventional rings (e.g. colour-rings), wing tags or remote tagging devices should apply to the Ringing Unit at the BTO, who will check their application and either issue the appropriate licence (in England) or make a recommendation to the appropriate Statutory Country Conservation Agency that a licence is issued (applicants from Scotland and Wales).

As is the case for licences to disturb, applicants will need to provide a detailed description of the work to be carried out, including the methodology, rationale and purpose of any scientific study. Applicants will also be asked to provide details of their qualifications and experience.

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41

It is normal practise to fit conventional metal rings when other devices are used, requiring a ringing permit from the BTO. In this case, for non-Schedule 1 species (and Schedule 1 birds in England), the licence to use unconventional marks will be issued as an endorsement to the applicant’s ringing permit.

In the Republic of Ireland, licences to capture wild birds for the attachment of wing tags and other marking devices are issued by the NPWS. Applications for licences to fit wing tags, radio tags and other marking devices in the Isle of Man should be addressed to the Wildlife and Conservation Office, DAFF. In Northern Ireland licences to take wild birds for the attachment of wing tags and remote tracking devices are issued by the NIEA.

Licences to take blood or tissue samples Removal of feathers for DNA identification analysis can be licensed by BTO for England. For Scotland and Wales licence applications should be made directly to SNH and the Countryside Council for Wales (CCW). Otherwise, anyone wishing to take blood or tissue samples from wild birds in Britain and Northern Ireland will need to apply to the Home Office for a licence.

Such licences are issued under the Animals (Scientific Procedures) Act 1986, which covers scientific procedures that are likely to cause pain, suffering, distress or lasting harm. Licensing work is carried out at six regional offices located in Belfast, Cambridge, Dundee, London, Shrewsbury and Swindon. Further details can be obtained from http://scienceandresearch. homeoffice.gov.uk/animal-research/aboutus. Where required, a Home Office licence only covers the actual taking of the tissue sample, so a licence to take or disturb a bird will also be required from the appropriate Statutory Country Conservation Agency and/or the BTO. In the Isle of Man, the Wildlife and Conservation Division of DAFF can issue licences for the use of a humane procedure for the sole purpose of enabling an animal to be identified, if it causes only momentary pain or distress and no lasting harm. The Animal Health Division of DAFF issues licences for regulated procedures under the Cruelty to Animals Act 1997.

In the Republic of Ireland, licences to take blood or tissue samples are issued under the Wildlife Act 1976 (as amended) and applications should be made to the NPWS.

7.1.2 Access Licences granted for ringing or nest visiting do not give the fieldworker the right of access to land. Access rights are covered by legislation in each country.

In Scotland, Part 1 of the Land Reform Act (Scotland) 2003 establishes for everyone a statutory right of access to most land and inland water for recreational purposes, educational purposes (concerned with furthering a person’s understanding of the natural and cultural heritage), some commercial purposes (where the activities are the same as those undertaken by the general public), and for crossing over land or water. Access rights must be exercised responsibly. The term ‘responsible’ refers to the legal requirement for those taking access not to cause unreasonable interference with the rights of any other person, including access rights and rights associated with land ownership. Land managers also have responsibilities under the Land Reform Act to respect access rights and not cause unreasonable obstructions to people crossing their land. If there is concern that access rights have been unreasonably withheld or restricted, then the Local Authority or the Local Access Forum can provide advice and assistance.

42 Raptors: a field guide for surveys and monitoring

The right of access in Scotland extends to individuals undertaking surveys of the natural heritage where these surveys have a recreational or educational purpose within the meaning of the legislation, and is considered to cover fieldworkers carrying out raptor surveys on a voluntary basis (including those that may be in receipt of travel expenses through an SNH grant). Access rights also extend to those carrying out, commercially or for profit, any activity that the person taking access could undertake otherwise (as a member of the general public).

While this indicates that those undertaking raptor surveys in a contractual capacity do not need to seek access permission, fieldworkers are advised to consider the circumstances of each project. Under the Scottish Outdoor Access Code, people organising surveys that are intensive over small areas or require frequent repeat visits are asked to consult any relevant land manager(s) and provide details of the proposed survey methodology. Fieldworkers carrying out commissioned surveys under contract to SNH will be asked to consult with landowners before taking access for raptor surveys. Full details of the new access rights, as well as guidance on the responsibilities with respect to access of those who own and manage land and water, are included in the Scottish Outdoor Access Code (available at www. outdooraccess-scotland.com).

In England and Wales, the permission of individual landowners should normally be sought before entering private land in order to survey raptors. However, extensive areas (over a million hectares) of open countryside (mountain, moor, heath and down) and registered common land have been opened for public access under the Countryside and Rights of Way Act 2000. Access is available on such areas (subject to restrictions) for ‘open-air recreation’, which would include the observation of raptors by volunteers (See www.countrysideaccess. gov.uk or www.ccw.gov.uk and the latest edition Ordnance Survey Explorer map series for more information and maps showing areas that have been defined as open access land). For survey work involving frequent repeat visits to a limited area, fieldworkers should continue to liaise with landowners. Individuals carrying out survey work for commercial reasons, or as part of their paid employment, should also seek the permission of the landowner.

In England and Wales, trespass is not a criminal offence but may be the subject of action by the landowner. If somebody is on open access land for reasons other than ‘open-air recreation’, they may be asked to leave (because they have no statutory right of access).

This does not apply to statutory rights of way, where a right of access to pass and re-pass applies at all times.

In the Republic of Ireland there is no general right of access and permission should always be sought from landowners before entering private land. Liability in case of injury may be an issue for landowners. Raptor fieldworkers carrying out surveys in their own time fall under the concept of ‘recreational users’ under the Occupiers Liability Act 1995 and are responsible for their own safety. Within Irish National Parks, which are State owned and run by the NPWS, there is open access for walkers. The forestry company Coillte (www.coillte.ie), which owns much of the forestry in the Republic of Ireland, also has a policy of open access to its lands but permission should be sought for vehicular access to forest tracks.

In the Isle of Man, fieldworkers wishing to carry out raptor surveys over private land will require access permission from landowners. Public access is permitted over areas of Crown and Common Lands (public ramblage) in the uplands. Surveyors are however advised to make contact with the DAFF Forestry Office before undertaking fieldwork.

Northern Ireland does not have general freedom to roam legislation. Most rural access is via public rights of way, which are covered by the Access to the Countryside (NI) Order 1983.

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Under common law, walkers on rights of way may only do things which are reasonably incidental to their legal right to pass and re-pass. This, therefore, may not include a right to undertake survey work and fieldworkers are advised to seek landowner’s permission prior to entering private land. Permission to enter public sector land, owned for example by the Forest or Water Service, may be best sought on a province-wide basis.

Where access permission is required this can be sought from tenant farmers, estate managers/factors, gamekeepers or landowners. If permission is granted by an agent of the landowner, it is always advisable to confirm whether the landowner is aware of the request. It is possible that landowners may want to see evidence of Public Liability Insurance before fieldworkers enter their land, although this would mainly be expected where raptor surveys are being undertaken on a commercial basis. In the UK, any fieldworkers working in a voluntary capacity under a BTO ringing permit, or collecting data for a BTO monitoring scheme are covered by the policy held by BTO (contact the Director of Services at BTO; address in Appendix 2). Raptor Study Groups may also hold Public Liability Insurance on behalf of their members and fieldworkers are advised to check on this if necessary before taking out their own insurance.

Fieldworkers are advised to respect reasonable requests to avoid areas where there is potential for conflict with land management, and to be particularly considerate if working at very early or late hours, or close to residential properties.

7.2 Minimising disturbance and good field craft As with any survey and monitoring fieldwork, the welfare of the birds is of maximum priority.

Fieldworkers should be aware that their presence may cause disturbance to the birds that they are surveying, and should not undertake fieldwork that might adversely affect the survival or reproductive success of birds.

Disturbance at or close to a nest may cause birds to abandon a breeding attempt. Advice is given in each species account on the appropriate timing and manner of visits to nest sites to minimise disturbance. However, some general principles apply to most if not all species of birds of prey. These include being particularly careful just prior to and during laying, and during early incubation, as many species are particularly sensitive and may desert their nests if disturbed at this time. At all times, nests should only be approached as closely as is necessary to obtain the information that is required, and species-specific advice should be followed regarding safe distances through the breeding cycle. It is important to minimise disturbance of vegetation around nest sites as this can lead predators to the nest or render the nest more exposed to the elements. Especially for species which may be vulnerable to wildlife crime, it is also important that the fieldworker ensures that they are not being watched, so as not to lead potential human ‘predators’ to the nest. Incubating or brooding birds that are flushed during visits to nests may dislodge eggs or small young from the nest cup. Any such misplaced eggs or young should be carefully replaced to ensure that they are incubated or brooded properly when the adult returns.

When carrying out watches from a distance, neutral coloured clothing should be worn and use made of natural or man-made shelter for concealment whenever possible. Advice on appropriate distances from nests for vantage point watches is provided in the species accounts (see also Section 3 of the introduction to species accounts). If birds exhibit alarm calls/behaviour, leave a nest site, or fly repeatedly around a particular area, apparently aiming to land but aborting at the last minute, this suggests the fieldworker is too close and should move away as

44 Raptors: a field guide for surveys and monitoring

quickly as possible to a distance at which agitated behaviour ceases. If the nest can be watched from a safe distance, a check should be made to see whether the bird returns. If this cannot be done without further disturbance, or if the bird does not return in a short time, the fieldworker should leave the area completely and not return that day. Any further visits to the site should be made in an appropriately cautious manner.

Reactions to disturbance vary between raptor species and also between individuals of given species. It is useful to keep a record of nests where disturbance events occur and the overall outcome of these nesting attempts. Such records can be used to assess the risk of monitoring the species in question and allow further precautions to avoid disturbance to be taken in subsequent years.

7.3 Weather Observers should not disturb birds in adverse weather (i.e. cold, wet or excessively hot conditions; Greir & Fyffe, 1987). In particular, eggs and small chicks that are still being brooded are very susceptible to chilling or overheating if the adult bird is flushed from a nest. Predators of eggs and chicks may also be more stressed in such conditions and might move in quickly if the nest is left unattended even temporarily by the adult birds. Unfavourable weather (e.g. a prolonged spell of snow) during laying in particular, but also later in the breeding cycle, might place energetic strain on the adults and any additional disturbance at such a time might be more likely to bring about desertion than if weather conditions are favourable.

Fieldworkers should be aware that weather conditions may affect their observations (Robbins, 1981), especially when searching for displaying birds that tend to be more active in good weather; many species will display most actively on fine but slightly breezy days. Nocturnal species that are surveyed by calls may be more likely to call on clear, dark, dry nights than on wet nights (e.g. Ruggieri, 1995; Lengagne & Slater, 2002) and calls will be difficult to hear in strong wind.

7.4 Time of day The activity patterns of birds of prey vary between species and through the breeding season (e.g. Fuller & Mosher, 1987). However, as a general rule, diurnal birds of prey tend to be more active in the morning and evening than during the middle of the day, and are therefore more detectable at those times. Whenever possible, guidance on the most appropriate times of day to carry out observational work based on the known activity patterns of each species is given in the individual accounts in this book. The time of day for surveying and monitoring may be particularly important for crepuscular species (for which the window of opportunity for making visual observations may be restricted) and for nocturnal species. If there is a need to disturb a nocturnal species at the nest or at a roost during the daylight hours, this should be done as close to dark as possible, so that the birds can return to the nest under cover of darkness or are not exposed to predation or mobbing (behaviour intended to drive away rather than capture a target bird) while looking for an alternative roosting site.

7.5 Frequency of site visits When surveying birds of prey, the frequency with which visits need to be made to sites depends on the particular aims of the work. If the aim is to determine the number of occupied home ranges or nesting ranges within a study area, then it will usually be necessary to visit some sites on at least two occasions, if evidence for occupancy is not found at the first visit. The first visit should generally take place early in the breeding season, before laying if possible, to ensure that pairs that occupy a site but fail to lay, or fail early in incubation, are not missed. Many birds Raptors: a field guide for surveys and monitoring

45

of prey are difficult to locate during incubation and for some species, only visits later in the season to record the presence of an active nest or vocal young, for example, will give rigorous confirmation of occupation (or lack of occupation).

If the aim is to record breeding success, then further visits are required in addition to those for establishing occupancy. At a minimum, one further visit will be required to look for fledged young and establish whether breeding has been successful. In practice, however, two or more additional visits may be required to verify the presence or absence of fledged young (if no young are found on the previous visit), or to count young in a nest prior to fledging (because they are more difficult to count once they leave the nest).

Guidance on the numbers and timings of visits that may be required for assessing occupancy and breeding success for each species is provided in the individual species accounts. Additional, appropriately timed visits may also be made if the aim is to collect information to confirm laying, clutch size, hatching and initial brood size. More frequent visits can also identify the stage (and perhaps the cause) of breeding failure if this occurs. The ideal timing of such visits varies between species and is discussed in the individual species accounts.

7.6 Observer effort This is a measure of the amount of time spent and ground covered by a fieldworker during survey and monitoring work. There are several important components to this with respect to raptor surveys: the total area covered; the number and timing of visits; and the duration of visits.

It is important that the area searched for the target species is defined accurately. This allows comparisons to be made between the numbers of home ranges or nest sites that have been checked and/or located in different years, and also means that the representativeness of the sample in relation to the population as a whole can be assessed. Information on the ground covered in each year should be recorded onto maps of the study area. It is also very useful to record details of the effort in terms of the number of visits to different parts of the study area.

The time that needs to be spent observing at each visit will depend on a number of factors, including the species, likely stage of breeding, ease of observation of the site or area in question and weather conditions. Guidance is provided for each species in the individual accounts. It is important to record the start and end times of each visit and each watch at any given nest site or area, so that effort can be quantified in this respect.

Recording observer effort allows for the identification of sites that have received sufficient survey visits at appropriate times of the breeding season, and of appropriate duration and time of day, to record observations of a target species. Importantly, recording of survey effort allows the identification of ‘nil returns’ from areas where no birds are found despite appropriate survey coverage.

7.7 Recording observations and site features Details of the timing and routes taken during survey visits, and each observation of a target bird of prey species, nest or other distinguishing sign, should be recorded in the field along with a map reference at the appropriate spatial scale. The basic equipment required is a pair of binoculars, a map and a notebook. A compass and/or handheld GPS unit are also recommended.

46 Raptors: a field guide for surveys and monitoring

It is recommended that fieldworkers record observations in a notebook. Such notes may usefully be supplemented by marking the area covered during the field visit, and the locations of observations (e.g. the path of a flying bird), on a photocopied map of the survey area at an appropriate scale. For some species, standardised recording forms have been developed for the submission of data for national surveys (examples are included in Appendix 3). Raptor workers may wish to carry and complete similar forms while they are undertaking fieldwork or design their own forms for other specific purposes. It is recommended, however, that a notebook is also carried for any supplementary information or observations for which there may not be enough space on the form. In some cases, where the observations may form part of the basis for statutory designations to protect sites, or as evidence for wildlife crime, reference to original field notes may be required, so it is important that these are as clear as possible and include details of locations and dates. Electronic recording devices such as handheld computers or dictaphones may also be used to record observations. These may have the advantage of enabling fieldworkers to record information more quickly, but it is advisable always to carry a notebook as a back-up, in case a device becomes damaged or the battery fails. In addition, it is recommended that any information recorded directly into an electronic device is downloaded and backed-up (e.g. through transcription, storage on a computer and printing a paper copy) as soon as possible.

Recommendations on the specific information to be recorded for each observation of a bird, nest or other sign, and during each field survey visit are given below. In addition, an annotated list of the information that contributors to the Scottish Raptor Monitoring Scheme are asked to submit for each site record (in this context a site refers to an individual home range of a given raptor species during the breeding season) is included in Appendix 3. Central to all of this is the recording of accurate map references using the National Grid for each country. This can be done from a map of an appropriate scale or using a GPS. The Ordnance Survey produce a useful free leaflet with guidance on taking map references and other tips on using maps (see www.ordnancesurvey.co.uk or available in most bookshops that stock OS maps). GPS units are now widely available and affordable and are recommended, both for safety reasons and for accuracy – because many of the habitats and landscapes where birds of prey occur, such as open moorland or woodland, may have limited features of use for pinpointing a location. In addition to their use for recording locations, many GPS units allow the grid references of specific points and the routes taken by an observer on a survey trip to be recorded. For the purposes of recording raptor observations, the guidance below specifies four or six figure grid references – which give locations respectively to the nearest 1 km or 100 m. Many GPS units provide ten figure grid references (locations to the nearest metre) and it is useful to record these but it should be remembered that the accuracy of devices may vary, for example with weather conditions.

7.7.1 Recording sightings of birds, nests or other signs A list of the recommended features to record for each observation of a bird, nest, or other sign is given in Table 1 below. Generally in raptor fieldwork, sightings of birds and other signs are relatively infrequent and there should be sufficient time to record all of the recommended features. If sightings of birds are very frequent, for example in a high density breeding population or at a winter roost, then it may not be possible to record all details for every sighting. Fieldworkers will then have to decide which features are most important in terms of the objectives of their study and focus on these. In such cases it should be noted that some features, such as location and habitat, may be common to a number of sightings, and can be recorded as such. At roost counts the recording of cumulative counts of birds over time intervals may be appropriate.

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Locations should be recorded as accurately as possible, using a six figure grid reference wherever feasible, for example for a perched bird, a bird displaying in a restricted area, a specific aspect of behaviour such as a food pass, or a fixed object such as a nest. A four figure reference may be more appropriate for a bird observed in flight or displaying over a large area.

Table 1. Features to record whilst observing raptors.

Feature

Notes

Full description of the observation

Species and numbers of bird(s) seen or heard

Description of nest or other sign (pellet, kill, feathers etc.)

A sketch and/or digital photograph of the location of a nest or other sign in relation to nearby features can be helpful for relocation at a later date

Sex and age

Of any bird(s) seen or heard, if distinguishable, and any features that might aid individual identification (wing tags, missing wing or tail feathers, unusual plumage features, etc.)

Behaviour and calls

Display, food pass, alarm call, etc.

Nest contents (number of eggs and/or chicks

Including any measurements of eggs or chicks and details of any rings or other marks placed on chicks

Date and time

24 hour clock recommended

Location

six or four figure grid reference (or more accurate reference from GPS)

Habitat

For the area where the observation was made or in which the nest or sign was located

Recording the behaviour of any birds observed is important because it can provide evidence of territoriality and/or the stage of breeding. The species accounts include specific recommendations on important behaviours to record for individual species, which may include calling, alarming, chasing or aggression towards conspecifics or other species (birds, humans or other mammals), displays, carrying food and food passes.

Raptor nests are often well concealed and once found, may be difficult to relocate from a grid reference alone, especially if the nest is observed from a distance (e.g. on a cliff ledge).

It is therefore recommended that a sketch of the position of any nest is made in a notebook, with details of nearby features that can help with relocation in subsequent visits to ring chicks or record breeding success. Photographing the nest area with a digital camera can also provide a useful record. Photo imaging software can be used to enhance an image and highlight relevant features which can be used to relocate a nest. When identifying such features, however, vegetation growth should be taken into account - features which may be prominent early in the season, may be less conspicuous later on. The location of any vantage point from which a nest is viewed should also be recorded as a six figure grid reference along with a compass bearing for the direction between the vantage point and the nest.

To minimise disturbance, it is recommended that visits to nests to record the contents are kept to a minimum taking into account the aims of the study, the health and safety of fieldworkers (Section 7.10) and requirements for an appropriate licence (Section 7.1.1).

Descriptions of the habitats where observations are made are important in terms of identifying habitat features that influence the distribution, abundance and population trends of raptors.

There is, however, no standard system of habitat recording that has been consistently applied to raptor survey work. Fieldworkers wishing to identify appropriate habitat description categories

48  Raptors: a field guide for surveys and monitoring

(e.g. heather moorland, blanket bog, unimproved grassland, plantation forestry, etc.) and/ or variables (e.g. height of vegetation around a ground-nest, height of tree-nest above the ground) to record for particular species are advised to check recent publications on that species (including books and scientific papers) for guidance. For rarer species, which are the subject of periodic national surveys within Britain and Ireland (see Section 2.3), the most recent published account of such a survey should include details of any habitat variables identified as important to record during fieldwork. Habitat and land management variables used for reporting under the Scottish Raptor Monitoring Scheme are listed in Appendix 3. Useful advice on the description and measurement of bird habitat is also included in Bibby et al. (2000). Participants in BTO ringing or nest recording schemes will be familiar with their hierarchical habitat coding system (Crick, 1992); this is designed to be used by birdwatchers and requires no expert botanical knowledge. It is based largely on vegetation structure but includes simple floristic categories within the broader habitat types. It also includes aspects of land management and human usage, so it covers agricultural and other man-made habitats as well as semi-natural ones.

In addition to the features listed in Table 1 above, it may be appropriate to make additional notes including the location of the fieldworker (as a six figure grid reference) and the distance and direction (compass bearing) between the fieldworker and the bird, nest or other sign that has been observed. Recording the flight direction of a bird carrying prey (as a compass bearing) is also often recommended in the species accounts as a means of identifying the direction in which to search for a nest. If wildlife crime is suspected, then additional features may be noted, as described in Section 7.9 below.

7.7.2  Recording details of survey visits In addition to the observations above, it is recommended that fieldworkers record specific information about the visit itself for each field survey visit (Table 2).

Detailed recording of the timing and areas covered in individual field visits to a study area is important for interpretation of any survey and monitoring data. As described above (Section 7.6), the number and timing of visits will influence the confidence that can be placed on particular records, for example in deciding whether a site was really unoccupied or whether birds may have been missed due to a restricted number of visits or non-ideal timing. In addition, recording survey routes and particularly the location of good vantage points for watches, will assist with orientation during repeat visits to the same area. It can also be useful to record the area which is visible from each vantage point.

Table 2. Features to record for each site visit.

Feature

Notes

Arrival and departure times

24 hour clock

Area covered

Mark on a map

Route taken

Mark on a map

Location of vantage points from which watches are made

six figure grid reference (or more accurate reference from GPS)

Arrival and departure times at vantage points

24 hour clock

Weather conditions

Cloud cover, wind speed and direction, precipitation, visibility

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During initial visits to a survey area, it may be possible to mark on a map extensive areas of habitat that are considered unsuitable for a target species (e.g. dense woodland for a species of open moorland) and that need not be covered in subsequent visits to that area. Depending on the habitats involved, such maps of unsuitable areas may need to be redrawn annually or may be valid for a number of years.

It can also be useful to record weather variables such as cloud cover (the percentage of the sky covered by cloud), visibility, rainfall and wind speed (e.g. for the Beaufort Scale, see www.bbc. co.uk/weather/features/understanding/beaufort_scale.shtml) and direction. The basic weather categories used by the BTO/JNCC/RSPB Breeding Bird Survey provide a useful model (www. bto.org/bbs/take_part/download-forms.htm). Generally it is recommended that surveyors avoid carrying out fieldwork in extreme weather conditions (e.g. strong winds, heavy rain or snow, thick fog) to avoid adverse effects on birds and for health and safety reasons. Where appropriate, the species accounts provide further guidance on any aspects of weather that may have particular influence on behaviour.

7.8 Handling and measuring eggs and young For many species of raptor, measuring chicks can give a good indication of their age and, in sexually dimorphic species, their sex (see Section 6.5.2 above). For a few species, published information is also available to allow estimation of the hatching date of eggs by measuring their density (Section 6.5.1 above). Handling and measuring eggs and chicks requires care, both to avoid damage to birds or eggs, and to ensure that measurements are taken accurately. Appropriate training to take the measurements described below can be obtained from a raptor worker with experience of handling chicks, or a licensed ringer (and note also the licence requirements in Section 7.1.1 above). Equipment for taking such measurements (wing rule, callipers, spring and electronic balances, bird bags and plastic weighing ‘cones’) can be obtained from the Ringing Unit at the BTO (contact details in Appendix 2).

Nest visits should be avoided in adverse weather (cold, wet or excessively hot) and appropriate health and safety precautions should be taken if nest checks require climbing trees or rock faces, or wading through water (see Section 7.10 below). If an adult bird is likely to be sitting (incubating eggs or brooding chicks), then it is a good idea to make a deliberate noise (e.g. snapping small twigs, coughing, muffled talking) when approaching the nesting area to alert the bird to the presence of the fieldworker. Even so, incubating females of many raptor species may sit tight until an observer is almost at the nest. Information on the appropriate ages to ring the chicks of raptor species is given in Redfern & Clark (2001). Well-grown young of some species are prone to jump from the nest if they are approached late in the nestling period and care should be taken not to cause premature fledging, especially with cliff or tree-nesting species. In general visits to crag or tree nests should be avoided once young are fully feathered and have no down on their heads. Chicks with down rarely jump although special care needs to be exercised on dry breezy days as occasionally a well-feathered chick with retained down on the head may be tempted to jump prematurely. Further guidance on specific sensitivities of individual species to nest visits is included in the species accounts.

The removal of raptor chicks from a nest and handling for measuring, ringing and tagging is likely to induce alarm behaviour from the parents, and all procedures should be carried out as quickly as possible. Some species, or individuals of a species, may be aggressive towards fieldworkers handling young and in this case the person ringing or measuring chicks may require an assistant to prevent injury from attacking adults.

50 Raptors: a field guide for surveys and monitoring

The following descriptions of standard measurements for chicks are based on The Ringers’ Manual (Redfern & Clark, 2001). Small young of raptors can be held in the standard grip used by ringers (Redfern & Clark, 2001). Older young and those of the larger species ideally may require two people present to handle them securely. Such large young can also be handled more safely if a purpose-made falconry hood is used and/or they are provided with an object (e.g. a bird bag or pencil) to grasp in their talons. If it is necessary to restrain a bird by holding the bill shut, the external nares (nostrils) must not be obstructed, to allow it to breathe.

7.8.1 Wing length Wing length is most frequently measured as the ‘maximum chord’ using a wing rule. The wing is straightened with all feathers in order, neither crossed nor bent, and is held in, as near as possible, the resting position. The ruler is then placed under the wing, with the carpal (‘wrist’) joint against the stop ridge (Figure 1) and gently flattened. The feathers are straightened carefully along the ruler and the measurement taken to the nearest millimetre.

Before attempting this measurement, fieldworkers should have considerable experience in the technique and should have checked that they can take consistent measurements. Wing length measurements will not be accurate if the feather tips are very abraded (worn) or broken.

Figure 1. ‘Maximum chord’ wing measurement, the most frequent measure of wing length.

For some of the species in this book, ageing and sexing data include measurements of the growth of individual primary feathers rather than the wing itself. Measurements of individual feathers are believed by some to be more repeatable between observers than maximum wing chord, and/or independent of the condition of a chick. Information on taking such measurements can be found in Redfern & Clark (2001), published studies (references in species accounts) and/or through seeking advice from the authors of such studies or experienced ringers.

7.8.2 Tarsus (leg) length The minimum length is the most frequent method used. This gives the length of the tarsometatarsal bone. The measurement is taken with the leg held at right angles to the tibia (the part of the leg above the ‘knee’) and the foot held at right angles to the tarsus.

The measurement is the distance between the notch of the ‘knee’ and the foot (Figure 2 (i)).

Ideally this measure is taken with callipers but a ruler can be used. Maximum length (tarsus and heel) can also be measured: the tarsus is held in the same way but the measurement is Raptors: a field guide for surveys and monitoring

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taken from the distal point at the ‘knee’ and not the notch (Figure 2 (ii)). A third method of measuring tarsus length may be easier for small chicks. The tarsus is measured from the centre of the ‘ball’ of the foot to the distal point of the ‘knee’ (Figure 2 (iii)). The method of measurement should always be recorded. It is recommended that tarsus length is recorded to the nearest 0.1 mm for tarsal lengths up to 100 mm, and to 1 mm if the tarsus measurement is greater than this.

(i). Tarsus measurement.

(ii). Tarsus and heel measurement.

(iii). ‘Foot’ and heel (from ‘ball’ of foot to heel) measurement.

Figure 2. Three ways of measuring tarsus (leg) length. In each case the measurement is the shortest distance between the points indicated.

52 Raptors: a field guide for surveys and monitoring

7.8.3 Tarsus width and depth These measurements are taken using callipers and should be measured to the nearest 0.1 mm.

Tarsus width is taken at right angles to the foot at the narrowest point on the tarsus (Figure 3 (i)). Tarsus depth is also taken at the narrowest point of the tarsus, parallel to the foot (Figure 3 (ii)). For standard or maximum measurements of tarsal width and depth, the callipers should touch the scales on the leg but not depress them. For some species, a ‘minimum’ or ‘tight’ measurement is recommended (see individual species accounts). This involves using the flat inner jaws of a calliper (not the sharper edges at the outer part of the jaw). While supporting the bird’s leg, the callipers are held across the narrow point of the tarsus and the jaws are pressed briefly and firmly (using the thumb of the hand holding the callipers) against the scales to measure a minimum tarsus width or depth.

(i). Measurement of tarsus width.

(ii). Measurement of tarsus depth.

Figure 3. Measuring tarsus width and depth.

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7.8.4   Foot span and hind claw For measuring foot span, the foot is held flat against a ruler. Foot span can be recorded as the length without the claws (Figure 4 (i)) or with the claws (Figure 4 (ii)), and observers must record clearly which measurement is taken. Foot spans up to 100 mm should be recorded to the nearest 0.1 mm, and to 1 mm for measurements greater than this. The length of the hind claw (Figure 4 (iii)) can be measured directly with callipers to the nearest 0.1 mm.

(iii)

(i)

(ii)

Figure 4. Foot span and hind claw measurement. Each measurement is the shortest distance between the points indicated.

7.8.5  Bill (culmen) and total head length Bill (culmen) length should be measured to a precision of 0.1 mm using callipers. In raptors, the standard measurement (Figure 5 (i)) extends from the bill tip to the edge of the cere (the bare skin at the top of the bill, between the bill and the facial feathers) on the upper mandible (top half of the bill). If the shape of the bill does not allow access for callipers, the measurement should be made very carefully using dividers and a ruler.

Total head length or head and bill length (from the base of the skull to the tip of the bill) is a valuable measure of body size, and a good sex discriminant in many groups of non-passerine birds, including some raptors. The measurement is taken from the tip of the bill to the back of the skull (Figure 5 (ii)). Carefully bending the head forwards will improve the measurement technique.

For total head lengths of up to around 100 mm, the measurement can be taken to the nearest 0.1 mm using callipers. If the measurement is to be taken on a regular basis, then it is useful to thicken the arm of the callipers that rests on the back of the skull (e.g. by gluing a piece of solid material onto either side of the calliper arm). Callipers may be too small for larger birds, in which case the measurement can be taken to the nearest 1 mm by gluing a plastic or metal ruler to a block of solid material and placing a further block of material with a slit cut through it over the ruler. With

54  Raptors: a field guide for surveys and monitoring

(i). Measurement of bill (culmen) length.

(ii). Measurement of head and bill length.

Figure 5. Measuring head and bill length. In each case the measurement is the shortest distance between the points indicated. the back of the skull placed on the fixed block, the moveable block can be slid up to the end of the bird’s bill and the measurement read off the ruler.

7.8.6 Mass Mass is measured in grams using a spring balance. Each chick should be placed in a cloth bag. Holding the balance by the hook or loop at the top, attach the bag to the hook on the bottom of the balance. With the bag hanging free, the mass is read off the balance. The bag is then weighed again without the chick and its mass is subtracted from the combined mass of bag and chick to give the chick’s mass. Eggs and very small chicks (with a weight that is small in comparison to that of the bag) may be weighed in a plastic weighing cone or on portable electronic scales. The weighing device should be sheltered from the wind to ensure an accurate measurement. Balances should be calibrated regularly with objects of known mass to ensure accuracy.

As the mass of an individual bird can vary through the day due to consumption of food, it is important to record the time of day at which birds are weighed. In addition, for raptor chicks, it is useful to record whether there is food in the crop at the time of weighing (see Figure 6), as some existing criteria for distinguishing between the sexes of chicks based on mass rely on a distinction being made between individuals with full and empty crops (e.g. Bijlsma, 1999).

Experience may be required to make this distinction for particular study species.

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Empty

Full

Figure 6. Variation in crop fullness of raptor chicks.

7.8.7 Measuring and weighing eggs Eggs should be measured using callipers. Length and maximum breadth are the two measurements required when calculating density (Figure 7; see also Section 6.5.1). It is best to hold each egg between the thumb and index finger and carefully slide the jaws of the callipers over the part to be measured; take the measurement when the jaws just scrape the shell and always move the jaws when they are slightly away from the egg to avoid damaging the shell.

It is a good idea to practise measurements on hens’ eggs first, to ensure measurements are repeatable and can be made as quickly as possible. Length and breadth should be measured to the nearest 0.1 mm.

Eggs should be weighed to the nearest 0.1 g. If a spring balance is used, each egg should be placed in a cloth bag or a plastic cone that is at least half as long again as the egg, to minimise the risk of it falling out. If it is windy, measurements can be made most effectively by sheltering the balance and egg (e.g. by lowering into an open rucksack). The balance should be held over something soft rather than rocks, in case it is dropped.

Measuring more than one egg in a clutch will allow a more precise prediction of hatching date from a nomogram. If eggs are being weighed repeatedly for density measurements, they can be carefully marked using a non toxic felt-tip pen so that length and breadth measures need only be taken once. When measuring and weighing eggs to judge the stage of incubation, always first check the blunt end of each egg for any signs of hatching.

7.8.8 Other measurements A range of other measurements may sometimes be taken to age or sex raptors. As these are non-standard, it is important to check the relevant source of reference for details of how they are taken, prior to using them in the field.

56 Raptors: a field guide for surveys and monitoring

Figure 7. Measurement of eggs: (i) breadth at equator (widest point); (ii) length.

7.9  Wildlife crime Raptors may be persecuted illegally (Etheridge et al., 1997; Scottish Office, 1998; Anon., 2000; RSPB, 2007a, b; Whitfield et al., 2003, 2004a & b, 2006b, 2008a) through poisoning, shooting, the destruction or taking of nests, eggs or young, or the illegal use of traps. Wildlife crime may also involve actions that result in the intentional or reckless disturbance of birds at their nests or other locations where it is illegal to do so, for example the use of photographic equipment from a hide close to a nest without a licence.

Raptors may disappear from an occupied home range, or fail to breed successfully, for a variety of natural reasons, including bad weather, a shortage of available prey, or predation of eggs, chicks or adult birds. If wildlife crime is suspected, accurate records of any observations or evidence should be made and reported to the Police as soon as possible. It is important not to disturb a suspected crime scene or to destroy evidence that may be invaluable to the Police. When recording incidents, fieldworkers in Scotland should be aware of the principle of corroboration in Scots law, which requires evidence to be accounted for by two sources. Ideally this would involve two eye-witnesses but additional sources of corroboration, such as a photograph or video footage, may be used in addition to the evidence of a single witness. In the specific case of egg theft or destruction, there is provision (Section 19A of the Wildlife and Countryside Act 1981, as amended) for convictions in Scotland on the evidence of one witness.

If a potential wildlife crime incident is observed, then a fieldworker should call the Police as soon as possible and ask for an incident number (this ensures that a record will be made of the report). Any observed or suspected perpetrator of an incident should not be approached. Rather, notes should be taken, including a full description of the suspect with details such as clothing, actions, words spoken, and whether the suspect is known or has been seen previously. Notes should also be made of the location of the observation point, the distance of the suspect from the observation point (and any obstructions that interrupt the line of view), whether or not optical Raptors: a field guide for surveys and monitoring 

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aids were used, and details of light and weather conditions. In addition, if a suspect is observed using a vehicle, then the registration number, make, model and colour should be noted.

If there is evidence of suspected persecution, the exact location (a six figure or more accurate GPS grid reference) should be recorded, along with full details of the evidence. If possible, the scene should be photographed or videotaped. Inclusion of an object of recognisable size (such as a pen or a coin) in a photograph, for example of a footprint, will help to indicate scale.

Evidence of persecution may include: the carcasses of poisoned or shot birds of prey; poison bait; the poisoned carcasses of other birds or animals in locations or circumstances that indicate that raptors may be at risk; or traps set illegally.

Some of the poisons used are extremely toxic to people (and dogs), so suspected poisoned bait or victims of poisoning should not be touched. Instead, carcasses should be covered if possible (without destroying evidence) until the Police or other authorised persons can retrieve them for analysis. The Police should be informed of the location of the suspected poison as soon as possible.

Fieldworkers are advised to be aware of and respect the legal use of traps and snares. Sources of information include: the Game and Wildlife Conservation Trust’s book on predator control (Game Conservancy, 2005); codes of practise (including fox snaring and traps for pest birds and mammals) published by the British Association for Shooting and Conservation (www.basc. org.uk); and the Partnership for Action Against Wildlife Crime (PAW), a multi-agency group comprising representatives of all of the organisations involved in wildlife law enforcement in the UK (www.defra.gov.uk/paw).

The general rule is to leave evidence – such as a trap, cartridge cases or a cigarette packet – in situ. With such items, it is DNA evidence that is likely to be of most use to the Police and handling may result in contamination by the DNA of the fieldworker. In this context, it is good practice for fieldworkers to ensure, when they visit a nest or observation point, that they do not leave any items (e.g. chewing gum or cigarette ends) that could confuse a possible future crime scene. Unless it is possible to await the arrival of the Police, it is recommended that an illegally set trap should be photographed or video-taped in the set position and then sprung with care using a stick. This is to avoid further danger to people or wildlife.

On leaving the scene of an incident, fieldworkers are advised not to discuss their findings with anyone they encounter in the area, to minimise the risks that evidence might be removed or altered.

When reporting incidents to the Police in England, Scotland, Wales, and the Isle of Man, the local Police Wildlife Crime Officer (PWCO) should be informed, and can be contacted through any Police Headquarters. In Northern Ireland the local police should be contacted. In the UK, RSPB investigations officers (www.rspb.org.uk/policy/wildbirdslaw) work closely with the Police and others involved in the investigation of wildlife crime, and can provide useful advice on wildlife crime incidents. They can be contacted through any RSPB office or incidents can be reported online (www.rspb.org.uk/ourwork/policy/wildbirdslaw/preventing/reporting.asp).

Staff of Statutory Country Conservation Agencies can also provide advice on wildlife crime and initial enquiries can be made to any office. Further information on reporting wildlife crime incidents in the UK can be obtained from PAW (www.defra.gov.uk/paw). Wildlife offences in the Republic of Ireland should be reported to the local NPWS Conservation Ranger (www. npws.ie) or to the local Garda (Police) station.

58 Raptors: a field guide for surveys and monitoring

7.9.1  Site confidentiality Because raptors may suffer from persecution by humans, it is common practice, for some species, to keep information on the locations of nest sites, or of territorial birds, confidential, and to store them securely. Fieldworkers are advised not to pass on information on the location of nest or roost sites, especially of scarcer species, in any circumstances where there is a suspected risk to the birds.

Raptor data, such as the locations of nest sites, regular flight paths and roosting areas, are increasingly of use for conservation purposes. These include the designation of protected sites such as Special Protection Areas (EU Birds Directive) and Sites of Special Scientific Interest, and environmental impact assessments for proposed developments such as windfarms. Contributors to the Scottish Raptor Monitoring Scheme are asked to provide locational data for nest sites as six figure grid references. It is also very useful if site location information is routinely provided to the Statutory Country Conservation Agencies on licensing report forms, to the RBBP and to the BTO as part of ringing or NRC returns. Such information is kept strictly confidential and stored in a secure database along with details of the data provider and/or owner; it can be made available, with appropriate permission, for conservation and site safeguard purposes.

Complete secrecy can be counter-productive, as sites have been lost, destroyed or disturbed because the relevant conservation agencies were not aware of them until too late (e.g. Spencer & RBBP, 1992).

7.10  Health and Safety This section contains notes on good practice that raptor surveyors may find helpful to consider before undertaking fieldwork.

Field surveys of raptors may involve visits to remote areas of countryside by lone workers.

Checking nests and ringing chicks may require climbing trees or cliff faces. Birds of prey and their chicks can be aggressive and larger species in particular have the potential to inflict serious wounds on handlers. It is good practice for raptor surveyors to consider the potential risks to their own health and safety while they are undertaking fieldwork, and to take appropriate actions to minimise these risks, for example, by: carrying and ensuring they are able to use suitable equipment for navigation and communication; wearing appropriate clothing for protection against adverse weather; carrying adequate supplies of food and water and a basic first aid kit. Similarly, it is good practice for fieldworkers to consider the health and safety of others who may be affected by their actions, and to pass on relevant health and safety information to those accompanying them on survey work.

When visiting remote locations, it is important to leave a note of the trip with a responsible person. This should include: the date and time of departure; the method of travel to and from site; the proposed itinerary; the expected time of return; vehicle identification; details of who to contact in the event of failure to return; and the appropriate time to raise an alarm. It is advisable to carry a mobile phone for emergency use (but note that it may not work in some remote areas).

Hypothermia is a significant hazard when working in exposed environments such as mountains and moorlands, especially where fieldwork may involve long periods of inactivity during vantagepoint watches. It is advisable for fieldworkers to ensure that they have appropriate warm and waterproof clothing and supportive footwear, plus a survival bag and high-energy food supplies.

Sun exposure is also a concern, and it is recommended that sun cream of an appropriate sun protection factor is worn at all times on areas of exposed skin.

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When working during darkness, it is advisable to carry a torch and spare batteries, wear bright clothes if working or accessing areas along roads, and avoid working alone if possible. It may be appropriate to inform the local Police and/or local residents about your activities and area of operations.

Wild animals or birds should be avoided at certain times of year or in certain situations when they may attack people perceived as intruders; this may include the birds of prey that are the subject of the survey (further advice is given in the species accounts) or, depending on the habitat, rutting deer or large nesting birds such as great skuas. Fieldworkers are also advised to take special care if survey work brings them into close proximity to livestock and other domestic animals (including farm dogs), and agricultural machinery or forestry operations. In addition, warning signs for hazardous sites, such as quarries, ravines or railways, should be heeded.

Before undertaking any fieldwork that involves climbing rocks, cliffs or trees, fieldworkers are strongly advised to undertake training in that activity, and in the use of appropriate safety equipment, such as helmets, harnesses and ropes. The Health and Safety Executive (HSE) publishes a number of useful leaflets, for example: AFAG401 Tree Climbing Operations and INDG369 Why fall for it, preventing falls in agriculture (available from www.hsebooks.com).

Fieldworkers who handle birds of prey are at risk of injury, especially from larger species, including cuts from sharp bills and penetrating injuries from powerful claws. Protective gloves (e.g. those used by falconers) should be worn when handling birds with talons whenever possible, and immunity to tetanus maintained. Particular care should be taken to avoid injuries to the eyes and safety spectacles should be used when working with some raptors, particularly owls (see advice in species accounts). Watch out for wasps, hornets and fleas if work involves opening nest boxes or checking other nesting cavities. It is strongly recommended that any fieldworker without experience of close approaches to raptor nests or handling chicks undertake training in appropriate procedures with someone who is experienced in handling raptors (and indeed evidence of such training will be required to obtain an appropriate licence – see Section 7.1.1). Similarly, a fieldworker with experience of handling birds, who wishes to undertake work on a new raptor species, is advised to consult with a raptor worker with experience of that species.

7.10.1 Diseases Raptor fieldworkers may be exposed to disease during survey work and ringers are particularly vulnerable because of direct contact with wild birds. If a disease is suspected, then it is important to inform the doctor of possible exposure to zoonoses (diseases of animals that can be transmitted to humans), specifying that nest visiting and ringing have been carried out if appropriate. Typical diseases that may be encountered are as follows: • Tetanus, which may result from the infection of even minor wounds and scratches with Clostridium tetani, a common micro-organism in soil and likely to be carried on talons and beaks. Fieldworkers are advised to ensure that they are immunised against tetanus and that their immunity is maintained by boosting at the appropriate intervals. This can be arranged through a local GP or Health Centre; • Weil’s disease, a severe form of leptospirosis that can be fatal if left untreated. The pathogen is carried by rats and excreted in their urine, and persists in water such as in puddles in rat-infested places. Thus visits to the nests of rat-eating species or in buildings or other locations where rats might occur may pose a risk;

60 Raptors: a field guide for surveys and monitoring

• Lyme disease or Lyme borreliosis, a bacterial disease caused by Borrelia spirochaetes transmitted by animal ticks and associated with rank vegetation. The disease is treatable but can cause severe symptoms if left untreated. A variety of animals may act as hosts ranging from sheep and deer in the uplands, to pheasants in some lowland areas of Britain, and on the Continent Borrelia spirochaetes have been found in passerines such as blackbirds; • Tick-borne encephalitis, a viral disease carried by animal ticks. Warm forested parts of Europe and Scandinavia, especially where there is heavy undergrowth, give the greatest risk from ticks in late spring and summer. A vaccine is available where prolonged exposure in the risk areas is likely. In Britain and Ireland, a related virus responsible for ‘louping ill’, a disease with symptoms varying from a mild flu-like illness to more severe disease requiring hospitalisation, can infect a wide variety of mammal and bird hosts, particularly grouse and hares, in moorland regions; and • Salmonellosis is a bacterial infection common in rats and mice (which may be found in the ‘larders’ at raptor nests), which can in certain circumstances spread to the birds as well. The bacteria abound in the droppings of the infected bird, which may not necessarily appear sick. If the bacteria are ingested, for example as a result of preparing or eating food with contaminated hands, there is a risk of food poisoning.

There are other groups of bacteria and viruses to which the same remarks apply: • Other pathogenic bacteria that may be present in wild birds (often from human-contaminated sources in the first place) include Campylobacter jejeuni and potentially pathogenic strains of Escherichia coli. These could be found at nests of carrion-eating raptors; and • Avian influenza: numerous strains of avian influenza viruses circulate in wild birds but most are relatively benign. All bird species are thought to be susceptible. Migratory birds such as wild ducks and geese can carry the viruses, often without any symptoms of illness, and show the greatest resistance to infection. People can become infected with avian flu as a result of close contact with infected birds, but this is rare. Historically, human infection with avian influenza viruses has usually caused mild conditions such as conjunctivitis (eye infection) and mild flu-like symptoms. More severe infections can lead to pneumonia, acute respiratory distress, viral pneumonia, and other severe and life-threatening complications. A highly pathogenic strain of avian flu, H5N1, is currently a cause of worldwide concern and can infect raptors. Up to date guidance on this issue in Britain and Ireland can be obtained through the websites of the Statutory Country Conservation Agencies and/or Government Environment Departments and advice for ringers and nest recorders is available on the BTO website.

There are a number of ways in which the risk of diseases can be minimised, such as: • Immunisation against tetanus and poliomyelitis; • Removal of ticks from the skin as soon as possible; tucking trouser bottoms into socks so that ticks cannot attach or climb up the leg, and making regular checks of skin and hair; light coloured clothing can make ticks more visible (but may conflict with requirements for fieldworkers to wear neutral or dark colours for concealment); • On extended fieldwork sessions, remember the need for adequate food, sleep and dry clothing. Self-neglect lowers the body’s resistance to any infection; • Anti-bacterial hand gels can be carried in the field and used to clean hands (particularly after handling birds, soiled bird bags and pellets); in particular, do not touch food with bare hands before washing them and note that a cigarette can transfer infection from hands to mouth; hands should be washed with soap and water and/or detergent after fieldwork.

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• During fieldwork, cuts and abrasions should be kept covered by a dressing; and • Wear disposable rubber gloves when cleaning out nest boxes or handling dead birds, and dispose of the gloves responsibly after use.

7.10.2 Health and Safety Legislation and Responsibilities This section provides some information on legislation covering health and safety that applies to fieldworkers, and gives sources of further information. The details are most relevant to fieldworkers carrying out studies in Great Britain with references provided for relevant sources of information for Northern Ireland, the Republic of Ireland and the Isle of Man. Those who undertake fieldwork in their own time on a voluntary basis are responsible for their own health and safety. Fieldworkers who contribute data on a voluntary basis to schemes that monitor birds, such as the Scottish Raptor Monitoring Scheme, are also responsible for their own health and safety. This includes schemes where fieldworkers may receive some support, for example travel expenses, for their survey work, as long as they are not actually paid a salary for the work (i.e. they are not employees or agents of the organisation(s) providing the expenses).

Volunteer fieldworkers should not put themselves in a position that could place them, or others, in danger, or undertake any work for which concerns exist about their own or others’ health and safety. Volunteers under 18 years of age who wish to participate in fieldwork for a monitoring scheme should ensure that the organisers are aware of their age and have made them aware of the associated risks. They should also ensure that their parents agree to them undertaking the activities. The BTO provides a useful leaflet giving general health and safety guidance for volunteers involved in its work (www.bto.org/survey).

Fieldworkers who undertake raptor surveys on a professional basis come under health and safety legislation. In England, Scotland and Wales, the Health and Safety at Work Act 1974 works on the principle that those who create risk from work activity are responsible for the protection of workers and the public from any consequences.

If a fieldworker is employed by an organisation to carry out raptor surveys, then the employer has a general duty to provide systems of work that are, so far as reasonably practicable, safe and without risk to health. A safe system of work may be defined as that which results from a systematic examination of a task in order to identify all the hazards, a so-called risk assessment (e.g. see HSE Guide: INDG163 Five Steps to Risk Assessment), and which identifies safe methods of work to ensure that any hazards are eliminated or minimised.

In circumstances where a fieldworker is self-employed and carries out fieldwork under a client/contractor relationship, both parties have duties under health and safety legislation.

Similarly, if a contractor employs sub-contractors to carry out some or all of the fieldwork for a contract, all parties have health and safety responsibilities. The extent of the responsibilities of each party will depend on the individual circumstances of the project. Further information on health and safety legislation and its application can be obtained from the Health and Safety Executive (www.hse.gov.uk).

The Health and Safety at Work Act 1974 is also the main health and safety law in the Isle of Man. Though the primary legislation adopted is broadly similar to that in the UK, there are differences, and the regulations are not the same. Further information on its application can be obtained from the Island’s Health and Safety at Work Inspectorate (www.hswi.gov.im).

62 Raptors: a field guide for surveys and monitoring

In Northern Ireland, the relevant legislation is the Health and Safety at Work (Northern Ireland) Order 1978 and further information can be obtained from the Health and Safety Executive for Northern Ireland (www.hseni.gov.uk) The health and safety regime in the Republic of Ireland is broadly similar to the UK. It is governed by the Safety, Health and Welfare at Work Act 1989, amended by the Safety, Health and Welfare at Work Act 2005; and administrated and enforced by the Health and Safety Authority (www.hsa.ie).

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64  Raptors: a field guide for surveys and monitoring

Part 2

Species accounts Raptors: a field guide for surveys and monitoring 

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INTRODUCTION TO SPECIES ACCOUNTS This section provides detailed information on survey methods for 22 species of birds of prey that breed regularly (or have done so in the past) in Britain and Ireland. Five additional species that occur irregularly are also considered briefly. The species accounts are based on the published literature (references cited in the text) and the accumulated knowledge of the authors and raptor specialists who have been carrying out survey work on chosen species for many years. Unpublished information/personal communications from the authors and specialists is not usually referenced individually in the text, but a list of all the advisers is included in the acknowledgements.

For each of the 22 regularly occurring species, accounts follow the same standard section headings. Further information on each heading is provided below (numbers refer to the corresponding section numbers in each species account).

1. INTRODUCTION This contains a brief description of the breeding and wintering status of the species in Britain and Ireland, gives notes on identification and differentiating between the sexes and age classes in the field, and the age of first breeding. If a species monograph or similar comprehensive reference is available, details are provided as a starting point for further reading.

Annual cycle The table provides a summary of current knowledge of the seasonality of home range occupation and breeding for the populations in Britain and Ireland. Any major reasons why this seasonality is difficult to establish for some species are noted. This information is used to derive appropriate visit schedules for surveying each species.

2. HABITAT, HOME RANGE, NESTS AND BREEDING Brief information is provided on the habitats used for breeding, the extent to which territoriality occurs and the likely size of home ranges (i.e. the density of pairs likely to be found within breeding habitats); emphasis is placed on information that is important for designing and planning survey work. The section on nest sites describes their usual (and range of likely) locations and the extent of fidelity to individual nest sites from one year to the next. The usual construction (if any) and size of nests, and the extent to which the nests of other species are used, is described in the section on nests. Subsequent sections on clutch size and incubation, and brood size and fledging, give brief details of basic breeding biology (laying dates and laying intervals, clutch sizes, tendency to relay, incubation schedule, role of the sexes, feeding rates (where known), length of the nestling period, and post-fledging dependence of young on their parents for food). The emphasis throughout is on information from Britain and Ireland, but if this is lacking, or if there is a need to highlight major differences between British, Irish and mainland European populations, additional material from elsewhere is included.

3. SURVEY TECHNIQUES The techniques that are recommended when checking for home range/territory/nest site occupancy, establishing whether breeding has occurred, and for finding nests (where appropriate) and measuring the annual breeding success/productivity of each breeding attempt are described. The recommendations are based both on the published literature

66 Raptors: a field guide for surveys and monitoring

(for which references are cited in the text) and the views of the authors and advisers.

The section begins with a ‘CAUTION’ about any known or suggested sensitivities of the species to disturbance at specific stages of the breeding cycle, any particular risks to the birds that may result from survey fieldwork, and any specific risks to the fieldworker (see also Section 7.10 of the Introduction for further information on health and safety). Recommended distances for viewing nesting areas so as to minimise the risk of disturbance are included where information is available. For many species these are based on alert distances (the distance between an approaching disturbance source and a bird at which the bird raises its head in an alert posture) as identified by Ruddock & Whitfield (2007) and Whitfield et al.

(2008b) from a survey of expert opinion.

3.1 Breeding season visit schedule This section describes the recommended number and timing of visits to be made to each part of a survey area to ascertain whether or not birds of a given raptor species are present (i.e. an area is occupied) and whether or not breeding takes place. It begins with a statement about any legal considerations that must be addressed if nest visits are planned, indicating whether the species is identified for special protection in Great Britain (Schedule 1 of the Wildlife and Countryside Act 1981, as amended), Northern Ireland (Schedule 1 of the Wildlife (Northern Ireland) Order 1985), the Republic of Ireland (Schedule II under Section 32 of the Wildlife Act 1976, as amended) or the Isle of Man (Schedule 1 of the Wildlife Act 1990 (Variation of schedules) order 2004), and thus whether any specific licensing is required for nest visits (see Section 7.1.1 of Introduction for further details). Additional text explains any specific difficulties in defining a schedule of survey visits and which of the (generally) four recommended visits are considered essential. The table describes the recommended timing and aim of each visit, usually: Visit 1 — to establish occupancy of a home range/nest site; Visit 2 — to check for breeding by locating active nests or follow up sites not found to be occupied during Visit 1; Visit 3 — to check for successful hatching; and Visit 4 — to measure breeding success by counting fledged young). Species-specific variations on this schedule are described, to take into account, for example, the ease with which the required information can be obtained for each species and any particular sensitivities to disturbance.

3.2 Signs of occupancy Methods for confirming whether home ranges, nesting territories and/or nest sites are occupied in any given breeding season are described (see Section 4.4 of Introduction for general definition of occupancy). Guidance is provided on whether the species should be surveyed by locating home ranges, nesting territories or individual nest sites (see also Sections 4.1 and 4.2 in Introduction for further information on definitions of territorial units). The recommended survey techniques are then described, including the timing of visits (seasonality and time of day), length and timing of watches (if required), and behaviour(s) to look out for to provide evidence of occupancy (including details of any aerial displays). For some species, active roost sites may provide evidence of occupancy, so brief details of how to recognise and locate these are given. We also provide a section on the recognition of signs left by each bird of prey species (faeces, pellets, kills, plucks, etc.) and the extent to which these can be used (alone or in combination with other evidence) to provide evidence for occupancy (see also Section 5.2 of Introduction for general information on the use of tell-tale signs to identify raptors). Finally, in this section, we summarise the criteria that, alone or in combination, allow confirmation of occupancy in any given year.

3.3 Evidence for breeding This section describes how to establish whether breeding has taken place in any given home range or territory, by outlining methods for locating active nests (together with any Raptors: a field guide for surveys and monitoring

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sensitivities that must be considered) and describing behavioural signs that can indicate that a breeding attempt is ongoing, even if a nest is not found. Guidance is also provided on establishing whether successful fledging has occurred, and on measuring the productivity of each breeding attempt by counting the number of young that fledge. Productivity can be difficult to measure for some raptor species (see Sections 4.5 and 4.6 of Introduction); hence, for each species, information is provided on the stage at which counts of young can be used as an estimate of the number that are likely to fledge, and methods that can be used to establish the minimum number that have fledged successfully.

3.4 Evidence for non-breeding In many groups of birds, including raptors, not all individuals or pairs that are capable of breeding do so every year. The proportion that do not breed in any given year is probably related to annual fluctuations in the availability of prey, with a higher proportion of birds breeding when feeding conditions are favourable. Non-breeders that do not occupy home ranges during the breeding season are very difficult to survey (see Section 3.3 of Introduction) and are not considered further in the species accounts. The recommended timing of first visits for each species is determined to maximise the likelihood of recording individuals that are present at breeding sites early in the season but that do not go on to lay eggs. Even so, it can be difficult to distinguish between non-breeding and failure during the early incubation period. Frequent visits to the nesting range around the time of laying and early incubation may be required to locate an active nest, establish whether eggs are laid, or observe other behaviours indicative of breeding; this is not always appropriate, given the sensitivities of some species to disturbance in the early stages of breeding. The visit schedule provided for each species in Section 3.1 of each account is designed primarily to assess whether territorial units are occupied, and to determine the success of breeding attempts; further visits (generally during the Visit 2 period) are likely to be required if the aim of the study is to determine rigorously the proportion of pairs that do not breed.

3.5 Ageing and sexing young This section describes any available information that can be used to determine the age and sex of chicks, including descriptions of appropriate body measurements, plumage or other characteristics (see Sections 6.5.2 and 7.8 of Introduction for further details including guidance on taking some of the most widely used body measurements of raptor chicks).

Growth curves are provided where we have managed to source data for a particular species, but it should be noted that many of these are based on data from a small number of broods and/or data for one specific population/race. In most cases, the information provided should be used as a guide only, and in fact the collection of further data on nestling growth would be very valuable for most species breeding in Britain and Ireland.

3.6 Use of egg density measurements For a small number of species, nomograms of egg density are provided. These can be used to estimate the hatching date of any egg measured in the field (see Introduction, Section 6.5.1).

This can help in planning the timing of subsequent survey visits to a nest to record hatching and/or fledging success. It has been possible to source appropriate data for only two of the species considered in this field guide, and in each case the collection of further data on larger samples of eggs would be of great value. For this reason, the information provided should be used as an approximate guide only.

68 Raptors: a field guide for surveys and monitoring

4.  SURVEYS OUTSIDE THE BREEDING SEASON This field guide focuses primarily on methods for surveying breeding populations of raptors.

For most species, surveys during the breeding season, when the ranges of individuals that attempt to breed are limited through attachment to a nesting area, provide the best opportunity to estimate population size in a given area. There are a number of reasons for survey work outside the breeding season, however, such as: assessing the size of wintering populations where a species is not sedentary throughout the year; assessing habitat use by a particular species during the winter months; or monitoring changes in the use of a wintering area by a particular species or assemblage of species. For raptor species that occur in Britain and Ireland during the winter months, we have therefore provided some brief suggestions for appropriate survey methods that could be used outside the breeding season.

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Barn Owl Tyto alba 1. INTRODUCTION The barn owl occurs throughout much of Great Britain, the Isle of Man, and Ireland. It is absent as a breeding species from the Highlands of Scotland, the Outer Hebrides, Orkney and Shetland.

Barn owl populations have undergone a long term decline during the last 100-150 years (Blaker, 1933, 1934; Shawyer, 1987; Gibbons et al., 1993; Toms et al., 2001, Toms et al., 2003), thought to be linked to the loss of hunting habitats and nest sites associated with agricultural intensification (Shawyer, 1987; Taylor, 1994; Taylor & Walton, 2003). The Scottish population appears to have increased in recent years (Shaw, 2007). British and Irish populations, and those in mainland Europe, are largely sedentary, although the natal dispersal distances of continental individuals tend to be greater (Toms, 2002b). Young barn owls from eastern Europe (the dark-breasted race guttata) occasionally reach Britain and Ireland but may also escape from captivity. There is no clear size difference between the sexes but they can usually be separated by plumage; most females are darker than males and also have a greater degree of flecking on their underparts (Taylor, 1994; Barn Owl Trust, 1989a). Most barn owls start breeding during their second calendar year. Once fledged, young birds cannot be separated from older birds in the field.

For further information on the biology and ecology of this species, Taylor (1994), Shawyer (1998) and Martin (2008) provide comprehensive accounts. The Barn Owl Trust (www.barnowltrust. org.uk) also provides a range of information on barn owl ecology and conservation.

Annual cycle Breeding Activity

Peak Period

Range

Occupation of home range

All year

Territorial display

February to April

Courtship

Early February (in mild weather), usually March to April

Duration (days)

Egg laying

Early April to late May

First clutch: March to July 6 to 21 Second clutch: (infrequent) June to August (birds that laid their first clutch early in the season only)

Incubation

Early April to late June

March to August

Hatching

Early May to late June

April to August

Young in nest

Early May to early August

April to November

Fledging

Mid-June to early August

June to November

Juvenile dispersal Barn owl

29 to 34

50 to 70

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2. HABITAT, HOME RANGE, NESTS AND BREEDING 2.1 Habitat Barn owls are found in a variety of open farmland habitats and in young conifer plantations.

In a survey across Britain and Ireland (Shawyer, 1987), 92% of the recorded breeding sites were below 150 m a.s.l., where snow cover in winter was 15 days per annum or less. In areas with a higher snowfall, breeding barn owls were rare. In southwest Scotland, most barn owls bred between 75–175 m a.s.l., with only a few pairs at higher altitudes in forestry plantations (Taylor, 1994). Regular breeding at higher altitudes (over 200 m and up to 310 m a.s.l.) has been recorded in southeast Scotland and on Exmoor, Devon.

2.2 Home range Barn owl home ranges are not exclusive. They may defend the immediate area around the nest (the nesting territory) but evidence for other territorial behaviour is weak (Taylor, 1994). Outside the breeding season, birds are known to forage up to 3 km, and occasionally up to 5 km, from their nest site, which equates to a home range size of up to 5,000 ha. In contrast, during the breeding season, the foraging range of breeding barn owls normally extends up to a kilometre from the nest: an area of up to 350 ha (Cayford, 1992; Taylor, 1994). Barn owl home ranges generally include areas of rough, tussocky grassland with a deep litter layer (optimum vole habitat) but the species may also occur in areas with little or no rough grassland within a kilometre of the nest site (Taylor, 1994; Ramsden, 1995; Shawyer, 1998; McGhie, 2000). In enclosed pastoral farmland in southwest Scotland, breeding barn owls were found to require at least 9-10 km of grassy woodland edge within a 1 km radius of a nest site (Taylor, 1989). Studies in areas of England, Scotland and Wales found that barn owls needed varying amounts of rough grassland within 2 km of the nest in order for local populations to be sustainable, as follows: 14-21 ha in arable areas; 31-47 ha in pastoral areas; and 17-26 ha in mixed farming areas (Askew, 2006).

2.3 Nest sites Barn owls nest in large cavities in trees, buildings, bale stacks, and in fissures in rocks, as well as nest boxes. They prefer dry, dark nest sites with a floor surface greater than 0.3 m by 0.3 m (Taylor, 1994). Nationally, about a third of barn owl nest sites are in trees but a big dry cavity is required so generally only old trees are suitable (Shawyer, 1987; Toms et al., 2000). In the west of Britain, barn owls use buildings more frequently than in the east, which appears to be due to the lack of suitable tree sites (Toms et al., 2000). They tend not to use buildings that are frequently used by people (Bunn et al., 1982; Shawyer, 1987; McGhie, 2000) and the conversion of many derelict rural buildings and farm steadings into modern houses has restricted the availability of sites for barn owls; with others lost as they deteriorate into unusable ruins (Petty et al., 1994; Ramsden, 1998; Toms et al., 2000). However, where nest sites such as old barns are converted into dwellings and provision for the owls is incorporated, they will often continue to nest with humans living directly below them (Ramsden, 1995). Birds that can remain out of site when at the nest are much less likely to be flushed and can tolerate all kinds of activity close to the nest (Barn Owl Trust, 2002). In the most recent survey of barn owls across Britain and Ireland in 1995–1997, the commonest trees used for breeding were ash and oak, the species most likely to develop sufficiently large cavities, although elm, sycamore and willow were also used (Toms et al., 2000). Nest holes in trees are predominately in a cleft or cavity in the main trunk (Bunn et al., 1982), at an average height of about 5 m from the ground. Trees used for breeding are generally located near the edge of large blocks of woodland (McGhie, 2000).

Barn owls will readily use nest boxes (Shawyer, 1987; Johnson, 1994) and barrels placed on trees in a coniferous forest can increase the local population size (Shaw, 1994b; Petty et al.,

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1994). Provision of nest boxes can be used as a conservation management tool in areas where the availability of nest sites in buildings and hollow trees is declining (Taylor & Walton, 2003).

2.4 Nests Barn owls do not build a nest but may scrape a slight hollow if the nest site has a soft substrate.

2.5 Clutch size and incubation Barn owls lay 2–9 eggs (Shawyer, 1998), with occasional clutches of up to 12 eggs. The BTO Nest Record Scheme records the average clutch size as 4.9 (n=485). The eggs are normally laid at intervals of 2–3 days. Greater gaps, often associated with poor weather (extremely low temperatures, snow or prolonged rain), of 3–7 days have been recorded (Taylor, 1994).

Egg laying occurs later when small mammals are scarce or when spring weather is cold, and young females lay later than older birds (Taylor, 1994). In Britain and Ireland, clutch size varies significantly with habitat and decreases as the breeding season progresses (Taylor, 1994).

Smaller clutches are laid in years when there are fewer small mammals and, in such years, a greater proportion of pairs will not lay (Taylor, 1994). Second broods are more frequent in years when small mammals are highly abundant. Incubation begins with the first egg and lasts for 29–34 days (Bunn et al., 1982), with most eggs hatching after 30–32 days. Only the female incubates, leaving the nest for brief spells (5–10 minutes) around three times a day.

The male begins feeding the female about one month before laying and provides all her food (at the nest site) during incubation. In southwest Scotland, prey-delivery rates were measured at 19 nests using automatic nest recorders (Langford & Taylor, 1992). Average daily rates (from 12:00h one day to 12:00h the next) of 16.4 items were recorded during laying and 8-11 during incubation. These high delivery rates, similar to those recorded during the nestling period at the same nests (see Section 2.6 below), resulted in the caching of surplus food at most nests, probably as an insurance against food shortage once chicks had hatched.

2.6 Brood size and fledging Hatching is asynchronous. As a result, the chicks in a large brood are of widely differing ages.

The female broods for the first 10 days, after which she hunts in addition to the male (Cramp, 1985). Maximum daily delivery rates (from 12:00h one day to 12:00h the next) of 14-16 items during the nestling period were recorded in southwest Scotland about 30 days after the hatching of the first chick, with a steady decrease thereafter (Langford & Taylor, 1992). One pair was recorded bringing 17 prey items to the nest in two hours (Bunn et al., 1982). The young can fly after 50–55 days (Cramp, 1985) but their flight feathers are not fully developed until 70–75 days after hatching and they return to the nest until they are 11–14 weeks old (Taylor, 1994). They become independent 3-5 weeks after leaving the nest, and normally leave the parental home range within a few weeks (generally between September and November).

Juvenile dispersal is largely completed within the first four or five months after fledging (Toms, 2002b). The abundance of small mammals influences chick survival and the number that fledge: 45% of chicks may die in years with low populations of small mammals compared to only 5–10% in years when they are abundant (Taylor, 1994).

3. SURVEY TECHNIQUES CAUTION Barn owls can be sensitive to disturbance at the nest site, particularly early in the nesting cycle, from prelaying through to hatching (Shawyer, 1987; Percival, 1990; Ruddock & Whitfield, 2007), so special care should be taken during these stages of the breeding cycle.

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However, nest inspections should not have a detrimental effect if carried out carefully at all stages of the breeding cycle (Taylor, 1991, 1994). Barn owls should not be flushed from nests or roosts in daylight because they may be mobbed by other birds and will be reluctant to return, which may affect their survival particularly in the winter months. If it is necessary to look inside a confined space for a nest site, it is strongly recommended that goggles or full face protection is worn, particularly if there is a risk of a more aggressive tawny owl being present. If searches for nest or roost sites and nest inspection visits require visits to old buildings and/or climbing, then appropriate health and safety precautions should be taken (see Section 7.10 of Introduction).

3.1 Breeding season visit schedule

The species is listed on Schedule 1 in Great Britain, Northern Ireland and the Isle of Man, and Schedule II in the Republic of Ireland (see Section 7.1.1 of Introduction). This is a difficult species to survey accurately because it is largely nocturnal and thinly distributed over a wide geographical area; compared with other owl species it is not particularly vocal nor does it defend a clearly defned territory (Toms et al., 2001). The survey methodology described here follows that used for the 1995-1997 UK survey (Toms et al., 2001), allowing for additional visits to monitor breeding success. To establish occupancy (which for barn owls requires the location of active nests, see below), two visits are required – Visit 1 and one additional visit between May and August (Visit 3 or 4). Two further visits are required to measure breeding performance (Visit 2 and Visit 3 or 4). If there is any uncertainty over the stage in the breeding cycle, Visit 2 should be delayed so as not to disturb birds during laying. Late visits in October may be necessary if birds have attempted a successful second brood.

Visit 1

November to January

To check for suitable nesting sites and signs of occupancy

Visit 2

April to June

To locate active nests with eggs.

Note CAUTION about timing of visits

Visit 3

May to June

To check for young and late/second clutches

Visit 4 (Two or more visits may be required)

July to August (October)

To check for fledged young and late nests/second clutches

3.2 Signs of occupancy

Given that the home ranges of barn owls are not mutually exclusive, the only definitive way to assess the numbers in a study area is to locate nest sites. Barn owls can be almost completely nocturnal but, in many areas, they are crepuscular. They can be seen hunting in the early morning shortly after dawn or in the evening about an hour before sunset or even earlier in winter (Bunn et al., 1982). If a barn owl is feeding young, it will carry prey directly back to the nest site and its direction of flight can be used to help locate the nest. Not all owls hunt in daylight, however, so fieldworkers should not depend on observing barn owls when locating nest sites.

3.2.1 Locating home ranges Information on barn owls can be obtained from local people but pairs can exist in an area without people knowing, so systematic searching is always required. Male barn owls may make advertising calls from their roosts (typically in the 6-7 weeks before laying but also prior to second clutches), and display flights (flying steadily over the territory, repeatedly changing direction and calling; Cramp, 1985), which may assist in identifying areas that are occupied and hence require subsequent systematic checking.

Study areas should be intensively and systematically searched for the presence of potential nest sites in winter (November to January), when deciduous trees are leafless and there is

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Barn owl

minimal risk of disturbance to early-breeding tawny owls. All suitable sites should be mapped or recorded as six figure map references, including farm buildings, tree cavities away from the centre of a wood, nest boxes, cliffs (including quarries) and bale stacks. If it is suspected that a barn owl is present at a particular location, then it should not be flushed; simply record the site at this stage. A barn owl disturbed in daylight may be mobbed by other birds and will be reluctant to return to the site, which may affect survival in the winter months.

To establish occupancy, all of these potential nesting sites must be visited again between May and August (Visit 3 or 4); this timing maximises the likelihood of finding breeding birds or evidence of breeding and early failure, while avoiding disturbing birds early in the nesting cycle. An earlier visit (Visit 2) can be made to check for nests with eggs, taking care to minimise disturbance, and two (or more) visits may be made between May and August to assess productivity. Later visits may be required if a pair of barn owls has attempted a second brood.

The sight of birds carrying food into a site can be taken as evidence of breeding and there is no need to approach the nest site any closer, unless checking the nest contents for a specific purpose. Watching a potential nesting area from a distance for an hour before sunset until an hour after sunset on a cloudless, still evening gives a 97% chance of observing a visit from a barn owl, if the site has an active nest (Toms et al., 2000).

Some barn owls may also be located by listening for their ‘song’, which is described as a loud, drawn out, hissing scream ‘shrrreeeee’, with a marked gargling or tremulous effect (Mikkola, 1983). Screeching by males begins in mild weather in February. The calls are made shortly after dusk or as the male leaves the nest site or roost (Bunn & Warburton, 1977). The fieldworker should listen for these calls around dusk and plot the locations on a map, before returning and searching the area for roosts and suitable nest sites at the appropriate time.

Some barn owls may also respond to broadcast calls, but they do not do so consistently enough for this to be used for survey purposes.

Later in the season, indirect signs may be more obvious around an active nest site, with downy feather extensions from the young becoming snared on foliage (surveyors should be careful not to confuse these with tiny moulted feathers from adult birds), and pellets deposited below the nest entrance of tree cavity sites. On warm days, flies attracted to discarded prey often provide a clue to the location of a nest site, and a smell of ammonia may emanate from the site. Some nest sites may remain clear of white splashings and other signs until the young start to climb about, however, so ‘clean’ sites do not necessarily mean that there are no barn owls breeding.

3.2.2 Locating roosts Barn owls can have a number of daytime roosts. Both the male and female will roost at the nest site before and during egg laying but the male will move to roost at nearby sites, often a paired nestbox if there is one, after the clutch is complete. The female will move to a separate roost once the oldest owlet is about four weeks of age (Toms et al., 2000). Care must be taken not to count roosts as additional occupied nest sites. Roosts can be located by systematically searching suitable buildings, trees and crags. They can be identified by an accumulation of pellets, feathers and white streaking (Section 3.2.3). In coniferous plantations in southwest Scotland, barn owls seldom roost during the winter in nest boxes that are subsequently used for breeding, being seen on less than 5% of visits to these boxes. Faecal droppings showed that they regularly visit these nest sites, however, as four out of five nest boxes that contained fresh droppings in winter were subsequently used for breeding. Any roosts or nest sites located should be recorded as a six figure map reference with a description of the site.

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3.2.3 Recognition of signs When searching for barn owls, watch out for pellets and feathers on the ground, on bales, or on ledges in buildings, and for long white streaks of droppings on beams, walls or tree trunks (Barn Owl Trust, 2002). Before entering a building, look for holes in the outside walls which a barn owl could use (a minimum of 75 mm wide) and check these for droppings or other signs (Barn Owl Trust 1989b). Fresh barn owl pellets are characteristically glossy black, fading to dark grey as they dry (Shawyer, 1998; Barn Owl Trust, 2002). Hence, with experience, it is possible to use the condition of pellets to ascertain how recently sites have been occupied (see Barn Owl Trust, 2002, for photographs of pellets of differing age, from one day to thirty months old).

The pH of barn owl stomachs is higher than that of many other predatory birds and there is less digestion of skeletal material (Smith & Richmond, 1972). Hence barn owl pellets are harder and more compact than those of other owls and contain most of the bones from their prey.

They tend to be wide relative to their length, with a size range of 30-83 mm long by 15-40 mm (Shawyer, 1998; Brown et al., 2003). Barn owl feathers are distinctive and highly variable and some individual owls can be recognised by the differences in pattern (Taylor, 1994).

3.2.4 Evidence of occupancy Finding occupied roost(s) indicates that barn owls are present in an area but the location of an active breeding attempt (observations of food being brought to a nest site) is necessary to confirm occupancy.

3.3 Evidence of breeding 3.3.1 Locating active nests See Section 3.2.1 for information on finding nest sites and determining whether they are occupied. If it is necessary to look inside a confined space for a nest site, it is strongly recommended that goggles and some sort of face protection (e.g. a fencing or welding mask) is worn. Talk quietly, to warn the barn owl of your presence so that it can depart carefully, but do not make a lot of noise as this may alarm the bird. In tree hole sites, be very careful of tawny owls, as these can be much more aggressive. Nest checks should be done as close to dusk as possible to avoid flushing adults during daylight.

3.3.2 Evidence for fledging Fledged barn owl chicks should be located by checking the nest site. As hatching is asynchronous, a large brood of young in the nest will be at a variety of ages. In buildings, the whole brood may be visible after fledging as they roost during the day. This is not so with tree nests where regular visits will be required to record the fledging of each chick. Barn owl young can easily hide and the immediate area around the nest site should be searched thoroughly. In buildings, the chicks can hide under the eaves, between hay bales and in any available crevice or hole. Fledged young can also be located by listening for their food calls (Cramp, 1985).

3.4 Evidence for non-breeding

Under extreme conditions of food shortage, female barn owls may not lay (Taylor, 1994); this tends to occur in the decline and low phases of vole population cycles. If a pair of barn owls is known to be occupying a home range but no active nest or fledged young are found during visits at the appropriate times, this provides evidence for non-breeding.

3.5 Ageing and sexing young Growth curves showing changes in body mass, wing length and head and bill length have been produced for British barn owls (Percival, 1992; Figure 37). These measurements in combination can be used to give at least an approximate estimate of the age of young. Mass should not be used on its own to estimate age, as this may vary in relation to a number of

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Barn owl

factors, including the foraging conditions for the parents, condition of the young, brood size, how recently a chick has been fed and the time of day (Taylor, 1993). Wing length is thought to be the best predictor of age (Taylor, 1994) and wing growth is linear after 20 days, so that

450 400

Mass (g)

350 300 250 200 150 100 50 0

0

10

20

30

40

50

60

70

80

60

70

80

60

70

80

Number of days from hatching 300

Wing length (mm)

250 200 150 100 50 0

0

10

20

30

40

50

Number of days from hatching

Head and bill length (mm)

75 70 65 60 55 50 45 40 35 30

0

10

20

30

40

50

Number of days from hatching

Figure 37. The relationships between chick measurements and age for the barn owl.

The data are plotted as 5-day means with 95% confidence limits. (From Percival, 1992; reproduced with kind permission of JNCC).

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chick age can be estimated from the following equation: Age (days) = (wing length (mm) + 22.3)/5.1

(v)

Shawer (1998) describes the growth of the wing feathers in owlets and use of the length of the emerging quill of primary seven to age nestlings. The majority of chicks can be sexed from the age of 40 days by the amount of flecking on the underbody (Taylor, 1994). Chicks with no flecking on the underbody (an underbody fleck score of 0) can be reliably sexed as males, while those with heavy flecking (underbody fleck scores of 3 or 4) can be sexed as females.

Intermediate birds (underbody fleck scores of 1 or 2) cannot be sexed reliably. Some female chicks also have a generally richer brown wash to their upper body and more pronounced black wing bars than male chicks.

3.6 Use of egg density measurements

Information on British barn owl eggs is available from which hatching dates can be estimated from measurements of egg density (Percival, 1992; Figure 38; see also Section 6.5.1 of Introduction). Further data collection is likely to be required before hatching dates can be predicted with precision but the data available can be used as an approximate guide to the period over which hatching will occur and visits to check on young might be made.

1.15

Egg density

1.1

1.05

1

0.95

0.9 -35

-30

-25

-20

-15

-10

-5

0

Number of days to hatching

Figure 38. The relationship between egg density and hatching date for the barn owl, showing how egg measurements can be used to estimate hatching date (where egg density = weight/(O.507 x (breadth)² x length). The data are 5-day means with the 95% confidence limits shown. (From Percival, 1992; reproduced with kind permission of JNCC).

4. SURVEYS OUTSIDE THE BREEDING SEASON Surveys outside the breeding season are likely to be incomplete, as roosting sites can be smaller and better hidden than nesting sites, and therefore easily missed. The variability of behaviour with respect to time of day (or night) between birds also means that observations of hunting or calling birds will provide only minimum estimates of the barn owl population in a study area.

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Buzzard Buteo buteo 1. INTRODUCTION The buzzard (common buzzard), with its catholic diet and habitat preferences, and a general decline in persecution, now breeds in almost every part of Britain. Substantial increases in the population have occurred during the last two decades (Clements, 2000; Holling, 2007).

Breeding numbers and range have also increased in Ireland (Norriss, 1991; Greenwood et al., 2003). Adult buzzards are largely sedentary in Britain and Ireland, in contrast to the majority of European populations that are migratory. Most immature buzzards undertake dispersive movements from their first September until they settle at around two years of age (Walls & Kenward, 1998). Fennoscandian buzzards are migratory and a few may reach eastern Britain.

Adults of both sexes are similar, although males may be identified from their smaller size when seen close to females. Before their first moult at one year old, juveniles can be separated from adults. Adults have dark brown eyes and a broad, dark sub-terminal tail band; juveniles have lighter eyes and faint, narrow tail bars with no broad sub-terminal band. Juveniles also have distinct teardrop streaking to the feathers on the underparts, often showing a lot of the whitish background feathers. Adults are never streaked but have barring on many of the breast and belly feathers, sometimes very heavy so that little if any white shows. Adults also clearly show the classic pale crescent across the breast usually absent in juveniles.

For further information on the biology and ecology of this species, Tubbs (1974) provides a comprehensive account.

Annual Cycle Breeding Activity

Peak Period

Occupation of home range

Range

Duration (days)

All year

Nest building

March

Late January to early May

Egg laying

Mid-April

Mid-March to early May

6 to 9

Late March to mid-June

36 to 38

Incubation Hatching

Mid- to late May

Young in nest Fledging

Late April to mid-June Late April to late July

Late June to early July

Juvenile dispersal

136 Raptors: a field guide for surveys and monitoring

40 to 60 days

Mid-June to late July August to November

From 25 days after fledging Buzzard

2. HABITAT, HOME RANGE, NESTS AND BREEDING 2.1 Habitat

Buzzards frequent all habitats that provide open areas for hunting, preferably with perches (trees, posts, rocks), and suitable trees or crags for nesting. These include moorland and other upland habitats, but buzzards prefer pasture or cultivated farmland with small woods or copses, and open forests. They will not nest within extensive closed forests but will breed in thinned plantations or near the forest edge and make use of clear-felled areas. They avoid high mountainous areas (Cramp & Simmons, 1980).

2.2 Home range

Buzzards generally occupy areas of 2–3 km², of which a core area of 0.5–1 km² is usually defended against conspecifics other than close relatives (Walls & Kenward, 2001). The size of the home range varies with the abundance of prey, particularly rabbits. The nests of separate breeding pairs have been found as close as 90 m apart (Swann & Etheridge, 1995), indicating that nesting territories can be very small. When buzzard densities are high, some feeding areas may be used almost communally and large groups can sometimes be seen feeding together in fields. Densities of 2.4 pairs km-² and 0.9 pairs km-² have been recorded in areas with dense rabbit populations compared to 0.1 pairs km-² in an area with few rabbits (Newton, 1979; Jon Hardey, pers comm.).

2.3 Nest sites

Buzzards can nest on cliffs (from small crags to large seacliffs), on bluffs and steep slopes in moorland without crags or trees, in coniferous, deciduous or mixed woodland of any size, in isolated trees and hedgerows. Nests have also been found on seaweed on a beach, on sand dunes, on top of a ruin and on a wall under a gorse bush. Tree nests are normally positioned at about two-thirds of the height of the tree (3-25 m from the ground) and close to the trunk or on side branches. Old crows’ nests in trees may also be utilised.

2.4 Nests

Buzzard nests are built by both sexes. They are normally substantial structures of sticks and heather with a shallow cup, lined with green foliage (Cramp & Simmons, 1980). Some pairs use the same nest for several years in succession, whereas others change annually. In woodland, the old nests of a particular pair of buzzards are generally found in discrete groups, with the occasional outlier. A pair may have up to 15 nests in their nesting range.

2.5 Clutch size and incubation

Buzzards lay from early April to mid-May, occasionally as early as mid-March (Tubbs, 1974; Maguire, 1979; Austin & Houston, 1997). Eggs are laid at 2-3 day intervals and clutch size is usually from 2–4 eggs; occasionally one, five and, exceptionally, six eggs are laid (Tubbs, 1974; Austin & Houston, 1997). The BTO Nest Record Scheme gives an average clutch size of 2.4 (n = 1,082). Clutch size may vary significantly between areas, probably linked to differences in prey density (Swann & Etheridge, 1995; Austin & Houston, 1997). The incubation period is usually 36–38 days per egg in Britain (Brown, 1976) and begins with the first or second egg.

The female carries out most of the incubation and always incubates at night; the male brings food to the female during incubation and she may leave the nest to receive and eat the food (Cramp & Simmons, 1980).

2.6 Brood size and fledging

The chicks hatch asynchronously at about two day intervals (Tubbs, 1974; Cramp & Simmons, 1980). Brood size varies with the availability of prey but is normally 1–4. The female stays Buzzard

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with the young for the first fortnight and broods them continuously for the first week after hatching (Tubbs, 1974). The male provides most of the food for the first three weeks with both parents provisioning young after 25 days (Cramp & Simmons, 1980). A study of radiotagged birds found that the young fledged at 43–54 days and remained within 300 m of the nest for another 2–3 weeks until their feathers hardened (Tyack et al., 1998). Cramp & Simmons (1980) note that fledging occurs at 50–55 days, sometimes later. Young buzzards remain within about 1 km of the nest for at least two more weeks, with about half dispersing by late October, others mainly in the following spring, and 80% by their second December (Walls & Kenward, 1998).

3. SURVEY TECHNIQUES CAUTION Nests should not be visited when buzzards are laying eggs as desertion can occur.

Nests with eggs or small young should not be disturbed in cold, wet or exceptionally hot weather. During incubation, nest visits should be kept brief and confined to checks of activity at known nests. Searches for new nests should be delayed until after the hatching period. If nest inspection visits require climbing, then appropriate health and safety precautions should be taken (see Section 7.10 of Introduction).

3.1 Breeding season visit schedule The species is listed on Schedule 1 in Northern Ireland and the Isle of Man (see Section 7.1.1 of Introduction). To establish occupancy and the presence of a breeding pair, it is recommended that all four visits are made. However, if time is limited and a home range appears to be unoccupied on the basis of the first two visits, then further visits can be omitted. Alternatively, if an area is well known to a surveyor, then Visit 1 may be omitted. Care must be exercised to avoid disturbing birds that may be laying, so it is recommended that Visit 2 should be confined to quick checks for occupancy at known nests (a maximum of 10 minutes duration) with searches for new nests delayed until Visit 3. Broods that have fledged early may start to disperse by early August.

Visit 1

Late February to March

To check for occupancy

Visit 2

Late April to May

To check activity at known nests (incubating birds should not be flushed from the nest unless there is a specific need to record clutch size)

Visit 3

June

To check for young, or for evidence of breeding and new active nests if no signs were seen on previous visits

Visit 4

July to early August

To check for fledged young

3.2 Signs of occupancy 3.2.1 Locating home ranges Home ranges can be located throughout the year by watching for displaying birds. Solo and mutual high-circling displays by buzzards are common (particularly by adult males), although they may be more regular between February and June and late August/September, when soaring conditions may be most favourable (Cramp & Simmons, 1980). Such circling displays may involve the territory holder(s) but groups of buzzards from nearby territories may circle together, particularly in areas of high buzzard density. The birds often call loudly while circling. In autumn, passage birds may also carry out this form of circling, as may immatures (the latter are less

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likely to be involved in such displays in the spring; Cramp & Simmons, 1980). When displaying, particularly in the weeks leading up to laying, buzzards may carry twigs or, less commonly, prey in their talons. High circling may also lead to sky-dancing (by males and only occasionally by females; Tubbs, 1974; Cramp & Simmons, 1980), involving plunging and swooping that may be repeated 12 or more times; this behaviour is most frequent in March–April and again in July–October. In open terrain, including farmland, displaying buzzards can rise to a considerable height and then wander, making it difficult to associate them with a specific area. Prytherch (2009) provides a very detailed account of buzzard social behaviour, including display and territorial defence.

Cold searching of known home ranges or suitable habitats in late winter or spring can also locate resident birds, which may respond to the intrusion by alarming. The regular presence of birds can also be detected by finding plucks (e.g. on fallen tree roots), pellets, or white faecal droppings below roosts or perches (see 3.2.3 and 3.2.4 below).

The number of soaring buzzards has been used to provide an estimate of the number of pairs occupying home ranges (Sim et al., 2000). Areas of suitable habitat need to be located in advance of the survey and the survey area divided into tetrads (2 x 2 km squares). It is recommended that counts are made in the first half of April during good soaring weather (dry with a wind speed of less than 30 mph and less than 50% cloud cover; Sim et al., 2000), although fieldwork may be started from the beginning of March (BTO, 1983; Taylor et al., 1988; Gilbert et al., 1998). Counts should be made between 09.30h and 16.30h for one hour in a 2 km square (Sim et al., 2000). Considerable regional variation in the soaring behaviour of buzzards is suspected, however, possibly related to the number of non-territorial birds within the local population as well as habitat. Counts of soaring buzzards should therefore be used with caution to estimate the size of local populations (unless such counts are calibrated against intensive territory-finding work; Sim et al., 2000); if repeated annually, however, they may provide an index for estimating population changes (Greenwood et al., 2003).

3.2.2 Locating roosts The locations of buzzard roost sites will depend on the terrain. In woods, they tend to be in denser stands of trees that offer more shelter. Roosts on crags are often sheltered under overhangs and may have copious amounts of faecal droppings. Roosts may also be located on steep banks with no exposed rocks. Active roosts will have freshly moulted feathers, especially down, and fresh pellets. Roosts may be in any part of the home range.

3.2.3 Recognition of signs Buzzard pellets are generally large and elliptical, consisting mainly of tightly packed fur, with few bone fragments (length = 45–60 mm; width = 25–30 mm; Brown et al., 2003). Kills, pellets and faeces are not generally distinctive enough to differentiate from those of other species (e.g. goshawk), however, and so should only be used as supporting evidence for occupation in addition to sightings of birds or moulted feathers.

3.2.4 Evidence for occupation Sightings of a pair or a single bird on several occasions over a localised area during the breeding season indicates that a territory is occupied. Freshly built nests, recently used roosts and fresh prey remains provide supporting evidence for occupancy but are not sufficient in the absence of sightings.

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3.3 Evidence for breeding 3.3.1 Locating active nests Nests can be located by checking crags, steep slopes, woods, and isolated trees. Some nests on crags are very accessible. It is easier to search deciduous woods in winter or early spring as the lack of leaves makes nests more obvious. Nests can be ascribed to a pair’s home range by locating associated displaying bird(s) from February to April. It can be difficult to locate nests within large blocks of commercial forestry but watching displaying birds can reveal nest locations as they will dive down into the plantation close to their nest site. Birds may also be seen sitting on prominent perches, such as crags’ close to the nest site. It will not always be possible to locate an active nest because buzzards may not breed every year but most pairs will give an indication of breeding behaviour by decorating a nest with small leafy branches and other fresh plant material. Some pairs may line more than one nest before laying, so that the number of sightings of adult birds as well as the number of active nests found should be borne in mind when estimating the number of pairs occupying home ranges in a given area.

Known nests should be visited to check for fresh material (new branches, leaves, down and moulted feathers) and for faecal droppings round the nest tree. Care must be exercised to avoid excessive disturbance during laying and early incubation. Incubating birds should not be flushed from their nest unless there is a clear need to record clutch size. If an active nest is not located during Visit 2, the search should be extended to all suitable nesting habitats within the home range during Visit 3. Successful nests can be more easily located once the young fledge because they remain close to the nest and call frequently, especially in the early morning.

3.3.2 Evidence for fledging Counts of buzzard chicks in the nest at about four weeks of age (with primary feathers at least halfway out of quills) can be used as a measure of brood size at fledging, as very few die after reaching this age. Counts can be made from a vantage point or (for more accuracy) by climbing to the nest. The estimated age of young at the time of such counts should be recorded. Fully feathered young are capable of leaving the nest so, if counts are made at this age, trees or crags adjacent to the nest should be checked carefully in addition to the nest itself. Recently fledged young can generally also be located by their calls and counted. Counts of fledged young are no longer reliable once dispersal starts.

3.4 Evidence for non-breeding Not all buzzards of breeding age breed every year. Studies in southern England have shown that the proportion of non-breeding adults in any one year can be high (66–73% of adults not laying eggs; Kenward et al., 2000; Walls et al., 2004). This proportion is made up of a mixture of birds, from unpaired individuals to territory-holding pairs that maintain nests but do not lay eggs. Non-breeding probably occurs more frequently in cold wet springs or when prey levels are low. To establish whether any given pair is not breeding is difficult, however, without very intensive fieldwork. In a territory that is apparently occupied early in the season, the absence of an active nest, despite several searches during the appropriate visit periods, and a decline in alarm response from the adults, are indicative of non-breeding or early nest failure.

3.5 Ageing and sexing young Chicks can be aged approximately by measuring their wing length (Figure 25; based on Dutch birds; Bijlsma, 1999) or, using length of the longest primary feather (Figure 26; based on Scottish birds; Austin & Houston, 1997). Measurement of the longest primary (the fifth from

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Buzzard

350 300

Wing length (mm)

250 200 150 100 50 0 0

10

20

30

40

50

Age (days)

Age (days)

Figure 25. Increase in mean wing length (with 95% confidence limits) of buzzard chicks with age. Data from 1–4 nests per year over eight years and one study area; each point based on measurements from 5–16 males and 5–17 females (from Bijlsma, 1999).

Length of longest primary (mm)

Figure 26. Increase in length of longest primary feather with age of buzzard nestlings (based on a sample of 33 young from Argyll, Scotland; Austin & Houston, 1997).

Reproduced with kind permission from Bird Study.

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the wing tip, including the vestigial outer primary) allowed most of a sample of 14, known age, young to be aged to within a day, and all to within four days, from the equation (Austin & Houston, 1997): Age = 12.75 + 0.125 (length of longest primary, mm)

(iii)

Based on buzzards in the Netherlands, Bijlsma (1997, 1999) describes the use of body weight in conjunction with other body measures for sexing (Table 4). The sample sizes are small (a maximum of 18–20 young of each sex) and the weights of Dutch buzzard chicks of a given age may be less than those of nestlings in Britain and Ireland, so these data should be used as a guide only. Although measurements for young of less than 26 days are included, sexing of such young is generally not reliable.

Table 4. Criteria for sex determination of three age categories (based on wing length) of buzzard chicks based on body mass (with and without crop), and maximum tarsus width (from Bijlsma, 1999).

Age (days)

Wing length (mm)

mass (no crop) (g)

mass (with crop) (g)

Tarsus width (mm)

♂

♀

♂

♀

♂

♀

<26

<192

-

>760

-

>800

<9.5

>9.5

26-30

192-225

<600

>800

<600

>850

<9.5

>9.5

>30

>225

<700

>830

<735

>870

<9.7

>10.0

Further data are required for reliable ageing and sexing of buzzards in Britain and Ireland.

Based on 96 young from Dorset, a minimum tarsus width (callipers squeezed tightly) of less than 6.0 mm at fledging was found to discriminate males from females with 95% accuracy (Walls & Kenward, 1995).

4. SURVEYS OUTSIDE THE BREEDING SEASON An index of buzzard abundance during the winter months can be obtained by carrying out counts of birds observed from defined survey routes (preferably randomly selected or at least representative of habitats in the area to be covered), either on foot or by car (see Section 2.2.2 of Introduction). Observers should cover a fixed route in a set time, and record observations of buzzards and the approximate distance of each bird from the ‘transect’ line. Weather conditions should also be noted. The data collected would be appropriate to be used as an index of change in numbers between years. In Britain and Ireland, such survey work would be best undertaken between November and February to exclude irregular influxes of immigrants during passage periods, and surveys should be carried out at approximately the same time each year to ensure comparability.

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Golden Eagle Aquila chrysaetos 1. INTRODUCTION The British golden eagle population is largely confined to the remote mountainous areas of the Highlands and Islands of Scotland, north and west of the Highland Boundary Fault (Watson, 1997). A few pairs occur in the Southern Uplands of Scotland and northern England. The species is absent from Orkney and Shetland. A reintroduction scheme began in 2000 in Ireland (Ó Toole et al., 2002; www.goldeneagle.ie) and the first chick fledged successfully in July 2007. Established pairs of breeding golden eagles in Britain are largely sedentary (Watson, 2002). Juveniles and immature birds can disperse over distances in excess of 150 km from their natal area, and immatures are nomadic before reaching breeding age and maturity at 4–5 years. Females are larger than males but the sexing of single birds visually is unreliable. Immature birds have white patches on the underwing and the base of the tail (e.g. see descriptive notes for the golden eagle survey form in Appendix 3). Occasionally, a bird in sub-adult plumage is found breeding.

For further information on the biology and ecology of this species, Watson (1997) provides a comprehensive account. Whitfiled et al. (2008a) reviewed the conservation states of the Scottish golden eagle population and identified illegal persecution (principally associated with grouse moor management in the central and eastern Highlands) and low food availability in the western Highlands, as key constraints.

Annual cycle Breeding Activity

Peak Period

Range

Occupation of home range

All year

Territorial display

January to March

Duration (days)

Nest building

January to March

October to March

Egg laying

Mid-March to early April

Early March to mid-April

3 to 6 (for clutch of 2)

Incubation

Mid-March to mid-May

Early March to early July

41 to 45

Hatching

Late April to early June

Mid-April to early July

Young in nest

Late April to early August

Mid-April to mid-September

Fledging

July to mid-September

Juvenile dispersal

August to January

Golden eagle

70 to 80

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2. HABITAT, HOME RANGE, NESTS AND BREEDING 2.1 Habitat Golden eagles occupy a range of habitats, from open montane areas, through Caledonian pine woodland to island seacliffs. They are closely associated with mountainous areas, and unenclosed and unimproved habitats such as deer forest and upland sheep-walk. They can also be found on actively managed heather moorland in central and eastern Scotland, and in the vicinity of enclosed pasture and coastal areas in the west of their range.

2.1 Home range Adult golden eagles hold more-or-less exclusive home ranges that encompass both their hunting range and nesting territory, are occupied all year round and actively defended against intruding eagles (Watson, 1997; Crane & Nellist, 1999, 2003), which are aggressively attacked and pursued. In areas of continuous suitable habitat, the nesting ranges of neighbouring pairs are usually spaced at regular intervals. In Scotland, breeding densities are influenced by the availability of live prey and carrion (Watson et al., 1992; Fielding et al., 2003a; Whitfield et al., 2008a), ranging between about 4-25 pairs per 1,000 km2 (Watson, 1997). Based on radio-tracking and intensive observations, home range sizes in western Scotland have been estimated at 864-6,687 ha (Haworth et al., 2006) and a predictive model of home range use has been developed (McGrady et al., 2002; McLeod et al., 2002a, b).

2.2 Nest sites Scottish golden eagles nest predominantly on crags (96%); tree nesting (4%), typically in an old mature Scots pine, occurs mainly in the eastern Highlands (Watson, 1997). Nest sites can be found at altitudes of under 200 m ASL near the western seaboard, rising to around 800 m ASL in the eastern Highlands (Watson & Dennis, 1992; Whitfield et al., 2008a). Nests are not necessarily built in the most inaccessible position or on the highest cliff; the advantages in nesting higher to reduce predation risk and possibly human persecution are likely to be balanced against the disadvantages of transporting heavy prey uphill (Watson, 1997). Nests are generally located at about half the maximum elevation of the surrounding land. Thus nests may be found on small crags, often in a walk-in position. Most crag nests have a northerly or easterly aspect, probably a reflection of past glacial action on the land rather than active selection by the birds (Watson, 1997).

2.3 Nests Territories may have 1–13 (normally 1–6) alternative nests (Watson, 1997). Nest material is added to one or more of these year after year, and some eyries can become extremely large, particularly those in trees. The size of the nest can vary from a pad of soft material on a vegetated ledge to a pile of sticks 2 m or more in height. Most nests are constructed of sticks and/or heather, with a soft lining of woodrush and grasses. On a nesting crag, many nests are obscured by vegetation or beneath a rock overhang and are easily overlooked. Old nests have a grey appearance and will often have green vegetation growing through within a year of non-use. Some nests have completely decayed after 10 years without addition of new material, although their position may be identifiable for some time after this.

2.4 Clutch size and incubation Egg laying in Scotland occurs between early March and mid-April (Watson, 1997). February temperatures can have an impact on laying date; Watson (1997) showed that in the years when February was coldest, laying was around 10 days later than in the warmest years. In Scotland, golden eagles lay 1–3 eggs. Most clutches are of two eggs, with 1-egg clutches quite

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frequent and 3-egg clutches comparatively rare (Watson, 1997). The laying interval between eggs is 3–5 days (Gordon, 1955). Relays are rare but may occur if the first clutch is lost early in incubation. Incubation commences with the first egg, lasts 41–45 days and is normally undertaken by the female, relieved for short periods by the male during daylight hours. A study in Idaho found that females incubated for 83% of daylight hours compared with 14% by males, with males relieving females on average twice a day for about 50 minutes on each occassion (Collopy, 1984). The male does not generally feed the female during incubation.

2.5 Brood size and fledging The normal brood size in Scotland is one, although broods of two are frequent (Watson, 1997) and broods of three are occasionally found in the eastern Highlands. In nests with more than one chick, the younger and weaker chick may die or be killed as a result of competition or aggression from its larger sibling (Edwards & Collopy, 1983). Smaller broods are associated with poorer food supplies and poor weather conditions. In Scotland, young eagles usually spend around 70–80 days in the nest (Watson, 1997). Studies in America have reported overall average delivery rates of 0.9–1.8 prey items per day during the nesting period, with males bringing over 80% of deliveries during the first two weeks after hatching while the female delivery rate gradually increases to about 50% as the requirement to brood nestings decreases (Watson, 1997). A study in Idaho reported a peak of provisioning in week eight when three items were delivered per day (Collopy, 1984). For the first few weeks after fledging, young eagles generally stay within about 100 m of the nest site (Watson, 1997). They seek out a secure perch such as a wooded ledge or tree branch and can be surprisingly inconspicuous except when food calling. Thereafter, juvenile eagles spend a variable period on their parents’ territory, extending from days to several months, before dispersing.

3. SURVEY TECHNIQUES CAUTION To minimise disturbance, initial checks of nest sites at all stages should be made from a distance of 750 m to 1.5 km away (Ruddock & Whitfield, 2007; Whifield et al., 2008b), for example a vantage point at the opposite end of the glen which gives a clear view of the eyrie. Nests should not be approached in March and early April, as golden eagles are particularly sensitive to human disturbance just before and during egg laying. Disturbance behaviour typically involves both birds circling together to a great height and often drifting away from the nest crag. Later in the season, observers should avoid nest disturbance during particularly hot, wet or cold conditions, as the absence of adults from the nest for extended periods may result in chilling or overheating of eggs or young. Site checks are best undertaken on dry, overcast days. Well feathered young (about 50 days or older) in the nest should not be approached as they may fledge prematurely. Appropriate health and safety precautions should be undertaken if nest visits require climbing (see Section 7.1 of Introduction).

3.1 Breeding season visit schedule The species is listed on Schedule 1 in Great Britain, Northern Ireland and the Isle of Man (see Section 7.1.1 of Introduction). In addition, golden eagle is listed on Schedule ZA1 of the Natural Environment and Rural Communities Act 2006 (England and Wales) which gives year-round protection to nest sites. To establish occupancy and the presence of a breeding pair, it is recommended that each home range is visited on at least four occasions. If time for fieldwork is limited and an observer believes a home range to be vacant on the basis of the first two visits, however, then subsequent visits can be omitted. A copy of the recording forms distributed to fieldworkers taking part in the 2003 survey of golden eagles in Great Britain is included in Appendix 3.

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Visit 1

January to early March

To check for occupancy.

Visit 2

April

To locate active nests.

Visit 3

June

To check for young.

Visit 4

Late July

To check for fledged young.

3.2 Signs of occupancy 3.2.1 Locating home ranges Ideally, historical data should be collected to identify all known eyries in the area to be surveyed, as the birds are often quite traditional in their use of nesting sites (Watson et al., 1992). Territories can be located during the autumn and winter months and checked for occupancy on visits between January and early March, before laying commences.

Golden eagles generally display less than other Aquila species but such displays can nevertheless be useful in finding territorial birds. Lone birds or pairs often high-circle to hundreds of metres above the ground, particularly on fine days in winter and early spring (Cramp & Simmons, 1980). Flight-play between a pair does occur but is infrequent. Mutual high-circling may be accompanied by a series of long dives by both birds, as well as some mock-attacks and fast manoeuvres high up. Undulating sky-dancing (high-circling, rapid diving and swooping) is frequent, particularly in late winter and early spring but also at times throughout the breeding cycle. It is performed by both sexes but probably more frequently by males (sometimes by pairs). Local topographical features (e.g. ridges, mountain tops) are often used to perform over. Calling is not a regular feature of golden eagle flight displays, although it may be heard occasionally during sky-dancing or high-circling.

The amount of golden eagle activity seen can vary greatly; birds can be active or idle at any time of day. Moreover, the presence of a breeding pair can be easily overlooked. It follows that the lack of any sightings during any one visit should not be regarded as evidence of a vacant territory or non-breeding (see Section 3.4). Evidence of recently used roost sites, fresh droppings or prey remains (Section 3.2.2 and 3.2.3), and/or a recently built-up nest can indicate the presence of golden eagles and may be signs that the territory is occupied, even if no birds are seen. Initial territory checks are best made from vantage points affording wide overviews of likely foraging areas. These vantage points should be on lower ground looking towards ridges and glen heads. Watches should last up to 4 hours and should be repeated on a subsequent visit if no birds are seen; they are best made in the period leading up to dusk to watch for birds returning to their roosts.

3.2.2 Locating roosts Active roosts in an occupied territory can be in trees, on ledges or on rocks. They are marked by pellets (which decay rapidly), faeces (splash that washes away in rain) and down and feathers.

These signs can be ascribed as fresh (soft faeces, new fluffy down and feathers), recent (dried faeces and matted down and feathers) and old (mildewed signs). Roosts may be up to 3 km from an occupied nest, so the presence of an isolated roost is not evidence for non-breeding or failure. Winter roosts may be close to the edge of a home range rather than within the core.

3.2.3 Recognition of signs Fresh golden eagle plucks show large pluck marks, usually in a neat and tight pattern. Such marks cannot generally be distinguished from those of the white-tailed eagle, however, and only remain intact in recent kills and in the absence of wind to disturb the feathers. Golden eagle pellets also should be identified only in association with other signs (e.g. moulted

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feathers), as they are similar to those of white-tailed eagles. Even if the pellets contain fish bones, there is no guarantee that they are not from golden eagle.

3.2.4 Evidence of occupancy For the 2003 survey of Great Britain, a home range was considered to be occupied if a pair of birds that could potentially breed was seen together or if there was evidence of a breeding attempt, including sighting(s) of a single bird in combination with a newly built-up nest (Eaton et al., 2007). For the previous (1992) survey, ranges were recorded as occupied by pairs only if both birds were seen (Green, 1996).

3.3 Evidence of breeding

In addition to the location of an active nest or fledged young, the precence of a freshly built‑up (‘greened-up’) nest in combination with sightings of a pair of golden eagles or a single bird provides evidence of a breeding attempt (Eaton et al., 2007).

3.3.1 Locating active nests The breeding year starts early for golden eagles and pairs can be seen refurbishing nests and engaging in display and territorial disputes on bright days in mid-winter. Nest building and repairs to existing structures reach a peak in January and February, in the lead up to egg laying. Nests should not be approached in March and early April, as the species is particularly sensitive to human disturbance just before and during egg laying (Tjernberg, 1983). Disturbance behaviour typically involves both birds circling together to a great height and often drifting away from the nest crag. If the eagles show signs of disturbance, the observer should move away as quickly as possible.

Vantage point watches on one or more visits during March and April should be used to confirm breeding activity. All known eyries should be checked for the presence of an incubating bird, a single bird rising above a nest site on approach, or for signs of fresh nest material. An incubating adult will often sit tightly, particularly if the off-duty mate is absent from the nesting territory. A lack of sightings but the presence of signs of roosting birds may indicate that a pair is occupying a range but is preparing nest sites away from those being checked. If no occupied nest is found, all crags and suitable woodland should be checked by scanning from a distance with a telescope or binoculars. The active nest may be on an inconspicuous crag low down in the homerange, especially if an area is not subject to regular disturbance. When an active nest is located, it is unnecessary to disturb an incubating bird unless there is a specific requirement to collect information on clutch size. In these circumstances, the fieldworker should deliberately make a noise on approach to the eyrie, to alert the sitting bird and allow it to leave without panic.

When an active nest is located within a traditional home range, the possibility of more than one breeding pair of golden eagles being present should not be discounted. The splitting of home ranges can occur, particularly of larger ranges and when food abundance is high. Therefore, all known nest sites in a nesting range should be checked, even if an active nest has been found.

3.3.2 Evidence for fledging Subsequent visits to occupied eyries should be made to record the number of young in June and fledged young in late July, or if an occupied nest has not been found, to confirm that the birds have failed or are not breeding. If a nest is inaccessible, counting young will require climbing (see Health and Safety information in Section 7.10 of Introduction) and care should be taken in the timing of visits to minimise the risk of causing premature fledging.

Well-feathered young of at least eight weeks old are the minimum requirement for a presumption of fledging. Successful nests can be identified in late summer and autumn by their flattened nature and the presence of nestling down, faecal material and prey remains.

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When young are likely to be close to fledging, nests should be viewed from a distance with binoculars or a telescope as disturbance at this time may cause premature fledging or fledged young to move from perches where they are safe from ground predators. Walking the ground is not recommended as eaglets can remain still, silent and inconspicuous, even if an observer passes only a few metres away. Alternatively, disturbed, eaglets may panic and injure themselves, for example by attempting flights over distances they are not yet capable of sustaining and landing awkwardly. Fledged eaglets tend to move uphill from the nest and can be located by scanning from a distance for signs such as down. It may be necessary to wait until an adult brings food to get a clear view of the young, either in a nest or after fledging, which may require several hours of observation (Gilbert et al., 1998).

An empty nest with a fresh lining is not necessarily indicative of breeding failure because immatures and single adults may nest build without breeding, or the pair responsible may be using an alternative but unknown eyrie. A well-built nest together with the presence of an adult bird is considered strong evidence of attempted breeding, however. If possible, suspected failed nests should be examined at the end of the breeding season for any clues, such as deserted eggs or shell fragments, dried splash and down. This evidence may be hidden under fresh nest material added by the adults after failure.

3.4 Evidence of non-breeding

A relatively high proportion of Scottish golden eagle pairs do not lay eggs in a given year although it is difficult to be precise because some pairs which appear not to have laid may have lost eggs early during incubation (Watson, 1997). This incidence of non-laying (or early egg loss) was found to be higher in two western areas (average 26%) compared to an area in the eastern Highlands (average 12%; Watson, 1997). Non-breeding can therefore be difficult to prove. Repeated sightings of a pair together away from nest sites during the incubation period and no sign of an occupied nest after extensive searching (checking all known nest sites and searching all potential new areas for an active nest throughout the breeding season) provides good evidence of non-breeding. Sightings of a single bird only on a number of visits may indicate the presence of a non-breeding bird. Information on the distribution of non-breeding birds is extremely valuable, as these are potential recruits to the breeding population.

3.5 Ageing and sexing young

The age of chicks may be estimated very approximately from a distance by plumage development (Watson, 1997). Up to about 25 days, chicks are covered in down and appear whitish from a distance. Between 25-50 days the dark contour feathers gradually eclipse the white down and for much of this phase the bird has a piebald appearance. The last of the down is lost from the head and neck. From 50 days onwards, the main growth period for the feathers of the wing and tail, the young are a uniform dark brown, Late in the nestling period the plumes on the back of the neck become fully developed. Photographs of golden eagle chicks in the nest at a range of ages are shown in Plates 58–63.

Measurements of a sample of immature golden eagles of the North American race canadensis (Bortoletti, 1984) suggest that it may be possible to sex large, well-grown young that are handled for ringing purposes by measuring the length of the hallux (rear) claw and culmen (Table 5). There is a degree of overlap in both measures but, when used together, these should provide an indication of the sex of most well-grown chicks. Edwards & Kochert (1986) used foot span from dead adult golden eagles of known sex and found this measurement 100% accurate for sexing. A growth curve (Figure 27), again using data collected from North America (Ellis, 1979), could be useful in ageing young. Asymptotic mass, reached at 45–50 days old when the rate of increase in weight levels off (Figure 27), might also be a useful

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criterion for sexing many chicks: at this stage females are typically 500–600 g heavier than males (Watson, 1997). All of these methods need to be tested further on Scottish eagles before general acceptance, however.

Table 5. Measurements of immature golden eagles: hallux and culmen (Bortoletti, 1984); and foot span of autopsied adult birds (Edwards & Kochert, 1986).

Male

Female

Mean (mm)±SD

Range

Mean (mm)±SD

Range

Hallux claw length

47.75 ± 1.62

44.9–51.3

54.01 ± 2.15

49.7–58.2

Culmen

39.36 ± 1.44

36.2–42.6

43.34 ± 1.36

39.9–50.0

Foot span

131.64 ± 0.61

145.44 ± 0.94

Figure 27. Growth curves of male (lower) and female (upper) nestling golden eagles, after Ellis (1979). Data from two Scottish birds are shown, a possible male ( ) after (Gordon 1955) and a probable female ( ) after MacNally (1964). From Watson (1997), reproduced with kind permission of A&C Black.

4. SURVEYS OUTSIDE THE BREEDING SEASON As golden eagles occupy their home ranges throughout the year, the population of resident adults and immatures could be surveyed outside the breeding season by foot searching as outlined above. Methods for censusing nomadic immatures have yet to be developed.

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Goshawk Accipiter gentilis 1. INTRODUCTION The Goshawk (northern goshawk) stopped breeding regularly in Britain and Ireland in the 1880s.

Breeding became regular again from the mid 1900s, as a result of deliberate (unauthorised) and accidental releases of falconers’ birds (Holloway, 1996; Petty, 2002). Numbers increased slowly at first, but populations in some areas increased rapidly from the late 1980s (Petty, 2002), and since then there have been over 200 pairs breeding in Britain (Gibbons et al., 1993; Ogilvie & RBBP, 2004; Holling & RBBP, 2008). Goshawks have been breeding in Northern Ireland since the early 1990s and a few pairs have been recorded in the Republic of Ireland in recent years (www. goldeneagle.ie). The success of these populations is variable and, in some, growth is thought to be limited by persecution (Marquiss et al., 2003). Adult goshawks are sedentary in Britain and Ireland (Petty, 2002). Juveniles disperse from their natal areas in late summer. Populations breeding in northern Europe are partially migratory, and some individuals may reach Britain from Scandinavia (Petty, 2002). Care must be taken in separating goshawks from sparrowhawks. In particular, female sparrowhawks often look much larger when they are flying with a slow wing flap, and may be confused with goshawk. The larger female goshawks can be separated from males in the field. Immature birds are distinguishable from adults by their browner plumage and heavily streaked breasts. Goshawks can breed at one year old.

Kenward (2006) provides a comprehensive reference, covering goshawks globally, but with a focus on Europe. Bosakowski (1999) and Kennedy (2003) also provide useful reviews, especially for North American populations.

Annual cycle Breeding Activity

Peak Period

Range

Occupation of home range

All year

Territorial display

March to April

Nest building

Duration (days)

September to late April

Egg laying

Early April

Mid-March to early May

3 to 12

Incubation

Early April to mid-May

Mid-March to early June

35 to 39

Hatching

Mid-May

Mid-April to mid-June

Young in nest

Mid-May to early July

Mid-April to late July

Fledging

Late May to late July

Juvenile dispersal

June to early August

Goshawk

38 to 46

20–40 days after fledging

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2. HABITAT, HOME RANGE, NESTS AND BREEDING 2.1 Habitat Goshawks are tree nesting raptors, which normally breed in large mature forests but can be found in smaller woods (20–50 ha) and even in wooded parks in some central European cities (Petty, 1996). They hunt over both open areas and within woodland.

2.2 Home range Goshawks defend only the nesting territory and hunt within large overlapping home ranges.

They may breed in the same locality for a number of years; for example, goshawks (although not necessarily the same individuals) have been recorded using similar nesting areas in commercial forestry for at least 10 years (Petty, 1989). Home range sizes and nest densities vary with the availability of suitable prey and woodland (Kenward, 1982, 2006); in suitable habitats, nest sites are regularly spaced (Petty, 1989). In lowland Britain, the distance between adjacent nests in woodland blocks varied from 1–3.7 km (Anon., 1989). More recently, nests have been found 750 m apart where there is no line of sight; the closest nests, where there is line of sight, have been 1,200 m apart. In contrast, in one area in Sweden, nests were 6 km apart (Widén, 1985). In southeast Alaska, home ranges of females and males during the breeding season averaged 4,153 and 4,785 ha, respectively (Hanley et al., 2005).

Nesting ranges, which are generally less than 5 ha in extent (Petty, 1996), are normally found in large blocks of mature forest. They can occur in woods smaller than 3 ha (Marquiss & Newton, 1982) but usually only where there is a lack of more extensive woodland. In one area of lowland Britain, woodland (of all types including restock) was found to comprise an average of 68% of the habitat within 750 m of 40 nest sites, ranging from 89% to as little as 17% (with the remainder of habitat predominantly farmland). Less wooded sites were used after core forest sites were filled.

2.3 Nest sites Nest sites are usually placed in areas with a high density of mature trees and well developed canopy cover (Bosakowski, 1999), surrounded by relatively open woodland (Petty, 1996). In two goshawk breeding areas in Britain, nests were found in stands of trees between 2.4– 3.8m apart in an area of coniferous trees, and 2.5–8.0m apart in an area with coniferous and broad-leaved trees (Newton, 1986). Trees as low as 12 m have been used (Marquiss & Newton, 1982) but the average height is often above 20 m (Anon., 1989). Trees used for nesting tend to be larger than the surrounding trees (they need to support the goshawk’s substantial nest) and conifers are used in preference to broadleaved trees in Britain (Anon., 1989). Larch is frequently used, as its branches provide both good support for nests and excellent nest building material. Marquiss & Newton (1982) suggest that the characteristics of the site are in fact more important than the tree species. Good flight access is required because courtship, feeding and roosting activities take place below the tree canopy, and fledglings need an open nursery area in which to practice their aerial skills (Petty, 1989). In closed canopy conifer plantations, nests are often found near openings, tracks, rides or areas of windblown timber (Petty, 1989), allowing access to the nest. In older, more open stands, where access is less restricted, nesting may occur anywhere. Old, very open stands with no secondary canopy development tend to be avoided for nesting unless there are no alternatives.

The nests from different years are often clustered within a small area, and individual nests may be used many times. The birds may move up to 2.5 km to another nest site, for example, if the site is disturbed early in the season, with some pairs having up to four different nesting areas within their nesting range (Petty & Anderson, 1996).

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2.4 Nests Goshawks build large untidy nests from branches and twigs, lined with green fronds and sometimes bark and pine needles (Cramp & Simmons, 1980). New nests may seem surprisingly small (75–90 cm in diameter) compared with old goshawk nests that have been re-used, but they are always larger than sparrowhawk nests in the same tree species. In a lowland British population, most pairs had only a few extant nests and re-use was common; only a minority of birds built new nests if existing nests were still usable. In northern England, several instances have been recorded of goshawks building a new nest but not using it, and instead moving to refurbish an old nest within 70 m. Conversely, an old nest may be refurbished before a new one is built. Goshawk nests cannot be separated from buzzard nests as there are similarities in construction; goshawk nests are usually larger but buzzards may take over old goshawk nests.

In conifers, goshawk nests tend to be built in the whorl of branches just below the base of the green crown at the top of the tree (Petty, 1989). In deciduous trees, nests are built in a stout fork usually about three-quarters of the way up (Anon., 1990). The height of the nest from the ground varies from 12–29 m, depending on tree age and height (Anon., 1989).

2.5 Clutch size and incubation Breeding tends to be earlier in southern Britain than in northern Britain. Goshawks lay clutches of 2–5 eggs (Anon., 1990), with an average of 3.8-4 for different altitudinal ranges in Britain (Marquiss & Newton, 1982; Anon., 1990). Clutch size in one British population has declined from an average of four eggs, 1980-87 (Anon., 1990), to 3.5 eggs in recent years. Eggs are laid at 2–3 day intervals and incubation is carried out mainly by the female (Cramp & Simmons, 1980). Incubation was reported to start with the second egg, and the average incubation period measured as 37 (±2) days from laying of the second egg to hatching of the first chick, in a study in lowland Britain (Anon., 1990). Replacement clutches may be laid 15–30 days after egg loss (Cramp & Simmons, 1980). Evidence for only one replacement clutch, laid in the same nest as a clutch that failed (after the disappearance of the male), was found for 57 breeding attempts where eggs were known to have been laid, 1980–87 (Anon., 1990).

In northern England, a post-mortem of an adult female found dead with developing eggs inside her suggested she was attacked by another goshawk, possibly the immature female that replaced her and went on to lay a clutch of eggs.

2.6 Brood size and fledging Goshawk eggs hatch over a 2–3 day period. The female generally broods the young for the first 8–10 days and remains close to the nest for at least 16 days, longer if the male brings sufficient food (Cramp & Simmons, 1980). The young typically move onto branches in the nest tree at 35–41 days from hatching (Petty, 1989; Anon., 1990); they make their first flights to adjacent trees at 38–46 days, with the smaller males fledging before the females. They remain within 300 m of the nest until 65 days old, when feather growth is complete, and typically disperse 65–90 days after hatching (Kenward et al., 1993; Marquiss et al., 2003). The average brood size at fledging has been recorded as 3.0 in Britain (Marquiss & Newton, 1982). In one British population, brood size at fledging has declined from an average of 2.8 between 1980-87 (Anon., 1990), to less than two in recent years. In Fennoscandia, the average brood size varied from 3.7 in years of favourable prey abundance to 1.9 in poor years (Sulkava et al., 1994).

3. SURVEY TECHNIQUES CAUTION Care should be taken to avoid disturbing goshawks during nest building and early incubation, as some pairs are prone to desert. It is recommended that nests are viewed from Goshawk

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distances of 300 – 500 m (Ruddock & Whitfield, 2007; Whitfield et al., 2008b). Obviously when searching for nests in woodland it will be necessary to approach potential nest sites more closely, but care should be taken to minimise disturbance. Visits to check use of known nests should take no more than 5–10 minutes (Visit 2), and searches for new nests should be delayed until young are likely to have hatched (Visit 3). If nest inspection visits require tree climbing, then appropriate health and safety precautions should be taken (see Section 7.10 of Introduction). Nest visits should be avoided after chicks reach the age of 30 days as they may fledge prematurely.

3.1 Breeding season visit schedule The species is listed on Schedule 1 in Great Britain, Northern Ireland and the Isle of Man (see Section 7.1.1 of Introduction). Boyce et al. (2005) reviewed methods used to detect occupancy of goshawks in North America and recommended three visits using foot searching or four visits for call broadcasting. Here, based on searching, four visits are recommended to confirm occupancy and breeding, even if no signs of occupancy are found during the earlier visits. Use of call playback for surveying is also described.

Visit 1

March to April

To check for occupancy and (until mid-March) the presence of new nests

Visit 2

Late April to May

To briefly view known nests for activity

Visit 3

June to early July

To check for young at known nests and search for additional active nests

Visit 4

Late July to early August

To check for fledged young

3.2 Signs of occupancy 3.2.1 Locating home ranges Goshawk nesting ranges can be used over many years but alternative nesting ranges used by the same pair may be up to 2.5 km apart. Repeated surveys of known nesting ranges may suggest a population decline if search effort is not widened to allow for such large-scale movements. For this reason, regular searches of all woodland blocks within a study area are recommended. In northeast Scotland, fieldworkers surveying goshawks first check all known nesting ranges and then widen the search around those that are apparently unoccupied until an occupied nesting range is found or the nesting territories of adjacent goshawk pairs are reached. This requires that extensive areas are covered but ensures that population estimates are comparable between years.

Before surveying new areas, it is recommended that fieldworkers collect old breeding records from ornithological sources and local people (Bosakowski, 1999). Forestry workers and gamekeepers sometimes know areas where goshawks have bred in the past, or are frequently seen. Areas of mature trees that could support breeding goshawks can be identified using OS maps, or preferably forestry stock maps that give the year of planting and tree species by compartment. All suitable areas should be systematically searched for signs that birds are present. The most obvious may be the nest (Petty, 1989) but it is also important to check low feeding perches (e.g. roots and stems of fallen trees) and the ground for pluckings, feathers and white faeces. Plucking points with evidence of more than one prey item are usually found within 200 m of active nests; on sloping ground they are normally uphill of the nest, giving the adults a clear flight-line to the nest. Moulted flight feathers and down are also found in

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occupied nesting ranges. In larch and broadleaf stands, searches should be made when nests and feeding perches are more obvious before leaves appear in the spring (Petty, 1989, 1996; Bosakowski, 1999).

Marquiss et al. (2003) describe the use of old nests to derive the history of newly discovered nesting territories by examining the layers of material. If nest lining and moulted feathers were present, it was assumed that eggs had been laid and incubation started. Nests were classed as successful if the top layer contained copious amounts of nestling down, faeces and the bones of prey, and unsuccessful if these signs were absent. Such signs were discernable up to three years after a breeding attempt.

Occupied nesting ranges can also be located by observing forests from vantage points that give a clear view over several square kilometres of forest. High-circling displays by single birds or pairs can be seen throughout the year but goshawks display more intensely over the canopy close to the nesting area in March and early April; these displays, performed by both males and females, are more frequent early in the morning in fine weather at the start of the breeding season. The full sky-dance involves: high-circling, flapping and soaring in tight spirals; undulating and slow flapping flight (gradually losing height); sometimes further circling to regain height; and plunging from a height of up to several hundred metres into the nesting wood with wings held towards sides (Cramp & Simmons, 1980). Wailing calls may be made just before, or during, the performance.

The presence of birds, especially single birds displaying, may not be linked to an occupied nest site, however. Marquiss & Newton (1982) recorded five areas where displaying birds were seen regularly but no evidence of breeding was obtained despite intensive searches.

Goshawks can also be more obvious during the two periods of the year when they call more frequently (Petty, 1989): during courtship in March and early April; and in July, after the young fledge, when they call incessantly when hungry. Prior to laying, the female is often found in the nesting area and she sometimes calls when observers approach. There is much vocalisation between the pair members at this time, particularly during bouts of nest building, copulation and prey delivery, and especially for 2â&#x20AC;&#x201C;3 hours around dawn (Penteriani, 2001). Nesting areas can be located or occupation confirmed during courtship with low risk of disturbing birds by listening for these calls around dawn at the edge of suitable habitat.

The playback of calls has been used to locate goshawks (Kennedy & Stahlecker, 1993; Penteriani, 1997; Bosakowski, 1999). Response rates vary with the stage of breeding, with maximal responses reported during the prelaying and post-fledging periods. Surveys using broadcast calls during brood rearing only will however miss pairs that have failed earlier in the breeding cycle because the adults become less territorial post-failure. Appropriate separation distances between broadcasting stations and transects depend on the power of the speaker system, topography, tree density and the presence of running water (for example Kennedy & Stahlecker (1993) recommended broadcast stations 300 m apart on transects 260 m apart, whereas Bosakowski (1999) used a more powerful signal that could be heard 400 m away, allowing for greater distances between transects). Areas close to loud rushing streams or rivers can be omitted as goshawks tend to avoid these areas for breeding (Reynolds et al., 1982; Spieser & Bosakowski, 1987). If the broadcast stations can be watched from about 20â&#x20AC;&#x2C6;m away, birds may be observed approaching the speakers, ensuring a higher detection rate (Bosakowski & Smith, 1998).

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3.2.2 Locating roosts Active roosts can be found during systematic searches of nesting ranges and can be identified by the presence of fresh faecal droppings, pellets and moulted feathers (Section 3.2.3). They are generally close to the nest site.

3.2.3 Recognition of signs Feeding perches with white faeces, plucks and carcasses may be found on tree stumps, upturned roots, large branches or old nests. Goshawk pellets and plucks cannot be separated reliably from those of buzzards, however, and identification must be confirmed by other signs (e.g. moulted feathers, active nests). Moulted feathers should be collected if found, as they can be used to identify individual birds (Bijlsma, 1997).

3.2.4 Evidence of occupancy Sightings of adult goshawks in combination with signs, such as moulted feathers and the remains of several kills, provide evidence of occupancy. Sightings on their own, even if birds are seen in the same area on a number of occasions, do not provide sufficient evidence.

3.3 Evidence of breeding 3.3.1 Locating active nests Nests can be found by searching nesting ranges in early spring (Visits 1 and 2), when the active nest will be built up with fresh branches. In thick, coniferous woodland, splashes below a female’s preferred perch may be a good pointer to nest location. Such perches are usually within 40-50 m, uphill of the nest and with a good flight line. Care must be taken, however, to avoid excessive disturbance during nest building and early incubation, as some pairs may desert easily at this time (Anon., 1989; Petty, 1996; see CAUTION above). At some nests viewed from the ground, the incubating female’s tail feathers are visible. Later, active nests have moulted down around the rim or on neighbouring branches, which can be seen with binoculars. A sketch and/or digital photograph of the location of the nest should be made as well as a record of its location (at least a six figure map reference). If, after the likely hatching date, a nest has no white faeces beneath but has fresh green vegetation and (especially) down shed by an incubating female, this may represent breeding failure. Fieldworkers should be aware also that a pair may have moved to an alternative site within the nesting range if a new or refurbished nest is abandonded. Any climbing to check for remains of broken or unhatched eggs should be delayed until late June, to avoid disturbing a site where incubation has been delayed (e.g. through relaying).

3.3.2 Evidence for fledging Large feathered young (at least 30 days old) in, or close to, the nest are evidence of successful fledging. Records of brood size are most reliable if well-feathered young can be counted in the nest, by climbing or observation from a suitable vantage point. Beware of climbing to nests when young are likely to be 30 or more days old (with very little or no down on the head) however, as chicks (particulary males or undernourished individuals) may jump. After hatching, the nest cup is likely to be covered with new nesting material (fresh twigs) and if chicks have fledged successfully the nest cup can rarely be seen at all. Searching beneath this material may reveal any unhatched eggs or the remains of dead chicks in the nest cup.

Recently fledged young that are not yet strong on the wing can be located by their begging calls and the number estimated, but this approach is unreliable when young can fly strongly and may scatter over 200 m from the nest.

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Goshawk

Wing length (mm)

Age (days)

Mass (g)

Figure 17. Change in the mean wing length (with 95% confidence limits) of goshawk chicks with age. Data from 2–44 nests per year over eight years and two study areas; each point based on measurements from 5–21 male and 5–13 female young (from Bijlsma, 1997).

Age (days)

Figure 18. Change in the mean mass (with 95% confidence limits) of goshawk chicks with age. Data from 2-44 nests per year over eight years and two study areas; each point based on measurements from 5-21 male and 5-13 female young (from Bijlsma, 1997).

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Footspan (mm)

Age (days)

Hind nail length (mm)

Figure 19. Change in the mean foot span (width of span including claws, with 95% confidence limits) of goshawk chicks with age. Data from 2-44 nests per year over eight years and two study areas; each point based on measurements from 5-34 male and 5-20 female young (from Bijlsma, 1997).

Age (days)

Figure 20. Change in the mean length of the hind claw (with 95% confidence limits) of goshawk chicks with age. Data from 2-44 nests per year over eight years and two study areas; each point based on measurements from 6-28 male and 5-19 female young (from Bijlsma, 1997).

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Tarsus length (mm)

Age (days)

Figure 21. Change in the mean tarsus length (with 95% confidence limits) of goshawk chicks with age. Data from 2-44 nests per year over eight years and two study areas; each point based on measurements from 6-29 male and 5-18 female young (from Bijlsma, 1997).

3.4 Evidence of non-breeding If displaying birds and other signs are seen regularly in a given location but no evidence of an active nest or fledged young is found subsequently, despite extensive searches at the appropriate visit dates, this suggests occupancy but non-breeding (Marquiss & Newton, 1982).

3.5 Ageing and sexing young Goshawk chicks can be aged approximately by measuring their wing length (Bijlsma 1997; Figure 17). Sexing should be possible visually based on foot and tarsus size from day 15 or 16 onwards, and often from age 12 to 13 days. Sexing should be confirmed by taking measurements, however, by first ageing young using wing length and then sexing using a combination of mass (which is thought to be quite a reliable indicator of sex in this species; Figure 18), foot span (Figure 19), hind claw (Figure 20) and tarsus length (Figure 21), in that order of priority. Based on measurements of Dutch birds, the foot spans of the sexes do not overlap after the age of 16 days (wing length > 99 mm; Figure 19), when females have a span larger than around 111 mm and males less than 105 mm (Bijlsma, 1997). Growth of foot span is complete by 21 days of age, when males have a span less than 116 mm and females equal to or greater than 119 mm. Similarly, measurements of Dutch birds suggest that both hind claw length (Figure 20) and tarsus length (Figure 21) differ significantly between the sexes after about 18-20 days of age and these can provide additional criteria for sexing (although they are more prone to individual variation in measurement by observers). On Gotland, only two of 87 males over 28 days of age (wing length > 200 mm) had a minimum tarsus width (with callipers squeezed tight momentarily) greater than 6.5 mm and only one of 82 females less than this (Kenward et al., 1993).

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Goshawks (of the nominate race gentilis) increase in size with latitude, with larger birds breeding in Scandinavia. Some Goshawks breeding in northern Britain are descended from these larger northern birds (Marquiss & Newton, 1982), so that the measurements given above should be used with caution in Britain and Ireland; further measurements of young goshawks from populations in Britain and Ireland are required before young can be aged and sexed reliably. For one British population, mass is reported to be the best predictor of sex, with small variations between males and females in foot span, hind claw and tarsus length.

4.â&#x20AC;&#x201A; SURVEYS OUTSIDE THE BREEDING SEASON There is no established method for surveying goshawk populations outside the breeding season. An index of wintering abundance might be obtained by carrying out counts of birds observed from defined survey routes (preferably randomly selected or at least representative of habitats in the area to be covered). Observers walking fixed survey routes in a set time span, several times each winter, and recording observations of goshawks and their approximate distance from the transect line, could generate data of use for indexing changes in numbers between years. Such survey work should be undertaken at similar times each year, between mid-November and late February, to exclude possible influxes of immigrants during passage periods (Wernham et al., 2002).

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Hen Harrier Circus cyaneus

1. INTRODUCTION The hen harrier (northern harrier) breeds mainly in the north and west of Great Britain, in Ireland and on the Isle of Man (Gibbons et al., 1993; Sim et al., 2001, 2007; Norriss et al., 2002). Recent surveys have indicated increases in breeding populations in many areas of Britain and Ireland, although numbers decreased in south and east Scotland and England (Norriss et al., 2002; Sim et al., 2007; Barton et al., 2006). The increases may be associated with the growing use of non-moorland habitats such as mature conifer plantations, second rotation forestry and scrub/brash (Norriss et al., 2002; Sim et al., 2007; Barton et al., 2006). Regional declines may be associated with continued illegal persecution (Sim et al., 2007; Natural England, 2008).

Hen harriers that breed in Britain are regarded as partial migrants (Etheridge, 2002; Etheridge & Summers, 2006). Many birds remain on or near their breeding grounds but some, mainly first-winter males, move into southwest Europe or Ireland in the winter. Irish breeders are probably largely sedentary (Etheridge, 2002). Northern European populations are completely migratory, with some wintering as far south as the Mediterranean shores of North Africa.

Many of the hen harriers wintering in southern Britain are believed to originate from the Continent (Clarke & Watson, 1997).

The grey and white adult male hen harriers can be distinguished easily from the brown ‘ringtails’ (females and immature birds). Separation of juvenile and immature birds from adult

Annual cycle Breeding Activity

Peak Period

Range

Site occupation and territorial display

Early April to early May

Late February to late May

Nest building

Duration (days)

April to late May

Egg laying

Late April to mid-May

Mid-April to late June

5 to 12

Incubation

Late April to mid-June

Mid-April to late July

29 to 31

Hatching

Late May to mid-June

Mid-May to late July

Young in nest

Late May to mid-July

Mid-May to late August

Fledging

Late June to mid-July

Mid-June to Late August

Juvenile dispersal

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August to September Hen harrier

females is more difficult; adult females tend to have paler underparts but there is considerable variation. Young brown males are smaller and less bulky in appearance; they begin to moult into grey adult plumage in the sping/summer of their first calendar year, during which time they will appear parti-coloured until the moult is completed by the autumn of the same year.

After the post-juvenile moult the plumage is generally like an adult male but has a darker area on the back (mantle and scapulars) and a brownish nape (hindneck) patch; these feathers may not completely disappear until birds are four or five years old (Watson, 1977). The plumage of immature females cannot be distinguished in the field from that of adult females (Cramp & Simmons, 1980). Most female hen harriers breed in their first year. Fewer first-year males breed, and those that do tend to be less successful than adults.

For further information on the biology and ecology of this species, Watson (1977) provides a comprehensive account.

2. HABITAT, HOME RANGE, NESTS AND BREEDING 2.1 Habitat Hen harriers require open terrain for hunting. Overall, in Britain and Ireland, the majority of pairs nest in heather moorland and forestry plantations (Bibby & Etheridge, 1993; Sim et al., 2001; Sim et al., 2007). In Ireland, second rotation pre-thicket coniferous forest was recently shown to be the most frequently used habitat, followed by new pre-thicket forestry (Norriss et al., 2002; Barton et al., 2006; Wilson et al., 2009). In western Scotland a significant proportion of hen harriers are now breeding in woodland habitats including mature and second rotation conifer plantations, newly planted native woodland and regenerating woodland and scrub (Haworth & Fielding, 2009). Use of woodland habitats for nesting may be dependent on the presence of suitable open areas for hunting nearby. Nests tend to be below 600 m a.s.l..

On the Continent, hen harriers will also breed in cereal crops. In the winter, they occur in open country throughout Britain and Ireland, with low-lying coastal areas in south and east England and in southwest Scotland being particularly favoured (Lack, 1986). In Scotland, females tend to winter on higher ground (above 200m a.s.l.) than males (below 100m a.s.l.)

(Etheridge, 2002).

2.2 Home range In the breeding season, hen harriers defend their nesting territory and hunt over a larger home range, which they share with other harriers. Males have larger home ranges than females (average respective home range areas of 7.3 km2 and 3.6 km2 in Scotland; Arroyo et al., 2005, 2006), and may feed as far as 10 km from the nest. Females were found to hunt mainly within 300–500 m of the nest (Arroyo et al., 2009).

Hen harriers are sometimes polygynous, normally with two, but up to six, females associating with one male. The incidence of polygyny varies between populations and, in Britain and Ireland, is most frequent in Orkney (Balfour & Cadbury, 1975, 1979; Watson, 1977; Picozzi, 1984; Amar & Redpath, 2002). Polygyny may increase with the abundance of voles, a principal prey species (Hamerstrom et al., 1985). The dominant (alpha) female lays first and will generally rear a larger brood than the second (beta) and other females. In southwest Scotland, there was no difference in breeding success between polygynous and monogamous females, despite the delivery of fewer food items to polygynous nests, as females and males compensated by delivering larger food items (Redpath et al., 2006). A case of polyandry in Northern Ireland was ascribed to a lack of females in the population (Scott & Hipkiss, 2006).

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2.3 Nest sites Most hen harriers nest on the ground in a dry, well-drained location; wet sites are avoided in Britain and Ireland, although they are used elsewhere. Analysis of ground nest characteristics in four areas of western Scotland (Redpath et al., 1998) showed that hen harriers preferred to nest in rank (tall) but not degenerate (old and woody) heather with an average height of 46 cm (approximately knee-deep). Nests tended to be nearer streams than expected by chance and there was also an indication of preference for northwest facing slopes (Redpath et al., 1998). As well as heather, nests in Britain and Ireland have been recorded in: rushes; bracken; willow; purple moor grass; mature bog myrtle with regenerating willow and birch; forestry brash with rosebay willowherb; open and closed canopy forestry plantations (amongst rank vegetation in clearings or rides); and restocked forestry (Watson, 1977; Petty & Anderson, 1986; Norriss et al., 2002). Nests within forestry plantations can be difficult to locate because the birds often fly along rides below tree height to reach them.

2.4 Nests The foundation of a ground nest is built of dead vegetation, usually heather, but it may include birch, rushes or other vegetation. The nest is lined with finer vegetation, with a 5 cm-deep cup. The material is gathered by both sexes, although primarily by the female, between 40-150 m from the nest, and is carried in the bill or feet (Cramp & Simmons, 1980; Watson, 1977). Nest building may continue during incubation. Male hen harriers will add small pieces of material to a nest if a female dies or disappears; the loose pieces lie on top of the eggs or nest cup and will not be incorporated into the nest, and this indicates nest failure.

Hen harriers have recently been recorded nesting in trees in mature closed-canopy spruce plantations in Northern Ireland (Scott et al., 1993; Scott, 2000). Nests are built 2–13 m above the ground, in trees with flattened crowns. Tree nests are less successful than ground nests (Scott & Clarke, 2007). Although tree nesting has not been recorded elsewhere in Britain and Ireland, fieldworkers should be aware of the possibility that birds observed either displaying over, or carrying food into, mature forest may be nesting in trees.

Male or female hen harriers may also build small, incomplete ‘cock’ nests, which are not used for breeding but may be built up and used in a subsequent year.

2.5 Clutch size and incubation Egg laying begins in mid-April, with most clutches started in early May, although the mean first egg date varies significantly between years (Etheridge et al., 1997). Hen harriers normally lay 3-7 eggs (Cramp & Simmons, 1980) at 48 hour intervals, with an average clutch size of five eggs (Etheridge et al., 1997). The BTO Nest Records Scheme gives an average clutch size of 4.6 eggs (n = 399) but includes a large amount of data from Orkney, where polygyny is associated with smaller clutch sizes. Exceptional clutches of up to 12 eggs have been recorded but these are believed to have been laid by two females (Watson, 1977). Incubation lasts for 29-31 days per egg and 29–39 days per clutch (Cramp & Simmons, 1980). It usually begins with the second- or third-last egg, although it can start with the first egg. Only the female incubates. Hen harriers are single brooded but the female may relay if the first clutch is lost early in incubation. In a large scale study in Scotland (1,459 nests located between 198895), Etheridge et al., (1997) identified 15 clutches as likely replacements; these were within 0.03–1.4 km of an earlier nest that had failed at the egg stage. Replacement clutches tend to be smaller than the original clutch and are normally started within 10-21 days of failure.

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2.6 Brood size and fledging The eggs hatch asynchronously. In bad weather or if there is a lack of food, the youngest and weakest chicks will die. In Wales, an increase in breeding success has been linked to warmer weather and reduced human interference (Whitfield et al., 2008c). The young are fed by the female, who broods them periodically until they are 14-21 days old. The male initially provides all the food, but the female starts to forage once the young are about 11 days old and may provide more than 50% of the food when the young are more than 20 days old (Watson, 1977). In southwest Scotland, average prey delivery rates at different stages of the nesting cycle were: prelaying, 0.39 prey deliveries per hour; incubation, 0.50, nestling, 0.67 and post-fledging, 0.70 (Dickson, 1995a). Higher prey delivery rates during the nestling period have been recorded elsewhere in Scotland (Balfour & MacDonald, 1970; Watson, 1977; Picozzi, 1978; Redpath & Thirgood 1997) and lower rates during the prelaying and incubation periods on Orkney (Amar et al., 2003). Well-fed male chicks fledge at 28 days and well-fed female chicks at 32 days. Fledging can be delayed for up to 7 days in poor weather or if feeding conditions are poor. The young are dependent on parental feeding for around 14 days after fledging. If undisturbed, they will remain close to the nest for some time. The average length of the dispersal period is not known: some juveniles have been observed 30 km away from the nest three weeks after fledging, while others were still near the nest site five weeks after fledging.

3. SURVEY TECHNIQUES CAUTION To minimise the risk of disturbance it is recommended that nesting areas are viewed from distances of 500-700m (Ruddock & Whitfield, 2007; Whitfield et al., 2008b).

Special care should be taken to minimise disturbance to hen harriers while they are laying, as nests containing one or two eggs may be deserted. Nests should not be disturbed in cold or wet weather around the time of hatching or when small young are present. Incubating or brooding females flushed from nests may dislodge eggs or small young from the nest cup.

Any such eggs or young should be carefully put back in the nest. Appropriate care should be taken if nest visits involve tree climbing (see Section 7.10 of introduction). Some females and occasionally males can be aggressive towards people at the nest, even striking an intruder’s head with feet and claws. Head protection is therefore recommended.

3.1 Breeding season visit schedule The species is listed on Schedule 1 in Great Britain, Northern Ireland and the Isle of Man, and on Schedule II in the Republic of Ireland (see Section 7.1.1 of Introduction).

Hen harriers are most obvious between March and May, before they lay, and again in late June or July, when successful nests have large or fledged young. To establish occupancy and the presence of a breeding pair, it is recommended that all four visits are made (as detailed below). However, if time is limited and a home range appears to be unoccupied on the basis of the first two visits, then further visits to that home range can be omitted. The methods given below are based on those used for recent national surveys of the UK, Isle of Man and Republic of Ireland (Sim et al., 2001; Norriss et al., 2002; Sim et al., 2007; Barton et al., 2006). Note that breeding attempts that fail at the egg stage are likely to be under-recorded by these survey methods. In some parts of their range hen harriers are persecuted and surveyors should be mindful of this.

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Visit 1

March to mid-April

To check for occupancy.

Visit 2

Mid-April to late May

To locate incubating females. It is important to locate nests as early as possible as some pairs may fail soon after laying. Exceptionally, some birds may not lay until early June

Visit 3

Late May to late June

To check for young or for evidence of breeding if no nest/other signs were found on previous visits

Visit 4

Late June to late August

To check for fledged young. Most visits should be made by mid-July, as young from early nests may start to disperse thereafter

3.2 Signs of occupancy 3.2.1 Locating home ranges During the first visit to an area, all areas of suitable habitat should be checked on foot, ensuring that the whole area is covered and passing within 250 m of every location with restricted visibility. Watches should be carried out from suitable vantage points for 2.5-4 hours. All unsuitable breeding areas should be marked on a map and can be omitted from repeat visits; these tend to include: land above 600m; improved pasture and arable land; extensive areas of degraded land with no heather cover and low vegetation; the vicinity of cliffs, rocky outcrops, boulder fields and scree; and areas within 100 m of hill farms and occupied dwellings.

Early observations of displaying birds are essential, as many breeding attempts fail before nests are found. Both males and females display, individually or as a pair. Hen harriers commonly perform both solo and mutual high-circling displays over their nesting areas, particularly early in the breeding cycle. Males in particular carry out flight-play manoeuvres, often while calling, and females may flight-roll and present talons in response (Cramp & Simmons, 1980). Solo high-circling by males may lead to sky-dancing, ranging from a simple series of undulating flights at about 30-150 m above the ground, through a version with steeper undulations closer to the ground, to full skydancing accompanied by calling. Females have been recorded sky-dancing, particularly making the ‘switch-back’ flight close to the ground, and mutual sky-dancing also occurs. Displaying brown ‘ringtails’ may be females or immature (first year) males. Careful observation is required to distinguish the smaller, slimmer male from the female. If several birds display together, the number of females and males involved should be noted. Several females associating with a single male may provide an indication of polygyny but not all of these females will necessarily nest.

Male hen harriers make food-flights, where they fly over and around the nesting territory carrying prey or another object (e.g. heather stick, clod of earth) in one foot. Full food presentation to the female begins intermittently prior to laying and continues as full provisioning of the female through to early chick rearing. Aerial food passes are made within the nesting territory, normally very close to the nest: the female usually calls on seeing the approaching male and may fly up to meet him. However, in the early stages of nesting, food may be passed to the female on the ground or even left near the nest for her to collect. During display, or when hungry during incubation or brooding, the female will ‘food beg’ if the male is present; these loud calls can be clearly heard and can help to locate nests.

Hen harriers may display over a large area before laying. Displaying birds that are first seen in an area late in the season may be birds that have failed and moved on. As hen harriers can occupy nesting territories close together, care must be taken to distinguish between neighbouring birds.

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3.2.2 Locating roosts If the fieldworker is visiting a known nesting range early in the season, old nests should be checked. Hen harriers frequently roost in these, and fresh faecal droppings and pellets may be found. Searches for roosts during the breeding season are not recommended because of the disturbance that this can cause.

3.2.3 Recognition of signs Remains of kills and faecal droppings can be used to support field observations. The remains of kills are difficult to locate, however, as hen harriers use a different plucking site for each feed. These may be found on open ground, on a burnt heather patch or in tussocks, where the female feeds after a food pass. Hen harrier pellets are not easily distinguishable from those of other raptors and should only be used to support direct evidence of occupancy.

3.2.4 Evidence of occupancy The criteria for ‘probable’ breeding attempts used for the interpretation of data from national hen harrier surveys can be used as evidence of occupancy (see below). Sightings of birds in the same area on more than one occasion provide stronger evidence for occupancy.

3.3 Evidence of breeding The following criteria were used during recent national surveys of the UK and Isle of Man to classify observations of hen harriers recorded during surveys as proven, probable or possible breeding attempts (Sim et al., 2001; Sim et al., 2007): PROVEN BREEDING

• food pass between two adults • adult carrying prey • used nest or eggshells, nest with eggs or young found • recently fledged young

PROBABLE BREEDING

• a pair seen in breeding season in possible breeding habitat* • a bird or pair apparently holding territory • courtship/display/agitated behaviour • bird(s) nest building • bird(s) visiting probable nest site

POSSIBLE BREEDING

• a single bird seen in breeding season in possible breeding habitat

* Classed as a ‘possible’ breeding attempt for the purposes of surveys of the Republic of Ireland 1998–2000 (Norriss et al., 2002).

These criteria were designed for use in surveys covering extensive areas of habitat with only 2-3 visits to each area per season, and population estimates were recorded as the total number of proven and probable breeding attempts (territorial pairs) recorded. Raptor fieldworkers carrying out more intensive studies, involving more repeat visits to survey areas, may record population estimates as the total of proven breeding attempts only.

The latest national survey of hen harrier in the Republic of Ireland, based on three survey visits to each area, used a modified version of the above criteria to distinguish between confirmed Hen harrier

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and possible territorial pairs (Barton et al., 2006). Confirmed territorial pairs were defined as for proven breeding above, but with the addition of: agitated behaviour or calls given by adults; courtship or display behaviour involving both a male and female and/or a pair seen visiting a probable nest site noted on two visits separated by at least a week. A possible territorial pair was recorded if courtship and display involving a male and female were noted on only one visit, or if only one displaying bird was ever seen (e.g. a displaying male seen twice but no female); if a pair were seen visiting a probable nest site on only one visit, or if a pair or female were seen in possible nesting habitat between mid-May and the end of June.

The requirement for observations of territorial behaviour on two occasions was introduced to reduce the possibility of double-counting of displaying birds which may have moved between survey visits (Barton et al., 2006).

3.3.1 Locating active nests Hen harriers can show strong site fidelity and may build a new nest each year in the same heather bank or within a few hundred metres of the previous year’s nest. They will move as the heather changes with age or burning. If it is suspected that breeding is taking place in the same patch of heather as in previous years, a search for the nest is feasible. This should be stopped if a female alarms from the air or from a ground perch as the bird may have slipped off the nest unseen. The fieldworker should then leave the immediate area and watch the site from a vantage point at a suitable distance (that does not result in alarm calls from the bird).

In Northern Ireland, some tree nests have been re-used for up to four years.

If information on nest locations is not available from previous years, watches should be carried out from suitable vantage points during Visits 2 and 3. The aim is to identify the locations of active nests by watching for females leaving and returning to nests (during incubation and brooding) or adults bringing food to young. Before full incubation begins, females may leave nests for long periods of time, particularly on warm days, and neighbouring females may fly in the vicinity of each other’s nests early in the season. Females will be observed most frequently leaving nests to receive food from the male, usually via an aerial food pass. During incubation, the female will normally feed away from the nest after a food pass, and the location of the nest can be identified by watching for her to return (she may gather nesting material before doing so). Females brooding chicks will usually return straight to the nest after a food pass.

Incubating and brooding females may also leave the nest to defecate, or to mob potential predators, so special attention should be paid to any interactions with other raptors and corvids. Indeed, it is well worth watching corvids active on a moor in order to catch sight of a female slipping off the nest to attack them.

Vantage point watches during the incubation period may need to last for four to six hours, as males can take up to six hours to bring food to the female, although most feeds are less than four hours apart. If the nest site is not identified after observing a food pass during the incubation period, the fieldworker might consider moving to check a different nesting area, as there is unlikely to be a further food pass for several hours.

Once the female stops brooding, the male and female may visit the nest every one to two hours to bring food to chicks, so it may take less time to identify a nest location. Watches should be carried out in the morning (06:00h or earlier to midday) or evening (16:00 to 20:00h) as the male may not visit the female during the afternoon (midday until 16:00h). Some published information suggests that hen harriers are not active early in the morning, but observations in Scotland have shown that they may begin to hunt within one hour of dawn. In an analysis of daily food provisioning in south Scotland, the first recorded delivery was at 05:30h and the last at 20:45h. Provisioning rates increased up to 07:00h, then remained fairly constant,

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with slight peaks in the late afternoon and early evening (Redpath & Thirgood, 1997). Males brought similar amounts of prey items irrespective of brood size and nestling age, and always provided more food than females; whereas females brought more prey and bigger items to larger and older broods (Leckie et al., 2008).

Once a bird is seen visiting a nest, a sketch map should be drawn and/or a digital photograph taken (see Section 7.7.1 of Introduction) to show its location in relation to any recognisable features (boulders, small trees, patches of distinct heather, muirburn). The position of the vantage point should also be noted along with a compass bearing to the nest location.

If visits are made to nests to record the contents, a fieldworker should deliberately make a noise on approach to alert the bird of his/her presence. Females may sit tight in late incubation or early brooding, and only flush from about a metre away. Some females may leave the nesting area while others may swoop agressively and repeatedly on a fieldworker. Some fieldworkers record whether female and male harriers are ‘bold’ or ‘timid’ in their response to nest visits on the basis that this may affect the success of the breeding attempt. Birds that defend the nest vigorously may be more active in deterring predators such as foxes, but may potentially be more at risk of illegal persecution if they swoop close to people who approach the nest. Nest visits should be as brief as possible, especially if it is suspected that the clutch is incomplete.

If a male is seen to display to more than one female, or polygyny is suspected for some other reason, observers should not approach the first nest that is located during a watch, but should instead make further observations to assess whether a male brings food to another nest close by.

3.3.2 Evidence for fledging Because of the high risk of predation of ground nests (Green & Etheridge, 1999), young can only be assumed to have fledged if they are observed and counted when capable of flight.

If possible, the nest and surrounding area should be checked carefully a week before the estimated fledging date, and a two hour watch carried out within the next week to check for the presence of fledged young. If there is insufficient time to carry out this final watch, then the number of fully feathered young in the nest can be used as an estimate of the number that will fledge. Once the young are fully feathered, the female no longer removes uneaten prey remains (legs, pelvic girdles and so on), and the presence of such remains in an empty nest is indicative of successful fledging. Predation risk increases as the young mature. If a predator has taken large young, evidence (bitten off feather quills, trails of down feathers) can often be found. There may be no signs to indicate that smaller young have been taken by a predator, however. If a nest is found empty, the surrounding area should be checked carefully for dead chicks or any signs of human intervention.

Tree nests in Northern Ireland are often unstable and young may be lost if they fall to the ground. A case of probable predation by buzzard has been recorded (Scott, 2000).

3.4 Evidence for non-breeding The number of apparently single hen harriers recorded during the 1998 survey of the UK and Isle of Man, considered by the authors to be mostly birds that did not attempt to breed in that year, averaged 0.28 per territorial pair (Sim et al., 2001). Hen harriers may occupy a nesting range early in the season and not breed there, although they may move elsewhere to breed.

If a pair occupies a nesting range but does not breed, the male may display into late May and bring food to the female, but she will not be observed returning to a nest. This behaviour will also be seen after nest failure, however, making non-breeding difficult to prove, except by very frequent watches of known nesting areas throughout the breeding season.

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3.5 Ageing and sexing young

Wing length (mm)

Young hen harriers can be aged approximately by measuring wing length (Figure 14; Bijlsma, 1997). Care must be exercised, however, as many broods contain a ‘runt’. These runt chicks are smaller than would be expected for their age because their growth is retarded through receiving less food than their larger siblings. Wing length should not be used to sex young because there is a considerable overlap in length between male and female chicks whilst they are still in the nest. Young can be sexed from day 20 onwards (wing >158 mm) after which there appears to be no overlap in claw span measurements of the two sexes (Bijlsma, 1997); males have a claw span of ≤ 60mm and females ≥ 62mm. Chicks weighing more than 450g are likely to be female, and those less than 400g, male. Well-feathered male chicks tend to have a grey tinge to the iris, while that of the larger female is brown (Picozzi, 1981; see Plate 80). After day 20, if both sexes are present in the nest, a visual comparison of tarsus length and thickness, and foot size, can also be used to separate the smaller males from females, without the need for measurements.

Chick age (days)

Figure 14. Change in the mean wing length (with 95% confidence limits) of hen harrier chicks with age. Data from 1-7 nests per year over four years and three study areas; each point based on measurements from 5-9 male and 5-8 female young (from Bijlsma, 1997).

4. SURVEYS OUTSIDE THE BREEDING SEASON Hen harriers may roost communally in winter, generally in rank ground vegetation (Clarke & Watson, 1990, 1997). They build roosting platforms (approximately 1 m across) by splaying out plant stems and tussocks. These platforms are often surrounded by faecal droppings and, sometimes, by pellets. The birds also use natural gaps in the vegetation. Most roosts

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have been found in lowland marshes or mosses, or in heather moors. In Northern Ireland, some birds roost in tree nests in the winter and others may gather in communal roosts in coniferous trees. Roosts can be located by observing hen harriers in the late afternoon and watching them back to the roost. To count the birds, a roost should be watched from a suitable vantage point from late afternoon until dusk (1.5 hours before sunset to half an hour after sunset or until it becomes too dark to see; Gilbert et al., 1998). From the vantage point, the fieldworker should record any harriers entering the roost, noting the time as well as sex and age if possible. If distinguishable, it is helpful to note the location of the roosting spot used by each individual bird. Roost counts can also be carried out as birds leave in the morning, in which case observers should be in position at a vantage point at first light. Gilbert et al. (1998) give further details of the methodology and annual timings of visits for surveys of wintering hen harriers in Britain (Clarke & Watson, 1990; Clarke & Watson, 1997). Care should be taken not to draw attention to the location, as instances of persecution are known to have occurred at roosts. Harriers counted at roosts in Britain and Ireland are generally of unknown breeding origin, and counts at roosts do not give any indication of the geographical areas used for foraging.

Hen harriers will also roost individually on old nests in breeding areas in the autumn (August to October) or in the late winter/early spring (February to April). These birds tend to be females and such roosts can be found by checking old nests for fresh faecal droppings and pellets.

Foot or road surveys could be used to provide indices of abundance of and information on habitat use by hen harriers in winter. In Britain and Ireland, because of the partially migrant nature of the breeding populations and the likely presence of immigrants from continental Europe, such surveys would record individual birds of mixed breeding origins.

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Hobby Falco subbuteo 1. INTRODUCTION The main breeding range of the hobby (Eurasian hobby) in Britain and Ireland lies in England, south of the Mersey/Humber line and extending into the borders of Wales. The British population has increased significantly in recent years and the species has spread north and west from its original stronghold in central southern England (Clements, 2001). A few pairs have bred in Scotland as far north as Highland Region (Ogilvie & RBBP, 2004; Etheridge, 2005; Crooke, 2007). Hobbies do not breed in Ireland, although occasional vagrants have been reported there. British and mainland European populations are completely migratory.

British birds winter in Africa, although the exact area is uncertain (Chapman, 2002). The sexes are not easily distinguished in the field. Juveniles resemble adults but are browner with buff underparts; they retain some of this plumage into their second calendar year. Male and female hobbies can breed at one year old but most do not do so until two years.

For further information on the biology and ecology of this species, Chapman (1999) provides a comprehensive account.

2. HABITAT, HOME RANGE, NESTS AND BREEDING 2.1 Habitat Hobbies breed in open lowland areas with mature trees, either in groves, in clumps, in lines or at woodland edges (Sergio et al., 2001); areas that support good numbers of large flying

Annual cycle Breeding Activity

Peak Period

Range

Occupation of home range

April to early May

Territorial display

Mid-April to May

Courtship

Duration (days)

May

Egg laying

Mid-June

Late May to early July

1 to 6

Incubation

Mid-June to mid-July

Late May to early August

28 to 34

Hatching

Mid-July

Late June to early August

Young in nest

Mid-July to mid-August

Late June to early September

Fledging

Late July to early September

Juvenile dispersal

Late August to mid-October

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Hobby

insects. Their favoured habitats include heaths, open woodland, and mixed farmland with woods and grassland. They also breed at lower densities in intensive arable farmland and in urban and suburban areas (Clements, 2001). Nesting territories are often near wetlands and on chalky or sandy soils. They are usually found below 400 m ASL although hobbies have been found breeding up to 1,900 m ASL in sub-alpine meadows in mainland Europe.

2.2 Home range Hobbies take up occupation of their home ranges, which are often in traditional use, in April and May. These are normally occupied by a pair but immature birds may attach themselves to a pair and help to raise the young (Chapman, 1999). Breeding densities in Britain vary from 1–6 pairs per 100 km² and, in mainland Europe, from 0.5–29 pairs per 100 km² (Clements, 2001; Sergio et al., 2001). Average nearest neighbour distances of 1.5-8.8 km have been recorded from England and Europe, although neighbouring pairs may nest as close as 200 m apart (Sergio et al., 2001). Home ranges may be large (relative to the size of the bird), as hobbies often forage 3–6.5 km from the nest (Chapman, 1999; Sergio et al., 2001), and the home ranges of neighbouring pairs probably overlap extensively. The nesting territory (within 100–500 m of the nest) is defended vigorously against other hobbies (Chapman, 1999), by both sexes. This aggressive behaviour varies considerably between different adults (Sergio et al., 2001) and with the stage of breeding (particularly for females), increasing from incubation to fledging (Sergio & Bogliani, 2001). Parr (1985) estimated the nest areas (the area within which the nest site of a pair of hobbies was located over a number of years; equivalent to the nesting range as defined in Section 4.2 of the Introduction) of hobbies in southern England to be 250–1,600 ha in size; such areas may contain 2–8 nest sites (Sergio et al., 2001). The previous year’s nest site may occasionally be re-used (up to 8% in different studies); new nest sites are generally within 1 km of this (but can be up to 4 km away).

2.3 Nest Sites Hobbies breed in nests built by other species, particularly those of crows built in the previous or current spring (Sergio et al., 2001) but also nests of raven, buzzard and kite, as well as squirrel dreys. The nests are usually in trees but, in recent years, nests on electricity pylons have also been used (Catley, 1994; Chapman, 1999; Sergio et al., 2001). The variety of tree species used probably reflects local availability and the species chosen by the nest builders; usually, most of the hobby nests in a given locality are in one main tree species (Sergio et al., 2001). Nests used by hobbies are generally in single trees, small clumps of trees, lines of trees, small open woodlands or in trees on the edge of larger open forests; they are invariably within 300 m of an open space. Hobbies may avoid breeding near goshawks. Nests are normally in the crown, upper branches or fork of a mature tree (12–32 m tall), at an average height of 15 m (range 4–32m, Chapman, 1999). Hobbies will use artificial nests (e.g. they used basket nests when crow nests became scarce in Berlin; Chapman, 1999).

2.4 Nests Hobbies do not add any material to the used nest in which they breed. Some of the lining may be removed but pine cones and needles are not (Nethersole-Thompson, 1931a).

2.5 Clutch size and incubation Hobbies lay from late May to early July (Fiuczynski & Nethersole-Thompson, 1980; Sergio et al., 2001). This late breeding may be timed so that the nestling period coincides with a late summer peak of flying insects and newly fledged passerines and swifts. Laying dates can vary significantly between years. Clutch size is usually 1–4 eggs laid at two or sometimes 3-day intervals (Cramp & Simmons, 1980). The BTO Nest Record Scheme gives an average clutch size of 2.7 (n=93).

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Single egg clutches normally fail to hatch. About half of pairs that fail early with eggs will lay a repeat clutch within 2–3 weeks (Nethersole-Thompson, 1931a), usually smaller than the first (normally two eggs, Chapman, 1999) and in a different nest (often close to the original nesting site but may be up to 1 km away). Incubation begins with the second egg, lasts for 28–34 days per egg and may vary with clutch size (Sergio et al., 2001). The female carries out most of the incubation, relieved occasionally by the male when she is off the nest (mean 1.3 hours per stint on 8 days during incubation, Parr, 1985). The male begins to feed the female from about 20 days before egg laying and continues throughout incubation. Average delivery rates are 2.3 (range 0–4.0) items per day prelaying and 2.6 (0–4.6) per day during incubation (Parr, 1985).

2.6 Brood size and fledging Hatching is asynchronous with an average age difference of 4.5 days between the oldest and youngest chicks in broods of four (Fiuczynski & Nethersole-Thompson, 1980). The male provides all or the majority of the food for the young and the female throughout the nestling period and into the post-fledging period (Parr, 1985; Chapman 1999). The female broods the young for 8-13 days after hatch and subsequently guards them; taking prey from the male and distributing it to the young. She may undertake some hunting trips in the late nestling and post-fledging period. Prey delivered to the chicks consists of small birds, insects and sometimes bats. Males in three study areas in southern England never regularly provisioned the female and young with insects; providing an overall mean of 5.9 deliveries per day (2.3-11.4) during the nesting period (Parr, 1985). In the east Midlands, an average of 4-7 avian prey items was delivered per day (Chapman, 1999). Outside Britain, much higher delivery rates of insect prey have been recorded (7-45 visits per hour, though feeding may be interrupted for 5-6 hours in wet weather; Sergio et al., 2001). The young fledge at 26-41 days (average of 31 days; Sergio & Bogliani, 1999). The little information available on the post-fledging period suggests young stay close to the nest (perhaps within about 50 m) for 1-3 weeks, after which their range gradually increases to 1-2 km from the nest site; they continue to receive food from the male and may be accompanied by the female (who may also feed them or compete for food from the male) until becoming independent at 16-46 days after fledging (Chapman, 1999; Sergio et al, 2001). Fledged young and the female may depart the nesting area before the male, although there is no evidence they migrate together (Newton, 1979). Cases of adults departing before fledged young, and the adoption and feeding of those young by foster parents (in addition to their own fledged young) have been recorded (Dronneau & Wassmer, 1989; Sergio et al., 2001).

3. SURVEY TECHNIQUES CAUTION To minimise disturbance, intensive nest searches are best carried out at a time when young are likely to have hatched. Nest inspections should not be undertaken during incubation as disturbance at this time may flush birds from eggs, increasing the risk of nest predation and territory abandonment. Appropriate health and safety precautions should be taken if climbing to nests (see Section 7.10 of Introduction). Nest visits should be avoided once young are older than about 25 days, as this may cause premature fledging. In the Netherlands, fieldworkers avoided visiting hobby nests because aggressive calls from the adults attracted predatory goshawks (Sergio et al., 2001).

3.1 Breeding season visit schedule The species is listed on Schedule 1 in Great Britain and the Isle of Man (see Section 7.1.1 of Introduction). To establish occupancy and the presence of a breeding pair, it is recommended that all four visits are made (as detailed below). A minimum of three visits is recommended to

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confirm that a nesting range is unoccupied. It is suggested that visits are timed around dawn and/or dusk to coincide with the periods when hobbies are most active and/or conspicuous.

Minimum recommended observation times are 3 hours beginning at sunrise or from three hours before sunset until sunset. Great care should be taken during Visit 2 as hobbies are sensitive to disturbance during early incubation.

Visit 1

April to May

To check for occupancy, sunrise to late morning

Visit 2

June

DO NOT VISIT NESTING TERRITORIES (see CAUTION). Observations can be carried out from vantage points to locate active nest sites

Visit 3

July to mid-August

To search for active nests and check for young (hobbies become more demonstrative as young grow), sunrise to late morning and afternoon until sunset

Visit 4

Mid-August to September

To check for fledged young, sunrise to late morning and afternoon until sunset

3.2 Signs of occupancy 3.2.1 Locating home ranges During May, hobbies may congregate over open water, wetlands and forest clearings to ‘hawk’ for insects. Watches for birds hunting cooperatively can reveal the presence of hobbies in an area, although some such birds may be non-breeders. In the early stages of nesting, hobbies can be secretive and difficult to detect (Clements, 2001), although they become more obvious when the young fledge. Home ranges can be located by scanning for displaying, soaring and hunting birds around suitable nesting areas (Fuller et al., 1985) in April and May. If it is still there, the nest used in a previous year may be visited by hobbies returning the following spring, and can be a useful starting point for early visits to the nesting range. Although birds may move some distance to occupy a new nest, sightings in the vicinity of an old nest can provide supporting evidence for occupation. In open country, fieldworkers should also scan for the male on his lookout perch; this will generally be on dead branches beyond the canopy of a tree or high on a pylon and within sight of the nest. Birds perched on pylons can be less visible as they may be hidden by the metal structure.

Aerial displays are rare but spectacular, particularly those of males (Cramp & Simmons, 1980). Males that display before the arrival of females make low circles over the treetops and high soaring flights over the nesting area, often accompanied by calling. With the female present, the male flies in and circles around her, calling, and both birds make display flights which may include chasing, diving together, and the male diving at the female (accompanied by calling). There may be an initial burst of such flight activity when the pair first arrive back, then the birds seem to disappear for 3–5 weeks (they may spend some of this intervening time soaring very high over the area) and only reappear shortly before laying. Food-passes from male to female may be elaborated into aerial displays, or may take place on a perch (Cramp & Simmons, 1980).

During the main part of the breeding season, hobbies are most likely to be seen close to the nest site early in the morning and late in the evening and are in fact surprisingly crepuscular.

They are often located by sound rather than being observed in flight, so familiarity with the calls, in particular alarm and contact calls (versions of the ‘kew kew kew’ call featured on the CD accompanying this book), is important. Hobbies are most vocal at dawn when the members of a pair may duet, particularly prior to egg-laying; although dusk can be better as fewer other Hobby

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birds are calling. Hobbies can move between arrival and egg laying in search of a suitable nesting area and the vocalisations can be used to follow pairs as they settle (several visits will be needed). Later in the season, fledged young are particularly vocal at dusk. Hobbies may also be more visible at dusk as they hawk for insects if weather conditions are good.

If possible it is recommended that observers work together in groups to locate hobbies, each one at a different vantage point and maintaining contact by radio or mobile phone. Vantage points should be spaced approximately 500m apart, depending on the terrain and the visible area. At this spacing, any calls should be heard by at least one observer. After covering an area, the search can be extended.

Within possible nesting ranges, large, mature trees should be checked for roosts, pellets, feathers from kills (such feathers will be scattered as prey are plucked at a considerable height), specks of ‘whitewash’ and rarely (as adult birds generally moult over-winter) moulted hobby feathers. Checks should also be made for fledged young in August (see 3.3.2).

3.2.2 Locating roosts On arrival at the breeding grounds, hobbies generally roost high up in mature trees, within 1 km or further from their future nest; the male and female may roost together or separately (Cramp & Simmons, 1980). Thus the location of a roosting bird or birds can give supporting evidence for occupation of a home range but may not assist in locating the nest.

3.2.3 Recognition of signs Hobby pellets are 20–26 mm in length, 10–15 mm wide, and generally rounded in shape.

In the early part of the season, they tend to consist mainly of shiny insect remains, with increased amounts of passerine remains after the young hatch (Cramp & Simmons, 1980; Sergio et al., 2001; Brown et al., 2003). They are difficult to distinguish from kestrel pellets.

Prey remains may be difficult to find as hobbies pluck their prey in trees.

3.2.4 Evidence for occupancy Observations of adult hobbies apparently holding territory (e.g. courtship display, aggressive behaviour towards conspecifics) in a given area on more than one occasion can be used as evidence of occupancy. As hobbies may move around early in the season before selecting a nest it is recommended that occupancy is confirmed by the presence of an active nest.

3.3 Evidence for breeding 3.3.1 Locating active nests Once the presence of an occupied nesting territory has been established, vantage point watches should be carried out to look for males bringing food to an incubating female and listen for calls between the pair as food is exchanged. Watches should last for up to 4 hours based on the rates at which males feed females (Section 2.4). It may be possible to watch the birds back to the nest after a food pass (although the nest should not be approached during incubation). Once the young hatch the male food delivery rate increases (Section 2.5) and a 2 hour vantage point watch near a suspected nest site should confirm breeding. Defensive behaviour of adult hobbies towards corvids or large raptors which might predate a nest can also reveal its location.

Intensive searching for nests should be delayed until after young have hatched and the activity of the adults increases (Visit 3). If vantage point watches have not revealed a likely nest

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location, all mature trees and electricity pylons should be searched for nests that could be used by hobbies, particularly those of corvids. If flushed from small chicks, an adult may not alarm but will be reluctant to leave the area. With larger young, alarm behaviour from the adults will indicate the presence of an occupied nest which may have faecal droppings or down on it. Woodpigeons may nest in association with hobbies (within 5-40 m, sometimes in the same tree). In the Netherlands and Italy, studies have reported respectively 89% and 65% of hobby nests with associated woodpigeons (averages of 5.4 and 1.1 woodpigeon nests per pair; Bijlsma, 1984; Bogliani et al., 1999). This phenomenon has also been noted in Britain (Chapman, 1999) and Germany. Woodpigeons appear to benefit through a reduced risk of nest predation (Bogliani et al., 1999) although it is less clear if there are any particular benefits to hobbies. Fieldworkers searching for hobby nests should pay attention to sudden outbursts of woodpigeon activity. Appropriate health and safety precautions should be taken if nest inspection visits are undertaken (and noting that special permission will be required for electricity pylons).

3.3.2 Evidence for fledging Recently fledged hobbies can be recognised from a fair distance by their blue cere and eye ring, especially when perched. Fledged young become progressively more vocal and active, making them easier to find. Counts should ideally be made at the nest site within 10 days of fledging, noting that the young tend to be less active in the middle of the day. Earlier counts may also be possible, for example, if large young leave the nest and move onto neighbouring branches prior to fledging, but these counts can be difficult, as the young may be hidden behind branches and leaves.

Systematic searches for nests are often successful in mid-August to late September (visit 4) and this can be a good time for locating new nesting territories which may have been missed earlier in the season. Fledged young will often flush when an observer is about 20m from a nest. On warm days with little or no wind, both adult and juvenile hobbies will hawk for insects and gradually gain height. A vantage point with a good 3600 view can detect these birds. Watches should be made from mid morning. The bulk of this activity will be within 500m of the used nest. If the young are located as they rise or as they return, the nesting area can be established.

3.4 Evidence for non-breeding If no evidence of an active nest or fledged young is found in an occupied nesting territory during visits at the appropriate times, this suggests that breeding has not occurred. Non-breeding birds display less frequently and generally leave the territory part-way through the breeding season but may remain on site until mid-August. Unpaired hobbies may also hold territories.

3.5 Ageing and sexing young Hobby chicks can be aged approximately using their wing length (Bijlsma, 1997; Figure 35).

Some young can be sexed after the age of 21 days (wing length >148 mm) using weight (Bijlsma, 1997; Figure 36): in general any chick weighing 230 g or less without a full crop is a male, and 260 g or more, a female. The wide variation in mass with age (at least in part due to variation in crop fullness at the time of measurement) means that chicks weighing 231–259 g generally cannot be sexed using existing measurement criteria. The patterning on the undertail coverts may be used in conjunction with mass, as an indicator of sex: females have well defined stripes on the undertail coverts, while males have either faint stripes or no stripes (Bijlsma, 1997). This difference may not be reliable, however, due to the amount of variation within each sex in the patterning of the undertail coverts (Ristow, 2004).

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Wing length (mm)

Age (days)

Mass (g)

Figure 35. Increase in mean wing length (with 95% confidence limits) of hobby chicks with age. Data from 1–4 nests per year over 13 years and three study areas; each point based on measurements from 5–10 males and 5–9 females (from Bijlsma, 1997).

Age (days)

Figure 36. Increase in mean mass (with 95% confidence limits; usually measured in the evening) of hobby chicks with age. Based on 1–4 nests per year over 13 years and three study areas; each point based on measurements from 5–9 males and 5–8 females (from Bijlsma, 1997).

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With experience, the calls of chicks can be used as a guide to sex, particularly when both sexes are present in a nest, as males have higher pitched calls. It is best to listen to the calls before handling chicks, as the pitch of female calls may rise during times of stress. Moving the face or a hand towards the young before removing them from the nest may initiate a bout of calling; chicks which are identified as male and female should then be separated immediately to avoid confusion during handling. Small chicks (less than about 14 days old) are much less vocal and care should be taken with chicks likely to be older than about 25 days, as they are prone to jump from the nest.

Photographs of hobby chicks at different stages of development are shown in plates 70–72.

4. SURVEYS OUTSIDE THE BREEDING SEASON The species does not occur in Britain or Ireland during the winter.

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Honey-buzzard Pernis apivorus 1. INTRODUCTION The honey-buzzard (European honey buzzard) was traditionally regarded as breeding mainly in southern and southwest England, but breeding pairs have been found increasingly in Wales, northern England and northeast Scotland (Gibbons et al., 1993; Murray, 1993; Roberts et al., 1999; Ogilvie, 2003; Ogilvie & RBBP, 2002, 2003, 2004). Breeding birds have not been recorded in Ireland. The breeding status of the species in Britain is poorly understood but it is believed to be expanding northwards and westwards. There are records of breeding for northern England and Scotland in the 1800s (Holloway, 1996), however, and it is possible that there has been irregular breeding and/or under-recording in these areas historically. British and mainland European honey-buzzards are long distance migrants that winter in tropical Africa (Toms, 2002a); some that breed in mainland Europe pass through Britain on passage. British birds have a short breeding season between their arrival in late April or May and departure from August onwards. The slightly smaller males can usually be distinguished by their greyer heads.

Juveniles resemble females and are difficult to distinguish in the field. There is uncertainty about the age of first breeding. The majority of yearlings and some adults probably summer in Africa (Bijlsma, 1993; Forsman, 1999) although there is evidence that some juveniles return to Europe in the spring of their second calendar year (Panuccio & Agostini, 2006), and breeding at one year old has been reported (Kostrzewa, 1998).

Annual cycle Breeding Activity

Peak Period

Range

Occupation of home range

Late April to May

Territorial display

Early May to early August

Courtship

From mid-May

Duration (days)

Egg laying

Late May to early June

Mid-May to mid-July

3 to 10

Incubation

Late May to early July

Mid May to mid-August

30 to 35

Hatching

Late June to early July

Mid-June to mid-August

Young in nest

Late June to early August

Mid-June to late September

Fledging

Late July to late September

Juvenile dispersal

Late August to mid-October

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Honey-buzzard

2. HABITAT, HOME RANGE, NESTS AND BREEDING 2.1 Habitat Honey-buzzards breed where there is woodland cover. Suitable woods are located close to areas with sufficiently large populations of social wasps, their main prey (Brown, 1976). The availability of amphibians as prey may be important when the birds arrive, to help build up body fat reserves while wasp numbers are still low. In Britain, honey-buzzards occupy upland coniferous plantations, central hill country with mixed farmland and woodland, and lowland woodland, at a range of altitudes from sea level to just below 500 m ASL (Roberts et al., 1999).

The climatic differences between the upland (wetter and cooler) and lowland habitats appear to have no effect on the productivity of the species. Woods used by nesting birds are usually extensive, but scattered woodland, interspersed with farmland, heath or moorland, is also used (Batten, 2001). Woodland cover within 25 km2 of a sample of nest areas in Britain ranged from 31–81% (average 46%; Roberts et al., 1999).

2.2 Home range Birds arrive on their breeding grounds in England and Wales from late April, and in Scotland from mid-May. They generally return to the same nesting range each year (Roberts et al., 1999). Home ranges are extensive and may overlap. Studies in the Netherlands, Germany and Austria have recorded maximum sizes of 1,150 to 2,200 ha for males and 980–4,500 ha for females; larger home ranges have been recorded in Sweden (Kostrzewa, 1998). In a British population adults appeared to forage mostly within 4–6 km2 of the nest site but during the nestling period travelled as far as 8–10 km (Cramp, 1980). Studies in Scotland found that most distinct forest blocks attracted single pairs of honey-buzzard but the largest woods supported 2–3 pairs at an average spacing of 2.7 km (2.2–3.6 km, n=5; Etheridge, 2007). The size of the home range may increase during the breeding season (Kostrzewa, 1998) and also varies between years, possibly linked to the abundance of wasps and bees. The male defends only the immediate vicinity of the nest site.

2.3 Nest sites Honey-buzzards nest in coniferous, mixed and broadleaved woodland. In the Scottish Highlands, two-thirds of 49 nests were built in mixed coniferous and deciduous forest and the remainder in coniferous plantations (although there may have been some observer bias as nests in the former woodland type were less difficult to locate). In mixed woodland most nests were in beech (55%) and pedunculate oak (39%), whereas in coniferous woods Douglas fir (75%) and Scots pine (19%) were favoured (Etheridge, 2007). In upland, central and lowland England and Wales, nests were found in coniferous, mixed and broadleaf woodland, with a suggested preference for nesting in conifers (35 of 52 nests between 1989-97; Roberts et al., 1999). Honey-buzzards return from migration after the buzzards and goshawks that nest in similar habitats have started to breed and pairs of either species may occupy old honey-buzzard nests. Honey-buzzards will breed close to buzzards but avoid goshawks, which may prey on honey-buzzard chicks. In the Netherlands, honeybuzzard nests are located a minimum of 1.2 km from the nearest buzzard nests, and 2.3 km from the nearest goshawk nests (Kostrzewa, 1998). In Britain, honey-buzzards have been found breeding within a few hundred metres of buzzards. In Wales, where goshawks are common, honey-buzzard nests are generally very well hidden, mainly in dense conifer stands where it may not be possible for birds to fly through or below the canopy unless they use rides or roads. Honey-buzzards may also be more secretive in their nest visits where goshawks are common.

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2.4 Nests Nests tend to be large, particularly if they have been in use for several years (Roberts et al., 1999), with an external diameter of 65–90 cm (Cramp & Simmons, 1980). They are constructed from sticks, often of the same species as the nesting tree, and the cup lined with a pad of green leaves. Sprays of green leaves are often also built into the nest itself.

In coniferous trees, nests are often placed against the trunk or in the live crown, making them difficult to see. In broadleaf trees, nests may be placed on side limbs and may be built amongst ivy. Roberts et al. (1999) found that the height of nests in Britain varied from 8–26 m above the ground, with most nests above 15 m. Some nests are built on the remains of the old nests of other species (carrion crow, buzzard, goshawk) or on squirrel dreys (although this has never been reported from Scotland). Honey-buzzards will re-use their own nests in subsequent years and old nests may be an important focal point for returning pairs. In Scotland, some woods had several nests which were used in turn each spring, possibly by the same pair, whilst at other sites a new nest was built each year.

One nest in an oak tree was used 5 times between 1978 and 1991, and another nest in a beech tree four times over a period of 17 years (Etheridge, 2007). In Britain, outside the New Forest, the average distance pairs moved between years was 250 m, with a maximum of 750 m (Roberts et al., 1999). In the New Forest this distance was greater: an average of 2 km and a maximum of 4.5 km; this difference may be attributable to the practice, by fieldworkers, of removing nests during the winter as a precaution against egg-thieves (Roberts et al., 1999). Nest building begins in mid-May, takes place in the early morning and can be completed rapidly (one nest was built in three days, Roberts et al., 1999).

Honey-buzzards that are not breeding may build ‘summer nests’ in July and August, which may be used for breeding in the subsequent year.

2.5 Clutch size and incubation In Britain, the clutch size is usually two eggs (Roberts et al., 1999), rarely three, laid at intervals of 3–5 days. Incubation may start with the first egg, and lasts for 30–35 days per egg, and up to 37 days for a clutch of 2 eggs (Cramp & Simmons, 1980). Both sexes incubate, with the female taking the larger share and probably incubating at night. The eggs tend to be heavily marked and show considerable variation in colour and pattern; characteristic markings may be used to identify individual females (Roberts et al., 1999). Replacement clutches are rare.

2.6 Brood size and fledging In Britain the brood size is usually 1–2, rarely three, young, with broods of two most common (Roberts et al., 1999). In Scotland, broods of 2 were most frequent (n=33) broods of one less common (n=7) and broods of 3 unusual (n=2) (Etheridge, 2007). Breeding success in Britain has been recorded as 1.7–1.8 young per breeding attempt (Roberts et al., 1999); Etheridge, 2007) and appears to be higher than that recorded in central Europe (Kostrzewa, 1998). The young are brooded for 7–10 days, mainly by the female who remains close to the nest for a further seven days. The male may either bring food to the female to feed the small chicks or he may feed them directly (Kostrzewa, 1998). Young are generally fed 3–6 times each day, increasing to 7–9 and occassionally 15 times when older (Cramp & Simmons, 1980). The young feed themselves after about 18 days. They leave the nest at 35–40 days and move to nearby branches before fledging at 40–44 days. The young become independent at about 75–100 days old, shortly before they migrate.

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3. SURVEY TECHNIQUES CAUTION If nest inspection visits require tree climbing, then appropriate health and safety precautions should be taken (see Section 7.10 of Introduction).

3.1 Breeding season visit schedule The species is listed on Schedule 1 in Great Britain and the Isle of Man (see Section 7.1.1 of Introduction). Honey-buzzards are unobtrusive and due to the difficultly of locating active nests in woodland, it is recommended that four visits are made to confirm occupancy, even if no signs of occupancy are found during the earlier visits.

Visit 1 (preferably several visits)

Mid-May to mid-June

To locate displaying birds over suitable habitat

Visit 2

June

To check for occupancy and locate active nests

Visit 3

July

To check for young

Visit 4

August

To check for fledged young

3.2 Signs of occupancy 3.2.1 Locating home ranges If the presence of breeding honey-buzzards in an area is suspected, watches for displaying birds should be carried out from a good vantage point (with ‘lots of sky’) overlooking the potential nesting range, particularly during the last two weeks of May. The absence of displaying birds at this time of year does not mean a site is unoccupied, however, or that breeding will not occur. Watches should last for at least four hours (Batten, 2001), preferably from 09:00h onwards and, if possible, repeat visits should be made to confirm any observations of presence or absence. As honey-buzzards may range widely, it is important to try and identify individuals from plumage and / or moult patterns in order to get an understanding of the numbers present in a given area; for this purpose, as well as locating and following birds at a distance, and determining if they are carrying food, a good telescope will be required. Two observers may be useful at this stage as more than one bird may need to be followed. Wet weather will not produce many sightings, but birds will often appear after rain has stopped (Batten, 2001). Honey-buzzards have a distinct ‘wing-clapping’ display flight (Cramp & Simmons, 1980), which occurs from mid-May to mid-June and again from mid-July. This display may be seldom seen, however, as it occurs erratically (Roberts et al., 1999) and often at a great height; many returning pairs settle quickly into their nesting ranges without obvious display flights. Wing-clapping may also take place when a single male or pair of males ‘advertise’ a territory, or when a male intrudes into another’s territory. The most commonly observed pair display is single or mutual circling over the nest site and surrounding area (Roberts et al., 1999). Synchronised soaring or gliding does not necessarily indicate a breeding pair: it could involve the resident male and an intruding female and may occur over a wide area. Care should therefore be taken not to interpret this latter display as evidence of breeding failure or of non-breeding if it occurs later in the season (Roberts et al., 1999).

3.2.2 Locating roosts Roosts generally occur near to the nest site during the breeding season, and may be found during searches for active nests, although they cannot be definitely identified as honeybuzzard roosts unless moulted feathers or other signs are found close by.

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3.2.3 Recognition of signs The remains of depredated wasp nests (combs, paper) can provide evidence of the presence of honey-buzzards. Ground nests of wasps are, however, often unearthed by badgers and this can cause confusion. Honey-buzzards break open bee and wasp nests for the insects and leave the honey and combs largely intact, whereas nests broken open by badgers have the honey-comb destroyed and the insects largely disregarded (Brown et al., 2003). Additional signs, such as moulted feathers, provide stronger evidence.

3.2.4 Evidence of occupancy Observations of a single honey-buzzard or a pair in the same area on several occasions during the breeding season provide evidence of occupancy.

3.3 Evidence of breeding Proving that breeding has taken place can be very difficult. The following criteria for establishing breeding status were used for the first national survey of honey-buzzards in the UK (Batten, 2001; Ogilvie, 2003): Confirmed breeding 1. Nest with eggs or young.

2. Recently fledged young.

Probable/possible breeding 3. Adults entering or leaving woodland, indicative of occupied nest (May to mid-August).

4. Adult carrying food (May to Mid-August).

5. Adult carrying sticks or spray into woodland.

6. Adult giving alarm calls.

7. Wing clapping over/into woodland.

8. Adult attacking other raptors/corvids.

9. Pair observed in suitable nesting habitat.

10. Adult in same area on at least two different days, at least one week apart, in May-July.

11. Long-distance direct flight to or from woodland.

12. Low-level circling over woodland.

13. Adult perched in tree-top in woodland.

14. Species observed in suitable habitat.

15. Wing clapping display in August.

16. Tree nests of social wasps found destroyed.

It is not uncommon to get just a single sighting of a honey-buzzard during many hours of observation. There are issues, however, related to the interpretation of criterion 14 in view of the distances that birds may travel from their breeding area and the potential for confusion with sightings of unmated, perhaps immature individuals and/or migrants passing through as early as the beginning of August, when breeding pairs are still feeding young (Ogilvie, 2003).

3.3.1 Locating active nests Once the presence of a pair on its territory has been established, observations of a honeybuzzard circling up from a wood before flying off, or of a bird flying or plunging with folded wings directly into a wood, are regarded as a good indication of breeding (Roberts et al., 1999). Several observers in telephone / radio communication from different vantage points may be used to pinpoint nest locations, and in this respect learning to interpret flight

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behaviour in and out of nest sites is important. This knowledge can be gained from working with a more experienced fieldworker. Alternatively, suspected breeding woods can be searched systematically for nests. Honey-buzzards are extremely secretive during incubation and lengthy searches may be required to find the precise location. Nests are often next to rides or near to clearings, which are used to approach and leave the nest by birds flying below the canopy. Many nests in conifers are extremely well hidden in the canopy and it may be necessary to climb several trees to locate such nests. Faecal droppings are not evident but moulted feathers, wasp combs and wasp paper can be found near to the nest (such signs may also be found around old nests, however). Occupied nests generally contain a lot of greenery, which may be visible from below. The alarm call is distinct (Cramp & Simmons, 1980) and some birds are very vocal whereas others may not alarm when the fieldworker is close to the nest. The adult may not leave the nest but may ‘mantle’ over it, even if the tree is climbed.

If breeding is suspected but a nest is not found during the expected incubation period, then searching may be more productive later in the season when young would be expected in the nest, at which stage there will be more signs and activity from the parent birds.

3.3.2 Evidence of fledging Evidence of fledging is provided by the presence of large young (of at least 30 days old).

These can be counted during a nest visit or after they have left the nest and moved onto the surrounding branches. Roberts et al. (1999) report that fledglings return to the nest to be fed and in one instance a nest was found in a suspected nesting area by imitating the call of an adult bringing food.

3.4 Evidence of non-breeding The incidence of non-breeding is higher in years with cold springs and when wasp numbers are low, and alternative prey are not available. Because of the difficulty of locating active nests, non-breeding is difficult to prove for honey-buzzards. If an occupied nesting range is located but no evidence of an active nest or of fledged young is found during the appropriate visits and prolonged observations, this suggests that the birds are not breeding.

3.5 Ageing and sexing young The age of honey-buzzard young can be estimated from wing growth (Figure 8). Photographs of chicks at various stages of development are included in Roberts et al. (1999). Sexing young by measurement is difficult, as there is considerable overlap in size. After the age of 35 days (wing length >287 mm), chicks heavier than 1,000 g with an empty crop and with a tarsus width of >10 mm are likely to be females. Other young cannot be sexed accurately, except

by DNA analysis (Bijlsma, 1997).

4. SURVEYS OUTSIDE THE BREEDING SEASON The species does not occur in Britain or Ireland during the winter.

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Wing length (mm)

Chick age (days)

Figure 8. Change in wing length (with 95% confidence limits) of honey-buzzard chicks with age. Data from 2–13 nests per year over 13 years and three study areas; each point based on measurements from 5–15 young (from Bijlsma, 1997).

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Kestrel Falco tinnunculus 1. INTRODUCTION The kestrel (common kestrel) is widespread throughout Britain and Ireland (Village, 2002), although numbers have decreased (Gibbons et al., 1993; Greenwood et al., 2003; Riddle, 2007). The British population may have declined by half since the early 1970s (Clements, 2008). British and Irish kestrels are partial migrants. In upland areas, some birds, mostly males, remain in their home ranges while others migrate south into lowland areas of Britain and Ireland, with a few reaching mainland Europe (Village, 1990). Kestrels breeding in lowland areas tend to be sedentary. Northern European populations are migratory, with birds moving into southern Europe and Africa for the winter (Village, 2002). Birds from countries bordering the North and Baltic Seas have been recovered in Britain and Ireland, particularly southeast England, in winter. Adult male kestrels are easily separated from females by their distinctive spotted chestnut back and blue-grey head and tail; females are predominantly brown, with varying degrees of grey on the rump and tail and barred upper plumage. Immature males gradually moult into the adult plumage in their second and third year (Cramp & Simmons, 1980). Juveniles cannot be distinguished easily in the field from females. About 60% of kestrels breed in their first year (Wyllie & Newton, 1999), with more young birds breeding in years when their main prey, voles, are more abundant.

For further information on the biology and ecology of this species, Village (1990) provides a comprehensive account. Riddle (1992) describes fieldwork techniques in detail.

Annual cycle Breeding Activity

Peak Period

Range

Duration (days)

Occupation of home range; establishment of home ranges that are not continuously occupied

All year in lowland breeding territories; late February to late April in vacated breeding territories; August to October for winter territories

Territorial display

All year

Courtship

March to May

Egg laying

Late April to mid-May

Late March to early June

Incubation

Late April to early June Mid-April to early July

Hatching

Late May to mid-June

Early May to late July

Young in nest

Late May to early July

Early May to early August

Fledging

Early June to early August

Juvenile dispersal

July to August

Kestrel

6 to 8 26 to 34

28 to 35

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2. HABITAT, HOME RANGE, NESTS AND BREEDING 2.1 Habitat Kestrels breed in almost any habitat that holds sufficient prey (small mammals or birds) and nest sites, including urban, industrial and suburban areas, parkland, open moorland with trees and crags, upland grassland, young conifer plantations, heaths, wetlands with trees, all types of farmland, quarries, saltings and dunes. They tend to avoid large, dense forests, treeless wetlands and montane areas. In Britain and Ireland, most nests are below 480 m ASL (Village, 1998) but nests are found at higher altitudes in mainland Europe. Winter territories are in habitats similar to those used for breeding.

2.2 Home range During the breeding season, home ranges overlap, the degree of overlap increasing with distance from the nest. Home range size varies from less than 1 km2 to over 10 km2 (Village, 1990) and is related to prey abundance; when prey populations are high, kestrels have smaller home ranges (Village, 1982, 1990). Breeding densities of 12–32 territorial pairs km-2 were found in three study areas in Britain (Village, 1990). The nesting territory is vigorously defended by the male against potential predators and other kestrels (Village, 1998), although he may solicit an intruding female during courtship. Individual females vary in their response to intruders. They are generally aggressive early in the breeding cycle; aggression declines prior to laying and during incubation and then increases again after the young hatch (Wiklund & Village, 1992).

Females are more aggressive if they have a large brood. The extent of the area around the nest site that is defended is highly variable. Kestrel nest sites are normally well dispersed but they may breed in close proximity if there are few suitable nest sites but abundant prey in a given area.

In extreme cases, small colonies will form (Village, 1990; Bustamante, 1994), but kestrels will still establish a nesting territory and defend it even within these groups. Village (1990) reports distances between nests of 40 m to over 5 km; in a farmland study area less than 7% of pairs nested within 200 m of their nearest neighbour, whereas nearly 40% of pairs in a grassland area nested within 200 m. More instances of nests in close proximity are described by Cramp & Simmons (1980). Winter home ranges are defended and exclusive (Village, 1990). They can be held either by local resident birds and/or by immigrants wintering in the area. In some areas where pairs are sedentary, the male and female may each hold and defend a territory (Village, 1990; Shrubb, 1993a).

2.3 Nest sites Kestrels are catholic in their choice of nest site. They can be tolerant of human activity and nest in close proximity to people. Kestrel nests are found on rock ledges on crags or in quarries, in tree holes and in nest boxes (Shrubb, 1993b). They may also use the old stick nests of other birds, mainly those of carrion and hooded crow, but the nests of buzzard, magpie and sparrowhawk are used occasionally and the use of nests of golden eagle, raven, jay, rook, woodpigeon and grey heron has also been recorded. Nests may also be located on a wide variety of buildings and other human constructions that provide sheltered sites, including churches, barns, straw stacks, bridges, cranes, electricity pylons, disused chimneys, limekilns and window ledges in high rise flats (Village, 1990; Riddle, 1992). In addition, nests have been found on the ground in long heather and even in rabbit burrows (Village, 1990), particularly on Orkney (Balfour, 1955).

Kestrels will readily use nest boxes (Riddle, 1992; Valkama & Korpimäki, 1999; Fargallo et al., 2001), if they are placed near grassy areas with good numbers of voles. Ideally two boxes should be erected close together, as one box may be used by owls.

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2.4 Nests Kestrels do not build a nest but will scrape a depression in the nest substrate, for example in hole nests or in the collapsed nest cup of an old crow nest. The depression may be lined with small pieces of vegetation nibbled by the incubating female from the immediate vicinity of the nest. Where the lining of an old nest remains intact, or there is little lining, kestrels will lay their eggs in the existing cup.

2.5 Clutch size and incubation Most British and Irish kestrels complete laying by mid-May, and in years of favourable weather and prey abundance, many will lay in April or even March. Eggs are normally laid at 2-day intervals and clutch size is related to laying date. Early clutches are larger (5–6 eggs), than later ones (3–4 eggs; Cavé, 1968; Village, 1990, 1986, 1989; Riddle, 1987) and clutches of 7–8 eggs can be laid in good vole years (Riddle & Sheppard, 1999). The BTO Nest Record Scheme gives an average clutch size of 4.7 (n=1,873). In areas where the vole population is cyclic, kestrels lay larger clutches in good vole years than in poor ones (Cavé, 1968; Village, 1986; Shaw & Riddle, 2003). Kestrels sometimes relay if they fail early in the breeding cycle. Incubation normally begins after the third egg is laid, although it may start earlier (Beukeboom et al., 1988; Village, 1990) and lasts 26–34 days (Village, 1990). The male delivers food to the female during courtship and incubation (5–13 items per day). Incubation is carried out almost entirely by the female who leaves the nest only briefly for feeds (Village, 1990), during which time the male will incubate. Desertion of clutches occurs more frequently in wet weather (Village, 1998).

2.6 Brood size and fledging Hatching can be synchronous or asynchronous, sometimes taking 4–5 days. Young kestrels are brooded by the female until they are about 10 days old (Village, 1990). The male provides food for the female who tears up prey to feed the chicks. After she has stopped brooding, the female may also hunt to provide food for the young and continues to feed the young. An average of 13 food items are delivered to broods per day, although this number may be halved in poor weather; and delivery rates can reach 19–22 items per day (Village, 1990). The feeding rate generally decreases in the evening. Chicks fledge after 28–35 days and are fed by their parents for a further 2–3 weeks, after which they begin to disperse from nesting territories. The majority of breeding failures take place at the prelaying or clutch stage (Riddle, 1993) and success rates are generally high once the eggs have hatched, although individual chicks may die (Village, 1990).

3. SURVEY TECHNIQUES CAUTION Kestrels should not be disturbed in their nesting territories while pairs are still displaying as this may cause the birds to move location. Care should also be taken while birds are likely to be laying. Nesting areas should be observed from a discreet distance during these times. Avoid visiting the nest after the chicks are three weeks old because they are prone to fledge prematurely from this age. If nest inspection visits require climbing, then appropriate health and safety precautions should be taken (see Section 7.10 of Introduction).

3.1 Breeding season visit schedule The species is listed on Schedule 1 in Northern Ireland and the Isle of Man. To establish occupancy and the presence of a breeding pair, it is recommended that all four visits are made (as detailed below). However, if time is limited and a home range appears to be unoccupied on the basis of the first two visits, then further visits to that home range can be omitted. Kestrels are most easily located when displaying early in the breeding season and around the time of fledging when they are active and noisy. Care must be exercised to avoid disturbing pairs while Kestrel

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they are displaying and laying; if there is any uncertainty over the stage in the breeding cycle, Visit 2 should be delayed. Broods that have fledged early may start to disperse by late July.

Visit 1

Late March to May

To check for occupancy

Visit 2

May

To locate active nests

Visit 3

June

To check for young

Visit 4

July to August

To check for fledged young

3.2 Signs of occupancy 3.2.1 Locating home ranges Kestrels that are intending to breed begin to establish nesting territories from March to late April (Village, 1986). Fieldworkers should search suitable habitat in study areas for occupied nesting territories from late March onwards. Kestrels will alarm if disturbed or if responding to other raptors or corvids entering the nest area. They may also be seen displaying over the nesting territory. Display flights involve both the male and female circling and chasing, often high into the sky; the male repeatedly dives at the female in mock-attacks and the female rolls sideways at the last moment to avoid collision (Cramp & Simmons, 1980). If the female perches, the male often continues to mock-attack her. Pairs may also ‘play’ with objects (e.g. play with sheets of cardboard in the air has been noted; Cramp & Simmons, 1980). A shivering or ‘winnowing’ flight is sometimes used when approaching the nest site and is a good indication of territorial behaviour. It is particularly frequent during the period immediately before laying and is also used for territorial defence (e.g. if a human approaches an active nest).

No attempt should be made to locate the nest site itself at this early stage in the breeding cycle, as disturbance may cause the birds to move away. Many nesting ranges are traditional and are occupied in most years, while others are only occupied in years when prey is abundant (Riddle, 1992).

3.2.2 Locating roosts Kestrel roosts are found on crags, buildings and in trees. Active roosts will have fresh faecal droppings and down, with fresh pellets on the ground below the roost. The white droppings often make roosts conspicuous. Moulted feathers will also be found and these are the key to linking the other signs to kestrels rather than to other species. Roosts can be found by searching the nesting territory or home range systematically for suitable sites but this should be carried out only after incubation is well established.

3.2.3 Recognition of signs Kestrel pellets are usually very light, grey and often laterally compressed and tapered at one end (length 20–40 mm; width 10–25 mm; Brown et al., 2003). They consist mainly of fur/ feathers and frequently contain the bones of small mammals (the main prey). The remains of insects and birds may also be present. Kestrel pellets can be variable and difficult to separate from those of other raptors, however, and identification should be confirmed by the presence of other signs. Kills of small mammals are generally consumed whole and small birds may be plucked some distance from the nesting site.

3.2.4 Evidence of occupancy The criteria for probable breeding (See 3.3 below) can be used as evidence of occupancy.

Occupancy should preferably be based on observations of birds on at least two occasions

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during the breeding season. Not all kestrels occupying winter territories remain in an area to breed, so multiple observations suggesting occupancy in winter should not be taken later as evidence for breeding occupancy.

3.3 Evidence for breeding Gilbert et al. (1998) define confirmed, probable and possible breeding as follows: CONFIRMED BREEDING

• A nest containing eggs or young is found • An adult is seen carrying food for the young • A used nest or eggshells are found (occupied or laid within the survey period) • Recently fledged young are found

PROBABLE BREEDING

• A permanent territory is presumed through observations of territorial behaviour on at least two different days separated by a week • Agitated behaviour or anxiety calls are given by the adults • Courtship and display behaviour are witnessed • A pair of kestrels is seen in suitable nestling habitat in the breeding season

POSSIBLE BREEDING

• A kestrel is observed in April and/or May in possible nesting habitat

Fieldworkers carrying out intensive studies may wish to confine the definition of breeding pairs to those where breeding is confirmed.

3.3.1 Locating active nests Once occupied nesting territories have been located, the areas should be searched systematically for nests. An active nest may have pellets, or occasionally moulted feathers, below it, and down on the edge. Incubating kestrels may not flush easily, especially during late incubation, and if the presence of a sitting bird cannot be detected through watches from a distance it may be necessary to visit the nest to check the contents (taking appropriate care if climbing is involved, Section 7.10 of Introduction). Any nesting territories where the birds are known to have failed early in the season, or that were apparently unoccupied during Visit 2, should be checked late in the season (June/July) in order to detect any relays or late breeding attempts.

Call playbacks may also be useful in locating kestrel nest sites. Salvati et al. (2000) used this technique to locate occupied nests in holes in Roman ruins and buildings in central Rome and suggested playback may be integrated with other techniques in locating breeding pairs. It may be particularly useful in separating neighboring sites in dense populations or in surveying large areas rapidly. Disturbance during such surveys should be minimised by using playback only in the early part of the breeding cycle (during incubation and brooding). Each site should only be surveyed twice. Playbacks should not be used to locate fledged young as they do not respond and may be disturbed if adults respond to calls.

3.3.2 Evidence for fledging Counts of large young in the nest can be used as an estimate of fledged brood size because their survival rates are high. Fledged young will remain in the vicinity of the nest for 7–14 days. They can be located by their calls and counted at this stage. For large broods, it can be difficult to keep track of individual young as they move around (Riddle, 1992) and a minimum figure for the number of fledged young should be recorded.

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3.4 Evidence for non-breeding Not all kestrel pairs occupying home ranges lay eggs each year. Sedentary pairs are more likely to miss breeding than partially migratory pairs or migratory birds (Village, 1990, 1998).

Non-breeding can be more common after cold winters (Village, 1998) and may be more frequent in areas where vole numbers are low (Village, 1990). If there is no evidence of an active nest or fledged young, despite several visits to a previously occupied nesting territory at appropriate times, this provides good evidence of non-breeding. The members of failed pairs often remain within the home range but territorial and courtship behaviour declines early in the breeding season. Pairs that are disturbed prior to egg laying may move elsewhere to breed and appropriate visits should be made later in the season to check for relays.

3.5 Ageing and sexing young

Wing length (mm)

Chicks can be aged approximately from their wing length (Dijkstra et al., 1990; Bijlsma, 1997; Figure 30). Wing length cannot be used to sex kestrels, however, as the measurements of males and females overlap considerably. Mass (Figure 31) can be used in conjunction with the colour and pattern of the upper tail coverts (Figure 32) to sex many young. From the age of 20 days (wing lengths >138 mm), females have brown upper tail coverts with broad, dark-brown bands. Males have greyish tail coverts with smaller bands. Some chicks cannot be sexed by these means, as their upper tail coverts do not follow this pattern but are browngrey. Mass (Figure 31) can also be used for approximate ageing, if the sex of chicks has been established using the tail coverts.

Age (days)

Figure 30. Increase in mean wing length (with 95% confidence limits) of kestrel chicks with age. Data from 140 nests per year over two years and two study areas; each point based on measurements from 5–59 males and 5–46 females (from Bijlsma, 1997).

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Mass (g)

Age (days)

Figure 31. Increase in mean body mass (with 95% confidence limits) of kestrel chicks with age. Data from 140 nests per year over two years and two study areas; each point based on measurements from 5–62 males and 5–47 females (from Bijlsma, 1997).

Figure 32. Sex differences in tail coverts of kestrel chicks (from Bijlsma, 1997).

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4. SURVEYS OUTSIDE THE BREEDING SEASON A winter territory is occupied if a bird is seen in a given area on several occasions. Winter territories can be delineated by mapping observations of kestrels during regular visits to the study area from the end of October until February (when breeding birds will begin returning).

A note of the age and sex of each bird observed should be made and behaviour recorded.

Such work can provide an estimate of the winter population size in a given area.

An index of wintering kestrel abundance can be obtained by carrying out counts of birds observed from defined survey routes (preferably randomly selected or at least representative of habitats in the area to be covered), either on foot or by car. Roadside counts are used widely in North America to measure the abundance and sex ratios of wintering American kestrels (Village, 1990). In his own studies in lowland farmland, Village set an 80 km route in each area and drove it three times a month from October to April to obtain counts of kestrels seen. Thus, observers should cover a fixed route in a set time, and record observations of kestrels and the approximate distance of each bird from the ‘transect’ line (weather conditions should also be noted). The data collected could be used as an index of change in numbers between years. In Britain and Ireland, such survey work would be best undertaken between mid-November and late February, to exclude irregular influxes of immigrants during passage periods, but surveys should be carried out at approximately the same time each year, as counts will decline during the winter due to mortality and emigration (Village, 1990).

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Little Owl Athene noctua 1. INTRODUCTION Little owls were introduced into several areas of England in the middle of the 19th century, and are now found breeding thoughout lowland England, in some areas of Wales and in southern Scotland (Gibbons et al., 1993; Gordon, 2007). Only occasional vagrants have been reported in Ireland (Hutchison, 1989) and they are absent from the Isle of Man. Birds breeding in Great Britain and mainland Europe are sedentary, seldom dispersing more than a few kilometres from their natal site (Glue, 2002a). Little owls cannot be sexed in the field.

Before their autumn moult, juveniles can be separated from adults by their paler, greyer and more uniformly patterned plumage (Cramp, 1985). Little owls can breed when one year old.

Further information on the biology and ecology of little owls can be found in Van Nieuwenhuyse et al. (2008) and Leigh (in press).

Annual cycle Breeding Activity

Peak Period

Range

Occupation of home range

All year

Territorial display

All year (but less display in winter)

Courtship

March to April

Duration (days)

Egg laying

Mid-April to mid-May

Mid-March to late June

2 to 5

Incubation

Mid-April to early June

Mid-March to early July

28 to 33

Hatching

Late May to early June

Mid-April to early July

Young in nest

Late May to early July

Mid-April to early August

19 to 28

Fledging

Late May to early August

At 28 to 32 days old

Juvenile dispersal

Late June to early September

2 HABITAT, HOME RANGE, NESTS AND BREEDING 2.1 Habitat In England and Wales, little owls breed in a wide range of habitats, generally below 122 m ASL but up to 320 m ASL (Glue & Scott, 1980). They mainly occupy agricultural areas but are

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also found in woodland, parks, gardens, cemeteries and quarries and occasionally on heaths, moors, wetlands and coastal areas. The presence of fence posts is important as these provide hunting perches (Loske, 1986).

2.2 Home range Male little owls defend their home range throughout the year (Finck, 1990), although they are less aggressive in the winter. Home range size varies according to the stage in the breeding cycle (Génot & Nieuwenhuyse, 2002). In southern England home ranges averaged 35 ha in water meadows and 38 ha in mixed farmland (Glue & Scott, 1980); in northeast France, birds actively foraged over 27 to 44% of their home range (Génot & Wilhelm, 1993). Various studies have reported densities of 0.02–41.67 territories per km² (Génot & Nieuwenhuyse, 2002). Nests may occur as close as 240 m apart, and little owls have been recorded breeding 2 m from a barn owl nest (Glue & Scott, 1980). The availability of nests sites appears to be the limiting factor in areas where food is abundant (Exo, 1992).

2.3 Nest sites In England and Wales, little owls breed in holes in deciduous trees (92% of nests examined in detail), rabbit burrows, or cracks in rock faces (Glue & Scott, 1980). They may also use manmade structures such as farm buildings, stone walls and haystacks. In trees, they nest mainly in clefts and hollow branches but they may also use the tree bole or roots, vertical holes in trunks, pollards, fallen branches or trunks, and magpie nests (<1% of nests). Nests are an average of 3 m (range 0.3-12.2 m; Glue & Scott, 1980) above the ground. The commonest trees used for nesting are oak, ash and fruit trees. Nest holes may be used for up to 10 years but individual females may or may not use the same nest hole from year to year (Génot & Nieuwenhuyse, 2002). Little owls will use nest boxes (Génot & Nieuwenhuyse, 2002) although the take up appears to vary between areas, perhaps related to the availability of natural sites (Barn Owl Trust, 2000). It may take several years for birds to take up residence, often using the box for roosting prior to any use for breeding.

2.4 Nests No nest is constructed, the clutch is laid on the floor of the cavity in use, although the nest chamber may be scraped.

2.5 Clutch size and incubation Clutch size varies from 1–7 eggs (Génot & Nieuwenhuyse, 2002) and has been shown to decrease with population density (Bultot et al., 2001). The BTO Nest Record Scheme gives an average clutch size of 3.5 (n=592), although Leigh (2001) found an average of 2.5 in northwest England (between 1993 and 2000). Eggs are normally laid on consecutive days but intervals of 2–4 days have been recorded in captive birds (Génot & Nieuwenhuyse, 2002) and the laying period can last 10–12 days for a clutch of 6–7 eggs. Weather and prey availability may affect both the duration of the laying period and the final clutch size.

Eggs are laid from mid-March to late June, with most birds laying between mid-April and the first ten days of May. Incubation may begin with the first or second egg or be delayed until the clutch is completed. It is carried out by the female (perhaps with assistance from the male; Mikkola, 1983) and usually lasts 28–33 days (Glue & Scott, 1980), although it may be longer or shorter (18 days (in captivity) to 35 days; Génot & Nieuwenhuyse, 2002). During this time the birds are secretive and the male feeds the female. Lost clutches are occasionally replaced and rarely, a second brood may be attempted after the first has fledged (Mikkola, 1983).

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2.6 Brood size and fledging Hatching may be asynchronus or nearly synchronus. If food is short, then not all young will survive and cannibalism may occur (Mikkola, 1983). For the first 10–15 days the male provides all the food while the female broods the chicks. After this time, the female also hunts. The chicks are normally fed between dusk and midnight, and again from 02:00h until dawn (Glue & Scott, 1980). The young first emerge from the nest at 19–28 days of age when they are very active but often hide in the branches or vegetation surrounding the nest (Glue & Scott, 1980; Mitchell, 1994). They fledge after 28–32 days (Nieuwenhuyse et al., 2008), exceptionally longer, and are dependent on their parents for a further month after fledging (Génot & Nieuwenhuyse, 2002). Breeding success depends on the condition of the female before laying (Gassmann & Baümer, 1993). High levels of rain in March, promoting a higher availability of earthworm prey, are associated with the production of larger broods (Gassmann et al., 1994).

3. SURVEY TECHNIQUES CAUTION Goggles and face protection should be worn if looking inside a confined space for a nest site, particularly if more aggressive tawny owls may be present. Appropriate health and safety precautions should be taken if working at night and if nest inspection visits involve climbing (see Section 7.10 of Introduction).

3.1 Breeding season visit schedule Visit 1 is required to establish home range use and to map territories, Visits 2 and 3 to confirm breeding, and Visit 4 to record breeding success. It is preferable to make all four visits even if occupation is not confirmed after the early visits. Little owls are most active around dawn and at dusk but frequently perch in the open during the day (Mikkola, 1983).

Visit 1 (several preferable)

March to April

To check for occupancy

Visit 2

Mid-April to May

To locate active nests

Visit 3

June

To check for young

Visit 4

July to August

To check for fledged young

3.2 Signs of occupancy 3.2.1 Locating home ranges Occupied home ranges can be located by listening for the males calling in March and April.

The positions of calling birds should be noted on a map of the study area. If a series of visits is made at this time, it is possible to delineate home ranges by mapping the locations from which calls are heard. The amount of calling is density dependent, in areas with low density populations little owls call less than in areas with high density populations. It is very difficult to determine the sex from the call alone, although female calls have been described as more high-pitched and nasal. During pre-copulation behaviour the female is said to give a begging display accompanied with snoring sounds and during copulation the male is said to utter a guttural chugging sound.

Little owls can also be surveyed by broadcasting the male territorial call. Depending on the weather, calls of responding male owls can be heard up to 600 m away (Nieuwenhuyse et al., 2008). Surveys should be carried out on still nights with a maximum of 500 m between broadcast points. The positions of calling birds should be noted on a map of the study area.

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Such surveys, which may be preferable to cold searching if large areas are to be covered, are best carried out during the owls’ courtship period in March and April. The most effective time for survey is just after dusk and before dawn, to coincide with activity peaks of little owls. Rain, wind (> 3 on the Beaufort scale) and low temperatures inhibit calling, although temperature has a greater effect at dusk than at dawn. Little owls at their normal perches also respond more effectively to strange calls rather than those of neighbouring birds (Hardouin et al., 2006).

Visual displays have not been highlighted as of use in surveying this species.

3.2.2 Locating roosts The presence of an active roost confirms occupation, as little owls remain within their home ranges throughout the year. Little owls will use cavities as roost sites, although they often roost out in the open on a post, tree, telegraph wire or isolated building (Mikkola, 1983; Mitchell, 1994). Some roosts can be located by searching suitable habitat. All holes in trees, rabbit burrows and cracks in rock faces or buildings should be checked. Active roosts will have fresh pellets, down and moulted feathers.

3.2.3 Recognition of signs Little owl pellets are generally fragile and small (15–40 mm by 10–20 mm; Mikkola, 1983; Brown et al., 2003). The exact colour and form depends on diet but they often contain insect fragments and may include plant material. Both ends are usually rounded but they can be tapered at one end and resemble kestrel pellets (Mikkola, 1983; Cramp, 1985; Brown et al., 2003). In England, pellet contents change from mostly small mammal remains in the winter and early breeding period to almost all invertebrate remains in the fledging period.

3.2.4 Evidence of occupancy A home range is occupied if a calling male is recorded on more than one occasion or an active roost is found.

3.3 Evidence of breeding 3.3.1 Locating active nests Once a home range has been located, it should be systematically searched for an active nest.

Faecal droppings (coffee-cream in colour) and pellets will occur below perches close to active nests. Down may also be seen at the entrance to a nest hole. Later in the breeding cycle, active nests can also be located from the characteristic food begging calls of the young, which are made from the age of 12–14 days onwards and become more pronounced as they grow older (Glue & Scott, 1980). Searches for potential nest sites can also be made in winter, prior to the spring surveys.

Some little owls will use one or more cavities near their nest site as ‘larders’ in which they prepare, and possibly store, prey items before feeding them to their chicks (Hibbert-Ware, 1938). Therefore, owls repeatedly carrying food into a cavity may not be visiting a nest, and this behaviour alone cannot be taken as evidence of breeding.

A mirror and light source attached to a long/extendable handle or pole can be a useful tool for checking cavities.

3.3.2 Evidence for fledging Fledged young can be located by listening for their food begging calls between dusk and midnight in late May and June. Counts of such young may not be accurate, however, as they may move between calls. The best estimate of the number fledged from a nest is obtained by Little owl

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counting well-feathered young in or around the nest before they disperse. This may require several visits because not all of the young may be visible or emerge on a given visit and some may hide in the foliage surrounding the nest site. The fieldworker should record the approximate age of the young at the time when brood size is recorded.

3.4 Evidence for non-breeding If no active nest can be found in an occupied home range after careful searching, and no young are located during the appropriate visits in June and July/August, this provides evidence for non-breeding.

3.5 Ageing and sexing young No measurement data for ageing and sexing have been found for little owls in Britain and Ireland. As a guide to ageing young approximately: • the short white down, with which the young hatch, changes to a greyer colour by the age of one week; • the eyes open at around eight days of age; • the down becomes sparser and the short facial feathers begin to develop after two weeks of age; and • the head, breast, nape and flanks are all well feathered by the age of three weeks and the young become mobile in the nest chamber.

Photographs of little owl nestlings at various stages of development are included in Plates 73 to 78.

4. SURVEYS OUTSIDE THE BREEDING SEASON Calling males can be located at any time of the year but they call less often in winter. Visits should be made at dusk on calm, mild nights when little owls can be located by listening or by broadcasting calls (Section 3.2.1). The location of calling birds should be mapped. Multiple visits will be required to delineate each home range accurately. These can then be searched during daylight to locate roosts and/or birds.

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Marsh Harrier Circus aeruginosus 1. INTRODUCTION The marsh harrier (western marsh harrier) is increasing as a breeding species in Great Britain (Gibbons et al., 1993; Underhill-Day, 1998; Holling & RBBP, 2008) with breeding recorded as far north as Orkney (Bell, 2007). A pair of marsh harriers that fledged two young in Northern Ireland in 2009 represents the first recorded breeding by this species since about 1840. In the Republic of Ireland, breeding has not been confirmed since 1917, although regular sightings of marsh harriers in suitable habitat suggest that the species is likely to recolonise in the near future. British and Irish marsh harriers are partial migrants (Underhill-Day, 2002a). A few individual birds, mostly females, winter in the south and east of England, south Wales and southeast Ireland. Ringing recoveries of British birds show that they migrate into Iberia and northwest Africa. Migratory birds from northern Europe and Scandinavia may cross the Sahara to winter in central and southern Africa as far south as the Transvaal (Underhill-Day, 2002a).

During migration, passage birds can be seen in areas where they do not breed or winter. Adult male marsh harriers have a distinctive plumage, with black wingtips, a grey wing panel and tail, and a dark brown back (Clarke, 1995). The adult female’s plumage is more variable; the body and wings are brown, and the crown and chin are yellow or pale. Juveniles and immatures resemble females (though they may lack pale markings on the head) and begin to moult into adult plumage in their second calendar year. Juvenile males can be separated from females by their smaller size. Marsh harriers do not breed until 2–3 years old (Clarke, 1995).

For further information on the biology and ecology of this species, Clarke (1995) provides a comprehensive account.

Annual Cycle Breeding Activity

Peak Period

Occupation of home range

Range

Duration (days)

Late January (southern England)/ late March (Scotland) to late May

Courtship

Late March to early May

Mid-March to June

Egg laying

Late April to mid-May

Early April to early June

2 to 14

Incubation

Late May to mid-June

Early April to July

31 to 38

Hatching

Late May to late June

Mid-May to July

Young in nest

Late May to late July

Mid-May to late August

Approximately 28

Fledging

Late June to late July

Late June to late August

At 35 to 40 days old

August to September

At 60 to 73 days old

Juvenile dispersal

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2. HABITAT, HOME RANGE, NESTS AND BREEDING 2.1 Habitat

Marsh harriers use a variety of wet and dry habitats. They nest in beds of common reed, crops (oil-seed rape and winter cereals) and rough grass (Underhill-Day, 1998). In both summer and winter, they hunt over dry arable farmland, reed beds, flooded grassland and salt-marshes (Underhill-Day, 2002a).

2.2 Home range

Marsh harriers defend only the immediate area around the nest, the nesting territory, which has a radius of about 100–300 m. They may breed as single pairs or in loose colonies (Clarke, 1995). Male marsh harriers are often polygamous (25–30% of nests), usually bigamous, but occasionally trigamous (Underhill-Day, 1998; Clarke, 1995). In Scotland, nesting territories are occupied from late March to early May, when the birds return from their wintering grounds.

In southeast England, some marsh harriers, mostly females and immatures, over-winter; these females may move into nesting territories as early as January (Cramp & Simmons, 1980). Most territorial defence is by the male (Fernandez & Azkona, 1994). In East Anglia, the home range of males varied with the stage of the breeding cycle from 569 ha during courtship to 1,407 ha during the post-fledging period (Underhill-Day, 1990). Males may hunt up to 7 km from their nesting territory. Females have smaller home ranges, but these increase in size when they start to feed young (from 100–1,300 ha).

2.3 Nest sites

Nests are normally found in freshwater or brackish reed beds, in other wetlands with tall emergent vegetation and few or no trees, or in tall crops adjacent to a wetland. Of 542 UK nests for which habitat was recorded between 1983-90 and in 1995, most (86%) were in reed beds, with smaller numbers in arable crops (13%), and the remainder in rough grassland. In 1995 the majority of reed bed nests were in wet areas (65%), with 18% in tidal beds and 12% in dry reed beds (habitat was unspecified for the remaining 5%). Also in 1995, most (87%) nests were within 10 km of the sea or a large estuary (Underhill-Day, 1998). The reed beds or wetlands can be extensive, or small (less than 1 ha in size). Nests within loose colonies are often only 50–300 m apart (Cramp & Simmons, 1980).

2.4 Nests

These are located in thick, marshy vegetation or crops. Each is a substantial pile of reeds, grasses or twigs. The average diameter is 50–80 cm, with a cup of 15–20 cm in diameter and an average height of 25–30 cm (Cramp & Simmons, 1980). Nests may be on the ground or over water, in which case they are normally 50–70 cm above water level. The male starts to build ‘cock’ nests and platforms after occupying a nesting territory. He will display vigorously until he attracts a female. If she adopts his nest site, the pair will build the nest together. Occasionally, the female will reject the site chosen by the male and move to a new one. The nest is usually built in 7–10 days (completed more quickly if it is built on the remains of an old nest), with material gathered from up to 300 m away (Cramp & Simmons, 1980). The nest becomes flattened during incubation and the nestling period and must be rebuilt constantly to maintain its structure in unstable wetland vegetation. Both sexes continue to bring fresh material to the nest, with the male contributing during incubation and the early part of the nestling period, and the female continuing to bring nest material until the young fledge (Fernandez, 1992).

2.5 Clutch size and incubation

Clutch size varies from 2–8 (Underhill-Day, 1984), with eggs laid at intervals of 2–3 days. Larger clutches are more successful than smaller ones in fledging at least one young. Incubation lasts Marsh harrier

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31–38 days per egg, usually starts with the first egg, and is carried out almost solely by the female (at least 90%). She is fed by the male, who may cover the eggs in her absence (Cramp & Simmons, 1980; Clarke, 1995).

2.6 Brood size and fledging Hatching is asynchronous and chicks are brooded by the female for the first 4–10 days (Cramp & Simmons, 1980). During this time, all the food is provided by the male and passed to the female, who feeds the young. As the young develop, the female may also hunt and may deliver as much food as the male. Food delivery rates generally increase from around 3–4 items per day when the young are 10 days old to 4–5 items per day at the age of 30 days (although 11–12 items per day can be delivered; Cramp & Simmons, 1980; Clarke, 1995).

The young leave the nest and move into the surrounding vegetation from 28 days, and fledge at 35–40 days (Clarke, 1995); they use nearby bushes or posts as perches. The food delivery rate to the young by some males declines after fledging, but females continue to bring food to the young until they are over 60 days old. By 73 days, the young have started to disperse from the breeding home range.

3. SURVEY TECHNIQUES CAUTION Nest visits during incubation or when there are small young can cause desertion and should be avoided unless it is essential to monitor the nest contents. Otherwise any visits should be delayed until the young are large enough to ring or wing tag (3–4 weeks old; guidance is provided in Section 3.3.1 below on estimating hatch date from observations of parental behaviour), and should not be made in poor weather. Great care should be taken to restrict damage to the surrounding vegetation, as tracks through a reed bed or other tall vegetation can lead predators or other people to the nest. Nests in reedbeds should be approached from the water side. After a visit, the nest should be watched from a suitably distant vantage point to ensure that the female returns to the nest and/or the parents continue to behave normally. If this does not happen within a reasonable time, the observer should leave the area completely and return at a later date. If desertion is suspected, the pair/nest site should be treated with extreme caution in future years. Fieldworkers entering reed beds should wear wellington boots or waders depending on water depth and consider wearing goggles to protect their eyes from reed stems. To minimise the risk of disturbance it is recommended that nesting areas are viewed from a distance of 300-500 m, although the reedbed nesting habitat may provide a degree of protection in terms of reducing the visible detection of disturbance by marsh harriers (Ruddock & Whitfield, 2007; Whitfield et al., 2008b).

3.1 Breeding season visit schedule The species is listed on Schedule 1 in Great Britain, Northern Ireland and the Isle of Man (see Introduction Section 7.1.1). To establish occupancy and the presence of breeding pairs, at least three visits are recommended (as detailed below). Visit 2 spans a broad period of time because of the wide range of laying dates in this species; multiple watches during this time will increase the chances of detecting active nests (see Gilbert et al., 1998).

Visit 1

Mid-March to late April

To check for occupancy. It is important that birds are located before incubation starts

Visit 2 (several visits can be made)

Late April to mid-July

To locate active nests

Visit 3

Mid-July to mid-August

To check for fledged young

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3.2 Signs of occupancy 3.2.1 Locating home ranges If the presence of marsh harriers is suspected, watches should be carried out in suitable habitats from mid-March to late April in order to locate nesting territories. Watches should be made from a vantage point that gives a clear view of the area and should start at dawn, as the male will generally feed the female shortly afterwards via a food pass (which may take place in the air or on the ground). If the prey is large, he may not feed the female again for several hours. In central Scotland, activity at the nesting area generally decreases around midday before increasing again in the early evening, depending on the number of chicks being fed.

In England, analysis of prey delivery patterns for males and females during the courtship to nestling periods showed no variation with time of day (Underhill-Day, 1989).

Male marsh harriers perform high circling displays above the nesting territory or up to 1 km away on fine days, soaring high with quick, jerky wing beats and calling irregularly (Cramp & Simmons, 1980). Pairs also engage in flight play, in which the male mock-attacks the female, who may perform flight-rolls or present talons. High circling by males may include a sky-dance or song-flight display but the form of this varies with wind conditions, whether or not food is being carried, and the proximity of other territorial males. These displays can be spectacular, including somersaults, rolls, twisting, and falling as though shot. A far-reaching call is often uttered each time a dive is completed, and the wings make a rushing sound during the descent. Two or more males may sky-dance at once, and, in areas of high population density, these may be joined by further adults or immatures.

It is recommended that records of dislaying marsh harriers and/or food passes over extensive areas of reed bed or other uniform vegetation should be supplemented by sketch maps or digital photographs showing salient features of the landscape beyond the nesting territory (trees, fence posts, dykes, buildings). This, along with a record of the observation points, should allow the fieldworker to relocate the display area quickly. Compass bearings should also be used to fix positions by triangulation whenever possible.

3.2.2 Locating roosts Searches for roosting birds during the breeding season are not recommended because of the disturbance that they cause.

3.2.3 Recognition of signs Searches for pellets or prey remains in nesting areas are also not recommended until after fledging, because of the potential for disturbance. Care must be exercised in identifying pellets, as they are similar in appearance to those of other raptors. They will be useful only when there is additional evidence (moulted feathers, recently used nest) to allow their specific identification.

3.2.4 Evidence of occupancy A nesting territory is occupied if a single bird or pair of marsh harriers is observed displaying, courtship feeding or nest building.

3.3 Evidence of breeding In estimating the numbers of breeding marsh harriers in the UK, 1983-95, Underhill-Day (1998) recorded a breeding attempt when observations were made of food being delivered to a nest site, eggs were known to have been laid, young were fledged, or where breeding Marsh harrier

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had taken place in the opinion of an experienced observer. Evidence of nest building or courtship feeding alone were not considered sufficient to indicate a breeding attempt. It was acknowledged that this recording system may have underestimated breeding numbers by missing some breeding attempts that failed at the egg stage. Gilbert et al. (1998) define evidence for a probable nest site as follows: a female carrying nest material stays at a potential nest site for an hour or more; and / or a female stays at the nest site for more than four hours and receives a prey delivery from the male during this time.

As marsh harriers can breed polygynously, breeding numbers are often reported in terms of the number of breeding males, breeding females, or known nests in an area (e.g. UnderhillDay, 1998; Ogilvie & RBBP, 2004).

3.3.1â&#x20AC;&#x201A; Locating active nests Once the presence of marsh harriers in an area has been confirmed, follow-up visit(s) should be made to confirm breeding. Watches should last at least four hours, preferably in the early morning or evening; nest locations may be revealed through observations of males and females nest building. Observers should also watch for males carrying prey to females, which occurs during nest construction and laying as well as during incubation and brooding.

The female will leave the nest to receive prey from the male by a food pass, which, initially, normally occurs on the ground. During the pre-laying and laying periods a food pass may be followed by copulation, either at the point of food transfer, or the male may follow the female to a favoured feeding perch. The female can be watched back to the nest once she has eaten.

After a food pass, the male may go to a favoured perch to preen.

After the first (alpha) female has laid, another female may gain access to the nesting territory and be courted and fed by the male. Fieldworkers should continue to watch the maleâ&#x20AC;&#x2122;s behaviour after locating a nest, to check whether he is polygynous.

When a nest location has been identified, a sketch map should be drawn showing its position in relation to landscape features, either close to the nest (shrubs, posts, gaps in the reed bed) or beyond (distinctive trees, houses) in a direct line through the nest from the vantage point. To augment field notes, a digital photograph can be taken of the nest location and surrounding area, and photo imaging software used to transfer any features or lines which can be used to relocate the nest on subsequent visits. When noting such features early in the year, account should be taken of possible changes in vegetation during the spring and summer which may alter or obscure them. A compass bearing should also be taken from the vantage point (recorded as at least a six figure map reference) to the nest. In large reed beds, several watches should be made from different vantage points; these will give different lines or bearings to the nest(s), which will help pinpoint their locations.

If the aim is to measure, ring and/or tag chicks, multiple nest watches will be required during the second visit period to provide an indication of the age of the chicks and the appropriate timing of a nest visit. The first sign of food being taken to the nest by the female indicates hatching; large chicks are fed at the nest by both parents.

If nest visits are undertaken in large reed beds, it is useful if the fieldworker who is visiting the nest is guided by an observer at a vantage point with an unhindered view of the nest site and a perspective of depth within the reed bed. Two-way radios or mobile phones (if reception is available) should be used so that the observer can guide the fieldworker to the nest. Observers can be stationed some distance from the nest site (normally up to 2 km, although distances

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of up to 4 km have been used successfully in good visibility) and should ideally be on site earlier in the day to confirm activity at the nest before a visit is made. The fieldworker visiting the nest should carry a tall pole (up to 2 m) with a large, fluorescent pointer at the top. This will reveal their position to the observer and the pointer can be used by the observer to guide the fieldworker.

3.3.2 Evidence of fledging To locate fledged young, observations should be made from a vantage point overlooking the nesting territory between mid-July and mid-August. The fledged young will sit in the vicinity of the nest on bushes or similar prominent perches and can usually be counted easily. The area should be watched until the fieldworker is confident that all of the young present have been located. Observations in Scotland suggest that very few young die after the feathers are almost fully grown, so counts of young in the nest at this stage may provide an estimate of fledging success.

If the outcome of a breeding attempt is not known, visits to confirmed or probable nest sites from late August may provide clues as to whether young fledged successfully or any cause of failure (e.g. presence of prey remains or unhatched eggs; Gilbert et al., 1998)

3.4 Evidence for non-breeding It is extremely difficult to prove that a pair of marsh harriers has not bred. Nests can easily be missed if no food is brought in during a watch. All nesting territories that may be occupied by non-breeding birds should be checked on several occasions for breeding behaviour (using watches of sufficient duration from suitable vantage points) and for fledged young, to ensure that a nest has not been missed.

3.5 Ageing and sexing young From measurements of marsh harriers in the Netherlands, chicks can be aged approximately using wing length (Figure 11; Bijlsma, 1997).

Measurements from the Netherlands also indicate that after the age of 19–22 days, most young can be sexed by a combination of mass and foot span without talons (for guidance on taking measurements see Introduction, Section 7.8.4). Females become heavier than males from around 14 days old (Figure 12; Bijlsma, 1997). After the age of about 22 days (wing length greater than 190 mm), any chick of more than 700 g is likely to be a female and any less than 600 g is likely to be a male. After the age of 19 days (wing length greater than 160 mm), females have foot spans equal to or greater than 80 mm while those of males are equal to or smaller than 78 mm (Figure 13; Bijlsma, 1997). Chicks that fall between the ranges for males and females for weight and/or foot span should be left unsexed. Iris colour is not useful for sexing the young of this species (Bavoux et al., 1993).

4. SURVEYS OUTSIDE THE BREEDING SEASON Marsh harriers can be counted at communal roosts. These often form in the autumn, when juvenile and adult birds roost together before migrating. Winter communal roosts occur at a few sites in southeast England (Clarke, 1995). Marsh harriers gather about an hour before sunset, perching on bushes among reed beds or on open ground. They move into the roost, which is generally in rank vegetation, at sunset and move out again at first light. Counts can be made from a suitable vantage point as the birds either enter or leave the roost. It Marsh harrier

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Wing length (mm)

Chick age (days)

Mass (g)

Figure 11. Change in the mean wing length (with 95% confidence limits) of marsh harrier chicks with age. Data from 4–33 nests per year over three years and two study areas; each point based on measurements from 5–36 male and 5–26 female young (from Bijlsma, 1997).

Chick age (days)

Figure 12. Change in the mean body mass (with 95% confidence limits) of marsh harrier chicks with age. Data from 4–33 nests per year over three years and two study areas; each point based on measurements from 5–43 male and 5–30 female young (from Bijlsma, 1997).

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Foot span without talons (mm)

Chick age (days)

Figure 13. Change in the foot span without talons (95% confidence limits) of marsh harrier chicks with age. Data from 4–33 nests per year over three years and two study areas; each point based on measurements from 5–21 male and 5–20 female young (from Bijlsma, 1997).

is important to be on site well before sunset (by mid-afternoon in mid-winter) or before dawn. Roosts can be found, initially, by following harriers as they return in the evening or by surveying suitable areas of habitat at dawn or dusk. Roosts often occur in the same localities in successive years if the vegetation remains suitable, although they can shift between years (Clarke, 1995). Marsh harriers counted at roosts are of unknown breeding origin and counts at roosts do not give any indication of the geographical areas used for foraging.

In areas with extensive wintering foraging habitat for marsh harriers, foot or road surveys could be used to provide indices of abundance in winter (see Introduction, Section 2.2.2) but few such areas occur in Britain and Ireland.

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Merlin Falco columbarius 1. INTRODUCTION The merlin is a widespread and locally abundant breeding bird in upland areas of Britain and Ireland (Gibbons et al., 1993). Populations in Britain are stable or increasing (Rebecca & Bainbridge, 1998). In Britain and Ireland, merlins are short-distance migrants; many disperse to lower altitudes after breeding, normally within 100 km of their breeding area, and smaller numbers move south into France and Iberia (Heavisides, 2002). Northern populations in Iceland and Fennoscandia are migratory, and Icelandic breeders winter mainly in Britain and Ireland.

Adult males, with their blue-grey upperparts, dark-streaked rusty underparts and smaller size, are easily separated from females and immatures (Cramp & Simmons, 1980). The brown immatures and females are difficult to separate in the field but one year-old males can sometimes be identified by their small size. Although most merlins do not breed until two years old, a small proportion (10-20%) breed at one year (Lieske et al., 1997; Newton et al., 1986).

There is no monograph for this species which covers the whole of Britain and Ireland. In Ireland, the merlin population in County Wicklow has been studied regularly since 1987 (McElheron, 2005), and Wright (2005) describes a 30-year study of merlins in the Yorkshire Dales.

Annual cycle Breeding Activity

Peak Period

Range

Duration (days)

Site occupation

Late February to late April

Courtship display

Late March to late April

Egg laying

Early May to mid-May

Late April to early June

4 to 8

Incubation

Early May to mid-June

Late April to early July

28 to 32

Hatching

Early June to mid-June

Late May to early July

Young in nest

Early June to mid-July

Late May to early August

23 to 32 (young from ground nests may disperse into surrounding vegetation from 23 days)

Fledging

Late June to early August

At 28 to 32 days old

Juvenile dispersal

Early July to early September

Merlin

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2. HABITAT, HOME RANGE, NESTS AND BREEDING 2.1 Habitat Within Britain and Ireland, merlins commonly nest on open, upland moors, at altitudes varying from 75 m to over 700 m a.s.l, commonly between 150-600 m a.s.l., the altitudinal range in which most of the suitable habitat lies (Williams, 1981; Rebecca et al., 1992; Wright, 1997; Dickson, 2000; McElheron, 2005). Merlins favour heather moorland but will breed in trees in copses and windbreaks in any open country with suitable populations of small passerines. They tend to avoid the centre of dense forests but will nest in trees within forests, usually less than 1 km from open hunting ground (Newton et al., 1978; Parr, 1991; Little & Davidson, 1992; Petty, 1995). Merlins do not breed in alpine habitats, bare or very steep areas (Heavisides, 2002). In winter, merlins move to lower altitudes and occupy arable farmland, rough pasture (marginal ground), estuaries, sand-dune systems and low lying heaths (Dickson, 1988).

2.2 Home range Breeding merlins do not hold an exclusive home range for hunting but defend only their immediate nesting territory. They will attack intruding merlins, other raptors, and corvids for about 0.8 km from an active nest (Dickson, 1992; Trimble, 1975). Individual birds vary in their response, with some being less aggressive and more tolerant of intrusion. Nests of neighbouring pairs may be 0.5–4.5 km apart and nesting territories tend to be regularly spaced in areas with many potential nest sites; nesting densities vary from 5–10 nests per 100 km2 in areas of open habitat (Cramp & Simmons, 1980). The distance between neighbouring pairs is greater in the north of Britain than in the south, perhaps linked to the variation in productivity of the habitat. Evidence that merlins defend home ranges in winter is lacking.

2.3 Nest Sites Merlins nest on the ground, on ledges on crags, on heather-clad boulders, and in the old tree nests of other birds, especially crows. They will also use man-made nest baskets or trays (Rebecca et al., 1991; Bauer & Cormack, 1995). A number of studies have reported varying proportions of nests in different locations (e.g. Northumberland, Newton et al., 1986; northwest Sutherland, Thompson et al., 1989; northeast Scotland, Rebecca et al., 1992; southwest Scotland, Dickson, 2000), with the majority of nests in most areas located on the ground, followed by trees and then crags/ledges and boulders. In a 3,000 ha study area in northwest Sutherland, however, all nests were on cliffs or boulders, and ground or tree sites were apparently not used although they were available (Thompson et al., 1989). On the Western Isles, some nests occur on small islands in lochs. Considering the results of the 1983-84 survey of Britain, Bibby & Natrass (1986) noted that merlins in afforested and grass dominated areas generally nested in trees and on heather moors they nested mainly on the ground; they found that ground nesting was proportionately more frequent in 10 km squares with more merlins and concluded that, in general, the best places for merlins are heather dominated, while tree nesting is more frequent in less favoured habitats. In Northumberland, tree nests (10-25% of nests recorded annually) were found to be significantly more successful than ground or crag nests; a difference attributed to the decreased vulnerability of tree nests to predation, especially by foxes (Newton et al., 1978, 1986). Other studies have reported no differences in breeding success in nests in different locations (Bibby, 1986; Bibby & Natrass, 1986; Rebecca et al., 1992). Many merlins breed within 300 m of the previous year’s nest and a few may re-use it. Pairs may also alternate between different parts of a moor, so that nesting areas can be up to 3.5 km apart (Rebecca et al., 1992; Dickson, 2000).

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In Britain and Ireland, ground nests are generally in heather of 30-70 cm in height (Rebecca et al., 1992; Wright, 1997; Dickson, 2000); and on slopes (normally on inclines of 20-45o, although they are also found on flat ground; Newton et al., 1978). Many nests are close to prominent features, such as small trees or stumps, fence posts or boulders in the heather (Rebecca et al., 1992). The aspect of the nesting slope appears not to be influential but a good view from the nest site may be important (Rowan, 1921-22). In areas used traditionally for nesting, ground nests may be found in young forestry plantations (Newton et al., 1978; Rebecca et al.,1992), until they are excluded by the growing trees. Merlins will nest in dense vegetation on top of large boulders (Newton et al., 1978) or on large heather-covered hummocks about 1.5 m high. Crag nests are either found in the vegetation on top of the crag (on smaller crags) or on open, heathery ledges (on larger crags). They tend to be more exposed than ground nests, as the heather on ledges can be sparser (the average height of the heather around nests on crags was 10 cm, Rebecca et al., 1992). Crags used by Merlins are usually between 10-30 m high, ranging from a few metres high (Newton et al., 1978) up to 100 m.

Competition with peregrines, which can kill merlins, may exclude merlins from some crags.

Merlins will nest close to hen harriers, short-eared owls and kestrels, and the association may generally benefit each species by giving increased awareness of and defence against predators.

Short-eared owls and hen harriers have, however, also been seen attacking merlins or their young. Merlins are vulnerable to predation by a wide range of other predators, including golden eagle, goshawk, red fox, mink, stoat and wildcat, and predation may be a major cause of breeding failure (Newton et al., 1986; Rebecca et al., 1992). In heather, adders may make use of merlin nests for shelter in the long heather and, when disturbed, may strike and kill chicks and possibly also adult merlins (Shaw, 1994).

Merlins also breed in trees in the old nests of crows, and occasionally in those of buzzards or ravens (Newton et al., 1978; Rebecca et al., 1992). The trees are generally either isolated or in small copses or open woodland on moorland or recently afforested ground, near the edge of forestry plantations (Parr, 1991; Little & Davidson, 1992; McElheron, 2005) or along the banks of streams. Merlins using the same home range may breed in trees in one year and then in a ground nest in a subsequent year. Little & Davidson (1992) found that most of the tree nests in Kielder Forest, Northumberland were up to 1 km (and a few up to 5 km) from the forest/moorland boundary; these nests were associated with unplanted areas within the forest. Merlins do not generally breed for more than one year in old corvid nests in sitka spruce but they may re-use nests in birch, rowan or Scots pine for several years.

2.4â&#x20AC;&#x201A; Nests Merlins do not build a nest but simply scrape a small depression in the chosen nest site. In ground or crag nests, the scrape is usually in bare ground under a dense canopy of heather or other vegetation. It may accumulate a considerable amount of dead vegetation (Rebecca et al., 1992), such as small heather twigs, bracken and other material, which is plucked by the female from within 1 m of the nest (Cramp & Simmons, 1980). Tree nests are also scraped and the eggs laid on bare twigs or the remaining lining of an old nest.

2.5â&#x20AC;&#x201A; Clutch size and incubation Merlins lay clutches of 1-6 eggs, although the normal clutch is four or five eggs, and recorded clutches of one or two eggs may have been incomplete (Crick, 1993). The BTO Nest Record Scheme gives an average clutch size of 4.2 (n=1,405). Average clutch sizes from regional studies in north England, northeast Scotland and southwest Scotland have been higher Merlin

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(Newton et al., 1978; Newton et al., 1986; Rebecca et al., 1992; Dickson, 2000). Eggs are laid at 2-day intervals, sometimes with a longer interval for the last egg. Incubation usually starts with the final egg (Rowan, 1921-22; Orchel, 1992) and lasts 28-32 days (Cramp & Simmons, 1980). Most of the incubation (up to two-thirds) is carried out by the female but the male may sit for 1-2 hours at a time (Newton et al., 1978). Hatching occurs 48-50 hours after the eggs begin to pip on the 28th day (Orchel, 1992). Merlins may relay if breeding failure occurs early in the season.

2.6 Brood size and fledging For the first 10 days after hatching, merlin young are brooded and fed mostly by the female.

The male hunts, bringing 3–8 prey items per day (Cramp & Simmons, 1980; Orchel, 1992).

In southwest Scotland, average rates of food delivery to the nest varied from 0.19 per hour during the prelaying and brooding stages to 0.51 per hour during the nesting and post fledging periods, with no significant diurnal variation in feeding rates (Dickson, 1995b).

Elswhere it has been reported that most feeds are delivered early in the morning and in the late afternoon or evening. The young fledge at 28–32 days (Newton et al., 1978). Those from ground nests may leave the nest and scatter into the heather after 23 days, well before they can fly (Dickson, 2003). After fledging, the young disperse from the nest site within 2-4 weeks (Rebecca et al., 1992; Orchel, 1992).

3. SURVEY TECHNIQUES CAUTION Care should be taken during visits in late March and April to avoid disturbance of merlins at occupied nesting ranges, as this may cause the birds to move. Visits during incubation or when the young are being brooded should be brief and merlins should not be disturbed from active nests in bad weather. Always leave the area quickly after examining the nest and do not attempt to watch the nest from nearby, as this may inhibit the return of the adults. To minimise the risk of disturbance it is recommended that nesting areas are viewed from distances of 300–500 m (Ruddock & Whitfield, 2007; Whitfield et al., 2008b). Be aware also that adults flushed from nests may dislodge small young and any such young should be put back when the nest is checked. If nest inspection visits require climbing, then appropriate health and safety precautions should be taken (see Section 7.10 of Introduction). No attempt should be made to climb to nests that could have large young (20 days or older) because they may ‘spook’ and fledge prematurely.

3.1 Breeding season visit schedule The species is listed on Schedule 1 in Great Britain and Northern Ireland, and Schedule II in the Republic of Ireland (see Section 7.1.1 of Introduction). To establish occupancy and the presence of a breeding pair, it is recommended that all four visits are made (as detailed below). However, if time is limited and a home range appears to be unoccupied on the basis of the first two visits, then further visits to that home range can be omitted.

Visit 1

Late March to April

To check for occupancy and locate potential breeding areas

Visit 2

Early May to early June

To locate active nests and a further check for occupancy

Visit 3

Mid- to Late June

To check for young

Visit 4

July to early August

To check for fledged young

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3.2 Signs of occupancy 3.2.1 Locating home ranges The field methods described here are based on those used in the survey of breeding merlins in Britain in 1993–1994 (Rebecca & Bainbridge, 1998) which covered a stratified sample of 10 km National Grid squares within the known breeding range of merlins. Parts of a survey area that do not require searching (open water, towns, villages, enclosed pasture, arable farmland and land above 700 m) should be identified and marked on a 1:25,000 OS map. Any known merlin nest sites from previous years should also be noted on the map. All suitable land within the survey area should then be visited between late March and mid-April and searched for sightings and signs of occupancy by merlins by passing within 500 m of all potential nesting habitat (including grass or heather moorland, bracken, young forestry plantations, the edges of mature forestry plantations and rides within 100 m of the plantation boundary, open areas within afforested blocks and open birch, pine and alder woods). Any old nests (crow, raven, buzzard) found should be mapped. Areas of grassy moorland that are found to have no potential merlin nest sites (trees, crags, steep stream banks) should also be marked on the map as unsuitable breeding habitat. Fence lines, isolated posts, stone dykes, grouse butts, hummocks, boulders, stream banks, crags, trees and recently burnt areas on heather moors should all be checked for faecal droppings, pellets, the plucked remains of kills and moulted merlin feathers (Section 3.2.3) and the locations of any signs found should be mapped. Prey remains, pellets and feathers should be removed so that any new signs can be recorded on the next visit. Watches should also be carried out over all suitable areas for periods of at least two hours, in order to locate merlins displaying, carrying food or hunting, or attacking corvids, other raptors or grey herons.

Displaying birds may be seen or heard; female merlins in particular can be very vocal and their calls can be heard at a distance of up to 1 km. Merlins may also utter a very quiet ‘tic’ call when displaying which is similar to the call given by the female when feeding young.

The display flights themselves can be quite inconspicuous but are most noticeable early in the breeding cycle on warm, sunny days (Cramp & Simmons, 1980). They may involve both birds of the pair circling high over the nest site and shivering their wings (the male may also change to using very slow wing beats for periods), accompanied by calling. The male may also perform short, fluttering flights between perches within the nesting territory, including low flights in the direction of the nest (also accompanied by calling). Aerial chasing and ‘play’ occur between the members of a pair but may also involve immature birds and take place after the breeding season or at communal roosts (Cramp & Simmons, 1980).

Areas where merlins are observed or where fresh signs are found should be visited on at least two occasions to confirm occupation. Care must be taken to avoid disturbing the birds, especially during April, as this may cause them to move sites.

3.2.2 Locating roosts Breeding merlins roost on the ground in deep vegetation, in trees or on crags close to the nest site. Tree and crag roosts can be recognised by the presence of fresh faecal droppings, down and moulted feathers and the presence of merlins at such sites can be established during checks of the nesting area. Active searches for roosts on the ground are not recommended, however, because of the potential for disturbance.

3.2.3 Recognition of signs Merlin plucks are found on prominent features (fence posts, hummocks, boulders, trees) and on the ground in patches of short vegetation. They consist mainly of the feathers of moorland Merlin

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passerines (Brown et al., 2003; Cramp & Simmons, 1980). In central Scotland, merlins may hunt emporer and northern eggar moths, and collections of the discarded wings of these moths in suitable nesting habitat can also provide signs of occupation. Merlin pellets are similar to those of other small falcons, although they are generally smaller than kestrel pellets and contain small feathers and some hollow bird bones, whereas kestrel pellets are composed predominantly of mammal fur. However, definite identification is difficult unless pellets are collected in association with other signs (particularly moulted feathers).

3.2.4 Evidence of occupancy Nesting ranges are occupied if a pair or single merlin is seen or heard, or if unambiguous fresh signs are found on at least two visits (freshly plucked kills, moulted merlin feathers, faecal droppings or merlin pellets; Rebecca et al., 1992; Rebecca & Bainbridge, 1998; Gilbert et al., 1998).

3.3 Evidence of breeding During the 1993-94 national survey of Britain (Rebecca & Bainbridge, 1998), breeding pairs were recorded if adults were seen returning to a nest, if eggs or young were found, if adults were repeatedly alarm calling at the appropriate time, or if signs of occupation indicated that a pair had probably bred and failed. Rebecca et al. (1992) also considered courtship display, including the feeding of the female by the male, copulation or nest scraping (Feldsine & Oliphant, 1985), as evidence of breeding.

3.3.1 Locating active nests Visits to all suitable breeding habitats within the study area to locate pairs before laying are important as merlins are much more difficult to locate once incubation starts. Occupied nesting ranges should be visited again in May or, at the latest, early June to locate nests with eggs.

To locate nests on the ground, a watch should be carried out from a suitable vantage point over the nesting area. If the merlins alarm or appear disturbed this suggests that the watch point is too close to the nest and the fieldworker should move further away. Each watch should last 4-6 hours, as it may take three hours for a bird to return to the site and change over with the incubating partner. Watches should be carried out in the morning (preferably before 10:00h and certainly before 12:00h) or in the evening (after 16:00h), especially on hot days. Merlins will normally call when they change over during incubation. Changeovers generally occur after a food pass, when the male brings food to the female. The food pass usually takes place on a low perch or on the ground, not at the nest itself. During the watch, particular attention should be paid to the male, as once he has passed food to the female, he will slip onto the nest to incubate the eggs.

If a fieldworker wishes to check a nest during the incubation period, some observers prefer not to approach the nest while the male is known to be covering the eggs. Males may take off when a fieldworker is still some distance from a nest, making it harder to find. They may also take a long time to return to a nest after disturbance, during which time the eggs are at risk of chilling. A precautionary approach is to wait until the female returns to the nest, allow her about 30 minutes to settle and then approach the nest. Females may be less likely to leave the nest for long periods after disturbance.

Once located, a sketch map should be drawn and/or a digital photograph taken of the nest location in relation to any nearby features (e.g. differences in the heather or slope, the presence of rushes, ferns or other plants, or the proximity of boulders or posts). The position of the observer should also be noted. If a nest visit is undertaken the nest should be approached carefully and the fieldworker should deliberately make a noise when close so as to alert the

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sitting bird. Moving carefully up to the nest once the bird has flushed, preferably from lower down a slope, will help to avoid trampling the eggs or young. Down or feathers stuck in the heather are a good indication of the proximity of a merlin nest.

Merlins may move on from a nest site early in the season. If no signs are seen at a site which was apparently occupied on a previous visit, all known alternative sites and areas of suitable habitat should be checked in case a pair has moved.

Some fieldworkers prefer to cold-search established sites and check all old nest scrapes before watching, as this can prevent the need for long watches. Searches should be carefully timed to avoid laying and early incubation, and this method is recommended only for experienced fieldworkers with local knowledge who are able to predict possible nest locations from the positions of plucks and other signs. Nests that usually occur on crags, in particular, can normally be located in May or June by searching the crag top and all the ledges. Only if this fails to locate a nest does the fieldworker need to watch the site.

Nests with small young (early to mid-June) can be easier to find, as visits by the male with food are more frequent from this time and on warm days the female may leave the nest to drink or dust-bathe. Watches to find nests with large young are more difficult, however, as the fieldworker must be hidden further away to avoid disturbing the adults.

Observations of interactions between merlins, other raptors and corvids can be helpful with respect to the location of nests by watching adult merlins back to the nest when the aerial attack is over. When merlins and hen harriers nest together, there may be many interactions early in the season which can help to locate the nests of either species.

As described above (Section 3.2.1), potential nests in isolated trees or small copses can be located during searches in late March and April by checking for old crow, raven or buzzard nests. On return visits, all such nests should be approached to check for incubating birds or young, and/or fresh signs. Nests with young will have down and droppings around and below them. If a nest is not located but fresh signs are found, the fieldworker should watch the area for 4-6 hours from a suitable vantage point.

Forest-nesting merlins pose a greater challenge. Plantations used for breeding are usually at least 15 years old, although merlins will fly over immature plantations to reach the edge of more mature forest. Tree nests are seldom directly visible in this habitat and searches must concentrate on signs. The open edges of the forest, especially those next to unenclosed grass or heather moorland, should be walked in April or early May and all elevated features (e.g. fence posts, large boulders) within 100m of the forest edge should be checked for signs.

Once these are found, the fieldworker should watch the area from a look-out point for 4-6 hours. Before laying, or when the young are no longer being brooded, the female merlin often perches on a tree crown close to her nest; and locating the nest is easier when it contains young and feeding visits are frequent. Once the approximate position of the nest has been established, that part of the wood can be searched. The nesting tree should have signs (droppings, moulted feathers) below it. Sitting concealed in the wood and listening for the young calling may also help locate the nest which will probably not be visible so the exact position might only be found by climbing the tree. Nesting trees should be clearly marked on a map with directions from any nearby features.

The technique of broadcasting merlin calls to locate nests or breeding pairs has been little used. In one study in Britain, alarm calls failed to elicit any response from sitting birds Merlin

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during May, but the method has not been tested thoroughly and may have potential at other times.

In habitats where nests are difficult to locate by watches and cold searches during the breeding season (e.g. forestry, gullies), they may be found after the breeding season when the entire area can be searched for nests or other signs of occupation with no risk of disturbance. This method is also useful if a probable nest has been missed because the nesting area could not be visited during the breeding season, or if a report of breeding merlins is received after the breeding season ends. The data gathered is minimal but occupation and successful fledging can generally be confirmed (see Section 3.3.2). Several new nesting areas have been found in this way in northeast Scotland.

Retaining records of new crow or raven nests within a study area can be useful for fieldwork in the next breeding season.

3.3.2 Evidence for fledging Successful fledging can only be assumed if young are fully feathered and capable of flight.

This can be difficult to assess as older young may leave the immediate area of the nest before they can fly; and, once on the wing they may remain in the immediate vicinity of the nest for only a short time before moving up to 1 km to an area where there is an abundance of prey. Successful fledging can be assumed if a large number of plucks are found close to a ground or crag nest site at the appropriate date, together with down trails, the latter made by young merlins as they leave the nest and their down attaches to the heather and other vegetation. Young may be counted by searching the heather around ground or crag nests and/or watching from a distance. Accurate counts of brood size at fledging may be impossible in forestry plantations, as the young may only be heard.

Because of the difficulties associated with counting fledged young, brood size at fledging can be estimated from the number of young of ringing age (14-21 days old). Losses of chicks can occur after this however (from ground, crag or tree nests) and a visit to confirm that the young have fledged should always be made if possible. Any recorded brood sizes should therefore be accompanied by details of the approximate age of young when counted.

3.4 Evidence for non-breeding If a breeding territory and all potential nest sites within the hunting range of a pair are apparently not occupied despite several visits, a visit late in the season should be made to confirm that merlins are not present. If occupancy by a pair is confirmed but no active nest is found after the appropriate visits, and the birds are not known to have moved to a different site within the nesting range, then this provides evidence for non-breeding. As with all raptors, non-breeding is difficult to separate from early breeding failure. Both members of a pair may remain on site for a few days after failing, they may display and the male may still bring in food to the female. It may take a watch of several hours to determine if birds have failed if a nest site has not previously been found. Fresh signs at the site will not persist when the birds move away.

3.5 Ageing and sexing Measurements of a small number (n=17) of merlin chicks in Orkney (Picozzi, 1983) suggest that young can be sexed from about 13 days old by measuring wing length and weight (Figure 33). Nine female chicks grew more rapidly and attained a greater weight (in excess of 235 g) than eight male chicks (less than 210 g). Females were clearly larger than males with respect to tarsus length, width and depth, bill (culmen) length, the length of the hind claw and the length of the middle toe (Picozzi, 1983; Table 6). Although European merlins tend to

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decrease in size from north to south, Picozzi (1983) concluded that differences in wing length of birds breeding from Shetland to Northumberland were sufficiently small that his results should be generally applicable.

Dickson (2003) used a similar method for merlins in Galloway, based on a sample of seven broods from 1971 to 1977.

Table 6. Measurements of hind claw, culmen, tarsus and middle toe of eight male and nine female merlin chicks in Orkney within five days of fledging (from Picozzi, 1983; reproduced with kind permission of Blackwell Publishing).

Min (mm)

Male Max (mm)

Mean (± SD)

Min (mm)

Female Max (mm)

Hind claw

9.7

10.8

10.4 (± 0.39)

11.0

11.8

11.4 (± 0.23)

Culmen

10.8

11.8

11.4 (± 0.32)

12.3

13.5

12.7 (± 0.37)

Tarsus length

32.5

36.5

35.1 (± 1.25)

37.0

40.5

38.0 (± 1.15)

Tarsus width

3.2

3.6

3.4 (± 0.14)

3.7

4.2

3.9 (± 0.16)

Tarsus depth

4.8

5.3

5.0 (± 0.17)

5.2

5.9

5.6 (± 0.2)

Middle toe length

32.5

36.0

34.3 (± 1.1)

36.0

39.0

37.4 (± 0.92)

Mean (± SD)

280

(a)

(b)

260

Weight of nestlings (g)

240 220 200 180 160 140 120 100 10

20

30

40

50

60

70

Length of 10th primary (mm)

80

90

50

70

90

110

130

150

170

Length of wing (mm)

Figure 33. Scattergrams of weight of nestlings against (a) length of outer (10th) primary and (b) wing length, for eight male (▲) and nine female (●) merlins. The broken line, fitted by eye, distinguishes males and females (from Picozzi, 1983; reproduced with kind permission of Blackwell Publishing).

Merlin

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Approximate age in days 9 11 13 15 17 19 21 23 27 29 300

280

260

240

220

200

Mass (g)

180

160

140

120

100

80

60

40

20

0 0

10

20

30

40

50

60

70

80

90

100

Length outermost pimary (mm) Figure 34. Scattergram for use in determining the sex and approximate age of merlin chicks.

Based on measurements of approximately 70 broods over 15 years in the Southern Uplands (mainly the Lammermuir Hills), Scotland (154 male and 125 female young). Age data based on 55 young of known age (Ian Poxton & Alan Heavisides, unpublished data).

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More recently, Ian Poxton & Alan Heavisides (unpublished data) have compiled measurements from a large sample of nestlings from the Southern Uplands of Scotland (mainly the Lammermuir Hills) since 1984. The length of the outermost primary feather (in mm) should be measured from its tip to where it emerges from the skin. Using these data (Figure 34), chicks can be aged approximately and the sexes separated with relative confidence after the age of around 18 days. Following the conclusions of Picozzi (1983) regarding size differences, there is no reason why measurements of merlin young from the Southern Uplands should not be generally applicable in Britain and Ireland.

The development of merlin chicks is illustrated in plates 64 to 69.

4.â&#x20AC;&#x201A; SURVEYS OUTSIDE THE BREEDING SEASON Merlins are elusive outside the breeding season and methods of assessing their abundance at this time have not been established. They may enter the communal roosts of hen harriers (Dickson, 1988) and can be counted in this situation (see species account for hen harrier). The majority of merlins probably roost individually however.

Due to the fleeting nature of merlin hunting behaviour, methods to provide indices of abundance in winter (e.g. via foot surveys) are likely to be difficult to implement.

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Montagu’s Harrier Circus pygargus

1. INTRODUCTION Montagu’s harriers are rare in Britain and Ireland, breeding regularly only in central, southeast, southwest and east England (Ogilvie & RBBP, 2004; Holling & RBBP, 2008). The breeding range in England and Wales was formerly more extensive and the species has also been recorded breeding in Scotland and Ireland. (Gibbons et al., 1993). Montagu’s harriers are migratory. Birds breeding in northwest Europe winter in the northern tropics south of the Sahara (Underhill-Day, 2002b). They return to breeding grounds in England from late April. The blue-grey males are distinctive and easily separated from the brown ‘ringtails’ (females or immature males). Firstsummer males can be distinguished from females by their smaller size and the presence of some adult male feathers (Clarke, 1996). Juveniles are easily separated from older birds by their distinctive dark buff to rufous breast, belly and undertail-coverts. A melanistic (dark) plumage morph has occassionally been recorded in Britain (e.g. Everett, 1991; Thomas, 2008). Montagu’s harriers do not normally breed until two or three years old (Clarke, 1996).

For further information on the biology and ecology of this species, Clarke (1996) provides a comprehensive account.

Annual cycle Breeding Activity

Peak Period

Range

Occupation of home range May

Late April to late May

Territorial display

May

Late April to late May

Egg laying

Late May

Early May to early June

Incubation

Late May to late June Early May to early July

Hatching

Late June

Young in nest

Late June to mid-July Early June to mid-August

4 to 8 27 to 30

Early June to early July

Fledging

Mid-July to mid-August

Juvenile dispersal

Early August to early September

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Duration (days)

35 to 40 (may leave nest at 21+ days and hide in nearby vegetation)

Montagu’s harrier

2. HABITAT, HOME RANGE, NESTS AND BREEDING 2.1 Habitat Essentially a lowland species, Montagu’s harriers breed in both dry and wet habitats. In Britain and Ireland, they were formerly found in arable farmland, heaths and young conifer plantations. The small population in England is currently confined to arable farmland. The habitat must provide both sufficient cover for nesting and open areas for hunting.

2.2 Home range Montagu’s harriers have extensive home ranges for hunting; males may hunt 8 km or more beyond the nesting territory although females are likely to hunt within or close to the nesting territory (Cramp & Simmons, 1980). Home ranges are not exclusive and overlap with those of other harriers. Pairs may occur on their own or in loose colonies, possibly depending on the available food supply, whether areas of suitable nesting habitat are limited, or the need for mutual defence (Clarke, 1996). Within colonies, the distance between nests can be as little as 20–30 m but is usually 200–300 m. In Scotland and Ireland, all breeding attempts have involved solitary pairs but loose colonies have been found in England. Montagu’s harriers are less aggressive in defending their nesting territory than other harrier species. A study in Italy found that the area defended around a nest ranged from 1.5–6 ha (Pandolfi & Pino d’Astore, 1992).

Montagu’s harriers are occasionally polygynous: one case was found in 71 nests in Cornwall (Cramp & Simmons, 1980), and 13 out of 776 nests were polygynous in Norfolk between 1923 and 1982 (Underhill-Day, 1990). Possible polyandry has also been recorded (Arroyo, 1996).

2.3 Nest sites Montagu’s harriers nest in arable crops, particularly winter sown ones (cereal or rape) that have grown to a suitable height by the spring. Their nests have also been found in young forestry plantations, wet and dry heaths, peatlands, heather moorland, shrubs (gorse and similar plants), marshes, ‘set aside’ in agricultural land, and dunes (Cramp & Simmons, 1980; Clarke, 1996). In England, and other parts of Europe, Montagu’s harriers will return to the same nesting range in successive years, and the new nest is generally built close to the old one. Movements of up to 7 km have been reported if the distribution of crops changes from year to year. The female is usually the more aggressive bird, but the male may also strongly defend the nest site.

2.4 Nests The nest is placed on the ground in dense vegetation of typically 50–100 cm in height (Clarke, 1996), tall enough to hide the female when she is brooding or incubating. The nest is built by the female from any available vegetation (reed-stems, heather, twigs, coarse grass. The normal height is 5–10 cm, with a diameter of 20–30 cm and a shallow cup of about 15–20 cm in diameter (Cramp & Simmons, 1980).

2.5 Clutch size and incubation Montagu’s harriers normally lay 3–5 eggs but clutch size can range from 1–8 eggs (Cramp & Simmons, 1980; Clarke, 1996; Arroyo et al., 1998) and exceptional clutches of up to 10 eggs have been recorded. Variability in clutch size has been related to weather, food supply and the breeding condition of pairs (Arroyo et al., 1998; Corbacho & Sanchez, 2000). Mean clutch size also declines as the season progresses. Eggs are laid at 1.5–3 day intervals. Incubation Montagu’s harrier

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normally lasts for 27–30 days per egg and 27–40 days per clutch. It usually begins with the first egg, although it is not uncommon for full incubation to be delayed until 2–3 eggs are laid. Only the female incubates, and is fed by the male, on average 5–6 times per day (Clarke, 1996); if larger prey items (e.g. rabbits, leverets) are brought, however, there may only be 2–3 visits a day. Breeding success tends to increase with clutch size (Corbacho et al., 1997).

2.6 Brood size and fledging Eggs hatch asynchronously but the first two chicks may hatch at the same time. If there is a reduction in the food supply, younger chicks have a lower chance of survival. The first eggs laid tend to hatch female chicks (Leroux & Bretagnolle, 1996), with later eggs hatching males.

The proportion of male chicks hatched was higher in smaller colonies than in larger ones. The sex ratio was also related to food availability with more female chicks produced in years of higher prey populations (Arroyo, 2002).

A limited number of observations have shown delivery rates of 23-26 items per day during the nesting period; feeding activity was reduced in the early afternoon (Clarke, 1996). Feeding rates may average one visit per two hours when young are small, and increase to one per hour when they are large (Glutz et al., 1971 in Cramp & Simmons, 1980). The young fledge 35–40 days after hatching but may leave the nest and hide in nearby vegetation after 21 days (Cramp & Simmons, 1980). They become independent 15–30 days after fledging and start to disperse from the nesting territory; birds that fledge later in the season take less time to become independent (Arroyo, 2002).

Productivity has been linked to prey abundance, with cyclic oscillations in vole numbers influencing breeding success in France (Leroux & Bretagnolle, 1996; Butet & Leroux, 2001) and the Netherlands (Koks et al., 2002); more young are produced in years with greater vole numbers. In western France, spring and summer vole densities were found to be good predictors of productivity (Butet & Leroux, 2001). In areas where voles are not abundant, birds (Sanchez-Zapata & Calvo, 1998) or lagomorphs (Arroyo, 1995) form the main prey.

3. SURVEY TECHNIQUES CAUTION To minimise potential disturbance, nesting areas should ideally be viewed from vantage points between 500-750 m away. Depending on location and topography, however, this can be reduced as far as about 200-300 m. Sensitivity to disturbance depends on individuals, so if a bird repeatedly flies around a particular spot, apparently aiming to land, but changing its mind at the last minute, this probably indicates that the observer is too close for comfort. The nests of Montagu’s harriers should not be visited unless there is a specific reason for doing so, and nest visits should always be kept to an absolute minimum. Trampling of tall vegetation will increase the risk of mammalian predation, therefore care should be taken to cause as little damage as possible to the vegetation surrounding the nest. Any visits to record the nest contents or to ring the young should be made as late in the breeding cycle as possible (when young are three to four weeks old) and should not be made in poor weather. After visiting a nest, the observer should watch from a suitably distant vantage point to ensure that the female returns to the nest and that the parents continue to behave normally. If the female does not return within a reasonable time, the fieldworker should leave the area completely and return at a later date. If desertion is suspected, the pair/nest site should be treated with extreme caution in future years.

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Montagu’s harrier

3.1 Breeding season visit schedule The species is listed on Schedule 1 in Great Britain and the Isle of Man, and on Schedule II in the Republic of Ireland. To establish occupancy and the presence of breeding pairs, at least three visits are recommended, although further watches during the second period will increase the chances of detecting active nests.

Visit 1

Late April to late May

To check for occupancy. It is important to try to locate birds before incubation starts as disturbance of incubating birds may increase the risk of nest predation

Visit 2 (several visits can be made)

Late May to late July

To locate the nest. No attempt should be made to visit the nest unless there is a specific need

Visit 3

Mid-July to mid-August

To check for fledged young

3.2 Signs of occupancy 3.2.1 Locating home ranges If the presence of Montagu’s harriers is suspected, suitable breeding habitats should be checked for displaying birds from late April to late May. Watches should be carried out from a vantage point for at least four hours. The vantage point should be far enough away from the potential nesting territory so as not to cause disturbance.

Montagu’s harriers (males in particular) perform a solo high-circling display, reaching heights of 300–600 m, but will also perform mutual high-circling, often with the male above the female. Pairs may also perform a ‘flight-drifting’ display, in which they float back and forth over their nesting territory, sometimes indulging in flight play (flight-rolls and presentation of talons by the male; symbolic ‘food passes’). Sky-dancing is performed predominantly by males (the female may or may not be present), often in fine weather. Individual males show variation in display, which may be related to age or prevailing weather conditions (Cramp & Simmons, 1980). Food passes from the male to the female, on the ground or in the air, begin before egg-laying, and the female remains dependent on the male for food well into the nesting period (Cramp & Simmons, 1980).

3.2.2 Locating roosts Searches for roosting birds during the breeding season are not recommended because of the disturbance that they cause.

3.2.3 Recognition of signs The areas around Montagu’s harrier nests should not be disturbed unless there is a specific reason for doing so and no attempt should be made to locate pellets until the young are well on the wing. Care must be exercised in identifying pellets, as they are similar in appearance to those of other raptors. They will be useful only when there is additional evidence (e.g. moulted feathers, a recently used nest) to allow specific identification.

3.2.4 Evidence of occupancy A nesting territory is occupied if a single bird or a pair of Montagu’s harriers is observed displaying (Clarke, 1996; see 3.2.1 above), or if other breeding behaviour (e.g. a food pass) is observed.

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3.3 Evidence of breeding 3.3.1 Locating active nests Nests can be located from late May to late June, depending on the laying date. Watches should be carried out from a vantage point that gives a clear view of the area; they may need to last for up to six hours to observe a food pass or other definite sign of breeding. If the harriers alarm or appear reluctant to approach, the fieldworker may be too close to the nest and should move to a more distant vantage point. The female is likely to be incubating if she is no longer seen during site visits. If the male is seen displaying at this time, however, this may mean that the female has moved or died, as displays are rare after incubation starts. The only definite signs of breeding are food passes (generally in the air) or observations of adults carrying food to the nest. A female may leave the nest for a food pass, to defaecate, to pick up nest material, to dry her wings after rain or to mob potential predators. All such behaviours indicate probable breeding.

The female should be watched back to the nest after she has left it, noting that she may not return directly but approach the nest in a series of short flights. Once she has settled, her position should be noted on a sketch map and/or a digital photograph of the area taken.

Only if necessary for a specific study should the fieldworker go to search for the nest (see ‘caution’ above). If the nest is in uniform habitat (e.g. in the middle of a crop or a large grassy area with no trees or posts), it is better if two fieldworkers co-operate to locate it, one directing the other from a suitable vantage point. Specific permission from landowners must be obtained before entering crops, and care must be taken in crops or long grass not to leave a trail to the nest, which might reveal its location to potential predators, or people.

Wherever possible, in crops, fieldworkers should use existing ‘tram lines’ to gain access to nests. If working alone, the location of the nest can be determined from a vantage point by taking a compass bearing and estimating the approximate distance to the expected nest site. The fieldworker should then walk in the direction of the compass bearing and count paces to reach the estimated distance, mark this spot with a clearly visible object (pole, rucksack) and progressively search out from that point. Objects in the distance (posts, trees, buildings) beyond the nest site may help give a line to walk along towards the nest. The female may be reluctant to flush from her eggs or young.

If the young are large, the female may hunt in addition to the male but she will probably remain near the nest. Adults with prey will be observed flying directly to the nest and the position of the nest can be determined as above.

Nests in arable fields may be at risk of destruction if crops are due for harvesting before chicks fledge. In such cases local staff of the Statutory Country Conservation Agencies and/or RSPB should be informed. They can advise on or undertake liaison with land managers over nest protection.

3.3.2 Evidence for fledging It can be difficult to count well-grown young before fledging because they leave the nest and move into the surrounding vegetation. Counts can be made of chicks while they are still in the nest (noting that they may leave from 21 days onwards). In such cases, the age of the young must also be recorded because losses can occur before fledging. Fledged young can be counted accurately as they remain close to the nest for 10–14 days after fledging. They use low perches in the nesting territory and will fly to meet adults bringing food (Clarke, 1996); food passes give an excellent opportunity to count the young. To maximise the chances of seeing all the young, a watch should be carried out over the nesting territory for up to four

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hours or until two food passes are seen. If there is more than one nest in the same area, care should be taken to avoid counting young from neighbouring nests that may fly towards any adult carrying food.

3.4 Evidence for non-breeding If an area is occupied but no sign of breeding behaviour is observed after multiple visits involving watches of sufficient duration from suitable vantage points, including some time to check for fledged young, then this provides evidence for non-breeding.

3.5 Ageing and sexing young Measurements from birds breeding in the Netherlands indicate that Montagu’s harrier chicks can be aged by measuring their wing length (Figure 15; Bijlsma, 1997). Mass can also be used to give an approximate age for younger chicks but not for older young (after about 10–12 days) unless they can be sexed before estimating age (Figure 16; Bijlsma, 1997); for Spanish birds, Arroyo (1995) found that the growth of the eighth primary (the third outermost wing feather), was independent of the sex or condition of the chick. Based on these findings, age can be determined using the following formula, once primary growth (pin stage) has started at 7–8 days of age: (ii)

Wing length (mm)

Age = (Length of eighth primary (mm) + 59.0)/7.73

Chick age (days)

Figure 15. Change in the mean wing length (with 95% confidence limits) of Montagu’s harrier chicks with age. Data from 1–8 nests per year over nine years and three study areas; each point based on measurements from 5–11 male and 5–9 female young (from Bijlsma, 1997).

Wing length cannot be used reliably to sex young. Based on a sample of 39 young from the Netherlands, Bijlsma (1997) suggested that foot width (without claws) can be used to separate many males and females reliably at 20 days or older (wing length greater than Montagu’s harrier

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Mass (g)

187 mm): males had a foot span of 52 mm or less, and females 55 mm or greater (young with intermediate foot span cannot be sexed reliably by this measurement). Females over 20–23 days old usually weigh over 330 g, while males are normally below 300 g (Figure 16).

Weights within a brood give a reliable contrast, as males are usually 40–50 g lighter than their sibling females after reaching the asymptotic (maximum) mass at 20–30 days of age. Iris colour can be used in conjunction with measurements. Males, from 12–15 days old, have a grey iris, while females have a brown iris (Forsman, 1999).

Chick age (days)

Figure 16. Change in the mean body mass (with 95% confidence limits) of Montagu’s harrier chicks with age. Data from 1–8 nests per year over nine years and three study areas; each point based on measurements from 5–13 male and 5–11 female young (from Bijlsma, 1997).

4. SURVEYS OUTSIDE THE BREEDING SEASON The species does not occur in Britain and Ireland during the winter.

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Osprey Pandion haliaetus 1. INTRODUCTION The osprey (western osprey) is generally considered to have recolonised Scotland in 1954, after ceasing to breed about 1916 (Thom, 1986). Recently, however, it has been suggested, from a re-examination of historical records, that individuals were present almost every summer in the intervening period, and that occasional breeding occurred (Dennis, 2007, 2008). Between 1954 and the early 1990s, the Scottish population grew exponentially, as would be expected with an establishing population; since then the growth rate has declined slightly, suggesting that limiting factors have begun to operate (Dennis & McPhie, 2003). Ospreys are now widely distributed in Scotland (Etheridge, 2005; Etheridge et al., 2006) and have expanded into northern England (Ogilvie & RBBP, 2004). Ospreys from Scotland have also been successfully reintroduced into central England and have bred there and also in Wales (Appleton et al., 1997; www.ospreys.org.uk). Ospreys occur only as passage migrants in Ireland and are likely to have become extinct as a breeding species by the 1800s when most of the country had been deforested (www.goldeneagle.ie). Ospreys are migratory, leaving Britain and northern Europe in the autumn to winter in west Africa, or, in the case of a few birds in recent decades, Iberia (Dennis, 2002, 2007), and returning in March and April. Male ospreys can be separated from females in the field; males are smaller and have lighter breast bands, head patterns and outer tail feathers. Adult ospreys may also be identified individually in the field by variation in their pattern of markings on the head and breast (e.g. Bretagnolle et al., 1994), as well as calls and behaviour. Plumage markings change slightly from year to year in individual birds but still often allow individual identification. Young birds can be distinguished from adults by the light edges to the feathers on their upperparts but generally they gain full adult plumage after 18 months (Dennis, 1997). Ospreys start breeding at 3–4 years old.

Annual cycle Breeding Activity

Peak Period

Range

Site occupation and territorial display

Early April

Mid-March to early May

Nest building

Duration (days)

Late March to late May

Egg laying

Late April

Incubation

Late April to late May Mid-April to late June

Hatching

Late May

Young in nest

Late May to early July Mid-May to late August

Fledging

Mid-July

Juvenile dispersal

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Early April to mid-May 35 to 43

Mid-May to late June 40 to 59

Mid-July to late August Late August to late September Osprey

For further information on the biology and ecology of this species, Poole (1989) and Dennis (2008) provide comprehensive accounts.

2. HABITAT, HOME RANGE, NESTS AND BREEDING 2.1 Habitat Ospreys are dependent on adequate supplies of medium-sized fish. They breed near marine bays, estuaries, lochs or rivers (Cramp & Simmons, 1980). The lochs used for foraging are generally shallow and eutrophic or mesotrophic (nutrient rich or medium levels of nutrients); oligotrophic (nutrient poor) lochs do not normally support sufficient fish for ospreys. Birds often frequent fisheries and trout farms. The most suitable breeding areas are in lowland agricultural or forested areas (Poole, 1989; Thiollay & Wahl, 1998; Lohmus, 2001) but breeding ospreys can also be found in upland valleys.

2.2 Home range Ospreys do not defend a home range. They forage over a wide area and may share productive fishing sites with other ospreys, although a hierarchy of males may exist. Male ospreys regularly hunt up to 10 km from the nest, and some individual males have been known to make regular flights of around 20 km. Non-colonial (see below) ospreys defend a nesting territory against other ospreys of the same sex and from potential predators. Male ospreys are particularly active in defending the nest site, and their female, during courtship, and spend more time at the nest site when it is close to other occupied nests (Mougeot et al., 2002) in order to prevent extrapair copulations. The Scottish osprey population has increased in distinct sub-populations that have built up around an original pair in each area (Dennis, 1995; Dennis & McPhie, 2003). In some parts of central and northern Europe (and on other continents), and more recently in Scotland, ospreys form small nesting groups or colonies in which active nests may be very close together (e.g. 60–70 m apart in one North American colony; Cramp & Simmons, 1980).

2.3 Nest sites When selecting a nest site, ospreys usually choose an open position (giving clear access from above when landing) within 10 km of foraging areas (lochs, rivers or estuaries). Ospreys in northern Europe normally nest in large, mature trees (alive or dead) with flat tops (5–40 m from the ground), often selecting trees that are prominent within their surroundings. In Scotland, Scots pine is favoured, with exotic conifers and deciduous trees also used (Dennis, 1987). Ospreys will also nest on electricity pylons, and historic nest sites in Scotland include ruined buildings and rocky islands in lochs (St. John, 1863; Baxter & Rintoul, 1953). In southern Europe, ospreys nest on sea cliffs. The same nest is often used for many years (Cramp & Simmons, 1980): for example, the Loch Garten nesting range in Strathspey has been occupied for more than 50 years with three different nests being used. If eggs are lost from a nest (e.g. through illegal egg collection), ospreys normally build a ‘frustration eyrie’ within 2 km of the original nest, which may be used the following year. If eggs fail to hatch or the young die, the pair usually stays with the nest and may build it up before departure.

2.4 Nests The nest is large and requires a sizeable and firm platform for a base. It is built by both sexes from branches (of lengths up to c. 50 cm), the male bringing larger sticks than the female (Green, 1976). New nests have an average diameter of 120–150 cm and a height of 50–60 cm, but the height increases to 70–80 cm or much more after several years use. The nest cup is lined by the female with mosses, lichens or grass. Artificial nests have been built for ospreys in Scotland since 1959 and have been readily accepted (Dennis, 1983, 1987). The Osprey

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provision of artificial nests is also used regularly for osprey conservation in other countries (Poole, 1989; Saurola, 1997).

2.5 Clutch size and incubation In Scotland, ospreys lay between mid-April and mid-May (Dennis, 1983), and can relay if the first clutch is lost early in incubation (Postupalsky, 1989). Females breeding for the first or second time tend to lay later than older birds. Earlier clutches are more likely to fledge young and are generally more productive. Clutch size varies from 1–4 eggs, laid at intervals of 1–2 days. Three eggs are normally laid in Scotland, with young females generally laying two eggs in their first breeding season (Dennis, 1983). Egg size within a clutch declines as laying progresses, with the third egg, on average, 94% of the size of the first. Incubation starts with the first egg, so chicks hatching from later eggs have less chance of surviving, as they are younger and lighter than their siblings (Poole, 1989). Incubation lastes between 34-43 days (Green, 1976; Poole, 1989; Dennis, 1997) and is carried out by both sexes, with the female taking the larger share and incubating at night. Males in Scotland were observed to take 5-6 stints per day, lasting between 205-441 minutes (Green, 1976). Courtship feeding of the female by the male begins before laying and during incubation the male also forages and feeds the female 2-3 fish per day (Green, 1976; Bustamante, 1995). The male generally eats the front half of the fish and then gives the rest to the female, incubating after he has passed the food to her. The amount of time that he spends incubating increases later in the incubation period (Green, 1976).

2.6 Brood size and fledging The young hatch asynchronously. After hatching, the male increases his food delivery rate, bringing an average of five fish per day during the nesting period (Bustamante, 1995). Green (1976) describes increasing fish delivery rates of about four per day in the first 10 days, 4–5 between days 10 and 20, and 5–7 until fledging. The female tears up the fish and feeds the chicks, even after they have fledged. The female broods the young continuously for the first 10 days, and then decreasingly until the young are around 28 days old and well-feathered. She then guards them from a nearby perch (Cramp & Simmons, 1980). Older osprey chicks are not aggressive to younger siblings if well fed but, if food is short, they will prevent younger siblings from feeding, leading to their death (Poole, 1989). Some males appear to be poor providers and young regularly die in their nests. In Scotland, young ospreys fledge at 40–59 days (Bustamante, 1995), depending on food supply and brood size. Poole (1989) gives a fledging period of 5055 days for migratory osprey populations, noting that non-migratory populations fledge later.

After fledging, the young generally stay near the nest site for at least a month, receiving fish from their parents (3–4 per day, delivered mainly by the male) until becoming independent at 18–46 days after fledging (Bustamante, 1995). Larger broods tend to have shorter postfledging dependence periods but generally fledge later. The female may leave the nesting area before the young, while the male continues to supply the fledgings with fish at the nest. The oldest chick tends to leave first, with the male leaving after the youngest chick.

3. SURVEY TECHNIQUES CAUTION Disturbance should be avoided while ospreys are displaying, incubating or brooding small young. To minimise the risk of disturbance nests should be viewed from distances of 500–750 m (Ruddock & Whitfield, 2007; Whitfield et al., 2008b). Fieldworkers must ensure they are visible to adult birds when approaching and leaving a nest. Appropriate health and safety precautions should be taken if nest inspection requires climbing (see Section 7.10 of Introduction).

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3.1 Breeding season visit schedule The species is listed on Schedule 1 in Great Britain, Northern Ireland and the Isle of Man (see Section 7.1.1 of Introduction). Osprey is also listed on Schedule ZA1 of the Natural Environment and Rural Communities Act 2006 (England and Wales) which gives year-round protection to nest sites. To establish occupancy and the presence of a breeding pair, it is recommended that all four visits are made (as detailed below). However, if time is limited and a nesting territory appears to be unoccupied on the basis of the first two visits, then further visits can be omitted.

For over 50 years the growth and spread of ospreys in Scotland (and more recently in England and Wales) has been closely monitored and coverage approaching 100% has been achieved annually. With the population in Scotland now approaching 200 pairs, this level of coverage is now difficult to maintain (Etheridge et al., 2008).

Visit 1

April

To check for occupancy

Visit 2

May

To locate incubating females

Visit 3

June

To check for young in the nest

Visit 4

July to early August

To check for, and count, fledged young

3.2 Signs of occupancy 3.2.1 Locating home ranges As male ospreys feed the females during courtship, occupied nesting territories can be located by recording the flight line taken by males carrying fish. The male may take the fish to a nearby perch after catching it, and may eat part of his catch before flying to the nest. A compass bearing can be taken along the flight path, plotted on a map, and the area in the flight path checked for the nest.

Some ospreys will display over their nest site after they return from migration. The pair may ‘highcircle’ together, and the male may chase the female. More elaborate ‘fish-flight’ displays occur, such as the ‘undulating sky-dance’, in which the male carries a fish (or nest material), gives a high-pitched call repeatedly, rises steeply with pronounced wing beats, hovers briefly displaying the item in his talons and dives with wings flexed (Cramp & Simmons, 1980). Such displays may be repeated several times and are most frequent on clear, sunny days near to the nest site before the onset of incubation. They have, however, also been recorded over feeding sites and directed at intruders (e.g. people). Most males in established pairs in Scotland do not perform aerial displays but new pairs, particularly in newly colonised areas, may engage in spectacular flights.

Young non-breeding males display regularly into early August. Watches to observe such display flights should be carried out in areas where ospreys are believed to be breeding or are considered likely to breed from the availability of suitable foraging and nesting habitat. Information from local sources (farmers, foresters, gamekeepers, estate workers, local birdwatchers) may be helpful in identifying such areas. Ospreys can also be observed nest building, collecting branches from the ground or breaking them off trees and carrying them to the nest.

3.2.2 Locating roosts During the breeding season, the male and female roost near the nest before eggs are laid and the female roosts on the nest from laying until the late nesting period; the male also perches for Osprey

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long periods near the nest during the day (Cramp & Simmons, 1980). Searching for roost sites away from nests is not considered a priority when carrying out surveys of breeding ospreys.

3.2.3 Recognition of signs Ospreys eat fish, generally to the exclusion of most other prey (Cramp & Simmons, 1980). Osprey perches located in woodland will have the remains of fish below them, as well as fresh faecal droppings and moulted feathers. Such signs can be used as supporting evidence for occupancy.

3.2.4 Evidence for occupancy Sightings of an osprey, or pair of ospreys, on more than two occasions, or sightings of birds building, rebuilding or using a nest, provide evidence of occupancy. Proof of occupancy by a pair requires sightings of two ospreys together at an eyrie on more than one occasion separated by a week, or incubation by one adult, or parent(s) feeding chicks (Gilbert et al., 1998).

3.3 Evidence of breeding 3.3.1 Locating active nests Nests can be located by cold searching suitable trees (in woods, small groups or single) at any time of the year. Searches should be systematic to ensure that the whole area is checked, as ospreys can nest within 100 m of each other. Nests in large woods are more difficult to find, and a combination of search methods is often most effective (such as cold searching plus watches to observe flight lines used for the delivery of nest material or prey). Once a nest is located, a description and, preferably, a sketch map of the site should be recorded along with the location (at least a six figure grid reference), including: the tree species (or other structure) in which the nest is located; its setting (in a wood, isolated tree and so on); and the height and position of the nest. Where marking schemes exist, all adult ospreys should be checked for engraved colour rings and a note made of the colour, inscription and location of any marks.

Osprey nests can also be located by systematic aerial searches (Henny et al., 1977) from a plane, helicopter or microlight. Counts for measuring occupation by locating active nest sites should be made early in the season (mid-May), while counts to assess the number of chicks in a nest should be made in mid-July. Ewins & Miller (1995) found that helicopters were more effective than planes for counting young. Both helicopters and planes have been used successfully to find nests in Scotland but require clear weather conditions (no rain). Evening or morning light conditions are most suitable.

When checking nests for incubating birds (Visit 2), initial observations should be made from a distance with a telescope. If an osprey is flushed from a nest, the fieldworker(s) should leave the site via an open area if at all possible, so that the birds can see them leaving; trying to sneak away through woods or other cover may cause nests to fail. The adult ospreys are likely to ‘escort’ the fieldworker(s) away from the nest site. Some individual birds may leave their nests when people approach to around 500 m but birds breeding in areas with higher human populations may continue to incubate when people approach to less than 100 m. A later nest check (Visit 3) should also be carried out from a distance if possible to check for the presence of young (to prove hatching) and to estimate the correct time to climb to the nest, if there is a requirement to ring large chicks (taking appropriate health and safety precautions; see Section 7.10 of Introduction).

3.3.2 Evidence for fledging Counts of large feathered young in the nest, either during nest visits or from a vantage point, provide the most reliable measure of breeding success. If counts are made from a vantage point,

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then this is best done when young are standing on the nest, for example when they are being fed. Several such counts should be made, if time allows, to confirm the number present, in case one or more of the chicks are lying in the nest out of sight. Young can also be counted soon after they have fledged, as they remain near the nest for about four weeks before dispersing.

3.4 Evidence for non-breeding Not all pairs that occupy nesting ranges breed every year, and non-breeding is thought to be more prevalent amongst younger birds (Dennis & McPhie, 2003). If a pair or single bird is recorded in and/or displaying over a nesting range on more than two occasions but an active nest is not found, despite the appropriate number of survey visits, this provides evidence for non-breeding.

3.5 Ageing and sexing young Based on data from the United States, the length of the culmen (bill) of young increases in a predictable manner with age, irrespective of sex (Poole, 1982; Figure 28), so that chicks up to 30 days old can be aged from bill length using the equation: Age (days) = 1.74 (culmen length (mm)) – 16.49

(iv)

Ageing of young older than 30 days is not reliable by this measurement.

Also based on ospreys in the United States, female chicks can be separated from males by mass after the age of about 35 days, when females are heavier than males (Poole, 1989; Figure 29); male ospreys mature faster.

Figure 28. The relationship between culmen (bill) length and age for osprey nestlings in three study colonies in the eastern United States (Poole, 1982). Reproduced with kind permission of Springer Science and Business Media, and Alan Poole.

Osprey

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In Scotland, chicks ringed at about five weeks are sexed through a combination of weight, wing length and tarsus thickness. Females are generally well over 1,400 g (males usually less than 1,450 g), with longer wings and a thicker tarsus. As a rule of thumb, if the osprey ‘K’ ring fits snugly it is a female and if it is loose it is a male!

It should be remembered, however, that the growth rate of young ospreys can vary widely, relative to the age of young, both within a brood and between broods, dependent on the food supply. For these reasons, further measurements to record the growth of young in Britain are needed to allow more reliable ageing and sexing.

Figure 29. Change in body mass of osprey nestlings (five males and five females; Poole, 1989) with age. Reproduced with kind permission of Cambridge University Press and Alan Poole.

4. SURVEYS OUTSIDE THE BREEDING SEASON The species does not occur in Britain or Ireland during the winter.

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Peregrine Falco peregrinus 1. INTRODUCTION The peregrine (peregrine falcon) breeds throughout most of Britain and Ireland (Gibbons et al., 1993; Banks et al., 2003; Hardey, 2007). The population is largely sedentary but birds occupying less productive home ranges may move elsewhere in winter. Populations across mainland Europe become progressively more migratory further east and north. Young peregrines in their first year can travel large distances but many remain close to their natal area (Ratcliffe, 2002). Some migrant peregrines from Scandinavia winter in the UK, although the numbers involved are unknown. Female peregrines are about one-third larger than the males but it is often difficult to separate the sexes, even when a pair is seen together. Females may be distinguished by their alarm call, which is generally lower in pitch than that of the male. Fledged young are paler and browner than the adults, with a distinctive pale brown edge to their tails; and immature peregrines in their first year can be recognised by their browner plumage. Peregrines can breed at one year old but most do not breed until the age of two years or more (Ratcliffe, 2002).

For further information on the biology and ecology of this species, Ratcliffe (1993) provides a comprehensive account.

Annual cycle Breeding Activity

Peak Period

Range

Site occupation

March to July

All year (for some pairs)

Courtship display

Duration (days)

Early March to late April

Egg laying

Early April to late April

Mid-March to early May

2 to 12

Incubation

Early April to late May

Mid-March to early June

28 to 35

Hatching

Early May to late May

Late April to early June

Young in nest

Early May to late June

Late April to late July

Fledging

Late June to early July

Early June to late July

Juvenile dispersal

August to September

July to January

35 to 42

2. HABITAT, HOME RANGE, NESTS AND BREEDING 2.1 Habitat

Peregrines need open areas with a plentiful supply of birds to hunt and secure sites for breeding (Ratcliffe, 1993). A highly adaptable species, peregrines nest in a wide range of habitats, including cities. In winter, peregrines may occur in areas where they do not breed, often frequenting estuaries and other areas with large concentrations of suitable prey, although they can be seen almost anywhere.

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2.2 Home range Peregrines do not hold exclusive home ranges (Newton, 1979; Ratcliffe, 1993); their hunting ranges are extensive and overlap with those of neighbouring pairs. Most large prey is taken within 2 km of the eyrie and few birds are captured beyond 6 km (Hardey, 2007). They defend a nesting territory; with the average nearest neighbour distance between pairs in different districts of Britain varying from 2.1–9 km (Ratcliffe, 1993). Peregrines may occupy their home range throughout the year but, during adverse weather, birds in less productive habitats may move away for short periods. Non-breeders and immature birds range widely and can be found away from breeding areas.

2.3 Nest sites In Britain and Ireland, most eyries are on cliffs or crags. Peregrines tend to use the largest suitable cliffs available, although the quality of ledges for breeding is important and large cliffs will be ignored if they do not provide adequate ledges. The cliffs may be broken, a series of small rock faces, a single sheer crag or a rocky gully (Ratcliffe, 1993). Inland breeding cliffs are often above or overlooking a river or a loch. Treleavan (1998) notes that coastal eyries are often set back from the sea, in a bay or inlet, with the breeding ledge two-thirds of the way down the cliff; on the Berwickshire coast, however, most breeding ledges are on the upper third of the cliffs. The selection of the breeding ledge is made by the female (Treleaven, 1977; Ratcliffe, 1993). A cliff ledge used for breeding is usually at least 50 cm long and 50 cm wide (Ratcliffe, 1993) but ledges as small as 30 cm by 40 cm are used. The ledge will frequently be under an overhang. Aspect generally appears to have no effect on the suitability of a cliff for breeding (Ratcliffe, 1993), although Treleaven (1998) found that preferred breeding ledges on coastal cliffs gave shelter from the midday sun and were above the height reached by spray during storms; in Berwickshire most sites are oriented to the east, sheltered from the prevailing westerly winds. Peregrines will frequently re-use breeding ledges. In the absence of cliffs, Peregrines will breed on the ground, for example on steep sand banks above burns or on heathery slopes. They occasionally breed in trees (Ratcliffe, 1984), using the old nests of other species, such as raven. Eyries on man-made structures such as power stations, bridges, quarry machinery, churches and electricity pylons are becoming more common (Ratcliffe, 1993; Harwood, 2000). The extent to which altitude limits nesting sites in the UK is unclear. Several pairs breed regularly at well over 850 m in the Grampians but these may be the exception; breeding at higher altitude may result from a lack of suitable crags at lower altitude (Ratcliffe, 1993). The presence of breeding golden eagles may have a greater effect than altitude, with peregrines tending to avoid areas with active eagle nests (Fielding et al., 2003b).

2.4 Nests Peregrines do not build a nest but scrape a shallow bowl with their feet in any nesting substrate (such as soil on a cliff ledge). A typical scrape will be 17–22 cm in diameter and 3–5 cm deep (Ratcliffe, 1993); scrapes in softer soils tend to be deeper. In Britain and Ireland, the old cliff nests of grey heron, golden eagle, buzzard, raven, hooded and carrion crow have been used by peregrines for breeding, while tree nests have been found in the old nests of raven, buzzard and crow. When old nests are used for breeding, peregrines may scrape out the lining.

2.5 Clutch size and incubation Peregrines lay from mid-March until the beginning of May. Coastal birds tend to lay earlier (late March) than inland birds, and those breeding at higher altitudes lay later (early May).

Laying can be delayed for 1–2 weeks if spring weather is exceptionally cold and wet (Horne Peregrine

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& Fielding, 2002). Eggs are usually laid at 2-day intervals. Clutch size varies from 2–6, with most containing three or four eggs. The BTO Nest Record Scheme gives an average clutch size of 3.3 (n=511). The eggs are covered by the adult female before incubation starts, especially in cold or wet weather and at night. Incubation is mainly by the female, with the male’s contribution varying between pairs and the female always carrying out the night shift (Ratcliffe, 1993). Courtship feeding of the female by the male begins several weeks before egg laying, and the male provides food for the female during laying and incubation. The eggs are incubated for 28–35 days; this variation has been attributed to differences in ambient temperature and possibly to the size of individual eggs (Ratcliffe, 1993). Incubation starts with the laying of the last or penultimate egg.

Peregrines will lay repeat clutches if the first clutch is lost or deserted early on, although birds tend not to relay if the clutch is lost towards the end of the incubation period or if the home range is on less productive ground. A second clutch is usually completed 24-25 days after the loss of the first (Ratcliffe, 1993) and relaying has been recorded in late June. Repeat clutches tend to be smaller than first clutches.

2.6 Brood size and fledging Hatching is fairly synchronous, the first and last eggs usually hatching within 48 hours. The female broods small young with occasional help from the male (Martin, 1980). The amount of brooding decreases as the young grow but is essential for the first 8–10 days, as the small chicks are very vulnerable to adverse weather (Mearns & Newton, 1988; Ratcliffe, 1993; Norris, 1995; Horne & Fielding, 2002). During the first 8–10 days, the male does all of the hunting and brings food to the eyrie for the female to feed the young. Later, both parents hunt. The young receive 4–11 feeding visits per day (at intervals of 10 minutes to 6 hours), with most provisioning taking place early in the morning (starting at dawn) and in the evening (Ratcliffe, 1993). The young fledge at 5–6 weeks, with the (smaller) males fledging before the females (Parker, 1979). Weir (1978) recorded fledging at an average of 40 days in the central Highlands. Fledged young disperse from their nesting territories after a further two or more months (Cramp & Simmons 1980).

3. SURVEY TECHNIQUES CAUTION Safe observation of eyries, without disturbing the falcons, depends on the individual pair. Eyries should be observed from a distance which does not cause distress to the birds. In general, to minimise the risk of disturbance, nesting areas should be viewed from distances of 500–750 m (Ruddock & Whitfield 2007, Whitfield et al. 2008b). Pairs in remote locations may be more sensitive to human activity whereas birds in urban areas, quarries or frequently visited sites may be more tolerant of disturbance. Activities above a nest are more likely to cause disturbance than those below (Ruddock & Whitfield, 2007). If a peregrine is flushed from eggs or small chicks, it is important to allow it to return quickly as eggs or small chicks can become chilled if the adult is kept off the eyrie, especially in cold, wet weather. Visits to measure and ring chicks should be made before young are 25 days old because after this disturbance to a nest may cause premature fledging. If eyrie inspection visits require climbing, then appropriate health and safety precautions should be taken (see Section 7.10 of Introduction).

3.1 Visit schedule The species is listed on Schedule 1 in Great Britain, Northern Ireland and the Isle of Man, and Schedule II in the Republic of Ireland (see Section 7.1.1 of Introduction). To establish

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occupancy and the presence of a breeding pair, it is recommended that all four visits are made (as detailed below). However, if time is limited and a home range appears to be unoccupied on the basis of the first two visits, then further visits to that home range can be omitted.

Visit 1

March to early April

To check for occupancy. If information from previous year(s) is available nesting territories where peregrines lay earlier or have poor breeding success should be visited first

Visit 2

Late March to early May To locate active eyries (incubating birds). Peregrines in montane nesting territories and may not lay until early May

Visit 3

Late May to mid-June

To check for young and/or for evidence of breeding if no signs were seen on previous visits

Visit 4

Mid-June to early July

To check for fledged young

3.2 Signs of occupancy 3.2.1 Locating home ranges As peregrines do not hold exclusive home ranges, they are surveyed by locating occupied nesting territories. Many territories are well known because they have been used for many years (Ratcliffe, 1993). When searching a new area, data on the location of any known nest sites should be sought from other fieldworkers, ornithological literature and local people. This will provide a starting point for survey work. As the population has expanded in Britain and Ireland, peregrines have occupied new home ranges, including those with unusual non-cliff sites. Potential new nesting territories should now also be identified by cold searching the survey area. Checks should include any steep bank, buildings and man-made structures, the old tree nests of other bird species, and areas of deep heather (for ground nests). Nesting territories, known or potential, should be visited and checked for occupation in March or early April. Visits should be made in reasonable weather, as peregrines will be less obvious if they are sheltering from adverse conditions. When checking known nesting territories, priority could be given to sites with a history of failure, as these may be deserted by the birds early in the season. It may necessary to delay first visits for montane territories (above 600 m) if there is late snow-lie. These territories should be visited when the weather conditions permit a safe search.

Fieldworkers should look both for birds and for other signs of occupation including active roosts, fresh kills (several should be present if the nesting territory is occupied) and moulted peregrine feathers (section 3.2.4). A suspected nesting territory should be scanned from a distance before it is approached, from below if possible as peregrines will sit on prominent perches, often high on a cliff, and may be located by their white breasts. They may be elusive, however, and slip off a cliff unseen, especially at coastal sites. For large cliffs, watches from vantage points can be used. These should be below the skyline (for example if the vantage point is on another cliff), at least 250 m away from but with a view of the potential nesting cliff site, and ideally with the sun behind the fieldworker (Treleaven, 1998). The response of a pair of peregrines to intrusion at an active nesting territory can vary. Most will fly above the eyrie giving the loud ‘cacking’ alarm call. Some will, however, remain silent during a site visit. A few will leave the area and may watch from a distance (Ratcliffe, 1993). Peregrines can be particularly tricky to locate at coastal sites especially on extensive cliff systems and in the proximity of seabird colonies. Noise from seabirds and strong winds, and the presence of large numbers of seabirds on the wing, can affect the detectability of peregrines. As a general rule, peregrines are more demonstrative later in incubation or when they have young, but assumptions cannot be made about the nesting stage based on behaviour alone.

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Peregrines make display flights, particularly early in the spring, and usually in the immediate vicinity of the nesting territory (Cramp & Simmons, 1980). Solo birds (mainly males) perform high-circling, undulating flights (including a characteristic ‘Z-flight’, in which the bird highcircles, flies level, banks over onto one side, descends sharply, levels off again and either lands or high-circles again) and figure-of-eight flights (in which the bird generally flies from the eyrie with vibrating wings, makes a figure-of-eight circuit in the horizontal plane, often close to the rock face, and lands back at the eyrie, calling). Pairs also high-circle and flight-play (including diving at each other, steep climbs, plunging and swooping together, chasing and brief flight-rolls). During flight-rolls, partners may ‘talon-grasp’, touch momentarily breast-tobreast or even bill-to-bill (the ‘aerial kiss’). Intense displays may be facilitated by strong wind (Cramp & Simmons, 1980). Food passes between male and female may take place in the air or while perched (e.g. on a cliff ledge or tree).

If a nesting territory is apparently unoccupied, the fieldworker should look for other possible breeding sites nearby. In moorland or hill country, all crags and steep banks in the area should be searched for a scrape. If a territory is unoccupied on the coast, the fieldworker should look at all cliffs or steep slopes within 2 km on either side of the usual nesting territory. Eyries on man-made structures are more challenging. The fieldworker should visit all potential sites in the area and check for birds or fresh signs (at least two of the following: fresh prey remains; pellets; or an active roost with fresh faeces, down and moulted feathers).

3.2.2 Locating roosts Active roosting sites will have fresh faecal droppings, down and possibly moulted feathers.

On crags, they offer the roosting bird shelter and are frequently under an overhang; they may be difficult to observe unless there is a clear view of the crag. Rocks beneath roosts (and eyries) often become discoloured (lime green to white) and can be very distinctive. Peregrines may roost away from the breeding site if a sheltered, safe roost is not available nearby.

3.2.3 Recognition of signs Peregrine plucks are frequently found on knolls or prominent rocks or ridges on the breeding cliff and tend to feature medium-sized birds such as pigeons, waders and grouse (Brown et al., 2003; Ratcliffe, 1993). The leg bones are often left attached to the pelvis and the keel bone may be notched, with pieces removed as the peregrine feeds. In Ireland, measurements of almost 400 pellets produced a mean length of 39.5 mm (range 15.8–87.4 mm) and a mean width of 18.2 mm (range 10.5–30.1 mm), with colour varying markedly from grey/ white to dark brown/black (Marc Ruddock, unpublished data). Peregrine pellets, however, are not distinctive enough to be used alone as evidence of occupancy and, in common with plucks and roosts, are best used in conjunction with other evidence (sightings of birds or moulted feathers).

Racing pigeon rings are commonly found at Peregrine breeding territories, especially in and below eyrie ledges and under frequently used perch sites. These rings can remain on the ground or under the surface for many years and they can be recovered using metal detectors in non-breeding season searches. They can be used to locate old breeding sites which are not in current use. Dates of occupation can be estimated from the year of registration on racing pigeon rings, which is useful for determining long-term occupancy and population trends (Dixon et al., 2006). Registration details can also be used to identify the origin of racing pigeons killed (Dixon, 2005) and to estimate the numbers of racing pigeons taken (Dixon & Richards, 2003).

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3.2.4 Evidence for occupancy The minimum criteria are the presence of a single bird or a pair, or of fresh signs of occupation (fresh plucks, active roost site, pellets, moulted feathers) that can definitely be attributed to peregrine(s), in a known or potential nesting territory during the breeding season.

3.3 Evidence of breeding 3.3.1 Locating active nests A second visit should be made to occupied nesting territories between late March and early May, by which time the birds may have laid. If fresh signs are found or birds are flushed, it can be assumed that the area is still occupied and a nest watch should be carried out. Peregrines that are flushed should be watched to see if they return promptly to the eyrie or nest. If they do, this suggests strongly that it is active, as peregrines flushed from empty eyries or daylight resting sites generally do not return quickly. If birds have not been flushed, the eyrie can be found by direct searching or by observation from a suitable vantage point. The fieldworker should watch for a change-over at the nest site, which may be preceded by a food pass.

Watches from vantage points should be of at least 3–4 hours’ duration.

A later visit should then be made in late May or June, after any eggs should have hatched. If not located previously, active eyries containing young will be easier to find by searching or observation, or listening for the calls of the young. At this stage there will be considerably more signs on the breeding ledge, especially faecal droppings and down, and the adults will be more demonstrative.

At many sites, particularly coastal cliffs, it is impossible to see eggs or chicks in the scrape unless it is feasible to climb or abseil to the eyrie (see Section 7.10 of Introduction for health and safety considerations). If there is a need to record clutch size, incubating peregrines can be flushed from the eyrie during good weather by loud noises (clapping, shouting). Despite such disturbance, some birds may not leave their eggs until the eyrie is reached (Nethersole-Thompson, 1931).

If climbing to nests to count eggs or ring chicks, fieldworkers should ensure that they are not beng watched by other people and that their actions will not reveal the position of the eyrie.

If no intermediate visits can be made after confirming occupation, or if it is not possible to observe or climb to an eyrie, the nesting territory should be visited between mid-June and early July to locate fledged young and confirm whether breeding has been successful.

3.3.2 Evidence of fledging Ideally, a visit should be timed so that the young have left the eyrie recently and are capable of flying. The minimum number of young observed should then be recorded, ensuring that the mobile juveniles are not double-counted (i.e. record the maximum number seen at any one time, or that are definitely different individuals) and that care is taken to distinguish young from adults.

Counts of fully feathered young in the eyrie may also be used as an estimate of the number likely to fledge. Young at this stage must not be approached in the eyrie, as this may cause premature fledging (Grier & Fyffe, 1987). This can occur with chicks as young as three and a half weeks that are not even fully feathered, so visits to eyries to ring and measure chicks should be made before they reach this age and eyries likely to contain large young should be viewed from a safe distance and not approached. In the event of accidental disturbance, an attempt should be made to return prematurely fledged young to the eyrie or its proximity, if it is safe for the fieldworker to do so. Adults will usually find and feed a chick that has survived a fall but such young may be more vulnerable to predators (Ratcliffe, 1993).

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3.4 Evidence for non-breeding Peregrines sometimes do not lay, especially in cold, wet springs. They may be recorded occupying a nesting territory during early visits or throughout the season but kills will not be brought to an eyrie. The birds may still alarm during a visit but will generally be less concerned by the presence of the fieldworker. The possibility that such birds laid and failed early in incubation cannot be ruled out unless several visits are made to the nesting territory during the appropriate stage of the nesting cycle (Visit 2 period above) or the habitat is such that all potential sites for active eyries can be checked.

3.5 Ageing and sexing young Many peregrine chicks can be sexed from their relative size from the age of about 16 days (primary feathers well out of pins) because the females are substantially larger. Cramp & Simmons (1980) give the mean tarsus length for male peregrines as 46.9 mm, with a range of 45–49 mm, and for females as 53.5 mm, with a range of 52–56 mm, but few data are available to indicate whether these differences are already present when nestlings are young enough to be approached and handled without risk of premature fledging. Information from a sample of 82 Irish chicks of ringing age (c. 16–25 days; Table 7) indicates that tarsus lengths for this population are larger than those described by Cramp & Simmons (1980; see above) and also that, at this stage of growth at least, there is considerable overlap between males and females in a variety of body measurements. The data suggest, however, that a combination of mass and body size measurements might be used to sex some chicks (Table 7). Further work is required on this species to establish firm criteria for accurate ageing and sexing of chicks in the wild. Clum et al. (1996) provide photographs and detailed notes on the feather development of captive–bred peregrine chicks and White et al.

(2002) provide a formula for estimating age based on wing length.

Table 7. Sex differences in measurements of 82 Irish peregrine chicks of ringing age (c. 16–25 days). Means and ranges are shown for each sex. (Source: M. Ruddock, unpublished data).

Male

Female

Mass (g)

695.7 (576–-886)

977.3 (820–-1,120)

Tarsus length (mm)

55.8 (40.2–-62.4)

61.2 (46.4–-71.0)

Hind claw length (mm)

19.7 (16.2–-19.1)

20.5 (18.2–-22.2)

Bill length (mm)

19.0 (15.5–-19.0)

20.4 (18.3–-23.4)

Middle toe length (mm)

52.5 (45.4–-52.7)

53.4 (47.7–-58.7)

4. SURVEYS OUTSIDE THE BREEDING SEASON After the breeding season, peregrines may continue to occupy their nesting territory but may use different crags from those used for breeding. Such birds can be located by direct observations or checking cliffs within the home range for active roosts or fresh signs. It is often difficult to locate both members of a pair and it may be easier to record the number of occupied territories than the number of birds. Peregrines that do not occupy nesting territories in winter, especially young birds or non-breeders, cannot be surveyed effectively. They may occupy temporary home ranges but are often nomadic. Some birds breeding in the far north of Scotland may be local migrants, moving to unknown destinations for the winter (Ratcliffe, 2002).

Methods to provide indices of peregrine abundance in winter (e.g. via foot surveys) are likely to be difficult to implement because sightings are likely to be infrequent.

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Raven Corvus corax 1. INTRODUCTION The raven (northern raven) is abundant in the north and west of Britain and widespread across Ireland, except for the central region (Gibbons et al., 1993; Mearns, 2007). Ravens used to breed in almost every county in Britain but were eliminated from most lowland areas in the 19th century (Ratcliffe, 1997). An increase in numbers and range has occurred in Scotland and parts of England in recent years. British and Irish ravens are largely sedentary, and once established in a home range, they seldom leave it. Immature birds may form large flocks, which can roam over large areas. Ravens breeding in the north of their range in mainland Europe (Fennoscandia) are medium-distance migrants (Cross, 2002). A regular presence of continental birds in Britain and Ireland in the winter is not suspected, however, although a larger number of single birds has been found wintering in southeast England in recent years; perhaps originating from the successful reintroduction programme in the Netherlands (Cross, 2002). Adult ravens generally cannot be sexed in the field unless a pair is seen together when the slightly larger male can sometimes be distinguished from the female. Immatures can be separated from adults only in the year of hatching by their duller, often browner plumage, shorter, squarer tails, red internal mouthparts and shriller calls. Ravens may breed at two years of age but most do not start breeding until they are three or four years old.

For further information on the biology and ecology of this species, Ratcliffe (1997) provides a comprehensive account.

Annual cycle Breeding Activity

Peak Period

Range*

Occupation of home range

All year

Territorial display

All year

Courtship

January to April

Duration (days)

Egg laying

Varies by region; late February to late March

Late January to May

3 to 7

Incubation

Early March to mid-April

February to June

20 to 25

Hatching

Late March to mid-April

March to June

Young in nest

Mid-April to late May

March to July

Fledging

Mid-April to July

Juvenile dispersal

August to December

35 to 50

* Later dates are probably repeat clutches; most juveniles will have separated from their parents by three months after fledging (i.e. by the end of October; Ratcliffe, 1997).

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2. HABITAT, HOME RANGE, NESTS AND BREEDING 2.1 Habitat Ravens are found in mountainous areas and along rugged coasts. They will also breed in lowland farmland, forest and parkland (Cross, 2002). They avoid large forests and areas of intensive farmland, where there is a lack of foraging habitat or carrion. Breeding densities vary between different regions of Britain and Ireland depending on the availability of nest sites and food (Newton et al., 1982; Dare, 1986; Ewins et al., 1986; Ellis et al., 1994). Many areas with an abundance of suitable crags or trees for breeding are not occupied, as the population is apparently limited by lack of food (the availability of carrion) or absent due to the historical or current influence of persecution by game-keeping and farming interests; Gibbons et al.

(1993) found low densities in upland areas with grouse moors.

2.2 Home range Ravens occupy their home range throughout the year (Dare, 1986; Davis & Davis, 1986; Madders & Leckie, 1999). The home range is probably not exclusive (Ratcliffe, 1997) but a pair actively defend a nesting territory, excluding other ravens, apart from their recently fledged young or flocks of immature birds. Raven nesting ranges can be regularly spaced with average nearest neighbour distances (between adjacent pairs) of 2.2–7.2 km in Britain and Ireland; but there are records of simultaneously occupied eyries as close as 350 m in high density areas (Ratcliffe, 1997). A pair is generally faithful to its nesting range from one year to the next.

2.3 Nest sites Within a raven nesting range, there may be up to 14 alternative nest sites; these may be up to 1 km or more apart, although they are normally closer, often on the same crag (Ratcliffe, 1997). Ravens may use one particular nest site for several years or change site each year, to some extent dependent on the number of alternative sites available within the nesting range and sometimes on harassment by peregrines or golden eagles. Some sites are known to have been used for a long time (Ratcliffe, 1997). Nests are built on crags, in gorges, in trees, or on man-made structures, including buildings, dams, bridges, pylons and masts (Ratcliffe, 1997).

Crags are preferred if available (Ratcliffe, 1997) and nests are generally found on the largest available rock-face, usually under an overhang to give shelter. The crags used range in height from under 5 m to over 100 m. On sea cliffs, nests tend to be on the upper third (Ewins et al., 1986), well away from storm waves. Most inland crag nests are located at 200–500 m ASL, although nesting at up to 890 m ASL has been recorded in Perthshire; tree nests are located mostly on lower ground (30–300 m ASL; Ratcliffe, 1997). Ravens use a wide variety of trees for nesting but, depending on availability, they appear to prefer conifers (Ratcliffe, 1997).

Large woods are avoided because ravens need open ground for foraging. Ravens prefer to use tall trees and the nest is often placed high in the crown, 15–30 m above the ground.

Nests may also be built at the base of a limb next to the trunk or towards the end of a lateral branch. In secluded hill country, small trees may be used and nests may be placed only 3–5 m above the ground. Quarries and man-made structures are commonly used for nesting where there is a lack of natural sites, for example, in hills in central Wales and southern Scotland, ruined farms and cottages are used when crags and trees are not available. Ravens will nest on buildings that are in use (e.g. a pair bred on Chester Town Hall in 1996; Ratcliffe, 1997).

2.4 Nests Both adults build the nest, which has a number of distinct layers. The outer layer (about 20 cm thick) is made from larger sticks or woody stems 25–150 cm long and 0.5–3.0 cm Raven

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thick, which are woven together, and may be lined by a layer of thinner twigs. The twigs are in turn lined by clay, earth, roots or sometimes dung and the deep bowl formed by these layers is then lined with grass and other plant material, before a thick layer of animal hair, often sheep’s wool, is added. Nests are about 0.5 m in height and 0.5–1 m across when complete.

They become larger as they are used in successive years, reaching up to 3 m in height and over 2 m across. Such nests will persist for many years, even if the ravens abandon them. They are frequently used by falcons for breeding (gyr falcon, Steen, 1999; peregrine, Ratcliffe, 1993; hobby, Sergio et al., 2001; merlin, Tommeraas, 1993; kestrel, Village, 1990).

2.5 Clutch size and incubation Ravens usually lay 4–6 eggs (mean 4.8 eggs), with occasional clutches of one, two, three or seven eggs. Regional variation is not significant (Ratcliffe, 1997). The BTO Nest Record Scheme gives an average clutch size of 4.7 (n=427). Eggs are laid in the morning, at intervals of one or sometimes two days (Goodwin, 1986). Incubation normally starts with the penultimate or last egg, although some ravens may begin to incubate earlier. The adults sit on the eggs to cover them before full incubation starts. Most incubation is carried out by the female, fed by the male (an average of seven times a day at a filmed nest in central Wales; Ratcliffe, 1997).

She may leave the nest for short periods (usually 5–10 minutes; an average of 11 times per day at the same nest; Ratcliffe, 1997). Raven eggs are relatively small for the size of the bird and the incubation period usually lasts 20–25 days (Cramp & Perrins, 1994; Boarman & Heinrick, 1999), considerably less than that of most birds of prey. Shorter times have been recorded (17–19 days) probably for pairs that started to incubate early in the laying period (Ratcliffe, 1997). Ravens can lay a second clutch if the first is lost early in incubation. These repeat clutches are generally smaller (mean 4.2 eggs) than the first (Ratcliffe, 1997). Ravens are one of the earliest nesting birds in Britain and Ireland, and may lay eggs from late January to early May. Within any one region, individual pairs may lay the first egg at widely differing times. Occasional early laying can occur in late January (or even late December), especially in coastal regions. On Fetlar in Shetland, first-egg dates vary from 24th February to 5th May (Ewins et al., 1986). Ratcliffe (1997) cites an overall range of late February to late March. In any given region, Ravens tend to begin laying later at higher altitudes (a delay of one day for every 50 m increase in altitude in northern England, Ratcliffe, 1997), although there is still a wide spread of laying dates at each altitude.

2.6 Brood size and fledging The chicks usually hatch over two or three days (Ratcliffe, 1997). The female broods newly hatched young intensely for the first 7–10 days and less intensely for a further 10 days (Cramp & Perrins, 1994; Ratcliffe, 1997). The male may cover the nest in the absence of the female (for periods up to one hour in duration). Both adults feed the chicks; the male provides all the food initially but the female leaves the nest to collect food as the young grow larger.

Observations reported in Ratcliffe (1997) have indicated that provisioning of young is most intense from dawn until 11:00h and between 15:00h and dusk; during these periods, the young may be fed frequently (an average of 64 visits per day, of which 70% are for delivering food; range 102 visits per day at 13 days old to 36 visits per day at 35 days old). The young fledge on average after 45 days (range 35–50 days). They then forage in a family group with their parents for 2–6 months. In late spring and early summer, these family groups can be distinguished from flocks of non-breeding birds, as the full plumage (lack of moulted primary feathers) of the young contrasts with that of the moulting adults (see also Section 1 above).

Following this, the young join flocks of immature birds (1–3 years old) which move around in response to local variation in food abundance. Pair bonds are formed in these sub-adult flocks and distinct pairs may be discerned within flocks.

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3. SURVEY TECHNIQUES CAUTION Ravens should not be disturbed from nests in bad weather, particularly early in the season or when they have small young. If nest inspection visits require climbing, then appropriate health and safety precautions should be taken (see Section 7.10 of Introduction).

3.1 Breeding season visit schedule To establish occupancy and the presence of a breeding pair, it is recommended that all four visits detailed below are made. However, if time is limited and a nesting range appears to be unoccupied on the basis of the first two visits, then further visits to that range can be omitted.

Broods that have fledged early may start to disperse by early August.

Visit 1

January to March

To check for occupancy

Visit 2

March

To locate active nests

Visit 3

Early April to May

To check for young

Visit 4

Early May to early June*

To check for fledged young

* Young from early broods may be feeding well away from the nest site by early June and may be difficult to locate or count accurately.

3.2 Signs of occupancy 3.2.1 Locating home ranges Where there are known traditional nesting ranges, fieldworkers should visit areas where ravens have been seen during January to March and search for pairs or single birds near possible nesting sites. If ravens are found, a search of the area should reveal a nest or an active roost (faecal droppings, pellets and moulted feathers, normally in a sheltered place). Early in the season, adult pairs display over the nest site, and resident birds will alarm when a nesting range is approached.

The aerial display thought to be most associated with territoriality is the ‘unison flight’, in which the pair drift around together in synchronised flight, usually high in the sky, for around 15 minutes, with wings almost touching at times (Ratcliffe, 1997). ‘Flight-rolls’ are also common but may be given at any time of year and can also be given by single birds and birds in flocks. Ravens commonly soar in thermals, both when in flocks but also over nesting areas during the breeding season, which may help to locate pairs initially. All of this behaviour can occur throughout the year so that territories can also be located in autumn and/or winter.

In areas in which there is no prior knowledge of traditional nesting ranges, or where the population is expanding, systematic searches of the survey area must be made. Observations of pairs of ravens and their behaviour should be noted and all suitable crags, trees, ruined buildings, pylons or other suitable man-made structures within that area should be checked for nests or potential roosts.

3.2.2 Locating roosts Roosts can be found on crags and in woodland. Roosts are often located near to nests, even in winter, and new nests are often built near a roost site selected by a newly established pair.

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The accumulation of fresh faecal droppings (usually larger quantities than any raptor roost), associated with pellets and moulted feathers, are obvious when on crags. Fieldworkers should return in the evening, however, to confirm by observation that ravens are using the roost.

While the female is incubating, the male usually has a favourite roosting place within 100 m; and when night-brooding stops the adults will roost together (Ratcliffe, 1997).

3.2.3 Recognition of signs Raven pellets are variable in size (usually 5–8 cm long by 2–3 cm thick; Ratcliffe, 1997). Their contents can be quite different from those of most raptor species nesting in similar habitat, particularly in upland areas where raven pellets tend to contain wool, rabbit, hare or vole fur, bones and often also insects. In spring, raven pellets often contain small rubber castration rings from lambs, although these are sometimes also found in pellets of kites and eagles.

Occasionally, pigeon rings are found in raven pellets, especially near occupied peregrine sites.

Raven pellets also have the characteristic ‘musty’ smell associated with corvids (Ratcliffe, 1997). In some situations, particularly in the lowlands, the pellets may not be distinctive enough to be distinguished from those of other predatory birds (e.g. buzzard, crows) unless associated with other signs, particularly moulted feathers.

3.2.4 Evidence of occupancy A nesting range is occupied if a single raven or pair is seen on at least two occasions during the breeding season.

3.3 Evidence of breeding 3.3.1 Locating active nests Searches should be made for active nests during March but could begin from late January. In open country, ravens flying to and from their nests can often be detected by watching over an area from a suitable vantage point. Ravens can be observed nest building in fine weather. They have an extremely strong pair bond and an established pair is seldom separated. Therefore, if a single raven is seen in an area between January and April, it is a probable indication of a nest nearby. The behaviour of such birds should be studied in an effort to determine a nest’s location. A single guard bird, usually the male, will often alert his mate to any intruder with a single resonant ‘cronk’, which develops into a series of agitated barks and ‘pruks’ with increasingly agitated flying, as an observer nears a nest. Prolonged, agitated calling can mean that a fieldworker is causing disturbance to an active nest and should withdraw unless a nest visit is planned.

If a nesting range on a crag is suggested by the behaviour of a pair, nests can be found by scanning the crag from a suitable vantage point. If the nest is not visible, the behaviour of the adult birds should indicate the part of the crag on which it is situated. Traditional nest sites on crags can be located by looking for white or lime green patches beneath them where droppings have splashed onto the rock face. Ravens may share crags with peregrines and both species may be very vocal at nest sites when they are in close proximity. Tree nests can be found by searching all of the trees in the area where the adults have been seen; pellets and droppings at the base of trees give extra clues as to the location of an active nest. Man-made structures should be checked in the same way.

As nest cleaning by the adults declines and larger young eject their faces over the edge of the nest, the outer structure becomes covered in white droppings. The degree of ‘white-wash’ gives an indication of brood size and development stage (Ratcliffe, 1997).

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3.3.2 Evidence for fledging Large, fully feathered young can be counted in the nest just before fledging, or just after they have fledged when they remain close to the nest. Later they join their parents to form family groups that forage within the home range. The adults and young can be separated by plumage (Sections 1 and 2.6 above), allowing a count to be made.

3.4 Evidence for non-breeding In a study in central Wales, occupancy of known breeding territories varied from 80–89% across years, and 12% of territorial pairs failed to lay eggs, although many of these pairs built or started to repair nests (Davis & Davis, 1986). If a pair of ravens occupies a nesting range but there is no evidence of an active nest or recently fledged young after the appropriate visits, this suggests non-breeding (or early nest failure).

3.5 Ageing and sexing young More data are required to allow reliable ageing of young. Young ravens can be aged approximately by their stage of feather development. They hatch with small patches of down on an otherwise featherless body and with eyes closed. The primary feathers first emerge at around 11 days of age; by three weeks, a thin covering of feathers has developed and the characteristic heavy bill has formed; by four weeks of age the young are well-feathered although plumage development continues for a further two weeks (Ratcliffe, 1997). The eyes begin to open at 12-14 days (Boarman & Heinrich, 1999). Body mass of 6 chicks (2 wild, 4 captive) from New England increased slowly from about 25 g at day 1 to a mean of 268 g (standard deviation 87.7 ) at day 9, then more rapidly to 1,093 g (standard deviation 95.7) at day 24, before levelling off at 1,179 g (standard deviation 148.4) by day 30 (Boarman & Heinrich, 1999). Male ravens are generally larger than females but, as there is considerable overlap between the sexes and chicks in a brood vary in age, it is impossible to sex the young reliably.

4. SURVEYS OUTSIDE THE BREEDING SEASON Ravens can form large flocks of non-breeding birds (Coombes, 1948). They are believed to consist of birds not holding territory, including juveniles and older paired birds, and to be indicative of a population surplus (Mearns, 2007). Such flocks may be seen throughout the year close to areas containing breeding home ranges but they generally forage well away from occupied nesting ranges. Flocks move in response to variation in the abundance of food and may contain sub-adults that will colonise an area subsequently. On Islay, large raven flocks were associated with improved grassland and the municipal refuse tip (Madders & Leckie, 1999). Ravens will also flock to scavenge on carcasses (Ewins & Dymond, 1984; Ratcliffe, 1997). The numbers of birds in flocks can be counted as they go to roost or as they feed on the open hill.

Ravens form communal roosts, either on crags or in woods (coniferous and broadleaved).

Crag roosts can be obvious, as the faecal droppings accumulate on the rock face and pellets and feathers are found on the ground below. Such roosts are used throughout the year but the numbers of ravens present tend to be lower during the breeding season than in the winter. Roosts are thought to contain mainly non-breeding birds. Established pairs of ravens roost during the winter at or close to one of their alternative nest sites; whether any join communal roosts outside the breeding season is still the subject of debate. Ravens may forage more than 20 km from roost sites (Cramp & Perrins, 1994). Roosts can be found by Raven

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watching raven flocks in the late afternoon and noting where they go as dusk falls. Counts at roosts should be made from a suitable vantage point overlooking the roost, beginning two hours before dusk and continuing until dark. Ravens may enter a roost after dark, however, especially on moonlit nights. In Perthshire, Scotland, ravens appear to move between several large traditional roosts (10â&#x20AC;&#x201C;30 km apart). Any given roost may be used for up to five years and then vacated. Smaller roosts develop for shorter time periods (days to months), particularly where there is a good food source.

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Red Kite Milvus milvus 1. INTRODUCTION In Britain and Ireland, native red kites survive only in Wales (Cross & Davis, 1998), where the population has expanded considerably in recent years (Wotton et al., 2002). The Welsh population has been augmented recently by reintroduction programmes at several locations in Scotland and England (Evans et al., 1997; Minns & Gilbert, 2001; Carter et al., 2003; Orr‑Ewing, 2007), using stock from mainland Europe. A failed nest in County Antrim in 2002 is the first recorded breeding attempt in Ireland since the early 1800s (www.goldeneagle.ie/ birds_of_prey/index.html; Scott & McHaffie, 2002). Reintroduction programmes for red kites are now underway in Northern Ireland (www.rspb.org.uk/ourwork/conservation/projects/ nikites/index.asp) and the Republic of Ireland (www.goldeneagle.ie).

British adults are sedentary. The young often disperse from their natal area, the pattern of dispersal varying between populations (Evans et al., 2002). Young from Scotland tend to disperse in a southerly or southwesterly direction, while birds from England and Wales do not show a directional preference. Northern European birds are partial migrants: some over-winter in breeding areas, while others move into southern Europe. Populations breeding in southern Europe are sedentary, apart from juvenile dispersal (Evans et al., 2002). A small number of ringed birds from Continental breeding populations have been recorded in England in winter.

Annual cycle Breeding Activity

Peak Period

Occupation of home range Territorial display

Range

Duration (days)

All year (some pairs January to October) March to April

Can be seen all year

Courtship

March to early April

Nest building

Mid-March to late April

Egg laying

Early to late April

Late March to early May

3 to 9

Incubation

Early April to late May

Late March to early June

31 to 32

Hatching

Early to late May

Late April to early June

Young in nest

Early May to early July

Late April to early August

Fledging

Late June to early July

Early June to mid-August

Juvenile dispersal Red kite

August to September

47 to 78

c. 21 to 28 after fledging

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Male red kites tend to be smaller than females but there is considerable overlap, and the sexes are difficult to distinguish in the field. Immature birds can be separated from adults until the completion of their first full moult in the autumn of their second calendar year; they are paler than adults, with pale tips to the wing coverts, a dark iris and a less pronounced fork in the tail (Carter & Grice, 2000; Carter, 2007). Red kites usually start t o breed at 2–3 years old (Davis et al., 2001) although some birds in reintroduction areas in Britain have begun breeding at one year old (Evans et al., 1998, 1999; Orr‑Ewing, 2007). Immature red kites may hold non-breeding territories in their first summer prior to breeding elsewhere in later years, up to 30 km away (Newton et al., 1989).

For further information on the biology and ecology of this species, Carter (2007) provides a comprehensive account.

2. HABITAT, HOME RANGE, NESTS AND BREEDING 2.1 Habitat Red kites utilise mature woodland for breeding and roosting and forage over extensive areas of open ground (preferably areas with livestock and rough grazing, although some arable land may be used). They tend to occupy well-wooded farmland below 600 m ASL (Minns & Gilbert, 2001). A study in Germany (Nachtigal, 1999) has shown that the species avoids areas of deep vegetation (e.g. winter cereals) during the breeding season because prey cannot be found. Red kites were formerly widespread in Britain and it is considered that this species should be able to find suitable nesting habitat and an adequate food supply in almost all areas of lowland Britain (Evans et al., 1997, Carter & Grice, 2000). The current Scottish and English populations are associated with the habitats identified for the reintroduction programmes.

The upland valleys traditionally occupied by the relict population in Wales appear not to be preferred habitat but rather a last refuge from human persecution (Evans et al. 1997), and the increasing population has expanded into more productive habitats (Newton et al., 1994; Wotton et al., 2002).

2.2 Home Range Red kites do not defend their home range but they defend a nesting territory, centred on the active nest, against other kites, raptors and corvids. Territorial disputes between red kites are seen frequently. Red kites usually forage within 3 km, occasionally up to 6 km, from the nest (Carter, 2007; Davis et al., 2001). In winter, most adult birds remain close to their home range, where they may roost together as a pair or with a small number of other adult birds that are presumably close neighbours (Davis et al., 2001). Some birds may move to a local or regional communal roost. About 20% of first-year Scottish kites from the two established reintroduction sites disperse from early August to early November. These birds tend to move in a south-westerly direction and some have reached Cornwall and Ireland. More females than males disperse. Early in the season, red kite pairs that are apparently settled in a nesting territory may move to an alternative territory, which can be several kilometres away. It is believed that disturbance (from people or other potential predators) may be responsible for such behaviour.

As populations in England, Wales and Scotland increase, the pattern is for gradual range expansion and increasing density within the core breeding areas, with birds forming loose colonies or clusters of breeding pairs. Based on the national survey in 2000 (Wotton et al., 2002) the highest recorded densities per 10 km square were 0.58 pairs km-2 in the Chilterns, 0.18 pairs km-2 in Wales and 0.09 pairs km-2 in northern Scotland. Active nests have been found within 70 m of each other although this is exceptional.

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2.3 Nest sites Red kites nest in trees, at heights of 4-30 m from the ground, usually between 12–15 m.

In northern Scotland, they prefer mature coniferous woodland and Scots pine is the most commonly recorded tree. In the Chilterns, most nest sites are in beech trees, and in the Midlands, pedunculate oak (Carter & Grice, 2000). In Wales, most nests are in sessile oak and larch, with a range of other tree species used including beech, sycamore, Scots pine and birch. The size of woodland used for nesting varies from extensive areas to small clumps of mature trees or narrow shelterbelts. In larger areas of woodland, nests are usually located close to the edge of a wood or a clearing or ride, to allow easy aerial access.

2.4 Nests Some Welsh pairs refurbish the same nest in successive years, while others habitually build a new nest every year, which may be just a few metres from the previous one (Davis et al., 2001). Other pairs frequently move between different nest sites, up to a few kilometres apart (Davis et al., 2001). In northern Scotland, pairs that breed successfully invariably re-use the same nest. A new one is normally built only after a previous breeding failure or disturbance in early spring (such as tree felling in the nesting wood), and may be from 500 m to more than 1 km from the previous nest. In broadleaf trees, the nest is often built in a substantial fork, either next to the trunk or on a lateral branch within the canopy. In conifers, the nest is usually against the trunk but, unlike those of buzzards, red kite nests are sometimes built at the end of a thin lateral branch and appear very unstable. New nests are untidy, flattish affairs, larger than those of crows but of a similar shape. They are about 30 cm in height and up to 100 cm in diameter, with a deep cup. Occasionally they are built on the remains of another bird’s nest (buzzard, raven, crow) or a squirrel’s drey. The nests are built from dead twigs (mostly 30–50 cm long) and lined with dried grass, other dead vegetation and sheep’s wool. They may also be decorated with ‘rubbish’ (e.g. pieces of plastic, paper or rags), which may be incorporated into the nest lining. All nests in northern Scotland were lined with sheep’s wool, which may hang in festoons from the nest and nearby branches. In contrast, buzzards and goshawks never use sheep’s wool or ‘rubbish’ for their nests. Crows may use wool but their nests are smaller. Kite nests are never ‘greened up’ by adding fresh vegetation, unlike honeybuzzard, buzzard and goshawk nests. Both sexes are involved in nest building: the male brings material, which the female uses to build the nest. The nests become increasingly messy as the young grow and faecal droppings build up.

2.5 Clutch size and incubation In Britain, red kites lay 1–4 eggs. Clutches of two and three are most common in the Welsh population (Davis et al., 2001), whereas in lowland England and Scotland, clutches of three are normal (Carter, 2007). Eggs are laid at intervals of 1–3 days and both sexes incubate, with the female taking the greater part (at least 80%). The male feeds the female during incubation, although she may make very short foraging flights while the male covers the eggs. Incubation lasts for 31–32 days per egg and often starts with the second egg. Kites can lay repeat clutches if the first fails early in incubation but this is rare. Replacement clutches tend to produce fewer young than first clutches (Carter, 2007).

2.6 Brood size and fledging The eggs hatch asynchronously. The young are brooded by the female for the first 14–21 days (Carter, 2007), with the male bringing all of the food during this time (Cramp & Simmons, 1980). Nest failure is most likely to occur soon after hatching (Walters Davies & Davis, 1973), especially in cold, wet weather. In Wales, older siblings will attack and kill smaller ones when Red kite

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there is a food shortage (Lovegrove et al., 1990). CCTV observations over several years at the nest of a Scottish pair have frequently shown the oldest chick in a brood attacking the youngest whenever prey arrived at the nest, despite an apparent abundance of food. This aggression started within a few days of hatching and continued until chicks were 3–4 weeks old. Only when the eldest chick was satiated was the youngest able to feed. This behaviour did not affect survival and all young fledged successfully. Young fledge when 47–78 days old (mean of 55 days). The marked variation in fledging dates is linked to differences in growth rate caused by variation in food provisioning by the adults (Bustamante, 1993). The fledged young become independent and disperse from the nesting territory about 3–4 weeks after their first flight (Carter, 2007).

3. SURVEY TECHNIQUES CAUTION Searches for nests in woodland should not be carried out between mid-March and mid-April (once kites start to display) as disturbance at this stage of breeding may cause the pair to move elsewhere. Fieldworkers should carry out watches outside woodland at this time. Red kites are also sensitive to disturbance when laying and incubating; birds should not be flushed from nests unless there is a specific requirement to record clutch size. To minimise the risk of disturbance it is recommended that nests are viewed from distances of 150–300 m (Ruddock & Whitfield, 2007; Whitfield et al., 2008b). If nest inspection visits require climbing, then appropriate health and safety precautions should be taken (see Section 7.10 of Introduction).

3.1 Breeding season visit schedule The species is listed on Schedule 1 in Great Britain (see Section 7.1.1 of Introduction) and the Isle of Man. To establish occupancy and the presence of a breeding pair, it is recommended that four visits are made as detailed below. If time is limited, however, and a nesting territory appears to be unoccupied on the basis of the first two visits, then further visits to that territory can be omitted. A more intensive survey methodology, including an early-season visit to map potential nesting habitat in the study area and visits to record clutch size and brood size throughout the nesting period, is described by Gilbert et al. (1998).

Visit 1

March to early April

To check for occupancy

Visit 2

Late April to mid-May

To visit known nests and locate new active nests (incubating birds should not be flushed from the nest unless there is a specific need to record clutch size)

Visit 3

Late May to late June

To check for young

Visit 4

July and August

To check for fledged young

3.2 Signs of occupancy 3.2.1 Locating home ranges As red kites do not defend exclusive home ranges, they are surveyed by locating occupied nesting territories. In the spring, red kites become more obvious once they begin to display over their breeding woods, and nesting territories can be found by scanning suitable woodland areas for territorial pairs in March. A high vantage point should be chosen, if possible, to give a clear view over the area. Display flights usually involve the pair following one another and flying in an almost synchronised fashion; they may chase each other through the canopy of the wood in which they intend to nest. Birds may sit on prominent perches and call loudly to the other member of the pair, who may be soaring or perched out of sight. They will also

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chase other raptors (buzzard, osprey), crows and other kites away from the chosen nesting territory. Repeated high soaring over an area often represents territorial behaviour by an unpaired bird. Any kites seen should be checked for wing tags. The colour and position (left or right wing) of any tag should be recorded, along with any letters or numbers (these can be difficult to read if a bird is seen at a distance) and the location.

Deciduous woodland can also be checked for red kite nests in the late autumn and winter, while the leaves are off the trees, but searches for nests in woodland should not be carried out between mid-March and mid-April (once kites start to display), as disturbance at this stage of breeding may cause the pair to move elsewhere. At this time, watches should be carried out from outside woodland.

3.2.2 Locating roosts No attempt should be made to locate the roosts of breeding red kites, as this causes excessive disturbance.

3.2.3 Recognition of signs Breeding red kites commence their annual moult in May, and this continues until late summer or early autumn. The presence of moulted wing and tail feathers is usually indicative of an occupied nesting territory. Red kite pellets and faeces are similar to those of buzzard, and the presence of other signs (moulted feathers, active nests) is needed to confirm identification.

3.2.4 Evidence of occupancy During the 2000 national survey of Britain, the following behaviours were used to identify birds potentially occupying territories (Wotton et al., 2002): • Aggression towards crows, buzzards or another kite; • A calling adult kite; • Circling by an adult kite over the same area of wood for more than two minutes (only for kites circling from a low height above tree level; Viñuela et al., 1999); • ‘Curl’ flights (as described by Viñuela et al.,1999), where a hunting female returns to circle above the nest every 4-15 minutes; • Courtship flights; • A kite diving into a wood or flying within a wood below the canopy. A kite entering a wood usually performs a circling flight above the nest and often a final ‘cork-screw’ dive into the nest site; • Agitated, wing-flicking display (deep, angular wing beats with a lot of carpal flexing and an erratic zigzag flight): often undertaken when an intruder is near the nest; • A kite carrying food, but only into a likely nest site; • An adult leaving a nest site. When a kite leaves the nest, it usually appears circling over the wood from below the tree canopy; • An adult kite carrying nest material; and • High perching by a single adult, particularly in the top of a conifer or dead tree, although non-breeding birds may also perch high up.

Sightings on more than one occasion provide stronger evidence.

3.3 Evidence of breeding For the national survey of Britain in 2000, breeding was considered to have taken place if an adult was seen sitting on the nest or if young were seen in a nest (Wotton et al., 2002).

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3.3.1 Locating active nests In deciduous woodland it may be possible to see nests from outside the wood in March and April, before trees are in leaf, without the need to access the wood. Kite nests can also be located by searching woods or groups of trees of a suitable height when the birds are incubating.

Resident birds will generally soar overhead, with characteristic fast wing beats, and alarm when the nest area is approached. If a nest is found, it is often possible to leave the wood without flushing the incubating bird. Occupied nests contain fresh material in the spring and become increasingly dirty as the season progresses. Nests containing young are ‘decorated’ (Section 2.4 above) and have faecal droppings below the tree. The area of ‘splash’ around the base of the tree can give an approximate indication of the age of the young. Nest contents may be viewed with a mirror attached at a 45˚ angle on a long (up to 20 m) extendable pole. Use of such a pole should be practised away from an active nest (Gilbert et al.,1998). Successful nests can be located after fledging as the young can generally be heard calling from outside the wood.

3.3.2 Evidence for fledging The number of fledged young can be estimated from the number of large, fully feathered young (of at least 40 days old) in or near the nest. The approximate age of the chicks (Section 3.5 below) should be noted when recording brood size. Young can also be counted soon after fledging in more open sites.

3.4 Evidence of non-breeding If a single kite or a pair occupies a nesting territory but an active nest or fledged young are not found after the appropriate visits, this provides evidence for non-breeding. Recording the length of time for which adult(s) are present in a particular territory during the breeding season can help in identifying those which may have moved elsewhere to breed. Immature birds may form non-breeding pairs in their first year, at locations where they may breed in later years. Stick carrying and the building of rudimentary nests can occur in these circumstances.

3.5 Ageing and sexing young Red kite chicks can be aged approximately using wing length and bill length (Table 3). Many nestlings from the northern Scottish population (of Swedish origin) of four weeks or older (with a wing length (maximum chord) in excess of 250 mm) can be sexed using mass and tarsus width (Figure 9); in this case, tarsus width is a tight measurement with calliper jaws pressed momentarily hard closed to gain a minimum measurement (compared with the usual measurement where the calliper jaws just touch the tarsus scales). There is potential for confusion between runt females and males using this method, however (Figure 9). Red kite populations in other areas may differ in measurements.

4. SURVEYS OUTSIDE THE BREEDING SEASON The social nature of the red kite becomes apparent in winter, when large numbers gather at communal roost sites. Large roosts may contain 50-60 birds, usually comprising immature, non-breeding birds and migrants. Local breeding adults may also join communal roosts but tend to stay close to their nesting areas in winter and may roost together with neighbouring pairs. Roosts are generally in mature woodland (conifer, broadleaved or mixed) and associated with reliable food sources such as refuse tips, abbatoirs and feeding stations (Davis et al., 2001). Communal roosting may facilitate social foraging in kites: because they often scavenge at animal carcasses large enough to feed several birds, there may be advantages to searching for food in groups (Hiraldo et al., 1993). Depending on the time of year, weather, and foraging success, red kites begin arriving at roosts from mid to late afternoon (Carter & Grice, 2000).

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Table 3. Changes in the wing and bill lengths and feathering of red kite young with age (English translation of information from Robert Schronbrodt; Duncan Orr-Ewing, pers. comm.).

Age (days)

Average wing length (mm)

Average bill length (mm)

Notes

1

21.20

10.50

Grey white to white streaky head and back down.

4 6 8 10

25.00 31.00 34.50 42.50

11.90 13.20 13.80 15.20

Neck beginning to go fox red in colour; brown on shoulders disappears up to 10th day.

12

62.00

16.70

Pins of primaries and secondaries emerge from skin at 13â&#x20AC;&#x201C;14 days, as well as pins of tail feathers.

17

105.00

19.60

At 15â&#x20AC;&#x201C;18 days tips of feathers emerge from pins in paint brush style. Feathers are emerging from back down.

23

175.00

20.80

Opening of feathers.

26

209.00

22.50

Body feathers begin to cover down on body.

30

249.40

23.70

Ragged incomplete feather coverage.

35

297.00

24.40

Complete feather coverage.

40 45

343.40 375.00

25.10 25.50

Move on to branches.

48 50

397.00 417.00

26.20 26.40

Able to fly.

1300 1200

Mass (g)

1100 1000 900 800 700 5

5.5

6

6.5

7

7.5

Tarsus width (mm) Figure 9. Mass plotted against minimum tarsus width for red kite chicks from the northern Scottish population sexed using DNA analysis; for chicks with wing length greater than 250 mm (aged c. four weeks or older). Most females (solid points) are larger and heavier than males (open triangles) by this age. (Source: RSPB, unpublished data).

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Roosts can be located by visually following red kites back in the late afternoon or evening, and by collecting information from local farmers, foresters or other estate workers. Roosts should be watched from suitable vantage points from about three hours before dusk and birds counted as they enter. Counts should be made in still weather, as the birds are much more active in windy conditions, increasing the risk of double-counting.

In areas with larger and more dispersed red kite populations, foot or road surveys could be used to provide indices of abundance in winter (see Section 2 of the Introduction). These will also give information on the areas used for foraging in winter.

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Short-eared Owl Asio flammeus 1. INTRODUCTION Short-eared owls are widely distributed across upland areas of Great Britain (Gibbons et al., 1993), and small breeding populations also exist in saltmarshes and other rough grassland in lowland areas. Small numbers breed on the Isle of Man, but short-eared owls are scarce in Ireland. Short-eared owls are opportunistic wanderers (Glue, 2002b), and the numbers breeding in a given area can vary significantly between years. This latter variation has been linked to cyclical changes in the abundance of voles (Korpimäki & Krebs, 1996; Petty et al., 2000), which are their principal prey in Europe. British short-eared owls disperse from their upland breeding haunts to lower altitudes in winter, and some movement westwards to Ireland probably also occurs (Glue, 2002b). Populations breeding in northern mainland Europe are strongly migratory, while those breeding in mid-Europe are partially migrant.

Birds from these populations have been recorded in Britain in winter, although the size of the winter influx is thought to be highly variable (Glue, 2002b). The sexes are similar in size and plumage, although males generally have paler faces and underparts and are less heavily streaked. After fledging, the young are darker than the adults, until they moult in the autumn (Cramp, 1985). Short-eared owls can breed at one year old (Glutz von Blotzheim & Bauer, 1980) if there is sufficient prey.

Annual cycle Breeding Activity

Peak Period

Occupation of home range and courtship

Range

Duration (days)

March to April

Egg laying

Late April (varies with vole population and weather)

Late March to early May (earlier laying in good vole years); occasional second or repeat clutches in June/July

Incubation

Late April to late May

Late March to late July/August

Hatching

Mid-May

Mid-April to June; occasionally into late July/August for second clutches

Young in/near nest

Late May to late June

24 to 29

Late April to August/September

12 to 17

Fledging

Late May to June; occasionally August/September for second clutches

At 24 to 27 days old

Juvenile dispersal

Late June to September

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2. HABITAT, HOME RANGE, NESTS AND BREEDING 2.1 Habitat In the breeding season, short-eared owls require an extensive tract of open land, with an adequate small mammal population. Habitats used include heather moorland, rough grassland in upland and lowland areas, young forestry plantations, bogs, and sand dunes and salt marshes near the coast (Glue, 2002b). In winter, they occupy similar habitats at lower altitudes, though not necessarily as extensive in area.

2.2 Home range In years when voles are abundant, short-eared owls are thought to defend exclusive home ranges (Clark, 1975; Mikkola, 1983) and hunt within this range. When the food supply is poor, however, and when they are feeding young, they will hunt outside of this defended area (Cramp, 1985). Studies in Scotland and Wales have reported home ranges of 18-875 ha with a similar range of sizes reported from Europe and a larger area (4,600 ha +) from a study in Idaho (Cramp, 1985; Calladine et al., 2005). Breeding density of short-eared owls varies between years with high densities associated with years of high vole abundance. In Britain, breeding densities of at least 5 pairs per 10 km square of suitable habitat were estimated for years of plentiful food supply by Gibbons et al. (1993). An analysis of short-eared owl records collected during the 2004 hen harrier survey suggested respective densities of 1-1.5 and 2-3 apparently occupied territories per 10 km square in Scotland and Wales respectively (Calladine et al., 2005). Home range occupation by short-eared owls is likely to be weather dependent and may be delayed by snow or by prolonged periods of rain.

2.3 Nest sites Short-eared owls nest on the ground. The nest is usually placed in heather, tall rushes, grass or bracken, and may be located under a tussock, next to a boulder, or under a fallen or young tree. They are widely reported as nesting within young plantations. A one-year study in southwest Scotland (Shaw, 1995) found that both first and second rotation plantations were occupied, with first rotation plantings supporting breeding short-eared owls for up to 12 years after planting. The highest densities were found amongst 3–7 year old plantings. The smallest occupied coup for second rotation planting was 62 hectares. In mainland Europe, short-eared owls also breed in cereal fields when vole numbers are high.

2.4 Nests The short-eared owl is the only Palaearctic owl to build a nest regularly. The nest consists of a shallow scrape, roughly lined with pieces of short (3–6 cm) vegetation (Mikkola, 1983; Cramp, 1985). Of a sample of 33 nests in Perthshire, Scotland, however, two were built (to 6 cm high) and contained sticks up to 12 cm long. Clark (1975) watched a female making a scrape and then lining it. There is no evidence that the male helps to build the nest.

2.5 Clutch size and incubation Clutch size may be greater in years when voles are abundant. The normal range is 2–8 eggs (Cramp, 1985), with exceptional clutches of up to 14 in good vole years (Adair, 1892). In Perthshire, Scotland, however, good vole years appear characterised by an increased density of breeding owls rather than larger clutches (with clutch sizes consistently 5–7 eggs). The BTO Nest Record Scheme gives an average clutch size of 5.4 (n=56). Incubation starts with the first egg and lasts for 24–29 days (average 26 days) for each egg (Mikkola, 1983). Eggs are laid at daily intervals. The female incubates and broods small chicks, whilst being fed by the male (usually at the nest, with the first feed delivered around nightfall; Roberts & Bowman,

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1986). Laying occurs earlier in good vole years than poor ones (Mikkola, 1983). Short-eared owls will relay as late as June if a first clutch fails. Second broods have occasionally been assumed (nests with eggs as late as July) in good vole years but an intensive study in Perthshire (including two exceptional vole years) has found no evidence for double broods.

2.6 Brood size and fledging The eggs hatch asynchronously and the larger first-hatched chicks have a better chance of survival than the others. Cannabalism among siblings may occur if food is scarce (Mikkola, 1983; Cramp, 1985). Once they are about a week old, the young may be fed during the daylight hours, although one study on moorland in Wales suggested that most feeds occurred after 17:00h and before 08:00h (Roberts & Bowman, 1986). At a nest with young in Scotland, activity peaks were recorded 2-3 hours after sunrise, early in the afternoon, and 0-2 hours after sunset; with visits continuing throughout the night (Cramp, 1985). The provisioning rate has been recorded as 2.1–3.9 voles per day per chick (Cramp, 1985). Once brooding is complete, the male and female feed the young. The chicks will leave the nest and hide in surrounding vegetation at 12–17 days old (Witherby et al., 1940); when they may scatter and move up to 100 m away. The young continue to be fed by the parents until they fledge at 24–27 days old (Witherby et al., 1940) and start to disperse from the nesting area some weeks later.

3. SURVEY TECHNIQUES CAUTION Short-eared owl nests should not be visited in cold, wet weather. It is recommended that vantage points for viewing short-eared owls are situated at least 500 m from areas of activity / nests to minimise the risk of disturbance. Surveys in 2006 and 2007 from fixed vantage points found that the detection distance of owls increased from about 500 m in the first year to just over 700 m in the second, suggesting that some owls may have shifted their centres of activity further from observers in the second year of the study (Calladine et al., 2008). Further evidence from the same study of a potential deterrence effect of observers was suggested by the fact that owls rarely came within 200 m of fieldworkers. It is therefore recommended that surveyors working on this species strive to be as unobtrusive as possible.

3.1 Breeding season visit schedule The species is listed on Schedule 1 in Northern Ireland and the Isle of Man and on Schedule II in the Republic of Ireland (see Section 7.1.1 of Introduction). Given the difficulty of surveying this species to establish occupancy and the presence of a breeding pair, it is recommended that all four visits are made (as detailed below). Broods that have fledged early may start to disperse by late June.

Visit1

Early March to mid-April

To check for occupancy [but see 3.2.1]

Visit 2

Mid-April to May

To locate active nests

Visit 3

June

To check for young (dispersed or still in nest)

Visit 4

July

To check for fledged young and any late nests

Short-eared owls are difficult to survey. There may be large year-to-year variation in the numbers of breeding birds present in an area, the adults may be visible for only a small proportion of the daylight hours, and nests are hard to locate.

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Short-eared owls can be active at any time of the day or night although the proportion of diurnal, crepuscular and nocturnal activity may vary throughout the year. In a study involving a small sample of short-eared owls on Orkney, adults were found to synchronise their hunting to threehourly cycles of activity shown by Orkney voles throughout the day (Reynolds & Gorman, 1999), although daylight hunting was conspicuous only in the spring and summer. Intensive fieldwork in three study areas in Scotland and across two breeding seasons (Calladine et al., 2008) showed that adult owls were visible for less than 5% of the daylight hours from March to July, and that the most reliable times to detect the owls varied with stage of breeding (see 3.2.1 below). The chances of seeing short-eared owls may also be higher after prolonged periods of heavy rain.

3.2 Signs of occupancy 3.2.1 Locating home ranges Observations should be made from suitable vantage points overlooking the area to be surveyed. To cover an area comprehensively, no part of the area should be more than 750 m from a vantage point (Calladine et al., 2008). On the first visit to a new survey site, areas unsuitable for hunting and breeding can be usefully marked on a map and excluded from further survey (Gilbert et al., 1998).

From March to mid-April (the settling period), encounter rates during the daylight hours are likely to be very low: in an intensive study, adult owls were only visible for 1-2 minutes per hour of watching (Calladine et al., 2008). Hence in order to detect pairs that do not go on to lay, many hours of observation or night vision equipment may be required. From mid-April to May (the incubation period), short-eared owls are most detectable in the four hours before dark or (to a lesser extent) in the four hours after first light. Two 2-hour watches from each vantage point in the four hours before dark are recommended in order to have a 75% chance of detecting breeding owls during incubation. In June (the main chick rearing period), shorteared owls are more visible throughout the daylight hours; two 2-hour visits in the morning (up to 8 hours after first light) or evening (from 4 hours before dark) are recommended to maximise the likelihood of detection. In July, when most broods fledge, adults are most active 2-8 hours after first light and less so in the evenings (Calladine et al., 2008).

The male short-eared owl carries out an elaborate display which may last up to an hour (Clark, 1975). It involves rapid ascent flights in tight circles with rhythmic wing beats (wings appearing to pause momentarily at the end of the downstroke and ‘bounce back up’ into the upstroke), interspersed frequently with ‘wing-clapping’, during which the bird loses height and may appear to ‘drop like a stone’ (Mikkola, 1983). As the bird gains height, it may wing-clap less and soar or hover, giving a characteristic advertising call. It may descend with shallow glides, each ending in a wing-clap before the ascent begins again. Such a display culminates in a near vertical stoop, with ‘rocking-flight’ (rolling from side to side with wings held in a deep ’V’ shape). Displaying short-eared owls may not always go on to breed. Two birds flying parallel, showing ‘wingclapping’, ‘V–flying’ or talon-locking may indicate males from two separate territories.

In Welsh moorland, few short-eared owls were seen actively hunting within 500 m of nests (Roberts & Bowman, 1986), whereas in young coniferous plantations in Dumfries and Galloway they generally remained within the coup used for nesting (Shaw, 1995).

For the purposes of estimating the number of territories in a given area, it is recommended that fieldworkers plot their observations of flightlines and behaviour (in particular behaviours indicative of territory holding or breeding, see 3.2.4 and 3.3 below) on large scale maps (Calladine et al., 2008).

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3.2.2 Locating roosts The daytime roosts of breeding short-eared owls are found in deep vegetation close to the nest. To avoid unnecessary disturbance, searches for these roosts are not recommended.

3.2.3 Recognition of signs Short-eared owl pellets may be found below posts and prominent features in the landscape (boulders, knolls). They are generally rounded at one end, tapered at the other and grey in colour (length = 22–82 mm; width = 11–32 mm; Glue, 1977b; Mikkola, 1983; Brown et al., 2003). They are similar in size to those of long-eared owls and cannot usually be separated reliably, although in open habitats, well away from trees (with the exception of very young trees in plantations), any pellets found are likely to be from short-eared owls.

3.2.4 Evidence of occupancy Occupation of a home range by short-eared owls and evidence for breeding (3.3 below) can be determined from behavioural observations as follows, representing ascending evidence (modified from Shaw, 1995; Gilbert et al., 1998; Calladine et al., 2008): Possible territory / breeding (a) Owl(s) seen in flight in transit (not hunting). (b) Owl(s) seen using an area for hunting.

Probable territory/ breeding (c) Owl(s) seen perched. (d) Owl(s) carrying prey. (e) Courtship display (wing-clapping).

Confirmed territory/breeding (f) Owl(s) giving alarm calls or mobbing potential predators. (g) Owl(s) repeatedly carrying prey into an area. (h) Active nest located. (i) Recently fledged young owl(s) seen.

Owls perched on moorland or posts in the open between March and May may be male birds in close proximity to females during the egg-laying or early incubation period (Calladine et al., 2008).

3.3 Evidence of breeding Observations equivalent to categories (f) to (i) in Section 3.2.4 above provide evidence for confirmed breeding (Calladine et al., 2008).

Behaviours indicative of territory holding and / or breeding may be seen relatively infrequently: of 464 sightings of short-eared owls over two breeding seasons, 162 (35%) involved such observations (Calladine et al., 2008). Of these, 53% involved birds sitting in the open for more than 30 minutes during daylight hours between March and May, 20% mobbing of predators, 17% birds carrying prey, 7% wing clapping and 3% fledged juveniles.

3.3.1 Locating active nests Areas over which short-eared owls have been observed (in particular areas where behaviours indicative of a confirmed territory have been recorded) should be watched from suitable vantage points that give a clear view of any possible nesting areas. During incubation, male short-eared owls may feed the female twice during daylight hours. There may be a higher Short-eared owl

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chance of sightings during the evening as the male may only feed the female in the morning if hunting the previous night has not been sufficiently productive (see 3.2.1 above).

During watches, hunting short-eared owls should be located and followed. When they catch prey, short-eared owls dive straight down into the vegetation. If a bird rises quickly, then it may have failed to make a kill and will resume hunting. If a kill has been made, the bird will often remain on the ground for several minutes. The prey will either be eaten or carried back to the nest (in the bill or feet).

Males carrying food fly directly towards the nest, usually at a greater height than usual. They normally deliver prey to the female at the nest although the prey may be dropped on the nest or, occasionally, the female may fly to the male to receive the food (Clark, 1975; Mikkola, 1983). As the male approaches the nest, he will usually land about 100–200 m away, apparently checking for the presence of potential predators such as corvids or other hazards (including people). The female may call from the nest encouraging the male to feed her. The male will then fly and/ or walk to the nest, usually disappearing completely into the tall vegetation and rising quickly without the prey. Sometimes a male that has been hunting will make a high, direct flight and a ‘gentle shiver’. If this behaviour is seen, the nest may be located directly beneath. It may be used by males that have been unsuccessful at hunting to alert the female that they are still around.

The ‘gentle shiver’ is not the vigorous ‘wet spaniel shaking itself’ used in courtship but a briefer action, although still obvious when seen through binoculars.

Hunting male owls may also cache prey. In this case, the male will be on the ground for a few minutes — longer than a rapid nest visit. Laying a cache of surplus food close to the nest may be a means of controlling juvenile cannabalism when prey is abundant (Ingram, 1959). Both adults may cache prey once the female stops brooding the young.

Based on visits by the male and/or sightings of a female, the likely position of a nest in relation to at least three local features should be carefully recorded by taking a digital photograph and/or making a sketch map. A search can then be made. Female short-eared owls will not flush easily when incubating or when brooding small young.

Both parents feed the young once the female has stopped brooding and after they have left the nest. As the chicks grow, the frequency of feeds increases and they will occur later in the morning and earlier in the evening than during incubation.

Adult short-eared owls may also reveal the location of a nest or fledged chicks by hovering above a visiting fieldworker and vocalising (‘barking’).

3.3.2 Evidence for fledging It is difficult to obtain accurate counts of brood size and the number of fledgings for shorteared owls, because the young hatch asynchronously and leave the nest about 10 days before they fledge. Counts of young before they disperse from the nest (to record brood size) can be made if the nest is found during incubation, by making a series of visits 2–3 days apart.

Young often die shortly after hatching however, and it cannot be assumed that small chicks will survive and disperse.

Dispersed young can be counted by observing the adults feeding them during a single evening or morning watch. They attract the attention of the adult carrying food with a ‘begging display’ (Clark, 1975), which involves calling, ruffling the body feathers, and vibrating wings close to

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the body. The young may also rotate and flap their wings to expose the more conspicuous underwing (Cramp, 1985), and may make a hissing call (not unlike the sound of cold water falling onto a hot stone). The adults either drop the food directly to the chick or land beside it and pass the food. These displays are very obvious and often mean that several chicks can be located as they respond to the adult. The position(s) of young should be carefully noted during the watch, in order to assess the minimum number present. The extent of down and the degree of development of flight feathers should be recorded as these can be used to estimate how soon an owlet is likely to fledge.

Brood size at fledging can only be estimated by counting flying young hunting over the home range shortly after they fledge. This gives a minimum figure because it is unlikely that all the fledged young will be observed, particularly if the home range is extensive.

3.4 Evidence for non-breeding Non-breeding is common in short-eared owls, and is particularly associated with years of low vole abundance. Distinguishing between breeding and non-breeding in this species where behaviours indicative of breeding are observed infrequently (see 3.3 above) is particularly difficult. If a pair of short-eared owls is recorded occupying a home range, and no evidence of breeding is obtained despite several visits involving watches of sufficient duration at appropriate stages of the season, then it is possible that breeding has not taken place. If this is the case, territorial and courtship behaviour will decrease and the owls may disperse before the end of May.

3.5 Ageing and sexing Limited data on ageing nestlings are available for a small sample of birds (two male and three female chicks) from a single brood of French birds reared in captivity (Arroyo et al., 2000).

These data suggest that nestlings up to 15 days old can be aged approximately, regardless of sex, from the equation: Age (days) = (Mass (g)+15.6)/18.2

(vii)

and chicks older than 15 days can be aged, regardless of sex, by measuring wing length, from the equation: Age (days) = (Wing length (mm)+30.1)/7.6

(viii)

From a larger sample of young, including nestlings measured in the field, Arroyo et al. (2000) demonstrated differences in growth rate between males and females, concluding that males and females should be aged separately if their sex can be determined (see below). Based on the same small samples of young (two males and three females), they provide the following equations for ageing chicks of more than 15 days old: Female age (days) = (Wing length (mm)+42.2)/7.9 Male age (days) = (Wing length (mm)+28.6)/7.9

(ix) (x)

These data require corroboration with a larger data set to confirm their generality but might be used to age young approximately.

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to dispersal from the nest is shown in Figure 42. A brood of three short-eared owl chicks of varying ages is shown in Plate 79.

Figure 42. Nestling growth of short-eared owl from hatching to dispersal. Age (in days) of chicks from upper left to lower right: 1-3, 5, 7, 9, 11, 13, 15. Drawings by Leslie A. Leroux.

From Wiggins et al. (2006); reproduced with kind permission of Birds of North America online (http://bna.birds.cornell.edu) and the Cornell Lab of Ornithology.

From 10–15 days old, some chicks and juveniles can be sexed by examining the markings on the secondary feathers (Arroyo et al., 2000). The underwing of males is paler with fewer thinner, dark transverse lines than that of females (Figure 43). In males (n=7), the average number of transverse lines per secondary feather was 2.4 ±0.5 (SD) with a range of 2–3, while the females (n=9) had an average of 3.7 ±0.7 (SD) with a range of 3–5. Transverse lines were also thinner on males and did not reach the edge of the feather (Arroyo et al., 2000; Figure 43).

The upper side of the secondary feathers is also distinct. Males show a clear contrast between the pale ochre bands on the outer web and the pure white of the inner web. Females have a darker inner web: near the rachis, the colour is similar to the ochre of the outer web and fades to dirty white near the edge of the feather. In addition, the white tips of the secondary feathers are much larger in the male (Figure 43).

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Figure 43. Secondary pattern in male and female short-eared owl nestlings. Drawings of the outstretched wings show the ventral view (underside) of the wing. Single feather drawings show the dorsal (upper) view of a secondary feather. Note the overall paler secondaries in males, and the clear contrast in the dorsal side of the feathers between the pale bands of the outer web (which are ochre) and the inner web (which is pure white).

From Arroyo et al. (2000); reproduced with kind permission of the Cooper Ornithological Society; copyright, Cooper Ornithological Society.

4. SURVEYS OUTSIDE THE BREEDING SEASON Short-eared owls may roost communally outside the breeding season (Glue, 1977b). Numbers vary considerably from year to year but individual roosts can hold as many as 30–40 birds (Clark, 1975). Typical roost sites overlook the surrounding hunting ground and have been found in grass-covered seawalls, in clumps of small trees or shrubs, in coarse grasses in recently afforested ground or sheepwalk, in deep heather and in reeds (Glue, 1977b). Short-eared owls may use the same roosts as hen harriers (Dickson, 1992). Wintering short-eared owls are primarily crepuscular and nocturnal (Bosakowski, 1987). They normally leave their roost after sunset but earlier departures tend to occur on heavily overcast days. The locations of roosts can be found by watching for concentrations of short-eared owls returning in the early morning or leaving in the evening; and numbers of birds using roosts can be counted by watching from a suitable vantage point as they leave the roost in the evening (Bosakowski, 1987).

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Snowy Owl Bubo scandiacus 1. INTRODUCTION Snowy owls have a circumpolar distribution, breeding in Fennoscandia, Arctic Russia, Alaska, northern Canada and northeast Greenland. They are highly nomadic and may migrate southwards in the winter, when a few may reach Britain and Ireland. The numbers of owls that are found in winter in southern areas may be linked to cyclic fluctuations in small mammal populations in the Arctic, with more individuals coming south when populations crash (Gross, 1947). Breeding has been recorded in Scotland and Ireland. A pair of snowy owls bred successfully on Fetlar in Shetland from 1967 to 1975 after which time the male disappeared and was not replaced, although 2-4 females were regularly recorded on the island in subsequent years and infertile eggs were laid several times (Thom, 1986; Gibbons et al., 1993; Pennington, 2007). In Ireland, a pair bred unsuccessfully in Glenveagh National Park in Donegal in 2001 and there is also anecdotal evidence that a pair bred successfully in West Donegal in 1999, with reports from local people of five white owls in an area where an adult pair were photographed. Birds have summered in other parts of Scotland and Ireland but breeding has not been recorded. The snowy owls that bred in Shetland were sedentary. Male snowy owls are whiter and smaller than the females. Immature birds can be distinguished from adults by their heavy barring until they moult at one year of age (Cramp, 1985; Mikkola, 1983). The age of first breeding is not known but is probably not until at least two years old (Cramp, 1985).

Annual cycle Breeding Activity

Peak Period

Range

Occupation of home range

All year (Shetland)

Courtship

Early April to mid May

Duration (days)

Laying

May

May

2 to 26

Incubation

Early May to mid June

Early May to mid June

30 to 34

Hatching

June

June

Young in nest

June to July

June to July

14 to 28

Fledging

July to August

At 43 to 50 days old

Juvenile dispersal

September

Note that most of the timings given here do not refer to Britain and Ireland but they should still give a reasonable approximation; exact timings are very variable across the breeding range, depending on snow thaw.

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2. HABITAT, HOME RANGE, NESTS AND BREEDING 2.1 Habitat In the Arctic, snowy owls breed in low open tundra, often near the coast (Cramp, 1985). In Norway, they breed on mountain plateaux at 1,100–1,500 m ASL (Bannerman, 1955). They avoid damp areas and use dry hummocks, tussocks and rocks as perches (Cramp, 1985). In Britain and Ireland, snowy owls have frequented arctic/alpine mountain plateaux and heather/ grass moorland as well as coastal farmland and machair.

2.2 Home range In the breeding season, the size of the home range varies with the food supply; in suitable terrain with a favourable food supply, it can be as small as 75 ha (Watson, 1957). Only the immediate nesting territory is defended. Snowy owls are solitary in winter. In Canada, males tend to be nomadic, while females defend territories of 150–450 ha in extent for periods of up to 80 days (Boxall & Lein, 1982).

2.3 Nest sites Snowy owls nest on the ground, normally on a raised hummock, rocky outcrop or ridge where the snow melts early.

2.4 Nests The nest is a slight scrape, which may be lined with small pieces of vegetation. Nests are not normally re-used in successive seasons (Watson, 1957). The nests in Shetland were on open moorland with grass, heather and rocky outcrops (Sharrock, 1976). in Glenveagh, Ireland, the nest was in blanket bog on the slope of a raised valley with rocky outcrops and dry heath nearby.

2.5 Clutch size and incubation Clutch size varies with the availability of food and ranges from 2–14 eggs (normally 3–9). The pair that bred in Shetland produced one clutch of four eggs, four clutches of five eggs, three clutches of six eggs and one clutch of seven eggs (M. Robinson in Cramp, 1985). In Ireland the pair which bred in Glenveagh in 2001 laid four eggs. The eggs are laid at 2-day intervals and are incubated for an average of 32 days (range 30–34 days) (Mikkola, 1983; Cramp, 1985). Incubation, which begins with the first egg, is carried out by the female who is fed on the nest by the male (Cramp, 1985).

2.6 Brood size and fledging The eggs hatch asynchronously and the young are brooded by the female for about 21 days (Cramp, 1985) or until they leave the nest. The male provides food to the female who feeds the young (Mikkola, 1983), with both sexes foraging for food once the young are well-grown.

There is evidence that the male may feed chicks once they have left the nest (Taylor, 1973); in Shetland, large young took prey from the male but he was often prevented from feeding young by the female (Tulloch, 1969; Mikkola, 1983). At one nest in southern Norway, prey items were delivered every 10–15 minutes between 23:00h and 01:00h (Hagen, 1960; cited in Mikkola, 1983 and Cramp, 1985). In Shetland, 91% of prey items were brought to young between 18:00h and 06:00h, and 60% of these were between 21:00h and 03:00h (Tulloch, 1969). From 14–28 days of age, the young may leave the nest and hide in the surrounding vegetation. They fledge at 43–50 days (average 45 days, M. Robinson in Cramp, 1985) but do not become independent for at least a further 2–5 weeks.

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3. SURVEY TECHNIQUES CAUTION Snowy owls should not be disturbed during laying or incubation. Due to the rarity of the species within Britain and Ireland, all observations on the breeding of this species should be made from a distance, unless there is a specific need to collect information on clutch or brood size.

3.1 Breeding season visit schedule The species is listed on Schedule 1 in Great Britain (see Section 7.1.1 of Introduction). It is recommended that at least two visits (Visits 1 and 4) are made to confirm occupancy and breeding, even if no signs of occupancy are found during the earlier visit(s). Snowy owls are most active between dusk and dawn although during midsummer at high latitudes they must also hunt by daylight. They can be located by searching for roosting birds (which are often conspicuous) during the daytime. Visits to view active birds should be made during the evening or early morning.

Visit 1

April to early May

To check for occupancy

Visit 2

May

To locate active nests

Visit 3

June to July

To check for young

Visit 4

August

To check for fledged young

3.2 Signs of occupancy 3.2.1 Locating home ranges Snowy owls are large and conspicuous and can sit motionless for long periods. Male snowy owls carry out display flights (usually when the female is close by), involving flying with wings held in a deep ‘V’ at the top of each stroke, causing undulating flight, with drops of 1.5–3 m between down-strokes. Such flights are probably most frequent and complete early in the season, may involve the male carrying prey, and may be followed by a ‘mantling display’ on the ground once the prey is dropped (Taylor,1973; Cramp, 1985).

Once a pair of owls has been seen or is suspected to be present, the fieldworker should search the area systematically, checking all rocky areas for sitting birds. The location of any snowy owl signs (moulted feathers and pellets) should also be noted. Searches are easier if there is no snow and snowy owls will use the first areas to become clear of snow.

3.2.2 Locating roosts Snowy owls roost on the ground during the day and are large and conspicuous enough to be seen from some distance.

3.2.3 Recognition of signs Snowy owl pellets are large, (49–153 mm long x 20–43 mm diameter), irregular and loosely compressed, containing large bone fragments from prey such as rodents, rabbits and birds (Mikkola, 1983; Cramp, 1985; Brown et al., 2003). They are distinctive in that they often contain snowy owl feathers.

3.2.4 Evidence for occupancy Sightings of a single bird or a pair on several occasions within the same area provide evidence for occupancy.

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3.3 Evidence of breeding 3.3.1 Locating active nests Snowy owls normally nest on dry hummocks or ridges, where the snow melts early. Systematic searches of all suitable areas should be made with appropriate care taken to avoid disturbing incubating females. During the day, the male may be found perched near to the nest. Nests may also be located through observations of hunting owls in the evening or early morning when snowy owls may carry prey directly back to the nest. Even if the owls are not observed going as far as the nest, the direction in which the prey is carried can suggest where searches should be made subsequently.

3.3.2 Evidence for fledging Counts can be made of recently fledged chicks close to the nest, and they are particularly conspicuous when an adult brings prey. Before fledging, large young are more difficult to count, as they leave the nest and hide.

3.4 Evidence for non-breeding If a pair of snowy owls occupies a nesting territory, and an active nest or fledged young are not found despite comprehensive searches at the appropriate times, then this provides evidence for non-breeding.

3.5 Ageing and sexing young No measurement data for ageing and sexing young have been found. As a guide, the white first down is replaced by grey second down from 5-10 days, and chicks appear grey from 8-14 days (Cramp, 1985). At 10 days old the face is dark grey with a characteristic white X-mark between the eyes, which looks more obvious by 18-20 days, and then gradually disappears as white feathers grow in over the face (Cramp, 1985; Mikkola, 1983; Figure 39). For developing chicks on Shetland, Tulloch (1969) reports that the eyes were fully open by 9 days and by 23 days the irides were the same golden yellow as the adults; the whitish primaries and tail feathers were visibly sprouting by about 30 days.

Figure 39. Facial patterns of young snowy owl at 10 days (left) and 18 days (Mikkola, 1983; reproduced with kind permission of A & C Black).

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4.â&#x20AC;&#x201A; SURVEYS OUTSIDE THE BREEDING SEASON The number of snowy owls holding winter territories in an area can be surveyed using the methods in Section 3.2.1. Snowy owls have crepuscular and nocturnal foraging habits in the winter, remaining largely inactive during the day (Boxall & Lein, 1989).

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Sparrowhawk Accipiter nisus 1. INTRODUCTION The sparrowhawk (Eurasian sparrowhawk) is one of the commonest and most widespread birds of prey in Britain and Ireland (Gibbons et al., 1993; Newton, 2002). Its absence from some northern and western areas is probably due to the lack of suitable woodland and scrub for nesting, rather than a lack of small birds for prey (Gibbons et al., 1993). Adults are sedentary in Britain and Ireland. Juveniles disperse in their first autumn before settling in a home range (Newton, 2002). Scandinavian breeding populations are migratory and many individuals cross the North Sea to winter in Britain, while others pass through and move on to southern Europe (Newton, 1986, 2002). Sparrowhawks show marked sexual dimorphism with females 60-100% heavier and 15% larger in leg and wing length than males (Moss, 1979).

Adult males are distinctive in the field due to their blue-grey backs and rufous underparts.

Adult females have dark grey-brown backs and barred brown underparts. Immatures have brown backs with a scaly appearance due to pale-tipped feathers, and the feathers of the underparts have terminal spots rather than bars so they appear more streaked than barred.

Sparrowhawks can breed at one year old, whilst still in immature plumage.

For further information on the biology and ecology of this species, Newton (1986) provides a comprehensive account.

Annual cycle Breeding Activity

Peak Period

Range

Occupation of home range

All year

Territorial display

October to June Most frequent in March and April

Nest building

February to May

Courtship

March to May

Duration (days)

Laying

Early May

Late April to early June

4 to 10

Incubation

Early May to mid-June

Late April to early July

33 to 35

Hatching

June

Late May to early July

Young in nest

Early June to mid-July

Late May to early August

Fledging

July to August

Juvenile dispersal

August to September

Sparrowhawk

24 to 28

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2. HABITAT, HOME RANGE, NESTS AND BREEDING 2.1 Habitat Sparrowhawks prefer to breed in mature woodland but in the absence of woods they can also nest in scrub, windbreaks or scattered trees. They are found nesting in city parks and other urban areas. Their foraging areas are diverse and range from dense forest to open country, as long as they support suitable populations of small birds.

2.2 Home range In Britain and Ireland home ranges are occupied all year round. Home range size is influenced by season, habitat, food supply, sex and social status (Marquiss & Newton, 1981; Newton, 1986; Selas & Rafoss, 1999). Throughout the year, the nesting range provides a focus of activity and a roosting area for established birds. During the breeding season, a nesting territory is defended against conspecifics and in the prelaying period there is minimal overlap between the ranges of neighbouring males; for much of the year, however, the ranges of neighbouring birds overlap (Newton, 1986). Except during periods when they are confined to their nests (prelaying, incubation and brooding), females tend to have larger ranges than males and to hunt over different areas; their home ranges generally contain more open country than males and this is reflected in differences in prey caught by the sexes (Newton, 1986). First year birds and individuals occupying poor habitats also tend to have larger home ranges. In southern Scotland, home range sizes at different times of year were found to vary between 16–874 ha for males and 3–3,528 ha for females (Marquiss & Newton, 1981).

2.3 Nest sites Sparrowhawks normally build a new nest in a different tree each year. They prefer to nest in large woods, and prefer conifers to deciduous trees. They tend to choose dense stands of trees (2–4 m apart; Newton, 1986; Selas, 1997), as long as there is flight access, in woodland of average age 37 ±18.5 years. Dense stands of trees help to protect sparrowhawks from predation. Goshawks prefer woodlands with lower tree densities and their presence is thought to force sparrowhawks into denser woodland (Newton, 1986). Sparrowhawks will use less favoured habitats (smaller woods or clumps of trees, more widely spaced trees, deciduous trees, scattered trees in city parks) when ideal sites are not available. In sparsely timbered parts of Ireland, overgrown orchards and quarries, old hedgerows, railway lines and belts of trees along streams are common nesting places (Newton, 1986). Distances between the nest sites of neighbouring pairs of sparrowhawks vary with the productivity of the habitat and the abundance of small bird prey; in Britain, mean nearest neighbour distances (in continuous areas of suitable habitat) ranged from about 0.5–2 km (Newton et al., 1977; Newton, 1986).

2.4 Nests Sparrowhawk nests are built in the lower canopy of trees, at a height of 1.5–25 m above the ground, with most nests at 6–12 m. Both sexes take part in nest building. The nest is placed in a fork in a tree or next to the trunk where two or more branches emerge at the same level.

It is a flat, bulky structure about 40–80 cm across and 10–30 cm deep, with a cup about 15–20 cm across and 5–10 cm deep. It is made from small branches up to 60 cm in length and is lined with bark fragments or small twigs (Cramp & Simmons, 1980; Newton, 1986).

Completed nests may sometimes be abandoned before laying and new nests made. A fresh nest is normally built every year so that long-established nesting ranges may contain clusters of old nests. Within tracts of suitable woodland, groups of nests tend to be regularly spaced, at distances related to habitat productivity and prey availability (Newton, 1986). Nests survive longest when built of larch twigs; those built with smooth twigs, such as birch, sycamore or

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Norway spruce, tend to disintegrate rapidly after use and nesting ranges in these types of woodland tend not to contain clusters of old nests (Petty, 1979).

2.5 Clutch size and incubation

In Britain and Ireland, sparrowhawks lay eggs between late April and early June, with the majority laying in early May. The average laying date is up to 10 days later in years with cold, wet springs, and there is a one day delay in the average laying date for every 60 m rise in altitude in southern Scotland (Newton, 1986). Birds that lay earlier produce more young than those that lay later. The eggs are laid on alternate days, usually in the morning, and clutch size varies from 3–6 eggs, occasionally seven (Cramp & Simmons, 1980; Newton, 1986). The BTO Nest Records Scheme gives an average clutch size of 4.6 eggs (n = 1,431). First-year birds lay slightly smaller clutches on average than adults (Cramp & Simmons, 1980; Newton, 1986). If the first clutch fails, a repeat clutch may be laid about two weeks later. Incubation lasts for 33–35 days per egg, beginning with the laying of the third or a later egg. The female incubates and is fed by the male (up to five times per day; Newton, 1986).

2.6 Brood size and fledging

Hatching may be synchronous or asynchronous, with larger clutches generally having a greater spread of hatching dates. The young are brooded for the first 8–14 days. Initially, the male provides food to the female, who feeds the young. Once the young are over three weeks old, the female also hunts. Feeding rates of broods increase from around six items per day during the first week to 10 items per day in the week before fledging (Newton, 1986). The chicks leave the nest and move to nearby branches when they are 24–28 days old and fledge at 24-30 days (Cramp & Simmons, 1980). They gradually increase in flying proficiency as they become independent and disperse 20–30 days later (Wyllie, 1985; Cramp & Simmons, 1985).

3. SURVEY TECHNIQUES CAUTION Care should be taken to avoid flushing female sparrowhawks from a nest during incubation or brooding as eggs may be dislodged from the nest cup and may not be incubated properly, or small young may be accidentally knocked out of the nest by the startled female.

If a nest visit is planned, flushing can be avoided by deliberately making a noise (talking, breaking a stick) when entering the nesting wood so that an incubating or brooding female is aware of an approach. Any displaced eggs or young found during nest inspections should be replaced carefully. Nests with large chicks (well feathered, over 24 days) should not be visited as the young may fledge prematurely. Appropriate health and safety precautions should be taken when climbing trees to inspect nests (see Section 7.10 of Introduction).

3.1 Breeding season visit schedule

The sparrowhawk is a Schedule 1 species in Northern Ireland and the Isle of Man (see Section 7.1.1 of Introduction). Due to the difficultly of locating active nests in woodland, it is recommended that all four visits are made, even if no signs of occupancy are found during the earlier visits. Sightings of birds are likely to be rare so the recommended survey method is to search for signs, including clusters of old nests, droppings and plucks.

Visit 1

April to early May

To check for occupancy and find new nests

Visit 2

May

To locate active nests

Visit 3

June

To check for young

Visit 4

July to early August

To check for fledged young

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3.2 Signs of occupancy 3.2.1 Locating home ranges The suggested timing of the first visit to search for signs of occupancy and new nests is April to early May, although woods may be searched systematically for old nests and plucking posts at any time of the year (with appropriate care taken at times when females may be laying, incubating or brooding small young). Groups of old nests from previous years indicate a nesting range and their position should be marked on a map. Since new nests are generally placed close to clusters of old nests, such areas should be searched first. Signs such as droppings and fresh plucks will appear before new nests and are also more obvious (Newton, 1986). Some nesting ranges have more than one cluster of old nests.

Sparrowhawks soar in all months of the year, particularly on bright, breezy days, and the behaviour is used to prospect before hunting, as well as for display, so may not necessarily indicate a bird holding a breeding home range. The high-circling display (generally by the female) tends to show a peak at the start of nest building and again around the time of laying (Cramp & Simmons, 1980).

Other solo flight displays include slow-flapping and undulating flight and may be combined with high-circling to form a more elaborate sky-dance by the male in the presence of the female.

Mutual high-circling is frequent around the time of egg laying, particularly in the early morning, and may be followed by the male sky-dancing or making plunges towards the female. Generally any calling that takes place during displays is only audible at close quarters (Cramp & Simmons, 1980). Sparrowhawks display over large areas, however, so that such observations of display should only be used to find general areas where sparrowhawks are present or as supporting evidence for occupancy.

3.2.2 Locating roosts Active roosts may be found during the searches for nesting ranges, as they are generally close to the nest site during the breeding season. They may be recognised by the accumulation of fresh faecal droppings, pellets, moulted feathers and down.

3.2.3 Recognition of signs Fresh sparrowhawk plucks of small birds occur on prominent features such as old stumps or logs if a wood has little ground cover, or in trees or old nests in woods with denser ground cover. Feathers from such plucks are sometimes scattered throughout the nesting range. It can be difficult to distinguish between the plucks of sparrowhawks and goshawks; sparrowhawks generally take smaller birds and, once incubation has commenced, moulted feathers are usually present nearby. Collecting feathers is recommended as individual birds may be recognisable from the variation in patterns (Newton, 1986; Bijlsma, 1997).

Sparrowhawk pellets are usually distinguishable from those of other raptor species, being small and compacted, rounded at one end and tapered at the other; they may range in size from less than 20 x 10 mm to 35 x 18 mm. They consist almost entirely of greyish feather material, with the occasional piece of bone or other hard parts (Newton, 1986; Brown et al., 2003). Sparrowhawk pellets are smaller than those of goshawk, and can be distinguished from owl pellets by their smaller size, lack of skulls and general scarcity of bone material (which sparrowhawks usually digest).

3.2.4 Evidence of occupation A nesting range is occupied if there is clear evidence from signs or observations of resident birds that sparrowhawks are present. Droppings and signs may be found in many woodland areas, but it is a concentration of signs that indicates occupation of a nesting range (Newton, 1986).

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3.3 Evidence of breeding 3.3.1 Locating active nests Nesting ranges located during first visits should be checked again in May for the presence of active nests, starting in the vicinity of old nests but bearing in mind that new nests may be built some distance from clusters of old nests, necessitating searches of the surrounding woodland.

Fresh plucks located in the spring may provide a cue as active nests are often close by (within 50 m and downhill on sloping ground) and fresh faecal droppings will also be found if birds are present. Fresh plucks will not usually be found after a pair have failed. From the ground, a new nest can be distinguished from old nests by its light airy structure, the white ends of freshly broken twigs, and daylight shining through. Old nests look solid and drooping in comparison and fallen leaves prevent light getting through. From around the time of laying, flecks of white down shed by the female begin to accumulate on the nest and surrounding branches. When the nest contains young, the ground and vegetation below become covered with droppings and the female may be heard alarm calling nearby (Newton, 1986). A description or sketch of the location of an active nest site should be recorded, as well as a map reference (at least six figure). If nest visits are made to record nest contents during incubation or brooding, fieldworkers should be alert to the possibility that a female sparrowhawk flushed from the nest may dislodge eggs or small young from the nest cup, sometimes with fatal results.

3.3.2 Evidence of fledging Fledged young can be located by their calls. Nests from which young have fledged successfully are generally covered with down; droppings will be splattered over a wide area below the nest and there will be a large number of plucks nearby. The number of fledged young can be best estimated by counting large young (more than 24 days old), either standing in the nest or on nearby branches. Once the young have fledged fully, it is difficult to count them accurately as they move around and may not be seen all together. The young from early broods may even disperse to the nest sites of pairs with younger chicks (Frumkin, 1994), where they remain for short periods, stealing food delivered to the nestlings.

3.4 Evidence of non-breeding Non-breeding is relatively common and about 20% of sparrowhawks may form part of a ‘floating’ non-breeding population (Newton & Rothery, 2001). A pair of sparrowhawks occupying a home range may not lay eggs if the female is in poor condition and/or the male is unable to supply sufficient food (Newton, 1986). If an occupied nesting range is located but no signs of an active nest or fledged young are found during the appropriate visits, then this provides evidence for non-breeding.

3.5 Ageing and sexing young Growth curves for Sparrowhawk young are available from both southwest Scotland (Moss, 1979) and the Netherlands (Bijlsma,1997). The Scottish young (from 49 nests) were measured over three breeding seasons from study areas in differing habitat types (coniferous woodland 200-400 m ASL in the Ae Forest and mixed farmland and woodland and small plantations on low ground in the Annan Valley). Hence, they are thought to represent a range of growth rates from good to poor based on geographical variations in prey availability (Moss, 1979; Newton, 1986).

For about 10 days after hatching, the age of young of either sex can be estimated from wing length (Figure 22a) or outermost (10th) primary length (Figure 22b) and tarsus length (length of tarsus plus heel, Figure 23a; tarsus, Figure 23b). After this, size differences between males Sparrowhawk

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Wing length (mm)

Age (days)

Outermost primary length (mm)

Figure 22a. Change in the mean wing length (mm, with 95% confidence limits) of sparrowhawk chicks with age. Data from 1–25 nests per year over seven years and four study areas; each point based on measurements from 6–20 male and 5–17 female young (from Bijlsma, 1997).

Age (days)

Figure 22b. Change in mean outermost (10th) primary length (with 95% confidence limits) of sparrowhawk chicks with age. Data from 49 nests in southwest Scotland over three years (from Moss, 1979; reproduced with kind permission of Blackwell Publishing).

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Tarsus and heel (mm)

Age (days)

Tarsus length (mm)

Figure 23a. Change in the mean tarsus plus heel length (mm, with 95% confidence limits) of sparrowhawk chicks with age. Data from 4–8 nests per year over two years and two study areas; each point based on measurements from 6–24 male and 5–24 female young (from Bijlsma, 1997).

Age (days)

Figure 23b. Change in mean tarsus length (with 95% confidence limits) of sparrowhawk chicks with age. Data from 49 nests in southwest Scotland over three years (from Moss, 1979; reproduced with kind permission of Blackwell Publishing).

Sparrowhawk

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Mass (g)

Age (days)

Mass (g)

Figure 24a. Change in the mean body mass (with 95% confidence limits) of sparrowhawk chicks with age (most young weighed between 16:00h and 19:30h). Data from 1–8 nests per year over three years and three study areas; each point based on measurements from 5–22 male and 6–22 female young (from Bijlsma, 1997).

Age (days)

Figure 24b. Change in mean body mass (with 95% confidence limits) of sparrowhawk chicks with age. Data from 49 nests in southwest Scotland over three years (from Moss, 1979; reproduced with kind permission of Blackwell Publishing).

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and females become apparent (Figures 22-24) and age can be estimated most accurately once a chick has been sexed. The primary feathers first emerge from their pins at 10-12 days in males and 12-13 days in females (Bijlsma, 1997). Young within a brood can be sexed visually, based on their size, from about the 12th day after hatching (Newton, 1986). The small feet and thin legs of males are easily distinguished from the larger feet and stouter legs of females, especially if both sexes are present in a brood. Sexing can be confirmed by measuring wing length (Figure 22), tarsus length (Figure 23) and mass (Figure 24).

4.â&#x20AC;&#x201A; SURVEYS OUTSIDE THE BREEDING SEASON There is no established method for surveying sparrowhawk populations outside the breeding season. Some sparrowhawks display throughout the winter but they do this over large areas and observations of such displays are unlikely to be useful for estimating absolute winter population size.

An index of wintering sparrowhawk abundance might be obtained by carrying out counts of birds observed from defined survey routes (preferably randomly selected or at least representative of habitats in the area to be covered), although sample sizes in terms of the number of birds observed are likely to be low in relation to the survey effort required.

Observers covering fixed survey routes on foot in a set time span several times each winter, and recording observations of sparrowhawks and their approximate distance from the transect line, could generate data of use for indexing changes in numbers between years. In Britain and Ireland, such survey work should be undertaken at similar times each year and between mid-November and late February, to exclude irregular influxes of immigrants during passage periods (Wernham et al., 2002).

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Tawny Owl Strix aluco 1. INTRODUCTION Tawny owls are found in wooded habitats throughout Great Britain, with the exception of the Outer Hebrides and the Northern Isles (Gibbons et al., 1993; Petty, 2007b). They are rare on the Isle of Man, and absent from Ireland. In Britain, they are sedentary over most of their breeding range and, once established, will remain in a home range for the rest of their lives (Southern, 1970; Percival, 2002). At the northern edge of their breeding range, in central Norway, tawny owls are partial migrants and females may leave their breeding areas for prolonged periods (Sunde et al., 2001). The background colour of the plumage varies from rufous brown (rufous morph) to greyish brown (grey morph), with the frequency of birds of different colour morphs varying throughout the geographical range. In England, Galeotti (2001) gives relative proportions of 55% rufous, 39% grey and 6% intermediate (n=31); whereas for Britain (n= 57) and the Netherlands (n=104), Cramp (1985) reports 65% rufous, 30% intermediate and 13% grey. The colour is independent of age or sex but related to climate, with rufous birds commoner in warm, wet areas and grey birds in a cool dry climate (Galeotti & Cesaris, 1996).

Female tawny owls are larger than males but the sexes are not distinguishable in the field by their appearance. Males can be distinguished by their ‘ocarina-like’ hooting call to which females may respond with a sharp disyllabic ‘kewick’ (Cramp, 1985; Redpath, 1994); especially in spring, when males and females may duet. Care should be taken, however, as females may make a similar hooting sound to the male (said to be hoarser, less clearly phrased, with a more wailing quality to the last phrase and slightly higher pitched) and males also use the ‘kewick’ contact call (Mikkola, 1983; Southern, 1970; Galeotti, 2001). The main prey of tawny owls is small mammals, particularly wood mice and bank voles (Southern, 1970) in woodlands or field

Annual cycle Breeding Activity

Peak Period

Occupation of home range

Range

Duration (days)

All year

Territorial display

October to December

August to April

Courtship

March

December to early April

Egg laying

Mid-March to early April

February to mid-April

2 to 4

Incubation

Mid-March to early May

February to mid-May

28 to 30

Hatching

Mid-April to early May

March to mid-May

Young in nest

Mid-April to late May

Mid-April to late June

Fledging

Mid-May to mid June

April to late June

Juvenile dispersal Tawny owl

At 28 to 37 days old

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voles (Petty, 1999) in open grassy habitats. These prey species exhibit large annual variations in abundance which influence the breeding performance of the owls. Unlike more mobile rodent specialists (such as the short-eared owl), British tawny owls do not leave their home range when food is scarce, but rather, they do not breed (Southern, 1970; Petty, 1999). Tawny owls can breed at one year old but do so more frequently at two or three years (Cramp, 1985).

2. HABITAT, HOME RANGE, NESTS AND BREEDING 2.1 Habitat Tawny owls are predominantly woodland birds (Cramp, 1985). They are most abundant in broadleaved woods but also occupy coniferous plantations, gardens and parks, and even urban areas (König & Weick, 2008). Tawny owls also occur in open habitats that have some tree cover, such as farmland with small copses or hedges (Hardy, 1992; Redpath, 1995).

2.2 Home range Tawny owls occupy more-or-less exclusive home ranges all year round and are strongly territorial. Established pairs defend a territory year round, the size of which varies with habitat and is generally smaller in dense woodland. Various studies have found territory sizes of about 20 ha or less in continuous, mainly deciduous woodland, increasing to 545 ha in coniferous woodland and more open habitats (Hardy, 1992; Mikkola, 1983; Cramp, 1985; Redpath, 1992; Coles et al., 2000). In Aberdeenshire farmland with less than 5% woodland, Hardy (1992) found that tawny owls had home ranges of up to 186 ha but utilised only 17-40% of the area for hunting. In coniferous woodland in Northumberland, home ranges varied in size from 16-545 ha (Coles et al., 2000). The size of woodland fragments is important in terms of the likely presence of owls; Redpath (1995) found that all woods over 4 ha in size held breeding tawny owls compared with only 45% of woods smaller than 4 ha.

2.3 Nest sites Tawny owls breed in woodland, copses, or isolated trees in hedges, parks or gardens. They prefer to use holes in trees or nest boxes for breeding. They will also use the old nests of other birds (crow, magpie, sparrowhawk, buzzard, jay, woodpigeon) or an old squirrel drey, old buildings or cavities in crags. In the absence of other suitable nesting sites, they will breed on the ground at the base of a tree, especially in coniferous woods (Mikkola, 1983). A variety of nest boxes is used by tawny owls, but the most usual is the ‘chimney’ box that simulates the stump of a broken off, thick hollow branch of a tree (du Feu, 2003). Tawny owls with access to good natural sites (large dry cavities in trees and crags) may be reluctant to move into nest boxes, but if tree holes or crags are lacking, the entire territorial population is likely to move into boxes over a few years (Petty et al., 1994). Nest boxes should have about 10 cm of litter (wood chips, conifer needles or leaf mould from the forest floor) in the bottom, so that the female can form a scrape for her eggs. This litter should be refreshed after the young fledge.

Nest boxes allow the reliable and consistent sampling of breeding performance in any given study area from year to year, although the results may not be representative of populations breeding in natural sites (See Section 6.6 of Introduction).

2.4 Nests Tawny owls do not build a nest. The female makes a scrape in soft substrates in which she will lay eggs. No extra material is added to the scrape, although old pellets may break up to form a nest lining.

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2.5 Clutch size and incubation Tawny owls lay 1–6 eggs, usually 2–3, but occasionally up to eight (Mikkola, 1983), generally at intervals of 48 hours. The BTO Nest Record Scheme gives an average clutch size of 2.6, (n=2,727). Incubation starts with the first or second egg (Southern, 1970; Cramp, 1985), and lasts 28–30 days. Only the female incubates, being fed entirely by the male (2–4 food items delivered per night; Cramp, 1985). Males will bring less prey to the incubating female when small mammals are scarce or when the weather is wet. Females are then less attentive at nests, and eggs can become chilled and fail to hatch (Hirons, 1982).

2.6 Brood size and fledging Tawny owl eggs hatch asynchronously. The young are brooded by the female for up to 15 days after hatching while food is delivered by the male. The female will then leave the young to hunt at night but normally remains close to the nest during the day. Most feeding visits by the male and female are at night, although some food may be delivered during daylight hours, for example during midsummer at high latitudes (Mikkola, 1983). The young fledge at 28-37 days and may leave the nest before they can fly, especially if the nest site is open (Mikkola, 1983; Coles & Petty, 1997). They may spend a few days on the ground, where they are vulnerable to predators, but soon become adept at climbing and move up into the surrounding trees and bushes (Mikkola, 1983). After fledging, the young are dependent on their parents for approximately three months (Southern et al., 1954; Coles et al., 2000). The number of young fledging increases with the abundance of small mammals (Southern, 1970; Wendland, 1984; Petty, 1999), and mortality can be high in some years (Petty, 1992; Overskaug et al., 1999; Petty & Thomas, 2003).

3. SURVEY TECHNIQUES CAUTION Nest inspections can cause desertion in tawny owls (Petty, 1992). The risk is greatest during egg laying and early incubation, and can be reduced by: i) obtaining data on clutch size only during the latter part of the incubation period; ii) avoiding visits to pairs with a history of desertion during incubation; iii) minimising further nest visits if a nest is visited during laying or incubation by measuring egg density (Section 3.6 below) to determine if the clutch is complete and to estimate the timing of hatching and any necessary visit to ring chicks; iv) timing nest visits close to or after sunset, so that females can return to the nest after dark; and v) avoiding visiting nests in isolated trees during the day, as some owls are reluctant to return to the nest across open ground.

Female tawny owls can be aggressive towards intruders when nests contain chicks, and some people have been blinded by such attacks. It is essential that fieldworkers wear goggles and head protection when approaching a nest with chicks. Avoid hard hats, however, as these may injure the birds. If chicks are to be ringed, they should be taken well away from the nest to be processed. Appropriate health and safety precautions should be taken if working at night and if nest inspection visits require climbing (see Section 7.10 of Introduction).

3.1 Breeding season visit schedule The minimum number of visits required for monitoring occupancy and breeding is two: one in late winter/early spring (Visit 1) to establish occupancy and one in summer (Visit 4) to confirm fledging. Multiple visits between late summer/autumn and winter/early spring (Visit 1) are Tawny owl

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preferable to map territories or confirm that birds are not present. The other two recommended visits (2 and 3) are required for surveillance of breeding performance. Tawny owls are largely nocturnal, except when they have large young in the nest, when they may be active from early evening. Suitable habitats can be surveyed through a combination of listening for calls after dusk and searching for pellets, roost locations, nest sites, fledged broods and moulted feathers.

Visit 1 (Several visits will be needed at this time if the aim is to map territories accurately)

Mid-August to March

To check for occupancy by locating territorial calling males

Visit 2

Late March to April

To locate active nests (note CAUTION about desertion above)

Visit 3

May to mid June

To locate nests with young (note CAUTION: requirements for head protection and goggles if nest visits are carried out )

Visit 4

Late June to July

To check for fledged young

3.2 Signs of occupancy 3.2.1 Locating home ranges Tawny owl territories can be located by visiting suitable habitats in the winter and early spring and listening for calls. Initial survey visits should be made shortly after sunset on dry, still nights between mid-August and April. The aerial display flight is probably quite common but rarely observed (Cramp, 1985) and hence not generally of use for surveying purposes.

Tawny owls respond well to the playback of the male’s territorial ‘hoot’ (Redpath, 1994; Freeman et al., 2006). To census an area, a series of transect lines or a grid should be set up across it.

The transects should be no more than 1 km apart in woodland, and 2.5 km apart in open farmland (corresponding to the distances at which responses can be heard in these two habitat types), with census points no more than 0.5 km apart along a transect line or grid. Fluorescent tape can be used to aid the location of broadcast points at night. At each census point, the fieldworker should play male territorial calls for approximately one minute and then listen for a response for five minutes, repeating this process for up to 30 minutes. Two studies (Redpath, 1994; Freeman et al., 2006) found that over 90% of owls responded during this time (although no response might occassionally be obtained from areas of woodland where evidence obtained on other visits (pellets, feathers, sightings) indicated that owls were present). Call censusing should be carried out from dusk on dry, still, moonless nights, as owls call less frequently on wet nights and when the moon is full (Ruggieri, 1995; Lengagne & Slater, 2002). The positions of any calling owls should be plotted on a map by taking a compass bearing and estimating the distance from the census point. In addition the type of response (‘hoot’, ‘kewick’ or other call) and sex (if distinguishable from calls) should be recorded. The accuracy of location is enhanced if fixes are obtained from 2 different places.

Repeat visits to an areas to map the locations of calling tawny owls are recommended, although Redpath (1994) suggested no more than three visits per winter as the birds may habituate to playback. During surveys in the eastern Highlands of Scotland, owls were found to respond well on one night, yet on another there would be no response; these differences were apparently not related to variation in the weather conditions. The owls’ responses also varied during the night with the best responses around dusk. Using male territorial calls is most likely to elicit responses

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from males (although females may respond to male calls; Appleby et al., 1999) so this method estimates the size of the territorial male population. Confirmation of pairing can be obtained either from records of female calls or by finding an active nest or fledged young in the breeding season. Records of males calling simultaneously can be used to estimate the location of territorial boundaries. Individual males have different calls (identified by sonogram by Appleby & Redpath, 1997; individual variation may be identifiable to the human ear, Southern, 1970; Cramp, 1985) and tawny owls respond with greater intensity to the playbacks of strange owls rather than to those of their neighbours (Galeotti & Pavan, 1991).

If call playback is not used, call surveys for 30 minutes at census points are only likely to reveal about half the birds that are present (Freeman et al., 2006). At least three repeat visits are recommended to increase the chances of detecting occupied territories.

3.2.2 Locating roosts The roosts of tawny owls can be located by searching woodland or groups of mature trees for signs (e.g. pellets below perches). Hollow trees are sometimes used for roosting outside the breeding season but only in open, exposed woodland. Tawny owls prefer to roost in coniferous rather than broadleaved trees. Roosts should be recorded as those of tawny owl only if an owl is seen or additional signs (e.g. moulted feathers) are found.

3.2.3 Recognition of signs Tawny owl pellets are generally grey in colour when dry and tapered at one end. They consist mainly of small mammal remains with some bird and invertebrate material and may be irregular in shape with protruding bone fragments (Thomas & Shields, 2008). The size range, based on several accounts, is 20–84 mm long and 10–30 mm in diameter (Mikkola, 1983; Cramp, 1985; Brown et al., 2003). Tawny owl pellets are similar to those of long-eared owls and pellets of these two species can be separated only with difficulty. Identification should be confirmed by collection at nests or confirmed roosts.

3.2.4 Evidence of occupancy The location of a territorial calling male on at least two visits or of an occupied roost provides evidence for occupancy of a home range. Working with a population of tawny owls breeding in nest boxes, Petty & Thomas (2003) classified a territory as occupied if a fresh scrape with feathers was found in at least one nest site within the territory between mid-March and midApril. This method was checked against records of occupancy from call playback and found to be more effective (call playback identified just over 90% of occupied territories determined by nest signs).

3.3 Evidence for breeding 3.3.1 Locating active nests All hollow trees within the home range (and nest boxes if present) should be checked. In the absence of these, all old crow, jay, sparrowhawk, buzzard and woodpigeon nests should be checked, as well as any other nests of similar size, squirrel dreys, old buildings and cavities in crags. Nests in conifers may be difficult to locate, and nests in cavities in trees or crags, or in buildings may be inaccessible. Ground nests may also occur, often at the base of trees, especially in coniferous woods.

Listening for calls between males and females at dusk or during the night may be used to locate a nest. Once a nest site is selected, the female usually roosts close by and the Tawny owl

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male about 40 m away, and at dusk they may duet. During egg-laying, incubation and the brooding of small young, when the female spends much time in the nest, her response to the male is said to change. At this time, when he arrives near the nest while she is inside and unable to see him, she may utter a tremulous hoot (in contrast to her coarser hooting call).

Listening for this ‘pu-pu-pu’ call from a female responding to the male’s arrival may be used to pinpoint the location of a cavity nest during the incubation or brooding periods. Note that this call is also produced, apparently by either sex, at other times of the year. ‘Bill clicking’ by adult tawny owls may also indicate that a nest is close. A detailed discussion of the diverse repertoire of calls of male and female tawny owls, along with interpretations, is given in Galeotti (2001). Females roost near to nests with well grown young and their presence may be betrayed by mobbing songbirds.

3.3.2 Evidence for fledging Chicks can be located by their calls just before and after fledging. Counts of large young with well developed flight feathers (around 21 days old) in a nest give the best estimate of brood size at fledging. Fledged young in small broods can be counted by listening to their food begging calls but it can be difficult to separate calling young in larger broods (Wendland, 1984; Sunde & Markussen, 2005).

3.4 Evidence for non-breeding As is the case with other raptor species, it is difficult to distinguish early breeding failure from non-breeding. If a territorial pair is located but subsequent detailed searching does not reveal an active nest, then non-breeding is likely. To help to confirm this, visits should be made in the early evening in early May to mid-June when the begging calls of young should be heard if they are present.

If nest boxes are used, tawny owls will visit them for up to a month before laying and flecks of down or small body feathers will be found around the entrance hole (Petty, 1992; Petty & Fawkes, 1997). Closer to laying, a deep scrape is formed in the debris at the bottom of the box. Owls that do not lay may still go through this process, so that non-laying can be confirmed if eggs are not laid in the nest box. To ensure that the owls have not moved to another nest, any possible alternatives within the nesting territory should be checked, and re-checked later in the season (Visit 4), to listen for fledged young, before it is concluded that breeding has not taken place.

3.5 Ageing and sexing young

Although female tawny owls are larger, it is impossible to separate males from females with a range of ages in a brood. Growth curves showing changes in body mass, wing length and head-and-bill length have been produced for British tawny owls (Percival, 1992; Figure 40).

These measurements can be used in combination to give at least an approximate estimate of the age of young. Changes in the body mass of chicks probably vary in relation to a number of factors, including the foraging conditions for the parents, brood size, how recently a chick has been fed and the time of day, so that mass alone should not be used to give a precise indication of age. Tawny owl chicks can also be aged approximately by their stage of feather development (Cramp, 1985).

3.6 Use of egg density measurements

Published information is available on changes in the density of British tawny owl eggs which can be used to estimate hatching dates (Percival, 1992; Figure 41; see Section 6.5.1 of Introduction). Further data collection is likely to be required to enhance precision, but egg measurements taken in the field (Section 7.8.7 of Introduction) can be used to calculate egg

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400 350

Mass (g)

300 250 200 150 100 50 0 0

5

10

15

20

25

30

35

40

30

35

40

30

35

40

Number of days from hatching

180

Wing length (mm)

150 120 90 60 30 0 0

5

10

15

20

25

Number of days from hatching

80

Head and bill length (mm)

75 70 65 60 55 50 45 40 35 30 0

5

10

15

20

25

Number of days from hatching

Figure 40. The relationships between chick measurements and age for the tawny owl.

The data are plotted as 5-day means with 95% confidence limits. (From Percival 1992; reproduced with kind permission of JNCC).

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density (see legend to figure 41) and estimate hatching dates (Figure 41). This can be used to determine the appropriate timing of visit(s) to check on young.

For tawny owls, an index of egg density can also be used as a guide to clutch completeness (Petty, 1992 and pers. comm.). The density index (DI) for each egg is calculated as follows: DI =

W

(vi)

(L B)

where L is egg length (mm), B is breadth (mm), and W is weight (grams). The density index decreases as eggs lose water (and hence weight) during incubation (Furness & Furness, 1981).

Any clutch with a DI of more than 0.540 for any egg may be incomplete and an additional visit is then advisable to establish final clutch size. Clutches where all the eggs have DIs of less than 0.540 may be considered to be complete. This method should be used as a guide, however, because the density of freshly laid eggs varies somewhat between individual females, but more data are required before this variation can be quantified.

1.15

Egg density

1.1

1.05

1

0.95

0.9 -35

-30

-25

-20

-15

-10

-5

0

Number of days to hatching Figure 41. The relationship between egg density and hatching date for the tawny owl, showing how egg measurements can be used to estimate hatching date (where egg density = weight/(O.507 x (breadth)² x length). The data are 5-day means with the 95% confidence limits shown. (From Percival 1992; reproduced with kind permission of JNCC).

4. SURVEYS OUTSIDE THE BREEDING SEASON In Britain, most tawny owls are thought to occupy and defend their home ranges throughout the year. As indicated above, they can be censused by locating and mapping these ranges outside as well as within the breeding season. The 1998 survey of tawny owls in Britain (Percival, 1990), repeated in 2005, involved a single 10 minute visit to each of a sample of tetrads (2 x 2 km squares) between mid-August and October. At this time territorial birds are most vocal as they defend their territories against prospecting juveniles from that year’s breeding season. Observers recorded the number of calling birds and details of habitat.

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White-tailed Eagle Haliaeetus albicilla

1. INTRODUCTION White-tailed eagles became extinct in Britain and Ireland by the 1920s, having been formerly widespread in the north and west of Britain and in Ireland (Love, 1983; Brown & Grice, 2005; Holloway, 1996). There have been a number of reintroduction programmes in Scotland, ultimately resulting in the successful re-establishment of the species in the west (Bainbridge et al., 2003). A new phase of reintroductions to the east coast of Scotland began in 2007. A release programme in the southwest of Ireland was also begun in 2007 (www.goldeneagle.ie).

Adult white-tailed eagles are predominantly sedentary, remaining in their home ranges all year round. Young birds disperse during their first year. In Scotland, there is a tendency towards natal philopatry, and elsewhere young birds may wander widely but tend to move back closer to their natal areas in spring (Nygård et al., 2000). Vagrants from Scandinavia and eastern Europe may reach Britain occasionally (Gibbons et al., 1993). The sexes have similar plumage but the female is noticeably larger than the male. Juvenile and immature birds generally lack the white tail of the adult, but the ages can be differentiated more rigorously using a combination of head, neck, bill and overall plumage colour (see Helander et al., 1989); immatures gradually moult into adult plumage by the age of 4–5 years (Cramp & Simmons, 1980; Love, 1983). White-tailed eagles usually breed for the first time at five years of age, although this can vary from three to 7+ years (Helander & Stjernberg, 2002; RSPB unpublished data). Bainbridge et al. (2003) noted that Scottish white-tailed eagles bred first at earlier ages than those in Norway and Sweden, and that this appears to be a feature of reintroduced or naturally re-establishing raptor populations.

1.1 Annual cycle Breeding Activity

Peak Period

Range

Occupation of home range

All year

Courtship

January to April

Duration (days)

Laying

Mid-March

Late Feb to late April

1 to 10

Incubation

Mid-March to late April

Late Feb to late May

34 to 46

Hatching

Late April

Mid-April to late May

Young in nest

Late April to early July

Mid-April to August

Fledging

Early July to August

Juvenile dispersal

September to January

White-tailed eagle

70 to 84

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2. HABITAT, HOME RANGE, NESTS AND BREEDING 2.1 Habitat Home ranges are located near open water, either coastal or fresh. The Scottish population is found on or near the coast in the West Highlands and Hebrides.

2.2 Home range White-tailed eagles defend their nesting territories. Some birds are very aggressive to intruders, while others are more tolerant (Love, 1983). The extent to which they defend the rest of their home range is not clear, and this probably varies between individual pairs. In winter, some birds congregate, while others maintain a defined home range (Cramp & Simmons, 1980). In favourable habitats in mainland Europe, separate pairs may nest only 1–2 km apart.

The Scottish population is still increasing and population density is low in most areas. On Mull, one of the most densely populated areas, the average distance between the nests of neighbouring pairs is 8.6 km (range 3.2–14 km; RSPB, unpublished data).

2.3 Nest sites White-tailed eagles build their eyries in a wide variety of locations, generally below 300 m a.s.l., and typically below 150 m a.s.l.. In Scotland, nests may be located in trees or on large and small crags; trees, where available, seem to be used in preference. Nest trees are generally 10–30 m in height (usually the largest available in an area), broadleaved or coniferous (including forestry plantations), and within or at the edge of woodland, although isolated trees may be used occasionally. Nests are normally located about three-quarters of the way up the tree (3–25 m from the ground); they may be built in the crown, against the trunk or on a branch or branches away from the trunk, but are nearly always sheltered from above by part of the tree. Cliffs used for nesting vary greatly in height and may be on the coast or a short distance inland. Nesting on the ground occurs in Norway (on small knolls on offshore skerries, or in areas where abundant food results in very high breeding densities) and in Iceland (Waterston, 1964). Such nests may be little more than scrapes in the ground, lined with grass and moss. A pair of eagles may have 1–11 nest sites within their nesting range, varying from 2–3,000 m (mean 480 m) apart (Cramp & Simmons, 1980). Exceptionally, inexperienced birds have moved breeding locations by more than 10 km between years before becoming settled on a nesting territory.

2.4 Nests Tree nests tend to be large (>1.5 m in diameter) and shallow when first built, becoming deeper as they are used in successive seasons. In Norway, one nest was approximately 3 m in height. The nest is built from branches (which may be over 1.5 m long and 5 cm thick), twigs, heather, seaweed and driftwood. The cup is generally shallow and is lined with grass, mosses or lichens. On Mull, unlike golden eagles, white-tailed eagles tend not to use woodrush for lining the nest and they tend to use larger sticks than golden eagles. Cliff nests can also be large but may start off as little more than decorated, lined scrapes.

2.5 Clutch size and incubation In Scotland, white-tailed eagles normally lay 1–3 eggs (mean of 12 clutches = 2.0; note that few data are available because clutch size is not normally monitored to avoid disturbance to incubating birds). The average clutch size in Norway was 2.1 eggs (Cramp & Simmons, 1980).

Eggs are laid at intervals of 2–5 days and incubation, which begins with the first egg, lasts 34–46 days per egg, but is usually 38 days. Both adults incubate, with the female generally taking the greater share (at least 70%) and incubating at night. Incubation changeovers

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generally take place every 3–4 hours during the day (Gilbert et al., 1998). Pairs may lay a repeat clutch if the first is lost, but this is rare.

2.6 Brood size and fledging The young hatch asynchronously and are brooded by both adults almost continuously for 14–21 days, after which brooding gradually decreases. Both adults bring food to the nest and feed the chicks, with the male doing more of the hunting earlier in the nestling period, and the female feeding the chicks. Food deliveries are most frequent in the morning and evening, although they can take place at any time of the day. The overall delivery rate is about one per 10 hours of observation, ranging from one every five to one every 13 hours over the whole nesting period, and varying between pairs (RSPB, unpublished data). There may also be day-to-day variation, depending on weather conditions. The young fledge at 70–84 days old (exceptionally 98 days). Initially, they remain close to the nest, and continue to be fed by their parents, gradually becoming independent over a period of some 35–40 days (Cramp & Simmons, 1980). On Mull, some young have been observed to be dependent for longer. Young begin to disperse from the natal area in September, although some may remain in its vicinity through the winter.

3. SURVEY TECHNIQUES CAUTION White-tailed eagles should not be disturbed from eyries with eggs or small young unless there is a specific need to record clutch or brood size. Eyries should be observed from a safe distance until young are 3–4 weeks old (and capable of thermo-regulation) and again after the age of eight weeks, when disturbance may cause premature fledging.

A distance of 500–1000 m is recommended (Ruddock & Whitfield, 2007; Whitfield et al., 2008b), although it is recognised that different pairs or sites may have different sensitivity to disturbance; for example a hide for public viewing of a nest on Mull, situated at 300 m from the nest, is clearly not problematic (Ruddock & Whitfield, 2007). If nest inspection visits require climbing, then appropriate health and safety precautions should be taken (see Section 7.10 of Introduction).

3.1 Breeding season visit schedule The species is listed on Schedule 1 in Great Britain, Northern Ireland and the Isle of Man. In addition, the white-tailed eagle is listed on two new Schedules created by the Nature Conservation (Scotland) Act 2004, which respectively provide birds with protection from harassment and give year-round protection to habitually used nest sites in Scotland. The Natural Environment and Rural Communities Act 2006 (Schedule ZA1), which applies to England and Wales, also gives year round protection to nest sites (see Section 7.1.1 of introduction). To establish occupancy and the presence of a breeding pair, it is recommended that each home range is visited on at least four occasions (as detailed below). If time for fieldwork is limited and an observer believes a home range to be vacant on the basis of the first two visits, however, then subsequent visits can be omitted.

Visit 1

January to March (*November onwards)

To check for occupancy and locate ‘built-up’ eyries

Visit 2

Mid-March to mid-April

To locate active nests

Visit 3

Late June to July

To check for young

Visit 4

August

To check for fledged young

* Ideally, visit known nesting ranges or new areas at least monthly, from November to mid-February, to develop an understanding of bird activity prior to laying and to look for signs of nest refurbishment.

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At the time of writing, because the population is still small, monitoring programmes for white-tailed eagles in Scotland, carried out by RSPB, involve weekly checks at most known nests from early March (Gilbert et al., 1998).

3.2 Signs of occupancy 3.2.1 Locating home ranges When surveying a new area, local advice should first be sought on the locations of any nesting ranges. However, as nests of adjacent pairs may be 3 km (or less) apart, fieldworkers should carry out systematic searches of all suitable nesting habitat within the study area to look for occupied nesting ranges; it should not be assumed that any recorded sightings of birds refer only to a single pair. Plumage characteristics may allow individuals to be recognised for periods of time (e.g. if a bird has not fully attained adult plumage or has missing or damaged feathers) and can be used to help establish the numbers of birds present and the individuals occupying a particular nesting range. Where release programmes are ongoing, fieldworkers should also check for wing tags (e.g. about 50% of the Scottish population is tagged). Nesting ranges should then be watched between January and March to locate the nest site, which may be close to an established roost. Watches of up to 3–4 hours duration can be carried out from suitable vantage points at any time of day, although until mid-February visiting all potential nest sites in the study area might prove more productive.

Whilst the literature suggests that white-tailed eagles can be very vocal in the spring, which can help in locating nest sites, those in Scotland tend to be quieter and rather unobtrusive.

In other breeding locations, adults perform high circling displays near, and up to a few kilometres away from, the nest site, calling frequently and often in duet (Cramp & Simmons, 1980). Such displays often occur by a cliff or other prominent point near the eyrie, with the birds rarely circling higher than 200 m above the ground. White-tailed eagles are also well-known for flight-playing (including talon-interlocking and cartwheeling) but this may be antagonistic rather than a pair displaying, and immature birds also indulge in flight play.

To date, in Scotland, these types of display have been observed only rarely, however, and are therefore likely to be less useful in survey work.

3.2.2 Locating roosts During the breeding season, active roosts may be on crags or in trees and will have fresh faecal droppings, down, feathers and pellets. Roosts can be found by checking all suitable crags and trees within the home range; they may be over a kilometre from the nest, but many adults roost on or right next to the nest.

3.2.3 Recognition of signs White-tailed eagle pellets are generally large, 90–110 mm long and 35–40 mm in diameter (Brown et al., 2003), although they can be much smaller. Whole feet (e.g. of gulls and buzzard) have been found in pellets in Scotland. White-tailed eagle pellets cannot be easily separated from those of golden eagle, although those containing the remains of fish or seabirds are more likely to originate from the former species. The use of pellets as evidence of occupation should ideally be supported by other signs.

3.2.4 Evidence of occupancy Sightings of a single bird or a pair of white-tailed eagles, of potential breeding age, between February and August, on more than two occasions, provide evidence of occupancy.

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3.3 Evidence of breeding 3.3.1 Locating active nests White-tailed eagles generally use the same nesting ranges for many years. New nests may be built, or old nests refurbished, at any time between September and March. Visits can be made from November until mid-February to check all known nests for refurbishment. New or refurbished nests can usually be distinguished from old ones not in use by the presence of freshly broken sticks built up into a distinct rim, or the addition of fresh grass or moss lining.

Occasionally, more than one nest in a territory is refurbished in this way in any one year.

There will usually be signs on the ground in the immediate vicinity of an active nest, including faeces, pellets, down and/or fresh sticks dropped from the nest. If the location of an active nest is not known, all mature woods or trees, crags or steep slopes in an area should be searched systematically, including offshore skerries and small islands. Adults may be secretive before laying, and, if disturbed during incubation, generally slip quietly off the nest and return once the disturbance is over. After hatching, adults are highly vocal if disturbed at the nest and remain in the immediate area alarm calling. Nest sites should not be disturbed from midFebruary until mid-May (until young are at least 3–4 weeks old) but they can be viewed with a telescope from a safe distance.

3.3.2 Evidence of fledging Eyries from which young have fledged successfully are littered with down and prey remains, and appear ‘flattened’. Counts of large, feathered young in the eyrie during June and July can be used as a measure of the number fledged. Nests should be viewed from a distance only after the young are eight weeks old, due to the risk of causing premature fledging, especially if young in tree nests have moved into the surrounding branches. After fledging, the young remain in the vicinity of the nest site for over a month but may not be seen together, so that an accurate count of fledged young may not be possible.

3.4 Evidence for non-breeding In Scotland, a small proportion of pairs do not breed in any one year (Bainbridge et al., 2003).

If an active nest or recently fledged young are not found but adult birds have been seen repeatedly within a nesting range, non-breeding may be inferred if new, active eyries have not been found after checking the area carefully.

3.5 Ageing and sexing young Females are generally larger than males, although there is some overlap (Cramp & Simmons, 1980). Helander (1981) and Helander et al. (2007) measured chicks of 4-8 weeks old from the two Swedish populations: a population along the Baltic coast which extends into central and southern Sweden, and an inland population in Lapland (northern Sweden). Each nest was visited once when nestlings were expected to be 4 to 8 weeks of age and the ages of nestlings were estimated based on the stage of development and feathering. In the earlier study (Helander, 1981) the sex of nestlings was assessed visually by size differences, whereas the later study (Helander et al., 2007) used DNA analysis to identify the sex of nestlings.

Between approximately 4 to 8 weeks of age, the wing length of white-tailed eagle nestlings was found to be strongly related to age, such that wing length could be used to estimate age (Figure 10). Wing length was however not found to be of use for sexing chicks.

Within broods, some young were sexed visually by the relative sizes of their beaks and feet but not all chicks could be differentiated by this method. Once nestlings were at least 25 days White-tailed eagle

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old, most could be sexed from measurements. The best predictor of sex was found to be the thickness of the tarsus at the thinnest point (tarsus width, see Section 7.8.3 of Introduction) which allowed the correct determination of 95% of females and 98% of males from the Swedish Baltic population based on a cut off of 13.8 mm. Allowing for measurement accuracy, individuals with a tarsus width less than or equal to 13.5 mm were classified as males, and those measuring 14 mm or larger were classed as females (Helander et al., 2007; individuals with tarsus measurements between 13.5 and 14 were presumably not assigned a sex based on this method). An index of tarsus thickness obtained by multiplying tarsus width and tarsus depth (see Section 7.8.3 of Introduction) was also found to be a good discriminator of sex for 91% of females and 96% of males from the Swedish Baltic population. Criteria for sex identification from the Swedish Baltic population were, however, not directly applicable to the population in Swedish Lapland, where nestlings are typically thinner, probably due to a more limited food supply. Many female nestlings from the Lapland population were mistakenly identified as males based on criteria for the Baltic population (Helander et al., 2007). Thus for the tarsus thickness index, threshold values for differentiating between the larger females and males were 215 for birds from the Baltic Coasts, and 200 for birds from Lapland (Helander, 1981).

The Swedish studies reported above indicate that sexing of white-tailed eagle nestlings in the field is feasible with a high degree of accuracy based on a limited number of measurements, but the criteria used to separate sexes may need to be adjusted for each population (Helander et al., 2007).

For a sample of Scottish white-tailed eagles, the mean tarsus thickness index was 228 for males and 288 for females, with a cut-off point of 250 suggested for differentiating between the sexes. Bill depth (at the cere) was found to be a useful supporting measurement for sexing: males had a depth less than 33 mm and females greater than 33 mm (RSPB, unpublished data). Young falling close to the cut-off points should be left unsexed.

40 Winglength - Lapland (cm)

Winglength - Baltic (cm)

40

30

20

10

20

30 40 Age (days) Baltic:

50

30

20 one male two males one female two females regression line for males regression line for females

10

20

30 40 Age (days)

50

males y = 0.92 x – 6.27; females y = 0.85 x – 2.99

males y = 0.94 x – 6.46; females y = 0.94 x –age 5.84 of 38 male and 32 Figure 10. Relationships Lapland: between wing length and estimated female nestling white-tailed eagles from two areas of Sweden. Although females tend to have slightly longer wings than males of the same estimated age, the difference is small at this stage of growth; overall for both sexes, age (days) = (wing length (cm) + 5.3)/ 0.91.

From Helander (1981); reproduced with kind permission from Bird Study.

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4.â&#x20AC;&#x201A; SURVEYS OUTSIDE THE BREEDING SEASON In some areas of mainland Europe, white-tailed eagles congregate at roosts in winter. These roosts generally contain immatures and some local breeding adults, although most territorial adults roost in their home ranges. Communal roosts may be in mature woodland or on crags.

They can be located either by observation of returning eagles, by gaining information from local people, or by cold searching suitable woods and crags for moulted feathers, pellets and faecal droppings. Counts can then be made, from a suitable vantage point overlooking the roost site, for two hours before dusk in the evening or from first light in the morning until two hours after dawn. In Scotland, communal roosts containing large numbers of birds are rare. Despite this, searching for winter roost sites can form a useful component of population monitoring because, in an increasing population, these roosting sites are often close to the eventual breeding sites.

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Species occurring irregularly in â&#x20AC;&#x201A; Britain & Ireland In this field guide we have focused on the raptors that breed regularly in Britain and Ireland.

A number of other species occur less regularly and/or do not breed; five of these occur sufficiently regularly to merit inclusion of some brief notes on survey methods.

Black kite (Milvus migrans) In April 2005, an adult black kite was located on the Black Isle, Scotland, interacting with red kites. It was sexed as a male on the basis of its behaviour, and during May was recorded nest building in the company of an untagged female red kite. This breeding attempt failed before eggs were laid, and the black kite was last seen in early August. In April 2006, the black kite was back at the same location, apparently holding territory and paired with a 6-year old wing-tagged female red kite. Their nest, containing two young, was found in late June and both fledged in mid-July. This appears to be the first successful breeding of a wild black kite in Britain and Ireland. For locating nesting territories and nests of this species, the methodology given for red kite can be used as a guide. Hybridisation between red and black kites has been recorded elsewhere in Europe (Wobus & Creutz, 1970; Sylven, 1977).

Pallid harrier (Circus macrourus) In 1995, a male pallid harrier bred with a female hen harrier on Orkney; the eggs were thought to have been predated, probably by hooded crows (Betts, 2007). For locating nesting territories and nests of this species, the methodology given for hen harrier should be used as a guide.

Rough-legged buzzard (Buteo lagopus) Rough-legged buzzards are winter visitors to Britain and Ireland. They arrive from October onwards and normally leave by late March or April, with the occasional bird staying into June.

Rough-legged buzzards can arrive in large numbers (Cramp & Simmons, 1980) in years when rodents are scarce in their breeding grounds in northern Europe (Scott, 1968).

Rough-legged buzzards occupy winter home ranges. In France, these ranges were associated with open habitats with abundant vole populations (Baker & Brooks, 1981; Michelat & Giraudoux, 1999). Winter home ranges in Scotland are found in lowland farmland with a mixture of woodland and open fields with patches of rough ground, in heather moorland, or in open woodland bordering hill ground. All of these habitats have large open areas that can support high density vole populations. Winter home ranges may be held by a pair of birds that roost together (Cramp & Simmons, 1980).

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Fieldworkers identifying wintering rough-legged buzzards should report them to their Local Bird Recorder, giving a full description and location (six figure (or more) map reference).

Winter home ranges can be determined by recording the location of the buzzards on repeat visits to the wintering area.

Gyr falcon (Falco rusticolus) The gyr falcon (gyrfalcon) is an occasional winter visitor to Britain and Ireland. They can occupy temporary home ranges in suitable habitats (Breider, 1996; Cade et al., 1998). Wintering gyr falcons in northeast Scotland have been observed to remain in the same area for several weeks, occupying either mountain or estuarine habitats. These birds have included both white and grey phase falcons. Some gyr falcons are transitory and do not occupy a home range. Gyr falcons taken into care after being caught on oil rigs have been released in Aberdeenshire, but none of these birds appeared to remain in the area. It is believed that many of the birds wintering in Britain are from the Arctic but there is a possibility that captive gyr falcons, or hybrids resembling pure gyr falcons, may have escaped.

Most adult gyr falcons do not leave their nesting territories in the winter (Poole & Bromley, 1988; Nielson & Cade, 1990). Juveniles, sub-adults and some adults disperse to wintering areas from August to April and may move over large distances. Different populations depend on ptarmigan or collared lemmings (both of which have cycling populations) as their principal prey. In years of low prey abundance, the gyr falcons may be forced to leave their normal wintering areas, when they are more likely to be seen in Britain.

Fieldworkers locating wintering gyr falcons should send details of the location(s) and a description of the bird to their Local Bird Recorder. Once again, the existence of a winter home range can be assessed by making repeated visits to the area where a the bird is first sighted, to determine whether it is still resident.

Eagle owl (Bubo bubo) It is uncertain whether the eagle owl (Eurasian eagle-owl) is native to Britain and Ireland or whether the sightings and breeding attempts that have been recorded involve individuals which escaped from captivity (Dennis, 2005). Given recent increases in continental European eagle owl populations, there is a possibility that wild vagrants may occur if they have not already done so. There is however, no evidence that the eagle owls breeding in Britain are of natural occurence or have formed a self-sustaining population (Melling et al., 2008), and this species has not been added to the British list.

A pair of eagle owls has bred successfully in northern England since 1996, rearing a total of 23 young (Dennis, 2005), one of which was found dead in Shropshire, over 200 km away.

Between 1–2 breeding attempts have also been reported from northeast Scotland between 1984 and 1994, and a male eagle owl has recently been recorded calling from another area of northern Scotland.

Eagle owls occupy their home range throughout the year. They defend their nesting territory but the home ranges of adjacent pairs overlap. They can be censused by a combination of listening for and locating spontaneous calls from breeding birds, broadcasting calls and listening for responses, and checking suitable nesting habitat (Penteriani & Pinchera, 1990); listening for the adult owls’ calls was found to be the most effective method. In Spain, calling occurs from autumn to spring, and the owls are most vocal in January and February (Ruiz-Martínez et al., 1996). The young will call when they are over five weeks old, most frequently in the three hours

240 Raptors: a field guide for surveys and monitoring

before sunset and after sunrise (Penteriani et al., 2000), which provides a useful cue for locating successful nests. Eagle owls tend to occupy areas that are remote from human settlements; they require a reliable supply of large prey and secure nesting and roosting sites (Cramp & Simmons, 1980). They breed in the old nests of other large birds, on ledges on crags, in holes or cracks in rock-faces, in large tree holes, and on the ground. In northern Europe, eagle owls can lay eggs from March to early May (Mikkola, 1983), with the young fledging three months later. Eagle owls are very sensitive to disturbance and may desert eggs or small young (Mikkola, 1983).

Fieldworkers finding eagle owls should proceed with caution, as the birds are prone to desert, are large and can be aggressive. Breeding attempts should be reported to the Rare Breeding Birds Panel and/or the Local Bird Recorder, and also to staff of the appropriate Statutory Nature Conservation Agency (see Appendix 2).

Raptors: a field guide for surveys and monitoringâ&#x20AC;&#x201A;

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242â&#x20AC;&#x201A; Raptors: a field guide for surveys and monitoring

Part 3

Feathers Raptors: a field guide for surveys and monitoringâ&#x20AC;&#x201A;

243

Introduction This part of the book provides an introduction to feathers, and includes colour photographs of the wing and tail feathers of 23 species of birds of prey (including the raven as an ‘honorary’ raptor) which occur regularly in Britain and Ireland, and one further species (the eagle owl) which has recently begun to breed. These photographs have been very kindly supplied by Marian Cie´slak, co-author of the excellent field guide Feathers: Identification for Bird Conservation, from the Natura Publishing House (Cie´slak & Dul, 2006).

The discovery of a feather, whether moulted, found with a kill, or even present in a pellet, provides evidence for the presence of a bird species. Cast feathers can also provide information on: age (for species in which juvenile plumage differs from adults); sex (for sexually dimorphic species); the individual (based on individual patterning or if DNA from the feather can be matched to other samples from a bird); and cause of death (if for example shot-holes are seen in the feather web) (see also Section 5.2.4 of Introduction).

Fieldworkers are most likely to come across wing or tail feathers of their target raptor species as these are the largest and strongest feathers and prove most persistent in field conditions.

Such feathers are likely to be lost as part of the moult cycle, as many raptor species begin their moult during the breeding season.

Wing and tail feathers The arrangement of wing feathers (remiges) and tail feathers (rectrices) for a bird of prey is shown in Figure 44. The longest wing feathers are the primaries which extend from the carpal (‘wrist’) joint towards the wing tip. They are assigned the letter ‘P’ and generally numbered from the carpal joint to the end of the extended wing. This is the descendant numbering system (Ginn & Melville, 1983), although it should be noted that some books and scientific papers use an ascendant system whereby primary feathers are numbered from the wing tip to the carpal joint (and it is therefore important, when referring to primary feather numbering, to indicate which system is being used). The shorter secondary flight feathers grow from the ulna (forewing bone); these are assigned the letter ‘S’ and always numbered from the carpal joint inwards towards the body. The innermost secondaries are also referred to as tertials or tertiaries, especially for passerine birds such as the raven (Redfern & Clark, 2001).

The primaries and secondaries together form the lifting surface of the wing. Tail feathers are assigned the letter ‘T’ and numbered from the central pair of feathers outwards.

All diurnal raptors, owls and the raven have 10 functional primaries on each wing and 12 tail feathers. A vestigial eleventh primary (P11) is present in most raptor families except the true hawks (Accipiters). The number of secondaries is more variable, increasing with the size of the bird and wing length (for the species featured in this book ranging from 10 (6 secondaries and 4 tertials) in the raven, 11 in falcons, 13-14 in kites, harriers, hawks and buzzards, 17 in the golden eagle to 20-21 in the osprey; Ginn & Melville, 1983).

Feather morphology Wing and tail feathers are forms of the contour feathers that make up the visible plumage of adult birds. They comprise a central shaft and a web or vane. There is some variation in the terminology applied to feather structure (Figure 45). In the nomenclature used by Cie´slak & Dul (2006), the term shaft is applied to the portion of the axis of the feather that,

244 Raptors: a field guide for surveys and monitoring

in life, protrudes from the skin, and the lower part which penetrates the skin and provides attachment is termed the calamus or quill. The calamus is separated from the shaft by a residual piece of skin termed the collar which is visible and/or detectable by touch. Under alternate terminology, the feather shaft may be divided into the rachis (between the webs) and the calamus at the base, below the web (e.g. Brown et al., 2003). The term quill may also be more loosely applied to the entire feather stem, or to an entire feather, especially a wing or tail feather (Campbell & Lack, 1985).

The webs which form the lifting surfaces of the wing and tail feathers are formed from barbs extending out from the shaft at an angle and lying parallel to each other. The barbs link together by means of hooklets and barbules. This construction ensures the elasticity of the feather web as well as the capacity of the barbs to re-establish linkage if the continuity of the web is interrupted. The part of the feather web on the side nearest the base of the wing or the tail axis is known as the inner web; the outer web lies on the other side of the shaft.

The outer primaries of most birds of prey have characteristic notches in the upper part of the two feather webs (Figure 44), known as emarginations on the outer or leading edge, and notches on the inner web (Redfern & Clark, 2001; Ferguson-Lees & Christie, 2005).

Alternatively, the indentation on the inner web may be termed an ‘inner emargination’, and that on the leading edge the ‘outer emargination’ (Brown et al., 2003; Cie´slak & Dul, 2006).

The extent and shape of the two emarginations facilitate the determination of the position of outer primaries on the wing and may also be useful in species identification. The inner primaries are rather uniform in shape. An indication of the place they occupied on the wing may be gained from their size as well as the angle of the upper edge of the inner web (always least sloping on primary 1).

Outer secondaries arch inwards towards the base of the wing; moving towards the wing base, secondaries become progressively straighter and shorter. Inner secondaries/tertials may even bend in the opposite direction, towards the wing tip.

The central feathers of the tail are the most symmetrical and may differ from the others in colouration. Moving away from the centre of the tail, the feathers tend to become progressively more asymmetrical in the widths and sometimes the colouration, of the two webs.

Moult Moult in birds is the process whereby old feathers are shed and replaced by new ones. In Europe, a wide range of bird species undergo an annual moult during which all body, tail and wing feathers are replaced over a relatively short time (3-4 months). Furthermore, during the period when the primary wing feathers are being replaced, all other wing, tail and body feathers are moulted. Thus, primary moult extends over the full duration of an annual moult period. Primary moult normally commences with the dropping of the innermost primary (P1) and progresses descendantly towards the outermost one (P10), with two or more feathers in moult at the same time. In resident species and short-distant migrants, the moult is timed to begin immediately after breeding in mid-summer and is completed before the onset of winter. Many long-distant migrants delay the start of moult until they reach their winter quarters.

Birds of prey have to maintain hunting and therefore flying efficiency during wing moult.

Primary moult is therefore protracted with only one or two primaries in moult simultaneously.

Moreover, with the exception of a few long-distance trans-Saharan migrants, moult begins at Raptors: a field guide for surveys and monitoring

245

the start of the breeding season. Female birds of prey do most if not all of the incubation and brooding of young. Primary moult normally begins during egg laying and this early stage of primary replacement is timed to coincide with the femalesâ&#x20AC;&#x2122; period of relative inactivity. Males need to maintain flying skills while they are provisioning incubating females, and start their moult several weeks later. Both sexes may stop moulting (arrest moult) during chick rearing but recommence once the young fledge. Smaller species complete their moult within one year whereas larger species may take two or more years In most species of diurnal raptors, owls and the raven, the moult of primary feathers follows the standard pattern, commencing with the first primary (P1) and proceeding to the wing tip (P10). There are some exceptions: moult in the falcons generally begins with the fourth primary (P4) and progresses sequentially along the wing inwards (ascendantly) and outwards (descendantly); in the barn owl primary moult begins with P6 and progresses ascendantly and descendantly; and in adult golden and white-tailed eagles primary moult occurs in an apparently irregular sequence. In all species, patterns of moult for secondaries and tail feathers tend to be more variable than for the primary feathers (e.g. see Ginn & Melville, 1983; Baker, 1993).

For the purpose of moult, the diurnal raptors that occur regularly in Britain and Ireland can be separated into three groups: (i) species that have an annual moult that begins at the start of the breeding season; (ii) the summer visitors that moult in winter quarters but may shed the occasional wing or tail feather on their breeding grounds; and (iii) the larger species whose wing moult is protracted and can extend over two, three or more years. Table 9 lists the species in each category. Moulting strategies in owls are slightly different, as shown in Table 10. In the raven the annual moult begins in March/April and is completed by September/ October (Ginn & Melville, 1983).

Table 9. Primary moult pattern in British and Irish diurnal raptors Resident and partial migrants with complete primary moult commencing in the breeding season

Migratory species with complete primary moult mainly in winter quarters

Partial primary moult commencing during breeding season, suspended during winter and completed over 2 or more years

Red kite Marsh harrier Hen harrier Goshawk Sparrowhawk Kestrel Merlin Peregrine

Honey-buzzard Montaguâ&#x20AC;&#x2122;s harrier Hobby

White-tailed eagle Buzzard Golden eagle Osprey1

moults also in winter quarters, suspends during migration

1

These species-specific patterns of moulting during the breeding season can provide valuable clues to the observant fieldworker. The presence of one or more freshly moulted inner primaries and/or outer secondaries in suitable habitat during the spring or summer may indicate an active breeding attempt and/or the presence of a nearby nest site. For females incubating or tending small young, these cast feathers will be very close to the nest, below a perch or plucking post. Moulted body feathers and wing coverts may also be present. The presence of moulted wing feathers at or near an empty nest that bears no signs of young being reared will

246â&#x20AC;&#x201A; Raptors: a field guide for surveys and monitoring

almost certainly indicate a failed breeding attempt where eggs had been laid. Even during the autumn and sometimes through to the following spring, the largest and strongest primary and tail feathers can still be found and provide useful clues to a previous breeding attempt.

However, a few moulted feathers with no other signs may indicate the presence of a nonbreeding immature or an adult at some distance from its nest.

Table 10. Primary moult pattern in British and Irish owls Partial primary moult post breeding, completed over 2-3 years or *6-8 years

Complete primary moult commencing in the breeding season

Complete primary moult commencing after breeding

Barn owl Tawny owl Snowy owl Eagle owl *

Little owl

Long-eared owl Short-eared owl

Introduction to the feather plates The colour plates show the wing and tail feathers for the adult plumage forms of 23 raptor species, including separate photographs for males and females of sexually dimorphic species.

For each species, the plates show feathers from individuals of typical colouration. Subject to availability, a full set of primaries is included along with 2-5 secondaries, (the outermost, one or more centrally located and inner secondaries). If tail feathers or rectrices differ markedly from each other then a full set from one side of the tail is included; otherwise some rectrices are excluded. Where possible, the feathers are numbered according to the formula shown in Figure 44, to indicate their location on the wing or tail. The positions of ‘missing’ feathers from a set of primaries or rectrices are marked by matchsticks so that the positions and numbers of remaining feathers can be determined.

In most cases the photographs show the feathers from a single bird. If a set of remiges or rectrices is incomplete and has been augmented by feathers from another bird, this is noted in the figure caption and the quill of the ‘odd’ feather(s) is marked by a red band.

To give an indication of size, feathers have been photographed against a scale of 2 cm intervals (marked at 10 cm intervals at the side of each plate). It is important to note, however, that measurements from this scale are not precise because the lower 1-4 cm of feather shafts have been inserted into polystyrene bases. For the purposes of identification, the reader is therefore encouraged to seek more precise details of feather dimensions.

Identification of species The plates illustrate the feather patterning for the birds of prey that fieldworkers are likely to encounter in Britain and Ireland, and provide a starting point for species identification. The first step in this process is to identify the type of feather which has been found – specifically whether it is a primary, secondary, tail or other feather (a covert or other body feather). For wing and tail feathers suspected to belong to a bird of prey, the size, colour and patterning can be compared with the photographs presented in this book.

To measure a feather accurately, it should be placed on a ruler, ideally with a stop ridge at the zero end (e.g. like the rulers available for wing measurements of birds) with the tip Raptors: a field guide for surveys and monitoring

247

of the calamus on the zero. The feather should then be gently smoothed so it lies flat on the ruler, and the reading taken from the feather tip (Brown et al., 2003). Details of mean, minimum and maximum lengths of wing and tail feathers for diurnal raptor species, together with sample sizes, are provided by Cie´slak & Dul (2006). Brown et al. (2003) also provide lengths for individual wing and tail feathers for all species for which feather illustrations are provided.

With regard to species identification, caution is required as the barred wing and tail feathers of diurnal birds of prey and owls are similar to each other. In addition, there may be great variation in feather colouration between the different age categories and also, in some species, between individual adults (e.g. buzzard). Raptor feathers can also be easily confused with those of some species of game-birds, particularly pheasant.

In the space available it has not been possible to provide photographs illustrating juvenile plumages or the range of plumage variation in individual raptor species. For further details of intra-specific feather variability and possible confusion between species, as well as the process of identifying feathers, raptor fieldworkers are encouraged to refer to Cies’lak & Dul (2006). Other useful sources of reference include Brown et al. (2003), Baker (1993) and two good websites with many photographs of feathers of European bird species, including raptors, at www. faunoekjmueller-magdeburg.de/FederSlg__Ubersicht/federslg__ubersicht.html (in German) and www.michelklemann.nl/verensite/start/index.html (an English version of a Dutch website).

For some raptors (and other bird species), the latter references and websites provide illustrations or descriptions of other body feathers besides wing and tail feathers.

In addition to natural variability within a species, exposure to sunlight, water and the rigours of flying and feeding cause feathers to fade and wear, resulting in changes in colour and shape in worn compared to fresh feathers. Furthermore, once a feather is moulted or otherwise lost from a bird’s body its appearance is likely to deteriorate due to the exposure to weather, chewing by mammals and insects and/or colonisation by algae and fungi.

In developing feather identification skills, it is recommended that field workers get to know the flight and tail feathers of their study species before progressing to less familiar ones. In addition to the photographic plates of feathers presented in this book and other guides to feather identification, reference collections of feathers compiled from identified remains (e.g. road kills) can be of considerable value (see Section 5.2.4 of Introduction for advice on collecting and storing feathers).

248 Raptors: a field guide for surveys and monitoring

P9

P10

P8 P7 Wrist or Carpal joint

P6

Alula

P5 Primary feathers

P4 P3 P2

P1 S1

Wing feathers (remiges)

S5

Secondary feathers

S10

S16 T6

T5

Inner secondaries (or tertials) S17–S21

T4 T3 T2 T1 Tail feathers (rectrices)

Figure 44. Female osprey alighting on nest (photo, Mark Hamblin) illustrating the location and nomenclature of wing and tail feathers. The central tail feather (T1) on the bird’s left hand side appears to be missing. Two of the secondaries (S1 and S2) are notably darker and have been recently replaced. Other relatively dark secondaries could have been moulted the previous winter and may be less than 6 months old; whereas those that appear bleached (e.g. S3, S4 and S12 on the right wing) are likely to be much older.

Primary and secondary moult in ospreys, as in other very large birds of prey, is a protracted affair that extends over several years (Tables 9 and 10). The alula consists of 3–5 short feathers and functions like the leading edge of an aircraft to provide lift to the wing in unsteady manoeuvres, such as landing.

(Outer) emargination

Outer web or vane

Calamus or quill

Inner web or vane

Shaft or rachis

Notch or Inner emargination

Figure 45. Feather morphology (after Cie´slak & Dul, 2006).

Raptors: a field guide for surveys and monitoring

249

Honey-buzzard

30

20

10

P10

P9

P8

P7

–

P5

P4

P3

–

P1

cm

Plate 1. Primaries of adult male honey-buzzard.

20

10

S

S

S

T6

T5

T4

–

Plate 2. Secondaries and tail feathers of adult male honey-buzzard.

250 Raptors: a field guide for surveys and monitoring

T2

T1

cm

Red kite 40

30

20

10

P10

P9

P8

P7

P6

P5

–

P3

–

cm

P1

Plate 3. Primaries of adult red kite.

40

30

20

10

S

S

S

T6

T5

T4

T3

T2

cm

T1

Plate 4. Secondaries of juvenile and tail feathers of adult red kite.

Raptors: a field guide for surveys and monitoring

251

White-tailed eagle

50

40

30

20

10 cm

P10

P9

P8

P7

P6

P5

P4

–

P2

–

Plate 5. Primaries of adult white-tailed eagle.

40

30

20

10

S

S

S

T6

–

T4

Plate 6. Secondaries and tail feathers of adult white-tailed eagle.

252 Raptors: a field guide for surveys and monitoring

–

T2

T1

cm

Marsh harrier

30

20

10

P10

P9

P8

P7

P6

P5

–

P3

–

cm

P1

Plate 7. Primaries of adult female marsh harrier (with relatively high proportion of rufous).

30

20

10

S

S

S

T6

–

T4

–

T2

cm

T1

Plate 8. Secondaries and tail feathers of adult female marsh harrier.

Raptors: a field guide for surveys and monitoring

253

Marsh harrier 30

20

10

P10

P9

P8

P7

P6

P5

–

P3

–

P1

cm

Plate 9. Primaries of adult male marsh harrier.

20

10

S

S

S

T1

–

T3

Plate 10. Secondaries and tail feathers of adult male marsh harrier.

254 Raptors: a field guide for surveys and monitoring

–

T5

T6

cm

Hen harrier

30

20

10

P10

P9

P8

P7

P6

P5

–

P3

–

cm

P1

Plate 11. Primaries of adult female hen harrier.

20

10

S

S

T1

–

T3

T4

T5

cm

T6

Plate 12. Secondaries and tail feathers of adult female hen harrier.

Raptors: a field guide for surveys and monitoring

255

Hen harrier 30

20

10

P10

P9

P8

P7

P6

P5

–

P3

–

P1

cm

Plate 13. Primaries of adult male hen harrier.

20

10

S

S

T1

T2

T3

T4

Plate 14. Secondaries and tail feathers of adult male hen harrier.

256 Raptors: a field guide for surveys and monitoring

T5

T6

cm

Montagu’s harrier 30

20

10

P10

P9

P8

P7

P6

P5

P4

P3

–

cm

P1

Plate 15. Primaries of adult female Montagu’s harrier (p5 and p6 from another juvenile individual).

20

10

S

S

T1

T2

T3

T4

T5

cm

T6

Plate 16. Secondaries and tail feathers of adult female Montagu’s harrier.

Raptors: a field guide for surveys and monitoring

257

Montagu’s harrier 30

20

10

P10

P9

P8

P7

P6

P5

P4

P3

–

P1

cm

Plate 17. Primaries of adult male Montagu’s harrier.

20

10

S

S

T1

T2

T3

T4

Plate 18. Secondaries and tail feathers of adult male Montagu’s harrier.

258 Raptors: a field guide for surveys and monitoring

T5

T6

cm

Goshawk 30

20

10

P10

P9

P8

P7

P6

P5

P4

P3

–

cm

P1

Plate 19. Primaries of adult female goshawk.

30

20

10

S

S

S

S

T6

–

T4

T3

–

cm

T1

Plate 20. Secondaries and tail feathers of adult female goshawk.

Raptors: a field guide for surveys and monitoring

259

Sparrowhawk 20

10

P10

P9

P8

P7

P6

P5

P4

P3

–

P1

cm

Plate 21. Primaries of juvenile female sparrowhawk.

20

10

S

S

S

T6

T5

T4

Plate 22. Secondaries and tail feathers of male sparrowhawk.

260 Raptors: a field guide for surveys and monitoring

–

T2

T1

cm

Buzzard

30

20

10

P10

P9

P8

P7

P6

P5

–

P3

–

cm

P1

Plate 23. Primaries of adult buzzard.

20

10

S

S

S

T6

–

T4

–

T2

cm

T1

Plate 24. Secondaries and tail feathers of adult buzzard.

Raptors: a field guide for surveys and monitoring

261

Golden eagle 50

40

30

20

10

P10

P9

P8

P7

P6

P5

P4

P3

â&#x20AC;&#x201C;

P1

cm

Plate 25. Primaries of adult golden eagle (p9 from another individual).

40

30

20

10

S

S

S

T

T

T

Plate 26. Secondaries and tail feathers of various individuals of golden eagle.

262â&#x20AC;&#x201A; Raptors: a field guide for surveys and monitoring

T1

cm

Osprey

40

30

20

10

P10

P9

P8

P7

P6

P5

P4

P3

P2

cm

P1

Plate 27. Primaries of adult osprey (p5 and p8 worn feathers).

20

10

S

S

S

T6

T5

–

T3

–

cm

T1

Plate 28. Secondaries and tail feathers of adult osprey.

Raptors: a field guide for surveys and monitoring

263

Kestrel

20

10

cm

P10

P9

P8

P7

P6

P5

–

P3

–

P1

Plate 29. Primaries of adult female kestrel.

20

10

S

S

S

T1

–

T3

Plate 30. Secondaries and tail feathers of adult female kestrel.

264 Raptors: a field guide for surveys and monitoring

–

T5

T6

cm

Kestrel

20

10

P10

P9

P8

P7

P6

P5

–

P3

–

cm

P1

Plate 31. Primaries of adult male kestrel.

20

10

S

S

S

S

T1

T2

–

T4

T5

–

Plate 32. Secondaries and tail feathers of adult male kestrel.

Raptors: a field guide for surveys and monitoring

265

cm

Merlin 20

10

P10

P9

P8

P7

P6

P5

P4

â&#x20AC;&#x201C;

P2

cm

P1

Plate 33. Primaries of adult female merlin.

10

S

S

S

T6

T5

â&#x20AC;&#x201C;

Plate 34. Secondaries and tail feathers of adult female merlin.

266â&#x20AC;&#x201A; Raptors: a field guide for surveys and monitoring

T3

T2

T1

cm

Merlin

10

P10

P9

P8

P7

P6

–

P4

P3

–

cm

P1

Plate 35. Primaries of adult male merlin.

10

S

S

S

T6

–

T4

T3

T2

cm

T1

Plate 36. Secondaries and tail feathers of adult male merlin.

Raptors: a field guide for surveys and monitoring

267

Hobby

20

10

P10

P9

P8

P7

P6

P5

–

P3

–

P1

cm

Plate 37. Primaries of adult hobby.

10

S

S

S

T1

Plate 38. Secondaries and tail feathers of hobby.

268 Raptors: a field guide for surveys and monitoring

–

T3

–

T5

T6

cm

Peregrine

20

10

P10

P9

P8

P7

P6

P5

–

P3

–

cm

P1

Plate 39. Primaries of juvenile male peregrine (from falconry bird).

20

10

S

S

S

T1

T2

–

T4

–

cm

T6

Plate 40. Secondaries and tail feathers of adult female peregrine (from wild bird).

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269

Barn owl

20

10

P10

P9

P8

P7

–

P5

P4

P3

–

cm

P1

Plate 41. Primaries of barn owl.

10

S

S

S

T6

Plate 42. Secondaries and tail feathers of barn owl.

270 Raptors: a field guide for surveys and monitoring

–

T4

–

T2

T1

cm

Eagle owl 40

30

20

10

P10

P9

P8

P7

P6

P5

–

P3

–

cm

P1

Plate 43. Primaries of eagle owl.

30

20

10

S

S

S

T1

–

T3

–

T5

cm

T6

Plate 44. Secondaries and tail feathers of eagle owl.

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271

Snowy owl

30

20

10

P10 P

P

P

P

P

S

S

S

S

S

T

T

T1

cm

Plate 45. Selected feathers of juvenile male snowy owl.

30

20

10

T6 T1

S S

P

P

P

P

P

P

P

P

T6

Plate 46. Comparison of selected feathers of adult (left) and juvenile female snowy owl.

272â&#x20AC;&#x201A; Raptors: a field guide for surveys and monitoring

T1

cm

Little owl

10

P10

P9

P8

P7

P6

P5

–

P3

–

cm

P1

Plate 47. Primaries of adult little owl.

10

S

S

S

S

T6

–

T4

–

T2

cm

T1

Plate 48. Secondaries and tail feathers of adult little owl.

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273

Tawny owl

20

10

P10

P9

P8

P7

P6

P5

–

P3

–

P1

cm

Plate 49. Primaries of adult rufous morph of tawny owl.

20

10

P10

P9

P8

P7

P6

Plate 50. Primaries of juvenile grey morph of tawny owl.

274 Raptors: a field guide for surveys and monitoring

P5

–

P3

–

P1

cm

Tawny owl 20

10

S

S

S

T1

–

T3

–

T5

cm

T6

Plate 51. Secondaries and tail feathers of adult rufous morph of tawny owl.

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275

Long-eared owl

20

10

P10

P9

P8

P7

P6

P5

–

P3

–

P1

cm

Plate 52. Primaries of adult long-eared owl.

20

10

S

S

S

T1

T2

–

T4

Plate 53. Secondaries of juvenile and tail feathers of adult long-eared owl.

276 Raptors: a field guide for surveys and monitoring

–

T6

cm

Short-eared owl

20

10

P10

P9

P8

–

P6

P5

P4

P3

–

cm

P1

Plate 54. Primaries of moulting short-eared owl.

10

S

S

S

T1

T2

T3

T4

T5

cm

T6

Plate 55. Secondaries and tail feathers of short-eared owl.

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277

Raven

30

20

10

P10

P9

P8

P7

P6

P5

P4

–

P2

cm

P1

Plate 56. Primaries of raven.

20

10

S

S

S

T1

Plate 57. Secondaries and tail feathers of raven.

278 Raptors: a field guide for surveys and monitoring

–

T3

–

T5

T6

cm

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Part 4

Development of raptor chicks Raptors: a field guide for surveys and monitoringâ&#x20AC;&#x201A;

281

Development of raptor chicks The photographs in this part of the book illustrate the development of nestlings for six species of birds of prey. The young of diurnal birds of prey (Falconiformes and Accipitriformes) and owls (Strigiformes) are classed as ‘semi-altricial’ (Campbell & Lack, 1985). They hatch covered in dense down and are unable to leave the nest. They are wholly dependant on the parent birds until after they fledge. The nestlings of the raven (not shown here) are ‘altricial’ (Campbell & Lack, 1985). In common with other passerines, they hatch naked (except for a thin covering of light downy filaments on their upper body and crown), blind and unable to leave the nest.

They are also dependant on the parent birds until after fledging.

We are grateful to the following people for supplying photographs: Golden eagle: Eddie Duthie, Lorcán Ó Toole and an anonymous photographer; Merlin: Logan Steele and Brian Cosnette; Hobby: Ron Downing; little owl: R.B.M. Hendreicks; short-eared owl: Mike Groves; hen harrier: David Jardine.

282 Raptors: a field guide for surveys and monitoring

Golden eagle

Plate 58. Golden eagle, 2 day old chick and hatching egg. The chick is weak and unsteady and covered in the first coat of down which is white (or white with pale grey tips). The cere is pale flesh-coloured (as are the feet and claws). A second chick is hatching using the egg tooth at the tip of the bill.

Plate 59. Golden eagle, 15 days. The chick can now sit up strongly and has a second coat of white or creamy white down, thicker and coarser than the first. At this age feather sheaths begin to emerge on the wings (although this is not clear from the angle of the photograph).

The cere (fleshy portion of the upper bill next to the forehead) and feet are pale yellow and the claws darkening to black. The egg tooth has gone.

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Golden eagle (cont.)

Plate 60. Golden eagle, 28 days. The chick is now able to stand and tear at food. Feather vanes are emerging from their sheaths in feather tracts on the body and wings.

Plate 61. Golden eagle, 34 days. As Plate 60 â&#x20AC;&#x201C; the feather vanes on the wings in particular have emerged further from their sheaths.

284â&#x20AC;&#x201A; Raptors: a field guide for surveys and monitoring

Golden eagle (cont.)

Plate 62. Golden eagle, 46 days. Body size is now approaching that of an adult. Feathers cover most of body and wings although feather growth is not completed and sheaths are still present around the feather bases. Down is still visible, adhering to the tips of feathers, particularly on the head and hind neck, belly and legs. The nestling on the right may be two days older than its sibling.

Plate 63. Golden eagle, 70 days.

Feather growth is complete and the bird is in its first juvenile plumage although wisps of down are still present for example on the back of the head (nestling down should not be confused with the newly grown under-down which is now visible on the breast of this juvenile and is present in all fully grown raptors). At this stage the bird is likely to be capable of flight – a fledgling - and may leave the nest but return for food. Nest visits should be avoided at this stage so that these so-called ‘flappers’ do not leave the nest prematurely.

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285

Merlin

Plate 64. Merlin, 1 day. The chicks are in their first cream-white down and one appears to be still damp after emerging from the egg, fragments of which are present.

Plate 65. Merlin, 3-5 days. The second down is present on the three eldest chicks (top and right). This is brown-grey above, paler grey below, and white with grey bases on chin, throat and belly. The egg tooth is still present.

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Merlin (cont.)

Plate 66. Merlin, 12-16 days. The chicks are now ‘balls of down with attitude’ - aggressive with feet and claws and very vocal. Feather sheaths are present on the wings and feather vanes are just beginning to emerge. They are now old enough for ringing.

Plate 67. Merlin, 16-18 days. Feather growth is now well established on the back and wings, and chicks can be sexed based on measurements (see Section 3.5 of merlin species account).

This is an ideal age for ringing.

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287

Merlin (cont.)

Plate 68. Merlin, 21-24 days.

Feathers cover most of the body but feather sheaths are still present and there are tufts of down adhering to the head, body and wings.

At this age caution needs to be exercised if approaching a crag or tree nest as chicks may jump prematurely.

Plate 69. Merlin, 28 days. The growth of the juvenile plumage is complete, although traces of down are still present on the head and body. The bird is capable of weak but sustained flight and has moved out of the nest so is likely to have fledged. Traces of down are still present on the head and body.

288â&#x20AC;&#x201A; Raptors: a field guide for surveys and monitoring

Hobby

Plate 70. Hobby, 10-12 days. The second (grey white) coat of down is present and the egg tooth has been lost. Feather sheaths are emerging on the wings (‘in pin’) and the chicks are (just) old enough for ringing (if it is possible to return to a nest, chicks are best left for several more days). Note the full crop on the left chick.

Plate 71. Hobby, 18-19 days. The sheaths for wing and tail feathers have appeared and the feathers have emerged 10-20mm (‘out of pin’). Body feathers are also starting to emerge from their sheaths. This is a good age to ring.

Plate 72. Hobby, 26 days. Feather growth is nearing completion though a ‘waxy’ sheath and possibly a blood supply remains at the base of each feather. Down is still present on the top of the head and wings. Some chicks of this age may have already moved out of the nest on to an adjoining limb or ledge. They are capable of sustained flight and may leave the nest prematurely if approached. Therefore, nest visits should be avoided.

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289

Little owl

Plate 73. Little owl, 1 day. The recently hatched chick is covered with short white down over the whole body to the base of the toes, except for the back of the tarsal joint which is bare.

The eyes are closed and the bill is flesh-coloured. The external ear area is also visible.

Plate 74. Little owl, 7 days.

The chick now has a greyish appearance and tracts of feathers are beginning to grow on the head, body and wings. The beak is greyish green in colour. The eyes are still closed.

290â&#x20AC;&#x201A; Raptors: a field guide for surveys and monitoring

Little owl (cont.)

Plate 75. Little owl, 11 days.

The eyes are opening and the feet are well-grown. The nestling is able to sit up.

Plate 76. Little owl, 15 days. The eyes are fully open and the flight feathers are beginning to grow, still ‘in-pin’.

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Little owl (cont.)

Plate 77. Little owl, 23 days.

The wing feathers are partgrown and the tail feathers are emerging from their pins.

Plate 78. Little owl, 39 days. At this stage the young owl will have left the nest and be capable of flight but still dependent on its parents for food, i.e. a fledgling. The flight and body feathers of the juvenile plumage are well-grown.

292â&#x20AC;&#x201A; Raptors: a field guide for surveys and monitoring

Short-eared owl

Plate 79. Short-eared owl brood with chicks at different stages of development, a typical feature of owl broods. The estimated ages of the chicks (top to bottom) are 13-15, 11 and 7 days (see section 3.5 of species account). Owls are born with eyes closed, and the eyes of the youngest chick in this brood are not yet fully open. At this particular site there were also three larger chicks, which had already left the nest but were found nearby.

Hen harrier

Plate 80. Hen harrier, 24-26 days. Females (left) have a rich chocolate iris colour whereas males (right) have a distinct greyish cast. Males are also smaller in size, with thinner tarsi and shorter toes than females (see section 3.5 of species account).

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Appendix 1 – Status and trends of raptor populations in Britain and Ireland Table A.1. The status of raptor populations in Britain and Ireland.

The latest breeding population estimates are given. A shaded box indicates an area where the species does not breed.

294 Raptors: a field guide for surveys and monitoring

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295

9

Breeding females

Territorial pairs

Marsh harrier3

Hen harrier4

Territories

Breeding Pairs

Pairs (pairs laying)

Golden eagle

Osprey

Pairs

Occupied home ranges

Buzzard6

Sparrowhawk5

Goshawk

Breeding females

36 (31)

Territorial pairs (pairs laying)

White-tailed eagle

Montagu’s harrier

86

Confirmed breeding pairs

Red kite2

205 – 210 (177 – 184)

441

130 (min)

633

1 (4)

Scotland

Confirmed (conf. + probable) breeding pairs

Units

Honey-buzzard1

Species

41,000

200

43

306 (min)

4 (6)

Wales

5 (4)

1 2 (1)

31,100 – 44,000

120

10 – 13

11

354

206 (min)

14 (31)

England

5-10 Pairs with nests

63

1

Re-introduction programme started 2008

Northern Ireland

57

Isle of Man

2

500 – 750 Pairs

8,600

3–6

132

Re-introduction programme started 2007

2

Republic of Ireland

Etheridge et al., 2008 RSPB, unpublished data (2005 national survey) Don Scott, pers. comm.

Etheridge et al., 2008

Etheridge et al., 2008 Holling & RBBP, 2008 Welsh Kite Trust, Holling & RBBP, 2008 Golden Eagle Trust, unpublished data

Etheridge et al., 2008 Holling & RBBP, 2008

Source(s)

S, E, W: 2008

S, E: 2003 I: 2009

UK: 2000 I: 2008

UK, IoM: 2000 I:1988-91

S: 2000 – 2004 E, W: 1995 NI: 94 – 2000 I: 2008

2005

Osprey Study Group, unpublished data

Eaton et al., 2007 Golden Eagle Trust, unpublished data

Baker et al., 2006 Irish Raptor Study Group

Baker et al., 2006 Greenwood et al., 2003

Irish Raptor Study Group

Petty, 2007 Greenwood et al., 2003

Holling & RBBP, 2008

S, E, W, NI, IoM: 2004 Sim et al., 2007 I: 2005 Barton et al., 2006

S: 2006 E: 2005 NI: 2009

2005

S: 2006 E: 2005 W: 2005 I: 2009

S: 2006 E, W: 2005

Year

296 Raptors: a field guide for surveys and monitoring

Pairs

Breeding Pairs

Hobby8

Peregrine

10

Breeding Pairs

Merlin

640 – 2,700

Pairs

Pairs

Short-eared owl12

Raven13

210 – 740

450 – 1,750 550 – 1,800

19,400

Territorial Pairs

Pairs

5,800 – 11,600

Pairs

3,400

477

2,200

400

England

Long-eared owl11

Tawny owl

Little owl9

544

800

Scotland

Pairs producing 545 – 1,000 eggs Pairs

Pairs

Kestrel7

Barn owl

Units

Species

12,900

10 – 40

10 – 40

300

264

80

36,800

Wales

0-3

530 – 1,730

140 – 210

87

25 – 40

Northern Ireland

0-5

22

1

< 40 Breeding pairs

30

0–4

Isle of Man

760 - 3,500

1-3

1,500 – 2,500

300 – 350

312 – 350 (occupied sites)

200 – 400

8,400

Republic of Ireland

Irish Raptor Study Group Sharpe et al., 2007

Greenwood et al., 2003: Park et al., 2005

Greenwood et al., 2003; Park et al., 2005 Sharpe et al., 2007 Irish Raptor Study Group

Baker et al., 2006 Sharpe et al., 2007

Baker et al., 2006

Birdwatch Ireland, unpublished data Sharpe et al., 2007

Shaw, 2007 Greenwood et al., 2003

Banks et al., 2003 David Norriss, pers. comm.

Baker et al., 2006; Clements, 2001

Rebecca & Bainbridge, 1998 Greenwood et al., 2003 Irish Raptor Study Group, unpublished data Sharpe et al., 2007

Baker et al., 2006 Greenwood et al., 2003

Source(s)

UK, IoM: 2000 Baker et al., 2006 I: (compilation of Ratcliffe, 1997; Gibbons et al., 1993 estimates 1976–96 – 1988–91)

S, E, W: 1988 – 91 NI: 1997 – 2000 I: 2005 IoM: 1998 – 2003

UK: 1988 – 91 IoM: 1998 – 2003 I: 2008

GB: 2000 IoM: 1998 – 2003

GB: 2000

S: Post 2004 E, W: 1995 – 97 NI: 1988 – 91 I: 2008 IoM: 1998 – 2003

UK, IoM: 2002 I: 2002

GB: 2000

S, E, W: 1993 – 94 NI: 1992 – 95, I: 2008 IoM: 1998 – 2003

UK, IoM: 2000 I: 1988 – 91

Year

Notes for Table A.1: 1. The first survey of honey-buzzard in Britain, organised by the Rare Breeding Birds Panel, found a total of 33 confirmed pairs (4 in Scotland, 24 in England and 5 in Wales) and a further 36 probable or possible breeding pairs (10 in Scotland, 21 in England and 5 in Wales; Ogilvie, 2003). Etheridge (2007) suggests that the Scottish population may be as many as 50 pairs based on the availability of suitable habitat.

2. Red Kite numbers have increased since the national survey of Britain in 2000 which produced respective estimates/counts of 259, 131 and 40 breeding pairs for Wales, England and Scotland (total 430; Wotton et al., 2002). A minimum of 588–705 pairs was recorded in 2005 and the maximum estimated at 900–970 pairs (Holling & RBBP, 2008).

A reintroduction programme in the Republic of Ireland began in 2007.

3. A resident female marsh harrier was recorded in the Republic of Ireland in 2008 (Aonghus O Domhnaill, pers. comm.).

4. The criteria for defining territorial pairs of hen harrier in Ireland differ slightly from those used in the UK and Isle of Man (see Section 3.3 of hen harrier species account).

5. Recent population estimates for sparrowhawk are not available for all countries so a combined total for the UK and Isle of Man is given in the table. Separate estimates are available for Scotland: 7,000 active nests, 2002 (Park et al., 2005); and the Isle of Man: 75‑80 breeding pairs, 1998 – 2003 (Sharpe et al., 2007).

6. Recent population estimates for buzzard are not available for all countries so a combined total for the UK is given in the table. Park et al., (2005) estimated 7,100 – 25,600 territory holding pairs in Scotland in 2003. The large range takes into account rates of change from Breeding Bird Survey (BBS) monitoring in Scotland between 1994-2003, which indicate an 81% increase (95% confidence limits 41% -132%) in abundance.

7. Recent population estimates for kestrel are not available for all countries so a combined total for the UK and Isle of Man is given in the table. Separate estimates are available for Scotland: 6,900 pairs producing eggs, 2003 (Park et al., 2005); and the Isle of Man: 120 breeding pairs, 1998 – 2003 (Sharpe et al., 2007).

8. Between 1-3 pairs of hobby have been reported from Scotland in recent years (Etheridge, 2005; Etheridge et al., 2006; Etheridge et al., 2008).

9. The Scottish population of little owls is unlikely to exceed a few tens of pairs (Park et al., 2005) and may be less than 10 pairs (Greenwood et al., 2003; Gordon, 2007).

10. The Scottish tawny owl population was estimated at between 3,900-5,700 pairs by Park et al. (2005) and 6,000 pairs by Petty (2007b).

11. Based on local atlas studies, and the fact that breeding of long-eared owls is almost certainly under-recorded (most records of breeding birds are of calling young, but 4060% of breeding attempts fail), Jardine (2007) suggests that the Scottish population may be 600 - 2,200 pairs.

12. Based on reported sightings of short-eared owls by fieldworkers taking part in the 2004 hen harrier survey, Calladine et al. (2005) estimated 423-658 apparently occupied territories in Scotland, 78-117 in Wales, and 1-2 in Northern Ireland (no estimate was available for England). These are likely to be underestimates because hen harrier fieldwork was not carried out at the best times of day for observing short-eared owls (which are likely to be most active in the early morning and evening) and will have omitted some of the grassy moorland habitats favoured by the owls.

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297

13. Recent population estimates for raven are not available for all countries so a combined total for the UK and Isle of Man is given in the table. Park et al. (2005) estimate 1,400 – 13,200 pairs in Scotland in 2003 based on extrapolations from the 1988-91 breeding atlas data (Gibbons et al., 1993; upper estimate) and Ratcliffe (1997; lower estimate), taking into account an 85% increase in abundance reported from Scottish BBS squares between 1994 and 2003. Sharpe et al. (2007) estimate 85-89 breeding pairs on the Isle of Man, 2002.

Table A.2. Population trends of raptors in Britain, Ireland and Europe.

Species in bold type are those for which Britain and Ireland hold at least 5% of the European population (excluding Russia; population percentages based on Greenwood et al., 2003 for all species except raven which is based on BirdLife International, 2004). Trends are estimated for the period between 1970 and 2000 for Britain and Ireland. European trends for 1970 – 1990 are taken from Greenwood et al. (2003) and exclude Russia (except for raven where the trend is taken from BirdLife International, 2004); trends from 1990 - 2000 are taken from BirdLife International (2004) and include Russia. It should be noted that many of the ‘increase’ trends represent recoveries in numbers and range from previously low populations affected by persecution and pesticides.

Species

Honey-buzzard

Proportion of Population trend Population trend European in Britain in Europe population in and Ireland (1970 – 1990) Britain and Ireland (1970 – 2000) <0.1%

Increase

Stable

Population trend in Europe (1990-2000) Stable

Red kite

2%

Increase

Increase

Decline

White-tailed eagle

<1%

Increase

Increase

Increase

Marsh harrier

<1%

Increase

Increase

Increase

Hen harrier

7%

Increase

Decline

Decline

Montagu’s harrier

<0.1%

Increase

Increase

Increase

Goshawk

<1%

Increase

Increase

Increase

Sparrowhawk

25%

Increase

Increase

Buzzard

4%

Increase

Increase

Increase

Golden eagle

5%

Increase

Decline

Stable

Osprey

2%

Increase

Increase

Increase

Kestrel

20%

Decline

Decline

Decline

Merlin

9%

Increase

Decline

Stable

Hobby

6%

Increase

Decline

Stable

Peregrine

19%

Increase

Increase

Increase

Barn owl

3%

Stable?

Decline

Decline

Little owl

2%

Stable?

Decline

Decline

Tawny owl

4%

Stable?

Stable

Stable

Long-eared owl

2%

Decline?

Decline

Stable

Short-eared owl

12%

Decline?

Stable

Fluctuating

Raven

1%

Increase

Increase

Increase

298 Raptors: a field guide for surveys and monitoring

Appendix 2 â&#x20AC;&#x201C; Contacts Scottish Natural Heritage www.snh.org.uk Great Glen House Leachkin Road Inverness IV3 8NW Tel: +44 (0)1463 725000

Licences www.snh.org.uk/licences/lic-intro.asp

Natural England www.naturalengland.org.uk Natural England 1 East Parade Sheffield S1 2ET Tel: +44 (0)845 600 3078 Email: enquiries@naturalengland.org.uk

Licences Wildlife Management and Licensing Service Natural England Northminster House Peterborough PE1 1UA Tel: +44 (0)845 601 4523 Email: wildlife.scicons@naturalengland.org.uk www.naturalengland.org.uk/conservation/wildlife-management-licensing

Countryside Council for Wales www.ccw.gov.uk Maes-y-Ffynnon Penrhosgarnedd Bangor Gwynedd LL57 2DW Tel: +44 (0)845 1306229

Licences www.ccw.gov.uk/landscape--wildlife/habitats--species/species-protection/licensing.aspx

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Department of Agriculture, Fisheries & Forestry, Isle of Man www.gov.im/daff Wildlife and Conservation Division Knockaloe Farm Peel Isle of Man IM5 3AJ Tel: +44 (0)1624 843109 The Wildlife and Conservation Division will be moving to new headquarters in mid-2010.

The new address will be, Thie Slieau, Whallian, Hope Road, St. Johns, Isle of Man.

Licences www.gov.im/daff/wildlife/licences.xml

Northern Ireland Environment Agency www.ni-environment.gov.uk Klondyke Building Cromac Avenue Gasworks Business Park Lower Ormeau Road Belfast BT1 2JA Tel: +44 (0) 28 9056 9605

Licences â&#x20AC;&#x201C; contact address above www.ni-environment.gov.uk/biodiversity/wildlife_management_and_licensing.htm

National Parks and Wildlife Service, Ireland www.npws.ie National Parks and Wildlife Service 7 Ely Place Dublin 2 Ireland Tel: 1890 202021 (Republic of Ireland only) +353 1 8883210

Licences www.npws.ie/en/WildlifePlanningtheLaw/Licences/

300â&#x20AC;&#x201A; Raptors: a field guide for surveys and monitoring

Joint Nature Conservation Committee www.jncc.gov.uk Monkstone House City Road Peterborough PE1 1JY Tel: +44 (0)1733 562626

Scottish Raptor Monitoring Group Raptor Monitoring Officer c/o RSPB Etive House Beechwood Park Inverness IV2 3BW Tel: +44 (0)1463 715000

Scottish Raptor Study Groups www.scottishraptorgroups.org Old Kippenross Dunblane Perthshire FK15 OLQ Tel: +44 (0)1786 821182

Northern England Raptor Forum c/o Yorkshire Dales National Park Authority Colvend Hebden Road Grassington North Yorkshire BD23 5LB Tel: +44 (0)300 456 0030 Email: contact@raptorforum.org

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English Raptor Study Groups In addition to the Northern England Raptor Forum, there are a number of raptor groups that cover counties, or other areas, within England. Natural England or the British Trust for Ornithology can provide contact details for licensed raptor workers in order to help ensure coordination of monitoring effort.

Wales Raptor Study Groups Bryn Llus Rhostryfan Caernarfon Gwynedd LL54 7PF Tel: +44 (0)1248 363800

Northern Ireland Raptor Study Groups www.niraptorstudygroup.co.uk Chairman 16 Bridge Road Lurgan Craigavon Northern Ireland BT67 9LA Secretary Cemetery Cottage 12 Church Street Greyabbey Newtownards BT22 2NQ Treasurer 18 Knockbreda Gardens Belfast BT6 0HH Tel: +44 (0)28 38 321837 Email: info@niraptorstudygroup.co.uk

Irish Raptor Study Group / Golden Eagle Trust Ltd. www.goldeneagle.ie 3 Castle Court Currabinny Road Carrigaline County Cork Republic of Ireland

302â&#x20AC;&#x201A; Raptors: a field guide for surveys and monitoring

British Trust for Ornithology www.bto.org The Nunnery Thetford Norfolk IP24 2PU Tel: +44 (0)1842 750050

BTO Scotland School of Biological and Environmental Sciences Cottrell Building University of Stirling Stirling FK9 4LA Tel: +44 (0)1786 466560

Ringing permits www.bto.org/ringing/index.htm Email: ringing@bto.org

Royal Society for the Protection of Birds www.rspb.org.uk

UK Headquarters The Lodge Sandy Bedfordshire SG19 2DL Tel: +44 (0)1767 680551

Scotland Headquarters RSPB Scotland Dunedin House 25 Ravelston Terrace Edinburgh EH4 3TP Tel: +44 (0)131 311 6500

Wales Headquarters Sutherland House Castlebridge Cowbridge Road East Cardiff CF11 9AB Tel: +44 (0)2920 353000

Northern Ireland Headquarters RSPB Belvoir Park Forest Belfast BT8 7QT Tel: +44 (0)28 9049 1547

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The Rare Breeding Birds Panel www.rbbp.org.uk The Old Orchard Grange Road North Berwick East Lothian EH39 4QT Tel: +44 (0)1620 894037 Email: secretary@rbbp.org.uk

Scottish Ornithologistsâ&#x20AC;&#x2122; Club www.the-soc.org.uk Waterston House Aberlady East Lothian EH32 0PY Tel: +44 (0)1875 871 330

Local Bird Recorders www.bto.org/birdtrack/bird_recording/county_bird_recorder.htm www.the-soc.org.uk/soc-recorders.htm

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Appendix 3 – Examples of raptor recording forms Included on the following pages are examples of raptor recording forms. These comprise a summary of the reporting spreadsheet for the Scottish Raptor Monitoring Scheme, and copies of recording forms for hen harrier, short-eared owl, golden eagle and marsh harrier that were provided to fieldworkers taking part in recent national surveys for these species.

Scottish Raptor Monitoring Scheme Reporting Spreadsheet The table below lists and describes the variables that contributors to the Scottish Raptor Monitoring Scheme (SRMS) are asked to submit each year with each site record. In this context, ‘site’ refers to an individual home range of a given raptor species during the breeding season.

These variables are incorporated into a standard reporting spreadsheet which is circulated to all contributors. A copy of the spreadsheet is available from the Raptor Monitoring Officer (see contacts in Appendix 2).

Contributors are asked to provide a six figure grid reference for each nest site if at all possible, to facilitate rigorous analyses of the information and maximise the value of the data for nature conservation purposes. All such location information provided to the Scheme is stored securely and used only for agreed purposes. If contributors do not provide a grid reference, they are asked to ensure that a unique site code and site name are given and are used consistently between years.

Geo-referenced data are requested to ensure that information submitted to the SRMS can be used to derive the most robust trend information possible for a number of variables (e.g. occupancy and productivity) for as wide a range of raptor species as possible. The ability to track sites across years is important in this respect. If the turnover of sites between years is high, i.e. most fieldworkers do not visit the same sites each year but visit different sites in different years, then year to year changes in a given variable, such as productivity, may result at least partly from the different characteristics of the sites checked in different years.

If the same set of sites is checked each year, then any changes are likely to be more clearly attributable to other environmental factors rather than to differences in site locations.

Provision of six figure grid references allows the locations and site codes received for each species in each year to be checked and the number of years in which data has been received for individual sites to be identified. This in turn allows the degree of site turnover and the robustness of trends to be assessed. Tracking sites across years also allows the identification of sites that have a history of failure, for example, and which can be investigated in relation to other factors.

For any given species, the potential to identify robust trends is also enhanced if the sample of sites (raptor home ranges) from which data are derived is as large as possible. To minimise bias, the sample must also be representative of the area or habitat under consideration and Raptors: a field guide for surveys and monitoring

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ideally sites should be selected at random. As sites monitored for the Scheme are not selected at random, there is a need to assess whether they are broadly representative of the spatial units (e.g. regions of Scotland) for which trends are desirable. To facilitate this, location information is required for as many sites as possible.

For the purposes of recording productivity, contributors to the Scheme are asked to try to make a visit to each site at an appropriate time (or times) to check whether any young have fledged.

Additional visits at intermediate stages of breeding to record clutch size and brood size are also desirable if it is possible to obtain information without risk to the breeding attempt.

Variable name (*= optional variable)

Variable description or recording options

Year

Year (e.g. 2009)

Observer

Name of observer

Contributors are asked to be consistent in spelling between years to facilitate automatic sorting of data.

Source

A note of the organisation with which the observer is affiliated e.g. a regional Raptor Study Group

Contributors are asked to be consistent in spelling between years to facilitate automatic sorting of data.

Species

The name of the raptor species to which the nest record belongs

The spreadsheet includes a drop-down menu of all species which breed regularly in Scotland.

Area / district

A discrete study area or sub-area covered by the raptor worker

Contributors are asked to be consistent in spelling between years to facilitate automatic sorting of data.

Site code

A unique code for a particular nest (typically a mixture of letters and numbers)

Contributors are asked to be consistent in spelling between years to facilitate automatic sorting of data.

Site name

A unique name for the nest site

Contributors are asked to be consistent in spelling between years to facilitate automatic sorting of data.

Grid reference

Grid reference with two upper case letters and 6 or 4 numbers, no spaces

Six figure grid references are requested for each nest site if possible. All such location information provided to the Scottish Raptor Monitoring Scheme is stored securely and used only for agreed purposes. If a grid reference is not provided, contributors are asked to provide a unique site code and site name and to ensure that both of these are used consistently between years.

Monitoring record

Recording options: Site monitored in previous years Site not monitored previously Site newly occupied by birds

Contributors are asked to provide details of whether or not a site has been monitored previously or whether it is known to be a newly occupied site by selecting an option from a drop-down menu.

Alternate 1 to 4*

Unique nest codes

Where appropriate, contributors are asked to provide site codes of possible alternate nest sites within the same nesting range (up to four can be listed in separate columns).

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Notes on recording

Variable name (*= optional variable)

Variable description or recording options

Notes on recording

Nesting habitat 1 and 2

Recording options: Montane (Arctic-Alpine) Heather moorland Grass moorland Mixed moorland Scrub Upland farmland/sheepwalk Machair Lowland pastoral farmland Lowland arable farmland Lowland mixed farmland Coniferous woodland - mature commercial Coniferous woodland - young commercial Coniferous woodland - mature native Coniferous woodland - replant native Clearfell/brash Deciduous woodland - mature Deciduous woodland - young Mixed woodland – mature Mixed woodland - young Marshland/reedbed Urban/industrial Estuarine Coastal Other - specify in notes

Contributors are asked to record one or two habitats, selected from a drop-down list, which are considered most important in an appropriate area around the nest site. Whilst the area of importance will vary between species, the area within 1 km of the nest site could be used as a guide. The most extensive habitat is recorded under ‘nesting habitat 1’ and the second most extensive (if any) under ‘nesting habitat 2’.

Nesting habitat 1 need not be the habitat within which the nest is located. For example, if a pair of red kites is nesting in a small conifer plantation but the majority of the area is mixed farmland, ‘mixed farmland’ should be recorded under nesting Habitat 1 and ‘coniferous woodland - mature plantation’ under nesting habitat 2. Nesting habitat 2 need not be used unless a second habitat is considered important for the study species or forms a significant proportion of the whole area available to the pair.

Management

Recording options: Actively keepered upland (e.g. muirburn, grouse butts, crow traps present) Actively keepered lowland (e.g. traps, release pens, supplementary food present) Not actively keepered (no evidence of active game management) Managed for stalking only (e.g. known stalker, high seats, recent signage present) Stalking with walked-up grouse Unknown

If one or both nesting habitats are managed for country sports, contributors are asked to indicate this using the drop-down menu, or enter ‘unknown’ if they are unsure whether any such management takes place.

Nest site

Recording options: Alder Ash Aspen Beech Birch Elm Gean Horse chestnut Oak Rowan Other broadleaf Douglas fir Larch Lodgepole pine

Contributors are asked to select the nest site location (the tree species for a tree nest, vegetation type for a ground nest or the type of cliff or building) from a list of options in a dropdown menu.

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Variable name (*= optional variable)

Variable description or recording options

Notes on recording

Norway spruce Scots pine Sitka spruce Other conifer Heather Grass Bracken Rush Bog myrtle Reedbed Dam Active quarry Disused quarry Coastal cliff/crag Inland cliff/crag Ravine Small rocky outcrop Farm building in use Derelict building Industrial/urban building Other building Pylon Bridge Other (specify in notes) Nest type

Recording options: New self-built nest Old self-built nest Old other speciesâ&#x20AC;&#x2122; nest Natural cavity Man-made cavity (e.g. in building) Scrape Nest box Nest platform Other man-made Other (specify in notes)

Contributors are asked to select the nest type from a list of options in a drop-down menu.

Distance to vehicular track*

Recording options: <100 m 100 m - 500 m 500 m-1000 m >1000 m (1 km)

Contributors are asked to indicate the approximate distance to the nearest driveable track (which may be private and only accessible to off-road vehicles). This request is optional but may be used to investigate potential impacts of human disturbance.

Distance to public road*

Recording options: <100 m 100 m - 500 m 500 m-1000 m >1000 m (1 km)

Contributors are asked to indicate the approximate distance to the nearest surfaced public road. This request is optional but may be used to investigate potential impacts of human disturbance.

Visit dates

Dates (dd/mm)

Contributors are asked to enter the dates of all visits to the site in the recording year. They can submit either all visits in a single row of the spreadsheet, with summary data about the nesting attempt, or (preferred option) they can submit a row for each visit, with nest contents at each visit specifed.

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Variable name (*= optional variable)

Variable description or recording options

Notes on recording

Checked for occupancy?

Recording options: Adult pair Single adult Single immature Immature pair Adult female Adult female/male unaged Adult male Adult male/female unaged Immature male Immature male/female unaged Immature female Immature female/male unaged Mixed adult/immature pair Unaged pair Unaged individual Fresh signs but no birds Old signs but no birds No signs and no birds Not checked

Contributors are asked to select from a dropdown menu to record whether the site was found to be occupied and the evidence for this (for example, a pair of birds, a single bird, of what age, or other fresh signs that the species was present e.g. splash marks, plucked prey, moulted feathers). If a site was not checked in the reporting year, contributors are asked to record ‘Not checked’ in this column. For analysis purposes it is important to know which sites were not checked each year.

Eggs laid

Recording options: Outcome unknown No Yes 1 1+ 2 2+ 3 3+ 4 4+ 5 5+ 6 6+ 7 7+ 8 8+ 9 9+

Contributors are asked to complete this column if they are able to visit at an appropriate stage of breeding, without risk to the breeding attempt, and record the nest contents (either from a distance or by visiting the nest) or infer that eggs were laid from the behaviour of birds.

Eggs hatched

As above

Contributors are asked to complete this column if they are able to visit at an appropriate stage of breeding, without risk to the breeding attempt and ascertain whether eggs have hatched (either by observing from a distance or by visiting the nest) or infer hatching from the behaviour of birds.

Large young

As above

Contributors are asked only to make an entry in the ‘young fledged’ column if they are certain that the young fledged (e.g. if fully feathered young are seen in or close to the nest). If young are ringed a short time before fledging or observed them in the nest at a distance, the ‘large young’ column should be used instead.

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Variable name (*= optional variable)

Variable description or recording options

Notes on recording

Young fledged

As above

See above.

Reason for failure

Recording options: Deliberate human Accidental human Predation - mammal Predation - avian Predation â&#x20AC;&#x201C; other (specify in next column) Predation - unidentified Poor weather Starvation Adult(s) disappearance Infertile eggs Other cause (specify in next column) Unknown cause

If a breeding attempt fails to produce fledged young, contributors are asked to select a reason for failure from the drop-down menu if there is evidence that enables an objective decision to be made with respect to the cause of failure.

Supporting evidence for failure

(Free text field)

Contributors are asked to provide supporting evidence for their conclusion with respect to nest failure. For example broken egg shells or chewed feathers close to the nest as evidence for a mammalian predator or for deliberate human intervention a shot or poisoned carcass, poison bait or an illegal trap set close by or evidence that someone had been close to the nest. If human persecution is suspected as much detail as possible in terms of supporting evidence is requested.

Persecution incident reported to RSPB

Recording options: Yes No

Contributors are asked to indicate if a suspected persecution incident was reported to the RSPB.

Persecution incident reported to Police

As above

Contributors are asked to indicate if a suspected persecution incident was reported to the Police.

Number of people see (potential for disturbance)*

Recording options: 0 <5 5 to 10 >10 >100

Contributors are asked to select from the dropdown menu the approximate total number of people seen within 1 km of the nest site during all visits made. This information is not essential but could help us to investigate the potential effects of human disturbance.

Other notes

(Free text field)

A space to specify further information where requested, or for further details that a contributor wishes to provide. To facilitate data analysis, contributors are asked to use existing recording fields and variables to enter information if at all possible.

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Hen harrier and short-eared owl The text below is reproduced from the instructions for fieldworkers for the 2004 national hen harrier survey of the UK and Isle of Man (Sim et al., 2007). Fieldworkers were asked to survey a sample of 10 km squares of the national grid, and to complete a form and map for each 10 km square. Fieldworkers were asked to record details of hen harrier sightings according to the instructions below. They were also asked to record, on a separate form, all observations of short-eared owls made during the hen harrier survey fieldwork (see Calladine et al., 2005; short-eared owl species account in Etheridge et al., 2006).

Recording form

When you have finished survey work for the day you should complete or (on a second or subsequent visit to the same area) update a survey form — please use clear handwriting. In the top part of the form enter: • • • • • •

the nearest place name to the surveyed area; the name of all observers surveying the 10 km square; the grid reference of the square; the county or region the square is located in; the name of the study group to which the observers belong; the number of pages and current page number, e.g. page 1 of 2 (where more than one page is used, please repeat all the top part information in case the forms become separated).

In the mid-part of the form enter the details of hen harriers seen in the 10 km square.

•

•

• • • • • • •

Record Number: number each nest or sighting of one or more harriers at one point (1, 2, 3 etc.), and mark the corresponding location on the map, preferably in red pen, (e.g. 1, 2, 3 ...) with that number. Remember to use the same numbers whenever you do an additional visit to the same nest or pair.

Grid Reference: two letters and six numbers e.g. SX 123234 (one letter and six numbers in Northern Ireland). This detailed information is of great value to RSPB and other conservation bodies, and all records will be kept in strict confidence.

Date: e.g. 01 05 = 1st May. Hen Harrier Numbers: record the number of adult males, immature males and females at each location.

Behaviour Code: record the behaviour of all harriers seen, using the codes given on the recording form. This will be used to determine whether breeding has been proved, probable or unlikely.

Habitat Code: the dominant habitat within a 100 m radius of each sighting or nest.

Heather moor type: say whether or not the moor is managed for grouse shooting. Such moors will typically have shooting butts and rotational heather burning.

Nesting Evidence: for each nest found record the number of eggs, chicks or fledged young, if known.

Comments: further information which you think may be useful, such as grazing pressure, nest success or failure and general comments. Also include any information on known or suspected persecution incidents.

There may be cases where no hen harriers are found in a 10 km square. If this occurs, please enter details of the visit dates and area covered and write ‘NIL RETURN’ in the boxes supplied for recording the number of harriers. Comments as to your opinion of the suitability of the habitat for nesting harriers would be welcome.

Maps

You will be required to photocopy the 1:50,000 map of the 10 km square onto the back of the recording form. You will need at least a further three photocopies of the Landranger map for each 10 km square. To obtain a suitable quality copy, on the photocopier increase the copy density or darkness to two or three stops darker than the normal mid setting. Adjust the zoom to reduce the size of the photocopy to 90% so that all of the 10 km square can fit onto A4 with space for the grid numbers. Please ensure that the grid numbers and OS map number are clearly written on the copy.

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Take a new field map on each visit to the study area/10 km square and mark clearly the boundary of the 10 km square on it. Areas where the habitat is unsuitable should be shaded with a highlighter pen and marked ‘UNSUITABLE HABITAT’. Areas where access is refused should be shaded a different colour and marked ‘ACCESS REFUSED’.

Once completed this map and form will constitute your return for the nominated 10 km square.

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Golden eagle The following form was used for the third national golden eagle survey of Great Britain in 2003 (Eaton et al., 2007). A complete census of the breeding population was conducted, for comparison with the results of the two previous surveys in 1992 and 1982. This survey was designed to provide valuable data on factors affecting golden eagle habitat use, and to provide information on the location of breeding sites for site and species protection purposes.

The survey aimed to cover all known golden eagle home ranges, past and present. Surveyors were asked to visit ranges that had not been occupied in recent years (and in some cases not for many years) as well as ranges presently known to be occupied. As well as checking for breeding eagles, observers were asked to check for non-breeding birds which may be resident or passing through, an important component of the survey.

Fieldworkers were asked to complete forms according to the instructions below.

The survey forms We have attempted to keep the survey forms simple, and the amount of data collected to a minimum.

However, we would welcome any further data observers may be willing to provide on separate (attached) sheets.

Please try to write legibly within the spaces supplied, and remember to put your name in the box provided along with the home range code (please check with your regional coordinator if you have any uncertainty regarding the correct code) on each sheet.

Form 1 Summary of eagle breeding activity This form is intended to summarise observations of breeding activity in a home range over the three (or two, if unoccupied) visits, and to record productivity if breeding was attempted. Incubation or brooding behaviour can be used as indication of egg or chick presence respectively, and should be used if efforts to see eggs or chicks are likely to disturb the birds. Very few chicks that survive to eight weeks do not subsequently fledge. Therefore, if at the last visit by a surveyor a chick is still in the nest but over eight weeks old, it can be recorded as ‘fledged’.

Please record details of all the birds that were recorded during the field season in the table provided, assigning each individual a number from one upwards. Although observers with experience (and possibly personal knowledge of the individual birds concerned) may be able to age birds with great precision, we would urge caution due to the great variation that can occur in the signs of age between individual eagles. Eagles should be assigned to one of three categories: •

•

•

2nd–3rd calendar year: underwing with distinct white patches, varying from just the base of the inner four primaries on some individuals to the base of all primaries and along the secondaries on others. Apart from white patch, upperwing uniformly dark brown with little contrast between coverts and secondaries, although some more advanced birds can show a paler panel. Tail has a white base sharply demarcated from dark band at tip.

Sub-adult: still white on the primary bases forming patch on underwing, although generally reduced from younger birds and may be small. Marked contrast between bleached upperwing (greater and median) coverts and dark secondaries. White tail base still present but less distinctly demarcated from dark tip than on younger birds.

Adult: no white on the wing, although some individuals may show a very pale tail base.

If you are uncertain about the age of a bird, please record it as ‘unknown’, or as ‘immature’ if not certain whether it is a 2nd–3rd calendar year bird or a sub-adult.

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There is space to add any notes concerning decisions made on the ageing and sexing of eagles, plus anything surveyors may feel noteworthy about individual birds.

Reverse side - summary of all visits made Please list all visits that were made to the home range in this table, regardless of whether birds were seen. Please give details of all birds seen, referred to by the numbers assigned on the first page of the form. Nest sites should be given a letter code (please keep to any previously used codes, if available) and full details given on Form 2 (see below). Please remember to record any new alternate nest sites and give them an appropriate new code. This form should also be used to give details on any signs recorded and used as proof of home range occupation in the absence of sightings of eagles.

The 1992 survey requested details of breeding success in home ranges in all years since 1983. We have decided against requesting this volume of information for this survey and appreciate some fieldworkers may have reservations about providing it. However, we would be grateful if surveyors would indicate in the box at the bottom of Form 1 whether they have this data and would be prepared to provide it if asked. There are specific research questions, and species protection issues, for which such series of data would be particularly valuable.

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Form 2 Details of all nest sites within home range Please use this form to list all nest sites, used and unused, which were surveyed in 2003 and any others known but not surveyed (although if possible, please visit all nest sites). Please record the basic nest details — whether a tree or cliff nest, accessibility, and estimated distance to the nearest footpath and track. The latter will be used in an analysis of possible disturbance effects on nest site choice by eagles, and is one of the reasons we are very keen to get information on unused alternates as well as the occupied nest sites. Please try not to just record this information only for those ranges or nest sites where you think disturbance may be problem, as if we only have this data we will have no means of making an appropriate comparison. In addition, we would be grateful if surveyors could record the dominant land use category within 6 km of nest sites. Codes are given for the four main land use types (deer forest, grouse moor, sheep, forestry); if surveyors are entering ‘other’ we would be grateful for brief details.

Reverse side — details of areas covered during surveying In order that we know which areas were covered during surveying, we would like details of all 1 km grid squares visited, with brief information about the visit and any eagles seen, using the numbers assigned to birds on Form 1.

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Form 3 Records of persecution Unlike the 1982 and 1992 surveys, this survey does not request details of breeding attempts in a home range over previous years. However, information on persecution would be extremely valuable for helping the work of the RSPB and SNH in preventing and prosecuting raptor persecution. Please record all incidences of raptor persecution that you have records of, or can recall, at any time dating back to the last golden eagle survey (1992). Even if you are unsure of the exact year, any details you can recall may be helpful. Please be as specific as possible about the details of any evidence of persecution. If there is no evidence of any persecution, please record this, so that this is clear when we later collate survey forms.

Reverse side â&#x20AC;&#x201D; nest site location.

The exact location of the active nest site can be recorded on the reverse of Form 3. Notes on exact nest locations made by observers in 1992 are going to be very useful during the present survey, helping surveyors to locate nests in home ranges that are not regularly surveyed. Likewise, any information recorded in 2003 may help surveyors in the course of the next survey. They will also be valuable in species protection work. Please record any information on nest location on the reverse of sheet 3: a written description, a sketch map or a sketch of the actual view of the nest. If possible, a photograph of the nest and its surroundings would be particularly valuable (please attach to the form and write the home range code on the back).

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Marsh harrier Recording form for the 2005 survey which covered potential breeding areas throughout the UK.

During incubation

After hatching

(tick one)

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Appendix 4 – Scientific names of species mentioned in the text Birds* American kestrel Falco sparverius Bald eagle Haliaeetus leucocephalus Magpie (Eurasian magpie) Pica pica Kingfisher (common kingfisher) Alcedo atthis Pheasant (common pheasant) Phasianus colchicus Woodpigeon (common wood pigeon) Columba palumbus Cormorant (Great cormorant) Phalacrocorax carbo Carrion crow Corvus corone Crow Corvus spp.

Ducks Anatidae Jay (Eurasian jay) Garrulus glandarius Geese Anser spp., Branta spp.

Grey heron Ardea cinerea Great skua Stercorarius skua Grouse Lagopus spp., Tetrao spp.

Gulls Laridae Hooded crow Corvus cornix Lesser spotted eagle Aquila pomarina Meadow pipit Anthus pratensis Pigeons Columbidae Feral pigeon/rock dove (common pigeon) Columbia livia Ptarmigan (rock ptarmigan) Lagopus mutus Rook Corvus frugilegus Swainson’s hawk Buteo swainsoni Swans Cygnus spp.

Swift (common swift) Apus apus Terns Sternidae

Mammals American mink Mustela vison Badger Meles meles Bank vole Clethrionomys glareolus

Bats Chiroptera Collared lemming Dicrostonyx groenlandicus Deer Cervidae Field vole Microtus agrestis Hare, leveret Lepus spp.

Mice Apodemus spp., Mus spp.

Orkney vole Microtus arvalis orcadensis Pine marten Martes martes Rabbit Oryctolagus cuniculus Rats Rattus spp.

Red fox Vulpes vulpes Sheep Ovis aries Stoat Mustela erminea Squirrel Sciurus spp.

Voles Clethrionomys spp., Microtus spp.

Weasel Mustela nivalus Wildcat Felis silvestris Wood mouse Apodemus sylvaticus

Reptiles Adder Vipera berus

Insects Bee Hymenoptera Emporer moth Saturina pavonia Flea Siphonaptera Hornet Hymenoptera Northern eggar moth Lasiocampa querqus Wasp Hymenoptera

Arthropods Ticks Ixodidae

Plants Ash Fraxinus excelsior Beech Fagus sylvatica Birch Betula spp.

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Bracken Pteridium aquilinum Bramble Rubus spp.

Common reed Phragmites australis Douglas fir Pseudotsuga menziesii Elm Ulmus spp.

Field woodrush Luzula campestris Fir Abies spp.

Gorse Ulex spp.

Hawthorn Crataegus monogyna Heather Calluna vulgaris, Erica spp.

Ivy Hedera helix Larch Larix spp.

Norway spruce Picea abies Oak Quercus spp.

Oil-seed rape Brassica napus Pedunculate oak Quercus robur Purple moor grass Molinia caerulea Common reed Phragmites australis Rosebay willowherb Epilobium angustifolium Rowan Sorbus aucuparia Rushes Juncus spp.

Scots pine Pinus sylvestris Sessile oak Quercus petraea Spruce Picea spp.

Sitka spruce Picea sitchensis Sycamore Acer pseudoplatanus Willow Salix spp.

* English names for bird species follow the list of vernacular names recommended by the British Ornithologistsâ&#x20AC;&#x2122; Union (www.bou.org.uk/recbrlstbni.html). Recommended international English names for bird species (Gill et al., 2009) are included in brackets where these differ from the vernacular names (see also editorial note, page xii). The scientific names of the raptor species for which survey methods are described are included in the species accounts.

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Glossary The glossary includes definitions of selected terms used in the text and also full names for all acronyms. Many of the definitions are adapted from Campbell & Lack (1985). Italics indicate a term defined elsewhere in the glossary. Terms which are defined in the text are not included in the glossary (their definitions can be found by checking the index).

Accipitriformes: sometimes known as accipiters or hawks, a large order (taxonomic grouping) of diurnal birds of prey that includes the honey-buzzards, kites, harriers, eagles, sparrowhawks, goshawks, buzzards and osprey.

Addled: an egg in which the developing embryo has died, as opposed to an infertile egg in which no development has taken place.

Assemblage: a collective term for a group of different species found in the same area.

Asymptotic: a mathematical term which may be applied to a growth curve, where the given parameter, such as body mass, increases rapidly for a period and then levels off as the bird reaches adult size. The asymptote is the maximum value reached.

Asynchronous hatching: when the eggs of a clutch do not hatch at the same time, but instead over a period of time; in some species of birds of prey, several days may elapse between the hatching of the first and last chicks. Asynchronous hatching generally occurs if incubation begins before all the eggs in a clutch are laid.

ASL: above sea level (for altitude measurements).

BBS: the BTO/JNCC/RSPB Breeding Bird Survey which monitors population changes of more than 100 widespread birds in the UK. Biome: an extensive, ecologically defined region such as tundra, savannah, grassland, desert, and temperate and tropical forest.

Brooding: parent birds brood small chicks by covering them, usually in the nest. The main purpose of brooding is to keep young nestlings warm, but also on occasion to protect against hot sun, rain or predators. In raptors it is usually the female that broods the young.

BTO: the British Trust for Ornithology.

CBS: the Countryside Bird Survey run by BirdWatch Ireland to monitor population tends of widespread birds in the Republic of Ireland.

CCW: the Countryside Council for Wales.

CEH: the Centre for Ecology and Hydrology (Natural Environment Research Council); formerly known as ITE. Cold searching: in the context of this book, cold searching means surveying an area without prior knowledge of the distribution of the target species and/or its nests, roosts or other signs of occupation or breeding.

Conspecific: a term used to describe organisms that belong to the same species.

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Corvids: members of the family Corvidae, a taxonomic group of passerine birds that contains the crows, magpies, ravens and jays.

Coverts: feathers which overlie the bases of the flight feathers of the wing (remiges) or tail (rectrices) on the upper and lower surfaces, and help to smooth airflow. Feathers covering the external ear region are also known as coverts.

Crepuscular: active primarily at dawn and dusk (during twilight). Crepuscular animals may also be active on bright moonlit nights. Many animals that are casually described as nocturnal are in fact crepuscular. Some species have different habits in the absence of predators. For example, in the Galapagos archipelago, the short-eared owl is diurnal on those islands where buzzards are absent, but crepuscular on the others.

Crop: part of the digestive tract; a pouch used to store food temporarily which extends from the oesophagus in some birds. When full it can be seen externally in some species as a bulge in the upper breast (e.g. see Plate 70).

Culmen: the dorsal (top) ridge of a bird’s bill.

DAFF: the Department of Agriculture, Fisheries and Forestry, Isle of Man. Dispersal: the movement of an individual bird from the place of birth to its first breeding locality (natal dispersal). If further movements take place after first breeding, then ‘breeding dispersal’ describes movements between a series of different breeding localities. In many monogamous bird species, female chicks disperse further than males. The term dispersal is also sometimes used in a more general sense, for example to describe the movements of birds away from a communal roost on a daily basis.

EN: English Nature, which became part of Natural England in October 2006.

Eyrie: the nest of a bird of prey, most often applied to nests on cliffs or crags or high in trees. It may refer to a scrape on a cliff ledge (e.g. peregrine) or a large bulky nest (e.g. osprey).

Extra-pair copulations: matings that take place between birds that are not members of a pair; for example if a female paired to a particular male mates with another male.

Falconiformes: an order of diurnal birds of prey containing kestrels, merlin, hobbies and peregrine. Falcons differ from Accipitriformes in several ways, including some parts of the skeleton, bill structure and the sequence of moult of the primary feathers.

Fidelity: faithfulness, returning to or remaining in an area (site-fidelity) or with a mate (matefidelity) over time. In some bird species a pair which has bred successfully may be more likely to show fidelity to a site and/or to each other than an pair which has been unsuccessful.

Fledging: used in this book to refer to the acquisition of the ability to fly by raptor chicks. This may coincide with the time of leaving the nest, or, in species where the young disperse from the nest before they can fly, may take place after leaving the nest. For each species the average age of fledging (days after hatching) is given. The precise point of fledging can be difficult to define, however, as, for example, the young of some species may regularly return to the nest after taking their first flights. The definition of fledging varies in the scientific literature (Middleton & Prigoda, 2001) and it may also be described as: the act of leaving the nest; or the acquisition by a young bird of its first true feathers (a bird may be said to have fledged when this process is complete) GPS: Global Positioning System.

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Growth curves: changes in a measured feature, such as body mass or wing length, over time; in this book these are used in the context of the growth of raptor chicks. If values for a measured feature are available for chicks of known age they can be plotted against time and the resulting growth curves can be used to estimate the age and/or sex of conspecific raptor chicks measured during a single nest visit.

Hallux: the first toe (or ‘big toe’) of a bird’s foot, usually opposed or directed backwards which allows for grasping and perching.

Immature: a young bird that is not yet sexually mature, the usual assumption of which is the attainment of full adult plumage. The immature stage of some species such as golden eagles may last for several years, during which time the plumage may change recognisably as the birds moult, and can be used to estimate age. (See also juvenile.)

Incubation: the process whereby the heat necessary for embryonic development is applied to an egg after it has been laid; such heat is usually derived from the body of the parent bird covering the eggs. There are various different definitions of incubation period in the literature. The incubation period per egg is often quoted. This may be defined as the average time taken for an egg to hatch once incubation starts; the time between the laying and hatching of a single egg; or the time that elapses, with regular uninterrupted incubation, from the laying of the last egg in a clutch to the hatching of that egg. The incubation period for a clutch of eggs can be defined as the time period from the start of incubation by the parent bird(s) until all eggs are hatched, or the time from the laying of the first egg to the hatch of the last egg. If full incubation starts with the first egg, as is the case for many raptors, then the young may hatch at similar intervals to those at which the eggs were laid (asynchronous hatching). If proper incubation starts with the final egg then the earlier eggs may have received some intermittent warmth and undergone some development so that hatching may occur in rapid succession but the precise period of incubation per egg will differ between eggs (Harrison, 1975).

Accurate determination of incubation period requires intensive observation of nests (and if incubation per egg is being measured, marking of eggs). The sources for the incubation periods quoted in this book did not always specify whether they were for an egg or a clutch.

Interspecific: between different species, for example interspecific variation in body mass means variation between individuals of more than one species; as opposed to intraspecific.

Intraspecific: refers to variation within individuals that belong to the same species.

ITE: the former Institute for Terrestrial Ecology, now renamed as CEH. Jesses: leather straps used to tether the legs of a hawk or falcon in falconry.

JNCC: the Joint Nature Conservation Committee. A Statutory Nature Conservation Agency with a UK remit (sometimes referred to as special functions).

Juvenile (juvenal): a young bird in its first flying plumage. Some authorities apply the term juvenile to young raptors up until the end of their first calendar year, and thereafter refer to them as immature.

Keratinous: containing keratin, a structural protein forming the basis of feathers and claws (as well as skin and hair).

Lagomorphs: an order (taxonomic group) of mammals which includes rabbits and hares.

Mantling display: a type of behaviour where a perched bird spreads its wings and tail to cover prey, usually to prevent the prey being taken by a potential thief.

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Mass: a measure of the amount of matter in a body, measured in grams. Although the terms mass and weight are sometimes used interchangeably, strictly, weight is the force of gravity acting on a body determined by multiplying its mass by the acceleration due to gravity.

Metapopulation: literally a population of populations; a collective term for a group of individuals of a single species that consists of a number of discrete populations between which there is some (limited) interchange of individuals, for example, butterflies occupying grassy clearings in woodland.

Monogamous: used to describe the pairing of a male and female to the exclusiveness of other individuals; however, pairs are often more accurately described as ‘apparently monogamous’ because paired males and females may seek extra-pair copulations if the opportunity arises.

Moult: the periodic shedding and replacement of plumage. Because they become worn over time, feathers must be replaced to maintain their functions, including flight performance. Within each tract of feathers, feather loss and replacement proceeds in a regular sequence that varies between different orders/families of birds. In many species, including raptors, flight feathers are moulted sequentially so that the birds retain the ability to fly. Some birds, however, shed all flight feathers simultaneously and are temporarily unable to fly during moult (e.g. ducks, geese and swans).

Neotropical region: as defined in zoogeography (the study of the distribution of species), this includes tropical America, South America and nearby islands.

NIEA: the Northern Ireland Environment Agency (formerly the Environment and Heritage Service).

NPWS: the National Parks and Wildlife Service, Ireland.

NRC: Nest Record Card – the recording system for the BTO/JNCC Nest Record Scheme which operates in the UK. Palaearctic region: includes all of Europe, Africa north of the Sahara, Asia north of the Himalayas, and the northern and central parts of the Arabian Peninsula.

Passeriformes: a large and diverse order (taxonomic grouping) of birds. Passerines are sometimes known as perching birds or song birds.

Passerines: bird species of the order Passeriformes.

Pins: a term which may be applied to the sheaths around the growing wing and tail feathers of a nestling bird. The pins split and are lost as the feathers emerge.

Polyandry: a female mated to more than one male.

Polygamy: mating with more than one member of the opposite sex.

Polygyny: a male mated to more than one female.

Population: a group of individuals of the same species occupying a particular geographical region.

Pulli (singular pullus): chicks; young birds prior to fledging.

Race: or subspecies, a discernibly different, geographically defined population within a species.

Random: a random sample from a population is one where every member of that population has an equal chance of being selected.

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Raptor: the traditional term for a bird of prey, derived from the Latin verb rapere, ‘to take by force’.

RBBP: the Rare Breeding Birds Panel.

RSPB: the Royal Society for the Protection of Birds.

Sexual dimorphism: differences in size and appearance (with regard to colouration this is sometimes called dichromatism) between males and females of the same species. In raptors the female is usually larger than the male, sometimes referred to as ‘reverse’ sexual dimorphism, because in many dimorphic species males are the larger sex. As the term sexual dimorphism is derived from morphology (the study of form), strictly speaking it should not be applied to differences in calls or behaviour between males and females, but the term is often used to include such differences as well.

SNH: Scottish Natural Heritage.

SOC: the Scottish Ornithologists’ Club.

SPA: a Special Protection Area for birds, a protected area classified under the EU Wild Birds Directive (79/409/EEC; often referred to as the Birds Directive).

Species: a number of different definitions exist in the scientific literature but essentially a species is a group of natural populations of a bird (or other organism) whose members can interbreed and produce viable, fertile offspring. The species is the basic level of taxonomy, which is the naming and classification of plants and animals.

SRMG: the Scottish Raptor Monitoring Group, which oversees the SRMS. SRMS: The Scottish Raptor Monitoring Scheme.

SSSI: a Site of Special Scientific Interest, a statutory (legally protected) nature conservation area in Britain. In Northern Ireland, equivalent sites are known as Areas of Special Scientific Interest (ASSIs).

Standard deviation (SD): a statistical term which describes the spread of data around the mean or average. If the standard deviation of a measurement such as the wing length of raptor nestlings of a given age (e.g. the growth curves of raptor chicks included in some species accounts) is close to zero then the data points are bunched tightly around the mean and the variation between individuals is small; if the standard deviation is large then this implies a high degree of variation between individuals. The SD therefore tells us a lot about the variability of data, and can be important in helping people think about why a particular dataset has a lot or little variation around the mean.

Standard error (SE): a statistical term; a standard error (sometimes called the standard deviation of the mean) is often calculated for a mean (average) value of a particular series of measurements, such as the mean mass of raptor nestlings of a given age (e.g. in the growth curves for raptor chicks included in some species accounts). A mean calculated from a sample of nestlings is in fact an estimation of the true mean, which would be arrived at if all nestlings within the population were measured. There is a 95% chance that the true population mean lies within approximately 2 standard errors either side of the measured mean.

Statistical confidence limits: these may be applied to the results of a survey to determine the size of a raptor population in a given geographical area based on surveys of a sample of study plots within that area. Because the entire population is not surveyed, the results of such surveys represent an estimate of the population size rather than Raptors: a field guide for surveys and monitoring

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a complete count. In such cases, it is normal to calculate 95% confidence limits that represent the range of values within which there is a 95% chance that the true population count lies. Statistical confidence limits can also be applied to measurements of raptor chicks and many of the growth curves in the species accounts show mean values and 95% confidence limits.

Statutory Country Conservation Agencies / Statutory Nature Conservation Agencies: a collective name for the Government funded conservation agencies in the UK, Isle of Man and Republic of Ireland: the Countryside Council for Wales; the Department of Agriculture, Fisheries and Forestry, Isle of Man; the Northern Ireland Environment Agency; the National Parks and Wildlife Service, Ireland; Natural England (which came into being in October 2006 and includes the former agency, English Nature); and Scottish Natural Heritage (website addresses and contact details given in Appendix 2).

These agencies have statutory or legal duties relating to nature conservation in their respective countries, including the conservation of birds of prey.

Stratified sampling: is a method of sampling from a population whereby members of the population are divided (i.e. ‘stratified’) into subgroups before sampling. It can be used to improve the accuracy of population size estimates. An example is provided by the 2004 hen harrier survey in Scotland. That survey covered a sample of study plots (in this case 10 km squares of the national grid) within the known range of the hen harrier in Scotland (which includes all 10 km squares for which there are records of hen harrier sightings since fieldwork for the first Breeding Atlas (Sharrock, 1976) began in 1968). All 10 km squares within the known hen harrier range were divided into three groups or ‘strata’. The first stratum (singular form of strata) comprised areas monitored regularly by members of the SRSG and a number of Special Protection Areas (SPAs) or potential SPAs, for which the hen harrier is formally recognised as a ‘qualifying interest feature’. These areas were selected for a complete survey (100% sampling). The remaining area from the known hen harrier range (362 10 km squares) was divided between two sampling strata. Stratum two consisted of 55 squares known, or suspected, to hold relatively high hen harrier numbers (based on recent survey work); a random sample of 26 (47.3%) of these squares was selected for survey.

Stratum three consisted of the remaining 307 squares from within the known range, for some of which there are few or no recent records of hen harriers; 43 (14.0%) of these were randomly selected for survey to assess whether there had been any recolonisations. Sampling intensities (i.e. the proportions of squares surveyed in each stratum) were selected in proportion to the expected number of territorial pairs within the strata (Sim et al., 2007).

Strigiformes: the order (taxonomic group) of birds which includes all owl species.

Study plot: a defined geographical area within which survey fieldwork is carried out. This term can be applied to an area identified by an individual fieldworker for survey work on a particular species. Surveys designed to produce estimates of raptor populations over large geographical areas may be based on fieldwork within selected study plots (e.g. 10 km squares of the National Grid) within that area.

Thermo-regulation: the process whereby a bird maintains a stable body temperature, irrespective of variations in the temperature of the surroundings. Birds are warmblooded and maintain their body temperature at 40±2°C. In common with most birds, raptor nestlings are unable to maintain their body temperature for a period after hatching. During this time they are kept warm by brooding.

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Index Notes: 1. Italicised page numbers indicate the pages of illustrations; there are frequently textual references on the same page.

2. Bold numbers indicate plate numbers.

3. All references are to the United Kingdom, except where otherwise specified.

4. ff: ‘and following pages/plates’ access to land 39 Accipitriformes 22, 282, 323 Accipiter A. gentilis see goshawk A. nisus see sparrowhawk Accipiters 244 adder 167 addled (eggs) 50, 323 adverse weather see weather aerial display 26, 67, 153, 179, 212, 235 see also display aerial photographs 10 aerial surveys 13-14 ageing and sexing young 33, 35-37, 68, 82 measurements for 50-56 alarm calls 28, 74, 106, 171, 227 ‘alert’ 10 alert distance 67 alula 249 altricial 282 see also semi-altricial Animals (Scientific Procedures) Act 1986 42 annual cycle 13, 35 Aquila chrysaetos see golden eagle ARTS (Automatic Radio Tracking Station) 31 ascendant 244, 246 ash 192, 205, 307 Asio A. flammeus see short-eared owl A. otus see long-eared owl ASL (above sea level) 323 assemblage 7, 10, 69 , 323 asymptotic 116, 148, 323 asynchronous hatching 21, 79, 323 Athene noctua see little owl Automatic Radio Tracking Station 31 avian influenza 61 bacterial diseases 61 badger 74 bald eagle (Haliaeetus leucocephalus) 13 bank vole 209

barn owl (Tyto alba) 3, 14, 15, 25, 36–38, 191–198, 205, 246, 247, 296, 298, 41, 42 Barn Owl Monitoring Programme 15 baskets, nesting 37, 166, 177, 218 bats 178 BBS (Breeding Bird Survey) 7, 14, 50, 297, 298 beech 71, 72, 79, 222, 307 bees 71, 69 bill (culmen), measuring 54, 55, 82, 83, 90, 148, 149, 155, 172, 173, 324 binoculars 46 biological markers 7, 33–35 biome 34, 323 birch 79, 102, 128, 167, 169, 307 Birds Directive (EU) 4, 59 BirdWatch Ireland 14, 296 black kite (Milvus migrans) 239 blood samples 11, 39 licences for 42 BOU (British Ornithologists’ Union) xiv, 5 bracken 102, 167, 169, 218, 224, 308 bramble 218 breeding behaviour of raptors 26 ff display 26 egg laying and incubation 27 hunting and feeding 27 interpretation of 28 evidence for 21 failure 7, 15, 20–23, 27, 46, 68 see also non-breeding pairs 16, 16, 17, 20, 295 rare birds see RBBP season 19 ff, 46, 47, 67, 244, 246, 247, 305 success see productivity Breeding Bird Survey see BBS British Association for Shooting and Conservation 58 British Ornithologists’ Union see BOU British Trust for Ornithology see BTO brood size 46, 66, 72, 306 BTO (British Trust for Ornithology) 3, 4, 5, 7, 14, 15, 29, 30, 31, 33, 37, 39, 40, 41, 42, 44, 49, 50, 59, 61, 62, 303, 323 Raptors: a field guide for surveys and monitoring

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Barn Owl Monitoring Programme 15 Breeding Bird Survey (with JNCC and RSPB) 6, 7, 50, 323 licences and permits see Ringing Unit Scotland 5 see also Ringing Unit Bubo B. bubo see eagle owl B. scandiacus see snowy owl Buteo B. buteo see buzzard B. lagopus see rough-legged buzzard buzzard (Buteo buteo) 3, 7, 14, 15, 20, 25, 26, 30, 32, 71, 72, 79, 81, 88, 107, 119, 136–142, 158, 167, 169, 171, 177, 185, 210, 213, 236, 246, 248, 295, 297, 298, 23, 24 buzzards see buzzard; honey-buzzard; roughlegged buzzard calls, calling 8, 13, 24, 28, 44, 45, 48, 297 see also perching-and-calling; vocalisations call playback 13, 121, 161, 212-213, 206-207, 220 Camphylobacter jejeuni 61 captive birds, escaped 24, 34 carpal joint 244, 249 carrion crow (Corvus corone) 72, 185 CBS (Countryside Bird Survey) 14, 323 CCW (Countryside Council for Wales) 42, 43, 299, 323 CEH (Centre for Ecology and Hydrology, formerly ITE) 3 census techniques 11 Centre for Ecology and Hydrology see CEH cere 54, 90, 181, 58, 59 chemical markers 7, 11, 35–35 chicks crop fullness 55, 56, 75, 142, 181, 324, 70 growth and development 8, 34, 35–37, 282, 58-80 see also growth curves handling and measuring 50–56 see also ageing and sexing young; fledging; immature birds; ringing Circus C. aeruginosus see marsh harrier C. cyaneus see hen harrier C. macrourus see pallid harrier C. pygargus see Montagu’s harrier claw 35, 60, 103 measurement 54, 108, 115 clothing for observers 44, 59, 60, 61 clutch size 46, 66, 72, 306 see also incubation Coillte (Ireland) 43 common buzzard see buzzard common kestrel see kestrel

364 Raptors: a field guide for surveys and monitoring

compass (bearing) 13, 27, 46, 48, 49, 95, 96 Conservation Ranger (Ireland) 58 conspecific 19, 48, 323 contour feather 148, 244, 247 ff copulations, extra-pair 151 cormorant (Phalacrocorax carbo) 35 corroboration (Scots law) 57 Corvidae see corvids corvids 8, 22, 25, 74, 78, 106, 160, 166, 167, 169, 171, 180, 181, 228, 236, 324 Corvus C. corax see raven C. cornix see hooded crow C. corone see carrion crow C. frugilegus see rook see also crows, corvids count units 7, 17 Countryside Bird Survey see CBS Countryside Council for Wales see CCW Countryside and Rights of Way Act 2000 39, 43 coverts 78, 110, 162, 163, 181, 246, 247, 314, 324 crepuscular 45, 179, 194, 203, 226, 231, 324 crime, wildlife/persecution 44, 47, 57-59 crop (digestive tract) 55, 56, 75, 142, 181, 324, 70 crown (of the head) 92, 282 Crown and Common Lands (public ramblage, Isle of Man) 43 crows 20, 79, 81, 137, 159, 166, 167, 169, 171, 172, 177, 185, 210, 213, 218, 236, 239 see also carrion crow; corvids; Corvus; hooded crow; carrion crow Cruelty to Animals Act 1997 (Isle of Man) 42 culmen, (measuring) length see bill DAFF (Departure of Agriculture, Fisheries and Forestry, Isle of Man) 41, 42, 43, 300, 324 demography 18, 29 see also population Department of Environment, Transport and Regions see DETR Departure of Agriculture, Fisheries and Forestry see DAFF descendant 244 ff DETR (Department of Environment, Transport and Regions) 4 diet 35, 136, 207 dimorphism, sexual see sexual dimorphism diseases 60–62 dispersal 10, 11, 18, 32, 34, 324 display 7, 17, 19, 26–27, 28, 33, 45, 48, 67 aerial see aerial display mantling see mantling display see also flight-play; mock-fighting; sky-dancing; soaring-and-calling display; ‘wing-clapping’

disturbance 2, 3, 8, 11, 13, 21, 35, 36, 39 ff, 44 ff, 57, 67, 308 DNA, use for identification 33–34, 42, 58, 75, 83 Douglas fir 71, 307 down 50, 83, 282, 58 ff trails of 21, 23 droppings 20 ff, 25, 61 eagle owl (Bubo bubo) 240–241, 244, 247, 43–44 eagles 30, 31, 236 see also golden eagle; white-tailed eagle EU (European Union) Birds Directive (1979) 4, 59 `ecological traps’ 11 eggs addled/infertile 22, 36, 50, 199, 310 and breeding failure 7, 15, 20–23, 27, 46, 68 density 35–36, 68 handling and measuring 36, 39, 41, 68, 198, 214, 216 laying and incubation 27 mass 35–36, 55 see also clutch size and incubation; nests elm 192, 307 emargination 245, 249 EN (English Nature) 324 see Natural England encephalitis, tick-borne 61 English Nature see EN English Raptor Study Groups 302 Environment and Heritage Service (former) 326 environmental impact assessments (wind farms) 13, 59 equipment basic 46 health and safety 59, 60 radio-tagging 32 night-vision 226 Escherichia coli 61 Eurasian eagle owl see eagle owl Eurasian hobby see hobby Eurasian sparrowhawk see sparrowhawk Europe 5, 6, 7, 61, 70, 72, 77, 85, 86, 91, 245, 298 European honey buzzard see honey-buzzard European Union 4, 6 European Commission 4 extra-pair copulations 151, 324 eyrie 86 ff, 144 ff, 151, 154, 185 ff, 233, 324 failure, breeding 7, 15, 20–23, 27, 46, 68 Falco F. columbarius see merlin F. peregrinus see peregrine F. rusticolus see gyr falcon F. subbuteo see hobby

F. tinnunculus see kestrel falcons 30, 170, 186, 234, 244 see also merlin; peregrine; gyr falcon; hobby; kestrel Falconiformes 8, 282, 324 see also falcons; Falco falconry 24, 51, 269, 325 feathers ix ff, 7, 8, 11, 17, 20, 23 ff, 30, 33 ff, 37, 42, 48, 51, 54, 73 243–280, 1–57 growth 51, 119, 244, 58 ff morphology 244–245, 249 see also alula; contour feather; fledging; moult; moulted feathers; pins; primary; quill; rachis; secondary; wing and tail feathers feeding 27–28 courtship 7 rate 33, 66 fidelity 324 site 29, 30, 34, 66, 106 mate 30 field vole 101, 112, 157 ff fieldwork(er) ix ff, 3 ff, 6–8, 19 ff frequency of site visits 45–46 good practice for 39–63 legal aspects 39–44 minimising disturbance and good field craft 44–45 observer effort 46 population estimates 16, 17 survey methods 11, 13 time of day 45 weather 45 wildlife crime 57-59 see also handling and measuring eggs and young; health and safety; licences and permits; recording observations and site features fir see Douglas fir fledging/fledgling 21–23, 32, 35, 50, 68, 241, 282, 309, 324 flight-play 26, 88, 104 food pass 21, 27, 48, 95, 96, 104, 105, 106, 113 ff, 170, 179, 180, 188, 189 foot 51 ff span, measuring 54 see also tarsus measurement; hind claw fox see red fox Game and Wildlife Conservation Trust 58 Garrulus glandarius see jay genetic markers 11, 25, 33–34, 35 Global Positioning System see GPS golden eagle (Aquila chrysaetos) 3, 5, 7, 9, 11 ff, 17, 19, 20, 26–28, 31, 32, 34, 39, 86, 88, 143149, 158, 167, 185, 233, 244, 246, 282, 295, 298, 25, 26, 58–63 Raptors: a field guide for surveys and monitoring

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recording forms 314–316 Golden Eagle Trust 295, 302 see also Irish Raptor Study Group gorse 111, 137 goshawk (Accipiter gentilis) 13, 14, 19, 26 ff, 32, 38, 65, 71, 72, 79, 117–126, 128, 246, 295, 298, 19, 20 GPS (Global Positioning System) 32, 46 ff, 58, 324 grey heron (Ardea cinerea) 25, 158, 169, 185 grid references, recording 15, 47 ff, 58, 59, 305, 306, 311 grouse 61, 188, 307, 311 butts 169, 307 moor 11, 143, 233, 316 growth curves 34, 36, 37, 68, 325, 327, 328 gulls 22, 25, 88 gyr falcon (Falco rusticolus) 234, 240 habitat 2, 6, 10 ff, 20, 25 ff, 34, 60, 66, 69, 71, 246, 297 description and coding 47–50 Haliaeetus H. albicilla see white-tailed eagle H. leucocephalus see bald eagle hallux 148, 149, 325 handling and measuring eggs and young 50–57 hare 61, 236 see also leveret harriers 14, 17, 26, 27, 30, 244 see also marsh harrier; hen harrier; Montagu’s harrier; pallid harrier hatching, asynchronous 21, 79 Hawk and Owl Trust 14 hawks 244, 323 see also sparrowhawk; goshawk hawthorn 218, 222 head and bill length 37, 55, 55 health and safety 8, 30, 41, 48, 50, 59-64, 67, 73 diseases 60-61 legislation and responsibilities 62-63 Health and Safety at Work Act 1974 62 Health and Safety at Work Inspectorate (Isle of Man) 62 Health and Safety at Work (Northern Ireland) Order 1978 63 Health and Safety Authority (Ireland) 63 Health and Safety Executive (HSE) 60, 62 Health and Safety Executive (Northern Ireland) 62 heather 20, 49, 86, 307 ff hen harrier (Circus cyanus) 3, 4, 5, 7, 12, 13, 14, 20, 23, 26, 27, 30, 32, 100–109, 167, 171, 175, 224, 231, 239, 246, 282, 295, 297, 298, 305, 311, 11–14, 80 recording form 312

366 Raptors: a field guide for surveys and monitoring

hind claw 54, 124, 125, 126, 173, 190 hobby (Falco subbuteo) 7, 14, 15, 20, 28, 176– 183, 234, 246, 282, 296–298, 37, 38, 70–72 holes, nests in 20, 25, 37, 158, 159, 161, 192, 196, 205, 207, 210, 241 Home Office 42 home ranges 11 ff, 17, 18, 19, 20, 27, 34, 45, 46, 47, 57, 66, 67, 68, 295, 305, 314 ff see also nesting range; occupancy; territory honey-buzzard (Pernis apivorus) 5, 14, 15, 28, 32, 70–76, 246, 295, 297, 298, 1, 2 hooded crow (Corvus cornix) 158, 239 hunting (in birds) 19, 21, 27–28, 30, 81, 245 hybrids, hybridisation 24, 239, 240 hypothermia 59 identification of raptors 7, 8, 24–28, 30, 33, 34, 37, 42, 66, 67, 72, 73, 122, 150, 245, 247–248 illegal (persecution; egg collection; poisoning) 2, 11, 14, 39, 40, 57, 58, 100, 107, 143, 151, 310 see also crime, wildlife; persecution; poisoning immature birds 11, 18, 22, 24, 32, 247, 309, 311, 314, 325 see also juvenile immunisation 60–61 inbreeding 34 incubation 20, 22, 27, 28, 33, 35, 36, 44, 45, 46, 50, 56, 66, 68, 246, 314, 320, 325 see also clutch size and incubation influenza, avian 61 insects 28, 74, 160, 177 ff, 207, 236, 248 Institute for Terrestrial Ecology see ITE Ireland see Northern Ireland; Republic of Ireland Irish Raptor Study Group 7, 295, 296, 302 see also Golden Eagle Trust Isle of Man 4, 7, 12, 24, 67, 73, 80 health and safety 62 legislation 39, 41, 42, 43, 58 population status and trends 295-297 see also DAFF isotopes, chemical markers 33 ff ITE (Institute for Terrestrial Ecology) 3, 325 see CEH jay (Garrulus glandarius) 158, 210, 213 jesses (in falconry) 24, 257, 325 JNCC (Joint Nature Conservation Committee) 4, 5, 7, 14, 50, 301, 323, 325, 326 Joint Nature Conservation Committee see JNCC juvenile 32, 34, 244, 248, 325 keratinous 35, 325 kestrel (Falco tinnunculus) 3, 7, 14, 15, 18, 19, 20, 37, 38, 157–164, 167, 170, 180, 207, 218, 234, 246, 296–298, 29–32 kills 7, 21, 24–25, 67, 105 kingfisher (Alcedo atthis) 25 kites 30, 236, 244 black (Milvus migrans) 239 red (Milvus milvus) see red kite

lagomorphs 112, 325 see also rabbit; hare Land Reform Act (Scotland) 2003 42 larch 79, 118, 121, 128, 218, 307 law see legal considerations for fieldwork; legislation leg see tarsus legal (considerations for fieldwork) 2, 39-44, 58, 67 see also legislation; licences legislation 8, 39-44, 54 England and Wales 39–43, 62 Europe 4 health and safety 62-63 Isle of Man 39–43, 41, 42, 62 Northern Ireland 40–44, 63 Republic of Ireland 40–43, 63 Scotland 39–43, 52, 62 see also licences and permits leptospirosis 60 lesser spotted eagle (Aquila pomarina) 32 leveret 112 licences and permits 39-42, 48, 60 handle eggs 36 nest visits 8, 39–41, 50, 57 photography 41 ringing 29, 39, 40–41, 50 taking blood or tissue samples 33, 42 wing-tagging and remote tracking 41–42 see also Ringing Unit; Schedule 1 little owl (Athene noctua) 15, 37, 38, 204–208, 247, 282, 296–298, 47–48, 73–78 Local Access Forum 42 Local Authority 42 Local Bird Recorders 14, 24, 240, 241, 304 long-eared owl (Asio otus) 15, 38, 213, 217–222, 227, 247, 296–298, 52–53 Lyme disease 61 magpie (Pica pica) 158, 205, 210, 218 mammals and predation 24, 25, 48, 58, 158, 160, 193, 209, 211, 248 see also prey; voles mandible 54 mantle 101 mantling display 57, 201, 325 maps 10–12, 43, 46, 47, 49, 50, 80, 95, 311–312, 318 marsh harrier (Circus aeruginosus) 14, 19, 30, 32, 92–99, 243, 246, 295, 297, 298, 305, 7–10 recording form 320 mass (of bird/chick) 34, 37, 55, 326 see also egg mass ‘Mayfield’ method 22 meadow pipit (Anthus pratensis) 14

measurements of chicks 35, 36, 37, 48, 50-56 of eggs 35–36, 48, 50, 56, 57 of feathers 51, 247, 248 merlin (Falco columbarius) 3, 7, 12, 14, 15, 20, 21, 25, 27, 38, 165–175, 234, 246, 282, 296, 298, 33–36, 64–69 metapopulation 34, 326 migration (immigration, emigration) 10, 11, 18, 29, 32, 34, 71, 246 see also dispersal Milvus M. migrans see black kite M. milvus see red kite mink 167 mobbing 45, 214, 227 mock-fighting, mock-attacks 26, 95, 146, 160 monogamous 17, 101, 324, 326 Montagu’s harrier (Circus pygargus) 15, 110-16, 246, 295, 298, 15–18 Moult 35, 244-247, 324, 325, 326 moulted feathers 17, 20, 25, 26, 33, 34, 244, 246, 247, 248, 309 nape 101, 208 National Parks and Wildlife Service see NPWS Natural England 299, 302, 324 Natural Environment and Rural Communities Act 2006 39, 87, 145, 153 Nature Conservancy Council 3 Nature Conservation (Scotland) Act 2004 39, 87 neotropical 34, 326 nesting range 19–20, 28, 45, 68, 306 nests and nest sites 10, 11-12, 13, 16, 19-20, 21, 22, 25, 27, 28, 33, 44 ff, 50, 57 ff, 66 ff, 246, 282, 297, 305 ff, 316, 318, 324 see also holes, nests in; licences for nest visits nest boxes 20, 37-38, 60, 62, 308 Nest Record Card (NRC) 15, 59, 326 Nest Record Scheme 4, 14, 37, 40, 41, 326 nestling see chicks, ageing and sexing young NIEA (Northern Ireland Environment Agency) 41, 42, 300, 326 nocturnal species ix, 13, 18, 24, 26, 28, 45 see also owls nomograms 35-37, 68 non-breeding birds 11, 17-18, 19, 21, 22–23, 68, 73, 314 Northern England Raptor Forum 301 northern goshawk see goshawk Northern Ireland 4, 7, 311 Environment Agency see NIEA health and safety legislation 62–63, 67 legislation and licensing 40–44, 58 Raptors: a field guide for surveys and monitoring

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population status and trends 295–297 Raptor Study Groups 302 northern harrier see hen harrier northern raven see raven Norway 6, 85, 86, 200, 209 Norway spruce 129, 222, 308 notch (feather) 245, 249 notebooks 46–48 NPWS (National Parks and Wildlife Service, Ireland) 41–43, 58, 300, 326 NRC see Nest Record Card oak 71, 72, 79, 192, 205, 307 occupancy 5, 12, 15, 16, 19, 20, 24, 25, 27, 28, 45, 46, 66, 67, 305, 309 Occupiers Liability Act (Republic of Ireland) 1995 43 Ordnance Survey 43, 47 organochlorines ix, 2 Orkney vole 226 osprey (Pandion haliaetus) 3, 7, 13, 14, 19, 20, 26, 27, 32, 37, 39, 81, 150–155, 244, 249, 246, 295, 298, 27, 28 owls 5, 6, 8, 12, 15, 18–26, 28, 40, 60, 158, 244, 246–248, 282 see also barn owl; eagle owl; little owl; long-eared owl; short-eared owl; snowy owl; tawny owl Palaearctic 224, 326 pallid harrier (Circus macrourus) 239 Pandion haliaetus see osprey Partnership for Action Against Wildlife Crime see PAW Passeriformes 8, 326 passerines 61, 166, 170, 177, 282, 326 passive integrated transponder (PIT) tags 33 PAW (Partnership for Action Against Wildlife Crime) 58 pellets 7, 17, 19, 20, 24, 25, 61, 67, 81 see also signs, recognition of perching-and-calling display behaviour 26 peregrine (Falco perigrinus) 2, 3, 5, 7, 13, 14, 15, 17, 19, 20, 26, 27, 28, 32, 33, 34, 35, 38, 167, 184-190, 233, 234, 236, 246, 281, 296, 298, 39, 40 permits see licences and permits; Ringing Unit Pernis apivorus see honey-buzzard persecution see crime, wildlife; illegal pesticides ix, 2, 3, 15, 298 pheasant (Phasianus colchicus) 32, 61, 248 photograph 10, 26, 48, 57, 58, 244, 247–248, 282, 318 licences for 40, 41 pigeons (Columbidae) 4, 158, 188, 236 see also woodpigeon

368 Raptors: a field guide for surveys and monitoring

pine 119, 144, 169, 177, 218, 307 see also Scots pine pine marten 38 pins (feathers) 37, 83, 135, 190, 77, 326 PIT (Passive Integrated Transponder) tags 33 platform terminal transmitters (PTTs) 32 point counts 12–13 poison 2, 11, 57, 58, 310 Police Wildlife Crime Officer (PWCO) 58 poliomyelitis 61 polyandry 101, 111, 326 polygyny 101, 102, 104, 107, 326 population 1–7, 10, 12–15, 16–18, 19–23, 24–28, 29–38, 39–63, 326 count units 16 estimates 10, 16-18 modelling 11 sampling 16 status and trends 294-298 see also demography; metapopulation; non-breeding birds; productivity prey 2, 14, 19, 20, 24–25, 27–28, 49, 57, 68, 309 see also hunting and feeding; kills, voles primary (feather) 51, 115, 131, 132, 135, 140, 141, 142, 173, 175, 190, 198, 234, 237, 244–247, 249, 314, 324 productivity (of breeding) 3, 5, 7, 13, 16, 21, 22, 29, 31, 66, 68, 71, 305, 306, 314 PTTs (platform terminal transmitters) 32 Public Liability Insurance 44 pullus/pulli 31, 326 purple moor grass 102 PWCO (Police Wildlife Crime Officer) 58 quill (feather) 24, 107, 140, 198, 245, 247, 249 rabbit 25, 112, 137, 158, 201, 205, 207, 236 race (of a species) 34, 68, 126, 148, 191, 326 rachis 230, 245, 249 radio-tracking 31-32, 144 random/randomised (selection, sample) 12, 14, 16, 126, 135, 142, 164, 306, 326 ranges see home ranges Raptor Monitoring Officer (SRMG) 5, 30, 301, 305 Raptor Study Groups x, 3–4, 7, 14, 16, 44 Scottish (SRGS) 5, 6, 7 Rare Breeding Birds panel see RBBP Rare Breeding Birds Panel (Republic of Ireland) 14 raven (Corvus corax) 5, 8, 15, 20, 21, 24, 28, 30, 40, 79, 158, 167, 169, 171, 172, 177, 185, 232–238, 244, 246, 282, 296, 298, 56, 57 RBBP (Rare Breeding Birds Panel) 5, 14, 304, 327 recording 7, 8, 15, 22, 28, 46-49, 47, 68 forms 47, 305–320

red fox 24, 25, 38, 167 red kite (Milvus milvus) 3, 6, 7, 13, 13, 14, 25, 30, 77–84, 239, 246, 295, 297, 298, 307, 3, 4 remote tracking 7, 31–33 licences for 41–42 Republic of Ireland 4, 7, 14, 58 access 43 health and safety 62, 63 legislation and licenses 39–42, 67 National Parks and Wildlife Service see NPWS population status and trends 295–297 ringing 29–30, 31, 33, 44, 49, 50, 59, 60, 66, 67, 70 forms 7 Irish Ringing Scheme 29 licences, permits and legislation 39–43 Ringing Unit (BTO) 29, 30, 31, 39–43, 44, 50 risk assessment 63 road surveys 12, 84, 99, 109 rook (Corvus frugilegus) 158 rosebay willowherb 102 rough-legged buzzard (Buteo lagopus) 239–240 rowan (mountain ash) 187, 307 Royal Society for Protection of Birds see RSPB RSPB (Royal Society for Protection of Birds) xi, xii, 2, 3, 5, 7, 14, 50, 58, 303 Scotland 2, 5 Russia 199, 298 safety see health and safety Safety, Health and Welfare at Work Act (Republic of Ireland) 1989, 2005 63 salmonellosis 61 sample, sampling x, 10–12, 16, 31 ff, 42, 46, 68, 244, 248, 305, 311 see also blood sample; stratified sampling; tissue sample satellite imagery 10 satellite tracking 32 SCARABBS (Statutory Conservation Agencies/RSPB Annual Breeding Bird Scheme) 14 Schedule 1 14, 39, 40 ff Schedule II 41, 67 Schedule ZA1 87, 145, 153 Scotland/Scottish 2, 3, 5 ff, 11, 12, 20, 31, 33, 34, 57, 58, 62 legislation and licenses; Scots law 39–43, 57 Natural Heritage see SNH Ornithologists’ Club see SOC Outdoor Access Code 43 population status and trends 295–298 Raptor Monitoring Group see SRMG Raptor Monitoring Scheme see SRMS Raptor Study Groups see SRSG Scots pine 71, 79, 144, 151, 167, 308

seabirds 35, 88, 187 season 34, 39, 40, 45 ff, 66–69, 314 seasonal movements 29 see also breeding season secondary (feather) 222, 230, 231, 244, 247, 249, 2, 4, 6, 8, 10 ff sexing see ageing and sexing sexual dimorphism 37, 50, 127, 244, 247, 327 short-eared owl (Asio flammeus) 1, 7, 13, 167, 210, 212, 222, 223-231, 282, 297, 305, 54, 55 recording form 313 sightings, of birds 5, 17, 20, 21, 30, 31, 47-49, 297, 311, 315 single birds and occupancy 17, 121, 143, 232, 235 sites see home ranges; nests and nest sites; occupancy; territory; study plot Sites of Special Scientific Interest see SSSIs sitka spruce 167, 160 sky-dancing 26, 104, 113, 130, 139, 146 SNH (Scottish National Heritage) 4, 5, 42, 43, 299, 318, 327 snowy owl (Bubo scandiacus) 199–203, 247, 45, 46 soaring-and-calling display behaviour 26 SOC (Scottish Ornithologists’ Club) 4, 5, 304, 327 sparrowhawk (Accipiter nisus) 3, 7, 14, 15, 19, 21, 25, 26, 27, 30, 38, 117, 119, 127–135, 158, 213, 246, 295–298, 21, 22 SPAs (Special Protection Areas) 4, 5, 327 spruce 102, 218 see also Norway spruce: sitka spruce squirrel 72, 79, 177, 210, 213, 218 SRMG (Scottish Raptor Monitoring Group) 5, 6, 30, 301, 327 see also Raptor Monitoring Officer SRMS (Scottish Raptor Monitoring Scheme) 5, 15, 47, 59, 62, 305, 306, 327 see also Scottish Raptor Monitoring Group (SRMG) SRSG (Scottish Raptor Study Groups) 5, 301 SSSIs (Sites of Special Scientific Interest) 5, 327 standardised counts 12 stand-watches (vantage point surveys) 13 statistical confidence limits 12, 327 status of raptors 6–7, 294–298 Statutory Country Conservation Agencies/Statutory Nature Conservation Agencies 4, 14, 15, 24, 39 ff, 58 ff, 114, 241, 328 stoat 167 stratified sampling 16, 169, 328 Strigiformes 8, 282, 328 see also owls Strix aluco see tawny owl study plot 10, 16, 328 surveillance 10–15 Raptors: a field guide for surveys and monitoring

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survey 10–15 and monitoring in Britain and Ireland 14–15 methods 6, 8, 11–13, 16, 66, 69, 239 see also transect surveys; point counts; aerial surveys; call playback survival rates 4, 11, 18, 29, 34, 35, 161 Swainson’s hawk (Buteo swainsoni) 32 swift (Apus apus) 177 sycamore 79, 128, 192 tail feather(s) 8, 26, 48, 81, 83, 122, 150, 202, 244 ff, 249 tarsus (measurement) 37, 51, 52, 53 tawny owl (Strix aluco)13, 15, 19, 32, 36 ff, 194 ff, 306, 209–216, 217, 220, 221, 247, 275, 296–298, 49–51 territorial pairs 6, 16, 17, 22, 295, 297 see also breeding pair territory 11, 17, 19, 20, 66, 67, 297 see also home ranges tetanus 60, 61 ticks 61 time of day for fieldwork/of observation 12, 45, 46, 55, 67 tissue samples, licences for 42 trace elements 35 training for surveying, ringing, marking and handling x, 29, 30, 33, 40, 41, 50, 60 transect surveys 12-14 traps and snares 11, 57–58, 307 Tyto alba see barn owl UK Raptor Working Group 4-5, 7 undertail coverts (feathers) 110, 181 see also coverts United States 20, 37, 155

legislation and licences 39 ff, 58 population status and trends 295–297 Raptor Study Groups 302 wasps 60, 71 ff weather (conditions; adverse/poor) 10, 13, 22, 45 ff, 49, 50, 55 ff, 248, 310 recording 12, 50 western barn owl see barn owl western marsh harrier see marsh harrier western osprey see osprey Weil’s disease 60 white-tailed eagle (Haliaeetus albicilla) cover image, 3, 6, 7, 9, 14, 20, 26, 30, 35, 37, 39, 85–91, 146, 147, 246, 295, 298, 5, 6 Wildlife Act 1976 (Republic of Ireland) 40, 41, 42, 67 Wildlife Act 1990 (Isle of Man) 39, 40, 41, 67 Wildlife (Amendment) Act 2000 (Republic of Ireland) 40 Wildlife and Countryside Act 1981 14, 39, 40, 57, 67 wildlife crime see crime willow 102, 192, 218, 222 windfarms 13, 59 wing 25 feather(s) 8, 26, 48, 244 ff, 249 see also primary (feather); secondary (feather); tail feathers length, measuring 37, 51 tagging and licences 29, 30–31, 41, 48 ‘wing-clapping’ courtship display flight 73, 74, 220, 227 winter roost survey, hen harrier 14 wintering populations 4, 11, 34, 35, 66, 69 woodland raptors 13, 28 woodpigeon (Columba palumbus) 158, 181, 188, 210, 213, 221 young birds see chicks; juvenile; immature birds

vantage points 12, 13, 44, 48, 49 see also stand-watches (vantage point surveys) viral diseases 61 visits to sites access 42–43 frequency 45–46 licences and permits 39–41 recording details 46-50 vocalisations 28 see also calls, calling voles 101, 112, 157, 158, 218, 219, 223 ff see also bank vole; field vole; Orkney vole volunteers ix, 3, 4, 5, 7, 14, 15, 43, 62 waders 94, 188 Wales 34 Countryside Council for see CCW health and safety 62

370 Raptors: a field guide for surveys and monitoring

zoonoses 60

“People studying raptors should find this book indispensable…”

Professor Ian Newton FRS

Raptors

a Field Guide for Surveys and Monitoring

a Field Guide FOR Surveys and Monitoring

Written and edited by a team from the Scottish Raptor Monitoring Group, the book draws on the knowledge and experience of more than 300 raptor specialists, in particular members of the Raptor Study Groups. It has been funded by Scottish Natural Heritage, with assistance from the other Statutory Nature Conservation Agencies in Britain and Ireland and from voluntary conservation bodies concerned with birds of prey. There are growing demands for high quality information on the numbers, distribution and population trends of these fascinating birds. This book aims to promote best practice for fieldwork, and should provide an excellent starting point for anyone beginning a raptor study.

raptors

This is the second edition of the highly successful field guide to methods for surveying and monitoring raptors. Incorporating new information and feedback from raptor experts on the first edition, the book covers all birds of prey (diurnal raptors and owls) which occur regularly in Britain and Ireland. Photographic guides to raptor feathers and the growth of raptor chicks are important additions, which fieldworkers will find invaluable.

Jon Hardey Humphrey Crick Chris Wernham Helen Riley Brian Etheridge Des Thompson

Price £18.99

Jon Hardey Humphrey Crick Chris Wernham Helen Riley Brian Etheridge Des Thompson