WTE skull with GE talons Derek Spencer, University of Highlands and Islands, Scotland
Characterising golden eagle territorial boundaries
Aims Confirming range boundaries Understanding nature of boundary interactions
Study Area Foinaven Special Protection Area (1000 km²), NW UK Classified for six golden eagle ranges Am studying 14 ranges Rugged, mountainous terrain Main prey- ptarmigan, grouse, voles, deer and sheep carrion, and assortment of other food
SPAs for golden eagles in the UK =>
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Foinaven SPA and surrounding ranges
PAT: Predicting Aquila Territories
These are PAT modelled territories
Sources: McGrady et al 2002; McLeod et al 2002a,b; Fielding et al 2003; Fielding pers comm
Summary of the PAT model Golden eagle ranges can be approximated by Thiessen polygons with a 6 km cut-off. Golden eagles are more likely to use habitat close to the range centre and close to a ridge. They are unlikely to use some habitats (water, closed canopy woodland, arable, improved grassland, urban etc.). These features were combined to produce an ‘expected use’ for each 50 m pixel within an eagle’s range. More comprehensive descriptions of the PAT model can be found in McLeod et al. (2002) and Fielding et al. (2003). Source: Haworth & Fielding, 2013
Field methods 2011-13 in the field Total of 275 days watching for golden eagles Focusing on boundary flights, displays, interactions Also studying range occupation, nesting success Line transects to assess food supplies Satellite tagging of young birds Historical investigations of ranges and land use
Territorial displays recorded (in order of frequency): Soaring – circling, spiralling upwards Patrolling – alone, along ‘boundaries’, and gliding Undulating – roller coasting, tumbling Talon tipping and grappling Arrow flights (chases) Eyrie drive past and looping (not just pair-bond reinforcement) – not as aggressive as above
Photo: Jeff Watson
Spent 275 days in the field over three breeding seasons Recorded all golden eagle flights (seen on 200 observation days) Recorded territorial boundary flights on 45 days, hence one every 6 days So, need to spend 48 hours in a given range to record just one territorial boundary flight! (Based on 8 hour observation day) Many field workers miss a lot of the activity I am about to show you!
Display flights across seven study golden eagle ranges
B
B N
N
B B
N
N
B N
No eagles’ land…
N
N
B
N N B
N
B N
Territorial boundary a long ridge!
Key findings‌ PAT model correctly identifies territorial boundaries Huge variation in activity between territories – why? Most activity around boundaries of non-breeding pairs’ territories Neighbouring territories with breeding pairs have relatively little territorial activity So, most territorial activity centres on establishing a basis for occupation and nesting
Thanks to Martin Price, Liz Masden, Des Thompson Huge cooperation from estates
Thank you for listening
Nests
Some nests are surprisingly exposed
Distribution
Population Model Outline • Growth rate = Gains – Losses – Gains = Immigration + Births – Losses = Emigration + Mortality
• Immigration & Emigration are negligible • Births (fledged) – sporadic detail but relatively well known • Mortality – poorly known • FCS = 40% sub-adults survival, approx 95% annual for adults
Productivity • Spatial and temporal patterns • Explanations – – – –
Eggs? Fledged? 1 or 2? Offspring condition Prey availability Parental condition Weather
• Possible managment actions – Landscape management (large scale) – Prey enhancement (local) – Intensive intervention (Irish example)
Changes in productivity • Function of two processes that may operate in tandem or independently. • Increases when more pairs are successful • Either more pairs laying and/or more pairs converting eggs into fledged young. • Increase also possible when the number of successful pairs is constant but the number raising twins increases.
Prey
Understanding diet
Some Detail
Compare 05 & 06, 2006 few pairs laying but larger FR Table 3.3. Mean productivity data for the Uists 2005-2008.
Year 2005 2006 2007 2008 All
Occupied and known outcome Laid Chicks 27 21 8 24 13 8 25 21 15 24 21 17 100 76 48
Fledged Number young fledged 5 7 7 7 10 11 11 11 33 36
% laid 77.8 54.2 84.0 87.5 76.0
% % chick fledge (chicks (fledge /laid) /laid) 38.1 23.8 61.5 53.8 71.4 47.6 81.0 52.4 63.2 43.4
%chicks fledged 62.5 87.5 66.7 64.7 68.8
FR 0.26 0.29 0.44 0.46 0.36
Year 2008
2007
2006
2005
2004
2003
2002
2001
2000
1999
1998
1997
1996
1995
1994
1993
1992
1991
1990
1989
1988
1987
1986
1985
1984
1983
1982
Fledged per pair
Productivity (Mull, Skye, Argyll, Lochaber ~ 25% of all pairs)
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
May Rainfall Seems Important
Factors affecting survival • How long does an eagle live? – Sub adult – Adult
• What determines survival? – Disease (related to condition, prey types...) – Starvation (combined with weather) – Accidents (broken bones in hunting accidents) – Intra and interspecific conflicts (WTE...) – External (persecution, windfarms, other...)
• Management actions
Hare density
Grouse density
Red deer density
Sheep density
Changes in sheep density
Competition with WTE?
WTE skull with GE talons
Illustration: Keith Brockie
New studies, regions, habitats and issues…since 1997 • Hundreds of new references…phenomenally well studied • Scotland in nine regions…world regions • >250/440 ranges visited • Variation in nature and land use of Scotland • Constraints and opportunities…real conservation
WTE skull with GE talons Conflicts over predators‌
Highlands crofters blame sea eagles for leap in lamb deaths Sheep farmers say reintroduction of predatory birds to Scotland threatens their livelihoods
Claws out on a silent moorland A heated battle rages over the birds of prey threatening to destroy Britain's grouse
Photo: Ewan Weston
From Whitfield et al. 2004
Changes in sheep density
V
Range use and movements‌
Alma…in her first year…
Climate change‌
Haworth et al. 2009
Photo: Laurie Campbell
Photo: Jeff Watson