Trend of White-tailed Eagles Breeding in Japan During the Past Quarter-century

Trend of White-tailed Eagles breeding in Japan during the past quarter-century

Saiko Shiraki

Tokyo University of Agriculture Abashiri, Hokkaido, Japan

Introduction

Nesting of WTEs (Haliaeetus albicilla) in Japan before 1991 ・The first evidence of nesting was reported in mid-1950s, in eastern part of Hokkaido (Haga 1955) ↓ ・17 nests were recognized in eastern and northern Hokkaido by 1990 (Nakagawa et al. 1991)

Sakhalin

Hokkaido

Sea of Japan

Aomori prefecture

Current breeding range of WTEs in Japan（Yellow part)

Introduction

Trend of number of sea eagles wintering in Japan

Number of eagles

Number of sea eagles in entire northern Japan in mid-February by an annual general counting survey (WGWS, 2017 Report)

3000

2000

1000

1985

1990 Total

2000

H. pelagicus

2010

2017

H. albicilla

Temporal change of nest distribution 10km mesh with more than one nest sites recognized as active in 1991-94 survey, includes nests had confirmed before 1991 by Nakagawa et al. (1991）

1991 ～1994

Methods ・Monitoring nests during breeding season ・Collecting information from local groups or researchers Northern group

34M Period of first confirmation ～1994

1992

Eastern group FST=0.187 100km

Temporal change of nest site distribution 1991-1994 34M

1995-1999

48M

Period of first confirmation ～１９９４ １９９５～１９９９

Temporal change of nest site distribution

1995-1999 1995-1999 48M

2000-2004 66M

～１９９４ １９９５～１９９９ ２０００～２００４

Temporal change of nest site distribution 2000-2004 66M

2005-2009 94M

～１９９４ １９９５～１９９９ ２０００～２００４ ２００５～２００９

Temporal change of nest site distribution

2010-2015 2010-2015

2005-2009 94M

145M 145M

～１９９４ １９９５～１９９９ ２０００～２００４ ２００５～２００９ ２０１０～２０１５ Aomori

Temporal Change of nest distribution of WTEs for 25 years 1991-1994 2010-2015 34M

・Coast of northern and eastern part of Hokkaido have been the major breeding parts since 1950s. ・Recently, nesting range expanded to inland along big rivers, Japan sea coast, and in southern part.

145M

～１９９４ １９９５～１９９９ ２０００～２００４ ２００５～２００９ ２０１０～２０１５

Nest sites would increase in south western part of Hokkaido and northern part of main island in near future.

Temporal change of number of nesting pairs confirmed in Japan Number of pairs

300 250 200

150 100 50 0

1990

1995

2000

2005

2010

2015

Number of pairs in 2015 was more than 8 times compared to early 1990s.

Temporal change of Breeding performance of WTEs in Hokkaido 1.4 1.2

80

1 60

0.8

40

0.6

20

0.4

Breeding Success (%) No. of fledglings /pair

0.2

0

No. of fledglings/pair

Breeding success (%)

100

0 '92 '94 '96 '98 2000 '02 '04 '08 '10 Year

12

14

Relatively good performance but declined gradually after 2000

Breeding population of WTEs in Japan has greatly increased in both of the number and range in 25 years ・Ca. 60% breeding success and 0.7 fledglings/pair in recent data (→ca. 90 fledglings/year) ・ At least 60% survival for juveniles produced in Hokkaido （Shiraki 2002）

Pretty good productivity and survival

Many mature eagles, probably produced from breeding pairs in Hokkaido, recruited for the natal population.

In spite of no positive conservation practices for WTEs, population has been increased

Plentiful food supplied from human activities in winter Discarded fish from fishery or fish factory

Commercial feeding by tour boats

70-80% of sea eagles feed on food supplied from human activities in mid-winter

Nesting at urban environment in recent years Ex. Nest tree location for newly-settled pairs Traditional nest sites

New nest sites

Distance to nest trees from the nearest paved roads (km) →Increase of possible nesting environment for eagles

Nesting on artificial objects in recent years

ăƒťShortage of large trees at preferable habitat? ăƒťAcclimation to people or human environment?

Breeding population of WTEs in Japan has greatly increased in both of the number and range in 25 years ＊Plenty of human-induced food in winter ・Ca. 50% breeding success and 0.7 fledglings/pair in recent data (→ca. 90 fledglings/year) ・ At least 60% survival for 1st year eagles （Shiraki 2002）

Pretty good productivity and survival Many mature eagles, probably produced from breeding pairs in Hokkaido, were recruited for the natal population ＊Increase in available nesting habitats at urban environment

→ Increase in nest sites

Thank you for your attention