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