Natal Dispersal and Seasonal Migration of White-Tailed Sea Eagles in Khabarovsk Krai (Russia) and Hokkaido (Japan)

Abstract

White-Tailed Sea Eagles (Haliaeetus albicilla) become sexually mature at 5–6 years and the conditions of habitats and flight paths for local and seasonal movements in the nomadic period between post-fledging and breeding territory occupation are important in terms of population demographic relevance. The purpose of this study is to elucidate post-fledging movements, seasonal migrations, and habitats of immature White-Tailed Sea Eagles by GPS tracking. GPS transmitters were attached to nestlings of White-Tailed Sea Eagles at the middle basin of Amur River (around Slavyanka; 49°50'N, 136°76'E) and Lake Chukchagir (51°59'N, 136°36'E) in Khabarovsk Krai, Russia, and at Abashiri (44°1'N, 144°16'E) in eastern Hokkaido, Japan, in the breeding seasons of 2017–2022. Habitats used by GPS-tagged immatures were investigated with satellite images and field observations. The dispersion of post-fledging sea eagles from their natal nests occurred in autumn (September–October) for both sites in Khabarovsk and Abashiri. The first destinations in dispersal movements were river tributaries or lakes in floodplains in Khabarovsk (n=4) and rivers in Abashiri (n=2). Start timing and the first destination of emigration from natal sites for both breeding areas was considered to be related with upstreaming of salmonid fish for spawning. All of three juveniles fledged in Khabarovsk and tracked at least until their first winter wintered at the coastal area of Primorsky Krai, Russia, approximately 800–1,000 km south of their birthplaces, however, one juvenile took a different migration route to the wintering ground than the other two. Besides, two eagles tracked for more than two years after their birth in Khabarovsk showed the same migration routes in spring and autumn, and in the first year and subsequent years, respectively. Meanwhile, juvenile eagles fledged in Abashiri (n=2) moved to the places up to about 150 km south of their natal sites in their first winter, despite the fact that some major wintering grounds for sea eagles exist around their birthplace. Previous study reported that some colour-ringed immature White-Tailed Sea Eagles fledged at nests in Nemuro (43°19'N, 145°35'E), located approximately 100 km southeast direction of Abashiri, had been observed around their birthplaces in winter (Shiraki, 2002). Not only food availability but also genetic factor may be involved in determination of the wintering area. White-Tailed Sea Eagles over one year old from the nests in Khabarovsk (n=2) and in Abashiri (n=1) visited the vicinity of their natal sites during spring and summer. As White-Tailed Sea Eagles are known to have a tendency to nest in the natal area, young eagles might assess breeding opportunities around their natal sites. Immature White-Tailed Sea Eagles with GPS mostly stayed at habitats with food supplied from human activities, such as small fish discarded in fishery, marine waste, Sika Deer (Cervus nippon) residue left behind after hunting or killed in collisions with vehicles or trains, during winter in both of Primorsky and Hokkaido.