Factors affecting the choice of breeding and non-breeding grounds in migratory birds are important in order to understand the mechanism determining their distribution areas and climate adaptations. The rook, Corvus frugilegus (Passeriformes: Corvidae), predominantly resides in Europe but exhibits migratory habits in the eastern Palearctic region. East Asian populations of rook migrate from breeding grounds in the Eurasian continent around the Amur river basin to wintering grounds in central and south China, the Korean peninsula, and Japan. In Japan, the wintering grounds of C. frugilegus have been gradually expanding since the 1980s. In addition, rook populations that have previously roosted in secondary forests have recently moved to urban areas in several cities, resulting in urban fecal pollution. To clarify the wintering ecology of rooks roosting in urban areas in northern Kyushu, we surveyed seasonal trends in abundance, daily behavior, and dietary habit of rooks in two cities, Saga and Kumamoto. Wintering rooks gradually increased from November to December and decreased from January to March. In the daytime, the rooks foraged at croplands at mean distances of 6.3 and 9.7 km from the roosts, in groups averaging approximately 150 and 90 individuals in Saga and Kumamoto, respectively. Examinations of regurgitation pellets and stomach contents revealed the rooks fed mainly on spilled rice grains, supplemented with wheat and barley grains, Toxicodendron succedaneum and Triadica sebifera fruits, insects (beetles), and the apple snail. The rooks formed communal roosts with carrion crows and large-billed crows in both cities by joining their autumn communal roosts.
Hattori, M; Sobagaki, T; Matsuda, H; Nakamura, S; Tokuda, M
The wintering ecology of the Rook Corvus frugilegus in Northern Kyushu, Japan
Urban Ecosystems