Rook

Rook (Corvus frugilegus) is a large social black corvid distinguished as an adult by pale bare skin around the base of its relatively pointed bill. Body shape, bill structure, plumage pattern and voice provide the strongest field characters. Age, sex and season may alter its appearance, so identification should combine several features and careful direct field comparisons with similar species in the same habitat (Wikipedia, general species account).

It feeds in farmland and open ground on invertebrates, grain and other foods, nests collectively in tall trees at colonies called rookeries and may migrate south from the coldest parts of its Palearctic range. Its movements and social behaviour vary through the year, with breeding birds generally more dispersed and non-breeding birds gathering where food is concentrated. Japanese records place it within the country's documented avifauna as a resident, migrant or visitor (Wikipedia, general species account; Wildlife of Japan occurrence records).