Slaty-backed Gull

Slaty-backed Gull (Larus schistisagus) is a large gull with a heavy yellow bill, dark slate-grey back, pink legs and broad white trailing wing edge. 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 breeds on North Pacific coasts and feeds opportunistically on fish, seabirds, carrion and refuse around shorelines and harbours. 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).