Black-tailed Gull

Black-tailed Gull (Larus crassirostris) is an East Asian gull with grey upperparts, yellow bill crossed by red and black bands, and a black tail band. 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 opportunistically along coasts, harbours and rivers, taking fish, invertebrates and scraps and nesting colonially on islands. 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).