Caspian Tern

Caspian Tern (Hydroprogne caspia) is the world's largest tern, with a heavy red bill, black cap, pale grey back and shallowly forked tail. 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 comparisons with similar species in the same habitat (Wikipedia, general species account).

It plunge-dives for sizeable fish over coasts and inland waters and nests on open islands, beaches and salt flats. 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).