Dunlin

Dunlin (Calidris alpina) is a small sandpiper with a slightly downcurved bill and a conspicuous black belly patch in breeding plumage. 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 probes mud for worms and other invertebrates and forms dense migratory and winter flocks on estuaries and tidal 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).