Steller's Eider

Steller's Eider (Polysticta stelleri) is a small sea duck whose breeding male has a white head, green nape, black collar and chestnut underparts. The combination of body shape, bill structure, plumage pattern and voice provides the most useful field characters. Age, sex and season can alter its appearance, so identification should use several features rather than colour alone. This supports comparison with similar species in the field (Wikipedia, general species account).

It breeds on Arctic tundra pools and gathers in dense marine flocks to dive for molluscs and crustaceans in winter. Its movements and social behaviour vary through the year, with breeding birds generally more dispersed and non-breeding birds more likely to gather where food is concentrated. Japanese records place it within the country's documented avifauna as a resident, migrant, visitor or introduced bird (Wikipedia, general species account; Wildlife of Japan occurrence records).