Scaly-sided Merganser

Scaly-sided Merganser (Mergus squamatus) is a slender fish-eating duck with a shaggy crest and distinctive dark scalloping across white flanks. 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 along clear forest rivers in eastern Asia, nests in tree cavities and dives mainly for fish. 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).