Smew

The Smew is a small merganser with sharply contrasting plumage. Adult males are mostly white, crossed by fine black lines around the eye, back and breast, producing a cracked-ice pattern. Females and immature birds have grey bodies, chestnut crowns and cheeks, and a clean white throat; this distinctive plumage is often called redhead. The short, hooked bill remains adapted for catching slippery prey (Wikipedia, general species account).

Smews breed beside northern forest lakes and slow rivers, nesting in tree cavities, especially old woodpecker holes. They dive for small fish, insect larvae and crustaceans, and frequently feed in loose groups. After breeding they migrate to unfrozen lakes, reservoirs, rivers and sheltered coastal water. Japan lies within the East Asian winter range, where the species is usually seen singly or in small parties (Wikipedia, general species account).