Scientific name: Bucephala clangula (Linnaeus, 1758)
Bird group: Ducks
Field characters. 42-50 cm. Male boldly black-and-white; neck and underparts white; back and tail black, with black streaks on scapulars and edge of flanks. In male "triangular" head is black glossed green with a circular white patch between eye and black bill. In flight wings are black with a conspicuous, broad white square on inner half extending almost to the front edge of the wing and partly broken by black line extending inwards from primary coverts. Legs orange, paler in female. Female with chocolate brown head without white patch, obscure whitish collar, mottled blue-grey upperparts, black rump, and white underparts; wing in flight as in male but broken by two black lines, wing-patch visible as white mark on sides when bird swims. Juvenile and male in eclipse much like female.
Voice. Generally silent. During display male has a sharp, nasal call.
Distribution. Common breeding bird in Scandinavia.
Habitat. Breeds in tall forests close to lakes, pools or rivers. Nest is built in holes of trees or in artificial sites such as nest- boxes.
Food. Mainly consists of molluscs, crustaceans, insect larvae; obtained during daytime, chiefly by surface-diving up to depth of 4 m. During autumn more plant material (seeds, tubers, roots, and leaves of aquatic plants). Food usually swallowed under water.
Eggs. Initially without markings, sometimes becoming blotched with pale brown markings during incubation. Ground colour bluish-green. Texture smooth, not glossy. Shape subelliptical/short subelliptical. Size 59 x 43 mm (52-67 x 39-45), weight 68 g (61-77). Eggs as in Barrow's Goldeneye, but distinctly greener.