Adult Description Large, stocky duck.

Distinctive wedge-shaped head with long bill.

Male bold black-and-white, with black cap, white back, and black undersides.

Female brown with black barring.

Male Description Breeding (Alternate) Plumage: Back, face, and chest white. Sides, belly, and tail black. Black cap. Nape greenish, sometimes with greenish line below eye. White patches on flanks. Extensive white in wings. Bill gray-green, yellow, or orange.

Nonbreeding (Basic) Plumage: Overall dark brown to blackish. Pale brown stripe through eye. Breast brown with white flecking. Back feathers white with black edges.

Female Description Brownish all over with black barring, especially on sides and flanks. Dark speculum in wing outlined in white. Bill pale greenish gray to olive green or dark gray.

Immature Description Immature female like adult, except darker and duller, without white at front of speculum. Immature male brownish black with varying amounts of white at base of neck and breast, usually with some white on back, head mostly dark.