Distinctive, large, rather gooselike duck of coastal wetlands, tidal mudflats, and nearby grassy fields. Striking plumage often looks simply black-and-white; at close range, head is deep glossy green, broad breast band dark rusty. Male has raised knob at base of red bill; juvenile duller overall, with whitish face and eyering. Less numerous and more local inland at lakes and along rivers. Often seen walking and grazing, at times in flocks.