Bufflehead

(The Cornell lab of Ornithology): "A buoyant, large-headed duck that abruptly vanishes and resurfaces as it feeds, the tiny Bufflehead spends winters bobbing in bays, estuaries, reservoirs, and lakes. Males are striking black-and white from a distance. A closer look at the head shows glossy green and purple setting off the striking white patch. Females are a subdued gray-brown with a neat white patch on the cheek. Bufflehead nest in old woodpecker holes, particularly those made by Northern Flickers, in the forests of northern North America."