There are sporadic reports of birds breeding in Quebec, Vermont, Massachusetts, Minnesota, South Dakota, and Colorado. Breeding habitat must include suitable nest trees. Buffleheads prefer to nest in the abandoned holes of Northern Flickers. Nesting habitat usually includes poplar or aspen trees near freshwater permanent ponds or lakes. Wintering coastal birds prefer the shallow water shelter of coves, estuaries, beaches and harbors.
Diets vary with the type of habitat and the season.
Birds wintering in saltwater habitats feed on clams, shrimps, snails, amphipods, isopods, and occasionally fish. In the fall, winter and spring they may consume more plant material such as the seeds of pondweeds and bulrushes. Adult Buffleheads feed almost exclusively under water. They prefer to feed in open shallow water or along the edges of emergent vegetation. Foraging birds divide their time almost equally between shallow dives and rest periods on the water surface.