The Bufflehead, confined as a breeder to the boreal forest and aspen parkland of North America, is our smallest diving duck. Its small size has probably evolved with its habit of nesting in the holes of the Northern Flicker (Colaptes auratus), an abundant resource too small to accommodate other, larger cavity-nesting ducks. Bufflehead also nest in boxes, facilitating management of this species and studies of its reproductive biology. Territoriality probably limits the breeding density of this aggressive little duck, although lack of suitable nest cavities may also be a factor in many areas.
Bufflehead breeding habitat is dominated by ponds and small lakes, where the birds dive for insect larvae and amphipods. In winter, this is primarily a coastal, salt-water duck, feeding on crustaceans and molluscs in shallow water bays and inlets. Almost exclusively monogamous, this is one of the few ducks that often keeps the same mate for several years. Females are also faithful to their natal and breeding areas, often reusing the same nest site year after year.
Although Buffleheads are not prized among sport hunters, shooting is a significant factor in their mortality. They are nevertheless among the few species of ducks whose numbers have increased markedly since the mid-1950s.