The bufflehead is a small sea duck of the genus Bucephala, the goldeneyes. This species was first described by Carl Linnaeus in his landmark 1758 10th edition of Systema Naturae as Anas albeola. The genus name is derived from ancient Greekboukephalos, "bullheaded", from bous, "bull " and kephale, "head", a reference to the oddly bulbous head shape of the species. The species name albeola is from Latinalbus, "white". The English name is a combination of buffalo and head, again referring to the head shape. This is most noticeable when the male puffs out the feathers on the head, thus greatly increasing the apparent size of the head.
Description
The bufflehead ranges from long and weighs, with the drakes larger than the females. Averaging and, it rivals the green-winged teal as the smallest American duck. Adult males are striking black and white, with iridescent green and purple heads and a large white patch behind the eye. Females are grey-toned with a smaller white patch behind the eye and a light underside.
Buffleheads have evolved their small size to fit the nesting cavity of their "metabiotic" host, a woodpecker, the northern flicker. Due to their small size, they are highly active, undertaking dives almost continuously while sustained by their high metabolism. They do not tend to collect in large flocks; groups are usually limited to small numbers. One duck serves as a sentry, watching for predators as the others in the group dive in search of food. Buffleheads are amongst the last waterfowl to leave their breeding grounds and one of the world's most punctual migrants, arriving on their wintering grounds within a narrow margin of time.
Breeding
Buffleheads are monogamous, and the females return to the same breeding site, year after year. They nest in cavities in trees, primarily aspens or poplars, using mostly old flicker nests, close to water. Nest competitors include mountain bluebird, tree swallow, and European starling. There was one recorded instance of a female Barrow's goldeneye killing a bufflehead adult female and her brood. Smaller cavities are preferred because of less competition with the larger goldeneyes. Females may be killed on the nest by mammals, such as weasels or mink, and by goldeneyes over nest competition. Average clutch size is nine, and eggs average. Incubation averages 30 days, and nest success is high compared to ground-nesting species like the teal. A day after the last duckling hatches, the brood leaps from the nest cavity. The young fledge at 50–55 days of age. Predators of adults include the peregrine falcon, snowy owl, bald eagle, golden eagle, red-tailed hawk, great horned owl, Eurasian eagle owl, and Cooper's hawk.
Diet
These diving birds forage underwater. They prefer water depths of. In freshwater habitats, they eat primarily insects, and in saltwater, they feed predominantly on crustaceans and mollusks. Aquatic plants and fish eggs can often become locally important food items, as well.
Relationship with humans
Because of their striking plumage, highly active nature, and proximity to humans on waterfront properties, buffleheads are one of the most popular birds amongst bird watchers. The bufflehead, also known as the spirit duck, was added to the coat of arms of the town of Sidney, British Columbia, in 1995. Buffleheads are hunted and are considered a gamebird. In contrast to many other seaducks that have declined in recent decades, bufflehead numbers have remained relatively constant. Habitat degradation is the major threat to this bird, since they depend on very limited coastal habitat on their wintering grounds, and very specific habitat in their boreal breeding grounds. Although buffleheads do use man-made nest boxes, they still need the forest habitat to thrive.
