The Bufflehead (Bucephala albeola) is a small American sea duck of the genus Bucephala, the goldeneyes. They range from 32-40 cm long (12.5-16 inches) and 270-550 grams (9.5 oz.-1.2 lbs), with the drakes larger than the females. Averaging 35.5 cm (14 inches) and 370 grams (13 oz), they rival the Green-winged Teal as the smallest American duck.

Adult males have a dark head with a large white cap behind the eye and a mainly white body with a black back. Adult females have a brown head with a smaller white patch behind the eye and a mainly brown body.

The name Bufflehead is a combination of buffalo and head, referring to the oddly bulbous head shape of the species.

They are migratory and most winter in protected coastal waters or open inland waters on the east and west coasts of North America and the southern United States. Bufflehead is an extremely rare vagrant to western Europe.

Their breeding habitat is wooded lakes and ponds in Alaska and Canada, almost entirely included in the boreal forest or taiga habitat. They nest in cavities in trees, often using old Flicker or Pileated Woodpecker nests, occasionally 425 meters (1400 feet) from water. Mountain Bluebird (Sialia currucoides), Tree Swallow (Tachycineta bicolor), Northern Flicker, and European Starling are nest site competitors and there was recorded instance of a female Barrow's Goldeneye killing a Bufflehead adult female and her brood. Smaller cavities are preferred to less competition with larger goldeneyes. A clutch may range from 5 to 10 eggs. Eggs are typically about 36.3 mm (1.4 inches) in breadth and 50.6 mm (2 inches) in length, weighing about 37.4 grams (1.3 oz) on average. The incubation period ranges from 28 to 33 days, during which the female is quite attentive. Locally, the clutch survival rate may range from 45% to 5% based on factors like cold weather, rain, competitors (i.e. grebes or other ducks) or predators (like Northern Pike). The female abandons the nest after 5 to 6 weeks, and the young fledge at 45 to 55 days of age.

These diving birds forage underwater. On freshwater they eat mostly insects and, on saltwater, they feed on predominantly crustaceans and molluscs. Aquatic plants and fish eggs often become locally important food items as well.

Buffleheads do not tend not to collect in large flocks; groups are usually limited to small numbers (less than 10). Predators of adults include Peregrine Falcon (Falco peregrinus), Snowy Owl (Nyctea scandiaca), Bald Eagle (Haliaeetus leucocephalus), Great Horned Owl (Bubo virginianus) and Cooper's Hawk (Accipiter cooperii). Females may be killed on the nest by mammals, like weasels (Mustela spp.) or mink (Mustela vison), and by goldeneyes over nest competition.

About 70,000+ Buffleheads are killed yearly by duck hunters[citation needed], which is probably overkill, but this only comprises about 1% to 2% of waterfowl-hunting in North America. Besides duck-hunting, habitat clearance is the other major threat to this bird, with extensive logging occurring in the boreal forests. Although Buffleheads do use man-made nest boxes, they still need the forest habitat.