Long-tailed ducks are mid-sized birds with long, dark tails and gray legs and feet. The species received its common name from the two long and slender tail-feathers that extend behind adult males. Plumage coloration and general size vary between adult males and females. While adult drakes range in size from 48 to 58 cm long, adult hens are between 38 and 43 cm long. Adult males weigh approximately 0.91 to 1.13 kg and adult females weigh about 0.68 to 0.91 kg. Long-tailed ducks of both sexes shift between three distinct plumages and adult males display an additional alternate plumage in the winter.
In the winter, adult males are white on their crowns, necks and throats that extend down to the breast. The white throat contrasts sharply with a large, black breast-band. Males also feature a gray patch surrounding their eyes, and a black patch that extends from their ears. Bills are dark with a pinkish band across the middle. Their bellies and undertail coverts are white. They exhibit black tail-feathers, rumps and backs. Wings are black with white scapulars at the base. Winter females have white faces, necks, and throats with brown crowns and brown ear patches. They also feature a broad breast-band, but it is brown in color. Their backs, wings and tails are also brown, while their bellies and undertail coverts are white. Females' bills are a dark blueish gray.
During the spring and summer, adult males feature black crowns, necks and throats that extend through the breast. Their backs, tails and wings remain black, but their scapulars are buff and mottled with black. Their gray eye patches remain, but are accented with white. Their bills are dark, with a blueish band. Spring females are overall brown, with brown faces and a small white patch surrounding each eye. They also often feature a white crescent across their lower necks. Their brown breast band extends further into the belly, but the undertail coverts remain white.
In late summer, males begin to develop a third plumage that is an intermediate between the winter and spring plumages. Their throats and necks become white and their bills develop a pink band.
Young long-tailed ducks look like miniature adult females, but young males begin to resemble adult males by late fall.
Range mass: 0.68 to 1.13 kg.
Range length: 38.1 to 58.4 cm.
Average wingspan: 70 cm.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: male larger; sexes colored or patterned differently