The adult male is all black except for white flanks and a blue-grey bill with gold-yellow eyes, along with a thin crest on the back of its head. It has an obvious head tuft that gives the species its name. The adult female is brown with paler flanks, and is more easily confused with other diving ducks. In particular, some have white around the bill base which resembles the scaup species, although the white is never as extensive as in those ducks. The females' call is a harsh, growling "karr", mostly given in flight. The males are mostly silent but they make whistles during courtship based on a simple "wit-oo".
The only duck which is at all similar is the drake greater scaup which, however, has no tuft and a different call.
The tufted duck is one of the species to which the Agreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA) applies.
The tufted duck breeds throughout temperate and northern Eurasia. It occasionally can be found as a winter visitor along both coasts of the United States and Canada. It is believed to have expanded its traditional range with the increased availability of open water due to gravel extraction, and the spread of freshwater mussels, a favourite food. These ducks are migratory in most of their range, and overwinter in the milder south and west of Europe, southern Asia and all year in most of the United Kingdom. One individual has been reported as far south as Melbourne, Australia. They form large flocks on open water in winter.
A cladistic analysis based on several morphological characters placed the surf scoter as a monotypic taxon, closest to the white-winged scoter (Melanitta deglandi) and the velvet scoter (Melanitta fusca), which are both sister taxa.[6][8] These three species form the subgenus Melanitta, distinct from the subgenus Oidemia, which contains the black scoter (Melanitta americana) and the common scoter (Melanitta nigra).
The only extinct Melanitta species, M. cerutti, used to be present in California during the late Pliocene, but it has been moved in the genus Histrionicus (Harlequin duck).[9]
The genus Melanitta is part of the Mergini tribe, a monophyletic group of the Northern Hemisphere.[8] It includes eiders, mergansers, goldeneyes and other sea ducks.[8][10] This tribe is part of the family Anatidae, along with the swans and geese.