Tufted Duck (Aythya fuligula)
The adult male is all black except for white flanks and a blue-grey bill. 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 Tufted Duck breeds widely 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 winter in the milder south and west of Europe, southern Asia and all year in most of the United Kingdom. They will form large flocks on open water in winter.
Further Information: Wikipedia