Mid-sized diving duck. Inhabits marshy and reed-fringed lakes to open reservoirs; locally on the sea in winter, especially when lakes freeze. Locally in flocks, and often associates with winter flocks of Tufted Ducks. Feeds mainly by diving. Male distinctive, with dark rusty head, pale gray body contrasting with black breast, and broad pale bluish band on bill. Female rather nondescript: gray-brown overall with diffuse pale head markings. Note sloping forehead and dark gray bill with pale band near tip. In flight grayish overall (lacks bold white wing stripe).