Feeding Behavior

Forages mostly underwater; rarely by dabbling or up-ending in shallow water.

Eggs

usually 8-11, sometimes 5-17. Olive-green to blue-green. Incubation is by female, usually 29-30 days. Female covers eggs with down when leaving nest. Young: leave nest 1-2 days after hatching, are led to water by female. Young are tended by female but feed themselves. Age at first flight 56-66 days.

Young

leave nest 1-2 days after hatching, are led to water by female. Young are tended by female but feed themselves. Age at first flight 56-66 days.

Diet

Varies with season and habitat. Eats crustaceans including crayfish, crabs, shrimps, amphipods, and others; also mollusks (including blue mussel), small fishes, marine worms, frogs, leeches. Aquatic insects are main food in summer (when lakes with no fish may be preferred). Also eats some plant material, such as pondweeds, especially in fall.

Nesting

First breeds at age of 2 years, but 1-year-old females go prospecting for future nest sites in early summer. Pair formation occurs mostly in late winter. Several males may court one female. In courtship, displays of male include throwing head far back with bill pointed skyward while uttering shrill call; also ritualized head-pumping, and short flights with exaggerated takeoff and landing. Nest sites are in large tree cavities, 5-60' above ground, sometimes in abandoned buildings; will use nest boxes. Nest is depression in wood chips at bottom of cavity, lined with down. Where nest sites are scarce, females may lay eggs in each others' nests.