Lesser Scaup - Ecology

Ecology

Lesser Scaup forage mainly by sifting through the bottom mud, usually after diving and swimming underwater, occasionally by dabbling without diving. They mainly eat mollusks such as mussels and clams, as well as seeds and other parts of aquatic plants like sedges and bulrushes (Cyperaceae), "pondweeds", Widgeon-grass (Ruppia cirrhosa), Wild Celery (Vallisneria americana) or wild rice (Zizania). In winter, but less so in summer, other aquatic animals – crustacean, insect and their larvae and small fishes – form an important part of their diet. It has been reported that both the Lesser and the Greater Scaup have shifted their traditional migration routes to take advantage of the presence of the Zebra Mussel (Dreissena polymorpha) in Lake Erie, which was accidentally introduced in the 1980s and has multiplied enormously. This may pose a risk to these birds because zebra mussels are efficient filter feeders and so accumulate environmental contaminants rapidly.

They nest in a sheltered location on the ground near water, usually among thick vegetation such as sedges and bulrushes, sometimes in small loose groups and not rarely next to colonies of gulls or terns; several females may deposit eggs in a single nest. The drakes court the hens in the winter quarters; pairs form shortly before and during the spring migration. When nesting starts, the males aggregate while they moult into eclipse plumage, leaving the task of incubation and raising the young to the females alone.

The nest is a shallow depression scraped in the ground and lined with plants and some down feathers. Breeding begins in May, but most birds nest only in June, later than usual for North American waterfowl. The clutch numbers about 9-11 eggs on average; up to 26 eggs have been found in a single nest, but such high numbers are from more than one female. Incubation is by the female only and lasts around 3 weeks. The young fledge some 45–50 days after hatching and soon thereafter the birds migrate to winter quarters already. Lesser Scaup become sexually mature in their first or second summer. The oldest known individual reached an age of over 18 years.

Before the start of the population decline (see below), about 57% of the Lesser Scaup nests failed each breeding season because the female was killed or the eggs were eaten or destroyed. The average brood size of nests where eggs hatched successfully was 8.33 hatchlings.