Anas strepera

Description

Gadwalls range in size from 18 to 22 inches long and 1 to 2½ pounds in weight, with both sexes being about the same size.

Males and females look very much alike most of the year, with generally drab plumage lacking distinctive markings. A white speculum is the most distinctive marking on a gadwall, but it is only visible when the bird is in flight.

During the breeding season the male's plumage becomes grayish with distinct vermiculation on the scapular and back feathers, the head turns brown, and the upper and lower tail covers turn black. The most distinguishing features of a male during this period are its long, acutely-pointed, silver-gray tertial feathers.

Distribution and Habitat

Gadwalls winter from southern Mexico and Guatemala to coastal Alaska, the Atlantic and Gulf coast regions of the United States, and many areas in between. Their summer breeding grounds range from the Atlantic coast of Canada to the far northwestern coast of Alaska, with the largest concentrations being found in the prairie pot-hole region of southern Canada and northern United States. Some populations can also be found breeding in Iceland, the British Isles, and northern Eurasia.

Gadwalls prefer marshes, sloughs, ponds, and small lakes with grasslands in both fresh and brackish water as breeding habitats. They are more commonly found on small prairie marshes than in temporary water areas, deep marshes, or open water marshes, and they generally avoid wetlands that are bordered by woodlands or thick vegetation. In the winter they prefer the brackish water marshes with abundant leafy vegetation.

Reproduction

Gadwalls engage in elaborate courtship displays prior to mating. They are generally monogamous in their breeding behavior, and pair bonds are frequently renewed each year.

The female usually chooses a nest site near her natal nesting grounds. The male stands guard while the female constructs the nest, which typically consists of a despression in the soil lined with leaves, grasses, twigs, and down feathers. The clutch of 7 to 13 eggs is laid at the rate of one egg per day, and is incubated by the female for about 26 days.

Gadwall chicks are able to procure their own food almost immediately after hatching and are only cared for by the mother for about 10 weeks.

If the nest is predated, the female will usually make another nest and lay a second clutch.

Diet

Gadwalls feed on aquatic vegetation, aquatic invertebrates, and seeds. Their main diet of plant material includes leaves and stems of aquatic plants, all of which are obtained by surface feeding. They can also be found in fields feeding on grain or in woodlands feeding on acorns. They supplement their plant diet with insects, crustaceans, amphibians, mollusks, and fish.

Habits and Behaviors

Gadwalls typically migrate in flocks of less than 100 individuals, but as many as 10,000 may migrate in separate groups to the same destination, arriving within hours of each other. Although they are diurnal in their daily behavior, migration flights usually take place at night.

Scientific Classification

phylum Chordata
subphylum Vertebrata
class Aves
order Anseriformes
family Anatidae
subfamily Anatinae
genus & species Anas strepera

Animal Diversity Web http://animaldiversity.org/accounts/Anas_strepera/

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