A gadwall is a medium sized migratory duck reaching a length of about 23 inches (57 centimeters) and a wingspan of approximately 35 inches (90 centimeters). Its native range covers Europe, Asia, the United States, and Canada. Often called a gray mallard because of its similar appearance, the gadwall is roughly the same size as a mallard, but has mainly dull gray plumage.
With a gray back, the gadwall has a white underside. Males have a black patch on the underside, close to the tail, with a gray to dull blue beak. Females have a yellow beak and tend to be a pale tan brown and gray. Females do not have the black patch near the tail and have a uniform white underside.
The gadwall molts twice yearly; during this time the duck is unable to fly, making it extremely vulnerable to predators. When possible during molting time, this species remains on bodies of freshwater, staying as far as possible from the shore. This is a strategic maneuver to avoid predators.
For most of the year, the primary diet of the gadwall consists of seeds, grains, algae, and green plant matter. In the lead up to breeding season, females begin to consume large amounts of fat and protein based foods such as invertebrates, insects, small fish, and tadpoles. This is because the female must build up large fat and protein reserves; when egg laying and incubation begins, she will rarely leave the nest.
Nests are built in sheltered depressions on the ground, close to freshwater. Between one and seven eggs are laid and take around four weeks to hatch. Males rarely participate in incubating or rearing the young. Juveniles are independent in snout 10 weeks after hatching. It takes up to two years for the gadwall to reach sexual maturity, and begin to breed.
Gadwalls are generally active only during the day except when migrating. This species will only fly at night while migrating, although the reasons for this are unclear. Both in the wintering grounds and the summer breeding grounds, the gadwall tends to live on or near marsh land, ponds, and small lakes, preferring still or slow moving waters.
Like any medium sized duck, the gadwall has a wide variety of predators, from domestic cats and dogs to foxes, coyotes, and large, predatory birds. Humans are also a threat to this species. Humans have hunted this species for both food and sport for many centuries. These birds are not considered endangered, however, because they have a large native range and can raise several clutches of eggs per year.