Duck, a swimming bird related to the goose and swan. There are about 150 species. Ducks may be found in every region of the world, except Antarctica. Millions of ducks once inhabited North America but great numbers have been killed off by hunters. More than half of the most popular game ducks are shot before they have reached the age of one year. Several species of ducks are valued as food. In length ducks range from 15 to 24 inches (38 to 61 cm). Their call is usually a deep, quacking noise. The male is called a drake, the female a duck or hen. The young are ducklings.

MallardMallard drakes have distinctive green heads while the hens are drab brown.

Ducks have spoon-shaped bills. In some ducks, the edges of the bill have rough, groove-like notches, called serrations, which hold elusive prey. In other ducks the serrations are finer and are used only to strain water from food.

The thick, soft feathers are made water-repellent by a film of oil that the duck, using its bill, presses out of a gland located just above the tail. Water cannot penetrate this film and it prevents the feathers from becoming water-logged and the skin from becoming wet and cold. Ducks vary in color from brilliant iridescent greens, bronzes, and purples to dull grays, lusterless whites, and drab browns. The drake is generally more brightly colored than the hen.

A duck has webbed feet. Three of the four toes extend forward, with the outer toes being joined to the middle toe by webbing. The fourth toe projects backward and is not webbed. The duck is a graceful swimmer and diver but on land it moves with a clumsy waddle. Some of the diving species remain submerged for long periods while pursuing fish. Ducks are splendid fliers. Several species can fly at speeds close to 50 miles per hour (80 km/h).