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The coypu or nutria (Myocastor coypu ) is a species of semi-aquatic, dog-sized rodent in the family Capromyidae. These animals are native to central and southern South America, but they have become widely established elsewhere, mostly as a result of animals that have escaped from fur farms or that have been deliberately released.

Coypus have a stout, 17-25 in (43-64 cm) long body, with a roughly triangular-shaped head, and a round, scaly, sparsely-haired tail, which is 10-17 in (25-43 cm) long. Adult animals weight 15-20 lb (7-9 kg), with males being somewhat larger than females. The eyes and ears of coypus are small, and the legs are short. The forelegs are much larger than the hind and have four webbed toes as well as a single free toe used for grooming the fur. The toes have prominent claws. The fur is soft, dense, and lustrous, consisting of long guard hairs over a velvety underfur. The color of the guard hairs ranges from yellow-brown to red-brown, while the underfur is blackish.

Coypus are semi-aquatic animals, and are excellent swimmers. They typically live in the vicinity of slow-moving rivers and streams, or near the edges of shallow lakes, marshes, and other wetlands. Coypus mostly live in freshwater habitats, but in some places they occur in brackish and saltwater wetlands as well. Coypus den in burrows dug into banks, or in mounds of reedy vegetation that are constructed when ground suitable for digging is not available. Coypus live in pairs or small family groups and sometimes in larger colonies.

Coypus typically forage during twilight hours over a distance of up to several hundred yards, travelling along well-worn pathways through the usually grassy habitat. Coypus are shy and wary when foraging, and flee quickly to their burrow when any hint of danger is perceived. Coypus are mainly vegetarian in their feeding, although they will also eat molluscs.

The fur of coypus is a valued product, and this species has been introduced as a fur-bearing species into various parts of the United States and Europe. Coypus are also cultivated on fur farms, where they will breed continuously, and can be quite productive. Cultivated coypus can have a white or yellowish fur, in addition to the darker colors of the wild animals.

Coypus are considered to be pests in many of the places where they have become naturalized because they damage irrigation ditches and earthen dams with their burrows, compete with native fur-bearers, and, when abundant, can significantly deplete the abundance of forage.

See also Beavers.

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