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(grouse), a family of birds of the order Galliformes. The Tetraonidae range from 30 to 110 cm in length and from 0.4 to 6.5 kg in weight. The body is plump. The nostrils are feathered. The legs, and sometimes the toes, are feathered and not spurred. In many species, the sexes are unlike in size and coloration.
There are 18 species of Tetraonidae, distributed in Europe, Asia, and North America. In winter the Tetraonidae keep to a limited area or range for food. They are preeminently birds of the forest, but some species inhabit valleys, mountain tundra, and steppes. Many species are polygamous. The nests are built on the ground or, in some species, in trees. A clutch contains from four to 16 eggs. The female incubates the eggs and rears the young. The diet consists of vegetable matter, such as shoots, buds, flowers, berries, and seeds. Young birds consume insects as well. The Tetraonidae are valuable game birds.
Eight species of Tetraonidae are found in the USSR—willow grouse (Lagopus lagopus), ptarmigan (Lagopus mutus). black grouse (Lyrurus tetrix). Caucasian blackcock (Lyrurus mloko-siewiczi). capercaillie (Tetrao urogallus). black-billed capercaillie (Tetrao parvirostris). hazel hen (Tetrastes bonasia). and Siberian spruce grouse (Falcipennis falcipennis).