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Tetraonidae Vigors, 1825
Grouse (pronounced /ˈɡraʊs/) are a group of birds from the order Galliformes. They are often considered a family Tetraonidae, though the American Ornithologists' Union and many others include grouse as a subfamily Tetraoninae in the family Phasianidae. Grouse inhabit temperate and subarctic regions of the northern hemisphere, from pine forests to moorland and mountainside, from 83° North (Rock Ptarmigan in northern Greenland) to 28° North (Attwater's Prairie Chicken in Texas). Presumably they evolved in this zone.
Grouse are heavily built like other Galliformes such as chickens. They range in length from 31 cm (12 in) to 95 cm (37 in), in weight from 0.3 kg (11 oz) to 6.5 kg (14 lb). Males are bigger than females—twice as heavy in the Capercaillie, the biggest member of the family. Grouse have feathered nostrils. Their legs are feathered to the toes, and in winter the toes too have feathers or small scales on the sides, an adaptation for walking on snow and burrowing into it for shelter. Unlike other Galliformes, they have no spurs.
Feeding and habits
These birds feed mainly on vegetation—buds, catkins, leaves, and twigs—which typically accounts for over 95 percent of adults' food by weight. Thus their diet varies greatly with the seasons. Hatchlings eat mostly insects and other invertebrates, gradually reducing their proportion of animal food to adult levels. Several of the forest-living species are notable for eating large quantities of conifer needles, which most other vertebrates refuse. To digest vegetable food, grouse have big crops and gizzards, eat grit to break up food, and have long intestines with well-developed caeca in which symbiotic bacteria digest cellulose.
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