Pucrasia[note 1]
Meleagris[note 1]
Bonasa
Tetrastes
Centrocercus
Dendragapus
Tympanuchus
Lagopus
Falcipennis
Canachites
Tetrao
Lyrurus
Grouse /ɡraʊs/ are a group of birds from the order Galliformes, in the family Phasianidae. Grouse are presently assigned to the tribe Tetraonini (formerly the subfamily Tetraoninae and the family Tetraonidae), a classification supported by mitochondrial DNA sequence studies,[2] and applied by the American Ornithologists' Union,[3] ITIS,[4] International Ornithological Congress,[5] and others.[6][1]
Grouse inhabit temperate and subarctic regions of the Northern Hemisphere, from pine forests to moorland and mountainside,[7] from 83°N (rock ptarmigan in northern Greenland) to 28°N (Attwater's prairie chicken in Texas).[8]
The turkeys are closely allied with grouse, but they have traditionally been excluded from Tetraonini, often placed in their own tribe, subfamily, or family;[2][8][9][10] certain more modern treatments also exclude them.[11][12] However, recent phylogenomic analyses demonstrate conclusively that they are sister to the traditionally-defined grouse, and they, along with the somewhat earlier-diverging koklass pheasant, may be treated as grouse (i.e., as basal members of the Tetraonini).[1] This is reflected in some more recent circumscriptions.[6][10]
Like many other Galliformes, grouse are generally heavily-built birds. The traditional grouse (excluding turkeys) range in length from 31 to 95 cm (12 to 37+1⁄2 in), and in weight from 0.3 to 6.5 kg (3⁄4 to 14+1⁄4 lb). However, if they are included, wild turkey toms are the largest grouse species, attaining lengths of 130 cm (50 in) and weighing up to 10 kg (22 lb).[13] Male grouse are larger than females, and can be twice as heavy in the western capercaillie (the largest of the traditional grouse). Like many other Galliformes, males often sport incredibly elaborate ornamentation, such as crests, fan-tails, and inflatable, brightly colored patches of bare skin. Many grouse have feathered nostrils, and some species, such as the ptarmigans, have legs which are entirely covered in feathers; 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 many other Galliformes, they typically have no spurs,[8] although turkeys do possess very prominent spurs.[14]
These birds feed mainly on vegetation—buds, catkins, leaves, and twigs—which typically accounts for over 95% of adults' food by weight. Thus, their diets vary 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.[8]