(Part of the) common name of many species of the Tetraonidae family (order Galliformes) and the general term for the family (18 species with numerous subspecific forms). Other common names used for members of the family are 'ptarmigan', 'prairie chicken' and 'capercaillie'. The family is confined to the Northern Hemisphere, north of about 26° N. lat. (circumpolar). Grouse are fowl-like birds of 30-90 cm in length and 0.5-6.5 (mostly 1.9) kg. They differ from other gallinaceous birds in having the nostrils hidden by feathers, a considerably raised hind toe, and at least partially (most cases fully) feathered tarsi without spurs. The bill is short and strong; the wings are short and rounded, and the tail (sometimes large) takes various forms. They are mainly terrestrial, but some species are partly arboreal, and adapted to many ecological niches. Generally, grouse have a sober-coloured plumage; mostly dark browns, greys and blacks in forest grouse and paler browns and grey predominating in grouse of open country. All species show at least some sexual dimorphism in plumage, and sexual differences are accentuated by special characters (e.g. wattles) and especially by behaviour during the breeding season. Some species show spectacular (highly organized) types of social display during spring, in which up to several hundred cocks gather to compete for females; e.g. the Black-, Sage- and Sharp-tailed Grouse. The same group-display grounds (called 'strutting', 'dancing' or 'booming' grounds) are often used year after year. These social displays occur mainly in open-country habitats, while grouse living in forests show solitary displays. Grouse are mainly browsers (feeding on edible plant material within reach) and grazers, eating cultivated grains when possible. Young birds are for mainly insectivorous. Some grouse species have become nearly extinct because of loss of habitat.