Grouse, common name for a game bird of the colder parts of the Northern Hemisphere. There are about 18 species. Grouse are henlike terrestrial birds, protectively plumaged in shades of red, brown, and gray. The nostrils are entirely hidden by feathers, and the legs are partially or completely feathered. The most common eastern American grouse is the ruffed grouse (sometimes miscalled partridge or pheasant), Bonasa umbellus, a forest bird noted for the drumming sound made by the male during its elaborate courtship dance. The ptarmigan (Lagopus lagopus), or snow grouse, is an arctic species that migrates to the NW United States in winter, when its plumage changes from rusty brown to white, matching the snow. Western American grouse include the prairie chicken, Tympanuchus cupido, once common in the East, and the sage grouse, Centrocercus urophasianus. The latter, called also sage hen, sage cock, or cock of the plains, is the largest of the group (25–30 in./62.5–70 cm long) and so named because its flesh tastes strongly of sage : the result of feeding on sagebrush buds. The males of both these species are distinguished by yellow air sacs on the neck that inflate to an enormous size during courtship. European species include the capercaillie and the black grouse. The red grouse is found in Great Britain. Striking fluctuations in the abundance of all grouse species occur in intervals of 7 to 10 years. A combination of factors, rather than a single explanation, appears to be the cause for this not entirely understood phenomenon. Fortunately, grouse have high reproductive rates, which enable them to restore their populations after a low-level period. . (source - www.1upinfo.com)