Grouse are heavily built birds like other Galliformes such as chickens. They range in length from 12 to 37 in, and in weight from 0.66 to 14.33 lbs. Males are bigger than females and the western capercaillie is twice as heavy. They are the largest member of the family. Grouse have feathered nostrils. Their legs are feathered to the toes, and in winter they 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.
These birds are among the upland game birds that are seen in the savannah and forests of North America. These birds can be found on the edges of the woods or even in the alpine above the tree lines of taller mountains in the warmer months. They have the ability to avoid being discovered by using their stealth or taking advantage of the coloring of their plumage and by hiding in the foliage of the trees or in the undergrowth of the forest floor. They will shelter themselves under the soft snow in the winter, using the snow as insulation from the cold and as a hiding place from their predators.
There are six types of grouse in North America, the Ruffed Grouse and Spruce Grouse are the most abundant and widespread. The Sharp-tailed Grouse has characteristics similar to the prairie chickens as they are found in larger flocks from central North America into the West and are most often found in open areas, where they are able to fly unobstructed. The Blue Grouse is separated into two sub-species, one called the Sooty Grouse, found near the Pacific Coast and the Dusky Grouse found in the interiors of the West. Then, there are the Greater Sage-Grouse of the mid-west prairies and the Gunnison Sage-Grouse found only in Colorado.
These birds feed mainly on vegetation, buds, catkins, leaves, and twigs, which typically accounts for most of the adults food by weight. 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.
Forest species flock only in autumn and winter, though individuals tolerate each other when they meet. Prairie species are more social, and tundra species (ptarmigans, Lagopus) are the most social, forming flocks of up to 100 in winter. All grouse spend most of their time on the ground, though when alarmed, they may take off in a flurry and go into a long glide.
Most species stay within their breeding range all year, but make short seasonal movements; many individuals of the ptarmigan and willow grouse migrate hundreds of miles.
In all but one species (Willow Ptarmigan), males are polygamous. Many species have elaborate courtship displays on the ground at dawn and dusk, which in some are given in leks. The displays feature males bright colored combs and in some species, bright colored inflatable sacs on the sides of their necks. The males display their plumage, give vocalizations that vary widely between species, and may engage in other activities, such as drumming or fluttering their wings, rattling their tails, and making display flights. Occasionally, males fight.
The nest is a shallow depressions on the ground, often in cover, with a scanty lining of plant material. The female lays one clutch, but may replace it if the eggs are lost. She begins to lay about a week after mating and lays one egg every day or two; the clutch comprises five to 12 eggs. The eggs have the shape of hen’s eggs and are pale yellow, sparsely spotted with brown. On laying the second-last or last egg, the female starts 21 to 28 days of incubation. Chicks hatch in dense, yellow-brown down and leave the nest immediately. They soon develop feathers and can fly shortly before they are two weeks old. The female (and the male in the willow grouse) stays with them and protects them until their first autumn, when they reach their mature weights (except in the male Capercaillies). They are sexually mature the following spring, but often do not mate until later years.