The Western capercaillie is a heavy member of the grouse family and the largest of all extant grouse species. Found across Europe and the Palearctic, this primarily ground-dwelling forest grouse is renowned for its courtship display. Males and females can easily be differentiated by their size and coloration. The cock is much bigger than the hen. The body feathers of cocks are dark grey to dark brown, while the breast feathers are dark metallic green. The belly and under-tail coverts vary from black to white depending on race. Hens have brown with black and silver barring feathers on the upper parts; on the underside, they are more light and buffish yellow. Both sexes have a white spot on the wing bow.
Western capercaillies are non-migratory and breed across northern parts of Europe and the Palearctic. They inhabit mature conifer and mixed forests with a relatively open canopy structure.
Western capercaillies are diurnal and their activity is limited to the daylight hours. They spend the night in old trees with horizontal branches. These sleeping trees are used for several nights; they can be mapped easily as the ground under them is covered by pellets. The hens are ground breeders and spend the night on the nest. As long as the young chicks cannot fly the hen spends the night with them in dense cover on the ground. During winter the hens rarely go down to the ground and most tracks in the snow are from cocks. Western capercaillies are social birds; hens and their yearling chicks live in small flocks while adult cocks are almost always solitary. Adult cocks are strongly territorial and occupy a range of 50-60 hectares (120-150 acres) optimal habitat. Hen territories are about 40 hectares (100 acres). Territories of cocks and hens may overlap. Western capercaillies are not elegant fliers due to their body weight and short, rounded wings. While taking off they produce a sudden thundering noise that deters predators. Because of their body size and wingspan, they avoid young and dense forests when flying. While flying they rest in short gliding phases. Their feathers produce a whistling sound.
Western capercaillies are highly specialized herbivores, which feed almost exclusively on blueberry leaves and berries with some grass seeds and fresh shoots of sedges in the summertime. The young chicks are dependent on protein-rich food in their first weeks and thus mainly prey on insects. During winter, when a high snow cover prevents access to ground vegetation, Western capercaillies feed on coniferous needles of spruce, pine, and fir as well as on buds from beech and rowan.
The breeding season of Western capercaillies starts between March and April and lasts until May or June. At the very beginning of dawn, the tree courting begins on a thick branch of a lookout tree. The cock postures himself with raised and fanned tail feathers, erect neck, beak pointed skywards, wings held out and drooped, and starts his typical aria to impress the females. The typical song in this display is a series of double-clicks like a dropping ping-pong ball, which gradually accelerate into a popping sound like a cork coming of a champagne bottle, which is followed by scraping sounds. Towards the end of the courting season, the hens arrive on the courting grounds, also called "lek". The cocks fly from their courting trees to an open space nearby and continue their display. About three days after mating the hen starts laying eggs in a nest that is usually hidden under low branches of a young tree or a broken tree crown. The average clutch size is 8 eggs but may amount up to 12. Brooding lasts about 26-28 days. After hatching the chicks are dependent on getting warmed by the hen. Like all precocial birds, the young are fully covered by down feathers at hatching but are not able to maintain their body temperature which is 41 °C (106 °F) in birds. They grow rapidly and at an age of 3-4 weeks, the chicks are able to perform their first short flights. From this time on they start to sleep in trees on warm nights. At an age of about 6 weeks, they are fully able to maintain their body temperature. From the beginning of September, the families start to dissolve. First the young cocks disperse, then the young hens. Both sexes may form loose foraging groups over the winter.
The most serious threats to the Western capercaillie are habitat degradation, particularly the conversion of diverse native forest into often single-species timber plantations, and birds colliding with fences erected to keep deer out of young plantations. A traditional game bird, the capercaillie has been widely hunted with guns and dogs throughout its territory in central and northern Europe. This includes trophy hunting and hunting for food. Since hunting has been restricted in many countries, trophy-hunting has become a tourist resource, particularly in Central European countries. Other threats include predation, pollution, and climate changes.
According to the IUCN Red List, the total population size of the Western capercaillie is 3,000,000-5,499,999 mature individuals. The European population is estimated at 666,000-1,060,000 lekking males, which equates to 1,330,000-2,110,000 mature individuals. Currently, this species is classified as Least Concern (LC) on the IUCN Red List but its numbers today are decreasing.