The western capercaillie (Tetrao urogallus), also known as the wood grouse, heather cock or capercaillie is the largest member of the grouse family. The largest known specimen, recorded in captivity, had a weight of 7.2 kg (15.9 lbs). Found across Europe and Asia, it is renowned for its mating display.
Male and female western capercaillie—the cocks and the hens—can easily be differentiated by their size and colouration. The male bird (or cock) is much bigger than the female (or hen). Cocks typically range from 74 to 85 cm (29 to 35 in) in length with wingspan of 90 to 125 cm (34–49 in) and an average weight of 4.1 kg (9.0 lb). The larger wild cocks can attain a length of 100 cm (39 in) and weight of 6.7 kg (15 lb). The largest specimen ever recorded in captivity had a weight of 7.2 kg. (15.9 lbs). The body feathers are coloured dark grey to dark brown, while the breast feathers are dark metallic green. The belly and undertail coverts vary from black to white depending on race (see below).