(northwest Mongolia and east Kazakhstan) The subspecies show increasing amounts of white on the underparts of males from west to east, almost wholly black with only a few white spots underneath in western and central Europe to nearly pure white in Siberia, where the black-billed capercaillie occurs. Variation in females is much less. The native Scottish population, which became extinct between 1770 and 1785, was probably a distinct subspecies, though it was never formally described as such; the same is likely of the extinct Irish population; the current introduced population is of the nominate subspecies urogallus. Hybrids Western capercaillies are known to hybridise occasionally with black grouse (these hybrids being known by the German name Rackelhahn) and the closely related black-billed capercaillie. Description Male and female western capercaillie can easily be differentiated by their size and colouration. The cock is much bigger than the hen. It is one of the most sexually dimorphic in size of living bird species, only exceeded by the larger types of bustards and a select few members of the pheasant family. Cocks (males) typically range from in length with wingspan of and an average weight of . The largest wild cocks can attain a length of and weight of . The largest specimen recorded in captivity had a weight of . The weight of 75 wild cocks was found to range from . The body feathers are 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). The hen (female) is much smaller, weighing about half as much as the cock. The capercaillie hen's body from beak to tail is approximately long, the wingspan is and weighs , with an average of . Feathers on the upper parts are brown with black and silver barring; on the underside they are more light and buffish yellow. Both sexes have a white spot on the wing bow. They have feathered legs, especially in the cold season, for protection against cold. Their toe rows of small, elongated horn tacks provide a snowshoe effect that led to the German family name "Rauhfußhühner", literally translated as "rough feet chickens". These so-called "courting tacks" make a clear track in the snow. The sexes can be distinguished very easily by the size of their footprints. There is a bright red spot of naked skin