Capercaille

The capercaillie is the largest member of the grouse family.  The species shows extreme sexual dimorphism, with the male twice the size of the female. Found across Eurasia, this ground-living forest bird is renowned for its mating display.

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 typically range from 74 to 85 cm in length with wingspan of 90 to 125 cm and an average weight of 4.1 kg. 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.

The hen is much smaller, weighing about half as much as the cock. The capercaillie hen's body from beak to tail is approximately 54–64 cm long, the wingspan is 70 cm and weighs 1.5–2.5 kg, with an average of 1.8 kg. Feathers on the upper parts are brown with black and silver barring; on the underside they are more light and buffish yellow.