Willow ptarmigan seeds and berries during the summer and largely subsisting on the buds and twigs of willow and other dwarf shrubs and trees during the winter. The willow ptarmigan is a medium to large ground-dwelling bird and is the most numerous of the three species of ptarmigan. Males and females are about the same size, the adult length varying between with a wingspan ranging from . The weight is . It is deep-chested and has a fairly long neck, a broad bill, short feathered legs and a moderately short rounded tail. In the summer, the male's plumage is marbled brown, with
Snow camouflage snow camouflage patterns. Charles Darwin mentioned the white winter coloration of the ptarmigan in his 1859 "Origin of Species": The white protective coloration of arctic animals was noted by an early student of camouflage, the naturalist Alfred Russel Wallace, in his 1889 book "Darwinism"; he listed the polar bear, the American polar hare, the snowy owl and the gyr falcon as remaining white all year, while the arctic fox, arctic hare, ermine and ptarmigan change their colour, and observed "the obvious explanation", that it was for concealment, at a time when Darwinism was at a low ebb. Later zoologists such