Willow ptarmigan a range of lower plant species. It is also believed that the greening of parts of the Arctic is affecting Willow Ptarmigan populations by altering the shape and size of the shrubs they are able to feed on. Male willow ptarmigans are territorial birds. Males arrive in the breeding areas and set up territories in April and May, aggressively defending them against male interlopers. When the females arrive a few weeks later, the male performs courtship displays such as aerial manoeuvres, strutting and tail-fanning. When she has chosen a mate and a nesting site, the female lays a clutch of
Snow camouflage to escape the conclusion that cryptic brown summer plumage becomes a liability in snow, and white plumage is therefore another cryptic adaptation." All the same, he notes, "in spite of winter plumage, many Ptarmigan in NE Iceland are killed by Gyrfalcons throughout the winter." Some animals of the far north, like the showshoe and Arctic hares, Arctic fox, stoat, and rock ptarmigan change their coat colour (by moulting and growing new fur or feathers) from brown or grey summer camouflage to white in the winter; the Arctic fox is the only species in the dog family to do so. However,