Willow ptarmigans weigh from one to almost two pounds and are the largest of the ptarmigans, with the white-tailed being the smallest, putting rock ptarmigans in between. Also, in winter their claws grow much longer than in summer, additionally increasing the bearing surface of their feet. Ptarmigans seem to always be exchanging feathers of one color for new ones of another, so they are camouflaged at all seasons. They have exceptionmlly thick, downy plumage in winter to hold in warmth. On cold winter nights they will burrow into snow to sleep, taking advantage of the added insulation of the snow.
Ptarmigans moult again in spring.
Rock and Willow females wear a breeding plumage of brown and yellow barred feathers while the white-tail hen is cooler toned. In the breeding season he remains conspicuously white while the female becomes almost invisible against the tundra. A ptarmigan of one kind or another lives in nearly every arctic and northern alpine habitat, as long as vegetation is present. The three species may share the same mountain in summer, but each has a distinctive habitat preference which reduces competition for food and nesting places. Willow Ptarmigan inhabit treeline areas and tundra where vegetation is relatively lush and able to support high densities of breeding pairs.