Willow Ptarmigan, Lagopus lagopus

Willow Ptarmigan, Lagopus lagopus, with summer colours.

The willow ptarmigan changes plumage each season in order to remain well hidden. In summer it is grey-brown, with dark wavy patterns across its body. Exact colouration varies between moults, but breeding males are usually a more reddish chestnut colour than females. In winter, both sexes adopt white plumage for maximum camouflage from predators, as well as for insulation from the bitterly cold temperatures. In spring and fall many combinations of brown and white can be seen as the ptarmigans change plumage. Males have a red comb above the eye, which may be either exposed – particularly during the breeding season – or concealed behind the feathers. The willow ptarmigan's legs and feet are covered in feathers for warmth.

The willow ptarmigan is essentially the low arctic ptarmigan, as its breeding range is almost completely restricted to this area, except for Iceland which is classified as High Arctic. The willow ptarmigan favours wet, vegetated tundra, and arctic scrubland. During winter storms, ptarmigan shelter in snowdrifts, where they are protected from strong winds and harsh temperatures. These birds are termed partial migrants, because they do not move further south than they have to in order to survive. They travel in large flocks from their breeding grounds to windswept areas of the tundra where vegetation is accessible for feeding. The willow ptarmigan is herbivorous, eating only vegetation such as shoots, buds, and dwarf willow or birch catkins.

The breeding season begins in April or May, at which time male willow ptarmigan are brown but male rock ptarmigan are still white; this may help ensure that females seek out males of the correct species. The female builds a nest in a depression on the ground, lining it with a mat of leaves and grasses. She incubates 6–11 eggs for at least 20 days. Her summer plumage – dark, with light patterns – provides good camouflage, blending in with the ground to protect her and the young. The chicks are active as soon as they hatch, a characteristic of ptarmigans, and can often fly by the time they are twelve days old! In the northern part of the bird's range, the young will be fully grown in six or seven weeks. By contrast, development in more southern areas usually takes three months. This difference with latitude is an adaptation to the short summers of the north. Unlike rock ptarmigan, willow ptarmigan are strongly monogamous and the male usually remains with the female to help defend the brood for up to eight weeks after hatching.