Willow ptarmigan a reddish hue to the neck and breast, a black tail and white wings and underparts. It has two inconspicuous wattles above the eyes, which become red and prominent in the breeding season. The female is similar in appearance but lacks the wattles and has brown feathers scattered among the white feathers on the belly. During winter, the plumage of both sexes becomes completely white, except for some black feathers in the tail. Immature birds resemble the adults. The willow ptarmigan can be distinguished from the closely related rock ptarmigan ("Lagopus muta") by its larger size and thicker bill and
Arctic fox regulation. Also, the Arctic fox has a beneficial mechanism in their nose for evaporative cooling like dogs, which keeps the brain cool during the summer and exercise. The thermal conductivity of Arctic fox fur in the summer and winter is the same; however, the thermal conductance of the Arctic fox in the winter is lower than the summer since fur thickness increases by 140%. In the summer, the thermal conductance of the Arctic foxes body is 114% higher than the winter, but their body core temperature is constant year-round. One way that Arctic foxes regulate their body temperature is by