The Arctic fox (Alopex lagopus), also known as the polar fox, is a small fox native to cold Arctic regions of the Northern Hemisphere. It is common in all three tundra biomes. Although some authorities have suggested placing it in the genus Vulpes, it has long been considered the sole member of the genus Alopex. The Arctic fox has smaller, more rounded ears, a more rounded braincase. It has a slightly shorter and broader muzzle than the red fox. Its feet are furrier than those of other foxes. The Arctic fox occurs in two distinct color morphs, “blue” and “white”. Each color phase also changes seasonally. It changes from “blue” moults from chocolate brown in summer to lighter brown tinged with a blue sheen in winter. The “white” is almost pure white in winter. In the summer it is grey to brownish-grey dorsally, and light grey to white below. The “blue” morph comprises less than 1% of the population through most of its continental range, but this proportion increases westwards in Alaska. In Greenland roughly half of Arctic foxes are of the blue morph, and in Iceland most of them are blue.
The Arctic fox has evolved to live in the most frigid extremes on the planet. Among its adaptations for cold survival is its deep, thick fur. It uses a system of countercurrent heat exchange in the circulation of paws to keep them from freezing, and a good supply of body fat. The fox has a low surface-area-to-volume ratio as evidenced by its generally rounded body shape, short muzzle and legs, and short, thick ears. Since less of its surface area is exposed to the cold, less heat escapes the body.
The Arctic fox will generally eat any meat it can find, including lemmings, Arctic hares, birds and their eggs, and carrion. Lemmings are the most common prey. A family of foxes can eat dozens of lemmings each day. During April and May the Arctic fox also preys on ringed seal pups when the young animals are confined to a snow den and are relatively helpless. When its normal prey is scarce, the Arctic fox scavenges the leftovers of larger predators.
Foxes tend to form monogamous pairs in the breeding season. Litters of between six and twelve pups are born in the early summer, a very large litter size for a mammal. The parents raise the young in a large den. Dens can be complex underground networks, housing many generations of foxes. Young from a previous year’s litter may stay with the parents to help rear younger siblings.
The white morph is generally associated with true tundra habitat, the blue more with coastal habitat.