Arctic Fox

The Arctic fox is a small canid that lives where almost nothing else with a pulse can — the open tundra and the frozen sea, through months of darkness and temperatures that would kill most mammals in hours. It manages this with a coat, a body shape, and a breeding strategy all fine-tuned to the extreme.

Overview

Arctic foxes are found across the entire circumpolar north, on land and out onto the sea ice. On the mainland tundra they specialise in lemmings; on coasts and islands they lean more on seabirds, eggs, and marine scraps. They do not hibernate. Through the winter they range widely — some individuals have been GPS-tracked crossing thousands of kilometres of ice between Svalbard, Greenland, and Canada in a single season.

Surviving the cold

The Arctic fox is, by several measures, the best cold-adapted land mammal:

• Fur. In winter it grows the deepest, densest coat of any mammal relative to its size, with insulation so effective the fox does not begin to shiver until around −70 °C.
• Shape. A round, compact body with short ears, a short muzzle, and short legs keeps the surface area — and therefore heat loss — to a minimum. Fur even grows on the soles of the feet; the species name lagopus means “hare-foot.”
• The tail. Long and thick, wrapped around the body and over the face when the fox curls up to sleep.
• Countercurrent blood flow in the legs and feet that keeps the core warm while letting the paws run just above freezing.

Diet and the lemming cycle

Arctic fox numbers rise and fall with lemmings, which boom and crash roughly every three to five years. In a peak year, prey is so abundant that a female can raise a litter of 15 or more pups — the largest litters of any wild carnivore — and foxes cache surplus lemmings and eggs in the permafrost for leaner times. In a crash year, many foxes do not breed at all, and populations shrink.

Where lemmings fail or are scarce, coastal foxes switch to nesting seabirds and their eggs, wash-up carrion, seal pups, and, in winter, the seal carcasses left by polar bears.

Reproduction and life cycle

Arctic foxes are usually monogamous and defend a territory around a den — often an ancient, many-entranced burrow system dug into a well-drained bank or esker and reused by generations of foxes, sometimes for centuries. Pups are born in spring, emerge at a few weeks, and disperse in autumn.

Threats and conservation

Globally the Arctic fox is Least Concern, but the picture is regional:

• The mainland Scandinavian population collapsed under 19th- and 20th-century fur trapping and has never recovered, sitting at a few hundred animals and classed as Critically Endangered despite decades of intervention.
• Red foxes, larger and more dominant, are expanding north as the climate warms and the tree line advances, taking over Arctic fox dens and killing pups.
• Warming itself is disrupting the lemming cycles the species depends on, with milder, wetter winters producing ice layers that seal lemmings away from the foxes above.