Arctic Fox

About the arctic fox

The Arctic fox, also called the white fox, polar fox, or snow fox, is a small fox native to the Arctic tundra of the Northern Hemisphere. It belongs to the genus Vulpes, the "true foxes," within the fox tribe Vulpini and the canid subfamily Caninae. It was first described by Carl Linnaeus in 1758 as Canis lagopus, and more recent genetic evidence has placed it among the other Vulpes foxes rather than in its own genus. Its closest living relative is the kit fox, from which it diverged around 0.9 million years ago; it split from the red fox roughly 3.17 million years ago.

Body length runs from 46 to 68 cm (18 to 27 in), and the animal stands only 25–30 cm (9.8–11.8 in) at the shoulder, noticeably smaller than a red fox. Males average 3.5 kg (7.7 lb), ranging from 3.2 to 9.4 kg (7.1–20.7 lb), while females average 2.9 kg (6.4 lb), ranging from 1.4 to 3.2 kg (3.1–7.1 lb). The tail runs about a third of body length. Foxes living farther north tend to be smaller than those farther south. The body is rounded and compact, with a short muzzle, short legs, and short, thick ears — a shape that minimizes the surface area exposed to cold and cuts heat loss.

The coat is the Arctic fox's signature feature, described as providing the best insulation of any mammal. Foxes shed twice a year, alternating between a short, darker summer coat and a long, thick winter coat that is twice the length of the summer one. There are two color morphs: white and blue. The white morph is brown with cream-to-light-brown sides and belly in summer, turning fully white in winter; the blue morph stays grey, brown, or black year-round with only slight seasonal lightening. About 90% of the global population is white, though the blue morph makes up 65–70% of the population in Iceland and 25–30% in Fennoscandia.

Behavior and diet

Arctic foxes are active year-round and do not hibernate, but they conserve energy in winter by cutting back on movement and curling tightly into a ball — tucking legs and head under the body and behind the tail — to reduce their exposed surface area. In autumn they build up fat reserves, sometimes increasing body weight by more than 50%, which insulates them through winter and provides an energy reserve when food is scarce. Their winter fur is 70% fine underfur, and the thickness of that fur increases by 140% from summer to winter even though body core temperature stays constant year-round.

The diet centers on small animals: lemmings, voles, other rodents, hares, birds, eggs, fish, and carrion scavenged from wolf and polar bear kills. Lemmings are the most important prey where available, and a family of foxes can eat dozens in a day; on some islands, including parts of Iceland, birds make up most of the diet instead. In April and May, Arctic foxes also prey on ringed seal pups while the pups are confined and helpless in snow dens. Berries, seaweed, and insects round out the diet, making the species functionally omnivorous. Foxes cache surplus food — including snow goose eggs, which they gather at rates of 2.7 to 7.3 per hour and store in bulk — and can still eat cached eggs, with only modest energy loss, up to a year later.

Breeding takes place in April and May after a roughly 52-day gestation. Litters can range from 3 to as many as 25 pups, the largest litter size recorded in the order Carnivora, though white-morph foxes inland tie their litter size to the multi-year lemming population cycle and may not breed at all when lemmings are scarce. Pups weigh just 60–90 g (2.1–3.2 oz) at birth, stay blind and deaf until 14–16 days old, emerge from the den at 3–4 weeks, and are weaned by 7 weeks. Both parents raise the young, usually in a monogamous pair, in large, elaborate dens that can cover 1,000 m2 (11,000 sq ft) and have been used by generations of foxes for decades.

Range and habitat

Arctic foxes are found throughout the Arctic tundra of the Northern Hemisphere, one of the few mammals adapted to survive the extremes of that environment. They den in frost-free, slightly raised ground, often in eskers — ridges of sediment left by past glaciers — choosing sites with many entrances, good drainage, and a southward face for warmth. Where red foxes share the range, Arctic foxes favor larger, maze-like dens that make it easier to escape a bigger predator, and will even reuse dens the red fox has abandoned.

The species must tolerate temperature swings of up to 90–100°C (160–180°F) between the outside air and its own core body temperature, which owes to its coat, its compact shape, and a countercurrent heat-exchange system in the legs that keeps its feet just above freezing (−1°C / 30°F) without losing mobility. Natural predators sharing this range include golden eagles, bald eagles, hawks, snowy owls, Arctic wolves, polar bears, wolverines, brown bears, and red foxes; domestic dogs are noted as an introduced threat in some areas.

Conservation status

The Arctic fox is listed as Least Concern (LC). No major range-wide threats are described here, though regional pressures are noted: in Scandinavia, where the red fox is also present, some Arctic fox populations are in decline, and conservationists there are supplying supplemental food. Social structures also shift toward larger, cooperative groups on the coasts of Svalbard and in Scandinavia, compared with the more consistently monogamous pattern seen inland and, most notably, in Iceland.