Arctic fox

The Arctic fox (Vulpes lagopus), also known as the white fox, polar fox or snow fox, is a small canid native to the Arctic regions of the Northern Hemisphere. It inhabits the vast expanses of the tundra biome and is exceptionally well adapted to living in extremely cold environments. The species is best recognised for its dense, insulating fur, which also provides effective camouflage throughout the year. Although many individuals survive only a single year in the wild, some may live up to a decade. Its compact body shape, thick tail and short limbs help minimise heat loss in freezing conditions.
The Arctic fox is an opportunistic predator and scavenger, feeding on small mammals such as lemmings and voles, as well as young seals, fish, birds and their eggs. It also consumes berries, seaweed and various invertebrates. During the breeding season, Arctic foxes typically form monogamous pairs and rear their young in extensive underground dens. At times, additional family members assist in caring for the pups. The species faces predation from golden eagles, wolves, polar bears, wolverines, red foxes and grizzly bears.

Behaviour and Thermoregulation

Arctic foxes must withstand considerable differences between the external environment and their internal core temperature. To reduce heat loss, the fox curls tightly into a ball, covering its head and limbs with its tail and adopting a posture that reduces its exposed surface area. It also shelters from wind and cold within its den. Although active year-round, the Arctic fox reduces movement during winter to conserve energy. It builds up substantial fat reserves during autumn, increasing its body mass significantly to provide insulation and a crucial energy source during periods of scarcity.

Reproductive Biology

With the arrival of spring, Arctic foxes focus on reproduction and securing a suitable den. They select frost-free, elevated ground where long-established tunnel systems provide warmth and protection. These dens, often located in eskers or other raised terrain, may be used by many generations. Preferred dens have numerous entrances and are oriented towards the sun to enhance warmth. Rugged terrain is often favoured as natal habitat, offering greater protection from predators.
Lemming abundance strongly influences reproductive success in inland populations. When food is plentiful, Arctic foxes may produce large litters of up to 18 pups, whereas reproduction may cease in years of scarcity. Coastal foxes, which rely on more stable marine resources, typically raise smaller litters of around five pups annually. Breeding usually occurs in April and May, and the gestation period lasts approximately 52 days. Litters can be exceptionally large for a carnivorous mammal, with up to 25 pups recorded. Young pups emerge from the den at around four weeks and are weaned by nine weeks of age.
While the species is generally monogamous, social flexibility increases when food is abundant. In regions with plentiful prey or high predator pressure, Arctic foxes may form larger social groups including both breeding and non-breeding individuals. Such cooperation enhances defence of territories and increases pup survival. Coastal areas of Svalbard and parts of Scandinavia show higher frequencies of these complex social structures, partly due to resource availability and the presence of red foxes. In contrast, Icelandic populations remain strongly monogamous, possibly due to kin-selection factors among older offspring remaining within parental territories.

Feeding Ecology

The Arctic fox consumes a wide variety of prey, allowing it to survive the extreme seasonality of its environment. Lemmings constitute the primary prey in many inland areas, with fox families capable of consuming dozens per day. In regions with abundant seabirds, such as northern Canada and sub-Arctic islands, seasonal bird colonies offer an important food source. Along coastlines, diets consist largely of birds and marine resources.
During spring, Arctic foxes target the vulnerable pups of ringed seals, which remain sheltered in snow dens. They also consume berries, seaweed and other plant material, making them opportunistic omnivores. A notable feeding strategy is food caching. Foxes store surplus food, particularly eggs, which can remain edible for months. Chemical analyses show that preserved goose eggs retain most of their nutritional value even after long periods, enabling foxes to rely on stored food throughout harsh winters.

Adaptations for Cold Survival

Arctic foxes thrive in some of the planet’s coldest climates, yet they do not begin to shiver until temperatures fall remarkably low. Several specialised adaptations contribute to their survival:

• Dense pelage: Their thick, multilayered fur provides the greatest insulation of any mammal.
• Furred footpads: The Arctic fox is the only canid with fur covering the footpads, improving traction and reducing heat loss.
• Compact morphology: A rounded body, short muzzle, small ears and short legs minimise exposed surface area.
• Colour polymorphism: Two main coat morphs exist—white and blue. The white morph has seasonal colour changes, shifting from white in winter to brown and grey in summer. The blue morph retains a dark coat throughout the year. Despite the dominant genetics of the blue morph, the white morph overwhelmingly dominates the population.

These adaptations collectively enable the species to endure extreme conditions where temperatures and food availability fluctuate dramatically.

Sensory Capabilities

The Arctic fox has functional hearing across a range from roughly 125 Hz to 16 kHz, with peak sensitivity at mid-frequencies. Although its hearing is generally less acute than that of domestic dogs or kit foxes, it remains finely tuned to detect prey beneath snow. The upper frequency range of hearing is somewhat lower than that of some other canids, but its sensory abilities are sufficient for successful hunting in the Arctic environment.