Arctic fox facts

Arctic fox
Scientific classification
Kingdom: Animalia
Class: Mammalia
Order: Carnivora
Family: Canidae
Genus: Vulpes
Binomial name
Vulpes lagopus
(Linnaeus, 1758)
Arctic fox range

The Arctic fox, (or 'white fox', 'polar fox', 'snow fox'), is Vulpes lagopus. It is a small fox which lives in the Arctic. The fox is about 10-12 inches high (25–30 cm) and it weighs from 6.5 to 21 pounds (2.7-4.5 kg).The females tend to be smaller than the males. The Arctic fox has a round body shape, short nose and legs, and short, fluffy ears. It has a deep thick fur which is brown in summer and white in winter. Arctic foxes live for about 3 to 6 years.

This fox can live in the cold north even when it is -30F. Their thick fur keeps them warm. The fur of the Arctic fox provides the best insulation of any mammal. Its broad, fluffy paws let it walk on ice and snow to look for food. The Arctic fox has very good ears so that it can hear small animals under the snow. When it hears an animal under the snow, it jumps and punches through the snow to catch its victim. The Arctic fox eats any meat it can find. They eat lemmings, arctic hares, eggs and dead bodies of animals. The foxes also eat plants sometimes.

Arctic foxes do not hibernate. They grow thicker fur in the Autumn, and put on more than 50% of their body weight as fat for insulation and as energy reserves.

Behavior

Arctic foxes must endure a temperature difference of up to 90-100 °C between the external environment and their internal core temperature. To prevent heat loss, the Arctic fox curls up tightly tucking its legs and head under its body and behind its furry tail. This position gives the fox the smallest surface area to volume ratio and protects the least insulated areas. Arctic foxes also stay warm by getting out of the wind and residing in their dens. Although the Arctic fox is active year-round and do not hibernate, they attempt to preserve fat by reducing their locomotor activity. They build up their fat reserves in the autumn, sometimes increasing their body weight by more than 50%. This provides greater insulation during the winter and a source of energy when food is scarce.

Reproduction

In the spring, the Arctic fox’s attention switches to reproduction and a home for their potential offspring. They live in large dens in frost-free, slightly raised ground. These are complex systems of tunnels covering as much as 1,000 m2 (1,200 sq yd) and are often in eskers, long ridges of sedimentary material deposited in formerly glaciated regions. These dens may be in existence for many decades and are used by many generations of foxes.

Fox pups animals
Pups of Arctic fox with summer morph

Arctic foxes tend to select dens that are easily accessible with many entrances, and that are clear from snow and ice making it easier to burrow in. The Arctic fox builds and chooses dens that face southward towards the sun, which makes the den warmer. Arctic foxes prefer large, maze-like dens for predator evasion and a quick escape especially when red foxes are in the area. Natal dens are typically found in rugged terrain, which may provide more protection for the pups. But, the parents will also relocate litters to nearby dens to avoid predators. When red foxes are not in the region, Arctic foxes will use dens that the red fox previously occupied. Shelter quality is more important to the Arctic fox than the proximity of spring prey to a den.

The main prey in the tundra is lemmings, which is why the white fox is often called the “lemming fox.” The white fox’s reproduction rates reflect the lemming population density, which cyclically fluctuates every 3-5years. When lemmings are abundant, the white fox can give birth to 18 pups, but they often do not reproduce when food is scarce. The “coastal fox” or blue fox lives in an environment where food availability is relatively consistent, and they will have up to 5 pups every year.

Breeding usually takes place in April and May, and the gestation period is about 52 days. Litters may contain as many as 25 (the largest litter size in the order Carnivora). The young emerge from the den when 3 to 4 weeks old and are weaned by 9 weeks of age.

Arctic foxes are primarily monogamous and both parents will care for the offspring. When predators and prey are abundant, Arctic foxes are more likely to be promiscuous (exhibited in both males and females) and display more complex social structures. Larger packs of foxes consisting of breeding or non-breeding males or females can guard a single territory more proficiently to increase pup survival. When resources are scarce, competition increases and the number of foxes in a territory decreases. On the coasts of Svalbard, the frequency of complex social structures is larger than inland foxes that remain monogamous due to food availability. In Scandinavia, there are more complex social structures compared to other populations due to the presence of the red fox. Also, conservationists are supplying the declining population with supplemental food. One unique case, however, is Iceland where monogamy is the most prevalent. The older offspring (1-year-olds) often remain within their parent’s territory even though predators are absent and there are fewer resources, which may indicate kin selection in the fox.

Diet

Fox with fish
A Arctic fox (Summer morph) with fish

Arctic foxes generally eat any small animal they can find, including lemmings, voles, other rodents, hares, birds, eggs, fish, and carrion. They scavenge on carcasses left by larger predators such as wolves and polar bears, and in times of scarcity even eat their feces. In areas where they are present, lemmings are their most common prey, and a family of foxes can eat dozens of lemmings each day. In some locations in northern Canada, a high seasonal abundance of migrating birds that breed in the area may provide an important food source. On the coast of Iceland and other islands, their diet consists predominantly of birds. 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. They also consume berries and seaweed, so they may be considered omnivores. This fox is a significant bird-egg predator, consuming eggs of all except the largest tundra bird species. When food is overabundant, the Arctic fox buries (caches) the surplus as a reserve.

Arctic foxes survive harsh winters and food scarcity by either hoarding food or storing body fat. Fat is deposited subcutaneously and viscerally in Arctic foxes. At the beginning of winter, the foxes have approximately 14740kJ of energy storage from fat alone. Using the lowest BMR value measured in Arctic foxes, an average sized fox (3.5 kg) would need 471kJ/day during the winter to survive. Arctic foxes can acquire goose eggs (from greater snow geese in Canada) at a rate of 2.7-7.3eggs/h, and they store 80-97% of them. Scats provide evidence that they eat the eggs during the winter after caching. Isotope analysis shows that eggs can still be eaten after a year, and the metabolizable energy of a stored goose egg only decreases by 11% after 60 days (a fresh egg has about 816kJ). Researchers have also noted that some eggs stored in the summer are accessed later the following spring prior to reproduction.

Adaptations

Alopex lagopus IMG 9019
Arctic fox sleeping with its tail wrapped around itself

The Arctic fox lives in some of the most frigid extremes on the planet, but they do not start to shiver until the temperature drops to −70 °C (−94 °F). Among its adaptations for survival in the cold is its dense, multilayered pelage, which provides excellent insulation. Additionally, the Arctic fox is the only canid whose foot pads are covered in fur. There are two genetically distinct coat color morphs: white and blue. In the winter the white morph is white in color and turns brown along the back with light grey around the abdomen in summer. The blue morph is often a dark blue, brown, or grey color year-round. Although the blue allele is dominant over the white allele, 99% of the Arctic fox population is the white morph. The fur of the Arctic fox provides the best insulation of any mammal.

The fox has a low surface area to volume ratio, as evidenced by its generally compact body shape, short muzzle and legs, and short, thick ears. Since less of its surface area is exposed to the Arctic cold, less heat escapes from its body.

Sensory modalities

The Arctic fox has a functional hearing range between 125 Hz–16 kHz with a sensitivity that is ≤ 60 dB in air, and an average peak sensitivity of 24 dB at 4 kHz. Overall, the Arctic foxes hearing is less sensitive than the dog and the kit fox. The Arctic fox and the kit fox have a low upper-frequency limit compared to the domestic dog and other carnivores. The Arctic fox can easily hear lemmings burrowing under 4-5 inches of snow. When it has located its prey, it pounces and punches through the snow to catch its victim.

The Arctic fox also has a keen sense of smell. They can smell carcasses that are often left by polar bears anywhere from 10–40 km. It is possible that they use their sense of smell to also track down polar bears. Additionally, Arctic foxes can smell and find frozen lemmings under 46–77 cm of snow, and can detect a subnivean seal lair under 150 cm of snow.

Distribution and habitat

ArcticFoxesLyd
The Arctic fox's seasonal furs, summer (top), "blue" (middle), and winter (bottom)

The Arctic fox has a circumpolar distribution and occurs in Arctic tundra habitats in northern Europe, northern Asia, and North America. Its range includes Greenland, Iceland, Fennoscandia, Svalbard, Jan Mayen and other islands in the Barents Sea, northern Russia, islands in the Bering Sea, Alaska, and Canada as far south as Hudson Bay. In the late 19th century, it was introduced into the Aleutian Islands southwest of Alaska. However, the population on the Aleutian Islands is currently being eradicated in conservation efforts to preserve the local bird population. It mostly inhabits tundra and pack ice, but is also present in boreal forests in Canada and the Kenai Peninsula in Alaska. They are found at elevations up to 3,000 m (9,800 ft) above sea level and have been seen on sea ice close to the North Pole.

The Arctic fox is the only land mammal native to Iceland. It came to the isolated North Atlantic island at the end of the last ice age, walking over the frozen sea. The Arctic Fox Center in Súðavík contains an exhibition on the Arctic fox and conducts studies on the influence of tourism on the population. Its range during the last ice age was much more extensive than it is now, and fossil remains of the Arctic fox have been found over much of northern Europe and Siberia.

The color of the fox’s coat also determines where they are most likely to be found. The white morph mainly lives inland and blends in with the snowy tundra, while the blue morph occupies the coasts because its dark color blends in with the cliffs and rocks.

Migrations and travel

During the winter, 95.5% of Arctic foxes utilize commuting trips, which remain within the fox’s home range. Commuting trips in Arctic foxes last less than 3 days and occur between 0-2.9 times a month. Nomadism is found in 3.4% of the foxes, and loop migrations (where the fox travels to a new range, then returns to its home range) are the least common at 1.1%. Arctic foxes in Canada that undergo nomadism and migrations voyage from the Canadian archipelago to Greenland and northwestern Canada. The duration and distance traveled between males and females is not significantly different.

Arctic foxes closer to goose colonies (located at the coasts) are less likely to migrate. Meanwhile, foxes experiencing low-density lemming populations are more likely to make sea ice trips. Residency is common in the Arctic fox population so that they can maintain their territories. Migratory foxes have a mortality rate >3 times higher than resident foxes. Nomadic behavior becomes more common as the foxes age.


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