The Arctic fox

 

The Arctic fox (Vulpes lagopus), also known as the white fox, polar fox, or snow fox, is a small species of fox native to the Arctic regions of the Northern Hemisphere and common throughout the Arctic tundra biome. It is well adapted to living in cold environments, and is best known for its thick, warm fur that is also used as camouflage. It has a large and very fluffy tail. In the wild, most individuals do not live past their first year but some exceptional ones survive up to 11 years. Its body length ranges from 46 to 68 cm (18 to 27 in), with a generally rounded body shape to minimize the escape of body heat.

The Arctic fox preys on many small creatures such as lemmings, voles, ringed seal pups, fish, waterfowl, and seabirds. It also eats carrion, berries, seaweed, and insects and other small invertebrates. Arctic foxes form monogamous pairs during the breeding season and they stay together to raise their young in complex underground dens. Occasionally, other family members may assist in raising their young. Natural predators of the Arctic fox are golden eagles, Arctic wolves, polar bears, wolverines, red foxes, and grizzly bears.

 

Arctic foxes must endure a temperature difference of up to 90–100 °C (160–180 °F) 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 foxes are 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 (11,000 sq ft) 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.

 

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 also 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.

Arctic foxes survive harsh winters and food scarcity by either hoarding food or storing body fat subcutaneously and viscerally. At the beginning of winter, one Arctic fox has approximately 14740 kJ of energy storage from fat alone. Using the lowest BMR value measured in Arctic foxes, an average sized fox of 3.5 kg (7.7 lb) would need 471 kJ/day during the winter to survive. In Canada, Arctic foxes acquire from snow goose eggs at a rate of 2.7–7.3 eggs/h and 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 816 kJ. Eggs stored in the summer are accessed the following spring prior to reproduction.

Adaptations
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. The white morph has seasonal camouflage, white in winter and 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. Two similar mutations to MC1R cause the blue color and the lack of seasonal color change. The fur of the Arctic fox provides the best insulation of any mammal.

The Arctic 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.

Size
The average head-and-body length of the male is 55 cm (22 in), with a range of 46 to 68 cm (18 to 27 in), while the female averages 52 cm (20 in) with a range of 41 to 55 cm (16 to 22 in). In some regions, no difference in size is seen between males and females. The tail is about 30 cm (12 in) long in both sexes. The height at the shoulder is 25 to 30 cm (9.8 to 11.8 in). On average males weigh 3.5 kg (7.7 lb), with a range of 3.2 to 9.4 kg (7.1 to 20.7 lb), while females average 2.9 kg (6.4 lb), with a range of 1.4 to 3.2 kg (3.1 to 7.1 lb).

 

 

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 (where it was hunted to extinction) 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 Canadian boreal forests (northeastern Alberta, northern Saskatchewan, northern Manitoba, Northern Ontario, Northern Quebec, and Newfoundland and Labrador) 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.

 

References
1. Grey Wolf Wikipedia article - https://en.wikipedia.org/wiki/Arctic_fox