Arctic Fox

Arctic foxes must endure a temperature difference of up to 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. 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.

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 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. 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.

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 . Among its adaptations for survival in the cold is its dense, multilayered pelage, which provides excellent insulation. There are two genetically distinct coat color morphs: white and blue. 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.

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 prey.

The Arctic fox contains advantageous genes to overcome extreme cold and starvation periods. Transcriptome sequencing has identified two genes that are under positive selection: Glycolipid transfer protein domain containing 1 (GLTPD1) and V-akt murine thymoma viral oncogene homolog 2 (AKT2). GLTPD1 is involved in the fatty acid metabolism, while AKT2 pertains to the glucose metabolism and insulin signaling. The average mass specific BMR and total BMR are 37% and 27% lower in the winter than the summer. The Arctic fox decreases its BMR via metabolic depression in the winter to conserve fat storage and minimize energy requirements. According to the most recent data, the lower critical temperature of the Arctic fox is at in the winter and in the summer. It was commonly believed that the Arctic fox had a lower critical temperature below . However, some scientists have concluded that this statistic is not accurate since it was never tested using the proper equipment. Arctic foxes maintain the temperature in their paws independently from the core temperature. If the core temperature drops, the pad of the foot will remain constantly above the tissue freezing point.

The average head-and-body length of the male is , with a range of , while the female averages with a range of . In some regions, no difference in size is seen between males and females. The tail is about long in both sexes. The height at the shoulder is . On average males weigh , with a range of , while females average , with a range of .

Vulpes lagopus is a 'true fox' belonging to the genus Vulpes of the fox tribe Vulpini, which consists of 12 extant species. |2=Kit fox }} |2=Swift fox The specific name lagopus is derived from Ancient Greek λαγώς (lagōs, "hare") and πούς (pous, "foot"), referring to the hair on its feet similar to those found in cold-climate species of hares. Looking at the most recent phylogeny, the Arctic fox and the red fox (Vulpes vulpes) diverged approximately 3.17MYA. Additionally, the Arctic fox diverged from its sister group, the kit fox (Vulpes macrotis), at about 0.9MYA.

The origins of the Arctic fox have been described by the "out of Tibet" hypothesis. On the Tibetan Plateau, fossils of the extinct ancestral Arctic fox (Vulpes qiuzhudingi) from the early Pliocene (5.08–3.6 MYA) were found along with many other precursors of modern mammals that evolved during the Pliocene (5.3–2.6 MYA). It is believed that this ancient fox is the ancestor of the modern Arctic fox. Globally, the Pliocene was about 2–3 °C warmer than today, and the Arctic during the summer in the mid-Pliocene was 8 °C warmer. By using stable carbon and oxygen isotope analysis of fossils, researchers claim that the Tibetan Plateau experienced tundra-like conditions during the Pliocene and harbored cold-adapted mammals that later spread to North America and Eurasia during the Pleistocene Epoch (2.6 million-11,700 years ago).

Besides the nominate subspecies, the common Arctic fox, V. l. lagopus, four other subspecies of this fox have been described: * Bering Islands Arctic fox, V. l. beringensis * Greenland Arctic fox, V. l. foragoapusis * Iceland Arctic fox, V. l. fuliginosus * Pribilof Islands Arctic fox, V. l. pribilofensis

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. and the Kenai Peninsula in Alaska. They are found at elevations up to 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.

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. In July 2019, the Norwegian Polar Institute reported the story of a yearling female which was fitted with a GPS tracking device and then released by their researchers on the east coast of Spitsbergen in the Svalbard group of islands. The young fox crossed the polar ice from the islands to Greenland in 21 days, a distance of . She then moved on to Ellesmere Island in northern Canada, covering a total recorded distance of in 76 days, before her GPS tracker stopped working. She averaged just over a day, and managed as much as in a single day.

, 1890]] The Arctic fox has been assessed as least concern on the IUCN Red List since 2004. because even though the animal was declared a protected species in Finland in 1940, the population has not recovered despite that. As a result, the populations of Arctic fox have been carefully studied and inventoried in places such as the Vindelfjällens Nature Reserve (Sweden), which has the Arctic fox as its symbol. The abundance of the Arctic fox tends to fluctuate in a cycle along with the population of lemmings and voles (a 3- to 4-year cycle). The pelts of Arctic foxes with a slate-blue coloration were especially valuable. They were transported to various previously fox-free Aleutian Islands during the 1920s. The program was successful in terms of increasing the population of blue foxes, but their predation of Aleutian Canada geese conflicted with the goal of preserving that species. The Arctic fox is losing ground to the larger red fox. This has been attributed to climate change—the camouflage value of its lighter coat decreases with less snow cover. Red foxes dominate where their ranges begin to overlap by killing Arctic foxes and their kits. An alternative explanation of the red fox's gains involves the gray wolf. Historically, it has kept red fox numbers down, but as the wolf has been hunted to near extinction in much of its former range, the red fox population has grown larger, and it has taken over the niche of top predator. In areas of northern Europe, programs are in place that allow the hunting of red foxes in the Arctic fox's previous range. As with many other game species, the best sources of historical and large-scale population data are hunting bag records and questionnaires. Several potential sources of error occur in such data collections. In addition, numbers vary widely between years due to the large population fluctuations. However, the total population of the Arctic fox must be in the order of several hundred thousand animals. The world population of Arctic foxes is thus not endangered, but two Arctic fox subpopulations are. One is on Medny Island (Commander Islands, Russia), which was reduced by some 85–90%, to around 90 animals, as a result of mange caused by an ear tick introduced by dogs in the 1970s. The population is currently under treatment with antiparasitic drugs, but the result is still uncertain. The other threatened population is the one in Fennoscandia (Norway, Sweden, Finland, and Kola Peninsula). This population decreased drastically around the start of the 20th century as a result of extreme fur prices, which caused severe hunting also during population lows. The population has remained at a low density for more than 90 years, with additional reductions during the last decade. The total population estimate for 1997 is around 60 adults in Sweden, 11 adults in Finland, and 50 in Norway. From Kola, there are indications of a similar situation, suggesting a population of around 20 adults. The Fennoscandian population thus numbers around 140 breeding adults. Even after local lemming peaks, the Arctic fox population tends to collapse back to levels dangerously close to nonviability.