Misunderstood Mesos: Arctic Fox (Vulpes lagopus)

Built to survive in some of the harshest conditions on Earth, Arctic foxes play an important mesocarnivore role in ecosystems of the far North.  Living in lands that remain below freezing for most of the year is a huge challenge for such a small mammal, but these highly adapted and cunning foxes find a way to flourish on the dark, frozen landscape.  Their bright white fur may provide their most recognizable trait, but the density and layering of the fur, not the color, is their primary adaptation to battle the brutal cold.

As with many northern mammals, their fur coat is double-layered and seasonal.  The plush, insulating undercoat builds to the highest density in winter for insulation, then sheds off in spring to prevent overheating throughout summer.  To keep their body temperature consistent year-round, there is an astounding 140% increase in fur density among winter pelage compared to summer.  Many biologists believe the fur of Arctic foxes may be the best insulating hair layer in the Animal Kingdom.

Two color morphs exist for Arctic foxes, the popular all-white phase, and a rare deep blue to gray color variation.  Studies have shown blue phase foxes tend to live near coastal habitats where the terrain is rockier, while white phase foxes live more inland where snow and ice are the predominant substrates.  All white phase foxes molt to a brownish color in summer for camouflage, but blue phase foxes remain the same color year-round.

Arctic foxes are smaller and more compact than other fox species, assisting with heat conservation.  Their short legs, little muzzle, and stocky ears all allow for a less mass to surface-area ratio, limiting heat loss.  Both sexes are about the same average size, measuring 20-22 inches long plus a long tail of around twelve inches.  Such an extended tail is an important adaptation used to cover the less-insulated head and muzzle while lying, further preventing heat loss.  Standing about ten inches tall, both sexes also weigh in at the same average weight of 9-10 pounds.

Another unique freezing weather adaptation provides the scientific name for the Arctic fox.  “Vulpes lagopus” translates from Latin to “fox with hare foot” signifying the similarities with the fur-covered feet of northern hares.  To prevent frostbite, Arctic foxes have fur covering the pads of their paws, a trait that is unique among all other canines.  Additionally, like gray wolves, Arctic foxes can regulate the temperature of their paws to just above freezing, therefore preserving valuable energy during winter.  Finally, Arctic foxes have such an incredible tolerance to cold, they do not begin shivering until the temperature dives below a frigid -94 F!

As their name suggests, Arctic foxes are widespread throughout the extreme northern regions of the planet.  Inhabiting the Arctic tundra and ice shelves of Europe, Asia, and North America, these hardy foxes spread as far south as the boreal forest of Canada where they tend to be outcompeted by the larger red fox.  During the last ice age, they traversed the frozen ocean to become the only native land mammal of Iceland.

Arctic foxes can either maintain a home range where most food is acquired or be nomadic and search for food over extensive expanses of land for survival.  Even those with home ranges are forced to conduct up to three-day expeditions away from their dens to locate adequate sustenance.  Nomadic foxes are constantly on the move, averaging up to thirty miles a day while seeking prey.  One fox was documented traveling up to ninety-six miles in 24 hours!

Arctic fox pairs are mostly monogamous and can share a single den for their entire lives.  Breeding occurs annually in April or May, with pups typically being born in late June after a 52-day gestation.  Surprisingly, up to twenty-four kits can be born in a single litter, which is the highest number of offspring among all carnivores!  However, most litters average around five kits with the dependent factor being food availability.  As with many predators, their biotic potential is influenced by prey population size.  When their nutrition is good, they produce more kits than when food is scarce.

The kits are cared for by both parents within their extensive underground den for the first few months, then might remain within their parent’s home range for years to come.  The offspring are even known to occupy their natal den after their parents die and produce a litter of their own, creating a family legacy in one den that can last for centuries.  Although they have been documented living up to 11 years old, due to their harsh living conditions most do not live much past their first year of life.

Arctic foxes hold the only mesocarnivore niche for the Northern polar region.  Where polar bears and wolves sit atop the food chain, foxes maintain a vital role between these top-level predators and the primary consumers of the tundra.  During spring and summer, lemmings are quite abundant, providing the main food source for most Arctic foxes living away from coastlines.  However, Arctic foxes remain generalists and will consume other rodents, birds, eggs, fish, and hares as the opportunity arises.  Due to a lack of other mesocarnivores, their control of rodent and bird populations is critical in balancing the far-north ecosystem.

Scavenging carrion is another foraging technique used by Arctic foxes for survival.  They are even known to follow polar bears on hunts to pick over the leftovers of a freshly killed carcass.  The foxes are also able to detect a carcass on their own up to twenty-four miles away!  Their excellent olfactory abilities allow them to find potential food buried deep in snow.  Ring seal pups often remain in lairs under the snow surface while their mothers are out hunting.  Arctic foxes can smell these helpless pups up to five feet deep in the snow then excavate them for a meal that could provide nourishment to a fox family for weeks.

As with all mesocarnivores, Arctic foxes also consume vegetation when available during spring and summer.  Most of their plant diet consists of berries, nuts, or seaweed if living near a coastline.  Due to a relative lack of herbivores, the dispersal of seeds within their feces is an important mechanism for plant survival on the polar tundra.

Although Arctic foxes are primarily nocturnal, they can be active at any time of day.  Most small rodents are nocturnal, so foxes have better success hunting at night.  They can also avoid larger predators, such as polar bears and wolves, easier through the cover of darkness.  During the day, fox families huddle within their dens to keep warm and out of the biting wind.  Arctic foxes do not hibernate but do slow their metabolism to conserve valuable energy during the peak of winter’s harsh conditions.

The intelligent carnivores have two methods of ensuring adequate energy resources through winter.  First, they store excess fat within their bodies that is slowly utilized during times of less food.  This subcutaneous fat may increase their body weight by up to 50% in autumn as they prepare for winter then helps keep them insulated.  Secondly, they store excess food in underground depressions to be retrieved later when food is scarce.  This behavior is known as caching and is common among canines.

Due to the extreme environment where Arctic foxes live, humans do not exist in nearly all their polar range.  Therefore, most foxes never even see humans in their lifetimes, so interactions are rare if not impossible.  Some native tribes of the Arctic traditionally hunted foxes for food and their incredible pelage, but most of these practices no longer occur.  European fur trappers prized the luxurious pelt, but extensive fur trapping of wild foxes has been curtailed in North America.  Still, fur trapping continues to threaten some isolated populations of Arctic foxes around the world.

However, human society is certainly harming Arctic fox populations from a distance through artificial climate warming.  As the southern edge of the Arctic fox range slowly increases temperatures, red foxes invade Northward and push out the smaller Arctic foxes.  Conservationists believe this red fox takeover is the largest threat to the future of Arctic foxes.

Arctic foxes exhibit incredible adaptations to survive within the most extreme conditions on the planet.  By keeping a check on rodent populations, assisting in disposing of carcasses, or spreading seeds across the tundra, Arctic foxes are a critical component of the far North ecosystem.  Unfortunately, human-caused global climate change now threatens these majestic mammals, so please keep their fate in mind when making decisions regarding climate change action.  Such an incredible animal deserves our protection.

For further reading:

IUCN Red List:  Arctic fox