Friday, March 05, 2021

Comparing the Island Fox and the Arctic Fox; The Fox of the Tundra

Santa Rosa Island fox, courtesy of NPS

In this installment of Foxes of North America, we'll look at the Arctic Fox. While the island fox lives on coastal islands that rarely experience a hint of snow, the arctic fox is a true species of the North and has adaptations that help it survive the harsh conditions of the polar regions.

Arctic fox; courtesy of Colby Brokvist: ColbyOutdoors Photography

Arctic Fox; The Fox of the Tundra

Tundra comes from the Finnish word tuntri, meaning treeless plain. The tundra is noted for its permafrost landscapes, extremely low temperatures, windswept plains, little precipitation and long dark winters. Yet, the arctic fox lives and reproduces successfully in this seemingly inhospitable environment. In North America, the arctic fox is found from western Alaska east across northern Canada. The arctic fox is a large North American fox species, weighing approximately 12 pounds.

Arctic fox; courtesy NPS
To survive extremely low temperatures that regularly reach -50 degrees F, the arctic fox has thick fur with two undercoats. This adaptation provides excellent insulation. (Compare to the island fox's fur.) A short muzzle, short ears and legs, as well as a rounded, compact body with a big bushy tail, also reduce heat loss. Arctic foxes have a special counter-circulating blood system that acts as a heat exchanger to cool, rather than warm, the blood flowing to their feet. Having cooler blood at their feet means less heat will be lost to the surrounding surfaces, thus requiring less energy for the fox to stay warm in frigid temperatures. In the summer, arctic foxes shed their long white coat and instead grow short, dark gray to bluish-brown fur.

Arctic fox in summer coat; courtesy NPS

The scientific name for the arctic fox is Vulpes lagopus. Vulpus is Latin for fox, while lagopus is Greek for "hairy foot". This is an accurate description of the fox's thickly furred pawpads; a trait also characteristic of rabbits and hares.

The tundra ecosystem has a simplified food web, because not many species can survive the harshness of the winters. For that reason, the diet of the arctic fox is less diverse than that of other fox species. Arctic foxes are capable predators of small prey, such as lemmings and voles. Individuals living along the coast take advantage of seabird populations, hunting birds and eggs. They also forage other available marine resources. Arctic foxes frequently follow polar bears and scavenge their leftover scraps. Arctic foxes are comfortable foraging on the pack ice as well. These winter weather foxes use the permafrost as a natural refrigerator to cache food in years of abundance for times when food is scarce.

Arctic fox; courtesy of Sean Beckett

Arctic foxes pair up in February and March and mate in April, which is late compared to their southern canid counterparts. (Island fox pups are born in April.) Arctic fox kits are typically born in May or June. They can have as many as 19 pups in a single litter. Extremely large litters of up to 22 kits have been observed. That's the largest litter size in order Carnivora! However, the average number of pups varies by local prey abundance and geographical area. More typical litter sizes for arctic foxes are 6–9 pups in inland areas and 3–6 pups in coastal populations. To handle such large litters, female arctic foxes have evolved 12–14 teats. Arctic foxes use dens primarily during the pup season (like island foxes). They build their dens in sandy soils where they can dig 2–3 feet before reaching the permafrost. Arctic foxes also make snow dens during blizzard conditions.

The fox of the tundra is an elegant creature that has adapted to survive in extremely cold environments. Arctic fox populations in North America are healthy and stable, so this species is not listed as threatened or endangered. That doesn't mean the foxes are without challenges. Red foxes have been expanding their range northward as a result of the warming climate, driving the arctic fox deeper into the polar regions. When red foxes encroach on arctic fox territory, the more aggressive red fox wins out. The extreme conditions of the northernmost arctic regions may limit the range expansion of the red fox, thus giving the arctic fox its best chance for long-term survival.

In the final installment of Foxes of North America, we will concluded with the progenitor of the island fox, the gray fox.

Series installments:

How is the Island Fox Unique?

Red Fox: Life on the Edge

Gemini Foxes: Kit Fox and Swift Fox;

The Island Fox's Origin - The Gray Fox


Cyper, B.L. 2003. "Foxes (Vulpes species, Urocyon species and Alopex lagopus)." In Wild Mammals of North America: Biology, Management, and Conservation, 2nd edition by G. Feldhamer, B. Thompson, and J. Chapman (eds), pg 511–546. Baltimore: Johns Hopkins University Press.

Elbroch, M. and K. Rinehart. 2001. Behavior of North American Mammals. pg 105–111. Peterson Reference Guides.

Henry, J. D. 1996. Living on the Edge, Foxes. Minocqua, WI: Northword Press.