Perhaps one of the cutest canids out there, the arctic fox is a small fox native to the Arctic regions of the Northern hemisphere and common throughout the Arctic tundra biome. The Arctic Fox is believed to have evolved out of Tibet, where fossils of their extinct ancestors have been found. The Tibetan plateau was likely once a tundra type habitat during the Pliocene era, and so they radiated outwards from there into North America and Eurasia.
Amazing Arctic Adaptations
Arctic foxes survive in some incredibly tough environments, but thousands of years of evolution has given them some incredible physiological adaptations to thrive in the Arctic biome. They have the most insulative fur of any mammal and their foot pads are also covered in fur; the only canid to have this feature. Famously, the arctic fox has two colour morphs: white and blue. This coat colour is controlled by the MC1R (melanocortin receptor 1) gene. A mutation in this gene prevents a coat from being completely white. The allele for the blue gene is actually dominant, but despite this 99% of arctic foxes have a completely white coat. For those foxes with the genes for a blue coat, the fur is dark greyish blue during the summer, and a slightly paler whitish grey in the winter. The white foxes have dark brown fur with paler bellies in the summer and a completely pure white coat in the winter, which is 200% thicker than their summer coat. This coat is the perfect adaptation for the icy winter months, but molts away to the brown winter coat in early Spring as the ice begins to melt.
Their small, compact bodies with short muzzles, ears and legs give them less body area over which they can lose heat. They will also reduce their activity as much as possible during the winter, preserving as much insulating fat as possible. In their dens, Arctic foxes curl into a ball to only expose their furriest and most well insulated areas, further preventing any heat loss. This, coupled with their thick coat, means that Arctic foxes will only start to shiver when the temperature drops to -70c.
Although they deal with incredibly cold winters, they also experience relatively warm summers, putting them at the mercy of some extreme temperature fluctuations. To prepare for the punishing winters, arctic foxes cache food for the winter in their dens. In particular, Arctic foxes that live near bird colonies will cache eggs, as they can be stored easily for a long time without spilling, and are rich in calories and nutrients. Arctic foxes can increase their body mass by as much as 50% during the summer and the autumn, storing fat both viscerally and subcutaneously to insulate them for the winter. Studies of their genome have found that they have specially adapted genes for fat metabolism, similar to other Arctic mammals like the Polar Bear.
Aside from sneaking some eggs from sea bird colonies, arctic foxes also predate on rodents, hares, birds, fish and carrion, even scavenging on larger carcasses left by large predators like polar bears. Their incredibly sensitive sense of smell means they can track these caracasses from as much as 40 kilometres away and can detect frozen lemmings in up to 77 centimetres of snow. Their hearing is also incredibly well developed, allowing them to track lemmings burrowing in the snow.
Fortunately, arctic foxes are classed as least concern on the IUCN red list, as their numbers are stable and their populations large. Historically, fur hunting was a major issue, but throughout the 21st century fur hunting drastically reduced and their populations are under far less pressure than they once were. There is some concern over sarcoptic mange, although no one is yet sure the extent of the disease.
In some more Southerly parts of their range, Arctic foxes are steadily losing habitat to the red fox, in warmer areas where their white coat puts them at a disadvantage when snow cover is decreased. The larger and more generalist red fox is taking over the Arctic foxes’ niche in some parts of their range. There is a large population of Arctic foxes in fur farms, and many of them are the blue gene foxes, which frequently escape and run the risk of swamping the white gene foxes in the wild, as the blue gene is dominant.
Although the Arctic fox is currently in a good state, there are no specific conservation charities that deal with their conservation. However, a relative of theirs, the Island Fox has been the focus of a charity called the Nature Conservancy. The Island Fox is only found on Santa Cruz Island, just off the southwestern coast of Ventura, California and historically they were the island’s only top predator. In the 1990s, golden eagles began nesting, attracted by the feral pigs, and soon turned their talons to the Island Fox too, who were completely naive to any other predators. Scientists brought breeding pairs into a captive breeding programme in 2000 and eventually 85 pups were released into the wild. Temporary fences were built whilst non native feral pigs were removed, and the golden eagles were relocated to the mainland. The Island Fox is now an incredible conservation success story, with their survival rate now at 96%, such an impressive recovery that the Island Fox has been removed from the endangered species list. The Nature Conservancy still tracks and monitors the foxes on the island, checking population numbers and also monitoring the incidence of canine distemper and rabies. The Island Fox actually has the fastest recovery of any endangered mammal thus far! You can learn more about the Island Fox Project and its success at Santa Cruz Island Fox Facts & Conservation Information (nature.org), and more about the Nature Conservancys’ work across the globe to conserve lands and waters with their teams of scientists, policy makers and volunteers at The Nature Conservancy: A World Where People & Nature Thrive.
Careau, V. Giroux, J.F. Gauthier, G. Berteaux, D. (2008) ‘Surviving on cached foods- the energetics of egg-caching by arctic foxes.’ Canadian Journal of Zoology
Fuglesteg, B.N. Haga, O.E. Folkow, L.P. Fuglei, E. Blix, A.S. (2005) ‘Seasonal variations in basal metabolic rate, lower critical temperature and responses to temporary starvation in the arctic fox from Svalbard.’ Polar Biology
Kumar, V. Kutschera, V.E. Nilsson, M.A. Janke, A. (2015) ‘Genetic signatures of adaptation revealed from transcriptome sequencing of Arctic and red foxes.’ BMC genomics
Lai, S. Berteaux, D. (2015) ‘ Spatio-temporal hotspots of satellite tracked arctic foxes reveal a large detection range in a mammalian predator.’ Movement Ecology
Pagh, S. Hersetinsson, P. (2008) ‘Difference in diet and age structure of blue and white Arctic foxes in the Disko bay area, West Greenland.’ Polar Research
Prestrud, P. (1991) ‘Adaptation by the Arctic Fox to the Polar Winter.’ Arctic
Tannerfeldt, M. (1997) ‘Population fluctuations and life history consequences in the Arctic fox.’
Vage, D.I. Fuglei, E. Snipstad, K. Beheim, J. Landsem, V.M. Klungland, H. (2005) ‘Two cysteine substitutions in the MC1R generate the blue variant of the arctic fox and prevent expression of the white winter coat.’ Peptides
Wang, X. Wang, Y. Li, Q. Tseng, J.Z. Takeuchi, G.T. Deng, T. Xie, G. Chang, M. Ning, W. (2015) ‘Cenozoic vertebrate evolution and paleoenvironment in Tibetan plateau: progress and prospects.’ Gondwana Research
MASSIVE THANK YOU TO RACHAEL DA SILVA FROM THE UK FOR THIS WRITE UP! PLEASE FOLLOW HER ON INSTAGRAM AND HER WILDLIFE ARTWORK AT TILLY_MINT08