Arctic fox
The Arctic fox (Vulpes lagopus) has a short snout, short rounded ears and a body size smaller than its close relative the red fox. It has a thick winter fur and a thinner summer fur, and appears in two colour phases: white and blue.
The Arctic fox is about 60cm long, and has a tail that is approximately 30cm long in addition. It weighs 2.5–5 kg.
Arctic foxes moult twice each year. The winter fur is thick with dense under-fur and long guard hairs. The shedding of the winter fur starts in May and the short summer fur is in place in July. In September the winter fur starts growing, and by November–December the winter coat is complete.
They appear in two colour phases: white and blue. The white phase is uniformly white in winter, except for some few black hairs on the tip of the tail, and brown-grey on the back/thighs and yellowish-white on the belly and the sides in summer. The blue phase remains dark charcoal coloured all year round, but becomes somewhat lighter in winter. 90–97% of the population in Svalbard are white phase, and within the circumpolar distribution area 97–99% are white.
Distribution
The Arctic fox has a circumpolar distribution and is found in a wide variety of tundra habitats. It reproduces in mountain tundra habitats in Fennoscandia, on the Arctic tundra of Eurasia and North America, Greenland, Iceland, Svalbard and other barren Arctic islands outside the coast of Siberia, Canada and the Bering Strait.
Throughout their distribution Arctic foxes are abundant, with the exception of Fennoscandia, Medny Island (in the Komandor Islands of Russia) and the Pribilof Islands in Alaska, where they have undergone serious declines.
New genetics studies show that there is considerable contact between populations; some foxes move over vast distances, sometimes using sea ice to move from land mass to land mass.
In Svalbard Arctic foxes occur almost everywhere on the archipelago, from the highest mountain ridges to the coasts and even on the drift ice. Arctic foxes were not been seen on the islands of Bjørnøya or Jan Mayen for many years, but recently they have been found denning on Bjørnøya.
They are especially abundant where there is access to plentiful food resources during the breeding season, such as on the west coast of Spitsbergen where large numbers of seabirds, eiders and geese breed. The population density of Arctic foxes is somewhat lower in the central regions of Spitsbergen where they must rely primarily on reindeer carcasses for food.
Ecology
The Arctic fox lives in two principle habitat types, inland and coastal and their life-styles are tied to these habitat types.
In inland areas (in North America, Eurasia and East Greenland) where Arctic foxes are characterised as lemming specialists, they rely on rodent populations that are cyclic (fluctuating with periodicities of three to five years). In such environments, where prey availability is unpredictable, there is large variation between years in litter sizes.
Coastal foxes that occur in regions without lemmings like Svalbard, Iceland and West Greenland are generalists, preying on food items both from marine and terrestrial food webs. Their annual food supply is more predictable and stable, and is available in excess in summer, but is restricted during the winter. Coastal foxes have more stable litter size between years, produce fewer cubs every year and the population size is more stable compared to inland foxes.
With the exception of a local sibling vole population in Svalbard, there are no small rodents, so Svalbard foxes concentrate their forage efforts on other types of prey. In spring and summer ringed seal pups, seabirds, geese, bird eggs, and rock ptarmigan are the major prey items. In the winter their diet consists mainly of rock ptarmigan, stored food that was gathered and cached in the summer and autumn, carcasses of seals and reindeer, and garbage from the settlements. Some foxes also specialize on feeding on remnants of seals killed by polar bears.
Arctic foxes in Svalbard have no natural enemies or competitors. Predation has not been reported on either adults or youngsters. Starvation during the winter is likely the main cause of mortality.
Life history and reproduction
The Arctic fox is monogamous. Pairs are territorial in the breeding season; home ranges are highly variable in size. Along the coast, close to bird cliffs, where food is available in excess in the breeding season the home range is generally small (3–5km2) compared to home range sizes in valley regions in central regions of Spitsbergen where prey is more scattered and unpredictable (60km2).
Mating takes place from the end of February until mid April. After a gestation period of 52–54 days, the annual litter which normally contains five or six cubs is born in a den in May or early June. Newborn fox cubs have a body weight of 50–65g.
When the young are three or four weeks old they emerge from the den. At four or five weeks of age they are weaned. The young are able to leave their dens for longish periods at eight to ten weeks of age and the dens are abandoned during August.
They are sexually mature during their first year of life (ca. 10 months old), but pregnancy rates are low until they are three years of age. After this age is reached more than 90% of females give birth annually.
The mortality rate of young in the denning period is low, ca. 20–25% from birth until they abandon the den. The mortality rate during the first winter is higher than 75%, but then decreases and remains low until an age of six years. Average longevity is about three to four years, but a 13 year old individual has been recorded from Svalbard.
Management status and monitoring
The Arctic fox population in Svalbard is stable and abundant. There are no population estimates available for the archipelago as a whole, but the density in one area, Adventdalen–Sassendalen (ca. 900km2), has been estimated to be 1–1.5 fox per 10km2.
The Arctic fox is known to be the major vector of the rabies virus in the Arctic. Rabies in Arctic foxes in Svalbard was registered for the first time in 1980, and most recently documented in 2011 (and prior to that, in 1999).
They are also the final host of the tape worm Echinococcus multilocularis, a parasite which can be fatal to humans. It has become established in the Grumant area in Isfjorden in association with a local population of sibling voles which is the intermediate host for this parasite. Transmission to humans is thought to occur via handling of fox faeces, so this activity should be conducted wearing gloves (if it takes place at all).
A valuable furbearer, the Arctic fox has been trapped for several hundred years in Svalbard. Trapping of foxes by Svalbard residents is permitted during a fixed winter hunting season.