There's a legend about the Arctic fox in Finland: every night the furry white animal runs along the northern mountains, setting off sparks whenever its big, bushy tail brushes against the rocks. In Finnish, those sparks are known as revontulet, or foxfire. We know the glowing "sparks" under another name: northern lights or aurora borealis.


Today, Finland is one of the few countries where the Arctic fox is endangered. Overhunting for the animals' warm fur in the Fennoscandia region (which also includes Sweden and Norway) devastated fox populations there in the early 20th century. The species has failed to recover in that region and remains protected in each country. Only a few dozen of the animals remain in the region.


Luckily, Fennoscandia is an isolated case. Arctic foxes can be found in abundant levels throughout the Arctic, including North America, Europe and Asia. Scientists estimate that hundreds of thousands of Arctic foxes roam the frigid tundra, an area too cold for trees to grow but where the animals are perfectly adapted to survive.


The foxes' white fur — which spurred the population spiral in Finland — also is a huge factor in the species' abundance. The thick coat, which is warmer than just about any other fur, protects the animals in temperatures as low as minus 58 degrees. In addition to the thick pelt on the body and tail, the fur also covers the animal's ears and the soles of its feet, allowing it to walk and tunnel through the coldest snow and ice. And in the winter months, the white fur also provides camouflage, allowing the species to hunt whatever prey they can find when temperatures are at their lowest.


The fox's fur isn't always white. As winter ends the fox sheds its white coat, switching to a coat of either brown or gray — once again, a perfect camouflage for when the ground is covered in plants and prey such as lemmings and birds are plentiful.


Another adaptation that has served the fox well is its keen sense of hearing. Those fur-covered ears can sense any prey moving around underneath even the densest of snow. When the fox hears an animal moving, it pounces — and those fur-covered feet allow it to dig and, eventually, dine.


Arctic foxes vs. climate change

It remains to be seen how well the Arctic fox's adaptations will serve the species as northern environments warm because of climate change. Research published earlier this year in Proceedings of the Royal Society B warns that lemmings — the favorite prey for the fox — are "highly sensitive to climate change." The study found that snowy owl populations in Greenland declined 98 percent after the area's lemming population collapsed. Although Arctic foxes are generalist eaters and will consume whatever they can find, they lack of lemmings had "noticeable effects on their reproductive performance" in the area. Previous research has shown that lemming populations tend to crash every three to five years, followed by a crash in Arctic fox populations. Both species usually recover under normal environmental conditions.


Climate change could also bring increased competition into the Arctic fox's habitat. Red foxes are increasingly moving north into areas where they did not live before, including Finland, Russia and other regions. Not only do red foxes eat the same prey, they are both bigger and more aggressive than Arctic foxes and have been known to attack their white cousins. It doesn't appear that red foxes kill the Arctic foxes, but Arctic fox mothers have been observed abandoning their young after a red fox attack.


Other changes could affect the Arctic fox. According to a report (pdf) from the IUCN's Species Survival Commission, warming temperatures could slowly turn tundra habitat into boreal forests — habitat that is news to the Arctic fox. Trees provide new places for prey to live and hide, and it is not yet known if foxes could adapt to that change.


And then there's the polar bear, to which the Arctic fox is tightly linked. Foxes have a habit of scavenging on the remains of kills left behind by polar bears. If polar bear populations decline as expected due to climate change, the foxes could lose a main source of their food.


Luckily, Arctic foxes are prodigious breeders, usually producing between five to eight cubs but sometimes producing as many as 25 cubs per litter. They mature quickly, reaching breeding age in less than a year, letting the whole cycle start all over again. If the species has enough prey to eat, then the Arctic fox won't be going anywhere any time soon.


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