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Forget hibernating, migrating or holing up - Arctic foxes take winter on the chin
(New Scientist Via Acquire Media NewsEdge) Forget hibernating, migrating or holing up - Arctic foxes take winter on the chin The incredible arctic fox For centuries polar explorers have marvelled at finding arctic foxes in the most extreme places. Now, finally, scientists have managed to track their wanderings SPRING 2008, and life seemed normal for one female Arctic fox living on Bylot Island in the far north of Canada. She had found a suitable den, teamed up with a mate, and together the pair had successfully raised a litter of 11 pups. Then, sometime around midsummer, a switch in her brain seemed to flip. She abandoned her home and headed north, off the island and onto the polar ice cap.
For most of the following winter she wandered the sea ice, enduring 24-hour darkness and temperatures that regularly dipped below -40 °C. As spring approached, she started moving south-west towards Baffin Island and eventually into a sweeping loop that took her more than 1000 kilometres in three weeks. She wasn't finished. In mid-May the miniature canine turned westward and covered another 1200 kilometres before eventually spending the summer traversing Somerset Island - a 25,000-square-kilometre expanse of low-lying, barren rock. Within a year, her skinny legs had logged close to 5000 kilometres. Had she chosen to travel the same distance southwards, she could have been on a subtropical beach in southern Florida.
Polar explorers and scientist have long marvelled at the Arctic fox's formidable grit. These feisty little animals spurn the strategies to deal with winter used by other occupants of the far north. They don't hibernate. They don't migrate to more hospitable climes. They don't seek solace inside a den or under the snow. Instead they take the brutality of their frozen environment on the chin as they roam over a landscape with no permanent landmarks and often devoid of any signs of life. In this harsh environment, keeping track of the Arctic fox's wanderings is challenging, to say the least. Only now, with the latest advances in wildlife tracking technology, are we finally getting an insight into these improbable journeys.
Seventeenth-century European seafarers searching for the North-West Passage through the Canadian Arctic were among the first to be struck by this astonishing lifestyle. These explorers frequently spent the winter aboard their vessels, locked in the sea ice, but no matter how far from land they were, they would find the fluffy white scavengers emerging from the ice fog like ghosts. The ability of these animals to navigate their way around a sheet of ice the size of Europe was well known even back then. More than once, rescue teams looking for lost explorers from previous expeditions fitted Arctic foxes with collars engraved with coordinates of supply dumps, reasoning that if the survivors were out there, the foxes would come across them.
As adventurers pushed into ever more remote corners of the Arctic, the mystique surrounding the species continued to grow. During his failed attempt to reach the North Pole on foot in the spring of 1895, Norwegian explorer Fridtjof Nansen encountered several sets of fox footprints on the ice north of the 85th parallel, several hundred kilometres from the nearest dry land, the remote Russian archipelago known today as Franz Joseph Land. Baffled by the sightings, he concluded he must have been much closer to land than he had thought. But it took Nansen another three-and-a-half months of exhausting slog to reach solid ground.
Truly foxed "What in the world was that fox doing up here?" he wrote in his journal the morning after seeing the first set of tracks. "It is incomprehensible what these animals live on up here, but presumably they are able to snap up some crustacean in the open waterways. But why do they leave the coasts? That is what puzzles me most. Can they have gone astray? There seems little probability of that." Since Nansen's day, polar explorers have recorded similar experiences, including one sighting less than 60 kilometres from the pole.
Early attempts to solve some of these riddles only added to the mystery. Robert Garrott, now at Montana State University in Bozeman, was part of a team that spent several years during the 1970s trying to track the winter movements of Arctic foxes near Prudhoe bay in northern Alaska. They fitted the animals with numbered ear tags, released them, and then waited to see where they turned up. Some were recovered more than 2000 kilometres away, deep into the high Arctic, but this technique could only record the animals' destination, and revealed nothing about how they got there.
In a valiant effort to learn more, Garrott and his colleagues decided to try out radio telemetry, the technology that had revolutionised wildlife tracking in the early 1960s. A radio collar fitted to the animal being studied transmits a signal that can be picked up by researchers on foot or in a plane, allowing them to follow their target wherever it goes. Early in the spring of 1979, the researchers ventured 32 kilometres onto the ice off the north shore of Alaska, pitching tents near where the current had swept floes free from the shore-anchored ice. After fitting a fox with a radio collar, they set out to follow it using two planes?- one to track the fox and the second as a back-up in case the first was forced down on the drifting pack ice.
"It was a great adventure," says Garrott. "But we learned absolutely nothing. The place is simply too big and the foxes are too mobile. We would catch one and put a collar on it and then we would never hear the signal again. They just disappeared?- gone outside the ability of the plane to keep track of them." If Arctic foxes were proving elusive in the wild, at least some of their secrets were surrendering to lab-based studies. As far back as the late 1940s, Laurence Irving and Per Scholander, two pioneers in comparative physiology working at the US navy's Arctic Research Laboratory in Barrow, Alaska, attempted to measure the cold tolerance of different species, using the point at which shivering begins to indicate environmental stress. Arctic ground squirrels succumbed at 8 °C and polar bear cubs at 0 °C, but when the scientists came to test Arctic foxes, their equipment could not generate temperatures cold enough to register a result. They eventually had two of the hardy animals flown to a more sophisticated facility in Washington DC, where shivering was finally observed after they had been exposed to -70 °C for an hour (The Biological Bulletin, vol 99, p 237).
There is no question that these creatures are built for life in the cold. Another early study revealed that their furry pelt has unrivalled insulation capabilities. And their physiology is tuned to the task of balancing energy loss and intake?- a must for any warm-blooded animal trying to survive in a world where food to fuel the inner furnace is both essential all year round and in short supply. For example, the Arctic fox's veins and arteries run closer to each other than in most other animals of similar size, forming a heat exchanger that uses heat from arterial blood to warm the blood flowing back through the veins. This saves energy by maintaining the outer extremities at a lower temperature than the body's core (Science, vol 175, p 988).
Why don't foxes' feet freeze? Despite these specialist adaptations, the thought of an Arctic fox wandering around for months on end, under such harsh conditions, continues to raise many questions. What do they eat while they are out on the ice floes? Do they all undertake long-distance journeys? Are the journeys random, or do they follow some preordained pattern?- an Arctic version of the annual trek recorded in March of the Penguins? If the latter, how do they find their way around an icescape that has no permanent landmarks, that drifts and spins at the mercy of the currents, melts and freezes according to the weather, and seemingly has little to offer in the way of a scent trail to follow for food? Even the advent of satellite-based tracking in the early 1990s did not provide an immediate answer. The first collars, which required large batteries to keep them working for a year or more, were far too heavy for Arctic foxes. Lighter systems developed for birds draw power from a tiny solar cell - clearly not a solution in the round-the-clock darkness of an Arctic winter. But now, at last, the technology has caught up, in the form of light, battery-powered collars tailored for the Arctic fox, including one equipped with an antenna laced with red pepper to discourage animals from gnawing it off. Last year, a team from the University of Quebec at Rimouski published results of a satellite-tracking study of the Bylot Island foxes (Polar Biology, vol 33, p 1021, and lower part of diagram). This came hard on the heels of publication of a similar study by a team from the University of Alaska at Fairbanks, who followed foxes collared at two locations on the north shore of Alaska (Polar Biology, vol 31, p 1421, and upper part of diagram).
The findings provide more evidence that Arctic foxes regularly travel enormous distances. A juvenile female in Alaska covered more than 2750 kilometres and a male from Bylot Island logged almost 2200 kilometres. The undisputed record holder, however, is our Bylot female, with her epic 5000-kilometre journey. Even that distance is almost certainly an underestimate of how far the animal actually travelled, says Nate Pamperin, who conducted the Alaskan study. He points out that the collars only transmit once every four days, and the distance calculations assume that the animals travel in a straight line between measurements. "On land, foxes move back and forth investigating every little feature," Pamperin says. "I'm sure it's the same on the ice where you have pressure ridges and such." Marathon journeys are not the only aspect of Arctic foxes' lifestyle that satellite tracking is revealing. One long-standing mystery was whether animals found wandering on the ice were on brief forays from land, or extended trips. The new studies suggest the latter - that ice can indeed be a second home. One fox from Pamperin's study appears to have lived on the ice for more than five months in one stint.
Both studies also found that the animals moved erratically, sometimes criss-crossing a large area, sometimes determinedly striking out in one direction for days on end. During her westward march, for example, the Bylot Island female travelled between 80 and 90 kilometres a day. The Canadian study also showed that while some foxes travel to land far from their original homes, this is not always the case. After covering nearly 2200 kilometres, the long-distance Bylot Island male was back close to the den he had left three months earlier. "It's not luck," says Dominique Berteaux, head of the Bylot team. "They know where they are. They have a very good sense of orientation, I'm sure." One unexpected finding was that these extended treks are far from universal. In the Alaskan study, only three of the 17 collared foxes from an undeveloped location made long-distance ice journeys. The Canadians reported similar findings, with just two of 12 collared foxes venturing out for long distances. "What we've found is that it is not typical," says Berteaux. Why some foxes choose such a dramatically different lifestyle remains a mystery, but what is clear it that around human habitation the lure of garbage dumps and other tasty food sources keeps them as homebodies. Among the 20 foxes collared near the Prudhoe bay oilfields in 2005, none turned out to be ice travellers.
Another unanswered question is what the foxes do with their time out on the ice, and in particular how they feed themselves. There is good anecdotal evidence that they spend at least some time scavenging the remnants of seal carcasses left on the ice by polar bears. There is also evidence that Arctic foxes feed on invertebrates, mainly tiny crustaceans known as amphipods, which can be found clinging to the undersurface of the ice. And for a brief period in the spring they prey on ringed seal pups, winkling them out from their lairs in the thick layer of snow sitting on the ice.
Such bounties are rare and widely scattered, though, and hints are emerging that taking to the ice might have less to do with what can be gained there and more to do with having nothing to lose. In the first two years of tracking, the researchers on Bylot Island detected a link between the number of foxes on the ice and a shortage of lemmings, their favourite land-based prey, whose population undergoes dramatic swings from year to year. Although it is too early to say for sure, it is possible that foxes decide to go onto the ice based partly on how much food is available on land in the autumn.
Living the life of an ice nomad may well be a wise gamble. In Alaska, the three ice travellers all lived longer than the 14 collared foxes that stayed on land. In the Canadian Arctic, most young foxes that remained on Bylot Island perished before the end of their first summer, probably as a result of starvation. By comparison, our intrepid female was still going strong when the battery on her collar gave out after a year. Who knows: she may still be on the move. n Garry Hamilton is a freelance writer based in Seattle and author of Arctic Fox: Life at the top of the world (Firefly Books, 2008) Ghosts of the Arctic "They roam across a landscape with no permanent landmarks and devoid of any signs of life" "Shivering was finally observed after the foxes had been exposed to -70 °C for an hour" Ready or not, Arctic morsel, here I come "One unexpectedfinding was that these extended treks are far from universal" (c) 2011 Reed Business Information - UK. All Rights Reserved.
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