Why One Arctic Fox Took the Longest Migration in the Species’ History

The effects of climate change can be tracked in a single animal’s record-breaking journey

Credit: Education Images/Getty Images

TTwenty-seven hundred miles — 2,743, to be exact — is how far one arctic fox traveled over sea ice and glaciers last year during a 76-day polar marathon. The fox’s journey began on the island of Spitsbergen, off the coast of Norway in the Svalbard archipelago, and ended on Ellesmere Island in Canada’s remote Nunavut Territory, a full continent away.

The migration was among the longest ever recorded for an arctic fox. The farthest northern point reached by the juvenile female was on the sea ice off Greenland at more than 87 degrees north, not far from the North Pole.

Researchers from the Norwegian Polar Institute and the Norwegian Institute for Nature Research studied the fox’s movements via satellite tracking; they captured her in Spitsbergen and placed a small transmitter on the fox which then transmitted daily location every three hours. The young fox, who lived on the coast and weighed a little over 4 pounds when weighed by researchers, started the trip in her blue fur pelage on March 26, 2018, and averaged about 28.5 miles a day. While on Greenland’s ice sheet, she more than tripled her time, averaging about 96 miles a day, the fastest movement rate ever recorded for the species.

Arctic foxes are an impressive species. In the barren tundra, they’re known as secret gardeners because during long winters they spend so much time in their dens — where they bring back kills that decompose, creating what’s essentially fertilizer, turning their mound-like homes into splashes of color in an otherwise drab landscape. Their long-distance roaming has been known since the days of early polar explorers like Fridtjof Nansen, who observed fresh fox tracks far offshore on the sea ice during his 1885 North Pole expedition aboard the Fram. “Why do they leave the coasts?” Nansen wrote in his journals, as confused by the animal’s behavior as modern biologists. And why do they travel so far from land on the ice, he wondered. “That is what puzzles me most. Can they have gone astray?”

“It’s exciting because it opens our eyes to how connected these different populations are. It’s amazing.”

Modern biologists say no. “This was not just a fox that sat on a piece of ice and floated over to Canada,” says Helle V. Goldman, chief editor of Polar Research, the journal that published the research June 25.

“It’s exciting because it opens our eyes to how connected these different populations are,” says Goldman. “It’s amazing.”

Eva Fuglei and Arnaud Tarroux, the study’s co-authors, suggest this animal’s travel is food-driven, with the sea ice serving as a platform linking distant populations. Being a very versatile predator — foxes are able to make a living off a wide variety of prey — means options. But even the most open-minded foodie is a prisoner of the menu, and when nothing’s on it, they hit the road.

Foxes aren’t good swimmers. Their puffy coats offer insulation, but only if they’re dry. So when they sojourn onto the sea ice, which they often do, they’re usually following polar bears on their seal hunts. Since bears prefer the fatty blubber of seals, they often leave the rest of the protein-rich flesh, which makes for a hearty meal for a hungry fox. Some stops on this fox’s itinerary, such as extended stays on the ice, suggest that seals may very well have been on the menu, which means ice bears would have been the chefs de cuisine.

The new findings, which support previous research that shows the species’ very wide-ranging travel, also suggest that there’s likely a healthy amount of gene flow among foxes throughout their circumpolar distribution. But since long-distance migration and gene flow between regions of the Arctic depend on the swiftly dwindling sea ice, some fox populations will become geographically and genetically isolated.

While this won’t necessarily mean the end of the species, as there are other island-bound populations of foxes which seem to be doing well, the long-term consequences of isolation in places like Svalbard, where this fox originated, remain unknown. Climate change isn’t a one-direction narrative. A major glacier in Greenland was recently found to be growing, not shrinking — and some mammals, like baleen whales in the Bering Sea, are doing well since the melt unlocks food formerly locked in the ice.

James Roth, an associate professor in the biology science department at the University of Manitoba, thinks this movement is both climate-related — and not. “This is where sea ice and climate plays a role,” he says. “If as predicted, and winter sea ice disappears in the fairly near future, then some of the fox populations are going to be cut off from one another and we may not see these types of migrations again because it’s not possible to walk that far.”

In 2010, an arctic fox was found to travel a similar distance, but not nearly as quickly. It took that fox over five and a half months to make the trip, while this fox did it in four months, making the newbie a record holder in terms of movement rate and speed. These new findings are also the first time an arctic fox has been documented on a cross-continental migration.

Roth, who has been studying arctic foxes in and around Hudson Bay since 1994, agrees with the co-authors that this behavior has as much to do with food availability as anything else. But the climate question and its implications are where things really get interesting. It’s not that a warming climate exactly made the fox leave home, but a warming climate does impact how other species reproduce, and even whether foxes remain monogamous.

Without a steady prey supply, foxes do not pair for life because they can’t rely on food sources, an interaction which sends them on their way — another complicated consequence of climate change. But the biggest effect, Roth suggests, is what happens down the line, since the biggest consequence of a changing climate for arctic foxes may come from other foxes.

As the tundra changes and the tree line moves farther north with a warming climate, so do red foxes, which are bigger and more aggressive than their northern cousins. There are no red foxes on Svalbard, but across the rest of their range—from Northern Canada to Russia—they often displace native arctic foxes, taking their dens and killing them in a bid for territory and prey.

“How are arctic foxes going to do in the long run in relation to climate change if they have to compete with a similar species that has a similar size?” says Roth. “That’s one of so many questions related to climate that we just don’t know. But we will soon, and research like this, and tagging more foxes, will help give us answers.”

Debut novel, NIMA, which takes on Mt. Everest, is now available: https://www.amazon.com/Nima-Adam-Popescu/dp/1944700854

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