fox hypothesis pounced on wrong conclusion

Erling Friis-Baastad The Canadian North has been undergoing a rapid warming trend since the early 1970s.

by Erling Friis-Baastad

The Canadian North has been undergoing a rapid warming trend since the early 1970s. This we know for certain but there’s a tendency to let that trend serve to explain many other changes, changes that are far too complex for a temperature rise alone to account for.

Consider fox demographics in the North. A widely accepted hypothesis held that a warming climate was sufficient to explain why populations of red foxes (Vulpes vulpes) appeared to expand across the Far North at the expense of the smaller Arctic foxes (Vulpes lagopus). More recent research has revealed just how limited and misguided that conclusion was.

“The red fox is sort of a poster child for climate change,” says Don Reid, a Yukon conservation zoologist with the Wildlife Conservation Society Canada. “But there’s archeological evidence, from Murielle Nagy’s work on a tributary of the Babbage River, that red fox were part of the system many hundreds of years ago.” Red fox bones turned up in Nagy’s historic Thule sites.

“Perhaps, more importantly, regarding red fox expansion across the Canadian Arctic, it was noted way back in the 1930s, and was very prominent in the 1960s,” says Reid. The significance of this is: the warming trend didn’t really get underway until the 1970s. “In fact,” he says, “from the 1940s through the 1960s was a period of cooling in many Arctic and boreal regions.”

Reid was the logistics person for a team of fox researchers who went into the North Slope as part of International Polar Year during the summers of 2008, 2009 and 2010. Herschel Island-based field researchers Daniel Gallant, a PhD student from Quebec, and Yukon biologist Brian Slough flew by helicopter over a large area from the Alaska border to the Babbage River in the east, and inland as far as 150 metres up the foothills on the North Slope. They surveyed more than 100 fox dens each year.

As well, the team was able to compare its 21st-century observations with data from previous initiatives, such as the North Slope Arctic Gas Project research of the early 1970s, and Yukon-government sponsored work in the region during the 1980s.

The data put paid to the hypothesis that global warming was allowing the red fox to take over from the Arctic fox. For the hypothesis to hold, the relative abundance of red foxes would have gone up over four decades and that of Arctic foxes would have gone down – across the region. “The red fox would have become the dominant animal, would have been taking over dens from Arctic foxes and been more common overall,” says Reid.

However, the scientists discovered that as far as fox species abundances went, there’d been very little change since the 1970s. The northern Yukon fox system is somewhat unique in the world, as it’s unusual to have both species living “cheek by jowl, without either taking the upper hand,” says Reid. The Arctic fox is actually still a bit more common in north Yukon and more natal dens tend to be held by Arctic foxes from year to year than by red foxes.

“If red fox were really in ascendency, you’d see a lot more of what had been Arctic fox natal dens being taken over by red fox,” adds Reid. There is a bit of back and forth, however, with some dens being used by Arctic fox one year, by red fox the next, and Arctic fox the next… Both species are present, but neither is taking over.

The hypothesis that climate change alone is sufficient to favour red fox expanding into, and taking over, Arctic fox habitat throughout the Far North depended upon one or two mechanisms. In one scenario, the warmer temperatures would have allowed red foxes to expend less energy staying warm. However, says Reid, the winter mean temperatures are still cold, in the minus 10s to minus 30s, “way below the lower critical temperature for resting metabolism of the red fox.” The red fox, having greater body mass than an Arctic fox, requires more energy just to keep warm.

Another mechanism by which warming was thought to benefit red foxes was that the greening of the tundra, following warming, favoured the rodents that foxes prey on. With rodents proliferating, the larger foxes should too, or so the thinking went. But Reid says that “a whole suite” of predators keeps rodent numbers so far down that this part of the hypothetical mechanism doesn’t hold.

So the time has come for a new hypothesis, one that looks beyond temperature to explain why red fox populations appear to have expanded in certain areas, but not uniformly across the North. Now, says Reid, the driver behind pockets of red fox proliferation appears to be “food supplementation by humans.”

Northern humans have increasingly congregated into larger communities since the 1960s. They brought carcasses off the land into community landfills and generated edible waste. Suddenly the big, hungry, opportunistic red fox found rich, localized nutrition sources in settlements like Baker Lake, Rankin Inlet and Repulse Bay, among others.

Where humans congregated, red foxes appeared to benefit and settle. Meanwhile, back on the North Slope, settlements shut down and subsistence hunting diminished since the 1980s. Dew Line stations are no longer manned by warm-hearted humans who give handouts to foxes. And, significantly, there are fewer people on the land to notice that neither fox species had gained the upper paw.

With that, the northern fox news ends, for now and with some cautions.

“When you see changes happening in this world of global change, one doesn’t immediately jump on the bandwagon that a correlation with a warming temperature means a causal relationship,” says Reid.

As well, climate changes are happening so quickly that it’s folly to count on any environmental hypothesis remaining “robust” very far into the future, he says. But it is a fairly safe bet that increased human activity across the North will have an ever-greater impact on species distribution and balance, and will increasingly challenge our ability to manage change.

This column is co-ordinated by the Yukon Research Centre with major financial support from Environment Yukon and Yukon College. The articles are archived at www.taiga.net/yourYukon