Download Fox Hypothesis Pounced on a Wrong Conclusion

YOUR YUKON
Erling Friis-Baastad
May 18, 2012
FOX HYPOTHESIS POUNCED ON A WRONG CONCLUSION
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 Islandbased 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.