Listing the wolverine

On a sunny day in late March 2010, a young wolverine known as F3 poked her head out of the mouth of a log-box research trap in Montana’s Absaroka Range, looked around, and then, in a blur of snow, surged off into the wilderness. Around her neck was a new GPS collar that we’d fastened in place two hours earlier, after determining - to our disappointment - that she hadn’t given birth this year. This device will download locations via satellite at two hour intervals until October 2010, when the collar will fall off and the information that it contains will become part of the sparse but growing collection of data on wolverines in the Lower 48.
 
The meaning of existing data on the wolverine is in question yet again as the US Fish and Wildlife Service announced on April 15th that it is undertaking a fourth review of the species’ status. A paucity of information has twice stymied attempts to list the wolverine under the Endangered Species Act, in 1994 and 2001. A third petition was turned down in 2008, despite the publication of a wolverine-focused edition of the Journal of Wildlife Management  that essentially doubled the number of existing peer-reviewed articles on wolverines in the contiguous US. These papers hinted at genetic fragmentation, loss of habitat, and threats due to mortality, but the USFWS concluded that wolverines were not warranted for protection because the US population was not distinct from the Canadian population. The current review is in response to environmental advocacy groups’ lawsuit following the 2008 decision, which they allege was based on politics rather than science. Much of the information under review will be the same that was considered in 2008, but two substantial research articles have been added to the literature in the past six months.

Last month, shortly before we collared F3 and watched her disappear into the snow-draped forest, scientists linked wolverine distribution to persistent spring snow in a paper published in the Canadian Journal of Zoology. Female wolverines den in snow, and rely on snow caves to protect and insulate their kits until the babies are ready to emerge in late April or early May. The paper’s authors found that all of the world’s known den sites occur in areas with persistent spring snow, and that 95% of telemetry locations during the summer also occur within this range. Researchers writing in Ecology in November of 2009 take this connection one step further by modeling Rocky Mountain wolverines’ dispersal routes among their high altitude habitat islands and showing that the most efficient paths follow landscape features that also have persistent spring snow. These models conform to data on genetic distance among populations. Put simply, wolverines need snow not only to den, but to reach each other to breed in the first place.
If all of this seems to be overstating the obvious, it’s nevertheless the first time that anyone has drawn statistically sound connections among wolverines and today’s major conservation challenges - connectivity and climate change. With an estimated effective population size of 28-52 individuals for the entire Rocky Mountain West, maintaining genetic and demographic connectivity would be an issue for wolverines even without the effects of global warming. Throw decreasing snowpack into the mix, and the potential synergy could be enough to knock wolverines off the landscape.
 
The publication of this new research doesn’t mean that the USFWS will reach a different conclusion about wolverines this time around, and even if they do, it doesn’t mean that the ESA has the teeth to cope with large-scale ecosystemic threats. But 16 years after the first petition for listing, we at least have enough information to begin to elucidate those threats. Given the challenges of studying the animal, this is an impressive accomplishment. Whether the wolverine is listed or not, though, we still have a lot to learn before we know how to protect wolverines over the long term. A pressing question for the research organization I work for: what role might Wyoming’s virtually unstudied wolverine population play in recolonizing the southern Rockies? After a collared juvenile male wolverine traveled from the southern edge of Yellowstone to Colorado last year, the repopulation of the Colorado Rockies no longer seems so far-fetched. Another question: why didn’t F3 reproduce this year, despite the fact that she’s the right age and has been hanging out with a male wolverine since last summer? Her kits could be the next to make the journey south, and contribute to the long-term persistence of the species in the US - but only if we can figure out what those future generations will need to survive, and only if the social will to study and protect them exists.

Photo: F3, carrying a new GPS collar, heads into the Absarokas in March 2010. Photo by Rebecca Watters.