Washington’s wolverines stage tenuous comeback

The carnivores are recolonizing the northern Cascades, but they face an uncertain climate future.

 

On February 1, in the snow-cloaked reaches of the northern Cascade Range in Washington, John Rohrer and Scott Fitkin cracked open the lid of a log cabin-shaped trap and, with a jabstick, anaesthetized the snarling wolverine within.

Once the animal had fallen unconscious, Rohrer, a wildlife biologist with the U.S. Forest Service, and Fitkin, a district biologist with the Washington Department of Fish and Wildlife, worked quickly. The two scientists and their crew measured and weighed the wolverine, photographed its teeth and chest markings, and gave it a shot of penicillin to fight infections. They monitored its vitals; if its body grew too hot, they were ready to tuck snow into its armpits. Most importantly, they fitted its neck with a radio-collar containing a satellite transmitter, whose readings would provide crucial information about the animal’s movements.

Forty-five minutes later, the wolverine sprang from the trap with a throaty growl. Fitkin, watching the 30-pound mustelid bound into the wilderness, wondered if there was perhaps a new sheriff in town. “It was clear he’d been around for a while, and he had a pretty big frame on him,” Fitkin recalls. “We thought, okay, this might be the region’s new dominant male.”

Even 20 years ago, a flourishing wolverine population would have seemed unlikely in the North Cascades. The creatures were eradicated from Washington by the early 1900s, the victims of trapping and poisoning. In the 1990s, however, tracks and camera traps began testifying to their renewed presence. Keith Aubry, a scientist with the U.S. Forest Service’s Pacific Northwest Research Station, became convinced that the recolonization was worth studying. In 2006, Aubry and his team collared a female named Melanie and a male named Rocky — the first two wolverines ever monitored in the Pacific states, and the initial study subjects in what was to become a decade-long, 15-wolverine tracking program.

Aubry’s first task was to figure out where the immigrants were coming from. He initially assumed they’d wandered west from the northern Rockies, where a few hundred wolverines roam Montana, Idaho and Wyoming. But DNA testing suggested that the northern Cascade colonists may have had a very different place of origin: the rugged coastal mountains of British Columbia. Washington’s wolverines, it appeared, represented the southern vanguard of a Canadian population, which was now recolonizing the species' historic Pacific Northwest range.   

Wolverines have slowly begun to recolonize the northern Cascades. Camera trap photo courtesy of the Washington Department of Fish and Wildlife.

In fact, all the western United States' wolverines may come from Canadian stock. Last year, Aubry and colleagues published a continent-wide analysis of wolverine genetics, which suggested that Gulo gulo had been completely wiped out from the contiguous United States by the early 20th century. America’s wolverines, then, likely descend from British Columbia and Alberta migrants, which began trickling down into the Lower 48 once the persecution ended.

America’s wolverines are, therefore, a remarkable wildlife success story, and their dispersal abilities an illustration of why habitat connectivity matters. In 2008, an Idaho native dubbed Buddy rambled 500 miles into California’s Sierra Nevada, where the creatures once flourished; the next year, a wolverine trekked from Grand Teton to Colorado. Wolverines hadn’t been spotted in either place since before the Great Depression.

Though the northern Cascades’ twenty-odd wolverines haven’t meandered quite that far, at least five different animals have wandered south of State Highway 2. Only one wolverine has been detected beyond I-90, but biologists hope that a series of wildlife underpasses and bridges — some completed, others planned — will allow the carnivores to someday make the trip. “How this is going to play out, where it’s going to end, is still an unknown,” says Aubry, whose tracking project is finally concluding this year. “This is essentially a giant regional experiment.”

No wildlife management story would be complete, however, without an ironic twist. Even as wolverines’ immediate prospects look bright, their long-term prognosis remains worrisome. The mustelids famously raise their kits in snow dens, selecting sites where snowpack lingers well into spring; such sites will almost certainly become more scarce as the climate warms. One 2011 study, also co-authored by Aubry, suggested that suitable wolverine habitat “will likely be greatly reduced and isolated” by the end of the century.

Despite the alarming forecast, the U.S. Fish and Wildlife Service recently declined to list the species as threatened, citing scientific uncertainty about whether the disappearance of snowpack will truly limit the animals’ population. A consortium of environmental groups filed a lawsuit challenging the decision in November 2014. 

Ultimately, the wolverine’s greatest foe may be our cognitive dissonance around global warming. “A lot of people say that it doesn’t make sense: ‘You’re saying climate change is a big threat, yet they’re currently expanding their range?’” Aubry says. “But these processes are happening on completely different temporal scales.” For all his success, the North Cascades’ new dominant male — and the rest of the country’s wolverines — may still be waiting for the other climatic shoe to drop.

Ben Goldfarb is a Seattle-based correspondent for High Country News.