Wolverines Face Recovery Roadblocks
Rebounding populations in Pacific Northwest contend with reduced habitat connectivity, climate change
Aja Woodrow plods alongside the road toward a road-killed deer near the town of Cle Elum in central Washington. He’s carrying a Pulaski — a combination axe/grub hoe commonly used for wildland firefighting. Today, however, Woodrow intends to put it to a more macabre use: severing the deer’s head.
This may sound like a scene from horror movie, but Woodrow has wildlife conservation on his mind. He’s a US Forest Service biologist working in partnership with the Washington Department of Transportation on a study of wolverine movement in the North Cascades. Road-killed deer and elk just happen to be effective, cheap, and plentiful wolverine bait.
photo by Jarkko Järvinen
Long absent from Washington’s Cascade mountain range, wolverines are staging a comeback. Biologists began documenting wolverines in more remote parts of the Cascades in the 1990s, and in 2006, the Forest Service began tracking wolverines to monitor the depth of the recovery. A decade later, wolverines are flourishing in the area. They’re nearly everywhere we would expect to see them in the North Cascades, and biologists discover new individuals each year. However, a huge barrier lies in the way of the wolverine’s continued recovery and expansion into the rest of the Cascades: Interstate 90, which bisects the mountain range.
Reduced habitat connectivity brought about by infrastructure projects is a growing problem around the world. As humans continue to build infrastructure to make our lives easier, that infrastructure becomes a barrier to movement of wildlife between patches of suitable habitat. This can be particularly problematic for small critters with low mobility like turtles, lizards, and salamanders, but it’s a problem for larger, more mobile animals like deer, wolves, and wolverines as well.
Adam Ford, an assistant professor of biology at the University of British Columbia-Okanogan, has studied the impact of roads on everything from leopard frogs to mountain lions. With some notable exceptions (e.g. the proverbial deer in the headlights), animals tend to shy away from roads, he says.
“Animals can hear cars, they can smell the effluents from cars, and of course they see them moving,” Ford says, all of which can cause animals to be averse to crossing roads. “Generally speaking, the wider the road, the more traffic on it and the larger the zone of influence the road has on the surrounding environment.”
Overpasses and underpasses intended to facilitate wildlife crossings have become increasingly common components of highway construction and maintenance plans. According to Ford, that’s for good reason.
“There are a lot of things that people have tried, and they vary in their efficacy, but the gold standard in mitigation is fencing and crossing structures, because then we get animals across the road safely for them and drivers, we resolve that connectivity issue, and we also resolve the mortality issue at the same time.”
Still, there are gaps in our knowledge of how animals interact with roads. Wolverines pose a particular problem for scientists seeking to study how wildlife respond to roadways because they’re uncommon and typically live in high elevation wilderness without many roads.
“In our Banff research, we’ve identified a group of species that we call HELS, or high-elevation localized species. Basically, goats, pikas, marmots, and wolverines, which typically don’t encounter roads as part of their home range,” says Ford. “We don’t know much about their interaction with roads because it just doesn’t happen that often.”
Dispersal is already a difficult challenge for species like wolverines that live on mountain peaks because of the rough terrain and tremendous distances that often separate populations and even individuals. Roads might make dispersal nigh on impossible. Knowing how roads impact these species and how we can mitigate that impact might be the difference between healthy populations and local extinction. In the case of Washington’s wolverines, it might determine whether they ever make it to the vast expanse of prime habitat waiting just south of I-90.
Woodrow, the Pulaski-wielding biologist, is doing his best to fill that knowledge gap. He’s using a network of fifteen remote cameras covering an area of hundreds of square miles to find out how significant a barrier I-90 actually is to wolverines in Washington.
Woodrow’s camera set-up is specially designed to capture pictures of wolverines. Each camera faces a “run-pole,” a homemade wooden device mounted to a tree seven to eight feet above the ground, with a deer head or limb dangling barely out of reach at the end. This run-pole forces the wolverine to move through a gauntlet of alligator clips that capture hair used for DNA analysis, then bare its chest to the camera. Wolverines sport unique blazes on their chests, equivalent to furry fingerprints, which allow researchers to identify individuals even if the DNA analysis fails.
Thus far, Woodrow has found Interstate 90 to be a formidable barrier to wolverines. “I ran cameras last winter and the winter before, and I had wolverines on the north side of the interstate, but not the south side,” he says. “We’ve got traffic volumes of one car per second, and the forecasts are for increasing flow… The [Department of Transportation] is in the process of widening [I-90] from two lanes each way to three lanes each way, which is going to further cause isolation between north and south.”
Despite the growing barrier, there is reason for hope. Plans are in the works for a series of wildlife crossing structures in the area. All told, 27 crossing structures are set to be installed in a fifteen-mile stretch near Snoqualmie Pass that connects the vast wilderness areas of the North Cascades to large chunks of undeveloped public land to the south. Construction on the first overpass began in September.
In addition, biologists affiliated with the US Forest Service and the University of California-Davis captured pictures of a wolverine three times on remote cameras southwest of Naches, Washington earlier this year. It’s only the second time in recent decades that a wolverine has been confirmed in Washington south of I-90. It’s too early to tell if that wolverine has stayed in the area, but it’s still an exciting development.
“The south Cascades — that’s habitat that’s just waiting [for wolverines],” says Woodrow. “It’ll be really interesting to see how related that wolverine is to the wolverines that I have north of I-90.”
Despite its proximity to Woodrow’s study area, there’s no guarantee it descended from North Cascades stock. Several wolverine sightings south of his project area have made news in recent years, but none appear to have dispersed from the North Cascades population. Three wolverines were sighted in northeastern Oregon in 2011, but only one was found the next winter. Tracks were found in 2013, but no sightings have been reported since. DNA tests of hair from the 2012 wolverine revealed that it descended from Idaho’s population rather than Washington’s. A lone wolverine also inhabits Tahoe National Forest in California. First sighted in 2008, it was most recently photographed earlier this year.
Despite their sustained range expansion and efforts to connect new habitat to their current range, wolverines aren’t out of danger yet. Population numbers are still low: Biologists estimate that there are only 300 wolverines in the contiguous United States. Wolverines are also expected to be among the species hardest hit by climate change in the coming years. As our climate warms, suitable patches of wolverine habitat are likely to shrink and distances between these patches will grow. Wolverines seem to rely heavily on deep snowpack that persists into late spring for reproduction. Thermal protection afforded by snowpack and the ability to cache food in snow are suspected as possible reasons for this relationship, though neither has been definitively demonstrated.
In 2013, the threat posed by climate change led the US Fish and Wildlife Service to consider listing wolverines in the Lower 48 as threatened under the Endangered Species Act. The agency ultimately decided against it, but a federal judge demanded in April that the USFWS reconsider its decision, again citing climate change as a dire threat to the species’ long-term persistence. That reassessment is still in the works.
Taken together, these factors render wolverine conservation a complex story, one of promising range expansion paired with new, uncertain threats. It’s a vexing problem for biologists like Woodrow.
“In fifty years, that’s a big question,” he says. “What’s wolverine habitat going to look like in fifty years?”
Regardless of what it looks like, habitat connectivity projects like the one in Washington are key to helping wolverines and other wildlife adjust to our uncertain climatic future. And thanks to the efforts of hard-working biologists like Woodrow and Ford, wolverines are much more certain to have a continued place in the Cascades ecosystem.