BY JESSE ALSTON – NOVEMBER 21, 2016
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.
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