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Trans-Canada Highway a barrier to female wolverines

“Our main finding is that male wolverines were not affected by the highway, whereas female dispersal and gene flow were highly restricted by the transportation corridor."
wolverine stock photo
The Trans-Canada Highway is proving to be a barrier for female wolverines.

BANFF – Few female wolverines are crossing the Trans-Canada Highway in Banff and Yoho national parks, raising red flags about connectivity and population health for the notoriously sensitive species.

A study by Mike Sawaya, Tony Clevenger and Michael Schwartz, which was recently published in the international journal Biological Conservation, looked at how the busy Trans-Canada Highway affects wolverine gene flow in the Canadian Rockies.

Roads break up ecosystems around the world and the effects of this fragmentation on biodiversity are still poorly understood, but Sawaya said these results show the highway is a barrier to females, which is concerning.

Sawaya, a carnivore research scientist, said that could affect wolverine reproduction, migration and recolonization, and decrease population viability.

“Our main finding is that male wolverines were not affected by the highway, whereas female dispersal and gene flow were highly restricted by the transportation corridor,” he said.

“Our results show that national parks are not protected from the effects of fragmentation on wildlife populations.”

The scientists used a non-invasive technique to collect wolverine hair for DNA analysis. On both north and south sides of the highway, beaver carcasses were tacked to trees at several locations. When wolverines climbed the tree, they snagged their hair on the attached barbed wire.

It was part of a much larger study in Banff, Yoho and Kootenay national parks, and neighbouring provincial lands, in which 2,586 DNA samples were collected between 2010-13. There were 49 individuals identified – 29 males and 20 females.

Sawaya said it’s important to note more crossing structures have been built at higher elevations near the Continental Divide, considered the heart of wolverine range, since the work was done.

He said the study concluded that while there’s ample male movement to ensure that genes are flowing around to different populations, the lack of female movement has implications for the overall population viability of wolverines.

“Wolverines tend to occur, especially at the southern end of their range, in habitat patches and those patches aren’t always connected and so if females are not moving around from those different patches, then that can certainly affect the reproductive output of the whole population, and let’s say if one patch were to go extinct for some reasons, it certainly affects the ability of that patch to be recolonized,” Sawaya said.

“That’s certainly the big implication of this, that female movement is required for healthy wolverine populations and so without it, it certainly limits their ability to recolonize, or expand the population into areas that it’s been extirpated.”

Research shows wolverines, especially females, are naturally philopatric, meaning they have a tendency to stay in, or habitually return to a particular area. A daughter is very likely to set up a home range adjacent to, or within the home range of her mother.

“Certainly we see that in grizzlies and mountain lions, but natural philopatric tendency is very strong in wolverines compared to other carnivore species and that strong philopatric tendency seems to be exacerbated by the highway,” he said.

“I think what’s going on is the highway is sort of reinforcing those home range boundaries and over time, that basically builds up in terms of genetic isolation because you don’t have that exchange going across that particular barrier.”

Males, on the other hand, disperse further distances in search of territory, food and mates.

“They’re going to disperse further distances, that’s just how their biology works to ensure that genes are getting mixed around on the landscape and that’s how a lot of carnivores species have evolved, is to disperse further,” he said.

“I think, in particular, the reason why the highway may affect females more than males is because they’ve got young to look after and I think they aren’t as likely to move across those boundaries in search of food … I think they’re more risk averse.”

Some species may take years to learn to use crossing structures to get across the highway, although one female was detected crossing the highway.

It’s believed a female wolverine, known as F15, may have been the wolverine caught on a wildlife camera traveling northward at Castle Underpass on Feb. 16, 2011.

Two days before that, Sawaya said she was detected by hair sampling at a nearby hair trap south of the underpass, while on April 25, she was detected at a hair trap north of the highway.

“In between those detections, there was a photo taken at a crossing structure heading the direction that would have made sense for this individual,” he said.

“We’ve had a number of documented wolverine crossings, but we just don’t know if they’re males or females, so that was a case where we had pretty good evidence where maybe females are starting to use the crossings.”

In 2017, Parks Canada began expanding and mitigating the highway with fencing and crossing structures in Yoho National Park.

Snow tracking surveys and connectivity models used to recommended where crossing structures would be built for this phase showed Kicking Horse Pass is a regionally important corridor for wolverines travelling north and south and across the highway.

According to the study, this was the one area where scientists believe two of four females may have crossed the road based on their DNA being collected at hair traps on both sides of the highway.

The female identified by DNA tests caught on camera at Castle back in 2011 was also detected along this high elevation corridor, located on the spine of the Continental Divide near where a wildlife overpass and series of underpasses were recently built.

“Our work certainly showed that seems to be one of the areas, or the only area, that it seemed like females were getting across,” said Sawaya.

“I would say it’s one of the most important areas in terms of connectivity for wolverines in all of the Canadian Rockies,” he said.

Tony Clevenger, a Canmore wildlife research scientist who specializes in identifying the effects of highways and other barriers on wildlife connectivity, said this work was part of a much larger study that began as part of research for the latest phases of twinning the highway.

With little known about the impacts of roads on wolverines in other parts of their range, he said it was an interesting opportunity to look at how major transportation corridors would affect gene flow and movements of wolverines, which he notes may be much more sensitive than grizzly bears in terms of disturbance.

“They tend to be really shy and really adverse to human activity and disturbance,” said Clevenger, who works for the road ecology program at Western Transportation Institute – Montana State University,

Clevenger said when the larger study began, not much was known about wolverines in Banff, Yoho and Kootenay, although there were often sightings at Lake O’Hara, Boulder Pass and Skoki.

Clevenger said there have been no wolverine crossings in the newest section of mitigated highway to his knowledge.

“It’s really unusual because the crossings up and around the Continental Divide were finishing up when we were completing the wolverine work,” he said.

“We thought we’d wait and see over the next five years because this is the prime place for them to be crossing.”

It is hoped, however, that it is only a mater of time before wolverines start using those crossings at higher elevations more regularly. It is possible that they have and the cameras have not picked them up, though.

“What we suspect is that those crossings that have been placed in the higher elevations should be more effective for wolverine passage because they’re in better wolverine habitat,” said Sawaya.

Sawaya said the results of the study highlight the need to mitigate highways both inside and outside of protected areas to protect wildlife from the effects of habitat fragmentation.

“This shows that highways can have nuanced effects on different species, and even within species can have nuanced effect,” he said.

“We know crossing structure types are preferred by certain sexes and species, as well as we know grizzly bears, females in particular, tend to prefer the big overpasses.”