A new study suggests that at least one reason bears in Banff National Park are crossing the Trans-Canada Highway is to find mates — vindication for a series of wildlife crossings installed by Parks Canada on the busy route to try to keep bears on either side of it genetically linked.
"It is clear that male and female individuals using crossings structures are successfully migrating, breeding and moving genes across the roadway," says the paper published Tuesday in the Proceedings of the Royal Society, Britain's national science academy.
The Trans-Canada Highway cuts through the heart of Banff National Park. For decades, scientists have been concerned that Canada's busiest east-west road link was isolating grizzly and black bear populations on either side of it — especially after high wire fences were built along the road to reduce wildlife traffic deaths.
So between 1982 and 1997, more than two dozen underground and overhead crossings were built to allow wildlife to move north-south.
In 2006, Montana State University ecologist Mike Sawaya began a three-year research project to see if the crossings were working. After analyzing DNA from nearly 10,000 hair samples collected from strategically placed strips of barbed wire, Sawaya has concluded that they are.
Last summer, he published research proving that bears were using the crossings. His latest paper suggests they're crossing for more than a patch of tasty berries.
"We found enough movement and migration across the highway to infer that, yes, the crossing structures are allowing the transfer of genes."
Sawaya said that grizzlies on either side of the road had been slowly becoming more genetically distinct from each other, although the effect wasn't pronounced in black bears.
DNA analysis of the hair samples shows that the two ursine neighbourhoods are gradually coming back together again.
"The grizzly bear population was fragmented and we're starting to see it be restored," said Sawaya. "If the crossings continue to work the way they are, I think we're going to see the dissolution of that genetic structure over time."
The research team even documented how individual bears — both black and grizzly — were able to mate with a number of different females and wound up with offspring on both sides of the highway.
Previous research conducted in California had suggested the only animals that use crossings are juveniles too young to breed. Sawaya found that wasn't true.
Almost half the black bears and more than one-quarter of the grizzlies that crossed were successful breeders. In fact, males who crossed most often seemed to be the ones with the most offspring.
And Sawaya said it's probable that the crossings are being used by other animals such as wolves, lynx or cougars for the same purposes.
"Certainly, you can draw more conclusions about other carnivores and other species that have similar characteristics. This is very indicative of how these crossing structures would perform for other large mammals."
It's good news for wildlife managers looking for ways to mitigate the effects of roads through wilderness.
Parks Canada now has a total of 44 Trans-Canada crossings in Banff, almost one every two kilometres. The solution was expensive — the overpasses cost about $1 million each — but Parks Canada carnivore specialist Jesse Whittington said they were worth it.
"For the first couple years, they didn't look like they worked very well," he said. "Over time, grizzly bears have learned to use them on a regular basis."
Whittington said the model has already been used in the U.S. for pronghorn antelope.
"There are people looking to Banff from all over the globe to see how well these crossings are performing," Sawaya said.
"At the time, no one really knew they worked. They just assumed intuitively that they would ... and it's comforting to find that, yes, they are working as they were originally intended."
— By Bob Weber in Edmonton