Wildlife crossings spanning the Trans-Canada Highway are allowing grizzly and black bears to spread their genes, according to a recent research paper written by a former Montana State University graduate student.
Paternity tests revealed that one particularly amorous male black bear mated with five different females in the process of siring 11 cubs as he crossed back and forth.
The first-of-its-kind study of Banff National Park bears by scientists with the Western Transportation Institute at MSU provides further proof that the crossings not only keep wildlife from being struck by vehicles, but also maintain genetically healthy populations of bears along the Trans-Canada Highway.
“Showing that the black bears and grizzlies using the crossings to traverse the highway are also breeding is a major finding,” said Michael Sawaya, a WTI scientist who wrote the paper as the final piece for his doctorate in ecology. “While there have been a lot of studies showing that wildlife are using these crossings, this is the first time anyone has shown that animals using the crossings are breeding often enough to ensure that the populations on either side of the highway are not being genetically isolated.”
To document the gene flow, the researchers collected some 10,000 hair samples from black bears and grizzlies at wire snares located at the crossings and compared the data with the DNA from samples collected far and wide within the surrounding habitat on both sides of the highway.
Parentage tests showed that 47 percent of black bears that used crossings had successfully bred, while 27 percent of grizzly bears had done so.
Sawaya said the study also reinforced a common assumption among ecologists that grizzly bears are much more shy of human infrastructure than black bears, though the project’s data suggest that once an individual grizzly is accustomed to using the crossings, that bear will cross the highway readily and, in the case of females, may pass the habit on to offspring.
The 44 crossings form the most extensive system of wildlife crossing structures on the planet.
“These wildlife crossing structures cost millions of dollars and this is one of the first studies that has shown that they are doing what they are intended to do,” said Steven Kalinowski, MSU professor of ecology, who co-authored the paper. “If the bears aren’t crossing the road and breeding, you’re going to have fragmented and inbred populations on each side of the road.”
The genetics paper is the third to come out of a three-year study of the crossings in the context of Banff’s black bear and grizzly populations. The project was launched in 2006 by Sawaya, Kalinowski and WTI researcher Tony Clevenger as a continuation of long-term research Clevenger has conducted in Banff since 1996. Previous papers discuss findings that show the number of bears in the Bow Valley and the proportion moving across the highway.
Sawaya’s research paper was published in the British journal “Proceedings of the Royal Society B,” and a photograph of one of Banff’s wildlife overpasses is featured on the publication’s cover.