Bears Find New Mates by Using Man-Made Wildlife Crossings

A network of wildlife crossings along the Trans-Canada Highway has succeeded in keeping populations of grizzly bears and black bears genetically diverse, according to new research from Montana State University.

The research team focused on bear populations in Banff National Park near Calgary, Canada. The park is bisected by Canada's Highway 1, which spans the country. Along the highway, a system of overpasses and wildlife crossings is in place to allow wildlife to freely cross the highway without putting motorists or the bears themselves in danger. The first-of-its-kind study revealed that bears are not only using the crossings, but are breeding with other bears on either side of the highway.

"Showing that the black bears and grizzlies using the crossings to traverse the highway are also breeding is a major finding," said ecologist Michael Sawaya, lead author of the research appearing in the Proceedings of the Royal Society B.

"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," he said in a statement.

The 44 wildlife crossings along Highway 1 constitute the most extensive system of wildlife crossing structures on Earth.

"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, a professor of ecology at MSU and co-author of the study. "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 researchers concluded that the bears were using the wildlife crossings to breed by conducting DNA analyses of hair samples obtained from wire snares placed within the crossings. Those DNA samples were paired with samples taken from all around Banff National Park.

One particular black bear was found to have mated with five different females, siring 11 cubs.

The results also indicated that black bears are more likely to use the wildlife crossings than grizzly bears, which are known to be leery of human infrastructure.