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Bears go over instead of under Banff highway
BANFF, Alberta — A new report from Banff National Park finds that wildlife crossings over the Trans-Canada Highway are indeed being used by both grizzly bears and black bears in important ways. About 20 per cent of local grizzly bears have used the crossings during the last three years.
The Trans-Canada between the eastern entrance to Banff and the border with Yoho National Park has six overpasses and 38 underpasses designed to allow bears, moose, wolves and other wildlife to be able to come and go without being threatened by traffic. The four-lane highway carries about 18,000 vehicles a day.
The crossings, supplemented by fences alongside the highway, were installed beginning in the 1980s and with several new overpasses in recent years. Parks Canada estimates roadkill has been reduced 80 per cent.
But if keeping critters off highways was the only challenge, it could be done with just fences. The harder question to address is the value of the expensive overpasses and underpasses.
To get a firmer handle on how the crossing structures were being used, researchers in 2006 strung strands of barbed wire at 420 sites across the wildlife overpasses. The barbs snag bits of fur, which can be analyzed for their DNA fingerprints. Some 497 trees used by bears for rubbing were also similarly outfitted.
The research documented that 15 grizzlies and 17 black bears used wildlife crossing structures to access habitat on both sides of the highway. What's more, the study found that 90 per cent of the time the bears used the overpasses, and not the culverts or underpasses.
"You can put in underpasses cheaper, but this data mean you can justify putting in overpasses," said Mike Sawaya, co-author of the study.
Tony Clevenger, a wildlife biologist based in Canmore, Alberta, has been monitoring the wildlife overpasses for the last decade. "We knew that the bears used the crossings. We just didn't know how many, what percentage of each species' population uses them, whether there is preference by male or females to use crossings and if there was a gender or species preferences for overpasses or underpasses."
He also noted that there is clear evidence that bears are learning how to use the structures.
Another report, from the same body of research, will be issued this fall. It will document the gene flow between bear populations in the Banff ecosystem.
The broader issue is of connectivity. A field of research called conservation biology has long maintained that species such as grizzly bears cannot be limited to small islands of habitat, as it limits their genetic diversity. In cases of islands that are too small, the inevitable result is a winking out of populations.
The work in Banff has been closely watched by wildlife advocates across the continent. Several other overpasses have been erected in Montana and Nevada, and others are planned in Wyoming and in Colorado.
Meanwhile, a design competition was held in 2010 with the intent of luring designers to Vail Pass, near where one of the first lynx released in Colorado in1999 was killed a few months later. Designers were asked to create a cheaper way of erecting overpasses across highways.
The winning team adapted an existing design used in other applications and modified it to work for highways. In theory, it will allow for highway crossings to be created at many more places. Several locations are being considered in Colorado. However, none have moved forward — yet.