Passages for Large Mammals

Each year, close to five million people travel the Trans-Canada Highway to visit Alberta's Banff National Park. In summer, at least 20,000 vehicles a day clog the road. Throughout the year, unending streams of traffic whiz up and down the high-speed commercial section between Calgary and Vancouver.

The Trans-Canada Highway cuts through the Bow River Valley and the habitats of elk, deer, moose, wolves, cougars, black bears, grizzly bears, and other species. So when 28 miles (45 km) of the highway (the section between Banff's east gate and Castle Junction) were widened, park and transportation officials joined forces to protect the corridor's wildlife. Parks Canada put up 8-foot-high (2.4-meter-high) fencing on both sides of the highway and built 22 underpasses - arched culverts, box culverts, and open-span bridges - and two 164-foot-wide (50-meter-wide) overpasses.

The result? The fence has cut ungulate (hooved animal) roadkill by 96 percent, and 35 months of monitoring animals' back-and-forth movement through the crossing structures has demonstrated that both ungulates and carnivores are using them.

Locating the underpasses and overpasses near the animals' natural travel corridors was crucial to the project's success. For carnivores, this meant placing the structures close to stream corridors or drainage areas. For ungulates, it involved doing the opposite - placing the structures far from carnivores (their predators) and with a clear view of the structures' entrance.

The park's overpasses and underpasses (like the underpass shown in this aerial view) have cut ungulate roadkill by 96 percent.

So far, equal numbers of species are using the overpasses and the underpasses (especially open-span bridges), but Parks Canada biologist David Poll thinks overpass use will surpass underpass use over time. "Once the new vegetation has grown," he says, "the animals will no longer see the highway as they approach or travel on the overpass, and they'll be less bothered by traffic noise."

Wolves and grizzly bears are more likely to use underpasses like these when there's no sign of human activity nearby. Parks Canada hopes that urging stricter limits on human activity near the crossing structures will increase the numbers of carnivores using them.

Despite the successes of the project, Parks Canada admits there's a lot more work to be done. For example, solutions must be found to preventing black bears and cougars from climbing over the fence. Parks Canada contractor Tony Clevenger has already begun exploring strategies ranging from eliminating the dandelions (a delicacy for black bears) on the highway side of the fence to placing additional wire mesh at a 90-degree angle on top of the fence. Parks Canada researchers are also urging stricter limits on human activity near the Banff crossing structures - a strategy they hope will increase the low numbers of large carnivores (especially wolves and female grizzlies) using the structures and a critical step to take as traffic continues to increase on the Trans-Canada Highway and more and more visitors come to the Park. "Distance from humans is the most important consideration in designing crossing structures for large carnivores," says Clevenger. "The further, the better."