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Bears Need Highway Overpasses, Too

Inside the dramatic world of transportation planning for wildlife.

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Beautiful Banff National Park in Canada began to install the first of several dozen underpasses and overpasses across the Trans-Canada Highway inside the preserve's boundaries in the 1980s. They connect on either side of the four-lane road to no sidewalks or trails. And they've never been marked on hiking maps of the park used by tourists. "We don’t advertise them," says Tony Clevenger, a wildlife biologist who's been working in the park for 17 years.

They look, for the most part, like typical pedestrian infrastructure: elliptical or boxy concrete culverts under the highway high enough for a human to pass through, or overpasses that would look entirely familiar to the vehicles passing below. All this highway engineering, though, is meant for the benefit of bears. And cougars, and wolves, and elk.

"We’ve got this important north-south transportation corridor for animals," Clevenger says of the park, which is located in the Canadian Rockies between Vancouver and Calgary. "But it's bisected by this important east-west transportation corridor for vehicles."

One of the larger overpass crossings in Banff.

The speed limit on the Trans-Canada Highway inside the park is 90 kilometers an hour. Outside the park, it's 110. That's what most people are driving. The road is one of the longest paved highways in the world, and it's a crucial artery for Canada. On an average summer day, about 25,000 to 30,000 vehicles drive through Banff, between park visitors and long-distance drivers, the equivalent of one car passing every three seconds. A lumbering bear barely stands a chance.

The park originally installed the crossings to protect motorists. A thousand-pound elk can wreck your car. On one 15-kilometer stretch of the highway, there used to be an average of a hundred elk-vehicle collisions every year. "I think the park realized sooner of later, they’d have a human fatality in some of these accidents," Clevenger says, "and they were going to be taken to court."

But over the years, critics and transportation planners, even some environmentalists have groused about the idea: Taxpayer money, building overpasses for bears? Is that really necessary? Would they even use the things? Researchers have been methodically studying the crossings since 1996 to answer this. And it turns out that, yes, animals deterred by fencing that now runs the full 70-kilometer length of the highway in the park actually cross the road an awful lot like a rational pedestrian would. It takes them a while, though, to adapt to the crossings after a new one is constructed: about four to five years for elk and deer, five to seven years for the large carnivores.

A cougar.

"We’re able to demonstrate thousands and thousands of crossings every year, by 10-11 species of large mammals," Clevenger says. "We knew there were families of adult sows with cubs, adult female cougars with kittens using them. We knew that from the tracks. But the critics out there, some among transportation agencies, would say, 'Well it’s always the same male black bear that’s going back and forth.'"

To put this notion to rest, Clevenger and colleagues with Montana State University's Western Transportation Institute recently concluded a three-year study of the DNA from 10,000 hair samples of bears non-invasively snagged from the crossings and other areas around the park (the collection technology is not very sophisticated: this requires a little piece of barbed wire). DNA from bear hair is pretty amazing. It can reveal not just the difference between a black bear and a grizzly, but the identity of the individual bear, its gender, its relationship to bears of the same family.

A family of grizzlies.
A grizzly.

The study found that about 20 percent of the bears in the geographically broad sample population were using the crossings, and with the same activity patterns they exhibit in the back country. These bears were not, for instance, making a run for it in the middle of the night when traffic volumes were low. And all of this means that this infrastructure is doing much more than protecting motorists. It has enabled the free flow of mama bears and bear genes across four lanes of high-speed traffic.

"The mitigation measures on the highway have basically restored connectivity across a major transportation corridor," Clevenger says, "as though the highway wasn’t even there."

A young moose.

In the process of studying all of this, scientists have also learned some curious things about the engineering preferences of different species. Grizzlies, for instance, prefer the overpasses, black bears the underpasses. Clevenger suspects that these patterns reflect the natural environments in which these animals evolved. Black bears evolved in the covered forest, grizzlies in open habitat.

This kind of knowledge doesn't appear in your standard transportation engineering manual. But, well, animals are kind of like the pedestrians of the wild. If that doesn't convince any remaining skeptics of the value of this investment, maybe this will: The average cost of a moose-vehicle collision, in hospital bills, lost work and property damage, is nearly $30,000. That's a separate line of research.

If that still doesn't do it for you – or you just want to see these animals in action – watch this great little 22-minute documentary of the importance of the crossings in the park, particularly in an era when climate change will disrupt the natural habitats of many species. All of the above images come from the film, called Highway Wilding, by filmmaker Leanne Allison. Below, the trailer:

About the Author

  • Emily Badger is a former staff writer at CityLab. Her work has previously appeared in Pacific StandardGOODThe Christian Science Monitor, and The New York Times. She lives in the Washington, D.C. area.