A British Columbia study analyzing 120 wildlife bridges found most are too narrow, potentially leaving many species split or dead on a highway
Most wildlife crossings in North America and Europe are too narrow, a group of British Columbia scientists have found, a situation that potentially limits the number of animals that can cross major highways and threatens their long-term survival. .
The study, published last week in the journal Biodiversity and Conservation, analyzed 120 wildlife overpasses, also called eco-bridges or green bridges, across North America, Europe, Asia and the United States. ‘Oceania.
“In general, we found that most overpasses did not meet expert guidelines,” said lead author Liam Brennan, a 22-year-old undergraduate student at the University of British Columbia (UBC ).
The ideal width of a wildlife passage depends on the species using it. Prey species like elk, as well as grizzly bear mothers and calves, are especially wary of narrow overpasses, said Brennan, who led the study alongside the BC government’s wildlife biologist. Emily Chow and UBC wildlife scientist Clayton Lamb.
Most scientists agree that most large animals will use a 50 meter wide eco-bridge. In Europe, about half of wildlife crossings met this 50 meter wide bar. This percentage fell to 28% in North America.
And across the planet, the average width of a wildlife bridge was just 34 meters, more than a third less than many animals need.
Why wildlife crossings are so important
Previous research has shown strong evidence that wildlife crossings—as well as fencing along a highway to direct animals to overpasses and underpasses—can significantly reduce wildlife-vehicle collisions.
This is especially important for species like grizzly bears; for them, dying in a collision with a train or a truck is one of the main sources of mortality.
Previous research along a section of the Trans-Canada Highway near Banff National Park found that a series of crossing structures reduced wildlife strikes by 80%. Collisions with elk and deer have dropped by 96%.
In many ways, wildlife collisions are a symptom of humanity’s ever-growing footprint. As people build more cities and extract more resources, the roads that connect them carve up the vast expanses of large prey and predator species upon which their survival depends. For these animals, crossing a highway safely is more than a chance to avoid death, it’s also a chance to spread life.
“This highway is like a brick wall that they can’t get through.” Brenan said. “They do form a barrier.”
Build a wildlife overpass and the animals, once separated from each other, may be able to find a mate. Without eco-bridges, says Brennan, many species face the prospect of inbreeding and, in the worst case, regional extinction.
The researcher says some wolverine populations divided by highways have been so isolated. In fact, they genetically diverged from each other.
Build a bridge over four lanes of traffic and the genetic link could be restored. But build a wildlife overpass that’s too narrow and prey species like elk or a family of grizzly bears will avoid it.
“They want to feel safe. They don’t like being in tight spaces,” Brennan said.
BC particularly narrow viaducts
In countries like South Korea and the Netherlands, researchers have found that high human population densities correspond to high concentrations of wildlife overpasses.
“Globally, I find it incredibly encouraging that people are coming together for the collective good of road connectivity for wildlife,” Brennan said.
To better understand the effectiveness of wildlife crossings, researchers tracked animal movements through 12 overpasses in western North America: Montana, Idaho and Washington in the United States, and Alberta and British Columbia. British in Canada.
Of the jurisdictions, British Columbia was found to have the narrowest wildlife passages.
Part of this is a matter of timing. Brennan says a passage outside Kelowna, B.C., serving deer and cougars was built long before there was scientific consensus on their width.
And in the case of three wildlife overpasses near Golden, the narrow twitches appear to have targeted deer populations, which aren’t considered as nervous of narrow bridges compared to some other species.
The problem, says Brennan, is that all of their sightings were made using at least two camera traps pointed at the crossings. This meant they could only count animals that used them, not those that lived in the area but possibly avoided them because they were too narrow.
“It’s really a plea for better data to draw more informed conclusions,” he said. “With stronger evidence, we can make stronger claims, and that would give us the opportunity to build overpasses of the right width.”
To not have enough time
The study follows COP16, a major summit where nearly 200 nations recently signed on to a global framework to protect nature from the biggest extinction crisis since the dinosaurs were wiped out 66 million years ago. .
On December 19, delegates in Montreal signed the historic Kunming-Montreal Agreement to protect and conserve 30% of the planet’s coastal and terrestrial areas with the aim of halting and reversing global biodiversity loss by 2030.
None of this work comes cheap. Wildlife crossings, for example, cost between US$5 million and US$15 million, and the wider the crossing, the more expensive the project, according to the UBC study.
“We need to restore biodiversity and ecosystems,” Brennan said. “We have to build them in the most cost-effective way.”
Previous research has shown that protected areas work, but have failed to slow the loss of biodiversity on the planet. Part of the failure is due to their closeness to people. More than 90% of them are in a human-dominated landscape scared of highways and other infrastructure.
Globally, two-thirds of the world’s critical wildlife corridors are unprotected; almost a quarter of these crossing points are also prime candidates for agricultural development.
That’s what makes places like the Yellowstone-Yukon Corridor so important, one of the busiest migration routes for large mammals in the world.
“This area of the Rockies, it’s really the last bastion of various mammals in all of North America,” Brennan said.
And in the years to come, increasing the efficiency and number of wildlife crossings could be a critical bridge as these animal migration patterns change.
Brennan says there’s “tons of research” showing that climate change will push animals to the polls or into the mountains to survive.
But if they can’t cross the highway and move north, their populations will dwindle and, in some cases, die.
All the more reason, says the young researcher, to widen the bridges.
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