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Researchers: Wildlife crossings critical for animals survival, proper design necessary

Animals Bridge
Posted at 10:25 AM, Jan 12, 2023
and last updated 2023-01-12 12:25:35-05

MISSOULA - Three recent scientific studies highlight not only how important wildlife crossing structures are but also that crossing structures are less useful if their design doesn’t encourage wildlife to use them.

On Wednesday, scientists from the Natural History Museum of Utah, the University of Ioannina and Northern Arizona University published a study providing more evidence of the importance of preserving wildlife migration corridors between Glacier and Yellowstone National Parks.

The study was published in “Scientific Reports,” an open-access journal put out by Nature.

Using data from nine studies conducted across four continents, the scientists developed a theoretical model, an equation, that could predict how long before half of the species stuck in an isolated region - such as a national park surrounded by human development — would go extinct.

Scientists use the word “relaxation” to refer to the loss of species over time in a contained area. The time to lose half of the species is the “relaxation half-life.”

Their regression showed, with fairly good accuracy, that the smaller the average population of species within an ecosystem, the quicker they’re likely to go extinct. And obviously, smaller wildlife refuges are going to contain smaller populations of species.

Using only species of medium to large-sized ungulates, carnivores and rabbits, the scientists calculated the relaxation half-life for Glacier-Waterton parks and Yellowstone-Teton parks. Then they ran the model for when the four parks are connected by three migration routes. The scientists also ran the numbers for Mount Rainier National Park to the North Cascades parks in Washington state.

The results showed that the groups of species in Montana survived more than three times as long if they had migration corridors than if they were limited to just one set of parks or the other.

The problem is that Glacier-Waterton and Yellowstone-Teton parks are basically isolated, mainly because of migration barriers such as railroads and highways. And that isolation is getting worse with increasing human development.

The scientists point out that now is the time to establish wildlife migration corridors and keep them open. They also encourage less housing development next to national parks.

The nonprofit Yellowstone to Yukon has promoted the same thing.

“A concerted effort will be required to enhance the capacity of national parks and related reserves in western North America to conserve intact plant and animal communities over the coming century. Implementing a regional-wide program to establish linkages among national parks and related reserves in western North America, including Yellowstone National Park, North America’s first national park, would greatly enhance the persistence of plant and animal communities in the northern Rockies and Cascades,” the scientists concluded.

Animal crossing structures, such as bridges or tunnels, can help wildlife get across highways and railroads. Previous research along a stretch of the Trans-Canada Highway near Banff National Park in Alberta found a series of crossing structures reduced total wildlife collisions by 80% while collisions with elk and deer were almost eliminated.

A dozen years ago, the Confederated Salish and Kootenai Tribes (CSKT) built 41 such structures across Highway 93. But some early efforts may need to be modified, based on some of the things biologists have recently reported.

In December, scientists with the University of British Columbia published a study in the journal “Biodiversity and Conservation” that found most overpasses in North America, Europe and Asia are too narrow.

Observations over the past decade show grizzly bear sows and cubs and prey species like elk avoid overpasses that are too narrow, less than 150 feet wide. However, in a survey of 120 overpasses, scientists found most weren’t wide enough, averaging only about 100 feet wide. The Animals’ Trail overpass on the Flathead Reservation is 197 feet wide.

Then, research out of the University of California Los Angeles shows that prey animals like elk and deer are less likely to use an underpass if they’re startled or frightened by traffic passing over.

The scientists reviewed 600 animal-activated videos collected by Montana State University road ecologist Anthony Clevenger that showed elk and white-tailed deer in the vicinity of a Trans-Canada Highway wildlife underpass near Banff National Park.

The videos showed that elk and deer browsing near the tunnel often either fled or became vigilant when vehicles passed and were much less likely to use the crossing.
The researchers urge highway designers to build entrances to animal crossings that shield wildlife from the surrounding hubbub.

"If we can figure out ways to leverage wildlife behaviors, we may be able to make wildlife crossings more effective,” researcher Eric Abelson told Science Daily. "For example, walls to dampen sound or to reduce the visual effects of passing headlights may encourage use of crossing structures. We hope that this study is just one of many that will examine different wildlife species and levels of traffic to better develop tools that increase the use of crossing structures by wildlife and, ultimately, protect the lives of humans and wildlife."

Contact reporter Laura Lundquist at lundquist@missoulacurrent.com.