Restoring the path of the pronghorn

Jan 28, 2012

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A population of pronghorn antelope have been migrating back and forth between the Red Desert and Bridger-Teton National Park for thousands of years, despite growing development threatening their path. Individual conservation efforts have protected parts of their route, but the Wyoming Department of Transportation is working on a project near Pinedale that might make the trip a whole lot easier. Wyoming Public Radio’s Rebecca Martinez reports.

REBECCA MARTINEZ: About his time every year, a group of three-to-four hundred pronghorn leave the winter range in Sublette County for greener pastures 150 miles north. They wander fields, swim across the Green River and trek over the Gros Ventre Mountains. It’s no sweat for a pronhorn, says journalist Emilene Ostlind, who followed the migration on foot for a few seasons. It’s the manmade stuff that causes problems outside the federally protected leg of their migration corridor in the Bridger-Teton Park.

EMILENE OSTLIND: Immediately they just go right into a subdivision. That's pretty hard for them to get through. There's roads and fences and people might have dogs out and trucks driving around and everything.

MARTINEZ: Ostlind says some pronghorn are thick-skinned and wander through gas fields unfazed. Others avoid them entirely, which requires more time and energy for the trip. Conservationists have worked to retrofit some obstructions to the pronghorn’s route. Landowners have put easements on their property to prevent development. Farmers have moved fences or left open gates during migration season. But some obstacles are more formidable.

OSTLIND: There's a major highway crossing at a place called Trappers’ Point just west of Pinedale that's pretty dangerous for the antelope.

MARTINEZ: Trappers’ Point is where the migration routes of all kinds of animals converge, forming a natural bottleneck. More recently, WYDOT constructed Highway 191 clear across it. To put it mildly, animal crossings have caused problems for motorists, and vice versa. Here’s WYDOT District Engineer John Eddins.

JOHN EDDINS: There’s over 100 carcasses per year, and of those hundred carcasses there’s about 25 to 30 property damage crashes.

MARTINEZ: Eddins says most of the carnage involves ungulates. Ungulates are animals with hooves, including elk, mule deer and pronghorns.
WYDOT has been able to mitigate the wildlife crossing problem in some parts of the state by posting warning signs and fences along the roadways. They’ve even built a few underpasses specifically for wildlife to take under the roads. Mule deer, which have made up most of the gore at Trappers’ Point, seem fine with using underpasses. Pronghorn antelope, not so much. Emilene Ostlind says they evolved in wide open spaces, and they won’t settle for less.

OSTLIND: They have very powerful binocular-like vision. They can spot predators miles away, and they can see almost all the way behind them. And when they see something that looks dangerous to them, they sprint away from it.
MARTINEZ: So when faced with a dark, subterranean tunnel, most pronghorn decide to take their chances with the highway. Pronghorn were built to run, but unlike deer, they can’t really jump over things like fences. Ostlind says Trappers’ Point is the most dangerous part of their migration.

OSTLIND: They all have to cross the highway and there’s a fence on either side and they have to crawl under the fence and run under the highway and hope that a car coming over the blind hill from Pinedale doesn't run into them.

MARTINEZ: WYDOT is hoping to fix this problem at Trappers’ Point altogether this year, while reconnecting that portion of the migration route. John Eddins says the agency has dedicated 9-point-7 million dollars to building six wildlife underpasses in the area and two 150-foot-wide overpasses antelope and other animals can use to cross the highway in the open.

EDDINS: The overpass will be vegetated with vegetation that matches the surrounding prairie: Brush, grass, etc.

MARTINEZ To passing antelope, an overpass should just look like a hill with fencing on either side. They should be completed in September.

Research biologist Hall Sawyer is skeptical of the idea of the overpass as a cure-all. He works with Western Ecosystem Technology to research projects like these for WYDOT. After the agency installed seven highway underpasses near Kemmerer, Sawyer says three years of monitoring data show that there were antelope who used the underpasses “under certain circumstances.”

SAWYER: These underpasses are orders of magnitude cheaper than the overpasses…

MARTINEZ: An overpass costs about three-times what an underpass costs to build…

SAWYER: And so from a construction standpoint, if we find out in Pinedale pronghorn are willing to move underneath the highway, that will save substantially in construction costs when these types mitigation of projects are completed in other parts of the state.

MARTINEZ: These types of projects are a success story in Canada’s Banff National Park. Tony Clevenger is a wildlife biologist at Montana State University’s Western Transportation Institute, and he works at Banff. He says in the early 1980s, there were about 100 vehicle-ungulate collisions per year along a stretch of the Trans-Canada Highway.

CLEVENGER: The stretch of highway was nicknamed the Meat Maker just because there was so much carnage and road kill on the side of the road.

MARTINEZ: Overpasses and underpasses allowed wildlife to pass the traffic unperturbed. Clevenger says 200,000 animals – including grizzly bears, moose and elk – have used them. While cougars and black bears – forest animals – use the underpasses, ungulates prefer the open overpasses. Clevenger says their collision rate has dropped by 90 percent.

CLEVENGER: A lot of the crossing structure preference really is a result of how these species have evolved and the typical behaviors and the habitat that they require for travel. Elk and deer, moose prefer open habitats. They need a wide field of vision to avoid predators.
MARTINEZ: This year, the Western Transportation Institute hosted an overpass design competition in hopes of making the technology cheaper and more efficient in days to come. No doubt WYDOT will be standing by.

For Wyoming Public Radio, I’m Rebecca Martinez