PLACES | 10.03.17
Encroaching development is putting pronghorns at risk, but new conservation strategies are giving these record-setting runners a leg up.
When the first flurries begin to swirl in western Wyoming’s autumnal skies, herds of pronghorn (Antilocapra americana
) gather impatiently at the foot of the Grand Tetons—the youngest and most jagged mountains in the Rockies. Temperatures drop, and the wind whips with a telling chill. The pronghorns know—innately—it’s time to move.
The journey ahead will not be easy. What this group of a few hundred animals faces is one of the longest overland migrations in the Western Hemisphere. Over the course of two or three days, the herbivores, a mere meter (3 feet) tall at the shoulder, must make it up and over a high-elevation mountain pass before heavy snow blocks their passage. In total, they will travel some 145 grueling kilometers (90 miles) to reach the sagebrush steppe of the Green River Basin where they’ll spend the winter.
Over the past decade, new federal protections, highway overpasses, and retrofitted fences have improved the pronghorns’ chances. But the question remains whether positive human interventions will be enough to offset the negative impacts and enable these enduring creatures to continue to heed their instinct to roam.
To avoid predators along the route, pronghorns tend to stick to open spaces with unobstructed lines of sight. This plays to their two main strengths: their acute vision, to spot potential threats, and their speed—up to 100 kilometers (60 miles) per hour—to outrun them. But in the mountain pass that separates the Gros Ventre Mountains and the Wind River Range, the pronghorns have to funnel onto single-file canyonside trails and narrow forest paths through dense stands of lodgepole pine (Pinus contorta). To move as quickly as possible through these high-risk areas, the uneasy animals often run for miles without stopping.
Path of the Pronghorn
Grand Teton National park
Green River Basin
Once the pronghorns make it past the southern reaches of this protected area, land management becomes a jurisdictional hodgepodge. Some of the land is privately owned; other portions are overseen by the state or federal government. Even under the federal umbrella, management of these lands is split between the Bureau of Land Management and the U.S. Fish and Wildlife Service. Balancing land use and conservation priorities under these conditions is no easy task, especially since many of these state and federal agencies were created to manage public lands for multiple uses: wildlife habitat, yes, but also recreation and resource extraction.
A few years later, Joe Riis, then a recent graduate from the University of Wyoming who had studied wildlife science, wanted more than a migratory map. He wanted to see what migration looked like on the ground. For two years, he lived out of his pickup and followed and observed pronghorns as they trudged over snow-covered mountain passes, sprinted through blinding willow thickets, and struggled across raging rivers. To photograph the pronghorns, Riis needed to predict the animals' movements, including where they would emerge from a river crossing. “That type of information, nobody knows, because no one has sat around the river for weeks and watched where the pronghorn exit,” he says. After years of patient camera trap placement, Riis’s photos captured, for the first time, not only where the pronghorns were going, but also what was standing in their way.
Hall Sawyer, now a research biologist with the environmental consulting firm Western Ecosystems Technology, Inc. says that most of the fences along the migration route have now been retrofitted, but that’s not to say they don’t still cause problems. “All it takes is a little bit of snow or snowdrift, and all of a sudden your 18 inches is gone,” Sawyer says.
Riis also says that domesticated animals can have an outsized impact. He once watched an untethered dog turn back a group of 100 pronghorns, preventing their progress for an entire day—a day they might not have been able to spare.
The critical pinch-point along the 145-kilometer (90-mile) journey is a spot called Trapper’s Point. Here, two large rivers, the Green and the New Fork, come together in a single valley. The traversable landscape naturally narrows the route to a single mile (1.5 kilometers) in width. But a housing development built in the 70s further reduced it to about a quarter of a mile (less than half a kilometer) wide.
While archaeologists have found evidence to suggest that bands of indigenous hunters took advantage of this bottleneck some 6,000 years ago, in modern times the killer in the valley has been State Highway 191. Riis describes it as a place that was, until recently, dangerous for both people and wildlife. “It was just carnage,” he says. Each year, an average of 100 collisions occurred between pronghorns and cars on this single 20-kilometer (12-mile) stretch of road just west of Pinedale, Wyoming.
The problem was clear, and researchers including Sawyer and Beckmann were producing ever-more accurate maps of the pronghorns’ locations to show exactly where an intervention was needed. To come up with a blueprint, the Wyoming Department of Transportation looked to Nugget Canyon—another area of the state known for collisions between cars and, in this case, mule deer. In the mid-2000s, the department built a series of underpasses. These structures not only allowed the mule deer to cross the highway safely, they also effectively paid for themselves over time by reducing the number of vehicle collisions along this stretch.
At Trapper’s Point, the Department of Transportation was keen to try something similar, but studies showed that pronghorn don’t use underpasses because the structures confine the animals and obstruct their vision. So instead, the department decided to experiment with a structure that would go over the highway. In 2012, they revealed two overpasses that allow the pronghorns to walk up and over the road, in the very spots where GPS data showed the animals crossing in large numbers in years past. Now, drivers traveling down Highway 191 see the overpasses rising gently from the horizon like ochre hills above an otherwise flat horizon.
Before, during, and after overpass construction, Beckmann’s team at the Wildlife Conservation Society observed pronghorn behavior to gauge the animals’ reactions to the new structures. At first, he says, the pronghorns were wary of these novel features on the landscape and preferred the known risk of the roads. But over time, their stress responses waned and the animals adjusted. Thousands of the pronghorns in the Green River Basin, including those that migrate from the Grand Tetons, now use the overpasses each year, and collisions between vehicles and pronghorns along this particular stretch of highway have been virtually eliminated. It’s an important victory, but hurdles still loom.
Beckman and his colleagues have found that the gas fields are changing pronghorn behavior. Between 2005 and 2009, the area that researchers categorized as high-quality habitat declined by 82 percent due to the gas operations. The pronghorns have simply abandoned the densest well areas during the winter and in their fall and spring migrations through the area.
So far, pronghorns seem to be hanging on. “This migration is happening,” Riis says. “It hasn’t been cut off by our development yet.” Therein lies the ray of hope. Despite the many threats, old and new, in the spring, as the snow melts and slowly recedes northward, the pronghorns will follow their undying instincts and turn around to make the epic journey in reverse.
ABOUT THE Photographer
Joe Riis is a wildlife photographer and National Geographic Photography Fellow known for his pioneering and award-winning photography of animal migrations in the West. Trained as a wildlife biologist, Riis collaborates directly with research scientists to communicate with and inspire the public on critical wildlife issues. His photography book Yellowstone Migrations (released September 2017) illustrates Riis’s decade-long project on the animal migrations of the Greater Yellowstone Ecosystem.
ABOUT THE Author
Breanna Draxler is a Seattle-based editor atbioGraphic
, where she edits features, writes stories, and manages production. A science journalist through and through, she was previously on staff atPopular Science
magazines. Breanna is originally from the Northwoods of Wisconsin and is fond of backpacking, urban biking, and experimenting with lactofermentation.
The fences protecting the unique biodiversity of Maui’s Kīpahulu Reserve have helped to keep invasive species at bay, but climate change is now carrying new threats up its slopes.
article | 01.09.18
Paradise Under Pressure
In the Golden State, dangerous drug cartels are growing pot on public lands—putting wildlife, water supplies, and outdoor enthusiasts at grave risk.
article | 03.28.17
Backcountry Drug War
Africa's rarest carnivores face mounting threats from disease-carrying domestic dogs, but scientists hope a new vaccination campaign will give Ethiopian wolves a fighting chance at survival.
photo essay | 02.27.19
The Last Wolves
is powered by the California Academy of Sciences, a renowned scientific and educational institution dedicated to exploring, explaining, and sustaining life on Earth.
Don't miss a thing.
Sign up to receive the latest updates and new stories frombioGraphic