Thousands of pronghorn died in the Red Desert two winters ago. A new paper shows why.

Two years ago, as one storm after another piled feet of snow across south-central Wyoming, pronghorn started walking to find something to eat. 

But quickly, they bunched up against a fence. Then another one. 

They kept moving, bumping into more fences. Mile after endless mile they trekked, running into impenetrable wires in every direction before thousands finally succumbed to exhaustion and died. 

One female walked a staggering 225 miles over 60 days, searching for food and bare ground, wandering north and south, east and west. She collapsed for the final time about 20 miles from where she started. 

“This was the perfect storm situation where all of these different forces came together to cause a mass mortality event,” said Ellen Aikens, co-author of a recent paper published in the journal Current Biology documenting the deadly consequences of so many miles of fencing. 

The Red Desert pronghorn herd die off was a catastrophe in the making, one biologists feared could happen. The paper’s authors hope their work and an associated short film produced by Wyoming Migration Initiative filmmaker and research scientist Pat Rodgers could help people better understand the importance of connected landscapes, especially as winters become harsher and wildfires become more extreme.

“We often assume that anytime we have a tough winter, that mass mortality with deer and pronghorn is unavoidable,” said Hall Sawyer, a wildlife biologist with Western EcoSystems Technology, Inc. and co-author on the paper. “But the fact is, if these animals can move freely across these landscapes, the likelihood of them dying is drastically reduced. It’s the antidote to these mortality events everyone is so concerned about.”

Fences to the moon and back

No one knows for sure how many miles of fence string across Wyoming or the West, but researcher Wenjing Xu arduously mapped fencing in Sublette County and discovered more than 4,300 miles, twice the length of the U.S. border with Mexico. Extrapolated out, she figures the western U.S. alone has more than 620,000 miles of fence, roughly enough to span to the moon and back.

Fences can be a barrier to all wildlife depending on the situation, but some are better at handling it than others. Mule deer and elk, for example, can relatively adroitly jump over common cattle fences, while pronghorn tend to crawl underneath. 

“They may try to jump, but they’re really bad at it,” said Bob Budd, executive director of the Wyoming Wildlife and Natural Resource Trust. “They try to go under if they can.”

But piling snow makes it harder to burrow under, and woven wire fence — the kind that forms in squares and not single barbed-wire strands — makes it all but impossible.

Little shows how much pronghorn struggle than GPS collar data from two years ago. Sawyer began placing collars on pronghorn in 2020 on behalf of the Wyoming Game and Fish Department, which wanted more information on the Red Desert pronghorn herd’s movements. But by the end of the 2022-2023 winter, more than half the animals in his study were gone.

“They died of starvation,” he said. “They couldn’t escape.”

Pronghorn search for areas where plants stick out of the top of the snow to provide them with critical calories to keep them alive in the winter. They also look for bare spots that make moving less costly and calorie-intensive. When they can’t find those, they essentially walk until they starve to death.

Aikens and Sawyer also discovered through the study that pronghorn particularly struggle when they wander into unfamiliar territory. The creatures generally know where they can cross under fences in their normal home ranges — they’ve found the loose wires or gaps where they can squeeze through. But during unusually severe winters, they move out of those home ranges looking for relief.

“You think, ‘I’ve seen pronghorn cross a road or fence’ and that’s because it’s the fences and roads in their neighborhood,” Sawyer said. “When they have to leave, it’s a whole new game. They have to figure out all these new barriers, and it’s a real problem.”

And for many of the Red Desert pronghorn, those new problems showed up in the form of more than 100,000 acres of land closed off by woven wire, impenetrable fence. 

Fenced in

Tom Chant’s grandfather settled in the Red Desert decades ago, managing sheep in areas closed off by woven wire fence, including one 10,000-acre section.

“Fast forward 75 years,” Chant said in the short film, “and we no longer have sheep.”

He knew fencing was problematic, but replacing fences is costly. After Sawyer’s research became public, though, Wyoming’s WYldlife Fund, the Wyoming Game and Fish Department’s fundraising arm, teamed up with the Wyoming Wildlife and Natural Resource Trust and Knobloch Family Foundation to ask Chant if they could replace that woven wire fence with wildlife-friendly fencing. And they had the more than $400,000 it would take to do all the work.

“If the fence can accommodate being a wildlife-friendly fence and control our livestock, I was all in,” he continued. 

The group spent last summer and fall replacing the fence, and pronghorn can now access 10,000 acres they’ve been blocked from reaching for decades. But the work isn’t done, said Amy Anderson, Game and Fish’s terrestrial habitat biologist in the Lander region. She wants landowners to know more money exists to convert fencing and willing hands stand ready. Game and Fish has even hired a full-time fence coordinator to help identify critical areas where wildlife can’t pass through fences and work with landowners and agencies and nonprofits to replace them. Almost 90,000 acres still remain inaccessible in the same area. 

“Landowners and producers are some of the hardest working people in the state and margins are slim,” said Chris McBarnes, WYldlife Fund president. “The reality is if we want our herds healthy moving forward in the future, we have to figure out a way to incentivize our private landowners and producers to create habitat for wildlife, and fencing is one component in that toolbox.”

As weather becomes more erratic and development continues encroaching on wildlife habitat, Aikens stresses how important it is to open lines of connectivity for animals like pronghorn so when the next storm hits or catastrophic wildfire burns through, the pronghorn, like so many other species, can find refuge.

Correction: This story was updated to fix a mispelling of Tom Chant’s name. —Ed.