Brandon Scurlock has worked as a wildlife biologist with the Wyoming Game and Fish Department (WGFD) for more than 20 years, but he’s never seen a winter like the one that’s still gripping large swaths of western Wyoming. In the Pinedale Region—where Scurlock studies big game migration patterns—a staggering 62 days of subzero temperatures have combined forces with a rare outbreak of pneumonia to decimate the world’s largest herd of pronghorn antelope. And the unusually high death toll has led Scurlock and other wildlife managers to recommend drastic tag reductions for next year’s pronghorn hunting season.

“The mortalities are very visible as the carcasses are starting to melt out on our winter ranges,” Scurlock tells Field & Stream. “Anybody driving the highways around here is going to see dozens and dozens of dead pronghorn.”

Scurlock and his field technicians first discovered the ongoing pronghorn mortalities back in mid-February. That’s when some of the pronghorns he’d collared for a migration study in 2019 began dying of a rare pneumonia-causing pathogen called mycoplasma Bovis, which normally affects domestic range cattle.

Disease Gives Way to Winterkill

The animals were turning up dead on a massive oil and gas field south of Pinedale known as the Pinedale Anticline. “There are a lot of plowed-out roads and plowed-out oil pads in there,” says Scurlock. “They were just going wherever they could walk because the snow was so deep.”

The wildlife disease lab in Laramie told Scurlock and his techs to remove the infected carcasses as a way of slowing the spread of mycoplasma Bovis throughout the famed Sublette Pronghorn Herd. “We did that for several weeks, and we were hauling 40, 60, 80 carcasses a day to the dump,” he recalls. “Toward the end of March, we started seeing truly emaciated winter-killed animals, along with pneumonia. At that point the mortalities became so widespread that we couldn’t keep up.”

Mule Deer Hunting photo
A WGFD file photo shows two pronghorns that died from pneumonia associated with mycoplasma Bovis infection. WGFD.

Inverted Snowpack Leads to Huge Losses

Hanks Edwards runs the Wildlife Health Laboratory in Laramie, Wyoming, where Scurlock and his field technicians submitted the dead pronghorns that ended up testing positive for mycoplasma Bovis back in February. He tells Field & Stream that most of the animals tested by his staff in recent weeks have died from starvation and fat loss brought about by harsh winter conditions—rather than disease outbreak.

“I certainly cannot remember a winter this bad,” he says. “We’ve lost a tremendous number of our deer in the Wyoming Range, and that’s not related to [mycoplasma] bovis. It’s just a result of winterkill.”

He says that much of this year’s winterkill can be attributed to an inordinate amount of snow accumulation at lower elevations. “This year, the snowpack is inverted,” he says. “The high country has gotten less snow than the low country and, of course, the low country is where all the animals are.”

The unusually deep and long-lingering snowpack on Wyoming’s winter ranges has buried forage like sagebrush and mountain mahogany, leaving deer, antelope, and elk starved for critical nutrition and unprepared to weather prolonged cold snaps. And a lack of wind, which typically sweeps through and scours some hillsides, exposing edible shrubs, has further exacerbated the problem. By most estimates, the conditions have killed ungulates by the tens of thousands.

Adjusting for the Future

According to figures originally published by the Jackson Hole News & Guide, some 50 percent of collared doe antelope in the Sublette Herd have died this winter. In the nearby Wyoming Range, 35 percent of collared mule does, and 95 percent of collared mule deer fawns have succumbed to the winter weather.

The stark statistics have prompted Scurlock and his colleagues to recommend a complete elimination of all doe-fawn tags in the eight hunt units where the Sublette Antlelope Herd resides. The biologists are also recommending that WGFD commissioners reduce buck antelope tags in the Pinedale region by at least 50 percent. Scurlock will make the recommendations at a Commission meeting in Casper scheduled for this coming Tuesday, April 18.

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“We need to eliminate hunting of the reproductive segment of this population and maximize the chances that these animals can rebound,” he says. “We’ll cut 1,225 licenses in the Pinedale region alone. We’re also going to recommend that our Commission delay the antlered opener, at least in the Pinedale area.”