On a Tuesday in early August, Brandon Scurlock received the second notification in as many days that one of the 50 GPS-collared pronghorn he’s been monitoring died.
An old female, PH143, had keeled over in the willows along the receded shoreline of Big Sandy Reservoir.
“It was a whole carcass,” recalled Scurlock, the wildlife management coordinator for the Wyoming Game and Fish Department’s Pinedale Region. He phoned the state’s Wildlife Health Lab for some guidance.
There was no sign of epizootic hemorrhagic disease, a midge-spread and sometimes devastating ungulate killer that tends to flare up during periods of drought. And there was no sign of internal bleeding or injury.
“I wasn’t too concerned,” Scurlock said. “Pronghorn die.”
Cracking open the mature doe’s femur, he gained some insight about why. In a healthy animal, the marrow within would be off-white and firm. Instead, it was red, gelatinous and “pretty nasty.” It was an indication that PH143 was in rough shape.
Two days later, the collar from another marked pronghorn transmitted a mortality signal, this one clear across the Green River Basin in the embattled Dry Piney Creek drainage.
“We started to think something might be going on,” Scurlock said.
By Sept. 13, a seventh collared pronghorn had died. Overall, 14% of the tracked animals in the ballyhooed Sublette Pronghorn Herd perished in the span of six weeks. One doe even took her last breaths in an irrigated alfalfa field.
Even though the animals died at a time of year when ungulates are typically in good shape and readying for winter, malnutrition is the suspected primary cause for the rash of deaths.
“Interestingly, all seven of those individuals were non-migratory,” Scurlock said. “I think that’s a poor strategy this year: To basically live [all year] on the winter range.”
Notably, 88% of pronghorn in the Sublette Herd are either migratory or nomadic, according to the U.S. Geological Survey’s migration database. Only 12% of the population resides in the same spot year-round. Yet this summer they accounted for 100% of the unusual deaths.
One explanation is that the vegetation in those low-elevation areas is especially parched. Coming off the warmest, least-snowy winter in the state’s history, with record late-summer heat all across the region, plant growth was bleak.
Surveying the antelope bitterbrush plant in the Prospect Mountains — not far from where Scurlock found PH143 dead near Big Sandy — Game and Fish terrestrial habitat biologist Troy Fieseler found “large-scale mortality” of the important winter browse species, with up to 90% of the shrubs dead in places.
“He measured basically zero growth on bitterbrush leaders,” Scurlock relayed.
On live plants in the hardest-hit areas, fresh leaders that sprouted this summer averaged just over a quarter inch — just 10% of the average growth.
“And it started defoliating a couple weeks ago,” Scurlock said of the bitterbrush. “Pretty rough shape.”
It’s no secret that record heat and widespread drought has wreaked havoc on Wyoming ecosystems and their inhabitants. Although the extraordinarily mild winter had some positive effects for wildlife like elk, there’s been significant fallout. The heat and aridity has hindered fire scar recovery, led to “unprecedented” black bear conflicts and triggered emergency orders for livestock.
There are some silver linings and bright spots.
Although wildfires burned more than 63,200 acres of Wyoming through late September, that’s just a fraction of the acreage that ignited during 2024 (810,000 acres, second most ever) and 2025 (250,000 acres).
And there have not been any major outbreaks of wildlife diseases that often correlate with drought.
“Going into the summer, as dry as it was, I anticipated to see more [epizootic hemorrhagic disease] outbreaks, but so far we’ve only had one, southeast of Lander,” Deputy Chief of Wildlife Martin Hicks told the Game and Fish Commission last week in Evanston.
Hicks also presented some promising data on the productivity of Wyoming’s pronghorn. Biologists and wardens surveying the state’s herds tallied more than 60 fawns per 100 does, a ratio that exceeds the five-year average.
“If you would make me wager a bet, I would have lost that bet,” Hicks said, “because I thought for sure our fawn production would significantly decrease.”
Even within the Green River Basin, there has been a mixed bag of impacts. Scurlock spent last weekend helping staff a hunter check station, and the migratory mule deer coming out of the Wyoming Range were looking plump and healthy, with good antler growth.
“Tons of body fat on them, but I think they’re going to need it this winter,” Scurlock said. “There’s not going to be much to eat.”
