Alpine antelope

ABSAROKA RANGE—Clusters of pronghorn scattered and slipped from sight as Andy Pil’s white U.S. Forest Service pickup truck rumbled up the rough road. 

That avoidant behavior is normal for pronghorn. But the geographical features the animals fled to for cover — mountain ridgelines and deep gullies — were out of the ordinary. The pronghorn in question that early August day were living high in the Absarokas — at between 10,000 feet and 11,500 feet of elevation, higher than any others in Wyoming and, potentially, the world. 

It wasn’t just pronghorn that seemed out of place. As Pils, a Shoshone National Forest wildlife biologist, crept his pickup down the rocky two-track road, a group of about 20 sage grouse waddled away. All around, hoppers scattered, too.

“I’m sure these sage grouse are chowing down on these grasshoppers,” Pils said.

As for what the pronghorn are eating, nobody knows. Other than tracking their movements, there’s never been an in-depth study, and there’s little in the way of scientific literature on the ecology of alpine-dwelling Antilocapra americana. 

“I wouldn’t even speculate if it’s forbs or grasses, or something else that they’re getting into,” said Hall Sawyer, a biologist for the Western Ecosystems Technology who studied the herd’s movements for the Wyoming Game and Fish Department. “But it’s a completely different diet than they would have anywhere else. 

“All we got from the study is, we pinned down some of the movements,” he added. “In terms of their life history and how that herd operates, most of it’s still a big mystery.” 

In some ways, it makes sense that sage grouse and pronghorn have made their summer homes on the eastern alpine front of the Absaroka Range. The heart of their uncharacteristic high-elevation habitat, around Francs Peak, Phelps Mountain and Carter Mountain, is arid, which has kept trees at bay and sightlines open — conditions that both plains species require. 

“Visibility is good,” Sawyer said. “It does look like you’re just on the high plains, except you’re at 12,000 feet.” 

Wyoming Game and Fish wildlife biologist Bart Kroger concurred. This swath of the wide-open Absaroka range, he wrote in an email, is “ideal” for pronghorn’s evolutionary strengths: “Excellent eyesight and running.” 

“In most cases these pronghorn can freely move from low elevation to the high elevation, and back again, without ever having to traverse through tree cover or rocky/talus slopes,” Kroger wrote. “These high-alpine plateaus also support a much more lush vegetative community for pronghorn to use as forage throughout the summer period, whereas the lower elevation habitats may dry up by early August.”

Kroger, his wildlife management colleagues and Sawyer do have some insights into the high-elevation pronghorn. Portions of both the Fifteenmile and Carter Mountain pronghorn herds head for 10,000-foot-plus slopes come summer. Based on Sawyer’s study, which tracked 118 individual adult female pronghorn from the Carter Mountain Herd, about 10% of the animals in the region engage in the “crazy migration” to the high country.

“We’re talking about hundreds of animals that do that,” Sawyer said.

Generally, pronghorn that utilize high-elevation habitat, like those from the Carter Mountain and Fifteenmile herds, are faring better than those restricted to low-elevation desert year-round, Kroger said. Wildlife officials estimated there were 388,500 “speed goats” in drought-ridden Wyoming at last count, about 9% below Game and Fish’s population goal. 

But pronghorn from the Fifteenmile herd that make a mountain living also struggle to reproduce relative to their lower-elevation counterparts. Kroger, the state biologist, said he typically sees about 25% fewer fawns alongside does dwelling above 8,000 feet. The benefits of lusher late-summer vegetation, he said, might be outweighed by high-elevation realities: exposure, harsher weather and more predation. 

“Having a fawn at 10,000 feet compared to 7,000 feet the first week of June,” Kroger said, “can be significant.”   

Nevertheless, the Fifteenmile and Carter Mountain pronghorn’s miraculous migration to the Absaroka high country goes on. From Bighorn Basin winter range they travel as far as 60 miles, gain 6,000 vertical feet, duck under fences and brave highway traffic — all to go somewhere pronghorn aren’t supposed to go.

“You can look at any natural history book or literature on pronghorn life history, and 11,000 foot alpine plateaus are not considered pronghorn habitat,” Sawyer said. “That’s what makes it so cool.”