Path of the Pronghorn persists after deadly winter

Only a few miles of sagebrush separated Frances Clark from a herd of roughly a dozen pronghorn that the local botanist and citizen scientist thought she might not see this year, or for years to come.

“I was thrilled,” Clark said of her encounter at Grand Teton National Park on May 23. “I was tremendously relieved that they were there, and there in some numbers.”

Clark’s sighting was one of the first times – if not the first time – that pronghorn were spotted in the park this spring.

Her observation and subsequent surveys by state and federal wildlife biologists have allayed fears that a brutal winter and new respiratory illness would wipe out one of the country’s most iconic migration routes: The Path of the Pronghorn.

By mid-May, starvation and pneumonia had killed every collared animal that took the path in 2022, venturing from the Sublette Pronghorn Herd’s winter ranges in the Upper Green River Basin to green summer pastures in Grand Teton.

While some were expected to make the journey, it wasn’t a guarantee, Wyofile first reported.

“I was worried that no pronghorn would make it back,” park wildlife biologist Sarah Dewey said. “The good news is that some pronghorn survived and migrated back. The memory for that migration is still in the herd.”

Because all the collared animals died, biologists can’t say with complete certainty that the pronghorn in the park made the migration route.

But they’re all but certain that the animals are migrants. Jackson Hole’s winter was severe enough to kill any pronghorn remaining in the valley when snow started falling.

The pronghorns’ return to the park is not, however, without risk.

Wildlife managers aren’t sure whether pronghorn can carry mycoplasma bovis, the respiratory pathogen thought to have killed 1,000 or so antelope near Pinedale this winter.

The question is whether the disease kills infected antelope or whether some can carry the disease and pass it along to other animals.

If the latter is true, state and federal officials wonder if pronghorn migrating to Grand Teton could carry the pathogen with them and spread it to the park’s bison herd, which is roughly 500 animals strong.

“That’s the million-dollar question,” said Samantha Allen, state wildlife veterinarian.

Researchers rarely detect mycoplasma bovis in wildlife.

This winter was only the second time it’s cropped up and killed a significant number of pronghorn in the Cowboy State, the first being 2020 when it claimed the lives of some 450 antelope near Gillette.

It has not been detected in Grand Teton National Park’s bison.

The disease is typically found in cattle, which can carry the pathogen with no clinical signs and aren’t often severely affected.

Infected bison, however, typically contract pneumonia and die.

Reports of the disease in farmed bison have shown that it causes death in up to 50% of infected animals. The fact that some bison have been documented surviving infection is a sign they can carry and transmit the disease, Allen said.

Pronghorn, on the other hand, appear to just keel over when confronted with the biological storm.

“All these pronghorn just seem to be dropping dead,” Allen said.

That’s a bad sign for pronghorn but could be a good sign for park bison. If pronghorn can’t survive long enough to carry the disease with them through the Gros Ventre Mountains, it might not reach the park.

But the Wyoming Game and Fish Department wants to gut check that assumption.

A pronghorn buck that died in Pinedale in May has biologists worried that some pronghorn may be carriers.

Allen said the state wants to sample more “apparently healthy” animals to determine if they’re infected, but asymptomatic.

Park officials, meanwhile, are on alert.

Grand Teton wildlife biologist, Dewey compared mycoplasma bovis to a related bacterium: Mycoplasma ovipneumoniae, which can lead to respiratory disease such as pneumonia in wild and domestic sheep and goats.

Domestic sheep have introduced the bacterium to wild bighorns through intermingling, including in the Gros Ventre mountains, where pneumonia die-offs have caused sheep populations to crater every time they reach about 500 animals.

Dewey doesn’t want to see something similar happen to Grand Teton’s bison herd. Similar die-offs, followed by disease persistence in the bison population could be “devastating,” she said.

“We don’t know exactly how mycoplasma bovis might impact bison, but it is very concerning,” Dewey said. “It is something that we’re thinking about and trying to learn as much as we can about.”

The hope is to prevent the pathogen from being introduced into the bison herd, she said: “We’re trying to avoid that at all costs.”

While research into pronghorn’s potential pestilence plays out, park and state scientists are keeping an eye on the pronghorn that made it back to the park. Like Clark, the botanist, they’re celebrating their return.

However, there aren’t all that many animals to celebrate.

In June, park scientists used a fixed-wing aircraft to fly over the park and count pronghorn in transects, or pre-established plots of land, that were about a half-mile apart.

That survey methodology isn’t a census, meaning it doesn’t capture a picture of all pronghorn in the park. Rather, it’s an annual study intended to gauge whether pronghorn population numbers in Jackson Hole are going up or down.

At this time of year, park officials typically counts about 200 animals. This year, they counted only nine. From other observations, Dewey said there are clearly more animals than that in the park: At least 25.

Aly Courtemanch, Wyoming Game and Fish’s Jackson-area wildlife biologist, has received reports of about 10 near Lupine Meadows, about 25 near Elk Ranch and smaller groups near Antelope Flats.

But, she said, “there’s definitely a striking lack of pronghorn compared to what you normally see.”

How many pronghorn return to the park remains to be seen. Game and Fish typically conducts its ground survey in August, when pronghorn begin to congregate for the breeding season.

In the past few years, biologists have counted north of 500 pronghorn in Jackson Hole – record high totals that include animals in Grand Teton, on the National Elk Refuge and in the Gros Ventre mountains.

Counts later this summer are all but certain to be far lower.

As it stands, park officials have seen three does with fawns.

Pronghorn often have twins. Each of the spindly, ungulate mothers only had one offspring this year. But Dewey said there are likely other animals with young.

“Pronghorn have endured severe winters before, and the population has rebounded,” Dewey said. “It’s really good news that some of the pronghorn made it back and that we have seen some signs of reproduction.”

Dewey said the recent rain will probably help the fawns survive.

“The forage is really abundant, so these animals have an opportunity to put on weight,” Dewey said. “If those fawns survive, it’ll be another generation that makes that migration, and it’ll build back.”

As nature takes its course, Dewey said it’s critical to conserve habitat outside of the park. Game and Fish also has slashed tags for this year’s pronghorn hunt, hoping to give the fecund animals a chance to reproduce.

The Path of the Pronghorn is recognized and protected on the Bridger-Teton National Forest, where it became the first federally recognized migration corridor in 2008.

The state of Wyoming has yet to establish similar protections for the southern reaches of the route, which stretch through gas fields and new suburbs.

“The key is really conserving habitat, and all types of habitat: The movement corridor and the wintering and summer areas,” Dewey said. “If we’re able to do that, I’m optimistic that this herd can build itself back up.”

In the meantime, visitors should give pronghorn space. Grand Teton regulations require people to stay 25 yards or more away from all wildlife, and 100 yards or more away from bears or wolves.

If animals respond when people approach, humans are too close.

“To be able to pack on the pounds to make that migration and be prepared for next winter, they really need to be spending time foraging rather than being vigilant because they feel threatened,” Dewey said.