A first-of-its-kind bighorn sheep study hopes to offer answers to an iconic Wyoming herd’s slow demise

A first-of-its-kind bighorn sheep study hopes to offer answers to an iconic Wyoming herd’s slow demise


Almost 2 million bighorn sheep once roamed the West’s mountains. They moved in waves so thick early explorers could hardly count their numbers. They provided endless food for Native Americans and settlers.

Until they didn’t.

By the late 1800s and early 1900s, only about 25,000 sheep likely occupied the western U.S. and Canada. No one knew exactly how many bighorn sheep lived in Wyoming before western expansion – it was likely in the hundreds of thousands – but by 1960, only about 2,500 remained.

Of the few remaining herds in the state, one stood out to biologists and land managers as worth protecting. The Whiskey Mountain herd, as it was called, summered high in the Wind River Range before wintering outside of Dubois in red cliffs and rolling foothills.

It only had about 500 animals remaining in the ‘40s, but biologists and land managers had a plan. They used wildfire, prescribed burns, seeding and fertilizer to maintain and improve the habitat, and by the 1970s, about 2,000 could be counted.

“I’ve watched it ever since I was a child, and I turn 65 this summer,” said Lynn Stewart, a Dubois taxidermist, hunter and former bighorn sheep hunting guide. “For the town of Dubois, it was such a drawing card for traditional hunters and nonhunters alike. It’s been there forever.”

It was a success by all measures. So much of a success, in fact, that Wyoming’s Whiskey Mountain sheep were sent everywhere from the Bighorn Range to Nevada and Oregon as a way to boost regional numbers and keep the local herd sustainable.

Then in 1991, a die off hit.

Numbers crashed, and they haven’t come back.

A big part of the reason is “abysmal” lamb survival, said Kevin Monteith, an assistant professor at the University of Wyoming. And it’s a problem Monteith and two graduate students, working closely with Game and Fish and others, hope to solve.

This spring marks the halfway point in a six-year study comparing the iconic Whiskey herd with others in Jackson and Cody as a way to see if the underlying issue could be disease, poor food quality, predators, some combination of the three or an unknown factor altogether. A team of biologists will spend June racing to find newborn lambs, placing tracking devices on their necks and then recording the cause of their probable demise.

The answer, if the team can find one, could not only help the Whiskey Mountain herd, but perhaps many other struggling herds across the West.

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For an animal that makes its living in some of the state’s harshest, highest climates, bighorn sheep are surprisingly susceptible to health issues, mostly non-native pneumonia pathogens.

Their numbers historically shrank because of market hunting and habitat loss, but it was pneumonia-causing bacteria that proved to be the death knell for many of the herds, said Steve Kilpatrick, executive director of the Wyoming Wild Sheep Foundation.

Domestic sheep typically carry the pathogens, and they pass them to bighorn sheep through nose to nose contact. Once in a herd, the disease often spreads quickly, causing healthy adults and lambs to keel over.

The Whiskey herd’s history – growing, healthy populations followed by a sudden die off and difficult time recovering – is not unusual among herds in the West. It also seems to be perhaps something more than just disease.

That’s why a coalition including Game and Fish, the sheep foundation, the Wyoming Governor’s Big Game License Coalition, the Wyoming Wildlife Natural Resource Trust are working to raise $1.3 million to pay for the project.

The first three years focused on issues such as the possibility of not enough food or poor food quality, particularly as they related to disease. The second three years begins now, and will look mostly at lambs while also comparing the herd to bighorn sheep in Jackson and Cody that seem to be faring better.

“The vast majority of the lambs we capture and collar we suspect will die, and we want to know when and from what they are dying,” Monteith said. “It’s a big missing gap at the moment. We know that pregnancy rates are high. They are putting lambs on the ground, they’re not just making it back to winter range with them.”


On its surface it sounds simple: Figure out when, where and why lambs are dying.

The logistics of that, however, are a bit more complicated.

Bighorn sheep lambs are born able to walk in remote mountain meadows. Within a few days they can travel distances with their moms and have likely moved on. They weigh about as much as a human infant – usually 7 to 9 pounds at birth.

No study in Wyoming has ever been able to successfully examine lamb survival because of the expense and logistics of working with wildlife in such remote areas.

Until now.

Ewes were captured in late winter as part of the project, and fitted with GPS collars and an internal transmitter. When an ewe gives birth, the transmitter pings her collar and lets Monteith’s graduate students – Rachel Smiley and Brittany Wagler – know where the lamb was born.

They then have less than two days to trek thousands of vertical feet through rugged Wind River country to find the lamb before it and the mother move on.

Processing lambs can take about 15 minutes, at which point it generally rejoins the mother and eventually heads onto summer range.

From there biologists wait to see if the lamb lives. As few as five lambs per 100 adults survive to adulthood in the Whiskey Mountain herd. Wildlife managers would like to see that at 30 lambs per 100.

“What’s happening on summer range, we don’t know, whether poor nutrition or pneumonia we don’t know,” said Greg Anderson, Game and Fish’s wildlife biologist in the Lander region.

Researchers hope the overall study, which includes detailed examination of habitat sections in the Jackson and Whiskey areas, body fat and health measurements of ewes, and the lamb work, will result in an answer.

“A lot of people are barroom biologists who theorize,” said Stewart, the Dubois taxidermist. “But at this point, it’s up to science to figure it out, and hopefully it can.”


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