Expert insights from Tom Stephenson, senior environmental scientist and leader of the Sierra Nevada Bighorn Sheep Recovery Program, California Department of Fish and Wildlife and Dr. Rae Wynn-Grant, co-host of Mutual of Omaha’s Wild Kingdom Protecting the Wild
The Sierra Nevada bighorn sheep is one of the rarest mammals in North America — an endangered subspecies found only in California’s Sierra Nevada, where it lives above 11,000 feet year-round. After falling to about 100 animals in the mid-1990s, the population climbed to roughly 700 by 2015, but then a string of severe winters cut it back toward 350. Today, it stands near 500, sustained by a state-led recovery effort of monitoring, translocation and moving mountain lions away from vulnerable herds. With disease from domestic sheep still the greatest threat, biologists are working to keep the herds growing and return the sheep to their historic range.
Photo courtesy of Sierra Nevada Bighorn Sheep Recovery Program.
Key takeaways
- One of three bighorn subspecies in the lower 48 and the only one built for cold, snowy, high-alpine life, with 60% living above 12,500 feet.
- The population fell to around 100 in the mid-1990s, peaked near 700 in 2015, dropped toward 350 after three severe winters and stands around 500 today.
- Recovery is measured in ewes. The goal is 305 adult and yearling females across 12 herds because females drive population growth.
- The biggest threats are disease from domestic sheep and mountain lion predation on small herds.
- Beyond monitoring and translocation, conservationists are now working to restore the long-distance migration routes the sheep lost.
Quick facts
- Common name: Sierra Nevada bighorn sheep
- Scientific name: Ovis canadensis sierrae
- Size: Adult males (rams) weigh 120-220 pounds; adult females (ewes) weigh 100-155 pounds
- Lifespan: 12-16 years in the wild
- Diet: Grasses, plants and shrubs
- Habitat: Live in the rocky Sierra Nevada mountains at high elevations; 60% live at elevations over 12,500 feet
- Conservation status: Endangered under federal and California law
- Current population: Around 500 as of summer 2026
What makes the Sierra Nevada bighorn sheep unique?
Sierra bighorn sheep are uniquely built for living in an extreme habitat all year long. They have a thick coat that insulates them against the cold. And they eat high-quality forage in the summer that turns into fat reserves to help them survive the winter.
Their wide-flared horns are the easiest way to tell a Sierra bighorn from other sheep. They’re made for the cold, too — kept short and close to the head, so less body heat slips away.
“These are not your typical sheep. They’re agile athletes who survive in the most extreme environments,” said Dr. Rae Wynn-Grant, co-host of Mutual of Omaha’s Wild Kingdom Protecting the Wild.
Why do Sierra Nevada bighorn sheep matter?
Sierra Nevada bighorn sheep matter because they’re the only large mammal that’s in the alpine year-round, providing food for other species and helping cycle nutrients through the landscape as they forage.
But, beyond their ecological role, these bighorn sheep are also an icon of the Sierra Nevada landscape.
“When people go into the mountains, they like seeing the trees and the meadows, but they also like seeing the wildlife that’s there. Sierra Nevada bighorn sheep are kind of an iconic, dramatic species to view, particularly if you get to see them during the rut, when they’re clashing horns,” said Tom Stephenson, senior environmental scientist and leader of the Sierra Nevada Bighorn Sheep Recovery Program, California Department of Fish and Wildlife.
How many Sierra Nevada bighorn sheep are left?
Today, around 500 Sierra Nevada bighorn sheep live in the wild. It’s a remarkable comeback from the roughly 100 that remained before the subspecies was listed as endangered. The key to rebuilding the population? The ewes — female bighorn sheep.
“The mating system in bighorn sheep allows for one male to breed many females. So, it’s really the females that determine how large the population can become,” Stephenson said.
That’s why recovery is measured in ewes, too. The goal is 305 adult and yearling females spread across 12 herds.
What happened in the winter of 2022-2023?
The winter of 2022-2023 brought record snowfall and avalanche activity to the Sierra Nevada mountain range, dealing a heavy blow to the bighorn sheep population. It was the last of three hard winters that pulled the population from a 2015 peak of around 700 down toward 350.
In 2015, every herd unit was occupied, and Stephenson said biologists were even discussing downlisting the subspecies from endangered.
“Sierra bighorn are actually quite good at rebounding from these severe winters — as long as there are some females left in a herd,” Stephenson said.
Despite the setbacks, Stephenson said the loss happened at a manageable moment.
“I’m glad it happened while we were still actively working on a recovery effort, because it means we’re able to adjust and rethink how to move forward,” Stephenson said.
Photo courtesy of Sierra Nevada Bighorn Sheep Recovery Program.
How do biologists monitor the sheep?
Recovering the Sierra Nevada bighorn sheep population starts with monitoring. The recovery team estimates the population size every year through ground surveys and GPS collars that show how rams and ewes move as well as their survival rate.
“A big part of this recovery effort has been to learn as much as we can. Capturing animals allows us to put the collar on, take our measurements, fly it back into its range, release it. It goes on about its business,” Stephenson said.
How does translocation work?
Once the team understands the population size, they’ll move on to translocation — moving Sierra Nevada bighorn from one part of the mountain range to another.
“All of our translocation stock comes from within this mountain range. We’re not bringing bighorn sheep in from other mountain ranges. Since this is a unique subspecies, we want to maintain that genetic uniqueness,” Stephenson said.
Stephenson’s team identifies areas for suitable habitat, using historical data to help inform them.
“We have a lot of information because of pioneering folks like John Muir, who wrote about where they saw bighorn sheep. We’ve even had bighorn sheep melt out of glaciers in the Sierra,” Stephenson said.
Then, the translocation begins.
- A helicopter crew locates a ewe, and specialists called “muggers” fire a net gun to catch it.
- On the ground, the team runs health checks and secures her in a crate.
- The ewe is flown to the new site.
- She’s released at the base of the steep terrain and bolts up into the habitat.
“The nice thing about bighorn sheep is we’re not using drugs, so they’re not disoriented when we release them. We release them right at the base of some steep, rugged terrain that they prefer, and they run up into that habitat,” Stephenson said.
Those steep slopes are home. Having grown up in the wild, they read the cliffs and sense predators on instinct.
“One of the pluses of moving animals that have grown up in the wild is that they’re just much more savvy about that wild environment and what the risks are — whether it’s navigating cliffs or avoiding predators,” Stephenson said.
Photo courtesy of Sierra Nevada Bighorn Sheep Recovery Program.
What are the biggest threats?
The biggest threat to Sierra Nevada bighorn sheep is disease from domestic sheep, followed by predation from mountain lions.
Disease from domestic sheep
In the 1800s, as settlers began to move into the Western U.S., they brought domestic sheep with them, which grazed in the Sierra. These animals carry a respiratory disease that doesn’t harm them but can be deadly to bighorn.
“Bighorn sheep don’t have any natural immunity to the respiratory diseases that domestic sheep have. And it can really decimate herds,” Stephenson said.
By working with land management agencies and private domestic sheep operators, the recovery team has created a buffer between domestic sheep and bighorn sheep in the Sierra so there’s no contact that would lead to an outbreak. With no vaccine yet available, keeping the two apart is the best protection bighorn have. Fortunately, since the time they were listed as endangered in 1999, there hasn’t been a disease outbreak.
Mountain lion predation
Today’s recovery primarily focuses on monitoring predators, namely mountain lions. Mountain lions are native to the Sierra and have always preyed on bighorn. But with bighorn numbers so low, even natural predation can threaten a small herd’s recovery.
“What would otherwise be a natural predation event has an outsized impact when the bighorn population is quite small,” Stephenson said of mountain lions.
The solution? Relocate the mountain lions preying on vulnerable herds — though only some can be moved.
“You can’t really move adult male lions very well because they have a strong homing instinct and they want to come back to their native home range,” Stephenson said.
But females and their dependent young? They’re able to be translocated and survive in a new home.
“We’re able to reduce predation on bighorn sheep by moving the lions, and the lions survive and establish a new home range in a new location,” Stephenson said.
Photo courtesy of Sierra Nevada Bighorn Sheep Recovery Program.
What’s giving researchers hope?
For Sierra Nevada bighorn sheep conservationists, a healthy core population, intact habitat and continued research give them hope for the future of this subspecies.
“We’re learning more every year about bighorn sheep ecology and where they’re successful in surviving and reproducing. Also, we adapt and come up with new management options like translocating mountain lions,” Stephenson said.
One of the areas of focus, Stephenson said, is reestablishing the long-distance migrations bighorn sheep once used.
“I think if we’re going to recover this animal, we have to recognize that when the population got so small, not only did we lose animals, but we lost the memory those animals had. And that memory of how to travel on these migration routes was undoubtedly critical to their survival,” Stephenson said.
Photo courtesy of Sierra Nevada Bighorn Sheep Recovery Program.
Sierra Nevada bighorn sheep frequently asked questions
Are Sierra Nevada bighorn sheep endangered?
Yes. Sierra Nevada bighorn sheep are endangered under federal and California state law.
How many are left?
As of 2026, there are around 500 Sierra Nevada bighorn sheep in the wild.
Where do they live?
Sierra Nevada bighorn sheep live only in California’s Sierra Nevada, where they range above 11,000 feet year-round.
What’s the difference between a Sierra Nevada bighorn and a desert bighorn sheep?
The most distinct difference between a Sierra Nevada bighorn and a desert bighorn is their horns. Sierra Nevada bighorn have wide-flared horns, while desert bighorn have a tighter curl. They also live in different habitats — Sierra Nevada bighorn in the high-elevation alpine, desert bighorn in a lower, hotter desert climate.
Why are domestic sheep a threat?
Domestic sheep carry a respiratory disease that’s harmless to them but deadly to bighorn sheep. That’s why conservationists work to keep the two apart.
The Sierra Nevada bighorn’s comeback is still being written. To see the recovery team in action — the helicopters, the high-country captures, the sheep bounding back into the wild — watch “Saving the Sierra Bighorn” on Mutual of Omaha’s Wild Kingdom Protecting the Wild.
Source:
California Department of Fish and Wildlife. Sierra Nevada. 2026. Accessed August 2026. wildlife.ca.gov/conservation/mammals/bighorn-sheep/sierra-nevada
All photos courtesy of Sierra Nevada Bighorn Sheep Recovery Program.
