Stone’s Sheep Mysteries

No look at sheep populations can overlook predation. And in this case, predation was the leading cause of death among collared sheep. Wolves were the most frequent killers, but it was the behavior of one particular predator that truly stunned the team.

“We had three separate ewes die within a one-kilometer radius, all from what we believe were wolverine attacks,” Birch said. 

“And all three happened in different years, but in the exact same feature on the landscape, an alpine shelf with cliffs and deep snow below.”

According to Birch, each kill followed a similar pattern. “The wolverine chased them off the ledge, ran them into deep snow where they couldn’t escape, and then killed them. It’s not random but calculated. That predator figured it out and keeps coming back.”

Wolverines are notoriously tricky and tenacious predators but taking down an adult sheep is no small feat. 

“Pound for pound, they’re the most formidable animal in the region,” Birch said. “We’ve actually seen wolverines take down full-grown caribou, too. They use deep snow as a weapon, slowing prey down, wearing them out. They’re incredibly smart and methodical.”

The team suspects it may be the same individual wolverine returning year after year. Precision of the kills and repeated use of the same terrain suggest learned behavior. 

“It’s like that spot has become a trap,” Birch said. “And the sheep, unfortunately, haven’t figured it out.”

The combination of GPS data, survival metrics, and predator behavior is now offering the research team a high-resolution understanding of how these sheep live and die in their environment. It also raises larger questions about how landscape features, changing snow conditions, and predator-prey dynamics intersect in a warming climate.

“This is the kind of thing you only catch if you’re tracking individual animals over time,” Birch said. In a region where nature still rules and surprises abound, each collar, each data point, and each death adds a critical piece to the conservation puzzle.

Seasonal timing and cause of collared Stone’s sheep mortalities from 2022-2024.

Just a few weeks after the March 2025 captures wrapped up, one ewe’s collar alerted to a potential mortality event. A crew was dispatched to the kill site shown above and confirmed that the ewe had been killed by a wolverine,. Other ewes in this area have also succumbed to wolverine attacks. However, no other wolverine predation has been recorded in the range.

Even as body condition improved in some years, another mystery emerged this year: a dramatic drop in pregnancy rates. Only 41 percent of ewes were pregnant in spring 2025, down from a typical 85–90 percent in past years. This was not linked to poor fat reserves, harsh weather, or a lack of mature rams, all of which were within acceptable ranges.

“It caught us completely off guard,” Birch said.  “We found good fat levels, had a mild winter, and observed actually higher than average mature ram ratios. Everything pointed to a healthy reproductive year, but the numbers told a different story.”

Ewes may be prioritizing the survival of existing lambs over investing in new pregnancies, a survival tactic observed in other ungulate populations under nutritional stress. 

“Some of these ewes may be choosing to skip a year to give themselves and their lambs a better shot long-term,” Birch said. “It’s nature’s way of hedging bets when resources, predation pressure, or climate signals are even slightly off.”

This reproductive suppression is an alarming biological signal and highlights the delicate balance these animals are trying to maintain in a rapidly shifting landscape. The team is now modeling variables like ewe age, body condition, and past reproductive history to see what’s driving this decline.
 

Beyond science, the Finlay-Russel project stands as a model for respectful and effective collaboration. 

Involvement of First Nations partners has been instrumental, not only in granting access to traditional lands but also in shaping stewardship goals that reflect the deep cultural significance of these sheep. The Kwadacha Nation and the Tsay Keh Dene Nation, whose territories overlap much of the study area, have been closely engaged in the project’s development and direction from the start. 

The Tsay Keh Dene, known as the “People of the Mountain,” have identified Stone’s sheep as a priority species under their Environmental Stewardship Initiative.

The research team also communicates with neighboring nations, such as the Takla Nation, to ensure transparency and respect across all territories. When burns are eventually carried out, it will be with local knowledge and consent, honoring both ecological and cultural values through joint decision-making and shared conservation goals.
 

By the end of 2025, the project aims to continue data collection, schedule targeted burns for 2026, and possibly put new collars on the sheep to monitor post-burn. This is all part of a deeper commitment to Stone’s sheep WSF pledged in 2024.

“Since the 1960s, when Dr. Valerius Geist did his groundbreaking research on Stone’s sheep, not that much has been done since,” said WSF President & CEO Gray Thornton

“Too much of our conservation efforts are reactionary; WSF aims to stay ahead of the game for this iconic species. To be clear, WSF’s aim, with our provincial partners, is to put more Stone’s sheep on the mountain!”

Stone’s sheep were first described to the scientific world in 1897 by American naturalist J.A. Allen. However, the species owes its name to Andrew J. Stone, an explorer and hunter who documented their distinct appearance during expeditions into the northern Rockies and provided specimens. Stone recognized not only their unique black, white, and gray coloration, but also their remarkable ability to thrive in some of the harshest alpine environments on the continent. Although Stone’s sheep range was explored by Daniel Harmon, Simon Fraser, Alexander Mackenzie, and J.A. Allen , it was not until Samuel Black recorded his observations in 1824 that thinhorn sheep in the Finlay River became known to Europeans. These sheep, however, were well known to First Nation people who inhabited Stone’s sheep country many centuries prior to any European scientist’s early visits. Stone recognized not only their unique black, white, and gray coloration, but also their remarkable ability to thrive in some of the harshest alpine environments on the continent. 

At first glance, the landscape today may appear unchanged from Stone’s time, But the ongoing study is revealing subtle shifts: in forage quality, weather patterns, and predator-prey dynamics. These quiet changes may hold the key to understanding what the future looks like for the sheep that bear his name.