Bighorn sheep face increasing avalanche dangers as the climate warms

An ominous forecast awaits bighorn sheep in the the Sierra Nevada mountains. There are likely to be more frequent avalanches as the world continues to warm.

Even though a decline in snow cover is anticipated as the climate changes, avalanches could occur more often, particularly at high elevations, which spells trouble for the bighorn sheep that inhabit these areas.

Endangered bighorn sheep and their history

The Sierra Nevada bighorn sheep (Ovis canadensis sierrae) are true survivors, built to handle some of the toughest conditions in North America.

They are smaller and leaner than their relatives, making it easier for them to scale the steep, rocky slopes of the Sierra Nevada at heights of 10,000 to 14,000 feet (3,000 to 4,200 meters). Their tan coats help them blend perfectly into the rugged landscape, keeping them safe from predators like mountain lions.

John Muir, in his 1894 book The Mountains of California, described the “perfect strength and beauty” of these wild bighorn sheep – agile creatures that effortlessly jump from one crag to another.

They have managed to survive threats from diseases and overgrazing by domestic sheep introduced into the Sierra Nevada. But today, these animals are endangered.

Now, a new menace looms in the form of avalanches, coupled with predation by mountain lions. These threats have caused the Sierra Nevada bighorn sheep population to fall by half since 2023.

Avalanches and bighorn sheep

Ned Bair, a researcher from the University of California, Santa Barbara, and his team have run simulations, analyzing the present (1990-2020) and future (2050-2080) climate.

The researchers aim to determine how avalanches might continue to affect bighorn sheep.

“There’s certainly going to be less snow in the future, and it’s going to impact the sheep, which are very fragile as is,” said Bair. “In dry winters, they don’t have enough forage. And in the big winters, they die of starvation and avalanches.”

Bighorn sheep: A struggle for survival

While bighorn sheep also inhabit other western mountain ranges, the Sierra Nevada subgroup is genetically unique. The approximately 350 sheep that remain of this species live at high elevations, feeding on grasses, herbs, and shrubs.

“They like to live in very challenging environments, hence the avalanche problem,” Bair explained.

Snow is critical for bighorn sheep as it provides them with water. However, it can pose threats, too.

Record-breaking precipitation during the winter of 2022-2023 in California led to approximately 18 meters (60 feet) of snow blanketing the Sierra Nevada.

That winter, avalanches led to the deaths of at least 73 bighorn sheep, with just one avalanche accounting for 12 of those deaths, as noted by the California Department of Fish and Wildlife.

Future snowfall in the Sierra Nevada

The researchers conducted projections on future snowfall amounts in the Sierra Nevada under climate change, basing their simulations on precipitation data from past dry years (2013 and 2018) and a wet year (2019).

As expected, snow cover is predicted to decrease generally in the Sierra Nevada in the future. This decline, however, will mostly occur at lower elevations, where snowfall may turn to rain. Higher elevations, where bighorn sheep dwell, will experience less change in snow cover.

As climate change amplifies the number and intensity of California’s atmospheric rivers, these high elevations could even witness an increase in snow accumulation. This snow could trigger more frequent avalanches at high altitudes, resulting in increased bighorn sheep fatalities.

Increased threats to the wild sheep

It remains unclear how the California Department of Fish and Wildlife’s Bighorn Sheep Recovery Program will respond to the rise in avalanches caused by the harsh winters.

Additionally, recovering wolf and mountain lion populations could pose increased threats to the wild sheep.

“It’s a hard population to sustain,” said Bair. “I think there are some real challenges with being assured of at least my children being able to see a bighorn sheep in the wild when they’re my age.”

The research will be presented by Bair at the annual meeting of the American Geophysical Union (AGU24).

Bair presented these findings at AGU’s Annual Meeting.

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