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The three grizzly bears found dead in Grand Teton National Park last month align with typical mortality patterns for the species.
“Unfortunately, we do have several bears that get struck by vehicles every year here in the park,” said Justin Schwabedissen, bear biologist for Grand Teton National Park.
In May, a 5-year-old grizzly was fatally hit by a vehicle inside the park. One week later, two yearling cubs were found dead near Colter Bay, likely killed by an adult male bear. Car deaths are unnatural but they happen every year while predations occur naturally in grizzly populations, Schwabedissen said.
And while discovering the carcasses is rare, he said, the cause of death is not.
Grizzly cubs face high mortality rates, with about 45% of first-year cubs and 40% of yearlings (ages one to four) dying, primarily due to natural causes. About 85% of all documented bear mortalities are human-caused, according to the federal Interagency Grizzly Bear Study Team.
Once grizzlies reach adulthood, mortality rates drop significantly, with less than 10% dying annually. Of these adult deaths, a smaller fraction result from human-related causes, such as vehicle collisions or management actions due to unsecured attractants.
In the Greater Yellowstone Ecosystem, grizzly bear deaths have fluctuated in recent years. In 2023, there were 47 documented grizzly bear mortalities. By late 2024, the number had risen to 65, nearing the record of 69 deaths set in 2018.
To add to ongoing research, interagency biologists started capturing grizzlies in May and will continue through October, part of a decades-long effort to research the threatened species, first listed as endangered in the 1970s. The research captures happen every two to three years in the park.
“We’re focusing on getting some data specific to this area,” Schwabedissen said, via blood and hair samples as well as placing GPS radio collars.
As people flock to bear habitat in warmer weather, the park is urging visitors to drive carefully and secure food and other bear attractants. It’s crucial, he said, in minimizing human-bear interactions and ensuring the safety of both bears and people.
“We just really encourage visitors, local residents, to think about bears and to do their part to protect bears across the Jackson Hole area and across the Greater Yellowstone ecosystem,” Schwabedissen said.
