Editor's note: This story has been updated to add more information from the National Park Service and observations from a bear biologist.
Fans of a prominent female grizzly in Grand Teton National Park were shocked and saddened when two of her cubs were apparently killed and cannibalized by a large male bear.
While brutal, it’s what male bears do.
The carcasses of two yearling grizzly cubs were found early Tuesday about 250 yards apart in a closed area of the park south of Colter Bay, the National Park Service reported Wednesday.
The carcasses showed signs of “depredation by a larger bear,” NPS reports.
The dead cubs were apparently the offspring of Grizzly 1063, who emerged from hibernation with three yearling cubs this spring.
She’s thought to still have a yearling cub after two were found dead, but the whereabouts of that cub were unknown as of Wednesday, NPS reported.
A Brutal Part Of Nature
Wildlife photographer Jeff Plumb had been watching Grizzly 1063 and her cubs over the weekend, and told Cowboy State Daily that he was heartbroken to learn that two of the cubs have been killed.
It’s a brutal reality that big, male grizzlies sometimes kill cubs that aren’t theirs in hopes of impregnating the females with their own offspring, Plumb noted.
“She came out Sunday night just past Colter Bay,” he said regarding the last time he’d seen all three cubs.
“That’s so sad. The male grizzlies want to put the female back in heat, and the only way to do that is to do away with the cubs,” Plumb added.
NPS bear biologist Justin Schwabedissen likewise said in an agency statement that large grizzly boars (male bears) will occasionally kill cubs.
“While it is incredibly sad to see a grizzly bear lose its cubs, depredation by other bears is a natural source of cub mortality in the Greater Yellowstone Ecosystem and has previously occurred in Grand Teton,” he said.
The U.S. Geological Survey’s Interagency Grizzly Bear Study Team has tracked and reported grizzly mortalities in the Greater Yellowstone area for years.
A spreadsheet from the team tallying grizzly deaths from 2015-2023 notes several instances of cubs being killed by other bears.
‘Devastating’ Loss
Plumb said he had developed a sense of connection with Grizzly 1063 and her cubs.
“I was just hanging out with her. Being a new mom, she was just trying to figure stuff out. Comparing her to 399’s quads, I thought hers came out bigger than these ones,” he said, referencing world-famous Grizzly 399’s 2020 litter of quadruplets.
“They were healthy, rambunctious and just wrestled all the time over food for stuff, running around and loving life,” Plumb said of Grizzly 1063’s two cubs that were killed.
He said he’s “devastated” by the loss.
“It’s part of nature, but you enjoy watching their story and watching them grow up,” Plumb said. “It’s heartbreaking. The thing about doing wildlife photography, when you put them in your lens, there’s a connection.”
He said he likes to watch bears and catch photos of them as they emerge from winter hibernation.
“I love watching their behavior, and it’s hard not to think about human emotions while watching them,” he said.
Plumb said he hopes that Grizzly 1063’s third cub survives and thrives.
“Now she’s got to be protective of that one,” he said. “I think I had heard somebody say this was her first group, the first set of cubs she’s ever had.”
Double-Edged Sword For 399, Her Offspring
Grizzly 399 also lived in the Grand Teton area and raised numerous cubs there.
She became famous because she was highly visible, frequently appearing near highways with her cubs, and drawing adoring throngs of fans.
Bear experts surmised that was a deliberate move on Grizzy 399’s part to protect her cubs from marauding male grizzlies.
She took her cubs into places crowded by humans, because large boars were hesitant to go to such spots, bear biologists said.
While that might have protected her cubs from being killed and devoured by boar grizzlies, Grizzly 399’s fans worried that put her and her cubs in danger of being struck by vehicles.
Those fears were realized in October 2024, when Grizzly 399 was hit and killed by a vehicle south of Jackson.
Roughly a year earlier in October 2023, one of Grizzly 399’s grown offspring, Grizzly 610, was stuck and injured by a semitruck along a stretch of U.S. Highway 89 near Grand Teton.
Grizzly 610 languished by the roadside for hours while her own cubs watched from a distance. But she later got up and walked away, and has since apparently fully recovered.
Tragedy struck Grizzly 399’s linage again earlier this month. Grizzly 1058, a 5-year-old male and one of her 2020 quadruplets, was hit and killed by a vehicle along Highway 26 inside the park.
Objections Raised About Hazing Bears
In the wake news the cubs’ deaths Wednesday, social media was lighting up with objections from some wildlife photographers and other bear advocates claiming that NPS hazing Grizzly 1063 and her cubs might have led to the cubs’ deaths.
They claimed the hazing might have caused the mother grizzly to become separated from her cubs long enough for a male bear to kill the cubs.
Grizzly 1063 and the cubs had been hazed away from “developed and residential areas at Colter Bay,” NPS reported.
“In accordance with park policy, staff hazed the bears when they lingered in these areas or remained immediately adjacent to nearby roadways,” NPS stated.
The agency claimed the hazing didn’t lead to the mother and cubs becoming separated. But instead, an aggressive male bear might have separated them.
“Each time hazing was deemed appropriate and implemented, GB1063 and her cubs remained together,” NPS stated.
“Based on observed behavior and evidence, it is likely that a male grizzly bear in the area led to the separation of the yearlings from GB1063 and was responsible for the depredation,” according to the agency.
‘More Questions Than Answers’
Retired federal ecologist Chuck Neal of Cody, who has studied grizzly behavior for decades, said it’s “not unusual” for male grizzlies to kill cubs. But it also doesn’t happen frequently.
What makes this case “beyond unusual and bordering rare” is that two yearling cubs were reportedly killed, he said.
In most cases of male grizzlies killing cubs, it’s cubs-of-the year that were just born that spring, he said.
“A yearling bear can run” from a male grizzly, and “not just stand there and squall for its mother they way a cub-of-the-year would,” he said.
The fact that more than one yearling was apparently killed make the incident even more perplexing, Neal said.
Was The Female In Heat?
“Is the park certain that the young bears were killed by the adult male bear or were they just scavenged when another bear came through the area and found the bodies?” he said.
“Something held the young bears in a vulnerable location in order to explain this ‘predation,’" Neal added.
Grizzly 1063 coming into estrus (coming into heat, ready for mating) might have been a factor, he said.
"Mid-May is the beginning of female bears coming in estrus which will attract adult males," he said. "But the particular mother still had her yearlings with her and normally would keep them with her through the remainder of the year before coming into estrus next spring.
“That could explain the young being confused and acting in vulnerable manner But this mother should not have been in estrus. Was there premature estrus?”
The incident seems to raise “more questions than answers,” he said.
Mark Heinz can be reached at mark@cowboystatedaily.com.
