Brown Bears Far Less Carnivorous Than Once Thought, According to Study

by Jon D. B.
UNITED STATES - 2013/08/27: Brown bear (Ursus arctos) or grizzly in Brooks River near Brooks Falls in Katmai National Park and Preserve, Alaska, USA. (Photo by Wolfgang Kaehler/LightRocket via Getty Images)

As Fat Bear Week roars on, brown bear biologist Charles Robbins is noticing bruins gorging on as many berries as they are salmon.

Each October, the beloved bears of Alaska’s Katmai National Park pack on seemingly endless pounds. Instinct – and a near unlimited supply of salmon in the Brooks River – drives them into hyperphagia: a hyper-feeding frenzy that fattens brown bears up for winter hibernation.

As the gorging commenced, Robbins, a Washington State University wildlife biology professor, studied North America’s northern brown bears. He took careful note of what each bruin took in. And as he found, each bear was balancing out their salmon feast with a whopping “eight hours per day” consuming berries.

During these fruit-feeding times, the bears were completely ignoring plentiful fish nearby. And it turned a few key theories on their heads.

Brown Bears are Omnivores, Not Strictly Carnivores

“Salmon are just loaded with protein. Loaded with energy. A very complete diet. Whereas the berries are a very incomplete diet,” Robbins begins for Alaska’s Anchorage News Daily. “They were working their tails off (to get the berries) and it didn’t make any sense to us.”

ALASKA, UNITED STATES – 2019/08/22: A Brown bear (Ursus arctos) is walking and looking for salmon on a beach along the shore of Lake Crescent in Lake Clark National Park and Preserve, Alaska, USA. (Photo by Wolfgang Kaehler/LightRocket via Getty Images)

Alongside colleagues, Robbins findings led to a new study published in Scientific Reports this fall. The result? Brown bears are not nearly as carnivorous as biologists previously thought.

Like many mammals (including their famously omnivorous black bear cousins), browns prefer – and rely upon – a balanced, omnivorous diet of both meat and plant matter when they can access it. And this is vitally important for bears in conservation-based captivity.

One of the most important results from Robbins study found that browns in captivity will gain the most healthy weight when given access to a combined omnivorous diet. “Bears are not carnivores in the strictest sense like a cat where they consume a high-protein diet,” he explains. “In zoos forever, whether it’s polar bears, brown bears or sloth bears, the recommendation has been to feed them as if they are high-protein carnivores.”

‘When you do that, you kill them slowly’

It turns out this has been wildly misguided, and “When you do that,” Robbins reveals, “you kill them slowly.”

In the case of polar bears – a species so closely related to browns that the two can mate and produce healthy offspring – Robbins found they typically die around 10 years earlier than they should. Most commonly, the cause is kidney and/or liver disease; both of which are telltale signs of malnutrition and an inappropriate diet.

Brown bears (which include their land-locked subspecies, grizzly bears) are harder to study in captivity in the U.S., however. Strict conservation laws do not allow for browns to be held in enclosures. But as the founder of the WSU Bear Center, Robbins has access to the only captive population of grizzlies in America. As a result, he’s studied their diet for decades, and his findings will certainly lead to the longevity of browns in his care.

As with all properly-guided conservation efforts, Robbin’s findings hold crucial information for places hoping to aid wild bear populations, too. This is the end goal, after all. Taking his research at its invaluable word will help national parks like Katmai better preserve what their wild bears need. Instead of placing the focus solely on salmon, parks can now ensure that berries and other foraged plant material are growing in ample portions to support healthy diets.

‘Salmon are super important, but it’s just too much protein.’

Fishing at Brooks Falls – Photo courtesy of L. Law, Katmai National Park & Preserve

“Salmon are super important,” Robbins reiterates. “But it’s just too much protein. They need to mix it with berries.”

As a result, the bear biologist would very much like both the National Park Service (NPS) and U.S. Forest Service (USFS) to “more tightly control commercial berry picking operations,” for a start.

“The whole ecosystem needs to be managed,” he says. Because on their end, brown bears “have the knowledge necessary to make those decisions. They have been evolving for 50 million years making these daily decisions. It just shows they know a great deal more than we knew at the time.”