Even Bears Need a Balanced Diet, WSU Study Shows

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Years ago, bear researcher Charles Robbins noticed something strange in Alaska.

The Washington State University wildlife biology professor was studying bears in the fall, a time when large cubs have virtually unlimited access to salmon. Salmon, a fish so calorie and nutrient dense that entire human cultures have flocked around the ocean species.

For bears preparing for hibernation, the annual bonanza of fish is key to piling on the pounds to get through the long winter.

Yet despite all that abundance, Robbins noticed that the bears spent more than eight hours a day eating berries, and during those times were completely unaware of the collapsing fish.

“Salmon is just loaded with protein. Charged with energy. A very complete diet. Whereas berries are a very incomplete diet,” Robbins said. “They were working hard (to get the berries) and it didn’t make sense to us.”

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This several-year-old field observation led to a study published in Scientific reports in September, finding that bears of all persuasions are not as carnivorous as previously believed. Instead, when given the choice, bears prefer a balanced diet. In fact, bears in captivity gained the most weight (a good indicator of health in their case) when fed a combination of protein, fat, and carbohydrates.

“Bears are not carnivores in the strict sense like a cat where they consume a high protein diet,” Robbins said. “In zoos forever, whether it’s polar bears, brown bears or sloth bears, the recommendation has been to feed them as if they were protein-rich carnivores. When you do that , you kill them slowly.

He found that polar bears in zoos typically die about 10 years earlier than they should, most often from kidney and liver disease. Both of these diseases can develop from long-term inflammation of these organs, potentially caused by many years of an unbalanced diet.

Robbins, the founder of the WSU Bear Center, the only research institution in the United States with a captive grizzly bear population, has studied bear nutrition for decades. Although his research did not look directly at black bears, the most common bears in eastern Washington and northern Idaho, he said that when they are able, black bears eat a almost identical diet to grizzly bears (brown bears are grizzly bears that live in coastal regions of Alaska).

The research has clear implications for zoos, but it could also influence the management of wild bears in the western United States, Robbins said. In most discussions of the needs of wild bears, salmon dominates the discourse. While salmon is certainly an integral part of a bear’s diet, Robbins pointed out that his research shows that berries, especially blueberries, are almost as necessary.

“Salmon is super important,” he said. “But it’s just too much protein. They have to mix it with berries.

He would like to see the US Forest Service more closely monitor commercial blueberry picking operations. Commercial blueberry picking is not permitted on Forest Service land, but there is an obscure industry that supplies restaurants and stores with gallons of blueberries during harvest season. Blueberries have not been grown successfully.

Seen in a broader context, Robbins said his research shows that “the whole ecosystem needs to be managed”.

“They have the knowledge to make those decisions,” he said of the bear’s food choices. “They’ve been evolving for 50 million years making these daily decisions. It just goes to show that they know a lot more than we knew back then.

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