More and more evidence that bears are not carnivores

Bears are not cats or dogs, and feeding them as they are probably shortens their lives.

A new study in Scientific reports on the diets of giant pandas and sloth bears adds more evidence that bears are omnivorous like humans and need far less protein than they are typically fed in zoos.

“Bears are not carnivores in the strictest sense of the word like a cat that consumes a protein-rich diet,” said lead author Charles Robbins, a professor of wildlife biology at Washington State University. “In zoos forever, whether it’s polar bears, brown bears or sloth bears, the recommendation is to feed them as if they were high-protein carnivores. When you do that, you kill them slowly.”

In separate experiments, researchers presented captive giant pandas and sloth bears at various US zoos with unlimited food of different species to see their preferences and then recorded the nutritional profiles of their choices.

In collaboration with researchers from Texas A&M University and the Memphis Zoo, feeding trials were conducted with a pair of giant pandas to measure their selection of bamboo. They found that giant pandas preferred the carbohydrate-rich bamboo crop found in tree stems to the more protein-rich leaves. At times, they consume almost all of the cultivated plant – for example, 98% of the time in the month of March. The researchers also analyzed data from five Chinese zoos that had successfully bred giant pandas and again found a high-carbohydrate, low-protein diet.

In a series of feeding trials, six sloth bears at zoos in Cleveland, Little Rock, and San Diego were presented with unlimited amounts of avocados, baked yams, whey, and apples. They chose the high-fat avocado almost exclusively, eating roughly 88% avocado to 12% yams and skipping all apples. This indicates that sloth bears prefer a high-fat, low-carbohydrate diet that may have a similar composition to their wild diet of termites and ants, as well as their eggs and larvae.

It’s also very different from the high-carbohydrate diet they’re usually fed in captivity. Sloth bears, which are native to India, typically live only about 17 years in U.S. zoos, nearly 20 years short of the maximum lifespan attainable in their care. The most common cause of their death is liver cancer.

The researchers noticed a similar pattern in previous studies of polar bears, which showed that captive polar bears, normally fed a high-protein diet, would mimic the high-fat diet of wild polar bears if given the chance. Polar bears in zoos usually die about 10 years earlier than they should, most often from kidney and liver disease. These two diseases can develop from long-term inflammation of these organs, potentially caused by many years of a poorly balanced diet.

The current study, along with previous ones, also shows that when captive bears are given dietary options, they will choose foods that mimic the diet of wild bears.

“There’s certainly this long-standing idea that people with PhDs know a lot more than a sloth bear or a brown bear,” Robbins said. “These bears all started to evolve about 50 million years ago, and in terms of that aspect of their diet, they know more about it than we do. We are one of the first who are ready to ask the bears: What are you doing do you want to eat? What makes you feel good?”

Robbins, the founder of the WSU Bear Center, the only research institution in the U.S. with a captive population of grizzlies, has studied bear nutrition for decades. He and his students first began investigating their unbalanced diets during a study in Alaska, watching grizzlies eat salmon. At the time, researchers theorized that the notoriously voracious bears would eat salmon, sleep, wake up, and eat more salmon.

Instead, they saw the bears eat salmon, but then wander off and spend hours finding and eating small berries. Seeing this, Robbins’ lab began studying the diet of grizzly bears housed at the Bear Center and found that they gained the most weight when fed a combination of protein, fat and carbohydrates in a combination of salmon and berries.

All eight species of bear, or Ursidae, had a predatory ancestor, but have since evolved to eat a wide range of foods, allowing them to spread over more areas without competing directly with native predators.

“It just opens up so many more nutritional resources than just being a pure, high-protein carnivore,” Robbins said.