“Bears are not carnivores in the strictest sense, like cats, they consume a high-protein diet,” said study lead author Charles Robbins, a professor of wildlife biology at Washington State University. “In zoos, whether polar bears , brown bears or sloth bears, it’s been suggested to feed them as high-protein carnivores. When you do that, you’re slowly killing them.”
In separate tests, scientists fed captive giant pandas and sloth bears an unlimited amount of food to observe their preferences and then recorded the nutritional status of their choices.
To gauge pandas’ preference for bamboo, the researchers conducted a feeding study on a pair of animals by collaborating with scientists at Texas A&M University and the Memphis Zoo. They found that giant pandas prefer bamboo stalks, which are rich in protein and carbohydrates, over woody stalks. They sometimes eat almost exclusively bamboo stalks, such as 98% of the time in March. The researchers also examined data from five Chinese zoos where giant pandas had successfully given birth and found that they thrived on a diet high in carbohydrates and low in protein.
In several sets of feeding trials, six sloth bears at the Cleveland, Little Rock and San Diego Zoos were given unlimited avocados, roasted yams, whey andapple. They opted almost exclusively for fatty avocados, eating about 88 percent avocados and 12 percent yams — ignoring apples entirely. This suggests that sloth bears prefer a high-fat, low-carb diet, which may have a similar makeup to their wild diet of termites and ants and their eggs and larvae.
This is also very different from the high carbohydrate diets they are usually fed in captivity. Sloth bears, native to India, typically only live around 17 years in U.S. zoos, nearly 20 years less than the maximum lifespan in human care. Their most common cause of death is liver cancer.
The researchers saw a similar pattern in previous studies of polar bears, which showed that captive polar bears are often fed a high-protein diet that, if given the option, mimics the fat-rich diet of wild polar bears. Polar bears in zoos often die about 10 years earlier than they should, most commonly from kidney and liver disease. Both diseases may be caused by long-term inflammation of these organs, possibly from an unbalanced diet over the years.
The current study, as well as previous research, also showed that when captive bears were given dietary choices, they chose foods that mimicked the diets of wild bears.
“There is of course the long-standing idea that humans with Ph.D.s know a lot more than sloth bears or brown bears. All of these bears started to evolve about 50 million years ago, as far as this aspect of their diet is concerned. , they know more than we do. We were one of the first people willing to ask bears. What do you want to eat? What makes you feel good?” Robbins said.
Robbins, founder of the WSU Bear Center, the only research facility in the U.S. with a captive population of grizzly bears, has studied bear nutrition for decades. He and his graduate students first began investigating their unbalanced diets and observed grizzlies eating salmon in a study in Alaska. At the time, researchers had speculated that the bears would gorge on salmon, sleep, wake up, and eat more salmon.
However, they saw the bears eat salmon, but then wander around, spending hours looking for and eating small berries. Seeing this, Robbins’ lab set out to investigate the diets of grizzlies housed in bear centers and found that they gained the most weight when fed salmon and berries with a combination of protein, fat and carbohydrates.
All eight species of bears, or Ursids, had a carnivorous ancestor, but later evolved to eat a wide variety of foods, giving them the ability to spread to more areas by not directly competing with resident carnivores.
“It just opens up more food resources than just being a direct, high-protein carnivore,” Robbins said.