When choosing, captive bears mimic the mixed diets of their wild peers
Pullman, Wash – Bears are not cats or dogs, and feeding them as if it would probably shorten their lives.
A new study in Scientific Reports The diet of giant pandas and sloth bears adds more evidence that bears are omnivores like humans and need far less protein than they are normally fed in zoos.
“Bears are not strictly carnivores like cats are, eating a high-protein diet,” said lead author Charles Robbins, professor of wildlife biology at Washington State University. “In zoos forever, be it polar bears, brown bears or sloth bears, the recommendation has been to feed them as if they were a high-protein carnivore. When you do that, you slowly kill them.”
In separate experiments, researchers presented a captive giant panda and a sloth bear in different US zoos with unlimited foods of different species to learn their preferences, then scored the nutritional profiles of their choices.
In collaboration with researchers from Texas A&M University and the Memphis Zoo, feeding experiments were conducted with a pair of giant pandas to measure their selection of bamboo. They found that giant pandas prefer carbohydrate-rich bamboo cane found in woody stems, over protein-rich leaves. At times, they consumed reeds almost exclusively – eg 98% of the time in March. The researchers also analyzed data from five Chinese zoos with giant pandas that had successfully bred and found, again, a high-carb, low-protein diet.
In groups of feeding experiments, six sloth bears at the Cleveland, Little Rock and San Diego Zoos were offered an unlimited number of avocados, baked potatoes, whey and apples. They chose the high-fat avocado almost exclusively, taking in roughly 88% of the avocado to 12% of the yam — and omitting the apple entirely. This showed that sloth bears prefer a diet high in fat and low in carbohydrates, which may have a similar composition to their wild diet of termites and ants as well as their eggs and larvae.
It is also very different from the high-carbohydrate diet that is usually fed in captivity. Native to India, sloth bears live only about 17 years in US zoos, nearly 20 years short of the maximum lifespan achievable in human care. The most common cause of death is liver cancer.
The researchers saw a similar pattern in previous studies of polar bears that showed that captive polar bears, which are typically fed a high-protein diet, would mimic the high-fat diet of wild polar bears if given the option. Polar bears in zoos usually die 10 years earlier than they should, and they often die of kidney and liver disease. These two diseases can develop from long-term inflammation of those organs, which is likely the result of many years of unbalanced diets.
The current study, along with previous studies, also shows that when captive bears are given food choices, they will choose foods that mimic the diet of wild bears.
“There is certainly an old-fashioned notion that humans with a PhD know much more than just a sloth or brown bear,” Robbins said. “All of these bears started evolving about 50 million years ago, and in terms of this aspect of their diet, they know more about it than we do. We are among the first to ask the bears: What do you want to eat? What makes you feel good?”
Robbins, founder Bear Center WSUIt is the only research institution in the United States with a captive population of grizzlies, and has studied bear feeding for decades. He and his graduate students began investigating their unbalanced diets while studying in Alaska, watching grizzlies eat salmon. At the time, researchers had theorized that the notorious bears would feed on salmon, sleep, wake up, and eat more salmon.
Instead, they saw the bears eating salmon, but then they wandered around and spent hours looking for and eating the tiny berries. Seeing this, Robbins’ lab began examining the diet of center-bear grizzlies and found that they gained the most weight when fed a mix of protein, fat, and carbohydrates in the salmon and berry mixture.
All eight species of bears, or Ursids, had carnivorous ancestors but have since evolved to eat a wide variety of food, giving them the ability to spread over more areas by not competing directly with the resident carnivores.
“It unlocks a lot more food resources than just being a direct, high-protein carnivore,” Robbins said.
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