Diet Woes: Will Polar Bears Make It? 

By Alyssa Olmeda & Carina Storrs

No other animal seems more threatened by climate change than polar bears. Will these icons of the Arctic be able to adapt their diets to survive in their rapidly transforming environment?

For a long time polar bears were thought of as fleecy, large white bears that thrive on the ice in the Arctic. However, just about no other mammal is more threatened by climate change than polar bears, as climate change continues to take a toll on their environment and access to food. 

With detrimental changes to their environment, we are left with this question: Will polar bears become extinct as a result of the melting of glaciers and sea ice that are making prey harder to come by?

Polar bears are hypercarnivorous bears that spend the bulk of their time hunting seals on the sea ice. As hypercarnivores, their diet is more than 70% meat and the rest non-animal foods such as fungi and fruits. 

According to Andrew Derocher, PhD, a professor of biology at the University of Alberta in Edmonton, Canada, and longtime scientific advisor to Polar Bears International (PBI), ringed seals are the dominant part of the bear’s diet. Polar bears catch these seals when they are around the sea ice to raise their young. However, there are at least eighty other species in their diet, ranging from mushrooms to insects to berries to porcupines. “If it moves and it is edible, polar bears will eat it,” says Derocher.

With dwindling sea ice and fewer seals, polar bears may be able to shift their diet to more of these terrestrial foods. But it will not be easy to entirely forgo seals. Earlier this year, a study estimated that it would take 1.5 caribou, 74 snow geese, 216 snow goose eggs, or—an even more impossible number—3 million crowberries to equal the calories in one adult ringed seal.^[i] 

Although some individual polar bears within the numerous populations across the Arctic (there are 19 populations total), may be able to get by with these diet swaps, there will not be enough of these other sources of energy to sustain an entire population, Derocher says. 

Thinking about the sheer quantity of all the other types of foods polar bears would have to eat to make up for seals “gives us a sense of the magnitude of the problem that the animals are facing,” says Terrie M. Williams, PhD, director of the Center for Marine Mammal Research and Conservation at University of California, Santa Cruz, who carried out the calculations with a colleague. 

Even if some individual polar bears do succeed at shifting their diet and finding enough alternative food sources, they may face another, even greater challenge. The guts of polar bears may have to adapt to be able to extract the calories they need from vegetables as well as fat and protein. Meeting this challenge may require their intestines to get longer, perhaps more like those of the brown bears they evolved away from hundreds of thousands of years ago, and the microbiome may have to shift toward gut bacteria that are better at digesting plants. “It’s the limiting factor,” Williams says. “The supposition is that polar bears, because they are an ursid [bear], will quickly be able to adapt…but we have no idea.” 

Ultimately enough individual polar bears will have to find sufficient food sources, and perhaps undergo gut adaptations to digest high quantities of those foods, in order to reproduce and get to the next generation, Williams says. 

It may be that polar bears transition to an entirely new kind of animal in 10 or 20 years. In addition to changing their diets and guts, the type of fur and amount of insulating fat might change in response to the warming Arctic, Williams notes. She adds that “at one level, it is exciting science, it’s like how fast can an animal adapt. [But] if they do not do it, it’s going to be really sad.” 

On a high, yet also low, note, not all populations of polar bears have been affected equally so far. Derocher found that the population in the Hudson Bay area of the Arctic has stabilized lately, after years of decline, while other locations such as the Beaufort Sea have been severely affected. Most of the Bering Sea population, where Derocher previously worked, doesn’t exist anymore. 

^[i] https://pubmed.ncbi.nlm.nih.gov/33627459/

Process

Alyssa and Carina are both very interested in the environment and science. Alyssa is especially interested in marine biology—it might be her major in college! The idea for this piece came about during a pair session when we were wondering what has been going on lately with polar bears. We decided to explore this question in a news story because Carina is a science journalist and Alyssa wanted to try out writing in a journalistic style. We started looking into research studies, and found a couple great experts to chat with who had done some of those studies. We learned that there are still at least as many questions as there are answers!