How do polar bears eat when there's no sea ice? Not well, study finds

For polar bears, summertime is definitely not when the living is easy.

They are apex predators, mighty hunters, and as Inuit and research scientists have long known, they prefer a good fatty meal of seal, caught from the sea ice.

But during the times of the year when there is no sea ice — and those times are getting longer, due to human-caused climate change — pickings are much more meagre.

In a new study published Tuesday in Nature Communications led by the U.S. Geological Survey (USGS), scientists used GPS tracking, video collars, blood chemistry and other data to track the lives of 20 polar bears over three summer weeks near Churchill, Man.

Some bears, as expected, stayed on land and did very little, conserving energy and living off fat reserves, almost like hibernation.

Others scrambled for food, foraging for berries and plants, chomping on antlers or birds — or in the case of one three-year-old female, swimming a remarkable total of 175 kilometres in the cold waters of Hudson Bay, stopping to rest on a beluga carcass that she briefly tried to eat.

An impressive range of tactics, but nevertheless, nearly every bear lost weight — an average of about a kilogram per day.

"What we found was that they had all these different behaviours and a lot of energetic strategies and none of that was able to prevent weight loss," said co-author Karyn Rode, a research wildlife biologist with the U.S. Geological Survey's Alaska Science Center who has studied polar bears for more than 25 years.

"What our study was really getting at was what are the limitations to polar bears' ability to adapt." 

Polar bears do have a reputation as resilient creatures, adaptable or even opportunistic as predators.

In a 2022 report from Polar Knowledge Canada, Inuit knowledge keepers from the Nunavut communities of Pangnirtung and Kimmirut shared how bear movements change without ice.

"When the sea ice is formed the bears are out on the ice more. When the ice is gone you cannot tell where the bears are," said Joe Arlooktoo of Kimmirut in the report, noting it depends on where their prey is.

The new study was inspired in part by observations from Arctic communities, said Rode. Those observations prompted the scientists from USGS, Washington State University and Environment and Climate Change Canada (ECCC) to quantify those movements, in terms of energy and food intake.

The tracking only lasted about three weeks for each bear, during August and September of 2019, 2021 and 2022.