It’s not easy to swim 175 km (109 mi.) when you’re starving to death. It’s not easy either to try to survive when you’re shedding body weight at a rate of 1 kg (2.2 lbs.) a day. And it might be hardest—or at least most tragic—of all if you’re a nursing mom and your calorie intake has dropped so low that you can no longer produce the milk you need to care for your young. As a new paper in Nature Communications reveals, all of those challenges and more are facing the world’s polar bears, thanks to vanishing sea ice in our warming world, denying the animals a platform that they need to hunt for seals. If the trend isn’t reversed soon, the estimated 26,000 polar bears in the wild could start to lose their hold on survival before the middle of this century.
The researchers were less interested in establishing the fact of the bears’ food plight; scientists are already aware of that problem. What they were more focused on learning was both how gravely the nutritional loss is affecting the animals’ health and the alternative food sources they’re scrounging for on land. To do their work, the scientists followed 20 different polar bears in Manitoba, Canada, from 2019 to 2022, fitting them with GPS trackers and video collars and periodically tranquilizing them and analyzing their blood, body mass, daily energy expenditure—basically a measure of calories coming in versus calories going out—and more.
“The polar bears in Hudson Bay [Canada] are probably at the edge of the range at which they can survive right now,” says Anthony Pagano, a research biologist with the U.S. Geological Survey and the lead author of the paper. “Most of the modeling work suggests that around 2050, they are going to be on land and away from their primary habitat [on the ice].” The contraction in range of the Hudson Bay community is…
