Western Hudson Polar Bear

Polar bear on land in Western Hudson Bay region (Credit: David McGeachy)

PULLMAN, Wash. — Polar bears are facing an unprecedented risk of extinction due to their inability to adapt to the lengthening summers in the Arctic, a recent study warns.

Inhabiting Arctic regions such as Canada, Alaska, Russia, Greenland, and Norway, polar bears primarily spend their lives on sea ice. This environment is crucial for hunting, resting, breeding, and raising their young. The extended periods these iconic animals spend stranded on land significantly increase their risk of starvation, scientists explain.

Researchers, who published their work in the journal Nature Communications, observed 20 polar bears over three summer weeks, documenting their attempts to preserve energy reserves through resting, scavenging, and foraging. Despite their efforts, the majority experienced rapid weight loss, shedding an average of about 2.2 pounds per day.

Just like in the United States, summer in the Arctic spans from June through August. However, climate studies project that global warming is making the hottest season of the year a little longer every year.

There has been speculation that polar bears might adjust to longer ice-free seasons caused by climate warming by adopting behaviors similar to their grizzly bear relatives, either resting more or consuming terrestrial food. However, the polar bears in this study employed both strategies with minimal success.

Still taken from video captured by a polar bear collar used in the study.
Still taken from a video captured by a polar bear collar used in the study. (Credit: U.S. Geological Survey and Washington State University)

“Neither strategy will allow polar bears to exist on land beyond a certain amount of time. Even those bears that were foraging lost body weight at the same rate as those that laid down,” says Dr. Charles Robbins, a co-author of the study and director of the Washington State University Bear Center, in a media release. “Polar bears are not grizzly bears wearing white coats. They’re very, very different.”

Adult male polar bears can reach lengths of 10 feet and weigh up to 1,500 pounds, in contrast to the grizzly bear’s eight feet and 800 pounds. Polar bears depend on the high-fat content of seals, which they most effectively hunt on the ice.

To gain insights into polar bear energy usage and behavior when land-bound, researchers equipped them with collars featuring video cameras and GPS. This setup tracked their activities in Manitoba’s western Hudson Bay region during the summer, a time when their preferred seal prey was inaccessible.

“We found a real diversity of bear behaviors, and as a result, we saw a diverse range of energy expenditures,” says Dr. Anthony Pagano, the study’s lead author and a research wildlife biologist with the U.S. Geological Survey Polar Bear Research Program.

He notes that while many adult males conserved energy by lying down, others actively sought food, consuming items like bird and caribou carcasses, as well as berries, kelp, and grasses.

Polar bear from the Western Hudson Bay region
Polar bear from the Western Hudson Bay region (Credit: David McGeachy)

The study, which took place in the western Hudson Bay — where climate warming is believed to affect polar bears more rapidly than in other Arctic areas — highlights the critical threat of starvation facing polar bears as the duration of ice-free periods increases. Since 1987, the polar bear population in this area has declined by an estimated 30%.

“As polar bears are forced on land earlier, it cuts into the period that they normally acquire the majority of the energy they need to survive,” Dr. Pagano explains. “With increased land use, the expectation is that we’ll likely see increases in starvation, particularly with adolescents and females with cubs.”

StudyFinds’ Patrisha Antonaros contributed to this report.

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