As safe habitats for polar bears continue to shrink rapidly due to the climate crisis’ impact on polar regions, scientists carried out a study to understand whether these majestic creatures can adapt to new environments.
Over three weeks in summer, Canadian researchers closely monitored 20 polar bears, employing collars equipped with video cameras and GPS to gain insights into their behaviour and energy expenditure when stranded on land.
The results, published in the journal Nature Communications on Tuesday, reveal a grim reality for these creatures as they grapple with the challenges of a changing environment.
Despite the bears attempting various strategies to maintain energy reserves, such as resting, scavenging, and foraging, nearly all of them experienced rapid weight loss, averaging around 1 kilogram, or 2.2 pounds, per day.
This weight loss occurred regardless of whether the bears were actively foraging or conserving energy through extended periods of rest, researchers from western Hudson Bay region of Manitoba, Canada, said.
Charles Robbins, the director of the Washington State University Bear Center and co-author of the study, says adapting to land like their grizzly bear relatives seems unlikey for polar bears.
“Neither strategy will allow polar bears to exist on land beyond a certain amount of time,” Mr Robbins says.
“Polar bears are not grizzly bears wearing white coats. They’re very, very different.”
Some adult male polar bears opted to conserve energy by resting, and burning calories at rates similar to hibernation. Others actively searched for food, consuming bird and caribou carcasses, as well as berries, kelp, and grasses.
Despite this diversity in behaviour, the bears faced a common challenge – the inability to replace the energy-rich fat of seals, their preferred prey, during the ice-free season.
“We found a real diversity of bear behaviours, and as a result, we saw a diverse range of energy expenditures,” Anthony Pagano, the lead author and research wildlife biologist with the US Geological Survey Polar Bear Research Program, said.
Although terrestrial foods provided some energetic benefit, the bears had to expend more energy to access these resources. Even those bears that went for long swims, covering distances up to 175 kilometres, faced challenges in feeding while swimming and bringing their finds back to land.
Only one bear out of the 20 managed to gain weight after stumbling across a dead marine mammal on land, highlighting the difficulty polar bears face in finding sufficient food during the extended ice-free period.
“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 says.
The polar bear population in the area has already declined by an estimated 30 per cent since 1987. Researchers warn that these findings likely extend to polar bear populations across the Arctic, putting them at an increased risk of starvation as the ice-free period continues to grow.