Polar bears are struggling to survive longer summers, and unlikely to adapt

In a concerning revelation, a recent study reveals that polar bears may not have the capacity to adapt to the increasingly longer summers caused by climate change.

The research indicates that spending more time stranded on land puts polar bears at risk of starvation.

Over a three-week period during summer, scientists observed the behavior of 20 polar bears stranded on land in the western Hudson Bay region of Manitoba, Canada.

These bears were deprived of their primary food source, seals, which are more readily available on ice. 

Declining sea ice and longer summers

“The Arctic marine ecosystem is experiencing rapid declines in sea ice extent, age, and thickness, which are altering ecological dynamics. Within this ecosystem, polar bears (Ursus maritimus) are an apex predator that use sea ice as a platform to hunt primarily ringed (Pusa hispida) and bearded seals (Erignathus barbatus),” wrote the study authors. 

“Polar bears acquire the majority of their energy resources during a brief period in the late spring and early summer when seals are giving birth to and weaning their pups. Climate warming is increasing the duration that some areas of the Arctic are ice free, which in turn forces polar bears in these regions to move to land.”

Stranded polar bears

In Manitoba, the bears experimented with various strategies to conserve energy and find food. They engaged in resting, scavenging, and foraging.

Despite these efforts, the outcome was disheartening: nearly all of the observed polar bears experienced significant weight loss, averaging about 2.2 pounds per day.

The study challenges the notion that polar bears might adapt to the changing climate by mimicking the survival tactics of grizzly bears, which can survive on a more varied diet and are more accustomed to terrestrial living. 

Charles Robbins, director of the Washington State University Bear Center and co-author of the study, pointed out the critical differences between the two species. “Polar bears are not grizzly bears wearing white coats. They’re very, very different,” he said.

Unlike grizzlies, polar bears have evolved to rely heavily on the high-fat content of seals, necessitating their access to sea ice for efficient hunting.

Energy expenditure 

The researchers used innovative methods to gather data on the bears’ behavior and energy expenditure during their time on land, including the use of collars equipped with video cameras and GPS.

This approach provided insights into the bears’ diet – which included bird and caribou carcasses, berries, kelp, and grasses – and their efforts to conserve energy by minimizing movement.

Despite observing a broad spectrum of behaviors and energy expenditures among the bears, the experts concluded that the energy benefits gained from terrestrial food sources were offset by the greater energy expenditure required to access these resources.

Only one bear in the study managed to gain weight, having found a dead marine mammal on land.

Study lead author Anthony Pagano is a wildlife biologist with the U.S. Geological Survey Polar Bear Research Program and a former postdoctoral researcher at WSU.

“We found a real diversity of bear behaviors, and as a result, we saw a diverse range of energy expenditures,” said Pagano. “The terrestrial foods did give them some energetic benefit, but ultimately, the bears had to spend more energy to access those resources.”

Implications of longer summers for polar bears

This research is particularly significant as it focuses on the southernmost extent of polar bear range in the western Hudson Bay, an area believed to be experiencing the impacts of climate warming more acutely than other Arctic regions.

The local polar bear population has already experienced a dramatic decline, estimated at 30% since 1987, underscoring the urgency of addressing climate change.

The findings from this study not only contribute to our understanding of polar bear ecology and the challenges they face as their natural habitat continues to change but also serve as a poignant reminder of the broader implications of global warming on Arctic wildlife.  

As the ice-free period extends, polar bears across the Arctic face an increased risk of starvation, highlighting the need for immediate and concerted conservation efforts to mitigate the effects of climate change and preserve these majestic animals for future generations.

“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,” said Pagano. “With increased land use, the expectation is that we’ll likely see increases in starvation, particularly with adolescents and females with cubs.”

The study is published in the journal Nature Communications. 

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