Climate: Not a lot of options for polar bears

 Eric Regehr, U.S. Fish and Wildlife Service
Polar bear photo courtesy Eric Regehr, USFWS.

New study shows food shortages will catch up to the Arctic predators

Staff Report

FRISCO — When it comes to finding food as Arctic sea ice melts, polar bears don’t exactly have a lot of options.

That’s one of the main reasons the Arctic predators are under the global warming gun, and a new study of how the bears respond metabolically during lean times underscores the existing science.

Researchers with the University of Wyoming set out to learn as much as they could by using satellite collars and surgically implanted monitors to track polar bear’s summertime movements and core body temperatures on ice and shore.

They found the animals are able to reduce their energy expenditure a little, but not enough to make up for the associated food shortages. Their findings suggest that increasing sea ice loss represents a significant threat to these carnivorous bears.

Polar bears walk ice sheet surfaces looking for food. In summer, when the ice melts, their hunting territories dwindle and they may move on shore, where food is less plentiful, to forage.

Some scientists have suggested that polar bears forced ashore can compensate by entering a low-energy state called “walking hibernation,” and that this strategy could help the animals survive despite the loss of on-ice foraging opportunities caused by climate change.

The University of Wyoming study showed that bears on both land and ice reduced their body temperatures and activity levels below those of bears actively hunting and feeding, but not to levels as low as those observed during energy-saving hibernation.

Instead, the observed declines mirrored those of a fasting mammal, the response of which doesn’t offer significant energy savings. The work suggests polar bears cannot use reduced metabolic rates to prolong their reliance on fat stores when food is less abundant. Thus, say the authors, the animals have limited metabolic options to respond to declining sea ice.

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