Dead Bear Walking

Walking hibernation (n.): a period of decreased metabolism undertaken by bears during the summer and fall in response to lack of hunting opportunities.

Polar bears face an existential crisis. Climate change is melting the Arctic ice, which shortens their seal-hunting season, which cuts their annual caloric intake, which robs them of the fat stores they need to survive the winter. Some scientists, however, have suggested there’s a way out: walking hibernation.

Hibernation, in general, is like an ursine magic trick. Some bear species can reduce their metabolism by 53 percent during the winter without significantly lowering their body temperature. And it’s not crazy to think that bears could do something similar during the hunting season, since their winter hibernation isn’t exactly a six-month sleep-in. Hibernating females give birth during the winter and produce nutrient-rich milk, all while fasting and losing tremendous amounts of weight.

If they can do all that, they should be able to enter walking hibernation during the summer, slowing their metabolism down like a meditating Buddhist monk, to keep themselves alive during a slow hunting season. Right? Right?

Wrong. In 2008 and 2009, researchers from the University of Wyoming tagged 25 polar bears to monitor their activity. They also implanted thermometers in a subset of the tracked bears. The results were published Wednesday in the journal Science. Although prior research had hinted that the bears could slow their activity, entering a state of walking hibernation in response to climate change–based calorie restrictions, the new study found no evidence to support the theory.

Polar bears living on the ice, which were able to carry out normal hunting activities, had the same core body temperature as hungry bears trapped on the shore. Overall, the metabolism of the shore-bound bears more closely resembled that of a starving bear than a hibernating one. So much for the walking-hibernation theory.

The findings do not augur well for the future of polar bears. “This suggests that bears are unlikely to avoid deleterious declines in body condition—and ultimately survival—that are expected with continued ice loss and lengthening of the ice-melt period,” write the authors in the Science paper. (The researchers write more on their study over at The Conversation.)

In retrospect, the walking-hibernation theory did seem a bit optimistic. Natural selection doesn’t generally account for hypothetical or farfetched scenarios—like the possibility that a single species would come along and completely alter the earth’s climate over the course of a century or two. Next theory?