Climate change has caused temperatures to rise and sea ice in the Arctic to melt. This is a serious problem for polar bears, who hunt seals along the slabs of solid ice. Seals have moved further north, leaving polar bears with dwindling food supplies.
Scientists had postulated that the polar bears could weather these food shortages by entering a so-called "walking hibernation" state. In 1983, researcher Ralph A. Nelson had hypothesized that this state was one "in which the biochemistry of hibernation is integrated with physical activity, but food and water intake are minimal," [PDF] giving scientists hope that by cutting down on their nutrient needs, polar bear populations could withstand the trials of climate change.
Unfortunately, new research disproves the walking hibernation theory. A new study published in Science detailing research led by the University of Wyoming’s John Whiteman found that although polar bears reduce their activity and body temperatures in summer, their metabolism doesn't slow and their nutrient needs don't drop.
From location transmitters, activity logs, and temperature probes, the researchers were able to put together a comprehensive understanding of the polar bears' metabolism. "We found that polar bears appear unable to meaningfully prolong their reliance on stored energy, confirming their vulnerability to lost hunting opportunities on the sea ice," Whiteman said in a statement.
The study required years of intense logistical coordination—so much so that Whiteman speculates "it may never be replicated." Dozens of polar bears were tracked, sedated, captured, studied, fitted with a range of monitoring equipment, released for 18 months, re-captured and, ultimately, re-released. "Many colleagues—even some on our research team—doubted whether the study was possible, until we actually did it," said University of Wyoming co-author Merav Ben-David.
University of Alberta scientist Andrew Derocher, who was unaffiliated with the study, told io9, "this study provides further insights into the long-term challenges facing polar bears throughout the circumpolar Arctic over the coming decades."
Those challenges may prove insurmountable for polar bears. In Science, Whiteman concludes, "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."