Don’t judge a bear by its temperature, or so suggests first-of-its-kind data on hibernation physiology.
There’s something as-yet-unknown going on with black bear hibernation that slows metabolic rates more than lower body temperatures alone can explain, reports ecological physiologist Øivind Tøien of the University of Alaska Fairbanks.
In the depths of Alaskan winters, closely monitored black bears dropped their temperatures only a modest 5.5 degrees Celsius on average, Tøien and his colleagues report in the Feb. 18 Science and at the annual meeting of the American Association for the Advancement of Science held in Washington, D.C. A standard physiologist’s calculation predicts that such a chill would slow metabolism to 65 percent of nonhibernating resting rates. But the bears’ metabolisms plunged down to even more energy-saving zones, averaging only 25 percent of the basic summer rate.
This sustained, big disconnect hasn’t shown up so far in research on any other hibernating mammal, says study coauthor Brian M. Barnes, also of UA Fairbanks.
Mammal hibernation matters to human medical research, says physiological ecologist Hank Harlow of the University of Wyoming in Laramie. Relying on mechanisms that scientists would love to understand, black bears spend five to seven months without eating, drinking or taking a single bathroom break. But unlike bedridden or spacefaring people, the hibernators don’t lose their muscle strength or bone mass. “Bears are just remarkable,” Harlow says.
This Alaska study is the first to manage continuous monitoring of metabolic rate and body temperature throughout bear hibernation in low-disturbance conditions, Tøien says. Other studies based on intermittent sampling with older instruments, indirect evidence or studying bears with lots of people nearby have left the matter “uncertain,” as he puts it.
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