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During hibernation, bear metabolism hits a new low

American black bear.
[Řivind Třien, Institute of Arctic Biology, University of Alaska Fairbanks]

Several American black bears, who were captured in Alaska after wandering a bit too close to human communities, have given researchers the opportunity to study hibernation in these large mammals like never before. A new study by Řivind Třien and colleagues shows that black bears only reduce their body temperatures slightly during hibernation – but their metabolic activity (the chemical and biological processes that keep them alive) drops dramatically. In fact, while they were hibernating, the black bears reduced their metabolism by a full 75 percent compared to their active, summertime levels.

This discovery was surprising because, normally, a hibernating animal's metabolism will slow down by about 50 percent for every 10 degrees Celsius that their body temperature drops. But, the bears in this study only lowered their body temperatures by five or six degrees and their metabolism dropped down to rates much lower than researchers had expected.

A young male American black bear, captured in south-central Alaska as a nuisance animal, is shown having just been placed in an artificial den. The bear is part of the hibernation research conducted by Řivind Třien, research scientist with the Institute of Arctic Biology at the University of Alaska Fairbanks, and first author of an upcoming paper in Science on bear hibernation, and Brian M. Barnes, senior author on the same paper and IAB director.
[Řivind Třien, Institute of Arctic Biology, University of Alaska Fairbanks]

Also, the black bears' metabolism remained very low for several weeks after the animals awoke from their slumbers – another finding that surprised Třien and his team.

In order to make these discoveries, the researchers placed the bears in structures that were designed to look like a black bear's den. The artificial dens were located in the woods, away from human disturbances, and they were had infrared cameras, activity detectors and other sensing devices to record the bears' movements. Třien and the researchers also implanted radio transmitters in each of the bears to record their body temperature, heart beats and muscle activity.

Since the bears spend five to seven months in hibernation without eating, drinking, urinating or defecating, the researchers believe that their findings could be used for a number of applications in the future – from improving medical care to making deep space travel possible. (Because, after all, if human beings are eventually going to leave Earth, this kind of hibernation might make the trip into deep space more bearable.)


This research appears in the 18 February 2011 issue of Science.