Scientists take first look at hibernating bears

By Anne K Walters Feb 18, 2011, 10:33 GMT

Washington - Researchers in Alaska have taken the first-ever detailed look at hibernating black bears, discovering that sleeping like a bear is more complicated than previously thought.

The scientists from the University of Alaska at Fairbanks and Stanford University took a rare look at five bears that had been captured by local wildlife authorities when they wandered too close to civilization.

The bears were kept in specially designed dens outfitted with infrared cameras and other equipment, while the animals themselves had sensors embedded in them to monitor their vital signs.

Scientists found that the bears' metabolic rate drops to 25 per cent of normal levels even though the animals' body temperatures fell by much less.

This is surprising because scientists had seen in smaller hibernating mammals that metabolism fell by about 50 per cent for each 10-degree-Celsius drop in body temperature. The bears' temperatures only fell by 5 or 6 degrees.

The bears dropped their heart rates significantly, to just 14 beats per minute from 55 beats per minute when not hibernating.

A video of one bear shows loud bursts of snoring in between periods when its heart was beating extremely slowly.

The animals do not eat, drink or defecate during the five months in hibernation, though they do occasionally wake briefly to reposition themselves.

'All they need is air,' said researcher Brian Barnes, who described the bears as essentially closed systems during their hibernation period.

Though people may not snuggle in for months during the winter, the findings about black bears, which are similar in size to humans, could provide important medical advances, researchers said.

For example, lowering a stroke victim's metabolic rate could extend the time during which treatment can prevent permanent neurological damage.

'If you could reduce the metabolic demand of people, it'll be favourable either during surgery or as a quick response during heart attack or stroke or trauma,' Barnes said.

'What that would do is give you more time. We like to say it would potentially expand the 'golden hour' - during which, if you reach advanced medical care, outcomes are better - to a golden day or a golden week.'

But researchers must now determine exactly how bears are able to lower their metabolisms so drastically.

Another potential application is for long-distance space travel, such as putting astronauts into deep sleep for trips to Mars or simply to retain muscle function during long periods of inactivity.

Also surprising was that the bears' body temperatures varied in a cycle over several days, with the animals shivering to bring their temperature back up before again falling to a steady low over two to seven days with a range of 30 to 36 degrees. One pregnant bear, however, kept her temperature at a normal level throughout the pregnancy.

The findings are to be published in the Friday issue of the journal Science and were presented by researchers at the American Association of the Advancement of Science meeting in Washington.