Hibernation: Bats and bears use the same amount of energy per gram when hibernating

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Larger animals usually need less energy by weight than smaller ones, but an analysis that looked at nine species found this wasn’t true during hibernation



Life



26 April 2022

A black bear takes a nap on a log

Black bears can hibernate for several months in winter – but does it save energy?

Shutterstock / critterbiz

Pound for pound – or gram for gram – hibernating mammals appear to use roughly the same amount of energy as each other, despite differences in overall size.

That finding comes from an analysis of nine studies about nine different species of hibernating animals. Roberto Nespolo at Austral University of Chile and his colleagues found that, per gram, a hibernating bat has a similar metabolism to a hibernating bear, for example, despite the latter being 20,000 times larger.

“This is very unusual as large animals consume less energy per gram than small ones [when not hibernating],” says Nespolo.

Most animals that hibernate tend to be on the smaller side and the study raises the possibility that hibernation stops being an efficient way to preserve energy once creatures reach a certain size. According to further analysis performed by Nespolo and his team, this figure could be as low as 75 kilograms.

Some bear species that hibernate are significantly heavier than this. Grizzly bears, for example, can weigh 110 to 300 kilograms. This may mean hibernation serves a different function, like being part of a reproductive strategy, since it also coincides with gestation, birth and the earliest period of life in newborn cubs, says Nespolo.

More likely, though, bears are just outliers to the analysis, says Øivind Tøien at the Institute of Arctic Biology in Fairbanks, Alaska. His research has found that black bears have a significantly lower metabolic rate when hibernating – including animals well above 75 kilograms. Even so, the finding may still be valid that there is a point where hibernation no longer offers energy savings as body mass increases, he says.

Interest in hibernation research has grown in recent years because of its potential implications for humans – both for developing new medical treatments and for providing insight into how we might induce hibernation in ourselves for, say, the long trip to Mars.

Journal reference: Proceedings of the Royal Society B: Biological Sciences, DOI: 10.1098/rspb.2022.0456

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