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

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


26 April 2022

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

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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’s the new finding from an analysis of nine studies about nine different species of hibernating animals. The research, conducted by Roberto Nespolo at Austral University in Valdivia, Chile and colleagues, found that, for example, a gram of hibernating bat has a similar metabolism to a gram of hibernating bear, 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 at a certain size hibernation is no longer an efficient way for preserving energy. 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 between 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 new-born cubs, Nespolo says.

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

Interest in hibernation research has grown in recent years because of its potential implications in 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: The Royal Society Publishing, DOI: 10.1098/rspb.2022.0456

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