Transcript:

This winter, in the sub-zero temperatures of Alaska, the arctic ground squirrel is waiting out the season in burrows three feet underground. I'm Jim Metzner, and this is the Pulse of the Planet, presented by the American Museum of Natural History. The sounds we're listening to were recorded when the arctic ground squirrel was out and about during a short spring and summer. But for about eight months of the year, the squirrels will lie curled up in their burrows, allowing their body temperatures to drop below freezing as they rest in a state of suspended animation, or torpor. And for reasons scientists still don't understand, the hibernation is punctuated by short spells of warming up.

"Every two or three weeks they begin to shiver and shake and create heat and warm their bodies all the way back up to normal mammalian body temperatures of around ninety-eight degrees Fahrenheit."

Brian Barnes is an Associate Professor of Zophysiology at the University of Alaska in Fairbanks.

"They don't wake up at that time, but actually, they're in slow wave sleep and remain that way for much of the time they're in high body temperature which is often only twelve or fifteen hours. They don't leave their nest; they stay curled in a ball for most of the time, asleep, doing something, we're not sure what, something that allows them to stay alive. For at the end of that twelve hour period, they cool slowly back down, all the way to those lowest body temperatures again for another three weeks. These animals are brain dead, essentially. You cannot measure any brain activity when they're in torpor...They come back into active brain state over the period during which they're at warm temperatures, but it's one of deep sleep."

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Pulse of the Planet is presented by the American Museum of Natural History. Additional funding for this series has been provided by the National Science Foundation. I'm Jim Metzner.