Q. Why do some animals hibernate?

A. It all has to do with energy efficiency, says Hannah Carey, professor of physiology at the UW-Madison School of Veterinary Medicine.

And it doesn't always have to do with winter. Some animals in the tropics hibernate, too. They snooze during the dry season when there are fewer seeds, plants or insects available for food.

The point, according to Carey, is that there are times of the year when a body has to work harder than usual because temperatures are extreme and food is scarce. Animals that hibernate have developed these long, seasonal naps as a system for conserving energy.

"To prepare, they eat more so their bodies store fat," Carey explains. "It's kind of like chopping wood to build a wood pile before winter so you can stay cozy inside on the coldest days."

By lowering their thermostat (metabolism), hibernators enter a state of "torpor" where they don't need as much fuel (food) or heat (energy). Instead, they switch over to drawing energy solely from the fat stores accumulated during more moderate and bountiful seasons.

Hibernating critters awake according to their biological clocks, whose alarms are set for times when food becomes more plentiful in their environment and the elements are less harsh.

Produced in cooperation with University Communications.

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