Power Naps May Save Dormice from a Long, Hard Winter

How do hibernating animals beat the winter? A power nap could help. Scientists have discovered that offspring that are born later in the year and have less time to accumulate enough energy reserves to last through the winter can beat unfavorable odds by power-napping.

During hibernation, dormice enter "torpor" in order to save both energy and water. In this state, the mice become inactive and show a marked decrease in their metabolic rate. Their body temperatures reduce and their heart rate slows. Yet dormice that are born late seem to use bouts of this same torpor during the summer in order to "catch up" with their earlier-born counterparts.

The scientists measured torpor using temperature loggers placed in dormice nests. These loggers detected the sharp drop in temperature which occurs during dormancy. In the end, the researchers found that late-born juveniles entered torpor more frequently and for longer periods, which allowed them to achieve higher growth rates. As a result, the late-born dormice reached a similar size to their earlier-born counterparts.

"The longer an animal stays in torpor, the more energy it saves," said Sylvain Giroud, one of the researchers.

That's not all that the researchers found, either. The dormice also employed torpor when food availability was limited. This allows the mammals to continue to maintain high growth rates and accumulate sufficient fat reserves to last through the winter.

"Torpor was only viewed as a means to save energy and water, but during the last decade other functions have emerged. These include slowing aging processes, promoting growth during early life and fattening prior to hibernation," said Giroud in a news release. "Juveniles have to reach a threshold of fatness in order to survive winter by hibernating. The more fat deposited, the more likely individuals will survive."

The findings reveal a bit more about how these mammals survive. By understanding the functions of torpor, the researchers can apply their discoveries to future studies.