Degrees of Hibernation

How garden visitors snooze away the coldest months.

- By Monica Cardoza

Many backyard guests—such as monarchs and orioles-make for warmer climates as temperatures drop. The rest hunker down. How they prepare and where they lay their heads sometimes differ even within the same species. But no matter how they overwinter, they do it for the same reason: to conserve energy.

As days shorten, animals take the cue from Mother Nature and add layers of fat while food is more available. These reserves essentially act as a big bank of energy that animals draw from while they're in the deep-sleeping state of hibernation,” says Kevin Brunke, natural history biologist with the Missouri Department of Conservation.

To make those reserves last, animals lower their metabolism and body temperature and slow their heart rate and breathing. “They burn fewer calories while they wait for more favorable foraging opportunities to become available,” Kevin says.

Deep Sleepers

Hibernation champs include groundhogs, ground squirrels, meadow jumping mice and some species of bats. These bona fide hibernators remain in a state of inactivity for several days, weeks or months and can sleep through loud noises and other commotion.