Animal Hibernation: A Long Winter’s Nap

When frost sets in and food disappears, non-migratory animals that depend on summertime insects and plants find a sheltered nook and slow things down—way, way down. Breathing, heartbeat and even body temperatures ease to a bare minimum in winter. Hibernation lasts several months and allows wildlife to survive freezing temperatures and conditions.

Why Do Animals Hibernate?

Winters are tough for many warm-blooded animals, especially when food sources are slim, which is why winter hibernation is so important. To prep for their seasonal slumber, mammals such as groundhogs, bats and bears gorge for weeks in fall to fatten up. Once heart and respiration rates slow, body temperatures drop and less overall energy is used, those fat reserves last for months. (Read more: How Butterflies and Bugs Hibernate)

Where Do Animals Hibernate?

Animals that hibernate are often hiding in plain sight. For example, bats settle inside manmade shelters—church steeples, attics, and the walls of houses—but you can find them in natural caves and tree cavities, too. Some animals that hibernate, including chipmunks, are light sleepers. Although they pack on the weight before winter hits, they also fill an underground storehouse to nibble on throughout the season.

photo credit: Danny Brown

Do Cold-Blooded Animals Hibernate?

Hibernation isn’t just for warm-blooded mammals, though. Toads, frogs, salamanders, turtles and snakes all hunker down against winter’s chill. Toads and tree frogs burrow deep into the soil, while spring peepers, wood frogs and spotted salamanders seek out crevices in logs or rocks, or snuggle below a thick layer of leaf litter. Once these cold-blooded creatures are safe and sheltered, their bodies start pumping out glucose, a natural antifreeze that prevents their cells from dehydrating as temperatures drop below freezing. Even more incredibly, their breathing and heartbeats may stop completely. Only their brains maintain minimal function as they wait out the winter.

The survival strategy of aquatic bullfrogs, snapping turtles and other water-loving wildlife is to dive deep. They settle on the bottoms of ponds where the water doesn’t freeze. Frogs sometimes bury themselves in mud to hibernate, leaving their nostrils exposed, and turtles breathe through their skin, even if completely submerged in mud. (Read more: Why Toads Are Valuable in the Garden)

The garter snake that’s been in your backyard all summer slithers off to an underground communal den, where it joins dozens to hundreds of its kind to pass the winter. Even land snails sleep through winter, sealing up the openings of their shells after they retreat into nooks and crannies or under dead leaves.

Heart Rate and Respiration During Hibernation

Heart rate, circulation and respiration slow down during hibernation to conserve energy. A hibernating bear’s heart can stop for up to 20 seconds and its respiration may fall to about a breath per minute. Core body temperature in hibernating animals also decreases. For example, the temperatures of Arctic ground squirrels may drop to 27 degrees Fahrenheit.