As cold weather sneaks in over the winter, many of us remain indoors as much as possible until it warms up a bit. There are plenty of animals that take the next step, by being practically immobile the entire season. Here are some of the animals that steer clear of winter altogether by hibernating.
Bats, nature’s only free flying mammal, are not winging it when it comes to colder weather. While some species migrate to warmer climates during the winter, many enter a state known as torpor. This is when a bat’s body’s metabolic, heart, and respiratory rates plummet to allow them to survive long periods without food. Their body temperature can also dip to near freezing. During this state, bats will seek out shelter in spots like caves, mine shafts, and attics. Unfortunately, hibernating bats have been heavily impacted by a disease known as white-nose syndrome, which has been decimating populations across the country. This has led to some species being listed as endangered. To see how you can help, click here.
When we think of hibernating animals, the bear is typically the first that comes to mind. While not all bears hibernate, the majority do. The time frame varies, with bears in northern Alaska hiding away in their dens for up to seven months. For Yellowstone area bears, it’s more like four or five months. To prepare for this long stretch of inactivity, they can eat up to 20,000 calories a day, which can lead to daily weight gain of three pounds. While they hibernate, they can lose around 30% of their body weight, but they often gain something better – cubs – in those long winter months.
Turtles are known for slowing it down, and that’s just what eastern box turtles do in the winter time. During this time, they enter into something called brumation. This involves inactivity, torpor, and a slowed metabolism. They’ll wile the winter away like this, burrowed in places like stream bottoms, stump holes, or animal burrows. This can last for three to five months.
Bumblebees, an important pollinator that helps produce many of our favorite fruits and veggies, have a year-long life cycle. Of course, the only members of a colony that live that whole year are queens, who mate before hibernating up to nine months. After emerging in the spring, queens will begin laying eggs, starting another life cycle for the next generation. The bees hibernate by digging into well-drained soil just beneath the ground’s surface.
While Alvin and the Chipmunks may sing their hearts out during the holiday season, their wild brethren are taking it much easier. During the cold months, chipmunks hole up in their burrows with stored food. Most of this time is spent in a deep sleep, in which their heart rate drops from around 350 beats per minute down to about 4. Their body temperature can also lower to the temperature inside. Every few days, though, they wake up, their body temperature stabilizes, and they eat and relieve the call of nature.
Fat-Tailed Dwarf Lemur
Humans may wish we could sleep through the winter months, too, and while we can’t, there is one primate that can. The fat-tailed dwarf lemur, native to Madagascar, can hibernate for up to seven months. You can see one preparing for its deep sleep at the Duke Lemur Center above. During this time, they go back and forth between torpor, with its lowered heart rate and body temperature, and more active periods called interbout arousals. These active stretches occur every six to 12 days and involve an increase in body temperature and heart rate, as well as a stabilization of breathing. Much like bears, the lemurs prepare for hibernation by gorging on food, which stores fat in their tails and helps sustain them over the long inactive months.
Frogs are cold-blooded, meaning they can’t produce body heat with their metabolism, so it’s off to hibernation they go in the winter. For aquatic frogs, this period is passed underwater, where they breathe in bits of oxygen through their skin. The colder the water, the higher the oxygen level. For terrestrial frogs, the choice typically falls on soil beneath the frost line or in cracks or crevices in logs and rocks. Their liver produces large amounts of glucose as they hibernate, which increases blood-sugar levels and limits the formation of ice crystals.
The garter snake is another cold-blooded animal that snoozes away the winter. It will hibernate between October and March or April, though it can be seen basking on rocks on warmer winter days. They actually hibernate in groups, to keep their body temperatures up. These groups will choose locations like natural cavities or burrows, under rock piles, or in stumps. While they hibernate, they will not eat, but they do absorb moisture through their skin to stay hydrated.
Thanks to Groundhog Day, we often associate groundhogs with winter. During the winter, they’re not generally looking for their shadows as a means to forecast weather, though. They’re hibernating, generally between late fall and late winter or early spring. During this stretch, their body temperatures can go from 99 degrees Fahrenheit down to as low as 37 F. Their heart rates also plummet to the single digits. Their breathing slows substantially, as well, much like ours catches when we wait to see Punxsutawney Phil’s winter forecast.
Another hog that snoozes away the winter is the hedgehog. They’ll either create their own resting place with dead leaves, twigs, and other materials, or they’ll settle into stacks of logs or compost heaps. The time they spend in hibernation varies with temperatures, but it can last from October through April. Like other animals, their body temperatures fall and their heart rate slows, but their breathing is noteworthy: they may only take a breath once every few minutes.
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