Which Mammals Hibernate?


There are many mammals in North America that hibernate during the winter months.  In this article we get to look at a few of these.

Why Do Mammals Hibernate?

Although amphibians, reptiles, and even some insects are known to hibernate during the cold season, hibernation is generally linked to mammals.

Mammals are endothermic, and this means that they generate internal body heat. For this reason, they need a constant supply of energy to keep their body functions running.

In the cold winter months, the mammals no longer have a constant supply of energy, due to the lack of food.

The best way to they can survive these harsh conditions is to simply shut down somebody’s functions, falling into a deep sleep.

Cute chipmunk

Here are just some of the many North American mammals that hibernate.

Adaptations of Hibernating Mammals

The reason behind hibernation in some animals is to escape the harsh weather conditions that come with winter.

Several mammals can survive the long and cold winter thanks due to this. As these animals prepare to hibernate, they use some special adaptation techniques;

The animals eat plenty of food before the onset of winter and store it in the form of fat. When hibernating, the animals survive on this stored fat as a way of nourishing its body.

Group of bats hibernating in the cave

The body temperatures drastically drop to come close to the outside temperatures.

The breathing and heart rate slows down, and the animal falls into a deep slumber — these aid in slowing down body functions so that the animal is using less energy. 

Here are just some of the mammals of North America that hibernate during the winter months.

Chipmunks

Many people often mistake these tiny mammals for squirrels. It’s probably because they closely resemble each other.

Chipmunks are small in size and usually weigh less than one pound. They normally have a brown and yellow coat with grey fur.

Cute chipmunk

Also, chipmunks have a black and white stripe that runs down their back, one of the distinguishing features from squirrels.

Something you may not know about chipmunks is that they hibernate. When it’s the winter season, a chipmunk’s body temperature drops drastically.

They fall into a deep sleep throughout the season, only waking up occasionally to feed. Unlike some other mammals which hibernate, chipmunks do not put on extra fat to take them through the winter.

They do, however, collect plenty of food, caching it in their burrows before winter comes.

This animal has special cheek pouches that they use to carry food, storing it in their burrows.

Alpine chipmunk sitting on a rock near Yosemite National Park in California.

There is usually enough room for them to keep enough food that will take them through the entire winter. Chipmunks are quite busy in the months preceding the winter season.

Although these little mammals hibernate, they do not spend the entire season in a deep sleep.

They wake up every few days, and at this time, their body temperatures rise to about 94 degrees. This is what is known as an active cycle.

Chipmunks eat some of the stored food, urinate and defecate. Afterward, they lower their body temperatures and go back to hibernating. 

Ground Squirrels

Squirrel with a bunch of honey agaric mushrooms, making provisions

Several people have asked me whether ground squirrels hibernate. Ground squirrels do hibernate.

Ground squirrels retreat into their underground burrows, where they spend the winter in the form of hibernation. They lower their body temperatures to about one degree higher than that of the temperature outside their burrows.

During their hibernation, ground squirrels roll into a ball so that the head is tucked in between the legs and tail on the skull.

They also adjust their heartbeat, slowing it down with their breathing rate.   Ground squirrels do not hibernate fully and wake up once a week for nourishment. 

The squirrels can stay awake for up to 20 hours before hibernating once more. On warmer days, ground squirrels tend to leave the burrow and forage outside for more food.

American Black Bears

When you think of animals that hibernate, the first thing that may come to mind is bears. There has been a debate as to whether the American black bears hibernate.

Black Bear with Salmon in Mouth on Rocks

Black bears do hibernate but not in the same way as typical hibernators such as chipmunks. American black bears enter a state of decreased activity referred to as torpor, a kind of winter sleep.

Typically, the black bears spend the warm months packing on enough fat. This is so that when food is scarce, and the conditions outside are unfavorable, the animals can survive off the fat it has stored.

Black bears enter their dens at the beginning of the winter season. They fall into a deep sleep, slowing down their metabolism to conserve energy.

A mother black bear looks lovingly at her cub

Unlike true hibernators that lower their body temperature to almost freezing, black bears change their body temperature down by 10 degrees.

Hibernating temperatures tend to be at 88 degrees, whereas when they wake up, they are at almost 100 degrees.

American black bears do not fall into a deep sleep and can arouse easily since they don’t drop their body temperatures to extremes.

They can wake up quite quickly if disturbed or if danger is lurking in the area.

Black bears do not have to eat, drink, urinate, or defecate during hibernation. The fat is broken down into water and calories, enabling them to survive. 

Bats

Bat group in grotto

Bats are considered unique mammals as they are the only ones that are capable of flying.  Bats are critical to humans because they help control the populations of insects in the summer and spring.

There are two types of bats; ones that migrate to warmer regions and those that hibernate. In late autumn, bats are already looking for a safe place where they can hibernate throughout the long, cold winter.

Not all bat species enter hibernation, and it is mostly the species that rely on insects for food that do.

Bats that live in regions where insects are scarce during the winter months are forced to hibernate in order to survive the season.

Species such as the big brown bat can hibernate for long periods ranging from sixty to eighty days. While in a state of torpor, the bat’  bat’s body temperature and metabolic rate rapidly slow. 

A bats heartbeat can drop from 400 beats per minute to as little as 25 beats per minute.  Bats can go for a few minutes without breathing at all.

Depending on the temperatures of the surrounding, a bat’s body temperature can drop to almost freezing.

All these slowed body functions help the bat conserve the majority of its energy. The bat can survive for six months on body fat that they have stored.

Woodchuck

Groundhog

The woodchuck also referred to as the groundhog, is one of the largest rodents in North America. They are among very few mammals that truly hibernate.

This animal prepares well for winter. It spends much of the warmer months eating plenty of food so that it puts on sufficient fat for the winter season. 

During the warmer seasons, they are active during the day foraging for food in the early mornings and evenings.

Groundhog Emerging from Snowy Den

Female woodchucks give birth to their babies in the early spring, with births mainly occurring in late March or in early April.

This timing is ideal because the babies have plenty of time to grow to dig their dens when winter approaches.

Woodchucks remain active until the frost occurs in October or November. After this, they will move into their burrows to hibernate.

Hibernation goes on until the weather becomes warmer, generally around February or March. As the temperatures drop, this animal’  animal’s body releases a hormone that works to guide it into hibernation.

As they enter into a state of hibernation, the heart rates slow down from 80 beats per minute to about four or five beats.

Black-tailed prairie dog (Cynomys ludovicianus) near its mound with colorful background

Woodchucks do not wake up from their deep sleep to feed. Instead, their bodies use up the fat layers that were built in the warmer months. 

Woodchucks have had fewer nutrition needs during hibernation.

There are plenty of other North American mammals that hibernate during the colder winter season, and we will cover these in a future article.

Bryan Harding

Bryan has spent his whole life around animals. While loving all animals, Bryan is especially fond of mammals and has studied and worked with them around the world. Not only does Bryan share his knowledge and experience with our readers, but he also serves as owner, editor, and publisher of North American Mammals.

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