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Many mammals in North America hibernate during the winter months.  In this article, we get to look at a few of these.

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

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

Want to know how mammals adapt to winter? Find out in this article I wrote.

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 fat. When hibernating, the animals survive on this stored fat as a way of nourishing its body.

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 uses less energy. 

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

If you want to know how to help wildlife in winter, this article is for you.


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

Chipmunks are tiny in size and usually weigh less than one pound. They typically have brown and yellow coats with grey fur. Also, chipmunks have a black and white stripe that runs down their back, one of the distinguishing features of squirrels.

Something you may not know about chipmunks is that they hibernate. During 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 other mammals that hibernate, chipmunks do not put on extra fat to take them through the winter.

However, they 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 holes.

There is usually enough room to keep enough food to take them through the entire winter. Chipmunks are pretty 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. 

If you want to know what sounds a chipmunk makes, you can find out in an article I have written here.

Ground Squirrels

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

Ground squirrels retreat into their underground caves, where they spend winter hibernation. They lower their body temperatures to about one degree above the temperature outside their burrows.

During their hibernation, ground squirrels roll into a ball so the head is tucked between the legs and the 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. Ground squirrels tend to leave the burrow and forage outside for more food on warmer days.

Do you know why animals migrate?  Find out in this article I wrote

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 American black bears hibernate.

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 called phlegm, 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 their metabolism to conserve energy.

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

Hibernating temperatures tend to be at 88 degrees, whereas they are at almost 100 degrees when they wake up. 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 quickly if disturbed or if danger lurks 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. 

Black bears aren’t just black; polar bears don’t have white fur.  Please find out more in this article I wrote.


Bats are considered unique mammals as they are the only ones 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 to hibernate throughout the 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 to survive the season.

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

A bat’s 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. A bat’s body temperature can drop to almost freezing, depending on the surrounding temperatures.

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

Want to know how bats evolved into the only flying mammals? Click here for an article I wrote.


The woodchuck, also known as the groundhog, is one of the giant 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 to put 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.

Female woodchucks give birth to their babies in the early spring, mainly in late March or 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 continues until the weather becomes warmer, generally around February or March. As the temperatures drop, this animal’s body releases a hormone that guides it into hibernation.

As they enter a hibernation state, their heart rates slow from 80 beats per minute to about four or five seconds.

Woodchucks do not wake up from their deep sleep to feed. Instead, their bodies use the fat layers built in the warmer months. Woodchucks have had fewer nutrition needs during hibernation.

Many other North American mammals hibernate during the colder winter season, and we will cover these in a future article.

If you want to know which bat species lives in Maryland, this article is for you.