Tree squirrels and flying squirrels don’t hibernate, but they do sleep more during winter. In cold climates, ground squirrels hibernate.
Why do some squirrels sleep more during winter while others hibernate?
And what is the difference between sleeping and hibernating?
In the following article, we answer these questions as well as how squirrels survive winter and why scientists are fascinated by hibernating squirrels.
What Is the Difference Between Sleeping and Hibernating?
When a mammal sleeps, the heart rate and breathing slow down and body temperature drop, but during hibernation, these effects are more pronounced and the metabolism is severely depressed.
During hibernation, an animal’s heart rate and breathing slow down, and their body temperature drops significantly for long periods.[1]
The hibernation state, also known as torpor, helps an animal survive for weeks without eating and drinking which means they use far less energy[2] than they would be sleeping.[3]
Do Squirrels Hibernate?
Squirrels generally don’t hibernate. They sleep more than usual but don’t go into a dormant state of hibernation.
In cold climates, ground squirrels are known to hibernate through the winter months. In North America, this includes the Arctic ground squirrel and Thirteen-lined ground squirrel.
Tree squirrels, like the Eastern gray squirrel and the red squirrel, and flying squirrels do not hibernate in winter.
In warmer climates in Africa and tropical regions, ground squirrels are active throughout the year and do not hibernate.[4]
Related: List of Animals That Hibernate
North American Squirrels That Hibernate
There are two squirrels in North America that hibernate:
- Thirteen-lined Tree Squirrel (North America)
- Arctic Ground Squirrel (North America)
| Physiological Changes During Hibernation | Arctic Ground Squirrels | Thirteen-Lined Ground Squirrels |
| Heart rate | Drops from 300 beats per minute to 3 or 4 beats per minute. | Drops from 200 beats per minute to 20 beats per minute. |
| Respiration rate | One breath every few minutes. | Drops from 50 breaths per minute to four breaths per minute. |
| Body temperature | Drops to below freezing. | Drops to just above freezing. |
1. Thirteen-Lined Ground Squirrels
The Thirteen-lined ground squirrel (Ictidomys tridecemlineatus) is a small squirrel. Their name comes from the thirteen alternating dark brown and tan strips running from their head down to the base of the tail.
Originating from the central North American prairie, the loss of natural habitat means these ground squirrels have adapted to living in pastures, golf courses, and parks.
They can be found as far as Ohio in the east, Arizona in the west, Alberta in the north, and the Texas coast in the south.
How Thirteen-Lined Ground Squirrels Hibernate
In preparation for hibernation, thirteen-lined ground squirrels gain up to 4 grams of fat a day in the fall. They hibernate in underground burrows from August until March.
During hibernation, their body temperature drops to just above freezing, and their heart rate drops from their usual 200 beats per minute to 20 beats per minute.[5]
Their respiration rate falls from 50 breaths per minute to about four breaths per minute.[6]
Thirteen-lined ground squirrels wake occasionally to snack on stored food, but even so, they lose up to a third of their body weight during hibernation.
2. Arctic Ground Squirrels
The Arctic Ground Squirrel (Urocitellus parryii) is the largest of its kind in North America. They are common in the mountainous regions of Denali and spend 7 to 8 months hibernating in an underground burrow.
How Arctic Ground Squirrels Hibernate
During hibernation, Arctic ground squirrels only breathe every few minutes. Their heartbeat drops from 300 beats per minute to 3 or 4 beats per minute, and their metabolic rate drops by 90%.[7]
Supercooling
According to the research, hibernating arctic ground squirrels’ body temperatures drop lower than that of any other mammal measured.
This phenomenon is called ‘supercooling’ and occurs when the squirrels’ body temperatures drop below the freezing point.
Every two to three weeks while in hibernation, Arctic ground squirrels shiver and shake for between 12 to 15 hours. This raises their body temperature until it’s back to normal. When the shivering and shaking stops, body temperature drops back down to below freezing.
This is unique to Arctic ground squirrels and scientists are still trying to understand it.[8]
Recycling Nutrients
A University of Alaska Fairbanks-led study found that Arctic ground squirrels recycle their body’s nutrients during hibernation.
Researchers proved their theory that these ground squirrels recycle nitrogen to retain their body tissue, including muscle, during extreme fasting.[8]
The study also complements previous research that suggested that hibernators recycle urea, a waste product that is excreted in the urine.
Why Scientists Are Fascinated by Hibernating Squirrels
A University of Alaska Fairbanks-led study found that the hibernating Arctic ground squirrels are amazingly resilient to muscle loss and long-term cellular damage thanks to their ability to recycle nitrogen within their bodies.
Scientists are looking into ways these findings could be used to make medical treatments to help the following:
- Prevent muscle loss in cancer patients.
- Prevent muscle loss in the elderly.
- Help treat traumatic injuries.
There is even a hope that they could use what they have learned from these squirrels to aid astronauts during space travel.[8]
When Do Squirrels Go Into Hibernation?
Ground squirrels in cold climates in the northern hemisphere hibernate in winter from August until March or April.
Thirteen-lined ground squirrels hibernate in underground burrows from August until March.
Arctic ground squirrels hibernate from late August until late April.[6]
How Do Squirrels Survive Winter?
Squirrels eat more in the fall and gain extra weight to survive the coming winter. They prepare their dens, nests, and burrows and store food provisions to carry them through winter.
Flying squirrels and tree squirrels don’t hibernate, but they do hoard food for the cold winter months and spend more time sleeping in their nests and dens.[9]
Ground squirrels prepare their burrows and a food supply for their long hibernation period.
How Squirrels Prepare for Winter
Here are four things all types of squirrels do to improve their ability to survive winter:
- Gain weight ahead of winter.
- Grow a thicker winter coat.
- Collect and hoard food.
- Prepare a winter den, nest, or burrow.
How Tree Squirrels Prepare for Winter
North American tree squirrels (like the Eastern gray squirrel) gather and bury food for their winter supply. These squirrels live in dens and nests. Dens are cavities in trees (often abandoned woodpecker holes) and are preferred over winter.[10]
Gray squirrels rely on their fat reserves and buried food stores to survive winter. They eat more in fall to gain their “over-wintering fat”.[11]
How Flying Squirrels Prepare for Winter
Nocturnal Southern flying squirrels and Northern flying squirrels in North America store food for winter in trees or underground.
They build nests in tree cavities and sometimes bird houses, lining their nests with shredded bark, leaves, moss, feathers, and other materials. [12]
Flying squirrels are sociable and share nests. During winter, single-sex groups of about eight can share a nest to keep warm over winter.[13]
As many as 20 Southern flying squirrels share a nest to keep warm over the winter months. They are known to stay in their nests for a few days at a time to stay warm.[14]
Related: Are Squirrels Nocturnal?
How Hibernating Squirrels Prepare for Winter
The preparation process for hibernating squirrels is different from the one of other squirrels. They generally store more fat ahead of time, as they don’t gather food during the winter.
| Preparation for Hibernation | Arctic Ground Squirrels | Thirteen-Lined Ground Squirrels |
| Weight Gain | Increase fat stores to 30 to 41.5% of their total body weight 5 – 7 weeks before hibernating. | Gains up to 4 grams of fat a day in fall. |
| Hibernation burrows | Constructs hibernation burrows with hidden entrances plugged with earth. | Dig deep hibernation burrows and plug entrances with soil and grass. |
How Hibernating Arctic Ground Squirrels Prepare for Winter
Arctic ground squirrels gain weight before winter. Their fat stores increase to 30 to 41.5% of their total body weight in the five to seven weeks before they start hibernating.
Arctic Ground Squirrels construct nests within underground burrows using lichens and dry grasses.
Their hibernation burrows (also known as hibernacula burrows) are constructed with hidden entrances plugged with earth. These entrances are only cleared when the squirrel emerges in spring. [15]
How Hiberntating Thirteen-Lined Ground Squirrels Prepare for Winter
Thirteen-lined ground squirrels gain up to 4 grams of fat a day in fall before hibernating.
They dig shallow emergency burrows and deeper underground burrows used for nesting and hibernation. They plug their burrow entrances with grass or soil.[16]
FAQs
Do All Squirrels Sleep During the Winter?
Yes, all squirrels sleep during winter, but only ground squirrels in cold climates hibernate. Tree squirrels and flying squirrels store food and sleep more during winter than in summer, but they do not hibernate.
Related: How & Where Do Squirrels Sleep?
How Do Squirrels Stay Warm In The Winter?
Squirrels gain weight to help them stay warm in winter. Tree squirrels and flying squirrels build dens and nests in tree cavities and will spend more time in them over winter. Flying squirrels share nests with other flying squirrels to keep warm. Ground squirrels will dig deep burrows for hibernation.
Where Do Squirrels Sleep During the Winter?
Hibernating ground squirrels like the Artic and thirteen-lined ground squirrels hibernate in deep burrows. Tree squirrels, like gray and red squirrels, and flying squirrels like the South and Northern flying squirrels will build dens in tree cavities or nests in trees.
Where Do Squirrels Hibernate?
The few squirrels that hibernate do so in dens, burrows, or in hollowed-out trees. They line their nest with additional insulation to keep warm.
Do Black Squirrels Hibernate?
No, black squirrels do not hibernate during the winter. They are less active than in the summer, but they don’t go into the dormant state known as hibernation.
Are Squirrels Out in the Winter?
Yes, most squirrels are out and active during winter. They are less active than in the summer, but nevertheless still active. They forage for food and take care of their young.
