If the weather’s turned cold and you’re not seeing squirrels running around or jumping in the trees, the question might pop up if squirrels hibernate for the winter. Well, it turns out that…
Tree squirrels do not hibernate in winter but they do sleep a lot more than usual in warm tree cavities and nests. Many ground squirrels hibernate in ground nests in winter, but they are often light sleepers and you might still see them outside on warm days.
Whether you’re looking at a ground squirrel that does hibernate or a tree squirrel that doesn’t, one thing we know for sure is that all squirrels start getting ready for winter in fall, when the weather starts cooling down. If you watch closely, you might even notice them preparing for a cold winter in four ways…
How squirrels live through winter
To understand how squirrels know when to prepare for winter and when to hibernate, we need to ask how squirrels know winter is coming.
All squirrels have an internal system that tells them when the days are getting shorter and the nights longer. This system is made up of many glands and organs in their body, where there are cells called neuroendocrine cells. These cells make and release hormones, such as melatonin for sleeping and waking.
As the days get shorter in fall, the squirrel’s neuroendocrine system releases hormones that tell the squirrel it’s time to get ready for winter. And when the nights are long enough, a ground squirrel’s hormones tell it that it’s time to go underground to hibernate.
All squirrels do four things to live through winter:
Squirrels store food for the winter
Squirrels are territorial and have an area around their nest that’s theirs, and they will fight to defend it and stop other squirrels from moving into this area. But they also have a range, or a much larger area, that they will explore during the day to look for food.
In fall, squirrels move around their range to collect as much food as they can. They bring this food back and bury it around their territory, close to their nest. This behavior is called scatter hoarding.
Squirrels scatter hoard for a few reasons, but one of them is to trick food thieves in winter. If a food thief finds a buried nut, the thief thinks that’s the whole food stash and moves on. This keeps the rest of the food stockpile and squirrel nest safe.
Gray squirrels often remember where they hide food and come back later to eat it. Red squirrels are more forgetful, and often forget where food is hidden.
Buried nuts and seeds that don’t get stolen or eaten usually grow into trees and shrubs when the weather warms up.
When winter arrives, ground squirrels go into their deep sleep but tree squirrels remain quite active. They eat whatever buried food they can find, even if it was buried by another squirrel. But by late winter, when all food is scarce, tree squirrels often strip off tree bark and eat tree buds to stay alive.
Squirrels store fat on their bodies
Squirrels eat as much as they can in late summer and fall to put on weight. They binge on berries, fruits, vegetables, bird eggs, nuts, insects, and pretty much anything else they can find. Many squirrels have increased their body weight by 25 – 50% by the start of winter.
This extra layer of fat keeps them warm in the cold of winter and “feeds” their body when it’s too cold to go outside for food or when there’s no food left to eat.
Squirrels make sure they have a warm nest for the winter
All squirrels sleep in nests and they often have several nests to choose from.
Tree squirrels enjoy spending winter in tree cavities that were made by woodpeckers or other animals. If there are no suitable cavities in their territory, these squirrels build their own tree nests using twigs and leaves.
Ground squirrels dig tunnels underground called burrows, where they live and hibernate.
Before winter starts, squirrels make sure to choose or build a suitable nest and line it with soft materials like moss, pine needles, feathers, or grass to make it warm enough for cold weather.
Squirrels also often huddle together, along with their babies, for extra warmth inside the nest.
Squirrels grow a thick winter coat
Squirrels grow a thicker coat and bushier tail in winter to keep themselves warm. This is called their winter coat. Some squirrels even grow long tufts or clumps of hair on their ears for extra warmth.
In summer, a squirrel’s coat thins out and the ear tufts disappear. This is a squirrel’s summer coat and it’s designed to protect the squirrel without making the animal too hot.
Where tree squirrels go in winter
Tree squirrels don’t hibernate but they do spend a lot more time sleeping curled up in a ball in their nest in winter. They still come out to eat food, as long as there’s no snow or sleet and the temperature stays above freezing.
If given the choice, tree squirrels choose a nest in a tree cavity for the winter rather than an open nest high up in tree branches. Some tree squirrels manage to jump onto a roof and build a nest inside a house, which is where they spend a lot of time during a cold winter.
Let’s take a look at what three common tree squirrels do in winter.
Where gray squirrels go in winter
Gray squirrels are tree squirrels so they don’t hibernate.
Gray squirrels are naturally most active in the early morning and late afternoon, which is true in all seasons. This is when they leave their nest to eat, explore, or groom themselves. The rest of the time they are sleeping on a tree branch or fast asleep in their nest, and they’re always in bed before the sun sets.
When it’s cold outside with snow or sleet, and temperatures drop to freezing, gray squirrels are happy to spend a few days curled up in their nest.
Gray squirrels are happiest living on their own, although they will share their nest with other gray squirrels in winter to keep warm. Females share their nests with babies, if they have any.
Where fox squirrels (brown squirrels) go in winter
Fox squirrels are tree squirrels that do not hibernate in winter. Instead, they choose a tree den in a large tree or build a tree nest high up and spend cold winter days in there. They often share their den with their breeding partner or other fox squirrels.
Fox squirrels are active in the day and sleep at night, no matter what season it is. They come out during the day to find food, climb trees, and groom. The rest of the time they are sleeping on a tree branch or in their nest.
But if it gets too cold, and there’s snow, ice, or freezing temperatures, fox squirrels stay in their nest for several days without leaving.
Where flying squirrels go in winter
Flying squirrels are tree squirrels so they don’t hibernate in winter, but they do:
- Slow down their metabolism in the colder months and lower their internal body temperature, to save energy when food is so scarce
- Grow a winter coat and tufts on their ears to stay warm
- Huddle together in nests when it gets very cold
Flying squirrels are nocturnal, which means they are active at night and sleep during the day. In summer and fall these squirrels are usually out of their nests all night to look for food and gather food for winter. But in winter, flying squirrels usually leave their nests only when the sun rises and when it sets.
If it gets very cold outside, flying squirrels will stay in a group in their nest, and will go into a light hibernation and inactivity, at least until things warm up again.
How ground squirrels hibernate in winter
Most ground squirrels hibernate in winter, but not all of them do and not all of them go into the same state of hibernation. In fact, sometimes ground squirrels of the same species have different hibernation behaviors.
For example, California ground squirrels hibernate but males usually come out of hibernation two weeks earlier than females. Also, young California squirrels and those that live in warmer areas often don’t hibernate at all.
Ground squirrels that hibernate go into their underground burrows to sleep through the winter. While underground, these squirrels go through several changes in their body that will help them survive the long winter.
During hibernation, ground squirrels lower their body temperature and stay quite still so they don’t need much energy. This means they don’t need to eat much and that their fat stores can keep them fed for longer. Ground squirrels also save energy by breathing slower and slowing down their heart rate and other vital organs.
Above ground, the weather might get cold and icy, but underground temperatures are more stable thanks to rocks and soil that retain heat. A ground squirrel’s nest is a few feet underground (2- 6 feet deep), and so the squirrel is more protected from the cold than tree squirrels.
They spend most of the winter sleeping in a state of hibernation, but many of them do wake up to urinate and on warmer days to come out and eat and drink water.
Once they’ve done what they need to do, ground squirrels go back into their burrow to continue hibernating.
How to tell if a squirrel is hibernating
If you find a lifeless squirrel in winter and you aren’t sure if it is hibernating or dead, there are a few things to consider.
If it’s a tree squirrel, then it’s most likely dead because tree squirrels don’t hibernate, unless it’s a flying squirrel that can go into a light hibernation. But if it’s a ground squirrel there’s a good chance that the squirrel is in a deep state of hibernation and simply not waking up.
Don’t try to force any squirrel to wake up. It’s best to leave the squirrel somewhere safe until spring arrives, where it can wake up naturally on its own.