Do Squirrels Migrate in Winter? Or is it Hibernation?

Hibernation period of Arctic ground squirrels
The prevailing confusion about hibernation in squirrels might have something to do with the fact that there are 280-odd squirrel species in the world, and not all of them hibernate. So, what do the non-hibernating squirrels do in winter? Do they migrate to warmer parts, or do they simply remain in their drey?
Smart or selfish?
Marmots are defenseless against predators during hibernation. So they hibernate in groups, keeping the weakest members towards the outer edge of their hibernaculum.
If you have squirrels in your backyard, you might have noticed that they disappear in winter. An annual occurrence nevertheless, this disappearing act of squirrels makes people wonder whether they hibernate, like bears and hedgehogs, or migrate like hummingbirds and Arctic terns, to deal with winter? There is no questioning the fact that their disappearing act has more to it than what meets the eye, but that is expected, considering that there are over 280 species of squirrels in the world.
What do Squirrels do in Winter: Migrate or Hibernate?
Squirrels do not migrate. Period. If they are not to be seen for a considerable period during the cold season, it's because they spend the entire time either hibernating or simply resting in their drey. Hibernation has more to do with food shortage than extreme weather. So the species have two options: (i) revive your fat reserves; or (ii) store food for winter. In contrast, animals migrate from one place to another primarily in search of food.
● Squirrels prepare for winter well in advance either by reviving their fat reserves―the hibernating species, or by collecting food and storing it in different places―the species that do not hibernate. Interestingly, those species that go with the second option, prepare three to four food stores, but don't mark them. Instead, they rely on their sharp nose, which helps them detect food stores in the ground even when it is covered with snow, to find it.
● As for hibernation, that will depend on which species you are taking into consideration. Most ground squirrels hibernate.
Arctic ground squirrel
Arctic ground squirrel
  • The Arctic ground squirrel (Spermophilus parryii), for instance, hibernates for 7 to 8 months.
Richardson's ground squirrel
Richardson's ground squirrel
Alpine marmot
Alpine marmot
  • Similarly, the Richardson's ground squirrel (Urocitellus richardsonii) and Alpine marmot (Marmota marmota) are known to hibernate for up to 9 months.
Thirteen-lined ground squirrel
Thirteen-lined ground squirrel
  • Even the thirteen-lined ground squirrel (Spermophilus tridecemlineatus) and Franklin's ground squirrel (Spermophilus franklinii) resort to hibernation.
Note that all these species are found in areas where winter is extreme as a result of which, food availability becomes an issue.
During hibernation, these squirrels lower their body temperature to a few degrees below the ambient temperature in their burrow. As they rely on fat stores in their body for energy, they lose a lot of weight by the time they resurface. The case of chipmunks though, is a little different. They do resort to hibernation, but don't store fat like other hibernating species. Instead, they wake up every few days and feed on stored food. And when they wake up for feeding, they also bring their temperature back to normal.
Hibernation or Torpor?
Experts seem to be divided over the question of hibernation in squirrels, with some of them saying that they do not hibernate, but instead enter a form of dormancy known as torpor. Both hibernation and torpor are characterized by low body temperature, low metabolic rate, slow heart rate, and slow breathing. If at all, it's the time frame that sets them apart. While hibernation can go on for months or as long as winter lasts, torpor lasts for a short period; a few weeks at the max. (Also, there is a concept called daily torpor, where the animal undergoes dormancy for a part of the day.) In essence, torpor is as good as a shortened version of hibernation.
Like we said in the beginning, not all squirrels hibernate. Some of them are active throughout the year, only taking short breaks when a significant fall in temperature makes things unbearable. They start preparing for winter in fall by collecting and storing food in their dreys. So, they never really face the problem of food shortage which is associated with winter, and considering that scarcity of food is one of the main reasons why animals resort to hibernation and migration, these squirrels don't have to resort to either.