Do hibernating squirrels and marmots have better resistance to cold than other mammals, even before they enter hibernation? It seems like they would be too cold to sleep all winter.

Question Answered by Greg Burak, Biologist, Fish and Wildlife Service,  Boise Office

That is a great question!  During hibernation, ground squirrels, such as the northern Idaho ground squirrel, enter long periods of time when they are inactive and sleeping.  This is called torpor.  While in torpor, the body temperature of a ground squirrel is about the same as the surrounding soil temperature, which can approach freezing (32 degrees). 

Hibernating animals can not stay in torpor through their entire hibernation period though – they need to “wake up” periodically, even for just short periods of time.  This is called euthermic arousal.  These short periods of euthermic arousal lead to temporary increases in body temperature and heart rate.  When hibernating squirrels enter torpor again, their body temperatures return to the surrounding soil temperature and their heart rate declines.  This repeating cycle of torpor and euthermic arousal occurs throughout their 8 months of hibernation.

What may be most important for ground squirrels to successfully survive hibernation is to enter it in as good a body condition as possible (in other words, healthy with plenty of energy reserves).  This allows them to survive the rigors of hibernation, such as when they repeatedly go in and out of torpor.  What also helps them survive is that they hibernate underground in areas that provide the best conditions for hibernation.  These areas provide the ground squirrel relatively consistent soil temperatures they need that are not too cold or too hot – (certain animals also estivate, which is similar to hibernation, but occurs during times of heat and dryness).  These factors allow ground squirrels to survive hibernation and successfully emerge in the spring.

The Squirrel Family

Squirrels are found in almost any type of habitat, from forest and grasslands to cities and towns.  There are three basic divisions of the squirrel family:  tree squirrels, ground squirrels, and flying squirrels. 

What is difference?

All members of the squirrel family look quite a bit alike. They are furry and have bushy tails, although the ground squirrel’s tail isn’t quite as bushy. They have strong, muscular hind legs. 

Tree squirrels are skilled climbers.  They have long bodies, long ears, and sharp claws.

Ground squirrels are stocky and are good diggers.  They live in burrows and prefer open habitat.

Flying squirrels are not capable of true flight.  Instead, they glide between trees using a thin membrane of skin that stretches between their wrist and ankles.  They tend to live in forested habitats.

Food Caching

As we learned Mr. Burak’s answer above, ground squirrels hibernate in the winter.  Flying squirrels and tree squirrels do not hibernate.  To get through the long winter months, they store food during the fall to eat in the winter.  This is called caching.

Unlike rodents that build “larders” -a single stash of food, typically kept in a nest or burrow- many tree squirrels use a strategy known as “scatter caching,” which protects their food by spreading it across hundreds or even thousands of hiding places.  Thanks to a really good spatial memory and a strong sense of smell, squirrels recover about 40%-80% of their cached food.

Calculate Squirrel Caching

Materials: 100 sunflower seeds in shells, cookie sheet, sand, squirrels in your neighborhood

  • Sprinkle the sunflower seeds on an old cookie sheet. Cover them with a fine layer of sand, making sure a few seeds are exposed.
  • Place the sheet near a tree as far away from human activity as you can.
  • Check your tray about 24 hours later. Count the empty seed shells and uneaten sunflower seeds.

You can calculate how many seeds the squirrels may have cached by subtracting the number of uneaten seeds and the number of empty seed shells from 100 (the total seeds).  For example:  100 – (20 seeds immediately eaten  + 60 seeds not eaten) = 20 seeds that were cached.

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