Did your teacher ever tell you that every square is a rectangle, but not every rectangle is a square? Similarly, hibernation is a type of dormancy, but not all dormant animals hibernate. That’s because hibernation is a really specific kind of dormancy.
Dormancy describes an animal that has slowed down its bodily functions for a little while, but hibernation has some very specific rules.
There are lots of different kinds of dormancy...
Winter has two big problems for animals. There’s less food and it is intensely cold. These environmental stressors cause a wide variety of animals to go into a state of dormancy. While hibernation is often used to describe any animal that goes into dormancy in the winter, there are three very specific requirements for an animal to be considered a true hibernator: reduced metabolism, slower heart rate, and lowered body temperature.
A much broader array of animals experience forms of dormancy other than true hibernation. For instance, brumation is another, special kind of dormancy that snakes and other reptiles use. While their metabolism does decrease, the drop is forced by the cold weather since reptiles can’t create their own body heat. This temperature change also means that reptiles can’t digest food for the whole winter. Instead, they spend the winter months in brumation waiting for warm weather to return.
Most animals going into dormancy need to store enough food or fat to last the entire winter though! Larger species, like bears, eat tons of food in the summer and early fall and convert it into fat to use over the winter. However, smaller species, like squirrels and mice, store food to eat slowly over the course of the winter.
The dormancy line-up
Rodents are the champions of hibernation. In addition to the many rodent species that store food and reduce their heart rate and metabolism, certain rodents can significantly drop their body temperature during the winter months. Arctic ground squirrels, who usually have a body temperature of 99 degrees Fahrenheit, can drop as low as 27 degrees Fahrenheit! This below-freezing body temperature can last for a few weeks before the squirrels have to briefly wake up and warm up. Then it’s back to hibernating and waiting for warm weather to return.