The following article was written by Woodcock Nature Center Educator Kevin Andros.
For humans, snowy days this December mean bundling up with hot chocolate or donning many layers to go sledding. But for many animals, the cold winds signal that it is time to enter a period of dormancy. What even is “dormancy” and do all animals enter this state? Dormancy is the catchall word for when an animal slows down some of their bodily functions for a length of time. This definition is intentionally vague because there are many different types of dormancy that can vary between different types of animals or even by species. This might seem pedantic but little details are important for science and learning about these intricacies is what makes nature a wonderful thing to learn about. With that out of the way let’s get into the different methods that animals have to survive the harshness of winter.
When I say hibernation, the first thing you probably think of is a bear cozied up in a cave all winter long. As cute as that is, hibernation is a misnomer for what bears do in the wintertime. Before I talk about what bears are doing compared to the “true hibernators,” we should outline the characteristics of true hibernators:
- body temperature becomes almost as cold as the air temperature
- heart rate and breathing slow down tremendously
- metabolic rate (the amount of energy used by the body) is reduced
In Connecticut, our true hibernators are only the groundhog, some species of bats, and jumping mice. Those are the only animals that display all three characteristics for long periods. The key reason this is such a short list, and why black bears aren’t included, is body temperature. Bears and most other mammals cannot bring their body temperature low enough to fit the definition of a true hibernator. A bear’s body temperature really only gets around 12 degrees cooler than normal, nowhere close to the ambient temperature. Groundhogs and bats that hibernate instead of migrate have body temperatures only a few degrees above freezing!
Don’t feel too sad for bears. Some scientists have started to call what bears do during winter “super hibernation” since they use some amazing strategies during their long winter rests. For example, they don’t need to wake up to use the bathroom like some hibernators, they have amazing systems to recycle their waste.
Many animals utilize torpor instead of hibernation. Topor can be thought of as a mini version of hibernation. It is similar in that the heart rate and metabolism are severely reduced but for much shorter periods of time. Also, the all-important body temperature does not get as low. Many of our local rodents, like the gray squirrel, deer mice and chipmunks, can enter periods of torpor during extremely cold days. They must awaken to eat every so often so their torpor usually only lasts for a few days.
Reptiles and amphibians go into a state of dormancy known as brumation. It has a lot of similarities to hibernation and many of the differences are very dense chemistry that we don’t need to get into. Just remember that cold-blooded animals are the ones that brumate rather than hibernate. Here at Woodcock there are painted turtles brumating at the bottom of our pond and in the forest there are dens of snakes brumating together. Sometimes different species of snake will even den together (I imagine nature enthusiasts would have a very different reaction to finding one of these than Indiana Jones).
Focusing on insects, many prefer migration over dormancy but we also see many species entering a state known as diapause. This is again very similar to hibernation where many bodily functions slow down but it is exclusive to insects as the complex processes that occur internally can’t happen in other types of animals.
Just as flowers will bloom in the spring and kids will stop getting snow days, the animals will no longer need dormancy in a few months. But for now, take the time to enjoy the more relaxed and lethargic state that animals feel in the cold, or that we feel after a big holiday meal.