Hirundo’s Guide to Surviving the Winter

Author: Nicole McAdam

Hibernation

Do you ever wish you could curl up and nap for a while during the cold and snowy winter months? Well, many animals do! You’ve likely heard of hibernation, the time when animals enter their dens for a deep, extended sleep and do not wake, regardless of external stimuli (MDIFW, 2014). Some mammals qualify as "true" hibernators, such as groundhogs, while other wildlife rest using different forms of dormancy to conserve energy in the wintertime. 

Brumation

In the cold season, ectothermic critters like salamanders, turtles, and snakes reduce their rate of breathing and activity, which can range from weeks to months, in a period called brumation. This state is triggered when the temperatures become very cold, and results in their body temperatures lowering to match that of the environment.

Typically, these animals reside in a sheltered area, or hibernacula, throughout this time. Snakes, like garter snakes, can even be found cuddled up in large groups under piles of rocks for winter. These critters are able to occasionally wake to drink water if the temperatures become warm enough (Gahbauer, 2017). In Maine, Wood frogs are a particularly interesting species to observe during the winter time, as they are capable of freezing almost completely solid! They are able to do this for days at a time, and produce a type of antifreeze that prevents them from becoming “frogcicles” in the wintertime.

As the days grow shorter, trees recognize that their efforts to continue producing chlorophyll (the green, sun-catching pigment) are not energetically worth it, due to the shortening days. In order to conserve as much energy as possible, they choose instead to halt chlorophyll production and drop their leaves. This leaf abscission (or dropping of leaves) allows the plant to focus its efforts throughout the winter on staying alive, keeping water and sugars moving through the phloem and xylem (the straw-like structures that move sugar and water throughout the tree).

Torpor 

Another type of dormancy experienced by critters in Maine is called torpor, and is experienced by birds and some mammals. Many people might be surprised to learn that our beloved black bears enter this torpor in winter, meaning they are not true hibernators. During this time, energy is conserved by reducing their activity and breathing rates. From a state of torpor, though, animals can be roused by external stimuli, unlike with official “hibernation”. In this state, animals often appear disoriented, but are fully equipped with senses and can use their fight or flight instincts when necessary.

Hyperphasia

Before these hibernating animals can even enter these forms of dormancy for the season   they first have to commit to a period of what is called hyperphasia, or eating… a lot. In doing this they are able to  bulk up significantly before the winter weather comes. This is a biological necessity, ensuring that the animal has enough energy stores to survive the winter, even with their reduced metabolism and energy conservation tactics. For a great example of hyperphagia in action, check out the bears of Katmai National Park in Alaska. Each year these bears are part of a friendly contest known as Fat Bear Week. Photographs of the bears from the time they emerge from dens in spring are compared with photos of the bears just before they den up again for winter. Watching how dramatically they change over the seasons shows just how important hyperphagia is for survival.

So, the next time you feel like taking a rest following a big meal this season, recognize that this is your body’s way of conserving energy to get you through tough times!

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References:

Did you know... (2014, January 9). MDIFW Blog. December 1, 2025,

Tedesco, L. (2025, October 26). How Maine’s Wildlife Prepares for the Long Winter Ahead. AZ Animals. December 1, 2025.

Gahbauer, S. (2017, February 21). How Canadian Wildlife Survives Winter. Nature Canada. December 1, 2025, Gahbauer.

Wood frog. Wood Frog: Reptiles & Amphibians: Species Information: Wildlife: Fish & Wildlife: Maine Dept of Inland Fisheries and Wildlife. (n.d.).