The Art of Winter Adaptation

As temperatures drop, winter survival strategies range from hibernation to specialized physical traits that enable animals to endure the cold. Several species of animals utilize different types of hibernation to survive the cold winter months.

In the winter session of the Wild Discovery Semester Program, we’ll be focusing on learning about the different strategies animals use to survive Maine winters.

True Hibernation

Characterized by a significant drop in body temperature and metabolic rate, true hibernators have the ability to conserve energy and survive for extended periods without the need for food or water. The jumping meadow mouse can lower their body temperature to near-freezing levels and may remain inactive for several weeks or even months. Other species that utilize true hibernation include chipmunks and certain species of bats. A few species, like the Arctic Ground Squirrel, can lower their body temperature below freezing and still survive due to a unique adaptation in their blood.

Different species may have different triggers for entering and exiting hibernation, such as changes in temperature, day length, or food availability.
Some species may wake up briefly during hibernation to urinate, defecate, or adjust their body temperature.

Little Brown Bat (Myotis lucifugus): These bats hibernate in caves, mines, and other sheltered places, lowering their body temperature, heart rate, and breathing rate.
Groundhog (Marmota monax): Groundhogs hibernate in underground burrows, with their body temperature dropping to near freezing, and their heart rate slowing to a few beats per minute.
Jumping Meadow Mouse (Zapus hudsonius): This small rodent hibernates in underground burrows, reducing its body temperature and metabolic rate.

Torpor

Torpor is a state of reduced metabolic activity and body temperature that lasts for shorter periods than true hibernation. Animals practicing torpor may enter a state of dormancy for several hours or days, depending on the prevailing environmental conditions, helping animals conserve energy during periods of inactivity or during times when resources are scarce. These animals may experience brief periods of arousal to consume stored food reserves, eliminate waste, or even give birth, before returning to their state of torpor. Some species, like bats, can enter torpor for just a few hours at a time, while others may remain in torpor for several days or longer. The depth of torpor can vary depending on factors like ambient temperature, food availability, and energy reserves. Some animals may enter torpor only during extreme weather conditions or when food is scarce, while others may do so on a daily basis.

Black Bear (Ursus americanus): Bears enter a state of torpor, with reduced body temperature and metabolic rate, but they can wake up and move around during warmer periods.
Raccoon (Procyon lotor): Raccoons may enter a state of torpor during cold periods, but they can become active during warmer days.
Striped Skunk (Mephitis mephitis): Skunks use torpor to conserve energy during cold periods, but they can become active during warmer spells.

Brumation

Brumation is a hibernation-like state practiced by ectothermic animals, primarily reptiles and amphibians, such as turtles, snakes, and some species of frogs. During brumation, these animals become less active, their metabolic rate slows, and they seek shelter to avoid the cold. Unlike true hibernation, their body temperature is not as drastically reduced, but they remain largely immobile and rely on stored energy reserves to survive. Reptiles may enter brumation at different times depending on their geographic location and environmental conditions. Compared to torper, brumation is a longer-term reduction in metabolic activity and body temperature.

Eastern Box Turtle (Terrapene carolina): This turtle species buries itself in mud or leaves to brumate during the winter months.
Eastern Garter Snake (Thamnophis sirtalis): Garter snakes brumate in communal dens, lowering their body temperature and metabolic rate.
Red-bellied Snake (Storeria occipitomaculata): This small snake species brumates in underground burrows or rock crevices, reducing its metabolic rate and activity.

Some species employ multiple approaches to hibernation, depending on their specific physiological characteristics and the prevailing environmental conditions. For instance, groundhogs may practice torpor, but they may also exhibit brumation traits during particularly harsh winters. Similarly, turtles may undergo brumation to survive the winter months, while frogs may utilize a combination of true hibernation and brumation. In addition to hibernation strategies, wildlife have evolved a variety of cold-weather adaptations, allowing them to survive and even thrive during the winter months.

Physical Adaptations

Thick Winter Coats: Animals like Moose, White-tailed Deer, and Red Foxes grow thick winter coats to insulate themselves from the cold.
Feathers and Down: Birds such as the Black-capped Chickadee and Downy Woodpecker fluff up their feathers to trap warm air close to their bodies.
Camouflage: Species like the Snowshoe Hare and Ermine change the color of their fur to white, providing camouflage against the snowy landscape and protection from predators.

Behavioral Adaptations

Migration: Some birds, like the Common Loon and several species of warblers, migrate to warmer areas during the winter months.
Caching Food: Animals like the Red Squirrel and Blue Jay cache food in the fall, providing a supply of sustenance during the winter.
Community Sheltering: Some species, like the Deer Mouse and Chipmunk, huddle together in groups to conserve body heat during cold periods.