Curious Nature: How animals cope in winter
To stay warm throughout the cold winter months, we bundle up with coats, boots, hats, and scarves. Animals, however, don’t have this same luxury.
A bear wearing a down coat and earmuffs would look ridiculous! Instead, animals have physiological factors that help them adjust to the cold and keep warm. There are three primary strategies animals use to adjust to their environment and stay warm throughout the colder months: hibernation, migration, or adaptation.
Mammals, like us, keep their bodies warm by maintaining a constant internal body temperature, known as homeostasis. Homeostasis is the balancing of heat loss, from outside temperature and wind chill, and heat gain from activity or solar radiation.
For larger animals, like bears, the heat they lose is proportional to the surface area of their bodies, while the heat they produce is proportional to their mass. This makes it easier for larger animals to maintain homeostasis, whereas smaller animals are forced to expend a lot of extra energy to stay warm. This plays into how these different animals cope with the changing seasons.
One way that animals combat the winter freeze is by hibernation. When animals hibernate (picture a bear in a den taking a long snooze), their heart rates, body temperature, and energy expenditures all drop. This allows them to expend less energy and use their fat reserves throughout the winter as energy.
Animals in the Rocky Mountain region who hibernate include black bears, ground squirrels, marmots, and chipmunks. For most animals, hibernation consists of falling into a deep sleep for most of the winter. However, there are some animals, like chipmunks, that enter a different type of hibernation, also known as torpor. These animals will actually wake themselves up throughout the winter. These animals do this because they do not have enough body fat to survive the long cold winter, so they have to wake up and eat stockpiled food to keep their energy budgets in the black.
But not all local animals hibernate to survive the winter. Some also migrate. Many bird species migrate away from the Rocky Mountain region after fall to avoid the harsh winters. Species like the rufous hummingbird travel all the way from Alaska to Mexico, a total of 3,900 miles, and stop in Colorado during July and August to breed. They spend their winters in Mexico and start the trip all the way back up to Alaska.
The last way that animals deal with the cold winter is by adapting to their surroundings. Animals who stay active throughout the winter in Colorado rely on many different things to keep them warm including fur and blubber.
The moose is an example of animals who have special fur that helps keep them insulated. A moose’s fur is actually hollow inside and this provides insulation from the harsh winds and prevents the moose from losing body heat. The moose will then shed this heavier outer fur in the spring and start regrowing it for the next winter. I guess we should be glad that humans don’t need to grow their own fur coats. Our coats and hats need to serve these functions of keeping our body heat in.
The varied strategies that animals use to survive the harsh winters are truly amazing, and we only scratched the surface here. But one thing is for sure — be glad that we don’t have to sleep all winter like the marmot, travel thousands of miles like the rufous hummingbird, or grow insulating fur like the moose.
This article was written by naturalists at Walking Mountains Science Center, who love winter as much as the animals around them. To learn more about animals in winter or other fascinating nature stories, visit walkingmountains.org/blog.