As I pass deer and hawks while driving, watch the birds at the feeders, and see the tracks of squirrels, foxes, and rabbits in the snow, I always wonder how warm they really are. I know animals have ways to keep somewhat warm in the winter, but how cold is too cold before it becomes a problem of survival?

A few years ago, when I was living in Wisconsin, we were visited by a polar vortex. It was -50 degrees Fahrenheit with the wind chill, and luckily my job required us to live onsite, because my poor car battery just gave up when faced with such extreme cold. The typical northern winter weather started late that year, but it seemed like it was never going to end. Every brief respite of slightly promising weather was quickly followed by another snowstorm or bout of extreme cold. This lasted all the way into May, and by April, the birds were making the news. Many birds had come back in April with those couple weeks of almost spring-like weather, but they were quickly forced to survive in freezing temperatures, with a snow covered land and plants that were also late to sprout, bloom, and fruit. In short, there was not enough food and some birds were literally freezing to death. People were keeping their bird feeders extra stocked, and I had never seen so many birds at our feeder. Even the birds that usually stuck around all winter had run out of food in their usual habitats.

Birds are not the only animals who utilize bird feeders during the winter. Squirrels, deer and even bears will approach feeders to get at the calorie rich nuts and seeds.

The animals that overwinter around here, much like the humans who have chosen to live here, had to find ways to survive the cold and scarcity of food. As humans, we began by building structures and fires and as time went by we transitioned into burning other things to keep our houses warm, huddling in layers, and going to the grocery store in opposition or in addition to preserving a summer harvest to last the winter. Animals don’t have the option of a grocery store. Many of them are storing food for winter or eating more in the fall and building up their fat stores. There is only so long they can survive by burning their fat stores or eating the less calorically dense food they can find in the winter. Even for those who have stored food away, eventually that food will run out, which is why we saw such an increase in birds at the feeder that Wisconsin winter. It was April, food was already sparse, and there were suddenly more mouths to feed.

That winter was an extreme example, but even in a typical winter, the animals who leave the tracks we see in the snow, or the deer and birds we see in fields as we drive by, have developed ways to survive outside. Some animals, like the groundhog, hibernate all winter. They, along with bears, bats, and some rodents, are in the category of animals that build up their fat stores during the fall and live off of that all winter. Needless to say, they are pretty hungry when they come out a few months later.

Children observing Liberty in the snow as they wonder how she stays warm.

Others rely on fur or feathers to keep them warm. When I visit Liberty, Audubon’s non-releasable Bald Eagle, with students in the winter they are often surprised she stays outside all winter and wonder if she ever gets cold. Eagles, like many birds, have different kinds of feathers to keep them warm and somewhat dry. They have down feathers, which are the smaller, fluffy ones right next to their skin that keep them warm. If you have one of those poofy coats, then it acts in much the same way. These feathers are covered by contour feathers that can act as an insulator, or in some birds are a waterproof layer, that lets the water droplets slide right off like a raincoat. Many animals with fur are similar. They have a thick undercoat and the fur at the top is a more waterproof layer. If you have a particularly fluffy dog, you might notice this, especially come the following spring when they are shedding some of that fur to get ready for warmer weather.

Many smaller animals who endure cold winters have a den or burrow underground. Both the ground and the snow covering can act as an insulator to keep their spaces at a warmer temperature than it is above ground or snow.

Looking at animals designed for hot or cold weather, you can see some other patterns in body structures that help animals survive whatever climate they are more subjected to. One of my favorite is simply ear shapes, especially in foxes. Look up a picture of an Arctic Fox, found in frequently cold climates, and you will notice they have smaller ears. Compare them to Fennec Foxes, found in the desert, who have larger ears and use the surface area to release more heat to cool down. Our Red Foxes are somewhere in the middle, as the Northeast US can run the gauntlet from freezing winter nights to hot summer days.

Red foxes have thick fur that covers their entire body to keep them warm in the winter.

We don’t have the space to explore the many behaviors and structures animals have developed in surviving the more extreme temperatures in their environment. But I bet, if you think about all the ways you manage to keep warm in the winter, you can find some similarities.

Audubon Community Nature Center builds and nurtures connections between people and nature. ACNC is located just east of Route 62 between Warren and Jamestown. The trails are still open from dawn to dusk as is Liberty, the Bald Eagle. The Nature Center is partially open, including restrooms, the Blue Heron Gift Shop, and some exhibits. More information can be found online at or by calling (716) 569-2345.

Chelsea Jandreau is a Nature Educator at ACNC.