Best in Snow: How Wildlife Weathers Winter

There are two types of people: people who enjoy winter … and everyone else.

For cold weather enthusiasts, winter comes as a welcome diversion from the daily grind and gives us a chance to test the limits of our bodies to achieve peak performance.

Barney Bear expertly skis while reading. Source: https://gph.is/2rSILVn

For everyone else, this time of year is synonymous with staying inside and enjoying the winter from within the warm confines of our homes, complete with hot cocoa, cozy blankets, and binge-watching TV.

Kevin McCallister (Macaulay Culkin) waves out the window in Home Alone. Source: http://gph.is/2gQjM1V

Whether you love winter or hate it, we can all agree on one thing: to withstand the cold days and long nights, one must be resilient and maybe a little crazy. This is even more so for the animals, insects, and plants that don’t have the luxury of escaping into a warm house when the freeze starts to bite a little too hard.

When thinking about the hardiest winter species, you may picture heavy-hitters such as lynx, polar bear, musk ox, walrus, caribou, and bison — all of which are the epitome of winter’s beefiest warriors. However, mastering the art of winter survival isn’t limited to only the biggest and baddest. From frogs that freeze solid to meat-eating songbirds, nature has some fascinating winter survival tricks for enduring these long months.

The Supers: Super winter species

River Otters

face of a river otter
North American river otter. Photo courtesy of Chris Paul/Creative Commons

These little cuties are built for the snow and cold. Much like human fresh pow enthusiasts, river otters make the best of winter by using the fluffy white stuff to slide down hills, frolic through snowbanks, and throw down in a game of snow-wrestling. But they aren’t just otterly adorable — river otters have some nifty tricks for weathering the weather. These all-terrain funsters have two eyelids, one of which is completely clear to allow them see in icy waters when closed. They also have two layers of fur, including a warm underlayer and a waterproof outer layer.

Otters can hold their breath for a long time — long enough to dig up their fave winter snackies: turtles and frogs hibernating on the bottom of rivers. Real-estate geniuses, otters will often move into beaver neighborhoods, where they can feed on fish trapped by river dams. And, since beavers are herbivores, the two don’t compete for food. Water that is deeply frozen may force otters to make long treks to warmer areas, but these mammals still find ways to have fun wherever they are.

Chickadees

Chickadee on animal bones
This chickadee was spotted foraging at a deer carcass in Massachusetts. Photo by Leah Riley/USFWS

Who would guess that chickadees are winter superstars? But they are. These little birds can go into regulated hypothermia, dropping their normal daily body temperatures by 12–15°F. This helps the birds conserve energy and store fat over the winter. Totally metal, chickadees even have a taste for blood.

In the winter, black-capped chickadees will eat fat or frozen meat from animal carcasses, along with such foods as insects, spiders, seeds, and plant matter. They also have a half-inch layer of feathers to keep them warm. Fascinated by these little birds? Read more about chickadees.

Organic Antifreeze

Most fish, frogs, and turtles will go to the bottom of waterways and hunker down for the winter, but some species have something extra to help them thrive during the winter: organic antifreeze.

Some fish species, including Arctic cod, Arctic flounder, and Antarctic eelpout, have proteins in their bodies that act as antifreeze, allowing the fish to thrive through winter.

closeup of tan frog with black and green lines and spots
Boreal chorus frog. Photo by Jay Fleming/NPS

Boreal chorus frogs, wood frogs, and other amphibians also have the ability to turn themselves into living blocks of ice. By filling their cells with special proteins and glucose, these frogs can essentially freeze their blood without damaging the cells. The frogs spend the winter in a dormant state, without breathing, eating, or even having a heartbeat, until they can thaw in the spring. These frogs can be found as far north as the Canadian Northwest Territories, so some frogs remain frozen for up to eight months out of the year!

Wooly Bear Caterpillars

Even invertebrates like some spiders, centipedes, mites, beetles, fireflies, and other insects share this antifreeze superpower, including the wooly bear caterpillar.

furry brown and black caterpillar n rocky ground
Woolly bear caterpillar. Photo courtesy of Christa R./Creative Commons.

Also known as “Adorable Bug-bears,” these fuzzy caterpillars were once seen as predictors of winter weather; the wider their rust band, the milder the winter — or so the story went. Wooly bear caterpillars are surprisingly resilient to the cold thanks to a substance in their bodies called glycerol — another form of organic antifreeze. As the weather turns colder, the caterpillars slowly freeze, but the glycerol prevents their inner cells from freezing, allowing them to survive even the most extreme winter weather conditions. Pair that with their ability to self-medicate against deadly parasites and you’ve got a tough little bug that is ready to throw down.

I’m Cold, Let’s Cuddle

Much like us humans, some species prefer to cuddle up and create their own warmth rather than brave the freezing temperatures.

Indiana Bats (Endangered Species)

large number of bats clustered together on rock ceiling
Cluster of Indiana bats. Photo by Andrew King/USFWS

Indiana bats find winter warmth by cuddling in large clusters that can reach densities of up to 500 bats per square foot. Because insects become so sparse during the winter months, bats must accumulate several layers of fat before entering hibernation. So, in other words, they get to get fat AND cuddle all winter.

Bats only have so much fat to last them through the winter. If they are disturbed too often, they can expend so much energy that they starve. This is part of the problem with white nose syndrome, a devastating disease that is marching its way across North America. A cold-loving, white fungus infects the skin of the muzzle, ears, and wings of hibernating bats. This resulting disturbance causes bats to exhibit strange behavior like flying outside in the daytime during the winter. Affected bats quickly use up their fat reserves and starve.

Tree Swallows

20 or so blue and white birds huddle on a branch in snow; 2 on offshoot
Tree swallows during spring snowstorm. Photo courtesy of Keith Williams/Creative Commons.

The snuggle-up strategy even has a scientific name: kleptothermy, which means stealing body heat from others. But we say it’s more like sharing than stealing. Much like the Indiana bat, tree swallows use kleptothermy. Instead of squeezing themselves into tight balls, the swallows must get close enough to share warmth — but not so close that they compress feathers and reduce insulation.

Ruffed Grouse

bird sitting in snow
Head Harbor Light Station/ Flickr Creative Commons http://ow.ly/wKZX50CXxIq

Ruffed grouse also cuddle together to stay warm, adding an extra level of insulation to their down feathers, built to trap heat. In the late fall, feathers begin to grow on their legs to protect from the cold and help conserve body heat. Grouse also grow extra bits of cartilage called pectinations on their toes; these help them walk on snow, roost, and burrow. These cuddle kings use these pectinations to build out thickets or snow forts for their winter retreats.

It’s So FLUFFY!

There’s fluffy and then there’s fluffy. Some animals keep warm in the winter by packing on the fur and feathers. Other floof boys and girls of the thic persuasion lay on the pounds and promptly lay down. We’re talking about animals like the Pacific walrus cows of Togiak National Wildlife Refuge in Alaska, which use their several-inch thick layer of body fat to withstand freezing temperatures. Whether packed with fluff or fat, these hardy species prove that it is only natural to put on a few … layers … when winter rolls around.

At left: The winner of Fat Bear Week 2020, a big brown bear in stream. Photo by N. Boak/NPS. At right: A polar bear shows off its thick fur. Photo by Lisa Hupp/USFWS

For many people, the top-of-the-mind animals in the fully fluffed-out-for-winter category is bears. You might think of brown bears — like the voluptuous participants of the National Park Service annual Fat Bear Week. Or perhaps you think of their biological, non-hibernating, sister species, the polar bear, who are able to keep up and moving thanks in part to their black skin that absorbs the sun’s light. Yep, you read that right — polar bears have black skin. Their fur may look white, but each strand is actually clear, allowing the sunrays to reach their skin.

It’s true, with these adaptations, that bears deserve their fair share of fluffy fame. Here are a few other examples of fluffy fauna and their famous layers.

Arctic Fox

white fox curled up near rocks in snow
An arctic fox blends into the snow. Photo by Keith Morehouse/USFWS

Living, quite literally, in the shadows of the polar bear is the artic fox. In winter, these adorable four-legged floofs are known to brave the sea ice to follow close behind the bears. Much like a desperate roommate, these scavengers pick whatever they can from polar bears’ leftovers.

In cold weather, Arctic foxes nearly double their body weight and fur density. This helps them endure extreme differences between their internal body temperature and temperature outside — important since they live in some of the most freezing parts of the world.

Like the waterfowl species in our blog How to birds keep warm in the winter, artic foxes use countercurrent circulation in their paws to keep warm on any terrain. In this process, veins that return cold blood from the feet run alongside warm arteries flowing from the body to the feet. The warm arteries heat the cold blood considerably before it reaches the body, reducing the foxes’ overall heat loss.

Snowy Owl

big white owl sits atop pole
Snowy owl. Photo by Photo by Alex Galt/USFWS

Equally iconic, the snowy owl are winter celebrities and with looks like that, is it any surprise? The layers and layers of white feathers are more than just an aesthetic. Snowies have so much insulation that their fluff tips the scales making them the heaviest owl species in the Northeast. Fabulous from their head to their feet, snowy owls have thick feathers that line their toes work like slippers insulating their killer claws. Snowy owls are diurnal, hunting all hours of the day and have been observed storing caches of prey for the scant days of winter.

Snowshoe Hare

At left: Snowshoe hare turning white for the winter at Silvio O. Conte National Fish and Wildlife Refuge. Photo by USFWS At right: A snowshoe hare with its fully white winter coat. Photo by NPS

Though the snowy owl is no doubt a winter fashion icon, few animals know how to rock an outfit change like snowshoe hares. Each fall, these little buns trade in their brown fur for a thick white coat. Like the polar bear, these white hairs are, in fact, hollow and work as insulation from the cold. In the deep snow of winter, predators also have a hard time spotting these fluffy mounds because their white coats blend seamlessly into their frozen surroundings. Completing the look is the snowshoe hare’s large hind legs and toes. These great big feet help them better navigate the slippery snowy slopes.

We can’t all be winter winners up for fun in the flurries or ready to embrace the cold. Whether you’re craving some cozy cuddles or laying on the fluff, it’s only natural! For now, take a tip from these hardy species. Try not to fight the forecast and remember sunnier days are only a few weeks away!

By Sydney Giuliano, Christina Stone, Susan Morse, Tina Shaw, Leah Hawthorn, Lisa Hupp, and Tom Koerner

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U.S. Fish and Wildlife Service

U.S. Fish and Wildlife Service

We’re dedicated to the conservation, protection and enhancement of fish, wildlife and plants, and their habitats.