Photo by Leroy Buckley.

February 1, 2024

Baby, It’s Cold Outside

A gray and buff dove perches on a snowy tree branch while puffing up its feathers for warmth. Snow is falling all around the bird, and in the background is a snowy forest.
Image by Gregory Sabin, Pixabay.

Tis the season for throwing another log on the fire or bumping up the thermostat. It’s also the time of year that we scan the weather forecast before leaving the house to determine how many layers of clothing will be necessary to stay warm. Will a hat and mittens be needed? Is waterproof apparel a must?

In the natural world, some organisms will move south where warmer weather ensures the availability of food and water resources. For others, some interesting strategies are required for finding food and water when temperatures plummet and snow or ice cover their habitat.

A Long Winter’s Sleep, or Perhaps Just Short Naps

Hibernation is a strategy characterized by a mammal reducing its body temperature, metabolic rate, respiration and heart rate, allowing the animal to enter a state of dormancy. Few Illinois mammals truly hibernate. Thirteen-lined ground squirrels, eastern chipmunks and groundhogs will enter a deep hibernation. Raccoons, striped skunks, Virginia opossums and American badgers will sleep for extended periods of time, awakening occasionally to feed or drink.

Of the 13 species of bats typically found in Illinois, at least six species will hibernate in the state. Bats wintering in Illinois generally begin to hibernate in October or November and emerge usually in early April when the weather warms and food supplies become readily available. Caves and abandoned mines are preferred hibernacula. On occasion, in areas with limited natural sheltering habitat, bats will hibernate in homes or businesses. If you do find bats in your living quarters you should follow established guides. Bats are protected under the Illinois Wildlife Code and cannot be killed or harmed without consulting with the Illinois Department of Natural Resources. Bats may only be removed from your home or business per the conditions of Administrative Rule 525, Section 525.75.

Shelter Becomes Prime Real Estate

Finding a burrow, hollow tree, abandoned building, rock crevice or leaf nest is a must for certain animals as they need to shelter out of the wind and weather.

A snowy tree with a hole in the side of its trunk. In the background is a snowy forest landscape.
Photo by AStoKo, Pixabay.

Unlike most mammals, opossums have a relatively thin fur coat, so finding shelter is critical to surviving brutal winter conditions. For additional thermal protection within their shelter, opossums collect dry vegetation and, with their tail, carry it to the den site. Opossums bearing evidence of frostbite on their bare ears and tail are most often older animals that have survived at least one winter.

In 1893 ornithologist Robert Ridgway noted that ruffed grouse could be found “throughout the state in wooded districts.” When faced with severe winter conditions, this woodland grouse dives into a snowbank, sometimes moving as far as 20 feet from the entrance and several inches beneath the crusty surface. Ruffed grouse conserve considerable energy when inside this “igloo” where the temperature remains at least 20 degrees Fahrenheit. Ruffed grouse are now extirpated from the state.

According to Bob Gillespie, site manager at Prairie Ridge State Natural Area the greater prairie-chicken also seeks shelter in a snow roost to escape wind and bad weather.

“Prairie-chickens are extraordinarily winter hardy birds and can withstand intense climatic extremes,” he explained. “Winter is often considered the safest time for greater prairie-chickens as they are past the stresses of the breeding and brood rearing seasons. In winter the birds flock together as the struggle for dominance is not as frenetic and the year’s chicks have grown and are hardy.”

“Even the nostrils of prairie-chickens are feathered, which helps keep snow from impeding their respiration and to essentially ‘pre-warm’ the air they breathe in, insulating their respiratory system,” he elaborated.

Fancy Footwear

As if building a snow cave wasn’t enough, prairie-chickens and ruffed grouse have morphological adaptations—their own versions of winter boots and snowshoes, if you will—that help them walk on slippery surfaces.

As winter approaches, prairie-chickens and ruffed grouse grow comb-like, fleshy projections on the edges of their toes. These specialized scales, scientifically known as lateral pectinate scales, increase the surface area of their feet and act much like ‘snowshoes’ by allowing the birds’ weight to be supported by slightly crusty snow. The pectinate scales drop off by spring.

Gillespie described the legs of prairie-chickens as being feathered down to their toes, providing protection akin to winter boots.

Birds aren’t alone in developing protective winter ‘footwear.’ Prior to winter, the hair on the feet of red foxes will thicken, providing protection for their bare foot pads.

A bison with snow in its fur stands in a snowy prairie. The bison sticks out its tongue.
Photo by USFWS Mountain-Prairie, CC BY 2.0, via Wikimedia Commons.

Wise Use of Muscles

Muscles connected to feathers allow birds to fluff their contour body feathers in a process called piloerection. By trapping air within their feathers, birds are able to increase insulation and to decrease the number of calories burned. In the effort to maintain body heat. In chilly conditions, a bird, such as the wild turkey with its nearly featherless head and neck, may tuck its head under feathers on its back to minimize heat loss.

Mammals have hair, which insulates their body from brutal winter conditions, damaging sun rays and precipitation. Generally, mammal hairs face backwards and downward, helping to protect the animal from the wind and precipitation. Various muscles control tracts of fur, allowing the mammal to shake off rain or snow. Muscle movements also can adjust the direction of the hair within the fur tracts.

Huddle Up

Sharing body heat is another strategy for winter survival. Striped skunks will gather in groups of a dozen or more when sheltering during the worst of winter weather conditions. Cuddling skunks are able to conserve body heat at a time when fat reserves are dwindling, and food is becoming scarce.

During the winter months, bobwhite coveys—10 to 20 birds in number—huddle in a circle. Ever vigilant for predators, quails huddle up with their heads facing outward and tails touching, an arrangement that allows each individual to share its body heat with its neighbors and to watch for predators.

Donning a Winter Coat

A red fox curls up to sleep in a snowy landscape.
Photo by Yellowstone National Park, Public domain, via Wikimedia Commons.

The coats of most mammals thicken prior to the onset of winter, providing an insulating layer of thick hair develops close to the mammal’s body and longer guard hairs serve as a ‘raincoat.’ Also, a protein layer that coats each hair keeps water from soaking through to the skin.

On the open prairie a bison faces bitter winds and driving snow. The bison’s protection from such harsh winter conditions is its dense underfur and coarse outers hairs. Bison have eight times more hair follicles than cattle. It’s no wonder that the pelage of the bison was a valued resource for indigenous peoples. A bison’s short eyelashes serve to keep ice from caking around its eyes.

Curling Up

Animals, such as the red fox, may curl up in a den during harsh weather, or may sleep in the open. Curling up to protect the most exposed parts of their body, such as their belly, helps to prevent chilling. Animals may construct places to shelter or may find a good spot to curl up. To save body heat, a squirrel may curl up in a tree hollow or drey (leaf nest created by the squirrel) and a mouse likes a nice nest to curl up in.

Nature’s Neoprene

Creating a barrier to the icy waters of winter is critical for aquatic mammals, such as beavers, muskrats and river otters. If you have the opportunity to watch these mammals for an extended period of time, you will likely see them grooming. They spread oil from the castor gland at the base of their tail throughout their fur, sealing their bodies from water and ultimately keeping themselves warm. Beavers’ and river otters’ dense fur coats trap bubbles of air when the animals submerge, in a process called entrainment, creating an additional barrier to cold water. The insulative value of the fur of these aquatic mammals was studied by engineers at MIT and imitated in the development of a new wetsuit material for scuba divers and surfers.

A brown river otter walks on top of an icy river. In the foreground are some snowy tree branches.
Photo by U.S. Fish and Wildlife Service – Northeast Region, Public domain, via Wikimedia Commons.

With a mere 100,000 hairs per square inch on the human head, a person has far less natural insulation than the river otter, which has 373,000 hairs per square inch. So, cover your head when it’s cold outside.

Amazing adaptations, effective strategies and good quality habitats allow birds and mammals to survive in even extreme winter conditions.
Gillespie pointed out that when a wicked blizzard descended on the wide-open Illinois prairie, greater prairie-chicken flocks would move south. He described these as sub-migratory movements, saying “Why not! Winter in central Illinois is not for the chicken-hearted.”

When winter makes you shiver, shiver and shake, remember the animals out in the cold and decide which of their strategies would work best for you. Hibernate? Migrate? Huddle and cuddle?

Kathy Andrews Wright is retired from the Illinois Department of Natural Resources where she was editor of OutdoorIllinois magazine. She is currently the editor of OutdoorIllinois Journal.

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