It never ceases to amaze me how animals can spend a night in the cold—even in severe cold with freezing rain or sleet—and still survive, seemingly none the worse for wear. However, their survival through the winter depends on a number of things, such as their physical condition going into winter, the length of winter, how cold it gets, the amount of freezing rain or snow, and the success of hard and soft mast remaining from last fall’s crop. Even then, snows or freezing rains can cover available food making it inaccessible. Each type of animal has a different way of preparing for and coping with the cold, often severe weather. 

     Of course, some species of animals migrate to warmer climates. Some take long journeys of thousands of miles, while others travel short distances or just wander to different areas. For those who stay, shelter becomes a major priority. Some creatures burrow in the mud under water to “tough out” the winter in sort of a suspended animation—a sleep! These include frogs and turtles. Others just burrow into the ground or under insulating snow. They find den holes in trees or crevices. Here they may even huddle up as a group to preserve heat. They make nests of leaves or other vegetation. I used to have a cat that made a nest out of old cedar leaves at the base of and under a cedar with all day exposure to the sun. Birds will find old tree cavities that were nests for woodpeckers, or they'll find shelter in birdhouses, under the eaves of houses or in conifers as they sidle up close to the trunk of a pine or cedar, especially at night. Most songbirds will find sheltered areas in the wooded lee of a hill or mountain, and generally follow the sun throughout the day—staying in the extra warmth it provides. Others will stick to sheltered swamps with heavy growths of cedar or woods with thick stands of pine or hemlock. 

     Food and water of course is the other main priorities for survival. Some smaller birds will eat their own weight daily which doubles or triples heat production and energy levels. Some northern species like the redpoll have a little storage pouch where seeds are stored to be used at night or during storms when the bird can't venture out. In addition to calorie or heat producing food, animals have special fat, called "brown fat" (I personally have an ample supply). Biologists tell us that this type of fat seems to generate heat. Many young of some mammals have it and hibernating mammals such as ground hogs have it. Warm-blooded animals can survive and stay warm in their shelters in the cold, because their bodies have the ability to maintain their temperatures. Another way animals generate heat is by shivering. However this uses energy quickly. It’s my understanding that people shiver for the same reason, but I can remember many a duck hunt where it didn't work too well for me!

     One common bird of winter, the little Carolina chickadee, has a high-speed metabolism, which quickly converts food into energy and warmth, keeping blood circulating to help ward off the cold. One study showed that the little chickadee’s heart beats some 340 pulses per minute in summer, but increased to 1,300 beats per minute in sub-zero weather. During warm weather, the chickadee’s normal temperature was found to be about 102 degrees F., but in cold weather, rises to 112 degrees F.! Yet at this time, the study showed, the chickadee’s feet may be only 30 or 40 degrees F., which doesn’t seem to bother this “little dynamo,” because the feet are controlled from the little feather-covered thigh muscle. On severely cold nights, small birds may go into a type of overnight hibernation, with body temperatures and heartbeats dropping, reducing its need for food. One study showed small birds can survive 15 hours without food in temperatures around five degrees. However, at 20 to 30 below zero, that drops off to ten then seven hours or only about half a winter's night. So food and shelter are the most important factors concerning survival.

     The most obvious way animals keep warm is by their fur and feather coverings. Birds like the little chickadee, junco or titmouse stay warm by fluffing up their feathers. They (and other birds) have an ample covering of downy, fluffy feathers, which are fluffed up, trapping warm air close to their bodies, insulating them against the cold. This and the layer of down underneath traps warm insulating air to protect them and keep them warm. It’s kind of like when people layer their clothing to keep warm. Warm air is trapped in each of the layers providing a buffer to the cold. Birds will further reduce heat loss while breathing by tucking their bills into their back or breast. The worst enemy of birds in winter is moisture in the form of rain, sleet, or freezing rain. Birds have an oil gland on the top base of their tail enabling them to waterproof their feathers to some extent by preening and spreading the protective covering. However, if a bird (other than waterfowl) gets wet, its heating system can't work and it will not survive the night, even in moderate weather in some cases. 

     Mammals have under-fur that does somewhat the same thing, traps warm air to provide an insulating layer. Mammals associated with water such as otters, beavers, and muskrats have a dense under-fur that traps air in and keeps cold water from penetrating and coming in contact with their skin. However, even they need to find shelter during severe wind and cold. Finding a muskrat dead on the ice because it was somehow shut out of its watery entrance back to its den is not unusual. White-tailed deer have a thick winter coat made up of long, hollow hairs. In this case warm air is trapped in the core of these hairs to keep its body heat in and the cold out.

     How do these critters walk around in the snow or on ice and not freeze their feet? Birds, ducks and geese in particular, have warm blood circulating to the feet, then back to the body through arteries and veins that run up and down the legs side by side, which slowly warms it up again as the process starts all over. Blood vessels near the surface constrict, but enough blood gets through to nourish foot tissue. The temperature of the feet will be nearly that of the ice! Of course, the muscles that move the feet are buried under a warm covering of feathers. Some animals, especially those that live in the Arctic, have a special kind of fat that stays soft and pliable even in sub-zero weather. If their footpads weren't resilient it would be extremely difficult for them to move, jump or grasp. 

     The cold of winter is a crucial time for wildlife. Each animal is equipped physically or is given special abilities to cope with or withstand winter in different ways. Apparently they work, because they seem to do a pretty good job of surviving. Places to hide in order to get out of the cold or to survive a sub-zero night, and food and water to eat and drink are extremely important to our wildlife in winter. 

© 2001 Spike Knuth. All Rights Reserved.