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Keeping Warm in Winter
It took a while for winter temperatures to arrive, but they surely arrived this past week as temperatures
fell well below freezing for several days on end. We humans complain about the cold temperature. In
fact, complaining about the weather seems to be an entrenched human habit. That is surprising since
we have learned so many ways to keep ourselves warm, dry, and relatively comfortable. But think
about the wild animals that live outside without extra clothes or heated homes. How can they be so
active on such cold days?
Energy management is a key to survival for wildlife in temperate and arctic regions. Birds and nonhibernating mammals maintain body temperatures well above air temperatures on all but the hottest of
days. While this allows them to move fast and aids them in capturing food and avoiding predators or
other dangers, their warm bodies are constantly losing energy to the environment.
Heat energy is transferred, always from warmer to colder places, by several different mechanisms,
namely conduction, convection, radiation and latent heat transfer. You are personally familiar with all
of these even if you have not used these words to describe the processes.
Conduction is the transfer of energy from one material to another through contact. For example, place
your hand on a block of ice and the heat energy flows from your warm skin into the colder ice.
Convection occurs when energy is carried away from a warm object by a fluid, usually air or water. This
is the basis for the so-called wind-chill effect. Wind will carry heat away from your body faster than
conduction alone. Radiation is the transfer of heat through space. Heat radiation from the sun warms
us, but all objects can lose energy through radiation. Finally, heat is transferred to the air when water
evaporates, changing its state from liquid to gas. This is the principle behind perspiration; if your body is
hot you perspire and then as the water on your skin evaporates the heat of your body is use d to turn the
liquid sweat into water vapor, cooling your body.
With all these ways to lose heat it is amazing that small birds and other animals can survive in the
subfreezing weather that we are experiencing. These animals have a variety of ways to keep themselves
warm. First, they must eat high energy food to maintain a metabolic rate that generates heat inside of
their bodies. That explains why woodpeckers visit suet feeders and finches eat lots of seeds. Both suet
and seeds have a fairly high energy content. Second, birds and mammals that live here in the winter
have excellent insulation. Birds are literally wearing a thick down jacket. When it is especially cold they
fluff up their down to further improve their insulation. Underneath their outer feathers is a layer of soft,
fuzzy down feathers that trap air and prevent convection from carrying away much of their body heat.
As a result, their outer feathers are much cooler than their skin, so the loss by radiation is also
diminished.
Some birds and hibernating mammals can drop their body temperatures which makes the difference
between their body temperature and the environment smaller. The smaller the temperature difference,
the less heat will be lost. People use this principle when they turn down their thermostats at night or
when they are away. If the inside of your house is cooler, less eat will be lost to the outside.
This winter take time to notice how well the wild animals of Ohio are able to survive the cold. And
maybe you can learn from the wild animals and take some energy management measures of your own
to keep your body warm and lower your household energy budget. Good luck keeping warm!
PHOTO: A downy woodpecker keeps warm by having excellent insulation in the form of feathers. This
woodpecker was feeding actively at the Huston-Brumbaugh Nature Center on a chilly February
afternoon in 2015 (Photo by CM)