Wednesday, February 4, 2009

Animals & Heat Loss

Nature Watch
February 4, 2009

By Susan Benson,
CNHM Director of Education

As I mutter about the cost of heating in my home this winter, I am at the same time reminded to be grateful for this heat. I cannot imagine what it would be like to be outdoors all winter long in these continual, below zero temperatures. If one ponders all of the ways that an animal can lose heat, it is astonishing that they can survive at all. For anyone who has studied physical science, they might recognize the terms convection, radiation, conduction, or evaporation, which are some of the challenges animals in our region face in the winter.

One way heat can be transferred away from an animal’s body is through conduction, in which an animal loses heat from their skin to the air, or from their foot surface to the ground. When temperature differences between an animal and its surroundings are greater, heat is conducted much more quickly. Animals with dense fur or more air in their fluffed up feathers conduct less heat into the surrounding atmosphere.

Moving air or wind can cause convection to occur as the wind takes heat away from animal’s bodies, but has a smaller impact when the thickness of an animal’s fur is greater. Animals can also lose heat through radiation, similar to a radiator in our house. We can lose heat to evaporation through our exhaled breath, or when animals sweat. The idea of putting plastic bags around your socks in winter has merit, as it keeps the warm water vapor from escaping, so although your feet get wet with perspiration, they still stay warmer. Studies have shown that radiant heat loss amounts to ten percent or less of an animal’s total energy loss, and so is disregarded as a significant factor in heat loss.

How do animals cope with these -22 degree nights? Animals can huddle together to decrease the surface area of their exposure. By increasing the thickness of the underfur as insulation, a deer mouse can increase its insulation by one-third in the winter. Many mammals increase the thickness of their fur behaviorally by raising their hairs, and birds fluff their feathers, trapping more warm air closer to their bodies. Some animals curl their extremities closer to their bodies. By sharing their lodges, beavers can keep the internal temperature above freezing. Many small mammal species (least shrews, meadow voles, and white-footed mice) that are solitary during the summer live together in social communes during the winter in nests under the snowpack. One vole species that had as many as ten individuals in one nest was found to be twelve degrees warmer than ground temperatures and up to twenty-five degrees warmer than air temperatures. Some small birds go through a controlled hypothermia every night, decreasing their body temperature a few degrees and reducing their heat flow.

Whatever way an animal copes with our winter cold, I continue to admire their abilities. I appreciate my insulative ability of my winter coat, hat and mittens that allow me to enjoy outdoor activities. Still, I wouldn’t trade it for what our animal friends have been exposed to this winter.

Nature Watch is brought to you by the Cable Natural History Museum. For 40 years, the Museum has served as a guide and mentor to generations of visitors and residents interested in learning to better appreciate and care for the extraordinary natural resources of the region. The Museum invites you to visit its facility in Cable at 13470 County Highway M or on the web at to learn more about exhibits and programs.

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