Life In The Cold: A Presentation of Cold Weather Adaptations
Cheyenne Mountain Zoo, Colorado Springs, CO
Life in the Cold was presented as a three hour Continuing Education Program for the Cheyenne Mountain Zoo docents. Obviously in thirty-five minutes I can only hope to present the general structure and format of the program, highlighting the major points covered each segment (warm-blooded, cold-blooded and plant survival strategies). It is not my intention to develop every point that was made during our workshop, but rather to outline the organization, structure and presentation of the program, providing guidelines for other docent groups who may wish to develop similar program.
The first segment was devoted to warm-blooded animal survival adaptations and strategies. This section comprised the bulk of the workshop. Survival options for homeotherms to avoid the worst of winter include migration (triggered by the number of daylight hours) and hibernation (more common among mid-latitude animals, a comparison of shallow and deep hibemators). If winter can’t be avoided, it must be confronted head-on by resistance. Resistance was the survival option focused upon. Resistance means an animal must continually maintain a body temperature above its surroundings. To understand how this is accomplished, we need to first understand the mechanics of how warm-blooded animals lose heat and how they generate heat.
Heat loss: conduction, convection, radiation (not significant) and latent heat exchange (respiration and evaporation, again not too significant)
Generating Heat: basic metabolism, muscle exertion (voluntary and involuntary) and heat absorbed externally
Strategies to lessen heat loss and lowering the Lower Critical Temperature are essential to surviving in the cold temperatures of winter.
Reduce heat loss: reduce surface exposure, reduce body-to-air temperature, maintain metabolism with food and increasing body insulation
Lowering the LCT: becoming desensitized to the cold, decreasing body temperature, reduce body weight, counter current heat exchange and increase in metabolic rate.
Finally, animals may arrive at the point where they have reached their LCT-and must now generate heat beyond their basic metabolism through burning brown fat and as a last resort, shivering.
The second segment dealt with cold-blooded animals. Cold-blooded animals cannot regulate their body temperature in the same manner as warm-blooded animals and, therefore, essentially assume the temperature of their surroundings.
Most are unable to reduce any significant quantity of heat in winter. Those that can warm above the ambient temperature have difficulty maintaining elevated temperatures for any length of time. Cold-blooded animals have the same options as warm-blooded animals – migrating, hibernating and resistance. What is significantly different is the resistance strategy. Resistance for cold-blooded animals is a sophisticated, biochemical strategy. Super cooling: allows the body fluids to fall below their freezing point without the formation of ice. Freezing tolerance: the ability to withstand formation of ice within the body.
The final strategy segment dealt with plants. Plants are not able to choose between migration and confrontation. Seeds of annuals and the below ground corm or rootstock of herbaceous perennials provide ways to avoid the rigors of winter. Other plants have evolved morphological and physiological adaptations for resisting the stresses of winter. Food production and growth stop in winter. Deciduous trees drop their leaves. Trees time the dropping of leaves in the fall and the opening of leaves and flowers in spring to the changing ratios of light and dark hours. Basically, plants must withstand two stresses (low temperatures and desiccation) to survive.
To accomplish this, plants must acclimate to subfreezing temperatures. Acclimation is an active and complicated process. Plants must also weather the winter drought by resisting diffusion of water vapor — not an easy task. It is important to understand the conditions under which plants most easily lose moisture.
Exposed plants face their greatest water loss problems under bright sunshine and calm conditions. Temperature differences between the leaf and outside air influence the transpiration process. The greater the elevation of leaf temperature above the air temperature, as occurs when the leaf is absorbing direct or reflected sunlight, the greater the vapor concentration difference between the leaf and air. Maximum water loss from winter-exposed foliage occurs when leaves are heated by the absorption of solar radiation and conditions are calm. An increase in wind speed reduces leaf-to-air temperature differences, thus reducing the vapor concentration differences between leaf and air.
Therefore, there is a decrease in water loss as wind speed increases.
The points outlined in each segment are abbreviated. They need fuller development that is not permitted in the short amount of time given. These are the main points that were presented and developed at our workshop. Again, the purpose of this paper is to present how the workshop was organized and not the complete development of each point. The session ended with a take home list of wildlife that might be encountered in our area during winter, a series of animal tracks to look for in the winter snow and a variety of bird feeder recipes for birds in our area.
Life in the Cold Example of outline [compressed here to save space] handed out for note taking.
I. Warm-blooded (mammal and bird) strategies
II. Cold-blooded (reptile, amphibian, fish, arthropod) strategies.
III. Plant coping strategies
Handouts also included diagrams illustrating warm-blooded animal heat loss, brown fat storage, counter current heat exchange and the following vocabulary list.
Life in the Cold
acclimation: physiological adjustments to changing environmental conditions, especially to increasing or decreasing temperature. This term is used in the plant literature in reference to seasonal changes to cold tolerance.
acclimatization: seasonal or long-term physiological adjustment, usually in response to temperature changes. Preferred by animal researchers over the term “acclimation”.
brown fat: adipose tissue characterized by a yellow to light brown color, having a high concentration of mitochondria and hence capable of high oxidation rates and heat production
counter current heat exchange: warm arterial blood gives up heat to cold blood returning from the
extremities through veins lying in close contact with the arteries.
desiccation: extreme and damaging water loss
freezing tolerance: an ability to withstand formation of ice within the body
heat loss: conduction: loss of heat by direct contact (foot to ground)
convection: transfer of energy via a moving fluid (free convection); heat lost by the wind (wind chill) or water (water chill)
latent heat exchange: heat energy associated with phase changes of water (water to vapor)
1. evaporation: loss of heat as perspiration on skin evaporates (water to vapor)
2. respiration: loss of heat as warm air is exhaled and cold air is inhaled
3. radiation: movement of energy through space; heat directly released from the body’s surface
hibernation: periods of winter inactivity during which the normal physiological process is greatly reduced (lower body temp, lower heart rate, lower rate of respiration) and therefore, energy requirements of the animal are lowered.
homeotherm: an animal that maintains a body temperature within a high and relatively narrow range independently of the temperature of its surroundings; often referred to as a “warm-blooded” animal
hypothermia: lower than normal body temperature
intercellular: between cells
intracellular: within cells
lower critical temperature (LCT): that temperature at which a homeotherm can no longer maintain normal body temperature by passive means and must increase metabolic heat production
metabolism: chemical processes occurring within an organism (including the liberation of energy from food and stored fat)
migration: movement, usually seasonal, from one region or climate to another piloerection: the ability to make, hairs “stand on end”
shivering: homeothermic increase in heat production by involuntary muscle contractions
hunt: moving to an alternate course
subnivean: beneath the snow pack
supercooling: body fluids falling below their freezing point without the formation of ice
torpor: a temporary physiological state akin to short-term hibernation; reducing energy expenditure in periods of extreme cold or food shortage
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National Wildlife articles
“The Art of Making Hay,” Apr/May, 1997.
“Brouhaha Over Polar Bear Hair,” Oct/Nov, 1998.
“When the Going Gets Cold,” Dec/Jan, 1991.
“Tough Little Turncoat,” Dec/Jan, 1990.
“Staying the Winter,” Feb/Mar, 1995.
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“Hibernating Bears Emerge with Hints About Human Ills,” The New York Times. Science Times, Apr21, 1992.