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A Little Bit More

Thermoregulation, an activity accomplished by moving into or out of the sun to affect body temperature, is practiced by all reptiles but is probably most obvious with turtles. Thermoregulation in turtles is most highly developed in the pond or basking turtles. These are the turtles one often sees piled upon one another on a log during warm weather, each one trying to get its share of the sun's warming rays. By controlling their heat gain, basking turtles are able to elevate their body temperature to some "preferred" level above the surrounding environment.

Air and water temperature are of prime importance in initiating or terminating sunning. A recently emerged turtle often orients itself to receive maximum solar radiation and as its temperature approaches its preferred level, it may alter its posture to reduce heat gain. Once a certain temperature (about 78-82F) is reached, it either retreats to shade or to the water where it can forage at maximum efficiency. Sunning serves several functions: it warms the muscles to allow for quicker movement, it is a marked aid in speeding up digestion, it probably helps the maintenance of healthy skin by decreasing skin parasites and algal growth, and may also help the turtle in the production of vitamin D.

Painted turtles are one of the most common pond turtles in North America. Named for the elaborate red and yellow patterns on its body, which seem to have been painted on, this turtle is the only one that ranges across the continent. Four subspecies, probably the result of glaciation, are recognized: The Eastern, Midland, Southern, and Western Painted Turtles. Each subspecies is fairly easy to distinguish but areas where their ranges overlap confuse identification due to inbreeding.

Painted turtles prefer slow-moving, shallow water with a soft bottom, basking sites, and aquatic vegetation. Their diet is omnivorous, with young turtles preferring diets high in animal material. As they age, their diet includes more vegetable matter. There are many animals that prey on painted turtles; Gray Squirrels, skunks, foxes, Raccoons, and garter snakes are just some of the animals that eat their eggs. Mink, Muskrats, snakes, larger turtles, and fish prey on the young, but humans with their pesticides and cars may be this turtle's worst enemy. Depending on the geographic location, painted turtles are less active, or almost completely inactive, during the winter. They may bask on warm winter days, however, and some have even been seen slowly swimming beneath the ice of a frozen lake. Respiration beneath the ice would seem impossible, but some aquatic turtles can augment their respiration by using the lining of their oral cavity as a sort of gill. Water is brought in through the nostrils and oxygen is extracted from the water by the highly vascularized pharyngeal passages of the mouth and throat, greatly increasing their ability to remain submerged during cold weather.

Turtles are often collected and brought home as pets. Commercial turtle food may prove adequate but it's best to provide fresh foods too to ensure a well-balanced diet. Mortality of pet turtles is often very high during the winter months; it's much better if your turtle is released in its original (or at least similar) habitat when fall begins.

Activities

T-shirt Test

The painted turtles are one of the turtles found farthest north and it's not surprising that their shells are so dark in color. Here's something you can try at school or home to see how a turtle's dark shell color helps it warm up while basking.

Select three T-shirts made of the same material. Select one white, one black, or very dark, and one of medium color. Spread the three pieces, plain side up, in a sunny location on the floor or outside and wait 10-15 minutes. Now place your hand on the middle of each piece and feel its warmth.

1. Can you feel a difference between each of the three?
2. How is the dark one different from the white one and what about the medium colored one?
3. If you have three thermometers, place one on each shirt and see what the temperature differences are.

You may even want to close your eyes and have someone else place your hand randomly on each of the three pieces to see how well you can tell without any visual cues. Dark colors absorb heat better than lighter colors.

Key Concepts

Growth and Development, Behavior and Regulation

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