Temperature Regulation in Turtles
While turtle species vary widely in size and habitat, all must control their body temperatures for essential functions. Turtles can achieve a considerable degree of stability in body temperature by regulating their exchange of heat energy with the environment. Turtles exposing themselves to the sun on a log in a pond are a familiar sight in many parts of the world, because few pond turtles are large enough to maintain body temperatures higher than the temperature of the water surrounding them. Emerging from the water to bask is the only way most pond turtles can raise their body temperatures to speed digestion, growth, and the production of eggs. In addition, basking may help aquatic turtles to rid themselves of algae and leeches. Exposure to ultraviolet light may activate vitamin D, which is involved in controlling calcium deposition in their bones and shell. A few turtles spend quite a lot of time in trees; these turtles have small shells that allow considerable freedom of movement for limbs. The big-headed turtle from Southeast Asia lives in fast-flowing streams at high altitudes and is said to climb on rocks and trees to bask. In North America musk turtles bask on overhanging branches and drop into the water when they are disturbed.
Small terrestrial turtles, such as box turtles and small species of tortoises, can thermoregulate by moving between sunlight and shade. Small tortoises warm and cool quite rapidly, and they appear to behave very much like other small reptiles in selecting suitable microclimates for thermoregulation. Familiarity with a home range may assist this type of thermoregulation. A study conducted in Italy compared the thermoregulation of Hermann’s tortoises living in their own home range with individuals that were brought to the study site and tested before they had learned their way around. The resident tortoises warmed faster and maintained more stable shell temperatures than did the strangers.
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