Thermoregulatory Influences on the Ecology of Two Sympatric Varanids in Sri Lanka

We studied the interaction between thermoregulatory behavior and ecology of two species of sympatric varanids, Varanus salvator and Varanus bengalensis, in south Sri Lanka. V. salvator was active by early morning but sought shade in the afternoon; any afternoon activity was in an aquatic environment. Although the regression of V. salvator cloacal temperatures on daytime ambient temperatures is significant (P = 0.02) and indicate thermoconformity, they maintain a relatively stable body temperature behaviorally by selecting appropriate thermal microhabitats. During the night they sought stable thermal microhabitats under dense bushes, thickets, and even in water (which is warmer than the night air temperature). This presumably enabled them to be active early the following morning. V. bengalensis commenced activity later in the day and tend to elevate body temperatures (P < 0.01) by basking. They also forage in the open thus thermoregulating while feeding. By evening they retreat into burrows and other refugia where body temperatures drop below air temperatures. Thus, both species tend to thermoregulate behaviorally by selecting appropriate thermal microhabitats and exhibit temporal partitioning of activity times.