Bartholomew and Tucker (1964) determined that varanids, while primarily heliothermic can through endogenous heat production, elevate their body temperature by as much as 2 degrees above ambient temperatures.. This is important for cool mornings as this way of getting warmer faster would prove advantageous in the field.
Other studies have shown that varanids are also capable of retarding the rate of cooling by shunting blood from the appendages to the core of the body (Brattstrom 1973). Varanids are able to increase their heat faster than they reduce it.Studies on Varanus giganteus have shown active individuals maintaining core temperatures that were 20 degrees or more above the ambient temperature (Strimple, REPTILES, 96).
Earll (1982) also showed that the mean oxygen consumption of adult V.bengalensis (at 30 degrees C it is 0.5 ml O2/g/hr) is significantly higher than expected on the basis of data for other large lizards, but not beyond the range for other varanids. Together these mechanisms tend to keep body temperatures higher than would ordinarily be the case, allowing varanids to more easily sustain the high levels of activity characteristic of their lifestyles. Furthermore, these features permit these lizards to operate over a wider temperature range than they otherwise could.When the environment gets too hot or too cold, varanids will engage in thermoregulatory behaviour. They will bask on rocks and hang out in burrows, rest in streams, sit in a warm or cool breeze etc.