Thermal Ecology of Habitat and Microhabitat Use by Sympatric Varanus bengalensis and V. salvator in Sri Lanka

Abstract

Habitat and microhabitat use by Varanus bengalensis and V. salvator differ considerably; V. bengalensis ranged further inland from aquatic habitats than the semiaquatic V. salvator, which was found mostly in riparian and aquatic habitats. When active, V. bengalensis used warm, open microhabitats, but inactive animals either took refuge in structures such as tree hollows, termite mounds, and burrows or remained in microhabitats which provided some cover but little protective refuge. The temperatures in refuges were stable but lower than daytime air temperatures, whereas the temperatures in the latter microhabitats were unstable. The habitats and microhabitats of V. salvator were, however, thermally stable and cooler than microhabitats of active V. bengalensis. Varanus salvator also used burrows for refuge. The body temperatures of the two species reflected their differential use of thermal habitats and microhabitats; active V. bengalensis, which used warm open microhabitats, had a high active body temperature, but inactive animals in refuges had low body temperatures. Varanus salvator, which used cooler microhabitats during activity and inactivity, maintained a stable but low body temperature. Its body temperature also approximated the ambient temperatures in the riparian and aquatic habitats. Thus, the two species had different thermoregulatory behaviors which required use of habitats and microhabitats with different thermal regimes.