The Thermal Biology of Free-Living Sand Goannas (Varanus gouldii) in Southern Australia

Abstract

The daily and seasonal activity patterns of Sand Goannas (Varanus gouldii) on Kangaroo Island, South Australia differed from those of conspecifics in semiarid and arid regions of Australia. On Kangaroo Island goannas remained active throughout the year whereas on the other areas they were inactive and remained in their burrows during the winter. Goannas emerged from burrows over a wide range of environmental temperatures and at different times after sunrise, but animals on Kangaroo Island generally emerged later in winter than in summer. These animals also showed seasonal differences in the length of time spent basking before becoming active, in heating rates and in mean activity temperatures. Cloacal temperatures of free-ranging goannas on three study areas were determined using radio-telemetry. Under similar environmental conditions, mean activity temperatures of goannas on all three areas were not significantly different (approximately 35.5 C). Activity outside burrows was generally restricted to the times when the most favorable environmental conditions prevailed. This meant that the lizards were exposed to a relatively narrow range of environmental conditions which facilitated thermoregulation.