Implications of the large surface area to body mass ratio on the heat balance of the greater glider (Petauroides volans: Marsupialia)

1. In a study of thermoregulation in the greater glider, a small arboreal marsupial with large gliding membranes, metabolic rate (MR), skin and deep body temperature (T_sk, T_b), and respiratory and total evaporative heat loss (E_ex, E_tot) were measured in relation to ambient temperature (T_a). 2. Although the surface area is twice that of marsupials of similar body weight, MR was not significantly different from the average marsupial metabolic rate. This must be attributed to an excellent thermal insulation and behavioural factors. 3. At T_a above the thermoneutral point, at 20°C, the greater glider became hyperthermic. T_b increased from 35.4°C at 20°C T_a to 39.1°C at 40°C. At 30°C, 55% of MR was dissipated by evaporation. This proportion increased to 105% at 35°C and 132% of MR at 40°C. The increase in E_tot was accompanied by intense licking of extremities and the ventral body surface. E_ex dissipated only 12% of MR at 40°C irrespective of an 8-fold increase in respiratory frequency from a basal value of 18 breaths·min^-1. 4. It is concluded that the greater glider can utilize its gliding membranes to reduce heat losses by increasing the insulative layer around the body surface. At high T_a, a clear contrast between the inefficient use of water for evaporative thermolytic processes, mainly salivation, and the limited availability of water in its arboreal habitat becomes evident.