Thermoregulatory Postures and Orientation to the Sun: A Mechanistic Evaluation for the Zebra-Tailed Lizard, Callisaurus draconoides

Abstract

The effects of thermoregulatory postures and orientation to the sun on steady-state body temperatures in the zebra-tailed lizard (Callisaurus draconoides) were determined using computer simulation techniques. The parameters evaluated for each posture included: (a) silhouette area (A/sub S/) as a function of solar zenith angle (Z) and relative aximuth angle (RAZ) and (b) the convective heat transfer coefficient (h/sub C/). Four simulations, incorporating micrometeorological data from the literature, were used to evaluate relationships between postures, orientation to the sun, micrometeorological variables and the mechanisms of heat transfer. The simulations show that for a given posture: RAZ orientation to the sun may account for a 1 C range in body temperature; (2) conductive heat gain is not an important mechanism for elevating the steady-state body temperature in the morning but may increase the rate of heat gain under certain conditions; (3) the posture of a lizard and its convective environment are more important in determining a lizard's body temperature than is its orientation to the sun.