Body temperature regulation in a desert lizard, Sauromalus obesus, under undisturbed field conditions

1. Mean selected body temperatures (MSBTs), measured by radiotelemetry, are presented for 15 chuckwallas on 26 animal days. 2. MSBT, during the period of activity, ranged from 37.3 to 39.8 degrees C (means = 38.8 +/- 0.2 SE degrees C) while MSBTs, from the time lizards attained their first high set point to the time that solar radiation ceased, ranged from 36.1 to 39.6 degrees C (means = 38.3 +/- 0.2 SE degrees C). 3. On cloudy, cool days, animals could not maintain high Tbs because of the absence of solar radiation. 4. On sunny March and April days, animals were active for 5-6 hr but Tb then fell rapidly to low levels. 5. From late April to mid May, animals were active for 7-8 hr and Tbs did not fall as drastically because of higher Tas after sunset. 6. August was the time of year (for this study) when chuckwallas had the highest effective 24 hr Tb but it was also the time when they had the shortest activity interval.