Energetic consequences of field body temperatures in the green iguana

We investigated body temperatures of free-ranging green iguanas (Iguana iguana) on Curacao (Netherlands Antilles), and how metabolic costs and benefits of food processing affect body temperatures. Body temperatures of free-living iguanas were measured by radio telemetry. We also used a model, with activity data and operative temperature from taxidermic mounts as inputs, to estimate body temperature of free-ranging animals. Estimated body temperature was highly correlated with telemetered body temperature (mean difference 0.8 degrees C). Thus, our model for estimating lizard body temperatures may be useful in field studies where telemetry is not possible. Data from both telemetry and estimation with the model showed that green iguanas maintained relatively constant body temperatures (minimum 32.9 +/- 1.4 degrees C; maximum 36.6 +/- 2.9 degrees C; mean +/- 1 SD) during the midday period (0945-1545). Temperature measurements of taxidermic mounts and ambient air showed that body temperatures between 29 degrees C and 40.5 degrees C could readily be attained on Curacao. Hence, the range of potential body temperatures was much greater than the range of actually achieved body temperatures. Thermoregulatory behavior, food intake, and locomotor activities were recorded along with temperature measurements. Relations between body temperature, daily metabolizable energy intake (MEI), and resting metabolic rate (RMR) were used to examine whether or not observed body temperatures coincide with temperatures at which energy gain from ingested food is high. Our data show that, in these herbivorous reptiles, food intake and digestion explain most of the variation in the observed field body temperatures.