Thermoregulation in African chameleons

Field active and laboratory preferred body temperatures and critical thermal limits were measured in six species of Kenyan chameleons: Chamaeleo bitaeniatus, C. dilepis, C. ellioti, C. hohnelii, C. jacksonii, and C. schubotzi. Given the opportunity, all six species are very competent heliothermic thermoregulators. Individuals typically spend the night low in shrubby vegetation with body temperatures equal to ambient air, and then climb to the top or edges of their bushes to bask when the sun shines. For most species, body temperatures quickly stabilize between 29 and 32°C, which they maintain while the sun shines (except C. schubotzi at 19°C). Preferred temperatures in the laboratory average 30 to 33°C, with voluntary minima of 27 to 29°C and voluntary maxima of 34 to 36°C. From the elaborate suite of behaviors undertaken and the distribution of environmental temperatures, it is clear that when solar radiation is available, these chameleon species do not passively accept environmental temperatures. Rather they regulate their body temperatures in the field, utilizing many of the behaviors that have become classically associated with heliothermic behavioral thermoregulation. All other chameleon species previously studied also have thermal preferenda around 30°C.