TEMPERATURE AND THE TROPICAL TORTOISE KINIXYS SPEKII - TESTS OF THERMOREGULATION

The mean body temperature (T-b) of active Kinixys spekii did not vary with sex or type of activity, or between hot days (maximum ambient tem perature T-a > 29 degrees C) and cool days. On hot days, T-b increased rapidly in the morning, and was constant during the late afternoon af ter midday inactivity. On cool days, T-b increased more slowly in the morning, and decreased during the afternoon. The slopes of T-b On T-a overall, and on hot days, were close to one, suggesting that tortoises were thermoconformers; the slope was greater than one on cool days. I n a second test of thermoregulation, T(b)s were compared with temperat ures of null models (T-m). Tortoises were clearly thermoregulators com pared to 'active-all-day' models. 'Activity-time' models had T-m more similar to T-b. Nevertheless, detailed comparison showed that tortoise s were thermoregulating in the late morning, and that this was by choi ce of microenvironment, rather than ceasing activity when T-b reached a high level. These results are discussed in relation to E, a measure of the effectiveness of thermoregulation based on comparison of T-b an d T-m with the set point range (T-set) selected in a thermal gradient. A set of three indices, which separate the variability of T-b, the di fference between T-b and T-m, and between T-b and T-set is suggested a s a more generally applicable summary of thermoregulation in ectotherm s.