Abstract

Ectothermic animals depend on environmental temperature to regulate their body temperature. The Chaco Tortoise (Chelonoidis chilensis) is widespread in South America; however, populations are threatened mainly because of the pet trade. We described the activity pattern of C. chilensis relative to environmental temperature under semi-natural conditions in a zoo enclosure. We also estimated thermal parameters under controlled laboratory conditions: selected temperature (Tsel) and critical maximum temperature (CTmax) between sex and size indicators. In the enclosure, 81% of the observations were from inactive tortoises and 19% from active tortoises. Tortoises were active over a wide thermal range (12.0°–38.0° C) and Tsel was 34.4° ± 0.3° C (mean ± standard error), with no significant differences among sizes or between sexes. Heavier tortoises spent significantly more time at the lowest temperature than lighter ones. The range of CTmax was 36.3°–42.0° C and this parameter was inversely related to tortoise length but did not differ between sexes. The results suggest a wide thermal range in C. chilensis, dependence of thermal behavior on body size but not on sex, and a wider range of body temperatures in smaller individuals than in larger ones. Knowing the parameters that influence thermoregulation contributes to the improvement of management strategies under semi-natural conditions, which, in turn, can be extrapolated to wild populations.