Aspects of comparative thermal ecology of sympatric hinge-back tortoises (Kinixys homeana and Kinixys erosa) in the Niger Delta, southern Nigeria

Aspects of the thermal ecology of two sympatric hinge-back tortoises, Kinixys erosa and Kinixys homeana, were studied in the rainforest zone of south-eastern Nigeria (West Africa). There were no significant differences in mean body temperatures (T-b) among K. homeana males, K. homeana females, K. erosa males and K. erosa females. In both species, there was a significant correlation between T-b, and air temperature (T-a), and the regression line of T-a plotted against T-b differed significantly from the line of ideal poikilothermy. These regressions did not differ significantly between sexes in either species. There were no significant differences in terms of mean T-b in K. homeana during the various day-hour intervals, whereas the mean T-b of K. erosa varied significantly among the various daytime intervals, attaining the higher values at 11.01-15.00 and 15.01-19.00 hours. In both species, T(b)s were nearly always below T(a)s, and the negative difference 'T-b - T-a' increased with increasing T-a. The hourly-time course of the difference between T-b and T-a showed significant differences in K. homeana (with the higher negative differences at 11.01-15.00 and 15.01-19.00 hours), whereas no such difference was observed in K. erosa. In general, tortoises of both species showed behavioural thermoregulation in their avoidance of overheating in tropical environments. taking advantage of shady forest environments.