Evaluation of artificial heating sources for the thermoregulation of Aldabra giant tortoises (Aldabrachelys gigantea) in Zurich zoo.

We recorded the thermoregulatory patterns of five Aldabra giant tortoises (Aldabrachelys gigantea) (25-193 kg) during spring (ZRH spring trial), after the installation of a heating area (concrete heat pad and basking lamp) at Zurich Zoo, Switzerland. The measurements were compared to published results on the same tortoises observed prior to the installation of the heater (ZRH summer and winter trials), and on wild tortoises on Aldabra Atoll. The mean environmental temperature outside the heating area was 23.3 °C, significantly lower compared to Aldabra Atoll (30.3 °C; range: 23.8-43.8 °C), and to the environmental temperature range at which tortoises maximize their activity in the wild (Ta-opt ; 25.8-31.7 °C). The heating area exhibited a mean temperature of 36.3 °C, and tortoises that made use of the heating area were able to maintain a mean core body temperature (Tbc ) of 30.0 °C, which was comparable to the Tbc of tortoises during ZRH summer and on Aldabra trials, and an improvement over the mean Tbc recorded during the ZRH winter trial (21.2 °C). The smaller individuals reached the upper limits of Tbc recommended for the species, probably due to heating pad temperatures above Ta-opt . We discuss current practices to provide external heating sources for tortoises and how this method can be used to provide an adequate thermal environment for large captive reptiles. Finally, we provide recommendations for the installation of artificial heating sources for tortoises and large reptiles.