DO SEASONAL AND BEHAVIORAL DIFFERENCES IN THE USE OF REFUGES BY THE LEOPARD TORTOISE (GEOCHELONE PARDALIS) FAVOR PASSIVE THERMOREGULATION?

Behavioral thermoregulation is used by tortoises (Family Testudinidae) to moderate the effects of daily and seasonal fluctuations in ambient temperature on their body temperature. Extensive use is made of refuges to facilitate this behavioural thermoregulation. The Nama-Karoo in South Africa experiences wide temperature fluctuations both daily and seasonally. We investigated the seasonal use of refuges by the leopard tortoise (Geochelone pardalis) and the orientation of the tortoises within the refuges. Turtles used a wide variety of refuges, with Lycium spp., Eberlanzia ferox, Opuntia ficus, and grass clumps being preferred. Seasonal variation in the use of these refuges depended on whether the refuges were used as forms or shelters. Tortoises in spring and winter often remained in the same refuge for the entire season or returned to the same refuge on consecutive nights. We found seasonal and behavioral variation in (a) the orientation of the tortoises within a refuge, and (b) the portion of the shell of each leopard tortoise within a refuge that was exposed to solar radiation. Tortoises in winter and spring maximized the amount of solar radiation received on their shells, while tortoises in summer and autumn minimized the solar radiation received. Consequently, using a combination of refuge type, and body orientation, leopard tortoises appear to passively thermoregulate and thus control for temperature fluctuations experienced in an extreme environment.