Thermoregulation in leopard tortoises in the Nama-Karoo: The importance of behaviour and core body temperatures

Despite being ectotherms, reptiles have an ability to thermoregulate which is enhanced by adopting a variety of behavioural mechanisms. Different behavioural postures, the use of retreat sites and selection of microhabitats enable reptiles to maintain their core body temperatures (T-b) above that of ambient temperatures (T-a) in winter or below T-a maximum in summer. This study describes the daily activity patterns of leopard tortoises (Stigmochelys pardalis) in relation to T-b and T-a, and the extent to which leopard tortoises can manipulate their T-b in response to seasonal changes in T-a. Ten and nine leopard tortoises were radio-tracked in 2002 and 2003, respectively and cloacal T-b and behaviours observed. Core T(b)s were measured using Thermocron iButtons (TM) surgically implanted into the body cavities of 4 and 5 adult telemetered tortoises for summer and winter 2003, respectively. There were seasonal differences in the extent to which certain behaviours were practiced and the time of day that these occurred. Leopard tortoises generally had unimodal activity patterns in winter and bimodal ones in summer. In winter tortoises were active at lower T(b)s, and at lower T-a, than in summer. Tortoises maintained their core T-b well below T-a minimum profiles in summer and well above these in winter. Core T-b closely followed the increase in T-a minimum profiles in the mornings, however tortoises exhibited an extended thermal lag when T-a minimum profiles cooled overnight. By using different behavioural mechanisms in summer and winter, leopard tortoises maintained their core T-b at different levels compared with T-a minimum and maximum profiles. Consequently although they are ectotherms, they maintained their core T-b independent of T-a. (C) 2013 Elsevier Ltd. All rights reserved.