Field body temperatures, activity levels and opportunities for thermoregulation in an extreme microhabitat specialist, the girdled lizard (Cordylus macropholis)
The girdled lizard Cordylus macropholis inhabits semi-desert areas along the west coast of South Africa. Unlike many other small diurnal lizards living in open habitats, it exhibits extreme low levels of aboveground activity and does not show overt thermoregulatory behaviours, such as basking or shuttling. It has an extreme low movement rate and confines routine activity to the microhabitat of the succulent Euphorbia caput-medusae. We document this restriction of activity in time and space in relation to aspects of this lizard's thermal biology. Throughout the day, a majority of the lizards was found sheltering ('covered') among the branches of E. caput-medusae plants, and surface-active ('exposed') individuals were seen during only a restricted time period (i.e. 1100-1700 h). Mean body temperatures (T(b)s) of both 'exposed' (29.4 °C) and 'covered' (28.4 °C) individuals were surprisingly low for a lizard inhabiting a hot and dry climate zone. This similarity of the T(b)s of both groups, as well as the correspondence between the ambient temperatures in the plant microhabitat and the T(b)s of 'exposed' lizards indicate that, for a considerable part of day, thermal conditions under plant cover allow achievement of T(b)s at a similar level as that maintained by the 'exposed' lizards. Moreover, the absence of sightings of overtly basking lizards supports the view that C. macropholis warm up by adopting the ambient temperature in their shelters thereby reducing the time spent in surface activity. All lizards observed were within the periphery of E. caput-medusae plants, indicating that C. macropholis is an extreme microhabitat specialist. The succulent provides more and safer hiding places than other common shrubs in the environment. In addition, estimates of ambient temperatures indicate that these plants offer superior opportunities for thermoregulation compared with other available shrub microhabitats.