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 th e west coast of South Africa. Unlike many other small diurnal lizards livin g in open habitats, it exhibits extreme low levels of above-ground activity and does not show overt thermoregulatory behaviours, such as basking or sh uttling. It has an extreme low movement rate and confines routine activity to the microhabitat of the succulent Euphorbia caput-medusae. We document t his restriction of activity in time and space in relation to aspects of thi s lizard's thermal biology. Throughout the day, a majority of the lizards w as found sheltering ('covered') among the branches off. caput-medusae plant s, and surface-active ('exposed') individuals were seen during only a restr icted time period (i.e. 1100-1700 h). Mean body temperatures (T(b)s) of bot h 'exposed' (29.4 degrees C) and 'covered' (28.4 degrees C) individuals wer e 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 betw een the ambient temperatures in the plant microhabitat and the T(b)s of 'ex posed' lizards indicate that, for a considerable part of day, thermal condi tions under plant cover allow achievement of T(b)s at a similar level as th at 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 ti me spent in surface activity. All lizards observed were within the peripher y of E. caput-medusae plants, indicating that C. macropholis is an extreme microhabitat specialist. The succulent provides more and safer hiding place s than other common shrubs in the environment. In addition, estimates of am bient temperatures indicate that these plants offer superior opportunities for thermoregulation compared with other available shrub microhabitats.