Solar Absorptance of Some Australian Lizards and Its Relationship to Temperature

Abstract

The absorptance to solar radiation, integrated across a wide range of wavelengths, was measured for selected species of Australian lizards. Some, but not all, agamids demonstrated the ability to change absorptance. None of the varanid lizards measured changed absorptance, including Varanus storri, which had been reported to change colour. An energy balance model was used to explore the effects of absorptance, changes in absorptance, and body size in varanid lizards, the dragon Ctenophorus caudicinctus (which changed absorptance from 77.0 to 87.7%) and the frillneck lizard (Chlamydosaurus kingii). Although higher absorptance values generally result in higher body temperatures, the effect of body size is great and must be taken into account in comparisons. Although some species with high absorptances are associated with relatively cool climates (Varanus rosenbergi) or with a semi-aquatic lifestyle (V. mertensi), the absorptances of other species are not as easily explained [such as the high absorptances of the tropical terrestrial V. panoptes (87%) and the tropical arboreal V. scalaris (86%)]. The absorptances of more species are required before the importance of climate and phylogenetic relationships can be fully evaluated. To facilitate future measurements, the apparatus used in this study is described in detail.