How distinct are sleep sites from active sites across habitat types in lizards?

Sleep poses constraints, such as increased vulnerability to predators, that can lead to differences in the use of habitat components across the diel cycle. However, very few studies have systematically evaluated site use of animals across both active and sleep phases. We quantified site use during the active and sleep phases in 412 individuals of eight species (six genera) of agamid lizards, from four habitat types (arboreal, semi-arboreal, rupicolous and ground). Sleep sites differed for five out of the eight species, in all habitat types except rupicolous. Semi-arboreal and arboreal lizards slept on narrower and more compliant perches, likely to detect and avoid predators, whereas ground-dwelling lizards slept in sheltered sites that probably afford a stable thermo-hydric environment. For most species, sleep sites differed from active sites in only a few characteristics, indicating that lizards respond to the potential costs of sleep while being constrained by their morpho-functional abilities. We found equivocal pattens of lower variability of sleep sites compared to active sites, which may be due to low variability in perch options or low costs of sleep in some habitat types. This study provides a large-scale test of diel shifts in habitat use and highlights the need to integrate sleep microhabitat use into ecological and conservation research.