Anti-predatory sleep strategies are conserved in the agamid lizardMonilesaurus rouxii

Sleep is an essential part of animal biology, yet its ecological aspects such as predator avoidance remain understudied, especially in the wild. Sleep behaviour is likely to be subject to selection pressure and evolution, leading to sleep strategies to ensure survival during this vulnerable state. How sleep strategies of animals respond to alteration of macro-habitat has been largely unexplored. This study aimed to determine the effect of habitat type on the sleep ecology of the agamid lizardMonilesaurus rouxii. We carried out field work in the Western Ghats (India) biodiversity hotspot, in two differing habitat types-natural wet evergreen forests and human-modifiedAreca catechuplantations. We collected data on perches used by lizards for sleep, both in terms of their structural characteristics and their use (e.g. lizard head direction). To determine perch selection, we compared perch use with perch availability in both habitat types. Habitat type had limited influence on sleep perch selection ofM. rouxii, with lizards selecting only unstable narrow-girthed plants, suggesting a highly conserved sleep strategy driven by predator avoidance. The majority of sleeping lizards displayed an 'inward' head direction, towards the potential path of a predator approaching from the ground. However, this strategy to select for narrow-girthed plants constrained lizards to use lower, unsafe sleep perches in plantations (driven by availability), which could have consequences for their survival. To our knowledge, our study is the first to examine in detail the effect of habitat alteration on sleep strategies in lizards. Significance statement Sleep strategies of animals in the wild could affect their chances of survival and their performance during active behaviours. 'Where' and 'how' animals sleep are important aspects of their sleep strategy. However, it is unexplored if these choices would change in response to human modification of the natural habitat. We compared sleep site selection in the semi-arboreal agamid lizardMonilesaurus rouxiiin two different habitats (natural and human-modified). Lizards always chose narrow, unstable perch plants to sleep, as they allow for early detection of an approaching predator. In the human-modified habitat (Areca catechuplantations), opting for narrow unstable perches led to lizards using significantly lower perches, probably leaving them vulnerable to predators approaching from the ground. Our results show that exploring sleep strategies in the wild is necessary to properly assess the effects of habitat modification on species.