Watch out where you sleep: Nocturnal sleeping behaviour of Bay Island lizards

Abstract

Sleeping exposes lizards to predation. Therefore, sleeping strategies must be directed towards avoiding predation and might vary among syntopic species. We studied sleeping site characteristics of two syntopic, congeneric lizards -the Bay Island forest lizard, Coryphophylax subcristatus and the short-tailed Bay Island lizard, C. brevicaudus and evaluated inter-specific differences. We measured structural, microclimatic and potential predator avoidance at the sleeping perches of 386 C. subcristatus and 185 C. brevicaudus.Contrary to our expectation, we found similar perch use in both species. The lizards appeared to use narrow girth perch plants and accessed perches by moving both vertically and horizontally. Most lizards slept on leaves, with their heads directed towards the potential path of a predator approaching from the plant base. There was no inter-specific competition in the choices of sleeping perches. These choices indicate an anti-predator strategy involving both tactile and visual cues. This study provides insight into a rarely studied behaviour in reptiles and its adaptive significance. 46 with their heads directed towards the potential path of a predator approaching from the plant 47 base. There was no inter-specific competition in the choices of sleeping perches. These choices 48 indicate an anti-predator strategy involving both tactile and visual cues. This study provides 49 insight into a rarely studied behaviour in reptiles and its adaptive significance.

Urban lizards use sleep sites that mirror the structural, thermal, and light properties of natural sites

“…When using vegetation at night, P. dorsalis was found on thin unstable perches, which has been hypothesized to aid in early detection of approaching predators via tactile cues (Anderson 1998); similar use of thin perches is seen in several reptile taxa (reviewed in Mohanty et al 2021). The suggested role of visual cues in aiding predator detection at night (Clark and Gillingham 1990;Mohanty et al 2016), however, is not fully supported in the case of P. dorsalis, as sleeping lizards were positioned in all possible head directions as opposed to a predominantly "inward" direction that would enable visual detection of a predator approach. Our observation of some sleep aggregations contrasts with the generally solitary behavior of the species during the active phase.…”

“…A vertical perch orientation could provide anti-predatory benefits by limiting the types of predators that could approach the sleeping lizard. Sleep sites are also known to be conserved in some other agamid lizards (e.g., Coryphophylax spp., Mohanty et al 2016), even in response to habitat modification (Monilesaurus rouxii, Bors et al 2020). The dependence of P. dorsalis on rough substrates as sleep sites might explain the lower perch height for lizard in urban areas, as perch sites are limited by the height of human-constructed walls in the urban study area.…”

“…We defined a "covered" sleep site as a site on a rocky substrate that was covered by vegetation or artificial substrate (e.g., tarpaulin sheet), which was adequate to change the light conditions at the site/hindered detection; an "exposed" site as one without any cover that hindered detection or light; and a "crevice" as any site within rock crevices or in gaps between concrete walls. For sleep sites on vegetation, we followed Mohanty et al (2016) to measure plant girth (in cm), perch type (e.g., trunk, leaf), perch width (e.g., branch circumference in cm), and distance to main trunk (in cm). We attempted to minimize any potential bias in detection of individuals (e.g., "covered" vs "exposed"), by searching all sites thoroughly along the survey trails.…”

“…Additionally, we measured head direction of the lizard as this may be an important indicator of visual cues available to the lizard upon waking and may influence the decision to or response of escape (Mohanty et al 2016). We recorded head direction as "inward"/ "outward"/ "angular" for vegetation, defined with respect to a potential approaching predator from the base of the plant (see Mohanty et al 2016) and "upward"/ "downward"/ "angular" for rocky substrates.…”

The ecology of sleep in non‐avian reptiles

“…Similarly, several species of diurnal snakes and geckos also sleep exclusively on thin vegetation at night (Martins, 1993; Montgomery, Lips & Ray, 2011; Ikeuchi, Hasegawa & Mori, 2012). Additionally, many of these species sleep on higher perches than those used for general activity (Singhal, Johnson & Ladner, 2007; Montgomery, Lips & Ray, 2011; Ikeuchi, Hasegawa & Mori, 2012; Mohanty, Harikrishnan & Vasudevan, 2016). Individuals of a species can also use multiple substrate types while sleeping, as long as the sleep perch is relatively narrow and unstable (e.g.…”