Big boys on top: effects of body size, sex and reproductive state on perching behaviour in the tropical rock dragon, Psammophilus dorsalis

Abstract

Perching behaviour, in relation to sex, body size and reproductive phases, was studied in the field in a population of the tropical rock lizard, Psammophilus dorsalis. Adult lizards (n = 14 males and 16 females) were marked by toe clipping in November 2001. They were observed at intervals (n = 10 times) over the next 18 months encompassing post-breeding (December-early March), recrudescence (late March-April) and breeding (May-August) phases. In the post-breeding phase, males perched at lower heights. They began perching higher during the recrudescence phase with the highest perches in the breeding phase. In comparison to females, the males perched higher than females all year round and showed greater among-individual variations in perch height. The bigger males perched at greater heights compared to smaller ones during recrudescence and breeding phases. No such trend was evident during the post-breeding phase and perch height was not related to body size. Females moved within a narrow range of heights from the substrata and showed no size-specific relationship in perch selection throughout the reproductive cycle. Selection of higher perches by the males, despite high predation risk, possibly helps in territory defence, courtship displays and in advertising their presence to conspecifics. Further, size-specific perch selection prior to and during the breeding period, suggests that size vis-à-vis age and reproductive cycle also influences selection of perch height in males. In females perching close to the substrata, refuge sites and food sources, seems to be associated with escape from predators, foraging benefits and, in turn, reproductive fitness. Thus, in the seasonally breeding P. dorsalis, sex and reproductive status determine the complex pattern of perching behaviour and, possibly, circulating levels of androgens drive the bigger boys on top in accordance with their size or age.