Predator-elicited foot shakes in wall lizards (Podarcis muralis): evidence for a pursuit-deterrent function

Under certain circumstances, prey may inform potential predators of their unprofitability by means of pursuit-deterrent signals. The evidence for pursuit-deterrent signaling in reptiles is scant and taxonomically biased. Wall lizards, Podarcis muralis (Squamata: Lacertidae) produce several distinct types of stereotyped foot shake displays, of which one, performed in antipredator contexts, is a likely candidate for a pursuit-deterrent function. We investigated this possibility by recording the responses of lizards in the field to a slowly approaching human acting as a surrogate predator. In addition to starting and flight initiation distances, we measured the presence of foot shakes, the leg that was shaken, and the distance from the observer at which the display was performed (display distance). Of a total of 484 approaches, 109 (22.5%) elicited foot shake displays. Roughly half the lizards displayed from the location where they were first sighted, while the other half moved a short distance, then displayed. There was no left-right preference in the leg used to display, but most lizards displayed with the leg closer to the approaching predator. Juveniles and subadults had smaller flight initiation distances than adult lizards. There were no sex-related differences in starting or flight initiation distances, but females, for a given distance, were more likely to display than males. Foot shake display frequency declined abruptly at 1 m. If lizards waited until the surrogate predator was this close, they mostly fled without displaying. Our results show that antipredator foot shaking in P. muralis is consistent with expectations from pursuit-deterrent theory.