Are fleeing ”noisy" lizards signalling to predators?

Abstract

Many prey signal to predators with the intention of deterring further pursuits. In the lizard Psammodromus algirus, individuals sometimes escape with noisy long runs on dry leaves, whereas on many other occasions they escape quietly and with short flights. We hypothesised that the duration of this noisy display might be considered as an auditory signal of their alertness and ability to escape directed to predators. We examined in the field the escape behaviour of the lizard P. algirus in response to a human observer acting as a predator and tested a series of predictions to analyse this hypothesis. During a noisy escape response, lizards escaped sooner and ran further and for a longer time, while passing potential refuges before hiding. Production of noise was not entirely dependent on environmental factors, such as temperature or microhabitat, and was not directed to warn conspecifics because most individuals were solitary. Lizards still made noise when concealed and in response to successive approaches, which might be interpreted as a signal of alertness to the predator approach. In addition, condition of individuals with noisy responses could be assessed from their ability to run further and for a longer time, and because, in contrast to quiet responses, speed and distance were not positively correlated with environmental temperature. Thus, they might be in a better condition or internal state because they were able to run at high speed under unfavourable conditions. We suggest that lizards with noisy escape responses might be honestly signalling their alertness and ability to escape to avoid being chased.