Elaboration of a movement-based signal in the presence of a predator

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Animals balance the need to avoid predators with the requirement to undertake other functional tasks. Animal communication strategies are inherently risky, as they provide information that can be used by eavesdropping predators to detect and localise prey. Given the risks of signalling, most animals modify their signals to reduce detectability during heightened predation risk. We examined signal structure in an Australian lizard (Amphibolurus muricatus) and predicted predator-induced changes that would reduce conspicuousness. To do this we facilitated signaller-intruder exchanges in the immediate presence of a simulated predator and quantified the temporal components of introductory tail flicking and other behavioural measures. Lizards signalled after the intruder was introduced and increased tail flicking time in motion in the presence of the predator, serving to increase signal conspicuousness. Interestingly, lizards also licked the substrate at a greater rate in the presence of the predator. These results contradicted our initial prediction that predator-induced plasticity primarily favours reduced detectability and suggests that signalling decisions in A. muricatus reflect a more complex balance of costs and benefits. We hypothesise that changes were necessary in the present context to overcome the limited attentional capacities of receivers, but the nature of movements ensure the signaller can still visually detect a looming predator and rapidly respond to danger. Although further studies are required, we demonstrate that predator-induced signal plasticity is multidirectional and may include increases in conspicuousness when necessary to preserve important communication function under threat.