Signaling against the wind: modifying motion-signal structure in response to increased noise.

Animal signals are optimized for particular signaling environments [1-3]. While signaling, senders often choose favorable conditions that ensure reliable detection and transmission [4-8], suggesting that they are sensitive to changes in signal efficacy. Recent evidence has also shown that animals will increase the amplitude or intensity of their acoustic signals at times of increased environmental noise [9-11]. The nature of these adjustments provides important insights into sensory processing. However, only a single piece of correlative evidence for signals defined by movement suggests that visual-signal design depends on ambient motion noise [12]. Here we show experimentally for the first time that animals communicating with movement will adjust their displays when environmental motion noise increases. Surprisingly, under sustained wind conditions, the Australian lizard Amphibolurus muricatus changed the structure and increased the duration of its introductory tail flicking, rather than increasing signaling speed. The way these lizards restructure the alerting component of their movement-based aggressive display in the presence of increased motion noise highlights the challenge we face in understanding motion-detection mechanisms under natural operating conditions.