LAUSR

Habitat characteristics influence the efficacy of animal communication, and population differences in signal structure due to habitat variation are well known for sound and colour signals. However, this variation in signal structure has not been reported for motion-based signals. Here we tested the motion-based signalling displays of two populations of an Australian agamid lizard, Amphibolurus muricatus, in the context of their respective habitats. We employed a novel approach that calculates the distribution of motion speeds of lizard signals and environmental noise independently, before computing the difference in these distributions to obtain a measure of signal–noise contrast. Our results revealed variation in signal structure between the two populations and support the hypothesis that this variation can be explained by differences in the signalling environment. Signals from both populations showed similar contrast values at their respective habitats, but differed significantly when considered in the habitats of the allopatric population. These results are consistent with the hypothesis that habitat structure affects signal efficacy and causes population differences in motion signalling behaviour as a consequence of adaptations to enhance efficacy.