Traffic noise affects colouration but not calls in the European treefrog (Hyla arborea)

Abstract

In terrestrial habitats, traffic noise is responsible for chronic noise exposure and impacts both signal detection and acoustic signal structure. Several species are known to adapt their call structures to cope with noise. However, compromised hearing affects more than acoustic communication, and noise should be consider as a stress factor that can also alter visual communication in the case of carotenoid-based signals. Here, we experimentally investigated the impact of traffic noise on the expression of secondary sexual signals in the European treefrog, Hyla arborea. Treefrogs use multimodal communication in the sexual selection process (mating calls and vocal sac colouration). We found that treefrogs seem unable to adjust their call structure. Nonetheless, males showed a significant decrease in colouration intensity. Our findings highlight for the first time the negative effect of traffic noise on colour signals. This suggests that anthropogenic noise could affect a wider range of species than previously thought.