Anthropogenic noise constrains acoustic communication in urban-dwelling frogs

Urban noise may hinder acoustic communication in a diversity of animal groups by reducing the distance over which vocal signals can be detected. Given the importance of such signals for mate attraction and territory defence, this acoustic interference may have wide-ranging consequences for individual fitness. I will present a mathematical model of the active space of frog calls in urban noise as a function of body size. Despite having lower auditory thresholds, larger species with lower-frequency calls are predicted to suffer the greatest reduction in communication distance in noisy urban environments. During a field study in Melbourne, Australia, my colleagues and I found that the southern brown tree frog Litoria ewingii called at a higher frequency in traffic noise. However, modelling indicates that the observed frequency shift would confer only a modest increase in active space. Furthermore, as females of certain frog species appear to prefer lower-frequency advertisement calls, this strategy may improve the audibility of calls but reduce attractiveness to potential mates. Calling more loudly would result in a larger increase in active space, but the high metabolic cost of this strategy could limit chorus tenure and ultimately reduce breeding success.