Acoustic communication in animals relies upon specific contexts and environments for effective signal transmission. Increasing anthropogenic noise pollution and different weather conditions can disrupt acoustic communication. In this study, we investigated call parameter differences in the bladder grasshopper Bullacris unicolor inhabiting two sites in close proximity to each other that differed in their noise levels. Calling activity was monitored via passive acoustic recorders. Weather conditions, including wind speed, temperature and humidity, were also recorded. We found that the interval between successive calls increased with higher noise levels at both sites, and the peak frequency became lower. The total number of calls detected also decreased with anthropogenic noise, but this relationship was only evident at the noisier site. In addition, grasshoppers shifted the timing of their calls to later in the night at the noisier site, possibly to take advantage of relatively lower noise levels. We also found that weather conditions, particularly temperature, had a significant influence on call parameters. Further studies are thus needed to disentangle the effects of anthropogenic noise and environmental variables on calling activity in this species. Our results lend support to the growing concern regarding the effects of noise pollution on animal acoustic signalling systems and also highlight the complexity of factors which affect sound signalling in natural environments.
Anthropogenic noise, bioacoustics, passive acoustic monitoring, Pneumoridae