The differential effects of low, intermediate, and high amplitudes of anthropogenic noise on the behaviour of an urban-living bird

Anthropogenic noise can vary greatly in several properties, including timing, frequency and amplitude. However, many studies have historically focused on the effects of high amplitude noise, even though ‘intermediate’ amplitudes of noise may also impact behaviour. In this study, we investigated the effects of low (≤50 dBA), intermediate (50–60 dBA) and high (≥60 dBA) amplitudes of anthropogenic noise on the behaviour of wild Western Australian magpies (Gymnorhina tibicen dorsalis). We found that the time magpies spent foraging and vigilant differed significantly under all noise conditions, with greater amplitudes of noise having a larger impact. However, while the vocalisation rate of magpies was significantly reduced under high compared to low noise conditions, there was no difference between vocalisation rates under low and intermediate, or intermediate and high noise conditions. Conversely, while foraging efficiency was significantly reduced under both high and intermediate compared to low noise conditions there was no difference in foraging efficiency between intermediate and high noise conditions suggesting that intermediate levels of noise may impact foraging efficiency in a manner indistinguishable from higher amplitudes. Our results highlight the importance of investigating the impacts of multiple amplitudes of anthropogenic noise on animal behaviour, as different levels of noise may differentially impact wildlife.