Are less vocal rainforest mammals susceptible to impacts from traffic noise?

Context: Traffic noise is believed to cause road avoidance and other barrier effects in a variety of wildlife species, and to force changes to call pitch or loudness in others; however, this has never been tested in the absence of other road impacts. Noise impacts on species that do not frequently vocalise are also poorly understood. We investigated traffic-noise impacts on the following three rainforest mammals that do not often vocalise: Hypsiprymnodon moschatus, Uromys caudimaculatus and Perameles nasuta. These species have previously been observed to exhibit varying levels of road avoidance. Aims: To determine whether traffic noise affects movement and behaviour of medium-sized, ground-dwelling rainforest mammals in the absence of other road-associated variables and potential impacts. We hypothesised that noise impacts would be greatest for species previously shown to avoid roads. Noise impacts on these less vocal species compared with more vocal species is also discussed. Methods: In north-eastern Queensland, Australia, mammals captured at least 500 m from any road were tracked after fitting with spool-and-line equipment. On noisy nights, traffic noise at levels similar to a busy highway was played continuously throughout the night from a line of 12 speakers mounted on trees. Speakers were silent on quiet nights. Key results: Traffic noise caused no increase in avoidance of the speaker line and was not a barrier to movements across the line. Overall, movement paths on noisy nights appeared similar in pattern (tortuosity) to those of quiet nights. At a finer scale, movements of H. moschatus and P. nasuta became more tortuous later in the track, suggesting a return to normal foraging behaviour and possible habituation to the noise. Conclusions: These three species with varying levels of previously recorded road avoidance, did not respond negatively to traffic noise. There was, however, a suggestion of habituation by H. moschatus and P. nasuta in response to the noise. Implications: The demonstrated lack of response to traffic noise in these less vocal species means that traffic noise is unlikely to cause road avoidance or barrier effects. Instead, lack of response and possible habituation to traffic noise may increase vulnerability to road mortality