Auditory masking of anuran advertisement calls by road traffic noise

Abstract

There is growing concern that anthropogenic noise could interfere with animal behaviours by masking the perception of acoustic communication signals. To date, however, few experimental studies have tested this general hypothesis. One common source of anthropogenic noise is the sound of roadway traffic. We tested the hypothesis that road traffic noise can mask a female's perception of male signals in the grey treefrog, Hyla chrysoscelis, by comparing the effects of traffic noise and the background noise of a breeding chorus on female responses to advertisement calls. In this species, advertisement calls are necessary and sufficient to attract females for breeding. Using a phonotaxis assay, we presented females with an advertisement call broadcast at one of nine signal levels (37–85 dB, 6-dB steps) in one of three masking conditions: (1) no masking noise, (2) a noise simulating a moderately dense breeding chorus, or (3) a noise modelled after road traffic noise recorded in two wetlands near major roads. Females showed similar increases in response latency and decreases in orientation towards the target signal in the presence of both the chorus noise and the traffic noise maskers. Moreover, response thresholds were elevated by about 20–25 dB in the presence of both noise maskers compared to the unmasked condition. Our results suggest that realistic levels of traffic noise could place constraints on the active space of the acoustic signals of some animals.