Non-masking noise suppresses bird song

Most research on the effects of anthropogenic noise on animal acoustic communication has dealt with masking noise (which frequencies overlap with those of animal vocalizations) and changes in noise-induced vocalizations have been explained as strategies to avoid masking. Still, few studies have addressed the impact of non-masking noise on animal vocal behavior. A previous experiment showed that vermilion flycatchers (Pyrocephalus rubinus) avoid singing during peaks of noise that partially mask their songs, suggesting this is a strategy to improve communication in masking noise. If this were the case, we expect that males should continue to sing when exposed to non-masking noise. Here we tested this idea by exposing 21 free-living males, via a speaker, to edited non-masking traffic noise with maximum frequencies of 2 kHz and 1 kHz. We compared the number of songs the focal male sang in a bout before, during and after noise playback. A low but significant proportion of males immediately stopped singing after the onset of 1 kHz (4/21) and 2 kHz (8/21) filtered noise playbacks. Number of songs between treatments did not differ when males were exposed to the 2 kHz filtered noise playback. However, males sang fewer songs after 1 kHz filtered noise exposure than before exposure. Our study does not discard the possibility that males reduce masking when stopping to sing during noise peaks, but it shows that masking release is not required for males to stop singing. Non-masking noise can disrupt bird song, potentially affecting sexual selection and breeding.