Frequency masking drives species-specific temporal avoidance strategies in boreal songbirds.

Interference in acoustic signal transmission can impair communication, and many vocalizing species use various strategies to avoid signal masking. Past studies have focused primarily on the effect of anthropogenic noise and overlap in sound frequency range, leaving a gap in our understanding of how an individual's vocal signal structure affects other animals in its acoustic community. Using playback experiments we tested whether 5 species of European boreal songbirds adjust their singing behavior to avoid overlap with 3 novel acoustic intruders from sub-Saharan Africa, each with a different song structure customized to each study species: (i) continuous songs of narrow, partially-masking frequency based on the study species' peak frequency, (ii) noncontinuous songs of broad, fully-masking frequency and (iii) continuous songs of broad, fully-masking frequency. All species showed evidence of temporal song avoidance only with competitors whose songs were broad-spectrum and completely overlapped in frequency range. The species differed in their behavioral response, either modifying the song rate, song duration, or the timing of their songs. These differences in behavior may be related to limitations imposed by the species-specific information encoded in different song parameters, and allow for predicting the consequences of changes in acoustic community structure.