Spectral and temporal call flexibility of House Finches (Haemorhous mexicanus) from urban areas during experimental noise exposure

Human activities can be noisy, especially in urban areas, and affect animals detrimentally. Traffic noise may interfere with acoustic communication through masking and may yield noise-dependent modification of acoustic signals. Such vocal flexibility in birds has been investigated most often for songs, but rarely for calls, even though calls are typically used more frequently. Here we exposed male House Finches Haemorhous mexicanus from urban areas in Mexico City to low and high levels of anthropogenic noise. We investigated: variation in call type repertoire use among birds caught at localities with different noise levels, call type use in response to experimental noise exposure, and whether there were immediate noise-dependent spectral or temporal adjustments. We found no locality-dependent call repertoires, as males from all sites shared most of their call types. Males in quiet areas called with higher frequency and longer duration than did birds from noisier areas. However, this case study lacked replication of sites, limiting the generality of conclusions that can be drawn. Under experimental noise exposure, we also found no shift in call repertoire use. However, in line with expectations, one of two dominant call types of relatively low frequency showed an increase in peak frequency under experimentally elevated noise conditions, and the birds also produced shorter versions of the two dominant call types in the noisier treatment. In summary, we found no evidence for noise-dependent call repertoire use in our case study but we confirmed experimentally that House Finches are capable of immediate spectral and temporal call adjustments in response to noise level fluctuations.