Great tits in urban noise benefit from high frequencies in song detection and discrimination

Field studies in urban environments have shown that birds sing with higher frequencies in response to noise, but so far there are no perceptual data showing benefits of high-frequency songs over low-frequency songs under typical urban noise conditions. In this study we investigated the potential effects of specific frequency use in different environments on the perceptual performance of trained great tits, Parus major, in the laboratory. Test signals consisted of song phrases shifted both up and down in frequency. The subjects had either to detect test songs or to discriminate between test songs in both urban and woodland noise conditions. In the detection experiment, auditory thresholds were on average 6 dB better for high- than low-frequency song variants in urban noise, while in woodland noise there was no difference in detectability. In the discrimination experiment, the great tits showed different patterns of discrimination in urban compared to woodland noise conditions. Discrimination between low-frequency song variants in urban noise was less efficient than discriminating between other frequency variants, which was not the case in woodland noise. Our analysis revealed that features concerning the high-frequency elements of the songs were used in urban noise, while the birds used more features of the whole songs to solve the discrimination task in woodland noise. Our results on the perceptual abilities of birds under urban noise conditions provide rare and novel insights on the receiver side complementing many studies on noise-level-dependent frequency use on the sender side.