Urban noise undermines female sexual preferences for low-frequency songs in domestic canaries

Increasing levels of anthropogenic noise represent a challenge for animals living in urban areas and birds, especially, may suffer from noisy conditions as they use singing to attract mates. Most anthropogenic noise is low in frequency and singing at high frequencies under noisy urban conditions may avoid masking and thus be a good strategy for breeding success in cities. Despite comparative, correlational and some experimental studies supporting this hypothesis, empirical studies on the impact of noise on sexual behaviour are largely lacking. Domestic canaries, Serinus canaria, provide an excellent model system to test unequivocal sexual responsiveness as receptive females perform copulation solicitation displays (CSD) to male song. We have previously shown that CSD rate was higher for low- than for high-frequency songs. In the current study, we tested whether a typical urban noise spectrum, with a bias towards low frequencies, could undermine sexual preferences. Using overlapping and alternating noise exposure regimes while broadcasting male songs we found that masking by urban noise reduced female responsiveness to low-frequency attractive songs. Under the same conditions the responsiveness to high-frequency songs remained unaffected and, consequently, the sexual preference for low- over high-frequency songs had faded because of the urban noise. We discuss to what extent our results can be extrapolated to other wild bird species and speculate about the adaptive value of the typical upward shift in frequency found in many city birds.