April 14, 2009
Communication is the basis of all social relationships between animals. Birds use acoustic signals (calls and songs) to attract and bond with mates, defend territories and warn of danger from approaching predators. Background noise reduces the distance over which a call or song can be heard. As well as natural noises (e.g. wind and rain), birds in urban habitats must compete with human-generated noise such as road-traffic noise, much of which occurs in the lower-frequency bands below 2,000 Hz. Birds in cities have been known to use a number of strategies for overcoming noise, such as singing at a higher pitch to reduce masking by the low-frequency noise, singing more loudly, or singing at night time when traffic noise is at its lowest.
I travelled to Phoenix to investigate the how birds there respond to traffic noise. In a collaborative project with researchers from GIOS and SoLS at ASU, I recorded the calls and songs of birds and measured noise levels at 24 neighbourhood parks around the city. We are particularly interested to see whether doves such as the Inca dove and mourning dove are calling at a higher pitch in noisy areas. Of all the birds that live in cities, we would expect them to have the most difficulty hearing each other in traffic noise. This is because they have very low-pitched calls that are overlapped by the low-pitched traffic noise. But these species are very common around Phoenix, which suggests that they can still attract mates and breed successfully in noisy urban environments. In the future, we would like to investigate the breeding success of doves in noisy and quiet locations, to see whether urban noise is actually having an impact on their populations.