Songbird community structure changes with noise in an urban reserve

Abstract

Urban noise has the potential to negatively affect bird fitness as it may interfere with communication and for instance, decrease predator detection or breeding activity. Regular exposure to urban noise may cause changes in bird communities and influence local distribution patterns. While some bird species may tolerate urban noise, others may not, which mechanisms underlie noise tolerance remain unknown. Whereas a large number of studies have focused on the responses of specific bird species or groups to urban noise, few have attempted to assess noise effects on species richness. Here, we assessed the association between (i) anthropogenic noise and bird richness, (ii) noise level and song modification and (iii) species noise tolerance and detection frequency, by recording these variables at seven plots within an urban reserve in Mexico City. We found that species richness is negatively affected by increasing anthropogenic noise, but also by the increase of shrub cover. Nevertheless, over 90% of our species did not display significant song modifications. This lack of response may be a result of our restricted sample size, although we cannot exclude a possible change in non-spectral components (e.g. change song timing) or that given a noise gradient, birds occupy areas where song modification is not necessary. Our results suggest that urban avian species richness is significantly affected by noise and vegetation cover. We expect that by limiting anthropo-genic noise and providing diversity of vegetation cover, cities could be made attractive to bird species with different degrees of noise tolerance, promoting urban bird diversity.