Silvereye Zosterops lateralis
Recent studies have shown that songbirds living in noisy environments sing at a higher frequency that their rural counterparts, but this phenomenon remains poorly understood. We conducted a field study of silvereye vocalisations over more than one million square kilometers of urban and rural Australia. We compared possible effects of urban noise of songs (which are learned) and contact calls (which are innate). We found silvereyes consistently sang both songs and contact calls at higher frequencies in urban environments. We also found that the syllable rate decreased in urban environments, which is consistent with the hypothesis that reflective structures degrade song and encourage longer intervals between syllables. This was the first study to demonstrate varied adaptations of urban bird vocalisations over a vast geographic area and provide insight into the mechanism responsible for this change.
In a related study, we examined how the bioacoustic attributes of vocalisations made by birds in urban environments differ from those living in rural environments. It is still not clear whether these differences arise from genetic divergence between urban and rural populations, or from plasticity or cultural evolution of song. We investigated whether the differences in songs and calls between urban and rural populations were associated with corresponding morphological and neutral genetic differences. Interestingly, we found that all morphological traits were similar and there were high levels of genetic connectivity between populations. This suggests that consistent directional shifts in song attributes of city birds are not accompanied by associated differences in morphology or genetics.
This research formed part of a PhD carried out by Dr. Dominique Potvin, entitled “The effects of urban noise, dispersal and isolation on vocalizations of the silvereye (Zosterops Lateralis)”. Dominique is now based at Museum Victoria, supervising a project on the effects of bushfires on frog behaviour, populations and communities in south-eastern Australia.
More information about this research can be found in these publications:
Potvin, DA, Mulder, RA & Parris, DK (2013). Acoustic, morphological and genetic adaptations to urban habitats in the silvereye (Zosterops lateralis). In Avian Urban Ecology (Ed. by H.Brumm & D. Gil). Oxford University Press.
Potvin, DA, Parris, KM & Mulder, RA (2013). Limited genetic differentiation between acoustically divergent populations of urban and rural silvereyes (Zosterops lateralis). Evolutionary Ecology 27: 381-391. Full text
Potvin, DA, Parris, KM & Mulder, RA (2011). Geographically pervasive effects of urban noise on frequency and syllable rate of songs and calls in silvereyes (Zosterops lateralis). Proceedings of the Royal Society B 278: 2464-2469. Full text
Photo: Catherine Payne