Birds use songs to impress mates, secure territories, and defend against predators, so any factor that can disrupt this communication, may interfere with daily life and the success of the species. One major disturbance that birds have increasingly been facing is urban noise. Previous studies have show that in order to improve communication, urban songbirds are singing differently and at higher frequencies compared to their woodland cousins in order to deal with noise pollution. However, until now, little research has been done on the more tropical relative of the songbirds, the sub-oscines.
According to Dr. Alejandro Ariel Ríos-Chelén and his colleagues from the Universidad Nacional Autónoma de México, the changes a bird makes to their song tunes depend on a variety of factors including the species. Their research shows that while some birds adapt their songs in noisy conditions by means of frequency changes, others like the vermilion flycatchers adapt their song by changes in song lengths.
The research team investigated whether male vermilion flycatchers adapted their song under noisy conditions in the same way as their sister group. They recorded the songs of 29 territorial vermilion flycatcher males in several areas of Mexico City. They registered noise levels at different times, both the pre-dawn and dawn chorus, measured song length, and counted the total number of elements in the birds' song to assess song versatility.
Researchers found evidence of individual song plasticity, as males sang less versatile, more elementary songs later in the morning when noise levels were higher. Researchers conclude that this individual shift in song seems to be more associated to time of the day rather than to the observed rise in noise. Nonetheless, this may affect mating and breeding successes, as females are often judge the quality of a male’s song.
They also found that males living in noisier places sang longer songs, while males inhabiting quieter places, like nearby parks sang both short and long songs.
The authors conclude, "While these results show that time of day has an effect on individual song versatility, we cannot discard an influence of noise... this study supports the idea that sub-oscine adaptation to noise is different in degree and mode to that taking place among oscines, suggesting heterogeneity in the capacity of bird species to colonize and survive in the urban environment."
The full article online in Springer's journal, Behavioral Ecology and Sociobiology.and this summary is taken from Alison Winter ENN