Bird Songs in the City
Just as people sometimes adjust their tone of voice to be heard in cities, researchers have found that songbirds do as well. In a study published in November’s issue of Behavioral Ecology, researchers from the Smithsonian Conservation Biology Institute’s Migratory Bird Center analyzed how songbirds are affected by both general noise and the acoustics of hard human-made surfaces in urban areas. Their findings suggest that some species are altering their bird songs to adjust to either human-made noise or human-made objects, but the birds seem to have more difficulty altering their song in the presence of both.
“In order to survive and reproduce, it is imperative for birds to be able to transmit their signals to each other. Now it seems they may be having trouble doing so in urban areas,” said Peter Marra, a co-author of the study and an SCBI ecologist and conservation scientist.
City noise masks certain lower sound frequencies, making it more difficult for birds to hear one another’s calls over long distances. In addition, hard surfaces—such as buildings—can reflect and distort higher frequency sounds by scattering sound waves and creating multiple reverberations. This affects how far the sound travels and changes the structure of the sound, which can make it sound very different by the time it reaches the receiver.
The results of the researchers’ analysis showed that although there was some variation by species, the birds tended to sing higher notes in areas where there was general noise. The birds tended to sing lower and deeper notes, however, in areas where there were many buildings and hard surfaces. But when the two conditions combined, the birds had trouble altering their songs to accommodate both factors.
By vocalizing, birds are able to identify and locate other members of their species, attract mates and defend their territory. So their ability to adapt to urban living could affect their survival. As urban areas develop rapidly, researchers will continue to investigate how sound from these busy areas affects birds and the effects of development on sound transmission.