In today’s Academic Minute, Dr. David Luther of George Mason University explains how urban-dwelling birds have responded to an increase in man-made noise.
David Luther is an assistant professor of biology at George Mason University in Fairfax, Virginia. His research interests include animal behavior, ecology, and conservation biology. His current project is focused on the ecology and evolution of acoustic communication in birds as well as the ecology, evolution, and conservation of terrestrial vertebrates that are endemic to mangrove forests.
Dr. David Luther – City Noise and Bird Songs
Most animals, like birds, use vocalizations to attract mates and defend their territories. The white-crowned sparrow has populations throughout the west coast of the United States, and in our latest study, we focused on the San Francisco population of these sparrows to investigate how animals communicate in the presence of loud human-generated noise, like rush hour traffic. The white-crowned sparrow is a great species to study because in the late 1960s Dr. Luis Baptista recorded many of their songs throughout California and the Pacific Northwest, thus we have a historical record.
We compared the recorded songs of these birds from 1969 with ones we recorded in 2005 and found that the birds have altered the way that they sing. They now use a higher frequency to compete with increased traffic noise. Here, have a listen to the 1969 song and the 2005 song. The sparrows are literally changing their tune to reduce interference from traffic noise.
To follow up on this finding, we compared studies of traffic noise from San Francisco in the 1970s and 2008 and found that it is significantly louder now than it was in the 1970s. Thus we found a correlation between the level of background noise and birds adjusting their songs to reduce interference from the noise. As a last measure, we played the historical and current songs to birds on their territories in the Presidio region of San Francisco. Male birds responded to both song types as if a rival bird was invading their territory, but they gave much stronger responses to the current songs, which means that the current songs are perceived as a greater threat.
All combined, our study supports the idea that the current songs are better adjusted to be heard in the local sound environment, for example the presence of human-generated noise. The findings are especially interesting because birds use their songs to attract mates, so with our loud noise we might be influencing the very evolution of these birds.