Persist and shout: Male bluebirds sing louder & lower to be heard over our racket
Birds “shout” to be heard over the noise produced by man-made activity, new research has shown.
The study looked at how eastern bluebirds altered their songs in response to increases in nearby background noise caused, in many cases, by human activities such as traffic. The focal birds occupied manmade nest boxes distributed across a noise pollution gradient — encompassing sites such as golf courses, cemeteries and retirement communities — in and around Williamsburg, Virginia.
The study found that birds altered their songs immediately after noise levels intensified, making “real-time” adjustments in order to produce songs that are both louder and lower-pitched. The results suggest that birds are able to perceive increases in noise and respond accordingly — not unlike humans do when in raucous settings.
Lead author Caitlin Kight is a behavioral ecologist currently based at the University of Exeter’s Penryn Campus in Cornwall, UK. She led the study while conducting her Ph.D. research in William & Mary’s Department of Applied Science. Kight said that the research could help improve our understanding of environmental constraints on animal communication, as well as enhance our awareness of what sorts of human modifications can impact animals and how we might be able to reduce any negative effects of these disturbances.
Kight explained that while manmade noises often seem very different from those found in nature, there can be surprising similarities among certain features, including volume, pitch or timing.
“Sounds caused by traffic, for example, may not be hugely different from those produced by waterfalls or heavy winds,” Kight said. “Animals that evolved in habitats with those natural features may therefore already have, within their existing repertoires of behaviors, the flexibility to respond to noise pollution. This certainly seems to be the case with bluebirds.”
The current study also is the first to describe real-time adjustment of song in a member of the thrush family. Previous studies have shown that birds in noisier areas tend to sing differently than those in quieter surroundings, but it was not immediately clear whether birds were able to make vocal adjustments in real time — that is, an immediate shift in response to increased noise made by a passing car, for example. Real-time modifications have now been observed in five different avian species.
Kight recorded songs produced by 32 male bluebirds and analysed two from each male — those produced during the quietest and loudest period of ambient noise — to investigate whether males change their songs between these two conditions.
She found that, as background noise increased, male bluebirds produced songs that were louder and lower-pitched. This suggests that the birds are able to both perceive and respond to increases in noise. Kight explained that the adjustment to the immediate sonic environment enabled the male bluebirds to produce songs that were more likely to be heard by potential mates or rivals.
Co-author John Swaddle, professor of biology at William & Mary, cautions against interpreting these findings as evidence that noise pollution has no adverse impacts on wild animals.
“Unfortunately, the world is getting so noisy that even the most flexible of species will eventually reach a threshold beyond which they will have difficulty communicating — which will impact their ability to breed successfully,” Swaddle said. “When we build roads and airports near human neighborhoods, we employ noise abatement protocols in an effort to mitigate against the negative impacts of noise pollution. It is time to apply similar caution to conservation, management and landscaping plans that impact wildlife and their habitats.”
The study, “Eastern Bluebirds Alter their Song in Response to Anthropogenic Changes in the Acoustic Environment,” features in the leading scientific journal Integrative and Comparative Biology.From a release submitted by the authors.