Mailing List

For all the latest news and features, sign up to receive our FREE updates by email:

Songbirds tweak their tunes to cope with clamor

Posted on 14. July, 2011.

Bookmark and Share

Some birds that live near noisy sites can alter their songs to deal with din. But closely related species with similar songs may tweak their tunes in different ways, according a new study led by Clinton Francis of the National Evolutionary Synthesis Center in Durham, NC. The study was published in the May 25 issue of Biology Letters.

Birds rely on songs to defend their territories and attract a mate. "When something interferes with their ability to hear each others' songs, it can lead to a communication breakdown," says Francis. “Noise can drown out other sounds in the environment too, like approaching predators.”

While some birds can cope with noise by altering their songs, less flexible birds may have to abandon noisy areas altogether. In order to help predict which species will be most threatened by an increasingly noisy world, Francis and his colleagues wanted to see whether two closely related species respond similarly to noise.

To find out, they surveyed two closely related species with similar songs – the grey vireo and the plumbeous vireo – both living near natural gas extraction sites in northern New Mexico, USA. Some of the gas wells are coupled with noisy compressors that extract the gas and transport it through pipelines creating a noise level greater than 95 decibels – comparable to a motorcycle less than 50 feet away.

The researchers counted and recorded plumbeous vireos and grey vireos living near natural gas wells with noisy compressors. They then compared this data with song and survey data they collected from quiet wells without compressors. The results showed the two species are just as common in noisy sites as quiet ones, but they alter their songs in different ways.

Each vireo's song is a short whistled phrase with multiple notes. According to Francis explained, "Plumbeous vireos raised the pitch of the lowest part of their song, while grey vireos raised the pitch of the highest part of their song." Singing higher-pitched songs may make them easier to hear above the low frequencies typical of human-made noise. Both birds also changed the length of their songs, but in opposite ways. Whereas plumbeous vireo songs got shorter with increased background noise, grey vireo songs grew longer. "Grey vireo songs in noisy sites were nearly one and a half times as long as their counterparts in quiet sites," Francis said.

The results back up other studies showing some birds can cope with noise by altering their songs. But given the different modifications made by closely related species, it may be difficult to predict what these altered songs will sound like in diverse bird communities.

The article, Different behavioural responses to anthropogenic noise by two closely related passerine birds by C. D. Francis, C. P. Ortega and A. Cruz is published in Biology Letters, 2011; DOI: 10.1098/rsbl.2011.0359.

In picture: Grey vireo. Photo courtesy of Clinton Francis, National Evolutionary Synthesis Center.

Click here to find out more about Avian Biology Research.

Click here to subscribe to Avian Biology Research.