Some gas wells are coupled with noisy compressors that extract the gas and transport it through pipelines. The compressors roar and rumble day and night, 365 days a year at greater than 95 decibels a noise level comparable to a motorcycle less than 50 feet away. "You need hearing protection if you're next to them," Francis said.
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, published this week in Biology Letters, 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, like a musical score, 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," Francis said.
Singing higher-pitched songs may make them easier to hear above the low frequencies typical of human-made noise, he added.
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, Francis said.
"Closely related species may use different strategies to deal with noise," he said.
The researchers report their findings in the
|Contact: Robin Ann Smith|
National Evolutionary Synthesis Center (NESCent)