A new study by George Mason University’s David Luther shows that a species of sparrow changes its song to be heard in noisy San Francisco.
With the addition of more cars and modern machinery in urban environments, the amount of sound in cities has drastically increased since 1969. When Luther learned how the overall sound of the city had increased, he wondered how birds in the area could be heard over the increasing noises of the city. To try and find an answer to this question, Luther compared songs of the White crowned sparrow (Zonotrichia leucophrys) over time in San Francisco’s Presidio district. Sound data clearly shows that the city sound in that district have been increasing over time so it was a great area to track any song changes.
Luther’s data showed that the birds have in fact changed thier song many times since 1969, pehaps searching for a tune that could best be heard.
“It’s the really low hum where almost all of this human-made noise is — in this very low bandwidth. The birds can often sing at the top end of that low bandwidth,” says Luther, whistling a lively bird tune, “and if there’s no traffic around, that’s just fine. But if they’re singing and there’s this,” he says, making a low humming noise, “the lowest portion of that song gets lost, and the birds can’t hear it.”
Luther explains how the constant noise in the city makes it so the original song of the sparrows could not be heard by others. Since male sparrows use this song to attract mates, its a big problem if no one can hear them. The sparrows have adapted their song in this area specifically to be heard over the city noise. Birds in different areas have been know to adapt different dialects of song. Researchers are calling the song of the sparrows in the Presidio district, the San Francisco Dialect.
Sparrows and many other birds also use songs to defend their territories. They sing to warn other male birds “this is my area, keep out”. After establishing that the sparrows songs were changing over time, Luther wondered if the birds would instinctually recognize the old songs and respond.
The researchers played song recordings on an IPod speaker in the Presidio district to observe the response of male birds to songs from different years. There was virtually no response to the old songs, but the new songs provoked an aggressive response from the male sparrows. This indicates that the old songs are not remembered and corroborates other findings that songs are mostly learned behaviors.
Even though their old song has been lost, the White crowned sparrow is a great example of the capability of birds to adapt to new environments.