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A study in San Francisco's Presidio District suggests birds are adapting to the increasingly noisy city.

Well it turns out city-dwellers aren’t the only ones miffed by urban noise pollution. Research has long suggested that wildlife – and birds in particular – may be impacted by the man-made sounds of the city, from car horns to traffic congestion. A new study confirms that sparrows in the Presidio District of San Francisco appear to have changed their tune and raised their voices to be heard over the increasingly noisy racket of the Golden Gate Bridge.

The researchers, George Mason’s David Luther and Louisiana State’s Elizabeth Derryberry, compared modern birdsong in the city to recordings of sparrows in the area taken in 1969. They also looked at historic noise-level data from the Environmental Protection Agency and San Francisco Department of Health, as well as traffic volumes over the Golden Gate Bridge across this time period.

They found that as noise in the city increased, so too did the pitch, or frequency, of the male white-crowned sparrow song. Higher frequencies of song allow the birds to keep twittering at each other over the low-frequency ambient noise of rumbling cars. Even more surprising, the authors write in the journal Animal Behaviour, the birds also seem in the last four decades to have literally changed their repertoire.

This longitudinal study, the first of its kind, adds to evidence scientists have long pointed to suggesting that urban birds sing louder than their rural brethren (and that they may even do so as a result of urban architecture).

It’s probably good news for these sparrows that they’ve figured out how to adapt (and good news for urban bird-lovers that this wildlife isn’t simply fleeing the city all together). But there’s also something sort of disturbing about the implication that cities can distort the natural environment right down to birdsong. In some ways, noise matters even more for birds than it does for humans: Birds sing to defend their territory and to attract mates (life’s two most important goals!), and excessive noise threatens that.

The researchers actually tested all of this by mounting an iPod speaker in the park and playing for sparrows songs recorded in 1969 and 2005. The birds responded more strongly to the modern songs than the 60s classics (as a measure of some ornithological metrics examining the number of songs, flybys and “wing waves”). The two eras have produced something like different sparrow dialects. This is essentially like the difference between how you hear Shakespeare’s English and Jon Stewart’s. (And this analogy works even better if you’re currently weighing whether or not to date Jon Stewart.)

Birds that haven’t kept up with the times – and the traffic volume – may, the authors write, have a hard time establishing and defending their territory:

Thus, there seem to be consequences to producing a song that is not adapted to local ambient noise levels in an urban population. It remains to be seen whether urban- dependent selection on songs also affects signal content in the context of female mate choice.

In other words, might male birds that haven’t adapted to city life fail to attract any ladies?

Top image: voronas / Shutterstock.com

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