If you think it’s hard to hear yourself talk over the traffic noise of a big city today, imagine what it’s like being a sparrow.
In fact there’s no need to imagine. Scientists have just published a study of how sparrow song has changed over the last 50 years in San Francisco.
The researchers, George Mason’s David Luther and Louisiana State’s Elizabeth Derryberry, compared modern birdsong in the Presidio District to recordings of sparrows taken there in 1969. They also looked at data about noise-levels from that time, as well as traffic volumes over the Golden Gate Bridge.
They found that the pitch of the male white-crowned sparrow song has risen over the years – they’re singing at a higher frequency now in order to be heard better over the lower-frequency growl of passing cars, lawn mowers, etc. Their song overall has changed, too. The two researchers call it “the San Francisco dialect.” And since their songs back then just couldn’t cut through the growing noise around them any longer, they’ve created a whole new repertoire of songs.
Since their songs back then couldn’t cut through the growing noise around them any longer, they’ve created a whole new repertoire of songs
“It’s the really low hum where almost all of this human-made noise is — in this very low bandwidth,” Luther said. “The birds can often sing at the top end of that low bandwidth. If there’s no traffic around, that’s just fine. But if they’re singing and there is noise, the lowest portion of that song gets lost, and the birds can’t hear it."
In their study, Birdsongs Keep Pace with City Life: Changes in Song Over Time in an Urban Songbird Affects Communication, Luther and Derryberry explain that sparrows in the Presidio used to sing in three distinct dialects when ornithologist Luis Baptista made recordings of them in 1969. When Luther worked with Baptista some 30 years later, those three song styles had dropped to two, and the higher-range of the two “dialects” was becoming the most popular among the sparrows.
In conducting the study, the two researchers set up an iPod speaker in the Presidio , shuffled the sparrow songs from 1969 and 2005 and waited for a reaction from the sparrows.
“The birds responded much more strongly to the current song than to the historic song,” Luther said. Also, the male sparrows flew toward the speaker while chirping a “Go away!” song when a song using the modern dialect was played.