FAIRFAX, Va., April 3 (UPI) -- Sparrows in San Francisco have changed their tune to be heard over growing city noise and the cacophony of car horns and engine rumbles, researchers say.
Biologists from George Mason University in Virginia compared recordings of bird songs from as far back at 1969 to examples today while charting the increase in noise in San Francisco's Presidio district based on studies from 1974 and 2008.
The study shows a strong link between the change in song and the change in noise, biology professor David Luther said in a university release Monday.
Just as people raise their voices to be heard when a car speeds past, birds making their homes near busy intersections have to tweet a little louder, Luther said.
But they've also changed their songs because some older bird tunes couldn't be heard in the increasing city racket, he said.
Sparrows in the Presidio used to sing in three distinct dialects when ornithologists made recordings in 1969 but they've since dropped to two, with one in a higher range on the way to being the only one sung, Luther said.
"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," Luther said, "and 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."
