Sparrows twittering louder to be heard
Just as we raise our voices to be heard when a car speeds past, birds making their homes near busy intersections have to twitter a little louder, says David Luther, assistant professor in George Mason University undergraduate biology programme.
"It shows a strong link between the change in song and the change in noise," adds Luther. "It's also the first study that I know of to track the songs over time and the responses of birds to historical and current songs," adds Luther.
Luther co-wrote the study with Elizabeth Derryberry, assistant professor of ecology and evolutionary biology at Tulane University, the journal Animal Behaviour reports.
"We've created this artificial world, although one could say it's the real world now, with all this noise - traffic, leaf blowers, air conditioners," Luther says. "A lot of birds are living in these areas, and what, if anything, is this doing to their songs?"
The bird they studied is the white-crowned sparrow, a small bird that sports a jaunty white cap with black stripes. Only male birds were studied, according to a George Mason statement.
Even birds from the same species don't sing the same song. "Some bird species sing in different dialects just like the way people talk differently if they are from Texas or California or New York, even different parts of New York," Luther says.
Sparrows in the Presidio used to sing in three distinct dialects when famed ornithologist Luis Baptista made his recordings in 1969. When Luther worked with Baptista some 30 years later, those song stylings had dropped to two, with one higher-range dialect clearly on the way to be the only song in town.
"One dialect had basically taken over the city," says Luther, adding that it is officially called the "San Francisco dialect". Songs need to be heard, not just because they sound pretty - birds use them to talk to each other, warn away rivals and attract mates.
"If you go into a bird's territory and play a song from the same species, they think a rival competitor has invaded its territory," Luther says. "It's just the same way if you're in your house and you hear strange voices, as if someone broke in."
If the rival bird can't hear the song, then it may come to bird fisticuffs. That can lead to injury or death.