Sparrows are one of the few members of the avian family that have adopted well living in cities with humans. But the increasing volume of harsh sounds like car horns and engines is changing their behavior too, with many Sparrows in San Francisco’s Presidio district changing their tune and making it louder to be heard among the noise, find scientists.
The study, “Birdsongs Keep Pace with City Life: Changes in Song Over Time in an Urban Songbird Affects Communication,” compares birdsongs from as far back as 1969 to today’s tweets.
“It shows a strong link between the change in song and the change in noise,” says David Luther, term assistant professor in Mason’s undergraduate biology program. “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.”
The researcher has backed his research with a comparison of increased noise levels in San Francisco from 1974 to 2008.
“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?”
He says that just as we raise our pitch to be heard in a crowd, birds also tweet a little louder when living among cars, horns and other loud noises. But for the birds, the change is more than increasing the volume. They also have had to omit some old songs that were not being heard in the cacophony.
For the study the researcher teamed up with Elizabeth Derryberry, an assistant professor of ecology and evolutionary biology at Tulane University and a research assistant professor at Louisiana State University’s Museum of Natural Science.
They studied the male white-crowned sparrow, a small bird that sports a jaunty white cap with black stripes. They investigated territories of 20 sparrows in the Presidio where there’s lots of traffic, especially in the morning rush hour when the birds do most of their singing.
They set up an iPod speaker, shuffled the sparrow songs from 1969 and 2005 and waited for a reaction.
“The birds responded much more strongly to the current song than to the historic song,” says Luther, adding that the sparrow flew toward the speaker while chirping a “get out of here” song. “The (current) songs are more of a threat.”
But the songs from 1969 did not get a reaction.
The researcher also reveals that even birds have different dialects depending on the region they live in.
“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.
“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, “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.”
Famed ornithologist Luis Baptista made his recordings in 1969 and found the sparrows of the area to be singing in three distinct dialects.
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.”
Birds use their songs to communicate with each other and if it was not being heard, they were not able to converse.
“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.”
Therefore songs are also used to guard territories and if a rival bird can’t hear the song, a fight is inevitable leading to injury or death.
The researchers now wish to know if the females are affected by the song changes.
“We want to understand if the females discriminate between these songs as well,” Derryberry says.
About their choice for the specific species she says,
“Here’s a bird that’s able to hang around,” she says. “A lot of species haven’t been able to adapt to and live in an urban environment.”