Ornithologists have come up with a twist on Aesop's fable about the country mouse and the city mouse. Their version involves city birds and country birds.
Scientists at the Max Planck Institute of Ornithology in Germany have proved that blackbirds that live in urban areas sing louder than their country cousins. The reason: They need to yell to be heard over the traffic noise.
"Birds, as well as mammals, exhibit the Lombard effect, i.e. they increase the amplitude of their vocalizations in response to an increase in background noise," says a study titled "Bird song and anthropogenic noise" (also known as noise pollution).
It's been known for some time that city birds also sing at higher pitches. Previous theories have held that they do this to differentiate their calls from lower-frequency traffic sounds, but this study argues that it's part of the birds' efforts to crank up the volume.
"This is just a useful side effect," the study says of the change in tone. "The real reason for this behavior is that songs at a higher pitch are also automatically louder."
The findings don't surprise Jim Williams, a bird expert who writes the Wingnut blog for the Star Tribune.
"Singing is very important to birds in terms defending themselves and finding a mate," he said. "There's no doubt that a city has a lot more noise than a nice, open marsh. If they can't be heard, they have to sing louder."
As for the instinct that makes birds realize that they need to scream to be heard, that doesn't surprise Williams, either.
