City dwellers compete with the din of traffic to be heard. And it’s not just urban humans. Sparrows living in San Francisco's Presidio district actually tweet their tunes in a higher register than they did in the past, to be heard over the rumble of cars on the nearby Golden Gate Bridge. So says a study in the journal Animal Behavior. [David A. Luther and Elizabeth P. Derryberry, "Birdsongs keep pace with city life: changes in song over time in an urban songbird affects communication"]
Researchers compared white-crowned sparrow songs recorded in 1969 and 2005. Over that time span, ambient noise levels went up. And the bird calls were essentially the same—but the more recent one was higher in pitch. The change presumably allows the song to better penetrate the traffic noise.
The modern calls carry more weight with the birds, too. Because when male sparrows heard the 2005 recordings played back in their territory, they responded more aggressively—swooping in on the speaker with a “get outta here" chirp and flapping their wings at the suspected intruder.
The researchers say most species simply can't handle the noise and cramped habitats of the city, and head to the country. The adaptable sparrow, however, simply changed its tune.
[The above text is a transcript of this podcast.]