You can tell what part of the Bay Area a male white-crowned sparrow is from just by a few notes of its song. The buzzes and trills of the North American birds can vary dramatically over just a few miles. (Think Bronx versus Brooklyn accents, but for birds.) These distinctive dialects have made the species a focus of ornithological attention for decades; since the 1960s, researchers have mapped 10 birdsong dialects across San Francisco, their borders shifting and evolving over time.
But in recent years many of the urban sparrows’ melodies had been “masked” by noise pollution, and the birds began singing at a higher frequency to overcome the cacophony of cars and city life.
That changed in March, when Bay Area counties went into coronavirus lockdown. Traffic disappeared, coyotes began prowling the traffic-free streets, and nature, famously, began healing. Elizabeth Derryberry, an associate professor of behavioral evolution and phylogenetics at the University of Tennessee, Knoxville, wondered about the white-crowned sparrows in the San Francisco region that she’d been studying since 2012. What would they sound like, unmasked?
Using recordings collected from April through June 2015 as a comparison point, Derryberry and four other colleagues analyzed the vocal performance of male white-crowned sparrows in the period from April to May of this year. The sample area spanned breeding grounds from the rural forests and grasslands of Abbotts Lagoon and Commonweal in Marin County, north of the city, to the more urban East Bay city of Richmond, and Golden Gate Bridge-adjacent Lands End. There, co-author Jennifer Phillips, a postdoc at California Polytechnic State University, San Luis Obispo, recorded four distinct songs, with four distinct trill patterns.
What the researchers found is that as the city’s sounds dimmed, the urban sparrows’ songs changed. They didn’t get louder, though you may have noticed them more. Instead, they got “sexier.” The birds were able to say more, and say it better, because they didn’t have to shout so much.
Pre-pandemic, urban and rural soundscapes varied widely in these birds’ habitats: The white-crowned sparrow’s San Francisco breeding grounds are typically three times noisier than that of less-dense Marin County. In these normal conditions, urban males often have to sing more loudly than rural ones, at higher frequencies and at lower bandwidths, to compete with the high “sound energy” of a city. But they face a tradeoff between having their songs detected at a far distance and communicating information in the signals that they’re sending.
San Francisco Bird Singing Before Shutdown