When behavioral ecologist Liz Derryberry saw a news report of coyotes crossing the Golden Gate Bridge in March, she immediately thought of her birds. For over a decade, Derryberry has studied the white-crowned sparrow and how urban noise has disrupted and degraded the species’ ability to communicate.
With most San Franciscans staying at home due to the coronavirus pandemic, she decided to seize an unprecedented opportunity to study how this small, scrappy songbird responded when human noises disappeared.
“I realized we gotta do this, and we gotta do this now,” she says.
By recording the species’ calls among the abandoned streets of the Bay Area in the following months, Derryberry and colleagues have revealed that the shutdown dramatically improved the birds’ calls, both in quality and efficiency. Male birds in particular rely on their songs to defend territory and find mates. (Read how coronavirus lockdowns are clearing the air.)
“The songs didn’t change as much as we predicted—they changed even more,” says Derryberry, of the University of Tennessee, Knoxville. “It highlights just how big of an effect noise pollution has.”
The research, published today in Science, is among the first to scientifically evaluate the effects of the pandemic on urban wildlife. It also adds to a burgeoning field of research into how the barrage of human-made noise has disrupted nature, from ships drowning out whale songs to automobile traffic jamming bat sonar.
“I was excited that someone was able to collect such great information on a rare event. It showed how quickly animals can recover,” says Sue Anne Zollinger, a behavioral physiologist at Manchester Metropolitan University in the U.K.
Just two days after Derryberry had her realization, her former Ph.D. student, Jenny Phillips, who’s based in the Bay Area, began recording background noise and birdsong at some of the same areas she had visited for her research: the Presidio neighborhood in downtown San Francisco, and other urban locations in Contra Costa County.
As an experimental control, Phillips, now a postdoctoral student at California Polytechnic State University, recorded sparrow sounds in nearby Marin County, which is more rural.
Derryberry then analyzed the results in her home studio, comparing the new recordings to previously recorded data of the birds before the pandemic. The white-crowned sparrow’s consistent tune—which starts with several whistles and ends with a series of complex trills—makes it an ideal study subject, she adds. (In an unexpected shift, these sparrows are singing a new tune.)
Though both scientists expected that the sudden quiet would affect the sparrows’ song, they were surprised by just how much.
Derryberry’s previous research had shown that urban white-crowned sparrows sing at a louder volume, in essence straining their voices to be heard, as well as sang lower-quality songs. Think of it like trying to discuss the nuances of philosophy while yelling into a bullhorn, Derryberry says: “You can’t yell far and have a lot of information.”
But during the pandemic, the urban birds’ calls became higher quality, each call packed with more information than before. The lack of human noise also allowed the urban birds’ tunes to travel around twice as far. As expected, the rural bird calls were the same before and during the pandemic.
“The most interesting and surprising thing was how much difference there was in the urban birds,” says Zollinger, who also studies noise pollution’s impacts on city birds. For example, Zollinger has discovered that vehicle sounds in the Dutch city of Leiden caused great tits to emphasize the higher-pitched notes in their songs—similar to the San Francisco birds. (Read how noises from oil and gas drilling can lower bird fertility.)
Not only that, great tits and other urban birds have altered stress levels—measured by the amount of cortisol in their blood—and lower growth rates in the nest, Zollinger says. “All of this adds up to some very important health consequences” for urban birds, such as a shorter life span, Zollinger says.
Megan McKenna, an expert on noise pollution and animal communication at Stanford University's Hopkins Marine Station, echoes Zollinger’s praise of the research, calling it “awesome” and “exciting to see.” She also points out the researchers studied a species flexible enough to survive in urban areas, but that the pandemic’s impact on shyer, more sensitive bird species remains unknown.
Ultimately, the rapidity at which the sparrows recovered is a promising sign for the species’ ability to cope, says Derryberry. Finding ways to reduce noise, such as creating traffic-free zones or times within cities, might be a simple, straightforward way to help urban wildlife.
She adds that city dwellers in general have begun to appreciate animals in their own backyards during the pandemic.
“That goes to show that reducing noise pollution isn't just a benefit to wildlife—it's also a benefit to people, even in a really awful time.”