Sept. 25 (UPI) -- During the first few months of the COVID-19 pandemic, as California issued lockdown orders and residents mostly stayed home, vehicle traffic in San Francisco and the surrounding area quickly declined -- and with it, noise pollution.
Research published Friday in in the journal Science suggests male white-crowned sparrows in the area took advantage of the newfound quiet by singing softer and "sexier" songs.
Interested in the effects of the lockdown conditions on wildlife, a group of scientists decided to leave their apartments to record sparrow vocalizations in and around San Francisco. Their recordings revealed the dramatic drop-off in noise pollution. Suddenly, San Francisco was as quiet as rural Marin County.
"The rush-hour roar was more like a gentle, sporadic purr," Jennifer Phillips, a researcher at California Polytechnic State University, said in a news release. "Usually, the Presidio is full of visiting tourists coming to see the Golden Gate Bridge, often in large groups. This season, only a few local individuals or couples were out for morning walks or bike rides. It was quite peaceful."
When the research team compared their recordings to field recordings collected from the same areas between 2012 and 2020, they found the birds' songs had quieted but were traveling longer distances.
"When the birds don't have to compete with loud background noise, they can essentially sing more quietly but still communicate over greater distances -- approximately twice as far," Phillips said.
During lockdown, the songs of male white-crowned sparrows also became sexier, featuring a wider range of notes, or pitches. Songs with greater variety provide more information to females looking for a mate.
"Our findings illustrate that behavioral traits can change rapidly in response to newly favorable conditions, indicating an inherent resilience to longstanding anthropogenic pressures like noise pollution," said study author Elizabeth Derryberry, a professor at the University of Tennessee in Knoxville.