San Francisco Songbirds Thrive in Quiet of Pandemic Lockdown
(CN) — As vehicle traffic in San Francisco decreased during the pandemic, animals that rely on sound to reproduce found reprieve in the absence of auditory commotion. One songbird in particular exploited the quieter soundscape to serenade his mates with sweeter than normal tunes, according to a study released Thursday.
Actions taken to stem the spread of Covid-19, whether voluntary or at the direction of public health orders, have led to conditions offering unique insights into the impact of human behavior on animals.
A study found that male white-crowned sparrows (zonotrichia leucophrys) increased the vocal performance of their songs as urban background noise decreased due to the Covid-19 pandemic. (Courtesy of JN Phillips) 
For researchers, collecting data in the field during the Covid-19 shutdown in San Francisco, California requires wearing a mask and practicing social distancing while trekking to sites by bike since many areas prohibit use of cars. (Courtesy of JN Phillips)
In the San Francisco Bay Area, researchers monitored changes in the birdsongs of male white-crowned sparrows known scientifically as Zonotrichia leucophrys both before and after stay-at-home orders.
Previous studies showed that white-crowned sparrows lowered the quality of their songs — which negatively impacted their ability to defend their territory due to an increase in anthropogenic noise, or the clatter of human activity.
Noise level surges, caused mainly by vehicle traffic, led to birds belting out songs with higher minimum frequencies, which increased the distances their tunes travelled, but at the expense of vocal performance.
That evidence was further supported Thursday by findings from the years-long study by University of Tennessee, Knoxville researcher Elizabeth Derryberry and her colleagues.
Scientists found that as vehicle traffic died down in Spring 2020, white-crowned sparrows again altered their songs by boosting their “vocal performance,” according to the study published in the journal Science.
The study, which examined habitats in both urban settings and rural environments in Marin County, California, shows that songbirds exposed to vastly quieter soundscapes intentionally decrease vocal amplitudes and minimum frequencies.
Researchers said the Covid-19 shutdown resurfaced noise level recordings not seen since 1954.
“Although noise recordings are not available from the 1950s, this benchmark indicates that a relatively brief but dramatic change in human behavior effectively erased more than a half-century of urban noise pollution and concomitant soundscape divergence between urban and nearby rural areas,” the study said. “In other words, the Covid-19 shutdown created a proverbial silent spring across the SF Bay Area.”
White-crowned sparrows in both rural and urban habitats exhibited the changes after reductions in background noise, though song tuning by the city-dwelling birds was more notable, a point researchers say likely afforded the birds heavier sway when competing over breeding grounds.
In Marin County, background noise typically comes from ocean sounds and wind, the study said.
Researchers said the findings reveal how quickly white-crowned sparrows can adapt to changing environments and that continued noise level reductions could increase diversity of bird species in the area.
Researchers did not immediately respond to a request for further comment.