The dramatic reduction in car traffic noise in San Francisco during the COVID-19 lockdown has allowed a common songbird to sing softer, more elaborate songs that are more appealing to the ladies
The response to the coronavirus pandemic has been an absolute disaster for the people of the United States, but how has it affected wild birds? A recent study of feral sparrows living in San Francisco found that they responded to traffic noise reductions by singing softer and more elaborate songs, and their resulting vocal virtuosity made them more attractive to women.
“When the city was noisy, they sang really loud,” said the study’s lead author, behavioral ecologist and ornithologist Elizabeth Derryberry, an associate professor at the University of Tennessee, Knoxville.
Like people trying to converse in a crowded pub, the sparrows screamed to be heard over the background noise of the big city, and this reduced the quality of their songs.
White-crowned Sparrows (WCSP), Zonotrichia leucophrys, are small pretty songbirds in a soft gray with bold black and white stripes on their heads. They are a well-studied model organism that has contributed to literally tens of thousands of studies on learning, communication, and signaling.
“I have been working at WCSP in San Francisco for some time and have been working on how noise affects communications prior to the lockdown,” Professor Derryberry said in an email. Professor Derryberry is an expert in integrating behavioral and evolutionary ecology to better understand animal communication and her primary model system is the White-crowned Sparrow.
Sparrows living in the San Francisco area have struggled with urban noise pollution for decades, so they learned to yell to be heard over the noise. But when the coronavirus shelter-in-place mandate was enacted in mid-March 2020, almost all car traffic came to a halt, and the once-busy highways suddenly went almost silent.
“Even then, I didn’t immediately think about how the lockdown might affect behavior.”
“It wasn’t until I saw photos on social media of light traffic on the Golden Gate Bridge that I realized how much less traffic (and therefore how much less noise) there is likely to be in these birds’ territories.”
“Oh my god, it’s empty”
Professor Derryberry has been studying urban and rural white-crowned sparrows and their songs in the San Francisco area for more than two decades, so the coronavirus shutdown provided a unique opportunity to study the impact of this newfound silence on these birds’ songs.
Professor Derryberry began quantifying the variation in background noise between urban (San Francisco and Contra Costa Counties) and rural (Marin County) areas, focusing on the breeding grounds of White-crowned Sparrows, which are common in these areas (Figure 1).
Professor Derryberry and her collaborators found that background noise in sparrow breeding areas had decreased significantly during the months of April and May during the COVID-19 shelter-in-place mandate: the number of vehicles on the Golden Gate Bridge suddenly dropped to 1954 levels, and overall noise pollution decreased by 50% (Figure 2).
How did this abrupt reduction in noise pollution affect the song of the sparrows?
The shelter-in-place order prevented Professor Derryberry from traveling to San Francisco himself, but a co-author on that study, behavioral ecologist Jennifer Phillips, was a postdoctoral fellow California Polytechnic State University, San Luis Obisporecorded background noise and birdsong in and around San Francisco.
Professor Derryberry and her collaborators then compared the bird songs recorded in the 1970s with the recordings made by Dr. Phillips taken in the same locations between April and May 2020, i.e. during the breeding season.
They found that when the background noise from the vehicles decreased, the sparrows sang 30% quieter on average than in previous years, and their songs could be heard twice as far away as in previous years when the sparrows screamed their heads off.
In addition, the sparrows also sang more elaborate songs with an extended vocal range that improved their overall performance. As expected, spectrographic analysis showed that urban sparrow songs changed more than rural sparrow songs, effectively reversing the effects of half a century of urban noise pollution.
But the most important questions concern the birds themselves: What did the sparrows think of the “COVID-19” songs? Did they respond to intruders during lockdown as usual?
Professor Derryberry and her collaborators found that the sparrows were less aggressive overall, consistent with an earlier study by Dr. Phillips, who found that city birds attack their rivals more quickly (ref). Perhaps the sparrows fought less when they could actually hear each other’s songs?
Professor Derryberry and her collaborators were unable to answer this question by conducting song playback experiments to compare the birds’ responses to song recordings from earlier years. But she and her team are already making plans for the next breeding season, when urban noise levels return to normal, to see how that affects the sparrows’ song and behavior.
The original song changes were made over decades, while sparrows born during lockdown will experience an entirely different soundscape as they raise families of their own the following year, begging the question: how will they react to this dramatic difference?
“We won’t be able to ask these questions after the fact, but we can (hopefully) test these questions in the spring to assess not only how their song has changed, but also how the birds themselves are responding to these dramatic changes in song.” short time.”
This study shows how quickly some bird species can adapt to a rapidly changing environment by changing their behavior.
“This study underscores how negatively noise affects communication BUT also how resilient these birds are,” Professor Derryberry said in an email.
As this study shows, bald sparrows can adapt to urban noise pollution, but this is not the case for most birds — and neither is most other wildlife. By working to reduce our overall noise levels, we can potentially have a positive impact on biodiversity nearby and in cities as a whole.
“People can take steps to reduce noise (using public transport, shopping locally, working remotely, driving electric cars), which will immediately have a positive impact on the wildlife in their soundscape.”
Elizabeth P Derryberry, Jennifer N Phillips, Graham E Derryberry, Michael J Blum and David Luther (2020). Singing in a Quiet Spring: Birds Respond to a Reversal in the Soundscape During the Half-Century COVID-19 Shutdown, science, eabd5777 | doi:10.1126/science.abd5777