White-crowned sparrow. Photo: Education Images/Universal Images Group via Getty Images

When San Francisco hushed during coronavirus shutdowns earlier this year, a common songbird responded by changing its tune.

Why it matters: Earlier work found birds alter their songs to compensate for urban noise. This study suggests they are "adaptable enough to shift back if noise pollution is removed," says Ken Otter, an ornithologist at the University of Northern British Columbia who wasn't involved in the study.

  • Alleviating noise pollution — through the adoption of electric vehicles or urban planning — could affect breeding and "benefit wildlife that rely on acoustic communication," says Otter.

During pandemic shutdowns, the background noise in urban areas near San Francisco was on par with rural areas and with that of the city in the 1950s, Elizabeth Derryberry of the University of Tennessee, Knoxville and her colleagues report today in the journal Science.

  • That created "a proverbial silent spring" — and a rare opportunity to study the songbird's response to less noise pollution.

What they did: The researchers compared recordings of different dialects of male white-crowned sparrows, Zonotrichia leucophrys, in urban and rural areas near San Francisco from spring 2015 and 2016 with those from April and May 2020.

  • During the quiet period, the urban sparrows sang more softly and the distance the song traveled more than doubled.
  • They also began to sing lower notes, what females perceive as a more challenging song that therefore may increase the male's sex appeal.

Last note: The signal-to-noise ratio of the sparrow song also doubled, which means people could hear four times more birds and may explain why people reported bird songs being louder during the shutdown, the researchers write.

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