If you thought birdsong sounded different during lockdown, it turns out you were probably right. The uniquely quiet circumstances of the covid-19 restrictions in San Francisco saw birds respond by lowering their pitch, singing sexier songs and making their songs clearer.
We know some birds react to human noise, particularly the low-frequency city sounds of car engines and air conditioning units, by singing more loudly and shifting to a higher frequency.
鈥淲hat we didn鈥檛 know was if you take sound out, what exactly happens 鈥� does it drop by the same amount? They did sing more softly. But they sang so much more softly than we thought they would,鈥� says Elizabeth Derryberry at the University of Tennessee.
Advertisement
San Francisco bird singing before lockdown
听
She and her team compared audio recordings of white-crowned sparrows (Zonotrichia leucophrys) made in San Francisco and surrounding rural areas in both April to June 2015 and 2016, and also compared them with new recordings from April to May this year. They found background noise in urban areas dramatically down, about 7 decibels lower than usual.
Without the low drone of cars and other human sounds, birds returned to singing at lower frequencies. This improved their vocal performance, doubling the distance they could be heard by a human or bird. They also became more appealing to potential mates, as birds find higher frequencies less attractive. 鈥淭heir songs are sounding like they did 30 years ago,鈥� says Derryberry.
San Francisco bird singing during lockdown
听
The result of the lockdown quiet could be higher quality mates, greater reproductive success, better genetic fitness and, ultimately, a more stable population, she adds. There is no reason to think the findings don鈥檛 apply to birds elsewhere, as Derryberry notes that some species such as blackbirds and great tits have previously shown even greater flexibility in response to human noise.
鈥淚t鈥檚 a two-sided tale of how our noisy cities are making life harder for animals that communicate by sound, but also a more optimistic reminder of the resilience and flexibility of nature,鈥� says Joseph Tobias at Imperial College London.
Science
