Birdsong became more beautiful during lockdown because humans weren’t drowning it out, scientists reveal

At the peak of lockdown the endless clamour of the human world temporarily ceased - countless industries paused operations, non-essential shops closed their shutters, roads fell almost silent.

Those people who were able to venture outside their homes, either to take their government-sanctioned daily exercise, or to travel to key jobs, experienced a very different world, and one which as many noted at the time, was full of birdsong.

A new study now indicates it was not just the sudden drop in noise pollution which suddenly allowed us to hear the birds.

The birds in fact changed their tune, and reacted to the novel serenity by singing at different pitches.

The study, carried out in California, examined changes in birdsong among white-crowned sparrows in the San Francisco Bay area, both before and after the COVID-19 pandemic shutdown, and in urban and rural environments.

In this area, the extent of the shutdown meant noise levels in urban areas were “dramatically lower”, primarily due to less traffic, which was “roughly characteristic” of traffic in the mid-1950s, the researchers said.

Through the 20th and 21st centuries, long-term studies have shown that birds living in close proximity to areas with heavy traffic have slightly changed how they sing, in order to cut through the continual rumble of the background road noise.

Lead author of the study, Elizabeth Derryberry, an associate professor at the University of Tennessee and expert in behavioural evolution, has been monitoring urban and rural populations of white-crowned sparrows in San Francisco for years.

With her colleagues, their research has shown that as urban noise levels have increased in the region (mainly due to ever-increasing traffic), these birds have shifted to sing songs featuring higher minimum frequencies, which increases communication distance, though at a cost of lower vocal performance.

This phenomenon has also been observed in the UK among bird species including great tits living in close proximity to the M25 motorway.

The authors of the new study say it provides strong evidence that previously reported regional changes in birdsong - changes that lowered song quality, which impacts male birds’ ability to defend their territories and attract mates - did result from increased anthropogenic noise.

The results are based on birdsong data collected between April and June 2015 and recordings made at the same sites from April to May 2020.

The researchers found the sparrows in the latter group, exposed to greatly reduced background noise, exhibited drops in vocal amplitudes and reductions in vocal minimum frequencies, which led to what Dr Derryberry described as a “sexier” vocal performance for the other birds in the population.

Asked if this had led the birds to experience a unique summer of love, she told The Independent: “I think it is kind of fun to realise that these sexier songs sound like songs recorded in the late 60s and early 70s in the original summer of love!” 

She explained “the songs have increased in bandwidth, and wider bandwidth songs are higher performance and more attractive.”

She added: “The study tells us that noise is having a large impact on animal communication, but that animals are resilient. When noise is reduced, birdsong bounces back.”

These changes were much more notable for birds in urban areas, the authors say, which likely gave these birds much greater capacity to compete for breeding territories.

The results reveal how quickly birds can adapt to changing environments and suggest that lasting remediation might lead to other promising outcomes, including higher species diversity, say the authors.

Dr Derryberry said: "I think we can take steps to keep noise levels down.  Not all roads need to re-open, and traffic may be lower if more people continue to work from home."

The research is published in the journal Science.