Birds sang lower and communicated better during confinement

The coronavirus quarantine in the spring of 2020 was the ideal time for many wild animals to return to the urban spaces that once belonged to them.

In social networks, videos of wild foxes circulated through the streets of London, wild boars in the center of Barcelona, ​​peacocks in the gardens of Madrid and even an adult puma walking through Santiago de Chile.

The reduction of human-generated noise also made it possible for many cities around the world to hear the singing of birds clearly again.

In California's San Francisco Bay, the drop in traffic noise during the quarantine months caused the region's white-crowned sparrows to change the frequency, volume and quality of their song, a study reveals. published today in the journal

The research, carried out by scientists from the University of Tennessee, the University of Texas and George Mason University, in the USA, compared the song of these birds between April and June 2015 and 2016 in specific places in the city, with the same sites and the same months of this year.

David Luther, a biologist at George Mason University and one of the authors of the work, tells by phone that the most relevant conclusion of the natural experiment is that it shows how these birds are capable of changing their behaviors according to the new conditions generated by humans. with a lot of speed.

“The results show how quickly birds can adapt to changing environments.

The study also suggests that long-term hearing decontamination could lead to similar behaviors, even in other species, ”says Luther.

Research confirms that as urban noise levels have increased in San Francisco in recent decades, thanks largely to continued increased traffic, these birds have started singing at higher frequencies and louder volumes, spending more energy and losing quality and ability to communicate.

During the quarantine, however, as the background noise was very low, the sparrows began to sing in a lower tone and with a lower volume.

This allowed them to communicate better, reach farther distances with their song and save energy to defend their territory.

Paola Laiolo, a CSIC researcher in the Mixed Biodiversity Unit, affirms that the findings of the experiment reveal the “incredible” plasticity of birds.

“As soon as the noise in San Francisco was gone, the sparrows changed their behavior and benefited from the new conditions.

In colloquial words, during the quarantine they did not have to scream so much or so hard and yet their singing was prettier and it went further ".

Diego Gil, a researcher at the Department of Evolutionary Ecology of the National Museum of Natural Sciences of the CSIC, agrees with Laiolo in recognizing that the study helps to understand the relationship between the behaviors of human beings and the behaviors of birds.

"We all would have loved to use the confinement of the coronavirus as a kind of natural experiment to find out how the noise of cars affects the song of birds," acknowledges Gil.

"It is impressive to see that in a matter of weeks these San Francisco sparrows have returned to sing at a much more serious frequency," adds the CSIC researcher.

The study, which showed that the levels of traffic during the quarantine in California were similar to those that could be during the 1950s, serves to refute the idea that during confinement the birds were singing louder because they were heard more.

“It's the opposite,” says Gil; “as the background noise pollution had decreased, there was the impression that the song had a higher volume, but in reality the birds sang quieter.” Laiolo and Gil affirm that a positive consequence One of these changes is that the energy saved by birds by reducing the volume of their song can be invested in defending their territory and improving their sexual reproduction.

The San Francisco experiment is similar to a study that Gil and his colleagues carried out a few years ago in Spain in which it was verified how the birds that live near the Madrid Airport advanced the time of the song so as not to coincide with the peak of the noise of the airplanes.

"We saw how these birds were optimizing that silent time slot so as not to have to compete with aircraft turbines," says Gil.

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