The study ‘Singing in a silent spring: Birds respond to a half-century soundscape reversion during the COVID-19 shutdown' published in the Science journal says that male birds changed their songs to attract females. No longer needing to ‘shout’ to be heard, these birds were able to change their range while singing less loudly.
They sang ‘less loudly but better’
They were able to give their voices a break for a few months! Usually bothered by noise pollution, city birds have to sing much louder than rural birds. But last spring's lockdown seems to have changed the situation, making their sound habits more similar. During lockdown, motorway traffic around San Francisco reached levels comparable to those of the 1950s. The author of the study explains:
The idea came to me when I saw the images of coyotes crossing the Golden Gate Bridge.
While some people were happy to see certain animals again, such as the return of dolphins to certain ports, she wanted to ‘observe [the birds'] reappearance in our soundscape.'
The researchers then compared recordings of birds made between April and June 2015 and 2016 with those made between April and May 2020. They were particularly interested in the white-crowned sparrow, and the result was astonishing. These birds did not have to sing at the top of their voices during the lockdown, quite the contrary! The birds of this species of sparrow sang ‘less loudly but better’ concluded the study. Especially the males, who lowered their volume but widened their range. In other words, the males engaged in softer and lower songs to attract females, songs that are normally inaudible due to noise pollution.
Their songs sounded better, sexier. They were better competitors and better performers in the eyes of the females.
The authors of the study concluded that if mankind reduces its noise pollution in the long term, a greater diversity of species could appear in the animal world.