Singing in a silent spring: Birds respond to a half-century soundscape reversion during the COVID-19 shutdown

Abstract

Actions taken to control the coronavirus disease 2019 (COVID-19) pandemic have conspicuously reduced motor vehicle traffic, potentially alleviating auditory pressures on animals that rely on sound for survival and reproduction. Here we evaluate whether a common songbird responsively exploited newly emptied acoustic space by comparing soundscapes and songs across the San Francisco Bay Area prior to and during the recent statewide shutdown. We show that noise levels in urban areas were dramatically lower during the shutdown, characteristic of traffic in the mid-1950s. We also show that birds responded by producing higher performance songs at lower amplitudes, effectively maximizing communication distance and salience. These findings illustrate that behavioral traits can change rapidly in response to newly favorable conditions, indicating an inherent resilience to long-standing anthropogenic pressures like noise pollution.

Rapid behavioural response of urban birds to COVID-19 lockdown

“…Empirical and experimental evidence demonstrates that urban birds avoid the masking effect of anthropogenic noise [9,10,35,36,56]. Our findings match these previous studies, but instead of advancing the dawn chorus [36,49,50,57], our historical urban data suggests that birds would delay their peak of activity (and consequently of detectability) to mid-morning. In our study context, this can be explained because civil and solar time are heavily decoupled in Spain since the country is located in the westernmost part of its time zone [58].…”

“…As observed in non-urban habitats, detectability during the lockdown decreased from dawn onwards, while at the same urban locations detectability was historically low at dawn and increased until reaching a peak two or three hours later. It is interesting to note that the Eurasian blackbird, a model species in urban ecology studies [8,9,13,49,50], was the only exception to this pattern. Overall, many species showed a “wilder” pattern of detection during the lockdown in urban areas.…”

“…Hence, the best option for birds would be to delay the peak of activity to after the morning rush hour [56]. Moreover, most of the previous studies have been carried out in more northern latitudes [9,49,59], where climate conditions can still be severe at night in early spring. Under these circumstances, individual survival can be challenged by a strong nocturnal energy demand [60,61].…”

“…Under these circumstances, individual survival can be challenged by a strong nocturnal energy demand [60,61]. There, dawn singing can become a relevant and honest signal of phenotypic quality of males, as only those individuals in best physical condition can undergo dawn fasting [49]. In Mediterranean regions, where spring nights are mild, the role of dawn singing as signal of male quality might be less important.…”

People power

“…Volunteer-assisted projects such as Soundscapes to Landscapes deploy acoustic recorders for monitoring biodiversity, and FrogID aims to establish a nationwide database of frog calls recorded on people's smartphones. Less than a year into the current global pandemic, researchers have also now established through acoustic monitoring of bird calls in San Francisco (United States), that reductions in road traffic noise during the recent state-wide COVID-19 shutdown had rapid knock-on impacts on song patterns of wild white-crowned sparrows 1 .…”