Reductions in humanmade noise resulting from the COVID-19 pandemic shutdown led birds in parts of California to adapt their songs to be higher quality, a new study reports.
The results are based on evaluating changes in birdsong in white-crowned sparrows in the San Francisco Bay area, both before and after the COVID-19 pandemic shutdown, and in urban and rural environments. The study provides strong evidence that previously reported regional changes in birdsong — changes that lowered song quality, which impacts male birds’ ability to defend their territories — did result from increased anthropogenic noise.
Elizabeth Derryberry and colleagues have been monitoring urban and rural populations of white-crowned sparrows in the San Francisco Bay area for years. Their previous work 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.
Here, Derryberry and colleagues sought to understand how these birds may alter their song following the drop in noise levels that occurred when traffic in the Bay area ground to a halt after the statewide COVID-19 shelter-in-place order in spring 2020. They compared birdsong data from April to June 2015 to recordings made at the same sites from April to May 2020.
The researchers report that 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 upticks in vocal performance. 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.
Reference: “Singing in a silent spring: Birds respond to a half-century soundscape reversion during the COVID-19 shutdown” by Elizabeth P. Derryberry, Jennifer N. Phillips, Graham E. Derryberry, Michael J. Blum and David Luther, 24 September 2020, Science.