Quieter Skies for Urban Birds

White-crowned Sparrow - Photo Wendy Miller

White-crowned Sparrow - Photo Wendy Miller

How the Lockdown Helped to Expose the Effects of Noise Pollution on Birdsong

In last month’s Song Sparrow, I wrote about the impact of light pollution on birds. Just as artificial light can disrupt the behavior and biological processes of birds, so too can human-caused noise. This fact has recently been highlighted by research conducted during the quiet months of the COVID-19 pandemic.

White-crowned Sparrow - Photo Wendy Miller

White-crowned Sparrow – Photo Wendy Miller

Last month, Science published a report on the impact of San Francisco’s lockdown on the song quality of white-crowned sparrows. In areas with heavy traffic, the sparrows had previously been observed to sing songs with higher minimum frequencies to make themselves heard amidst low-frequency road noise. In other words, in essence, they had reduced the range of their songs in order to “shout” over the sounds of traffic. During the lockdown, however, traffic noise levels subsided to a level not heard since the 1950s — and, within weeks, the sparrows’ songs regained their full bandwidth, leading to improved communication between the birds.

Many people around the world reported that birdsong became louder during the pandemic, due to its greater prominence in the absence of traffic and other background noise. In fact, however, many birds were able to sing more softly during the months of the lockdown. San Francisco’s white-crowned sparrows, for example, were reported to have sung 30% more quietly on average, despite which they were able to hear each other from about twice as far away.

Great Tit - Photo Hedera Baltica

Great Tit – Photo Hedera Baltica

While the pandemic has brought renewed attention to the impact of noise pollution on birdsong, it does not mark the first time that the effect has been observed and studied. For instance, a 2017 study in the Washington D.C. area demonstrated that Eastern wood pewees sang longer and broader bandwidth songs during road closures, which improved the birds’ ability to find mates and defend their territories. Similarly, a 2003 study in Leiden, The Netherlands, revealed that great tits in high-traffic areas sing with a higher minimum frequency. Subsequent research on the same species found that the birds had difficulty in communicating alarm calls when attempting to compete with road noise, increasing their vulnerability to predators.

Last year, researchers at Queen’s University in Belfast discovered that noise pollution interferes with the ability of European robins to communicate aggressive intent. The lead author explains, “The birds receive incomplete information on their opponent’s intent and do not appropriately adjust their response. Where song is disguised by background noise, in some cases the male ends up fighting more vigorously than he should, but at other times gives in too easily.”

In addition to hampering communication, excess noise can be a stressor for birds — just as it is for people. One experiment conducted in Munich, Germany, showed traffic noise to be associated with cellular aging in juvenile zebra finches. Another experiment on zebra finches found that noise affected hormone levels in the birds and was associated with smaller chicks. Noise from oil and gas drilling has also been linked to lower reproductive rates and smaller chicks in Western bluebirds, although the exact causal mechanism is uncertain.

Zebra Finch - Photo Lip Kee Yap

When our lives and traffic patterns return to normalcy, what can be done to protect birds (and ourselves) from excessive noise pollution? Authors of the above studies have variously recommended technical solutions to reduce road noise (e.g. the authors of study on great tit alarm calls suggest “modifying asphalt composition, tires, or roadside noise buffers”), temporary road closures, and preserving roadless areas in conservation areas.

Individual contributions matter too, and they go beyond opting for quieter vehicles or choosing to drive less. For one, there are many well-known reasons to go easy on yard work for the benefit of birds and other critters, limiting mowing and leaving autumn leaves to lie on the ground. The reduction of noise pollution from mower, leaf blowers, and other gas-powered lawn equipment is one more added ecological benefit.