I often go trail running in the the wooded hills behind my house during the "blue hour" — that time of night after the sun sets, but before it's truly night out. Sometimes I also call it "bat time" as the winged mammals like to fly circles looking for insects to gobble, too. At one curve in the trail, I almost always hear the specific call of a pair of great horned owls — that classic, melancholy "hoot, hooooooot" sound.
But I've noticed that when a plane flies overhead — a semi-distant drone (they are taking off about 25 miles away), the owls hoot louder. The same things happens with the birds in my rear garden when planes, and especially much louder helicopters, fly above. Those times when I'm working outside, there for a few hours in relative silence, save the clacking of my laptop keys, I've noticed the birds raise their songs even when a loud truck goes past my house on the road below.
My amateur observations about birds getting louder to make up for human noise pollution is now backed up by science. In new research published in the journal Bioacoustics, Dr. Katherine Gentry of George Mason University in Virginia studied the Eastern wood pewee, a common songbird, in the Washington, D.C., area.
Gentry and her team recorded at three different parkland sites: Some of them were near constant traffic, and others were near roads that were closed on a regular schedule for 36-hour periods. The researchers took specific note of the birds' calls, including data on the duration of songs, and maximum and minimum loudness. They also collected the noise of the traffic nearby — if there was any — at the same time. (Some of the areas they recorded in had regular 36-hour road closures.)
When compiled and analyzed, the study found that birds did indeed get louder when traffic was zooming by, and quieter, which meant a broader bandwidth and lower sounds, as well as longer singing times, during the regular road closures.
Why noise matters
This is important, since quite a bit of birdsong is about attracting or communicating with a mate. When birds get louder, their song is less nuanced and shorter, and may not quite communicate what they're trying to get across. That's why, as the scientists wrote in the research paper, "... traffic noise is associated with a decline in reproductive success and species richness, contributing to the decreased biodiversity of ecological communities and reduced fitness of individuals near roads."
Ultimately, this is both a recognition of our less-obvious impacts on wildlife and more specifically, a scientifically backed reasoning behind closing roads — even just short-term traffic calming has measurable impacts. This kind of conservation strategy could help songbirds like the Eastern wood peewee, whose population has declined by more than 50 percent since cars have become the significant mode of transportation in places like D.C.
Birds can adapt to some of the environmental pollutants humans throw at them — including noise — but small changes like cutting traffic in certain areas at certain times can make a big difference for them. Since often these road closures are enacted so that there are more cycling and running areas available in parks on weekends, these car-free areas can be beneficial to both humans and wildlife alike. After all, urban humans benefit from the quiet, too.