Listening to the urban choir
How biologist Jenny Phillips listens to birdsong in an age of cities
Rahul Rao • June 4, 2020
Living among humans and shrouded by human noise, songbirds like this sparrow have adapted their song [Rhubarble, flickr | CC BY-NC 2.0]
Perhaps you were woken up today by the calls of a singing bird — perhaps trying to mate, or simply to communicate. In an Anthropocene world, those birdsongs are changing. Songbirds today, many of whom live in the midst of human cities, are singing into increasingly noisy skies. Their songs must compete with the din of planes, trains, and automobiles — and birds have been adapting their song to compensate.
Enter scientists such as Jenny Phillips, a biologist at Cal Poly San Luis Obispo. Phillips and her colleagues study birdsong in order to understand how human noise continues to change the notes those birds are singing. In this Scienceline audio profile, Rahul Rao talks to Phillips about how she records birdsong — and what she learns by listening to those birds.
Birdsong and urban noises in this audio piece were provided by Jenny Philips.
[Birdsong, urban noise in the background]
Rahul Rao: This is the song of a male white-crowned sparrow in California. His song is how he communicates to the world. His song is how he finds mates and defends his territory.
Rahul Rao: But you’ve heard birdsong before. Now, listen to the background.
[Urban noise is more audible, birdsong]
Rahul Rao: This sparrow lives in San Francisco, within earshot of the Golden Gate Bridge. Here, the bird must compete for airtime with the hundreds of thousands of people and cars who blare past on an average day.
[Background noise ceases]
Rahul Rao: As human noises threatens to drown out birdsong, birds like this sparrow have adapted. Scientists have begun to notice.
Jenny Phillips: I think my research gives a voice to species around us that can’t necessarily advocate for themselves.
Rahul Rao: That’s Jenny Phillips, currently a [postdoctoral] researcher at Cal Poly- San Luis Obispo. She studies how the noise we make is impacting how birds communicate.
Jenny Phillips: It just lets people know about how we as humans influence animal behaviour and success, and that’s kind of the first step to making change in the way we develop the world.
[Bird chirping, as a section break]
Rahul Rao: Recording birdsong isn’t so simple as leaving a mic out in open air and hoping a sparrow happens to flutter across it. Jenny says that finding birds is something that takes a lot of observation and patience.
Jenny Phillips: To record birds, you kind of have to be very quiet yourself and patient. So I spend a lot of time hiking around outside, looking for territory, and basically, you know, spend time observing the vocal birds — for white crowns, it’s usually the male that sings, although females do sing as well — and kind of figuring out where his favourite song perches are.
Rahul Rao: Only after Jenny has learned those patterns can she record their song.
Jenny Phillips: Then I’ll come back a day or two later with all my recording equipment, and you kind of just have to…sneak up on them and try and get a good angle, you know, get the bird singing right at you to get a really nice recording.
Rahul Rao: Once she has the song on record, Jenny analyses the birdsong on her computer. There’s a few things she looks at: for instance, the lowest and highest notes a bird can hit, which are the bird’s minimum and maximum frequencies. Jenny also looks at something she calls the bird’s bandwidth.
Jenny Phillips: Bandwidth would be…just the range. So the difference between that minimum frequency and maximum frequency. So, it’s like, you know: a singer like Mariah Carey, who has a wide bandwidth, she can sing a large range of songs. A normal person like me has a small bandwidth, cause I’m not a singer [laughing]
Rahul Rao: Birdsong isn’t just about what notes a bird can hit. It’s also about how well it can hit them.
Jenny Phillips: Vocal performance, which is the one of the main things I studied, is basically a measurement where you’re taking into account how fast a bird can repeat notes, so how fast it can go like da-da-da-da, but also the bandwidth of those notes.
Jenny Phillips: You can kind of think about it like dribbling a basketball. So it’s easy to dribble a basketball fast, if you’re keeping it low to the ground. But if you want to bounce it high, you have to dribble it a little bit slower. So you can do high and slow, or low and fast. Unless you’re a really good basketball player, then you can probably maximise both. There are some performers that are high performers, that can sing a wide bandwidth while singing fast notes, while other, lower performers can only repeat those notes at a lower bandwidth.
Rahul Rao: Jenny and her colleagues have found that city birdsongs have changed. In order to stand out from the urban background noise, sparrows have had to adjust their frequency, singing at higher pitches. But at the same time, their bandwidth has decreased. They aren’t able to hit as many notes. And they aren’t able to hit their notes as well. In order to make themselves heard in the city, those birds have literally become worse singers.
Rahul Rao: And Jenny and her colleagues think they know how this city sparrow’s song is spreading.
Rahul Rao: Dana Moseley, a biologist at James Madison University in Virginia, is one of Jenny’s collaborators.
Dana Moseley: And what we found was really this new mechanism, or at least evidence of this new mechanism, for how bird populations have come about to be singing higher. That mechanism is through learning, through development, and through cultural selection.
Dana Moseley: If birds are choosing the higher-frequency songs to adopt into their repertoire, then they’re going to have a more effective signal. We know that their signal would be less masked by that low-pitched urban noise.
Rahul Rao: Another one of Jenny’s colleagues is Liz Derryberry, a biologist now at the University of Tennessee in Knoxville, formerly at Tulane University in New Orleans, where Jenny was a graduate student.
Liz Derryberry: She [Jenny] is starting to think about multiple sources of selection, and how do those interface [sic]. How do both of those operate? And also thinking about not just communication, like the signal, but also thinking about fitness consequences. How does this actually affect an individual’s ability to breed, you know, successfully, and raise young? And [how does this affect the ability] for a population to persist in an area?
Rahul Rao: Birdsong is far more than just what wakes you up on a weekend afternoon. Again, these sparrows use their song to mark their territory and to attract mates. When they don’t sing as well, they’re more vulnerable to urban wildlife, and make it harder for them to reproduce.
Jenny Phillips: So we know humans aren’t going anywhere soon, but if we kind of manage our noise levels, just kind of think about it and do our best to do this type of mitigation, it gives animals the chance to cope and adjust to anthropogenic noise, rather than just, you know, scare them away right away.
Rahul Rao: And rural birds don’t live in noise-free areas either. Even away from dense city centres, there are still plenty of humans making noise out in the country. For instance, take this recording Jenny made.
[Bird chirping; agricultural machinery steadily growing louder in the background]
Jenny Phillips (in-recording): May 5th, they’re cutting the hay next door.
Rahul Rao: For Scienceline, I’m Rahul Rao.
Jenny Phillips for the birdsong sounds.