Songbirds affected by human noise pollution

Songbirds have been singing, and learning how to sing, for likely millions of years. But now there’s evidence that in recent years us noisy humans are disrupting the process. Sue Anne Zollinger is from Manchester Metropolitan University and she studies how birdsong is changing. She spoke with Chris Smith about the impacts that humans are having on birds, and on birdsong...

Sue Anne - Well, lots of noise that annoys us as humans is also what's interfering with birds being able to hear, and properly learn like traffic noise, airline noise, and other kinds of industrial noise pollution, that makes it harder for us to communicate also when we're exposed to it.

Chris - How do we know that's going on?

Sue Anne - We know birds do a lot of things differently in noisy places. So if you look at the songs of birds that live in noisy cities, their songs have started to diverge a little bit from what we hear in their traditional habitats, like quiet forests or grasslands. And those kinds of changes depend on the species. So lots of species around the world start to sing in slightly higher pitch in cities, and that's thought to help them avoid the loudest part of that low frequency rumble that you get from road traffic noise. Lots of birds, we know, sing louder, but they're not able to sing as much louder as they need to, to be able to really belt it out over the din of that traffic noise often. And sometimes they also change when they sing. So sometimes in really busy urban areas, birds start to sing earlier in the morning, or later at night to try to avoid those peaks of traffic that you get at rush hour.

Chris - So they're compensating, but it doesn't necessarily solve the problem, every time.

Sue Anne - That's right.

Chris - You've been doing some experiments on this, haven't you and you sent us some clips of this. So let's have a listen to these. The first one that you've got here is the gold standard. And perhaps you could begin by just telling us how you did the experiments and what this gold standard song that we're going to hear is.

Sue Anne - We wanted to look at how the noise would influence development. So during that process Mimi was just talking about where they have to go through this process of listening, learning, and imitating the song that they hear. And so we had half of our birds growing up in a quiet room and half of them in a room filled with traffic noise, like you would experience in the city. And we wanted all the birds to have the same opportunity. So this golden tutor that we're going to listen to is the song that all of the birds heard.

[TUTOR BIRD SONG]

Chris - So the first group of birds you mentioned, had a pristine environment as it were, they were exposed to that song we just heard, they had to learn it. And this is the result I presume, you're going to play for us now, of them learning that song.

Sue Anne - That's right this is the example of a juvenile from that quiet room. What I hope you can listen to in this song is that he doesn't sing exactly the same song, but he copies a lot of those syllables that have the same kind of rich harmonic structure you can hear in the tutor.

[GOOD LEARNER BIRD SONG]

Chris - And now we're going to delve into what happens when you expose them to motorway noise. This is the traffic group. What are we listening for this time?

Sue Anne - This guy, he doesn't copy any of those syllables. So it's a little hard for us to hear as humans, because we don't have the good ability to hear those fine differences. But what I want you to listen for is that none of the acoustic structures are the same. So it sounds a little more rough and click-like. It's kind of harmonically, not as nice.

[BAD LEARNER BIRD SONG]

Chris - So an example of a less good learner caused by exposure to noise pollution. How does that actually affect the birds downstream though, Sue Anne, what objective evidence have we got that it is?

Sue Anne - We know from some field studies that females in urban areas prefer the songs of males from quiet areas, so that if you give them a choice where they have an option to select one or the other, that they prefer the song like the traditional songs and not the ones that are shifted to adapt to traffic noise. So if males aren't able to sing good quality songs because of disruption of learning, by traffic noise, that they're going to have less success in attracting good quality females and defending good quality territories.

Chris - And presumably then, that means that that could unpick the beneficial effects of what natural selection is trying to do, to improve the quality of the species, you'll end up selecting poorer quality males.

Sue Anne - Yeah. It could also be, you know, that females also need to learn. So they go through this process, even if they don't end up singing the songs, of learning what songs are good. We don't know yet, but it can be that females' preferences, and their learning of what songs are good quality is also disrupted by noise. And so it might be that females in noisy areas aren't able to make good choices for good quality.

Chris - Are we being a bit shortsighted and just focusing only on sound in terms of mate selection here, are there other potential impacts on birds, of us making noise pollution? Because I know for instance, if you look at humans, if they live near a busy airport or a busy road, they have higher blood pressure because of stress. Is it true for birds that when they have to tolerate us, that it causes knock-on effects?

Sue Anne - Definitely. So that's something that I've been studying in my lab for the last 10 years or so. We know that birds in urban areas, or even just exposed to noise in a laboratory, that they have disrupted stress physiology, they age faster, and there are reductions in reproductive success. So how many successful offspring they can produce. On top of that, by disrupting non-song communication, like alarm call detection, that risks that they are more vulnerable to predation, for example, if you don't hear the warning that the predator is more likely to catch you.

Chris - I'm also thinking of one of our human behaviours, is to route aircraft, for example, over areas where people aren't. Now, birds are going to make a beeline, if that's the right phrase to use, for areas which are sparsely affected by humans. And so therefore, are we potentially taking and exporting our noise to them in other ways, which is going to prove equally disruptive.

Sue Anne - Yeah, that's right. We know that a lot of areas that are too noisy for humans, we plant up with really lovely habitats, looking for birds, trees that are going to protect the humans nearby from those loud noises. And so birds are kind of drawn to those. And we consider those almost like an ecological trap, that we attract in, animals, wildlife, birds, to these beautiful looking areas, but that this loud noise actually has very serious consequences on their fitness, their ability to thrive and procreate properly there.