A Look At Unconventional Bird Calls

IRA FLATOW: You’re listening to Science Friday. I’m Ira Flatow. You know, spring has officially sprung, and one of the first signs of the season, those early morning birds. Oh, I love them. They start chirping outside your window. You know, every bird species has its own song, but sometimes, the call can come from an unexpected place. For example, can you guess what bird makes this sound?

[BIRD WHISTLING]

Did hear that? Maybe we’ll play it again, [INAUDIBLE] it’s hard– listen again.

[BIRD WHISTLING]

Wow, sounded like a little toy helicopter or something. But that sound is made by the tail feathers of a humming bird zooming by. Researchers published a study this week in the Journal of Current Biology, looking at this type of tail feather call. Christopher Clark is an author on that study. He’s also an assistant professor of biology at UC Riverside. Welcome to Science Friday.

CHRISTOPHER CLARK: Thank you, good to be here.

IRA FLATOW: What kind of hummingbird was that?

CHRISTOPHER CLARK: Yeah, that’s a Costa’s Hummingbird, a species that we have living in my backyard and on campus in Riverside, in Southern California.

IRA FLATOW: And this bird does a sort of dive bomb, is that where the sound comes from?

CHRISTOPHER CLARK: Yeah, exactly. So the males have these courtship territories that they set up at the beginning of the breeding season, and they have a couple of displays they do for the females. But the one that you just played, the male ascends about 30 or so meters, or 100 feet up in the air, and then dives at high speed past the female and has his tail spread for a good part of that dive, making that pitch, or that high pitched sound.

IRA FLATOW: So what is the bird doing with the feathers to create this sound?

CHRISTOPHER CLARK: So they’ve evolved– so the tail is basically a musical instrument. And they’ve evolved really narrow outer tail feathers. And so when the male spreads his tail, the inside edge of that outer tail feather is fluttering up and down at that pitch that you heard, and then the sound is being amplified by the neighboring tail feather in order to generate the sound that can carry for quite some distance.

IRA FLATOW: And this is done for what reason?

CHRISTOPHER CLARK: It’s a mating display, it’s a courtship display.

IRA FLATOW: Why did I not know that?

CHRISTOPHER CLARK: Of course.

IRA FLATOW: Yeah. And so we actually have a clip of this dive, let’s hear that now.

[BIRD SOUNDS]

IRA FLATOW: Those are four different hummingbirds, correct?

CHRISTOPHER CLARK: Yes. Yeah, that’s right. So I’ve spent the last 10 years or more studying this whole group of hummingbirds and the sounds that they make with their tail feathers, and also with their wings. So the tail is basically a musical instrument, and it’s evolved have a different shape in each species. So that’s like one species having a guitar, another species having a ukulele, and so on. And then the other thing that you heard going on in that clip, in all of the species, they were making sounds multiple ways. So in some of those, they were making tail sounds as well as wings sounds. And in one of the examples in there, they were making a vocalization, a mouth sound as well as a tail sound.

IRA FLATOW: All right, let’s listen to them again. There are four different sounds, here. So perk your ears up on this one.

[BIRD SOUNDS]

IRA FLATOW: Wow. Do they do they keep going on and on, repeating, or is it just one quick sound like that?

CHRISTOPHER CLARK: Most of the time, when a male is displaying to a female, he’ll perform over and over and over again. The different species are different. So some species do just do one dive, but Black-chinned hummingbird, the first sound that you played, they’ll make that– “zz-zz, do do do do do do, zz-zz, do do do do do do,” and repeat that 10 or 15 or 20 times in a row.

IRA FLATOW: Wow, and do we know if the females are actually responding?

CHRISTOPHER CLARK: We don’t have any direct data on female preferences, and in fact, we also don’t know who the females are mating with. So those are areas that we hope to study in the future. But if you sit and watch a female as the male is performing the display, there’s a number of times the female very carefully tracks the male with her head as he flies by. I’ve also seen females even have their eyes closed, almost like a person listening to a symphony or an orchestra, with their eyes closed, to better appreciate just the acoustic component of the display. So certainly, from observation of birds on their territories, the females are into this, they are most certainly evaluating males on their displays, and we just don’t know exactly what part of the display they’re evaluating, or who they’re deciding to mate with, exactly, when one female goes– basically, what they’ll do is a female will visit one male, and then presumably, she visits another male, and visits several males, and then decide which male she wants to mate with.

IRA FLATOW: Wow. That’s quite interesting. Let me bring on another guest. When you hear a bird song, you probably think it’s a male trying to woo a mate, just like that. But certain female birds are also singing and making calls. And my next guest is here to tell us what they’re saying, and she’s collecting their calls through a project called femalebirdsong.org. Lauryn Benedict, associate professor of biology at the University of Northern Colorado, in Greeley. Welcome to Science Friday.

LAURYN BENEDICT: Hi, thanks for having me.

IRA FLATOW: How did you get interested in all these bird calls?

LAURYN BENEDICT: Well I’ve been interested in birds and bird songs for a long time. And I really started looking closely at California Towhees, which are these little drab, brown birds, that everyone said were uninteresting. And when you look closely, you find that the males and the females are actually really communicating with each other with this individual duet vocalization. And I thought that duet it was so fascinating. It wasn’t just the male’s song that was really influencing behavior, it was that female responding, too.

IRA FLATOW: Yeah, and that’s interesting, because we usually don’t think of the female birds making the calls.

LAURYN BENEDICT: Yeah, I think there’s a definite bias to assume that pretty much any bird song that you hear out there is a male. And it’s true, that in North America, so in the US, most of the songs that you hear are given by males, but certainly not all of them. And we really want to draw awareness to that, and we want to ask everybody, if you hear a singing bird, look closely. Make sure you know if it’s a male or female, because it could be a female.

IRA FLATOW: And you collect these female bird songs through your website. Have you seen any patterns so far? What type of female birds make bird songs?

LAURYN BENEDICT: Yeah, we’re just getting going with this project, and we love having more people upload songs, so that we can start to find bigger patterns. So far, generally, it seems as though females do sing an awful lot more in tropical locations. We know that a lot of tropical species have female songs, and in some tropical species, females actually sing more than males do, which we’re not used to, if you live in the United States, maybe. But it also seems that the species with female song are often ones where the partners will mate for life, and they’re non migratory, so that male and female are doing similar things, day to day. They’re defending a territory, they’re doing similar behaviors to raise young and take care of the nest, and all of those things. So whenever we have males and females that both live on the same territory, year round, that really seems to be where females sing just as much as males do.

IRA FLATOW: Now let’s get to some of the calls that you have given us. You study the Canyon Wren, let’s hear the difference between the male and the female calls in that species. So first, let’s hear the male call.

[BIRD CALL]

OK now let’s hear the female call.

[BIRD CALL]

Wow, they’re different, Lauryn.

LAURYN BENEDICT: Yeah, aren’t they strikingly different?

IRA FLATOW: Yeah. Why is that? Here Is that so they can distinguish between one and the other?

LAURYN BENEDICT: I think that’s a pretty good guess. And we’re actually working to figure that out. And the male song is sort of the iconic sound of western canyons, people know this song, and love this song. It’s such a beautiful song. And I’ve had so many people say to me, oh, I’ve heard that other sound, the female song sound, I didn’t know what it was. But once you really start looking at the birds, you recognize that females sound totally different from males when they do that song. And maybe it is because they need to signal something that includes that they are females.

IRA FLATOW: Yeah, are they responding to a male call, or do they initiate that on their own?

LAURYN BENEDICT: They sing it on their own. And they actually do sing less often than males. Males, if you go out into a canyon, you’ll hear the male song, all the time. And you’ll hear the female song only occasionally. But they definitely sing when they have another female nearby. And so it’s probably a signal to those other females. And the fact that it sounds different from the male song allows them to have their own private communication channel among the females.

IRA FLATOW: That’s interesting. Christopher Clark, as someone who studies the hummingbirds, do if female hummingbirds create songs or calls?

CHRISTOPHER CLARK: Oh that is an excellent question. In fact, I have a paper submitted to an ornithology journal that, for all I know, Lauryn might have been a peer reviewer on, describing female song in Costa’s hummingbird. So it’s not published yet, but yes, there are examples of hummingbirds that do that, too.

IRA FLATOW: What do they sound like? What does a female– give me a little imitation.

CHRISTOPHER CLARK: OK so the Costa’s hummingbird, the sound you played a bit ago, was made with the tail feathers and it was a “wheeeoooo.” One of the really funny things about Costa’s hummingbird is their vocal song sounds very similar to that. It’s kind of this “wooo-eee-ee-oo,” with just this little break in the middle. And the female Costa’s that we found were singing more or less exactly that same song. So they also sounded just like the males.

IRA FLATOW: Wow, there are some species of birds, Lauryn, where the male and a female duet with each other. And I know you have a clip, and we’re going to play that clip for us right now.

[BIRDS CALLING]

IRA FLATOW: That’s quite fascinating. So which bird, Lauryn, started it first, the male?

LAURYN BENEDICT: Isn’t that a beautiful song? It is, that’s a Venezuelan troupial, and the male begins, and the female is then joining in, and you can sort of hear that, if you listen for it. And in that species, actually, sometimes, females will begin and males will join in, or it can go either way. They generally sometimes sing alone, but then either sex can join its partner and sing these beautiful duets.

IRA FLATOW: And Christopher, when does a hummingbird decide it’s going to vocalize, versus using its tail feathers to create a sound?

CHRISTOPHER CLARK: A lot of the species that– a lot of species do both. So the pattern that seems to hold is that in the group of hummingbirds that I study, the males either make wing sounds or they sing to guard their territory. And then if they sing, or if they make wings sounds, they also include those in some of the displays they do for females. And then, in addition to that, they also have a dive that they do, and basically, they have to dive and go fast in order to get fast enough to make their tail feathers make sound. So it’s not an either/or. Just like humans, we both vocalize, but we also make non-vocal sounds by clapping our hands. A lot of the birds that make non-vocal sounds have a variety of ways that they make sound, so it’s not it’s not just a one or the other.

IRA FLATOW: I try to attract hummingbirds to my feeder in the backyard. I’ve been mildly successful. Can I hear these sounds? Can I position myself, are they audible to non-experts like we laypeople?

CHRISTOPHER CLARK: Oh absolutely. The hearing range of birds is– we don’t really know how well they hear high frequency sound, but it’s about the same frequency range as humans. And so basically, if a bird can hear it, so can you, and vise versa. And so some of the sounds that the birds make are somewhat quiet, some of the wing or tail sounds are somewhat quiet, and so they might be easy to overlook. Also, Costa’s hummingbird in particular, the sound is so high pitched that it’s hard to localize. And so when a male is diving, I mean, I’ve spent years studying them, and I still sometimes have a hard time spotting the male. He’s tiny, he’s flying at the speed of freeway traffic.

And so you can hear the sound and look around and not see the bird. And so you don’t know what it is, where the sound is coming from. But in fact, if you know what you’re listening to, and know what to look for, sure enough, there is a male shooting by it at 60 miles an hour as he dives to a female.

IRA FLATOW: Wow. I’m Ira Flatow, this is Science Friday from WNYC Studios. 60 miles an hour, did you say?

CHRISTOPHER CLARK: Yeah, 60 miles an hour. The whole point of diving, the bird ascends to a height, and then it uses gravity to speed up and go faster in the dive than they can in level flight. Hummingbirds are really good at flying, and when we measure them in wind tunnels, they can fly 40 miles an hour or so at their top speed. But the maximum speed we’ve measured in a dive is about 60 miles an hour.

IRA FLATOW: Lauryn, how much does environment play a role in how these calls or songs develop? There’s one species, but populations that live in different areas, can they communicate, do they develop some sort of bird song dialect?

LAURYN BENEDICT: There are birdsong dialects, and we don’t know how much of that is driven by habitat and the environment, or just learning the local language or dialect when you move to a new place. And in fact, there are species in which males sing dialects, they might only be separated by, say, a few miles from another dialect, but they sound different, just the same way that we might say that a fizzy carbonated drink is “soda,” and somebody else might call that “pop,” birds do that, too. And females do the same thing. So in, for example, White Crowned sparrows, they’re really well known for males having different song dialects. If you get females to sing, they will also sing the same dialects that those males do.

IRA FLATOW: Does this tell us anything about the evolution of bird calls in birds?

LAURYN BENEDICT: Yeah, that’s a really fascinating question. And actually, something we know about female song is that the ancestor of songbirds seems to have had song that was given both by males and by females. So in places where females don’t sing, it’s not because the males suddenly became fancy and left the females behind, it’s probably because the females lost that trait for some reason. So instead of asking, why did males start singing, to really understand the evolution of the straight, we need to ask why is it that some females stopped singing? What is it about certain environments, or certain places, or certain lineages of birds, that that female song suddenly became less advantageous?

IRA FLATOW: So you think that they both were singing originally, and then the females just stopped singing?

LAURYN BENEDICT: Yep, that seems to be the case. Yeah, or that the females reduced singing, and just don’t sing as much as their deep ancestors might have sung.

IRA FLATOW: Christopher, is that the same with hummingbirds?

CHRISTOPHER CLARK: Well we know much less about song, in general, in hummingbirds than we do in passerine, or some other groups. So as I mentioned, we do have an unpublished case of a female song in one species. A lot of hummingbirds sing, there are some species that have evolved to the males don’t even sing. So neither males, nor females, sing. Those are the ones that produce sounds with their wings when they fly around. And when they do, it’s the males that produce the sound, primarily. The females, sometimes, have a really slight version of it, but it’s not clear if it has separate function in females. It might just be a male thing. So in hummingbirds, which are distantly related from the songbirds, as far as I know, my guess is that song is primarily a male thing, but I could be wrong. One of the fascinating things about Lauryn’s work, and the attention to female song, is that it’s been incredibly overlooked in passerines, and maybe it’s also been incredibly overlooked in hummingbirds. It might be that if we actually go out and look, we’ll find female song in many more pieces of hummingbird.

IRA FLATOW: Lauren, are you looking for people to send you recordings of birds?

LAURYN BENEDICT: Always, absolutely.

IRA FLATOW: Tell us how to do that.

LAURYN BENEDICT: So on the website, femalebirdsong.org, it gives lots of tips and suggestions. And for all of you out there who are listening to and recording birds, if you use ebird, you can upload sound files through ebird, that go directly to the Macaulay Library of Natural Sounds. And you can tag those and indicate on the meta information that it’s female song, and that then makes it available for anybody who wants to look in the library. There are also great libraries through xenocanto.org has a library. And then other data, just observational data, you can always put into something like ebird or i-naturalist, or other public databases, noting your observations of female song.

IRA FLATOW: There’s some great stuff we can do this weekend. Lauryn Benedict, associat professor of biology at the University of Northern Colorado in Greeley. Christopher Clark, assistant professor of biology at UC Riverside. And you can listen to all of those bird calls up on our website at sciencefriday.com/birdcalls. Thank you both for taking time to be with us today.

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