The Organ That Gives Birds Their Voices

ARIELLE DUHAIME-ROSS: This is Science Friday. I’m Arielle Duhaime-Ross. Have you ever wondered how a bird sings? Or how birds make some of their less melodic sounds, like squawks, trills, or chirps? It all happens in the syrinx, a vocal organ unique to birds. Reptiles, amphibians, and mammals, including humans, use their larynx to produce sounds. But birds have a syrinx.

And the syrinx varies widely between species. But there’s still so much that scientists don’t yet understand about how it works or even its evolutionary history. And better understanding the syrinx of living birds gets scientists one step closer to figuring out what dinosaurs sounded like, because no, Jurassic Park isn’t scientifically accurate.

Joining me now to talk about her recent studies about the syrinx is my guest, Dr. Julia Clarke, Professor of Vertebrate Paleontology at the University of Texas, Austin. Dr. Clarke, welcome back to Science Friday.

JULIA CLARKE: Thank you for having me. It’s a pleasure to be here.

ARIELLE DUHAIME-ROSS: To start us off, how did you get started down the path of researching the birds’ syrinx, the bird’s vocal organ?

JULIA CLARKE: Yeah, it’s been a long journey. I attribute it in part to finding the earliest known fossilized remains of the syrinx in a specimen that I was working on from Antarctica. And that was probably 10 years ago.

And what we found was that the three-dimensional morphologies that happened to be preserved in this exceptional fossil were not really directly comparable across birds. We didn’t have similar data from most species of living birds. And so we had to come up and generate a very new type of data on the syrinx.

ARIELLE DUHAIME-ROSS: Huh. OK, So one of the papers you and your team recently published focused on the syrinxes of ostriches. Why ostriches? And what did you find out about how they make sounds?

JULIA CLARKE: We have two major lineages of living birds. One we call the paleognaths and the other is called the neognaths. And ostriches are part of the paleognath group. And so if we think of that really deep split within living birds, we want to understand not just the syrinx of songbirds or parts of one side of the tree, but we need to understand the syrinx better in the other part of the tree.

And ostriches are part of that other branch, and they’re accessible. We could go to an ostrich farm that was just north of Austin, Texas, near Waco. And we could, with a very nice collaborative relationship with the farmers there, have access to baby and adult animals that happened to die on the farm. And we could look at males, we could look at females, we could record them.

ARIELLE DUHAIME-ROSS: Got it. And so what did you find with regards to ostriches specifically?

JULIA CLARKE: What we noticed was that there were almost no recordings of ostriches in any of the databases of avian vocalization out there. There were under about 10 recordings total. And that was striking for something that we could– is proverbially in our collective backyard.

So when we started studying the ostriches, what was striking was how vocal they were and how many different types of calls they produced. And these calls included types that had never been described in the literature. That was incredibly cool. There’s gurgles, peeps, the so-called famous boom call that’s produced by male ostriches.

ARIELLE DUHAIME-ROSS: I actually think that we have one of those recordings.

JULIA CLARKE: [LAUGHS] OK.

ARIELLE DUHAIME-ROSS: And we can play a boom and a rattle. So we’re going to play that right now.

[OSTRICH BOOMS]

[OSTRICH RATTLES]

That’s incredible. So we didn’t understand the diversity of those calls or how they were made before you did this research?

JULIA CLARKE: Well, we’re still getting at that. I think, with the boom call, that’s one of the most striking and kind of– it had gotten a bunch of attention. And this is a male call that is produced with a mouth closed, and they inflate the neck, the esophagus. So the neck kind of expands out, looks kind of like a big pink sausage. And that got a lot of attention.

But all of the other calls, like what you heard with the gurgle or the rattle call, those had not been described. The sonograms hadn’t been uploaded to these different resources. So that was striking.

And before we started this work, I think we can say we didn’t know what the vocal organ of living female ostriches looked like. And we were able to confirm that, although the females don’t produce the boom call, their vocal organs are nearly identical to that of males–

ARIELLE DUHAIME-ROSS: Huh.

JULIA CLARKE: –and that there might be even more calls produced in the wild that we were unable to– weren’t represented in the recordings we have. But there’s one tantalizing egg-laying call that females might importantly use their perfectly robust vocal organ to produce in the wild.

ARIELLE DUHAIME-ROSS: One of the things that really strikes me about the work that you’re doing is that it highlights how many gaps in our knowledge existed and also still currently exist, right? Why are there so many gaps in how we understand syrinxes, the birds’ vocal organ? Ostriches are well-known, well-loved species. Why hasn’t this been examined before?

JULIA CLARKE: So I think there’s two parts to that story. I do think that, if you look across animals, it’s striking that new technologies, new ways of imaging the tissues or looking at how the tissues produce sound have advanced significantly. We can stain the tissues and then image them in three dimensions.

I think it’s kind of amazing. If you thought the entire history of musical instruments, like representations of musical instruments, were all two dimensions, how much you would lose about how a musical instrument functions, [LAUGHS] you know?

ARIELLE DUHAIME-ROSS: Exactly yeah, totally. All right, so technological advances.

JULIA CLARKE: That’s part of it. The whole field of anatomy languished a bit while we discovered new kind of approaches, like genetic approaches, genomic approaches. And anatomy is a very time-consuming thing. But it is deployed by paleontologists like me because we need to make sense of the fossilizable structures.

ARIELLE DUHAIME-ROSS: So OK, you’re a paleontologist, and you’re interested in ancient birds and their predecessors, dinosaurs. How can studying living birds help us figure out what dinosaurs sounded like?

JULIA CLARKE: Yes, this has been the question driving a lot of this research. And the motivation for this kind of really time-consuming, detailed anatomy is to make sense of structures that can preserve in deep time. That is, like, little remnants or whatever we can get from an extinct dinosaur, that we can bring these new data from living animals to figure out, OK, what were they doing? What does this mean about the origin of the precursors to birdsong?

I guess one might think of it this way, is you have these tantalizing fossils, these incredible fossils of extinct dinosaurs. You have this phenotype that is of such interest to ornithologists and such interest to me, which is song, which is sound, which is vocal communication. And how would you approach that in something that is silent in a rock?

And to do that, you have to generate new kinds of data or data that is extremely detailed that allows you to kind of take a structure and bring it to life, so to speak, to notice where the muscles might have attached, to notice where geometries might have changed. And this is what really fascinates me about this question. And the reason I’ve been studying it so long is that we still don’t have all the answers. So I got to keep– [LAUGHS] keep going.

ARIELLE DUHAIME-ROSS: This was so much fun. Dr. Clarke, thank you so much for taking the time to talk with me.

JULIA CLARKE: Oh, thank you for your interest. And I hope you can never look at a bird vocalizing the same way again.

ARIELLE DUHAIME-ROSS: I definitely can’t. Dr. Julia Clarke is a Professor of Vertebrate Paleontology at the University of Texas, Austin.

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