The Science of Birds - Bird Songs - Part 1

Episode Date: September 22, 2020

Episode: 5SummaryThis episode is Part 1 of 2 about Bird Songs. The voices of birds dominate nature’s soundscape. Bird songs and calls can be heard in almost every environment on the planet. In this episode, I’ll cover the characteristics of bird songs and how they are produced. We’ll also get into the question of whether bird songs are learned or instinctual.Research CitationsWillow and Alder flycatcher study proving their songs are innate (Kroodsma. 1984. The Auk)Links to Some Things Mentioned in this EpisodeLyrebird singing (YouTube video clip)Birdsong for the Curious Naturalist, book by Donald KroodsmaAttributionsSuperb Lyrebird - Recording XC570705 on Xeno CantoRuffed Grouse drumming - Recording XC132863 on Xeno CantoPileated Woodpecker drumming - Recording XC71727 on Xeno CantoMusician Wren singing - Recording XC242524 on Xeno CantoNorthern Raven 'song' - Recording XC496700 on Xeno CantoWillow Flycatcher singing - Recording XC134878 on Xeno CantoAlder Flycatcher singing - Recording XC139577 on Xeno CantoBrown Thrasher singing - Recording XC320485 on Xeno CantoWinter Wren singing - Recording XC142584 on Xeno CantoLink to this episode on the Science of Birds website‍Support the show

You're walking around in the Blue Mountains of Southeastern Australia, in the shade of a forest filled with tree ferns and the fragrance of eucalyptus leaves. Suddenly, you hear this sound coming from behind some bushes near your path. If you know your bird sounds for this region, you might at first think that you're hearing some kind of weird roundtable discussion among several bird species, including a rainbow lorikeet, a common mina, a pied curawong, a yellow-tailed black cockatoo, and a few others. But, and maybe you figured this out already, what you heard is actually the song of one bird, a single individual. This part of Australia is home to the superb liar bird. This large

ground-dwelling bird has a long, elegant tail and an amazing ability to mimic other birds. And it can mimic other sounds in its environment. There's a famous BBC documentary clip with David Attenborough, where he shows us one of these lyrebirds mimicking a camera shutter, a car alarm and a chainsaw. You should be able to find this clip on YouTube. It's really impressive. Birds are never very far from us, no matter where we are on Earth. Even when we can't see them, we can usually hear them. If we slow down occasionally and use our ears to survey which birds are singing nearby, we can often be surprised by the diversity of species and of bird sounds that are all around us.

Hello and welcome. This is a lot of the world. is the Science of Birds. I'm your host, Ivan Philipson. The Science of Birds podcast is a lighthearted, guided exploration of bird biology for lifelong learners. Today's episode is all about bird songs. This is actually part one of two, since there's so much to talk about around this subject. And a podcast is the perfect medium to explore bird songs, so I'm pretty jazzed about covering this topic with you. I hope you find it as fascinating as I do. Okay, do Let's dive in, shall we? Birds are noisy.

Compared to most mammals and other animals that we encounter on a daily basis, birds make a lot of racket. Besides having feathers and the ability to fly, singing is one of the things that really stands out about birds. We're delighted and fascinated by the voices of birds. Humans, too, are a noisy bunch, so it's not surprising that we're interested in these creatures that also use sound extensively. Birds make sound in a variety of ways, not just with their voices.

Some species make sounds with their feathers. For example, the common snipe makes a winnowing sound with its tail feathers as it makes an aerial display dive. A male roughed grouse beats its wings rapidly to make a drum-like sound while perched on his favorite log in the forest. Here's an example. That sound is very low in frequency, which helps it travel through dense forest vegetation. So you might need to listen with headphones to hear it.

And of course, you're familiar with the actual drumming sounds made by woodpeckers, like this pilliated woodpecker. In these next two episodes, we're going to focus just on the vocal sounds of birds and leave those other sounds, those non-vocal sounds, for a future episode. How do birds sing? How are their voices produced?

Humans make sound waves with the larynx, our so-called voice box. Air pushed out from the lungs vibrates the vocal cords in the larynx, and this makes a sound. Pitch and volume are changed by movements of muscles around the larynx. Further modifications of the sound result from movements of the tongue and lips. What comes out in the end is the melodious noise of the human voice, like the smooth one you're hearing right now. Bird voices are produced in a similar way, but there are a couple big differences.

For starters, birds don't make sound with their larynx. They have a larynx, but it doesn't serve that function. Instead, they have an anatomical structure unique to birds called a syrinx. That's spelled S-Y-R-I-N-X, serenks. Compared to the human larynx, the syrinx of a bird is located further down in the respiratory pathway, closer to the lungs. It sits above a bird's heart. This is where the airway, the single tube of the trachea,

forks into two tubes called bronchye, which connect to the lungs. The syrinx lives at that fork. Thin membranes in the syrinx vibrate as exhaled air rushes past them. This makes a sound. Muscles in the syrinx contract and relax to manipulate the sound, the bird's voice, to change its pitch and amplitude. There are a few distinct anatomical forms of the syrinx found in different bird groups. Of these, the syrinx of songbirds is arguably the most.

sophisticated. Another huge difference between the voices of birds and mammals like us is that many birds can produce two independent vocal sounds simultaneously with their syrinx. These birds can control the two sides of their syrinx independently. Here's an example of a bird making two song sounds simultaneously. That was an Australian magpie. As a bird's voice moves from the syrinx and out into the world for all to hear, it can be modified by things like the length and diameter of the trachea. The shape and size of a bird's bill also can change the sound, as well as the way a bird moves its bill while it sings.

As for the trachea, some types of birds, including swans and cranes, have really long ones that increase the resonance of their voices. An example of this is the trumpet manukode from the island of New Guinea. This member of the Bird of Paradise family has a super long trachea, which is coiled up like a garden hose just under the skin of its chest. The bird is only about 12 inches or 31 centimeters long, but its trachea is 30 inches or 75 centimeters long. What exactly is a songbird?

I used that word a few minutes ago, and it's a common one that we all know. Isn't any bird that sings a songbird? Well, in the poetic sense, yes. but technically, scientifically, no. In ornithology, songbird is the common word we use for members of a particular evolutionary lineage known as the Aesine Passerines. We can also just call them Aesines.

This is a subset of the order Paceriformes, otherwise known as the perching birds. Aasine comes from the Latin word Aasin, which translated one way means bird which gives omens by its cry. Besides being great at giving omens, the ASEAN passerines have some of the world's most amazing vocal abilities. About half of the planet's bird species, about 5,000 of them, are songbirds. So in the evolutionary sense, this is a wildly successful group. These are the wrens, thrushes, finches, starlings, warblers, larks, chickadees, and there's no way I'm going to list all of them here.

Suffice to say, there are many bird families that belong to the ASEAN passer. these birds belt out many of the world's most impressive songs. For example, here is the musician wren. But not all songbirds sing quite so nicely. They don't all sing like Beyonce or Ella Fitzgerald. Common ravens, for example, are actually big-fat songbirds, meaning they are osine passerines. They, of course, sound like this. So Ravens sing more like the avian equivalent of Bob Dylan. Now remember that I said songbirds are a subset of the perching birds, which is what we call birds in the order Pasarformis.

Remember that? Well, the other major subdivision of that order is the sub-ossine passerines. Sub-ausine passerines. There are about 1,000 species of these guys, of these, sub-ausenes. The best-known examples from this group are the tyrant flycatchers of the Americas. They sing too, but their voices are often more mechanical sounding and less musical than those of true songbirds. We'll come back to the sub-ausines in a little bit. Besides all these perching birds, that is, birds of the order Pasariformis, composed of the songbirds and sub-a-s

scenes, beyond those guys, many other birds vocalize. Most birds do, actually. Think about chickens, geese, eagles, owls, parrots, and so on. We know their voices really well. They just don't sing so pretty. One of the biggest scientific questions about birds' songs is, are they learned or are they instinctual? This is a nature versus nurture question. the kind of research question that scientists tackle all the time, especially with human behaviors.

Like, is artistic ability something you learn from your parents, or are you just born with it? Or is it a combo of these? And what about laparophobia, that all too common fear of rabbits that makes us really nervous when Easter rolls around? Is that learned, or did I inherit it? Birdsong is actually one of the most well-studied behaviors in non-human animals. Many scientific studies over decades have given us an answer to whether bird's song is learned or instinctual. The answer is yes. Because you see it depends on the bird you're talking about. It turns out that some types of birds learn their songs while others are hardwired by their DNA

to sing a particular song. More than half of the world's bird species learn their songs. That we know of, there are four groups, i.e. evolutionary lineages, that do so. The songbirds we were talking about earlier constitute one of these groups. But parrots and hummingbirds also learn their vocalizations. And the fourth group is really just one species, the three-waddled bell bird that lives in Central America. Most of the research on vocal learning has focused on songbirds, which you may recall are multitudinous. Studies have revealed some interesting parallels between the way humans and songbirds learn to communicate with sound. You probably know that young human children are particularly good at learning languages,

but then as we age and become beaten down by the harsh realities of life, our brains become less good at soaking up languages. We don't learn them as easily. Similarly, many songbirds are better at learning when they're young. These birds have a sensitive period, also called a critical learning period, when they're able to memorize song details from an adult bird. In general, it's within the first year of life that these birds develop their song repertoires.

However, some types of birds are open-ended learners that can keep adding to their song repertoires throughout their lives. For example, mimics, like the Northern Mockingbird, are open-ended learners. When I lived in California, there were a few evenings where I heard the beeping sound of my car alarm being turned off. I thought someone was unlocking my car, maybe trying to steal it. It was confusing. But I was relieved when I figured out that the sound was only a cheeky mockingbird in my neighborhood,

engaging in some open-ended learning. Often, it seems, there is also a genetic, instinctual component to a songbird's learning. Many of the species studied so far are apparently born with what we call an auditory template. This is a sort of filter or framework that allows the bird to learn the correct song from members of its own species rather than some other random bird in the neighborhood. Another similarity with humans is that young birds, fledglings and up to a year or so old, will often sort of babble to themselves as they're figuring out how to properly sing. These adorable practice vocalizations are called sub-songs.

This is much like a human toddler prattling on nonsensically about who knows what. Subsong seems to be a necessary step in the process for birds. First is the learning phase, then we have this practice phase. I want to point out that there's lots of variation to how birds learn their songs. So some of what we're talking about here is very generalized, just to keep that in mind. Now, let's consider those birds that don't learn their songs. These birds are genetically programmed to sing a particular song or set of songs. Remember that we have that division within the perching birds known as the sub-ausenes.

These are the flycatchers, Cottingas, wood creepers, and ant birds, as well as birds from a few other families. In the eastern U.S., there are two small flycatchers that look, to us humans, pretty much identical. The willow flycatcher and alder flycatcher. The only way you can tell these little buggers apart when you're out in the field is by their voices, their songs. Here's the willow flycatcher. And here's the alder flycatcher. These simple songs also sound pretty similar, don't they?

Even if you can't immediately tell the difference, you'll have to trust that to the trained ear or computer algorithm, these songs are different enough to reliably distinguish the two fly flycatcher species. In a 1984 study of these two flycatcher species by Donald Kruzma, 10-day-old nestlings were taken from their nests and into the lab. These baby birds were played recorded songs of the opposite species to see if they would learn the wrong song. But nope, they ended up singing precise renditions of their own species song. This was a controlled experiment and it demonstrated that the songs of these birds are baked in from birth. They are

instinctual, not learned. The author of that study, Donald Krudzma, is one of the world's experts on birdsong. He's written several books, including the recently published bird song for the Curious Naturalist, Your Guide to Listening. I don't have it yet, but you might want to check it out if this topic really interests you. Okay, let's go ahead and move on to talk about some characteristics of songs. I've been throwing the word song around as though it's something that we can clearly define with respect to bird vocalizations. Well, we can't.

Bird watchers and field guides talk about bird songs as something separate from bird calls. Many of us might have a sense of the difference between calls and songs, but, scientific there isn't a clear way to define these as distinct forms of vocalization. The sounds that we humans think are pretty, or at least complex, more lengthy and interesting, we tend to call those songs. The sounds that are shorter in duration and simpler, we label those calls. For the moment, let's talk about characteristics of the longer, more complex, quote-unquote, songs. Each of these is some combination of notes, which are of a certain frequency or pitch. Notes strung together form syllables, and these in turn form phrases.

Phrases are discrete chunks of a bird's song that might be repeated. A song contains one or more phrases. Different parts of the song can vary in loudness, in amplitude, and there's also variation in the timbre, the tonal quality of a song. For example, I'm going to play you the song of a White Crown Sparrow. The opening note here is a relatively pure tone. This is followed by some notes with more overtones or harmonics. These notes sound more buzzy. Pure tones or whistles, like that first note in the White Crown Sparrow song, are less distorted by vegetation or other objects. so many forest birds use more pure tones in their songs. Open country birds, on the other hand, tend to have buzzier songs.

Like musicians, birds have repertoires. Some sing only one song. These are the one-hit wonders. At the other end of the spectrum, we have birds with hundreds or even thousands of unique songs that they can cycle through. The Grand Prize winner in this category is the Brown Thrasher, a North American bird in the Mimity family, which means it's a cousin of the northern mockingbird.

Research on the vocal abilities of the brown thrasher has shown that an individual of this species can have over a thousand different songs in its repertoire, over 2,000 by some accounts. Here's a nice example of this bird's vocalization. Listen to the numerous short songs in the sequence. Another champion songster is the winter wren, an incy-weensy-brown ball of a bird that has an amazingly complex song. A male winter wren can really rock out for such a tiny bird.

One researcher noted that if you account for the size difference, a winter wren has ten times the vocal power of a crowing rooster. A male winter wren has only a few songs in his repertoire, but each of them is very complex, lasts five to ten seconds, and is repeated up to 40 times before the next song. Here is the winter wren. Now, here's the same song played at one quarter the speed, so you can appreciate its complexity. Isn't that Isn't that awesome.

In this episode, which is part one of two on bird songs, we've covered how bird songs are produced by the syrinx, we talked about the definition of songbird, as well as learning versus instinct, and the characteristics of a bird's song. In the next episode, we'll get into the functions of songs and calls, as well as geographic variation in songs, and some fun subtopics like the Don Chorus and female song.

So that is all for this episode, Thanks so much for listening and learning with me today. With each episode, I hope to make the Science of Birds podcast better and better. I'd love to hear any thoughts or comments you have about the show. Just let me know by sending me an email to Ivan at Scienceofbirds.com. And hey, if you love birds and want to learn more about their biology, please subscribe to the podcast. You can also see the show notes for this episode,

which is episode 5, on the Science of Birds website, scienceofbirds.com. On the website, you can subscribe to our email newsletter, which would be most excellent indeed. So check out scienceofbirds.com. I'm Ivan Philipson, and I'll catch you next time. Cheers.