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WebExtra Feature—supporting material for "A Birding Interview with Donald Kroodsma" Birding Volume: 41 Number: 3 Pages: 18-20.

Birdsong: Topics Close to my Heart

Donald Kroodsma
36 Kettle Pond Road
Amherst, Massachusetts 01002

Talking about birdsong, as in my interview in the current issue of Birding (May 2009, pp. 18–20), isn't enough. You have to hear birdsong to appreciate it, of course. And for some birdsong, you just need to "see" it—in the form of sonograms—to believe it. Here are four topics dear to my heart that I'd love to share with you.

Songbirds Learn to Sing
That statement rolls off the tongue easily, but what a remarkable statement it is. Young songbirds must hear and imitate the songs of adults, and in that way they learn to sing much as we learn to speak. As a result, both human speech and birdsong occur in dialects, which are learned traditions, or culture, passed down from one generation to the next. In this learning process, both humans and birds babble. Just as we practice our speech, so the birds practice their songs.

And what fun to listen to young children and young birds working to get it right. When my daughter was a little under two years old, I captured a marvelous sequence of babbling from her. (Sounds for this WebExtra are taken from the CDs that accompany my two books, The Singing Life of Birds and Birdsong by the Seasons.) She babbled what sounded to me like bow wow wow wow va wa...wee wee wee...m' hi daddy ba ma ba wow wa wa...den da daddy daddy! da daddy bow wow wow wow...dere da ditty...hey diditty...hey daddy... nyeh...na no...down. She's thinking of dogs and cats and the little piggy who went to market, and dad, of course, even though none of us are in the room.

In North America, many young birds begin their practice singing during August, after most adults have stopped singing for the year, and they sound much like my daughter (and each of us when we were that age) as they babble their sounds in nonsensical sequences. On a CD that comes with Birdsong by the Seasons, I provide a number of examples of this "babbling"—from such species as Red-eyed Vireo, Warbling Vireo, Black-capped Chickadee, Tufted Titmouse, Carolina Wren, House Wren, Veery, Common Yellowthroat, Song Sparrow, and Baltimore Oriole. Later, during October, when the practice is a little more advanced, you can listen to a Ruby-crowned Kinglet, a White-throated Sparrow, another Song Sparrow, and more Black-capped Chickadees. Once you know how to listen, you hear these young birds everywhere.

Winter wren

Winter Wren illustration by Nancy Haver, courtesy of © Houghton Mifflin Harcourt.

Try listening to the young male yellowthroat in August. He's down in the cattails, never to be seen, at first calling djerp djerp, giving himself away as a yellowthroat, and then butchering his attempts at his witchity-witchity song. For comparison, listen to this example of an adult song.

Meanwhile, a young Song Sparrow calls from nearby in the bushes, but by his scratchy attempts at songs you'd never know who it was. By October, however, hear how much he has improved. And by May of the following year, he'll be the superb adult male singer that we all know and cherish.

I love listening to young White-throated Sparrows. The adults have such an elegant song, consisting of a few long whistles followed by the triplets, what I think of as Oh Sweet Sweet Canada Canada Canada; and as an adult, each bird perfects just one song. But listen to the uncertainty in this October bird. He can't get beyond the first two notes, and with them he can't decide whether the Oh should be higher or lower than the Sweet, and only in the last attempt is there a hint of the Canada triplet.

Hermit Thrush

Hermit Thrush illustration by Nancy Haver, courtesy of © Houghton Mifflin Harcourt.

Listen as a Hermit Thrush
Birds can hear details in their songs that we can't. Good evidence of their ability lies in Winter Wren songs. As we listen to a western bird sing (eastern birds are simpler; they are a different species, I submit), we hear a blur of rapid notes and trills, but young Winter Wrens must hear the details as sharp and crisp, because we can show in sonograms that the young birds learn to sing these details that we hear only as a blur. (Okay, okay; if you want to hear the eastern species of Winter Wren in North America, I've included a sample of that, too.)

So just what do these birds hear? What is it like to hear as a Winter Wren or as a Hermit Thrush? I like to think that, as I slow down songs so that my ears can begin to hear the details, I'm beginning to hear as the bird itself hears.

Hermit Thrush Sonogram

Hermit Thrush sonogram courtesy of © Houghton Mifflin Harcourt.

Let's try this for a Hermit Thrush. First, take a look at the three sonograms here, chosen from the dozen or so different songs that he sang. Think of them as musical scores for birdsong and they become more friendly, I think. The song begins on the left and reads across to the right, as we'd expect, and each song is a little less than a second and a half long. Now look at that beautiful whistle that begins each song; it's about a quarter second long and held on the same pitch, or frequency. The vertical scale on the left is frequency, in thousands of cycles per second (abbreviated kHz for kilohertz, but we don't need to worry about that term). The whistle in the top song is at 4,200 cycles per second, roughly the highest note on a piano, and the whistle of the lowest song is an octave lower, about 2,000 cycles per second; the whistle of the middle song lies in between, at 3,000 cycles per second. You can see a lot of "activity" in the last second of the song, and that's what you need to hear, at slower speeds, to appreciate.

Now let's listen. First you hear these three songs at normal speed, just as the bird sings them. Then you hear the same three songs at half speed, then at one quarter speed, and last at one-eighth speed (as speed is halved, frequency is also halved, so that the songs become both slower and lower). Go ahead, listen to the whole sequence again, and then again. As I listen in this way, eventually I become the Hermit Thrush, singing as he does, hearing as he does, and that's a pretty special place to be. (That's only part of the Hermit's magic, though. He uses his repertoire of different songs in a special way to create an extraordinary performance, but that's another story, not told here.)

Wood Thrush

Wood Thrush illustration by Nancy Haver, courtesy of © Houghton Mifflin Harcourt.

Songbirds Have Two Voice Boxes
Some of the thrill that we get from hearing the Hermit Thrush's songs at slower speeds results from his use of two voices simultaneously. Yes, two voices. Each songbird has two voice boxes, not just one, and with two he can sing a duet with himself, singing two different songs simultaneously. And no bird does it better than the Hermit Thrush's cousin, the Wood Thrush.

Wood Thrush Sonogram

Wood Thrush sonogram courtesy of © Houghton Mifflin Harcourt.

I think of the Wood Thrush's song as beginning with soft bup bup bup notes, but you have to be close enough to hear them. Next is the exquisite flute-like ee-o-lay phrase, with the notes delivered slowly enough that they sound wonderfully musical to our ears. Ending the song is a somewhat harsh, percussive trill or flourish that contrasts sharply with the beauty in the ee-o-lay (at least to our unaided ears). It is useful both to hear and see the Wood Thrush's song.

Now let's take a closer look and listen to that song. First, we'll hear the ee-o-lay phrase at half speed; then we'll listen at quarter speed. Quarter speed is best, I think, for revealing the beauty in the ee-o-lay phrases.

Ruffed Grouse Sonogram

Wood Thrush sonogram courtesy of © Houghton Mifflin Harcourt.

The terminal flourish is something else. The two voices are working together so quickly here that quarter speed isn't slow enough, so I slow them down to about one-tenth normal speed. And as I listen, I love watching the sonogram so that I can see what I'm hearing. Look at the much-expanded flourish of this Wood Thrush song, and you'll see what he's up to. With the air passageways through his right voice box closed, he gates air through the left voice box from the left lung, holding the tension of the membranes steady to produce a beautiful whistle held on the same frequency, all in just a little over 0.1 second. But look what happens about halfway through that whistle: He opens the passage through the right voice box, with just a little air at first (see how the sonogram isn't as dark at first); then he first tightens the membranes slightly so that the frequency rises, and then he loosens the membranes so that the frequency falls. And the rest of the song, well, is just extraordinary, with the precision breathing and coordinating of the two voice boxes producing some of the finest sounds on the planet. With his left voice box, he produces a series of low-pitched notes that are in perfect synchrony with the higher-pitched notes from his right voice box. (The highest-pitched elements in the sonogram are a "harmonic" of the left voice box and are centered at an exact frequency multiple—8,000 cycles per second—of the "fundamental" at 4,000 cycles per second.)

Using some editing software on my computer, I can isolate these two voices so that we can hear them first in succession and then simultaneously. Now, with the sound slowed down ten times, listen first to the contribution from the left (lower-pitched) voice box, then the right, and then to the two together, as the bird sings it. Go ahead, play it again.

Ruffed Grouse

Ruffed Grouse illustration by Nancy Haver, courtesy of © Houghton Mifflin Harcourt.

Listen to These Two Species of Ruffed Grouse
How brash of me, all by my lonesome and without consulting the official committees who are in charge of these things, to declare two species of Ruffed Grouse in North America. But I have heard them tell their story, and no one else seems to be listening. Here's the scoop, and after listening, I'll let you help make the call.

Ruffed Grouse Sonogram

Ruffed Grouse sonogram courtesy of © Houghton Mifflin Harcourt.

Take a look at the two sonograms of Ruffed Grouse drums shown here. In these sonograms, each vertical mark is one wing beat, and you can see the general rhythm of the drum by the two birds; they begin slowly and end in a whir. Now look at the details. In the one from Massachusetts, the bird gradually increases the wing beat speed, rising to a peak at about 11.5 seconds; then it trails off. Now look at the drum from British Columbia; see how erratic he seems at first, to about 12 seconds; then, in a great rush he races to a peak of wing beat speed, with most of the wing beats then occurring after that peak. When seen in the sonogram, the differences are striking.

And, when listened to carefully, the differences are equally striking. Listen several times to the drum of the Massachusetts grouse to get a feeling for the rhythm. Watch the sonogram as you listen, and you'll see and hear the gradual increase in wing beat speed, and you'll see and hear the symmetry in wing beat speed about that peak at 11.5 seconds.

Now brace yourself to hear the other species. To hear it, you need to go to the website of the Macaulay Library of Natural Sounds at the Cornell Lab of Ornithology. Once you're on the webpage, type 59280 into the box and click on "Find." What you see before you now are the specifics of this particular recording number; it was made by William W. Gunn on 22 May 1962 in British Columbia. (By contacting curator Greg Budney at the Library, I learned further that this bird drummed during the afternoon at Miracle Beach Provincial Park on Vancouver Island.) Next, by clicking on the "Play" button, you can listen to this bird beating a different drum; alternatively, click on the "Visualize" button and watch the drums float across your screen as you listen. It's an original recording, not a recording in which everything is served up neat and clean to you, so listen as if you were listening in the field, patiently (and with joy). Hear how different the rhythm is? He begins slowly, and then it's a sudden acceleration to the peak with an extended taper of wing beat speed after that peak.

Want to listen to more Ruffed Grouse? You can take a virtual tour of Ruffed Grouse all across the continent. Go back to that first web page for the Macaulay Library and in the online archive box type "Ruffed Grouse." Now you can choose recordings of drumming grouse from New England to Washington state. (Search the archives for other species, too, and you soon realize what a marvelous resource you have here.)

When you realize there's only one recording of this "new species" of Ruffed Grouse, the special 59280, you may feel a bit embarrassed for me. But I'm calm. Let's put that recording in perspective. Grouse drums are, as far as we know, "innate," which means that the qualities of the drum are somehow encoded into the DNA. Because the genes of this one Vancouver Island grouse are no doubt like the genes of other grouse there, I'll wager that all Vancouver Island grouse sound like this, and that further listening and recording will convince others of the existence of this second Ruffed Grouse species in the Northwest.

Here's the challenge. Will you be traveling to Vancouver Island or more widely in British Columbia, or up to Alaska, or through Washington and Oregon west of the Cascades? Before we can settle this issue, we need recordings from other birds in this region to know how widespread these different drums are. And you don't need high-quality recording gear to capture the rhythm of these drums, either. Let me know what you find out. Together, maybe we can report our discoveries to Birding magazine, as you can bet that thousands of birders throughout North America will be interested in the outcome of this fascinating puzzle.

I should point out that other grouse have been split recently into two species. The erstwhile Blue Grouse was recently split—re-split, actually—into two species: the Dusky and Sooty Grouse. And the bird formerly known as the Sage Grouse was recently found to consist of two species: the widespread Greater Sage-Grouse, along with the Gunnison Sage-Grouse, new to science. And much of the split was based on, you guessed it, the sounds and display features of the birds. I predict a future split in Ruffed Grouse, too, and you can be in on the fun.

Acknowledgments
For this Birding WebExtra, I offer a hearty thank you to Houghton Mifflin Harcourt for granting permission to use figures and sounds from The Singing Life of Birds: The Art and Science of Listening to Birdsong (2005) and Birdsong by the Seasons: A Year of Listening to Birds (2009). I also thank the Macaulay Library at the Cornell Lab of Ornithology for giving permission to use the songs of the adult Common Yellowthroat, White-throated Sparrow, and western Winter Wren.