Probing the Avian Instrument

June 1, 2005

Tweet Mystery of Life
(Originally published in the July-August 1994 issue)

To fathom the intricacies of bird song, a Duke zoologist has concocted experiments using paraphernalia that range from the most sophisticated--soundproof chambers, videotape recorders, audiotape players, and computers--to the humblest--lollipop sticks, rubber bands, and helium.

Steve Nowicki is about to become a father. Before dawn on a spring morning, he and his graduate students rise from warm beds in the rustic cabin, shivering and sipping hot coffee in the chilly darkness. They don layers of clothing against the cold and sleepily pull on stiff hip waders, emerging from the cabin as the sun rises dimly over a still lake. They drive bouncing and swerving along rutted back roads in the damp Pennsylvania woods until they reach the swamp. Swatting at breakfast-bent mosquitoes, bracing themselves against the cold water, they wade into the slough, binoculars at the ready, ears cocked for the faintest sound.

With luck, over the next hours they will spot an evanescent flash of brown feathers or hear a tell-tale twitter that marks their quarry--a swamp sparrow carrying food. If they are luckier still, they will pinpoint a sparrow's nest of newly hatched baby birds. Gently, the will ease both nest and birds into a cloth bag and return to their cabin. There, Nowicki and his students will become the birds' fathers and mothers, every half-hour faithfully feeding the baby birds "meat glop"--a health-giving mix of ground sirloin, tofu, baby carrots, vitamins, and minerals.

Thus does Nowicki, a Duke associate professor of zoology, obtain the fascinating animals whose complex trills, warbles, and chirps, and exquisitely pure tones he seeks to decipher. He and his colleagues concoct experiments using paraphernalia that range from the most sophisticated--soundproof chambers, videotape recorders, audiotape players, and computers--to the humblest--lollipop sticks, rubber bands, and helium. From those experiments have come intriguing insights into the talents of nature's most accomplished musicians.

What's more, Nowicki's own fine-tuned teaching abilities have brought students flocking to his rigorous undergraduate courses on neuroscience and animal communication. An ex-trombonist and adept juggler, he has developed his own brand of scientific street theater to jump-start students' minds and drive home intellectual points.

To illustrate a discussion of auditory processing, he's had a rock band perform. To make points about evolution and the mind, he's picked arguments with actors dressed as Darwin, Freud, and a giant frog who invaded his class. Rumor has it that, to illustrate the fallibility of perception, he even showed up for class once dressed in drag. (He points out proudly that his wife, Susan Peters, also a professional biologist, expertly sewed the frog's head. He is mum about where he got his dress.) Because of his determination to communicate, his clear compelling lectures, his imaginative exams, and his commitment to his students, he was awarded the 1992-1993 Robert B. Cox Trinity College Distinguished Teaching Award.

His baby birds even like him. After all, they luxuriate in a sort of sparrow spa in his laboratory. They get free food, a comfortable soundproof chamber, and free singing lessons via tape recordings. In fact, other scientists' studies of the solitary birds find that they experience lower stress and longer lives in captivity than in the wild. (Incidentally, nor are the swamp-sparrow parents particularly upset at the lost of the nest and its nestlings. They typically immediately rebuild the next and lay more eggs.)

To Nowicki, songbirds represent stunningly complex examples of animal communication. A typical bird song, lasting about two seconds, is a rapid-fire aria of fifty or more "notes," each as short as ten thousandths of a second. The bird can rattle off these notes up to five times faster than a human can speak syllables. Besides their songs, birds may have a repertoire of five to twenty calls--a collection of bird war whoops, alarm calls, love songs, and lullabies to their offspring. Even weirder is that birds are fully capable of singing duets with themselves. Their vocal organ, the syrinx, has two vibrating membranes that can somehow produce and modulate two independent tones at the same time.

Such extraordinary abilities can teach humans about their own speech abilities, says Nowicki, which is one reason his studies are funded by the National Institutes of Health. What's more, he says, bird song can yield powerful insight into the intricate mysteries of animal communication--the process by which an animal encodes and transmits a "thought" across space to another animal, where it is decoded and transformed back into thought.

If bird song seems remarkable on its surface, Nowicki's deeper studies of this tweet mystery of life have revealed it to be even more amazing. Until Nowicki's work, most scientists believed that the syrinx, located just beneath the bird's breastbone, was the only part of the bird's "instrument" that figured in its song-production. To Nowicki, such a theory was like arguing that the only important part of a clarinet was the reed. He believed that birds use their beak and throat to change the resonances of their song, much like humans singers use their mouths and throats to control their song harmonics. To test his theory, Nowicki had his captive songbirds sing solos in a harmless helium atmosphere. If only the syrinx mattered, helium wouldn't affect how it vibrated because the birds' song would remain unchanged. But if the windpipe were important, the song would resonate differently, just humans chattering away with a lungful of helium sound like Alvin the Chipmunk.

In fact, the helium did change the birds' song, causing new harmonic overtones to appear. The discover marked a critical new understanding that a bird's instrument consists of practically its whole breathing apparatus. "That discovery had very important implications for how a bird's songis wired up neurobiologically, how the bird learns his song," says Nowicki. "It adds a level of complexity to the problem of motor control that was previously unexplored." But like all good science, the experiment raised even more questions. "Having, I think, demonstrated that something is going on, we are now left in the position of trying to figure out what exactly it is," he says.

So, Nowicki and his students began high-speed videotaping of their birds singing, attempting to understand how a bird alters its head, throat, and beak to create its song. They also began experiments in which they fit the birds with "braces" to understand the beak's role. For brief periods at a time, they insert a small lollipop stick in a bird's bill and hold it in place with a rubber band. Their object is to fix the bird's beak open at a certain angle. "We think the bird does use its beak to change the effective length of its vocal tract, thereby changing its natural frequencies," says Nowicki. The birds remain unflappable during the procedure, quickly commencing to sing with their braces on.

So far, the researchers have found that the beak is, indeed, a critical part of the bird's song. The next step will be the daunting technical challenge of understanding specifically how the bird changes the shape of its vocal tract to control its sound.

While such studies probe the nature of the avian instrument, Nowicki is also trying to understand the new meaning behind bird song. "Ever since Darwin, bird song has been cited as an example of an exaggerated male trait, like the peacock's tail," he says. "Darwin proposed a distinct form of selection to account for these exaggerated traits--sexual selection as opposed to a natural selection." This sexual selection has to do with traits that evolve either to better attract mates or otherwise increase reproductive success. Whether such traits be peacock tails or ram horns, bigger is better up to a point, says Nowicki. "Now, the interesting question is what is 'bigger' in bird song?" he asks. Perhaps, scientists believe, the most successful male birds sweep females off their skinny bird feet by singing more kinds of songs--a correlation that they have found in some bird species but not others.

But the most fascinating discovery by Nowicki and graduate student Jeffrey Podos is that songbirds basically "wing it" when they sing: "If you listen to a song sparrow, you'll hear an individual sing about eight or twelve basic song types. But if you record those song types and analyze them closely, you'll realize that almost every time a bird sings a song, even of the same type, it does something slightly different." Thus, like human cabaret singers belting out old hits, birds add a little variety each time they sing even a standard song. This variety is very likely an important spice of bird life, says Nowicki. He and his students have discovered that their isolated baby birds learn to sing a multitude of song variations, to see how accomplished the birds can become.

But to really explore the meaning of this song complexity, Nowicki decided to "ask" the birds in the field what they hear when songs vary. "You know, we can measure in the lab until the cowbirds come home, but ultimately the question has to be validated perceptually by the birds," says Nowicki. So this summer, Nowicki and University of Miami zoologist William Searcy mounted an expedition to Pennsylvania whose aim was, basically, to mildly annoy male birds. His equipment: wooden marking poles, binoculars, a tape recorder, a loudspeaker, and an infinite amount of patience. His technique involves first pinpointing a male songbird's territory and installing a loudspeaker at its center. Then the scientists play a variety of songs, measuring how the male bird reacts.

At the first chirp of a recorded song, the bird will aggressively fly close to the loudspeaker. But it soon grows used to the song, wandering away until it renews its threat when the zoologists begin to play a subtly different version. By measuring the bird's response to different variations, the scientists can begin to understand what the bird perceives.

Nowicki and Searcy's summer expedition was also meant to make bird love, not just war. The scientists planned to capture adult female birds, give them a bit of hormone to put them in a loving mood, and play them recorded songs of avian amour. If the male songs are alluring, the female will fluff her feathers and adopt a ready-for-love "precopulatory" posture. "So, with these experiments, we'll get to see if this kind of variation has functional significance for courtship," says Nowicki.

Nowicki brings the same studious observation to his teaching as he does to his field work. He does something slightly embarrassing but highly useful the first week of his popular undergraduate course in neuroscience: Before class begins, he stands in front of the room with pictures of all 100 or so students spread in front of him. As student enter, he points to them, reciting their names, with the goal of eventually learning all of them. "I do it partly because it just gives me an excuse to stare at the students a bit," says Nowicki. "I try to get a sense pretty quickly who are the students who have a lot of scientific background, who are the students who are just intrinsically sharp, who are the students who are going to need more help. I also try to look into their eyes when I lecture."

As his class has grown from forty to seventy to 115, such individual attention has become more difficult, but he has persevered. His course's popularity has skyrocketed not because of its easiness. It's a rigorous semester that spans the breadth of neurobiology from molecule to neuron, and from jellyfish to the human consciousness.

Says zoology major David Finley, "It's an extremely interesting class, but it's not easy at all. The information he gives you, he doesn't expect you to just spit back on an exam. For example, on tests, he invents new organisms and asks you to use what you know to tell him what experiments you could do to answer questions about them." But it's not just the message that attracts students, says Finley, it's the medium of Nowicki's delivery. "He created a class dynamic that was just amazing," says Finley. "He commanded your complete attention; nobody flipped through the Chronicle or did crossword puzzles. It was how vivacious and dynamic he was in the classroom that caused you to be interested in what he said."

Nowicki's ambitious aim in the course is to help students begin to grasp the vast intellectual realm that attempts to explain how mind arises from body. "We want to do no less than help students try to understand the fullness of our own mental experiences, from their feelings about their mother to their feelings about Beethoven's Fifth Symphony. Of course, science is nowhere near that goal, but we don't want to forget it's the ultimate goal of neuroscience."

Nowicki's course also emphasizes how mind evolved from primitive forms. "We take the perspective that the higher-level processes that we're doing in class--teaching and learning--are in some way related to a toad catching a worm."

Certainly, Nowicki's street theater assures that nobody falls asleep. "I want to break down their intellectual complacency," he says of his thespian efforts. "I want them on the edge of their chairs, wonder what will happen next." Along with that suspense comes learning, he says. "The point isn't just to have a good time; the point is to also try to hammer home the complexity of some of these issues." Only once, he says, has a bit of theater fallen really flat. For a discussion of body structure, he had a fake Hollywood "wound" installed on his arm under fake skin, so he could dramatically rip off the skin to reveal the tendons and arteries beneath. The moment came, he ripped off the skin, the sight was satisfyingly yucky, and--laughter. "I was expecting fainting or worse," says a disappointed Nowicki. Perhaps, he theorizes, the MTV generation is too used to gore in its entertainment.

Besides his large neurobiology class, Nowicki teaches a smaller seminar on animal communication. He and University of North Carolina zoologist Haven Wiley have informally joined their Duke and UNC classes to explore scientific literature on animal communication. The students read assigned scientific papers and then report on and discuss them in class. A typical class might range through reports on communications in frogs, toads, damsel flies, warblers, and crickets.

Nowicki finds that the smaller class leads to more personal involvement by the student. "When this class works at its best, the students get very motivated and they get very excited. In fact, the students are just hard to shut up," he says with obvious pleasure. "The students get very passionate about whether animals can think or not. And they get passionate about our concern for animals and animal rights; because if animals can think, then what are our responsibilities and obligations to them? And they get passionate about human evolution and the origin of our own sense of self-awareness."

Nowicki sees the zoology department as a gateway for students into science, as well as into intellectual inquiry in general. "I really think that this department is an asset to Duke, partly because we happen to have many faculty who think broadly, even artistically, in a way that could become very highly integrated into a liberal education." Department chair Fred Nijhout, who studies butterfly wing patterns, is also an artist; professor Stephen Wainwright, who studies animal structure, is also a sculptor.

"This department also really values teaching, which makes me feel good about working on trying to be a good teacher," says Nowicki. "And what also excites me is just the wonder of knowing about things, and ours is a department where that kind of wonder is valued."