Birdsong: A Natural History

Several years ago on a Sunday afternoon I wandered through the one-story cinder-block building at one of the most famous addresses in bird studies -- 159 Sapsucker Woods Road: Cornell University's Laboratory of Ornithology. I had been let in, the door locked behind me, and I had the place to myself. To research an article I was writing on birdsong, I planned to review some of the literature in the lab's private library, including materials that were available nowhere else, but within minutes I found myself drawn to another kind of archive. Passing through an unlit hallway hung with the paintings of Louis Agassiz Fuertes, the greatest of bird artists, and an early associate of the lab, I made my way to the southeast wing of the building and opened the gray metal door to Room 125. Stepping inside, I felt a rush of cool, dry air. The windowless room, tightly packed with rows of metal shelves, was austere: white walls, a cement floor, exposed ductwork and girders, and bare lightbulbs hanging from the ceiling. It had the sterile functionality of a hospital room, and it appeared, if anything, cleaner and more orderly. The only sound was air moving through the vents. It would have been difficult to imagine a more lifeless space, yet all around me, stored on wall-to-wall shelves, was the aural life of the planet. This was the archive of the Macaulay Library of Natural Sounds, the largest collection of its kind in the world. The shelves, which rose above my head, contained more than 130,000 individual recordings, some in neatly labeled boxes containing seven-inch reels of tape, others on standard cassettes in makeshift containers with hand-scribbled labels.
Walking down the narrow aisles, I found boxes that held the sounds of crickets chirping, mountain gorillas thumping their chests, triggerfish squirting water, and prairie dogs barking. It was birdsong, though, that had drawn me there, and birdsong that dominated the Library of Natural Sounds. There, arranged taxonomically from ostrich to raven, were the songs of nearly six thousand of the world's nine thousand or so species of birds. On one shelf were the babbling-brook arias of mockingbirds, on another the flutelike ee-oo-lays of wood thrushes, and on others the wistful melodies of white-throated sparrows, the caroling of robins, and the songs of birds I had never seen nor heard: the superb lyrebird, laughing kookaburra, black-and-gold cotinga, snowy-headed robin chat, and more. If I looked, I could find the sounds of my childhood, the ok-ka-leee of a red-winged blackbird and the squeaky-gate call of a blue jay. And somewhere, surely, was Keats's nightingale and Shelley's skylark. The room was brimming with sound. But of course I heard nothing. The silence was profound.
This archive of sounds is invaluable. A second set of recordings made from these originals is kept in a vault in a limestone cave for safekeeping. Several recordings hold the voices of birds now extinct. Many are the only known aural records of rare and elusive species. Recordings like these are critical in one of the newest fields in zoology: bioacoustics, the study of how animals use sound to communicate. In recent years, scientists have discovered that elephants use infrasonic sounds to send messages across great distances; that hippos are able to communicate simultaneously in water and air; that small insects known as treehoppers send vibrations through the stems of plants to communicate with other treehoppers; that vervet monkeys use one kind of alarm call to signal that a leopard is nearby and a different one to signal the presence of a snake. But it is birds that have attracted the most attention. It has always been birdsong that has most enthralled and mystified us. Frogs croak, crickets chirp, wolves howl, and lions roar, but birds sing.
Today, many ornithologists are listening to bird vocalizations and studying their intricacies in ways that were beyond the grasp of their predecessors only a generation ago. Avian bioacoustics has flourished in just the last few decades, a result of two inventions from the mid-twentieth century: the tape recorder and the audiospectrograph, or sonograph. The latter, which produces a visual representation of sound, allows ornithologists to measure the details of a bird's song as concretely as Darwin measured the beak of a finch. These tools make it possible to look for answers to some ancient questions: Why do birds sing? What do their songs mean?