A Song for Every Occasion: New Technology Is Revealing That the Notes, Warbles and Chirps of Birdsong Say More Than Anyone Had Guessed
Rankin, Bill, National Wildlife
AT 4:30 A.M. IN AN UPSTATE New York meadow, a 1980 Pontiac rolls along the grass and comes to a halt in the dark. Overhead, stars are beginning to fade from the night sky. Dawn approaches.
The car door pops open and out steps John Bower, a shaggy-haired, bearded graduate student from Cornell University. A former farm boy with an affinity for cross-country skiing and ice hockey, Bower has come to this meadow to pursue ornithological studies.
He walks to the trunk, opens it and, with a flashlight in one hand, pulls out eight microphones and carries them to microphone stands already arranged in two rows 50 yards apart and about 200 yards long. As he mounts a microphone on each stand, the sky lightens to gray, then turns pink. Scattered trees grow visible among the rolling meadows, and the first chirps of birds greet the sun. By the time Bower's done hooking up cables to the microphones, the birds sing in full chorus.
The birds and their songs are the source of Bower's interest in the meadow. When the morning is bright enough, he begins monitoring the comings and goings of song sparrows, a common, brown bird with a streaked buff breast. As Bower wanders the field taking notes, his microphones are collecting data of their own. A transmission of meadow sounds travels down the cables back to Bower's Pontiac, where they feed into $15,000 worth of digital eight-track recording equipment. "The whole front seat of the car is turned into a little recording studio," says Bower. Most spring mornings, Bower stays out until about ten, recording five hours of bird song on high-resolution tapes.
The birds in Bower's field are not just twittering blithely for lack of something better to do--they are creating a complex musical conversation fraught with subtleties that biologists are only now beginning to decode. Dedicated birders have been able to recognize bird species by their distinctive songs since time immemorial, but the story behind the songs lay hidden until 40 years ago, when ornithologists began using then-new, portable tape recorders and other equipment to capture songs for analysis. Now a younger generation of scientists like Bower is going into new technological realms, using personal computers, digital audiotape and other cutting-edge gear to make quantum leaps in the study of bird song.
Fewer than half of the 8,700 known bird species actually sing, creating musical sounds through a kind of double voicebox that lies at the base of the windpipe, where it branches into the lungs. There, two sets of membranes and muscles vibrate at high frequencies as air is exhaled from each lung. While singing, the bird can alternate between the two lungs, even singing in harmony with itself.
While the structures that make bird song possible have long been known to anatomists, the structure of the songs themselves remained a mystery until the 1950s. During that decade, biologists started playing taped bird songs into sonographs, devices that analyze sound frequencies and create a picture of them. "Until we could actually produce a picture that looked like musical notes, we had no way to publish an accurate description of the songs," says Sandra Vehrencamp, a biologist at the University of California at San Diego. "We gave them names like phoe-be-be-be. But you can't render a more complex song that way."
By poring over sonograms in the decades that followed, ornithologists discovered that bird songs have some similarities to human language. Each song is composed of phrases that, in turn, are made up of smaller units called syllables. Each species follows its own rules for using phrases and syllables, but individual birds bend those rules slightly to create their own distinct songs. These uniquely modified songs comprise the individual bird's repertoire.
The number of song types in an individual bird's repertoire varies from species to species. Each song sparrow has a repertoire of only eight songs on average, a number similar to the repertoires of individual juncos, cardinals, and western meadowlarks. …