Bird Song: Biological Themes and Variations
by C. K. Catchpole, by P. J. B. Slater
Cambridge University Press, 248 pp., $32.95
Have you ever lain awake at night wondering how, when, and why birds sing? If so, Bird Song may be the book for you. But no one should imagine that it is about the charming and euphonious (or sometimes cacophonous) things birds say to one another. Catchpole and Slater present a competent and logically organized synthesis of the vast scientific literature on bird song, concentrating almost entirely on experimental investigations by researchers. “Bird song” is defined here in the narrowest sense as “long, complex vocalizations produced by males in the breeding season.” All avian utterances that do not conform to this narrow definition, and there are many, are excluded from consideration. The text has citations to nearly seven hundred scientific sources, and its dry prose makes liberal use of technical jargon. It begins with a concise review of the neurophysiology of sound production and sound reception in birds, discusses how songs are learned, and concludes with an inquiry into the evolutionary function of song and its variability in nature. It tells, in fact, a story of remarkable scientific advances.
Surprisingly little was known about the functional and acoustic complexity of bird song until the second half of this century. Although birds are eminently accessible to study, being found even in the centers of our busiest cities, rigorous scientific inquiry into their vocalizations awaited the invention of high-fidelity tape recorders and speakers. These are the basic tools that both field and laboratory workers use to record bird sounds and later to play them back to the birds used in tests. Since the earliest playback experiments, conducted in the 1950s, continuing technological advances in both sound and information processing have stimulated ever deeper inquiries into the structure of song and its function.
Birds have been the main object of studies of animal vocal communication because they are both ubiquitous and relatively cheap and easy to maintain in captivity. The birds under discussion here are members of the great “passerine” order, comprising nearly half of all birds, and distinguished anatomically from non-passerine birds by their grasping feet, with the first toe turned backward. But birds are by no means the only animals to “sing.” Myriad frogs and insects produce sounds to attract mates or to proclaim territories. There are even singing mammals, including a number of monkeys, the South American bamboo rat, and, of course, whales.
Birds produce sound in a structure called the syrinx, located deep in the throat at the juncture of the bronchi, the two main branches of the windpipe. A membrane on each side regulates the passage of air. It was first thought that sound emanated from vibrations of the membranes, but it is now acknowledged that the source is air turbulence, produced much in the manner of a whistle. The truly remarkable feature of sound production by birds is that the two sides of the syrinx can act independently, so that some birds are literally able to produce a chord. The song of the common cat-bird, for example …