Vertebrate Bioacoustics: Prospects and Open Problems

Abstract

Vertebrate bioacoustics has made great gains in the last two decades in terms of increased understanding of the functional morphology of the vocal tract: how sounds are produced by the larynx (or syrinx in birds) and then filtered in the vocal tract. Despite this fundamental progress, many unusual features seen in the vocal anatomy of particular vertebrates remain poorly understood. This results mainly from the fact that these potential vocal adaptations were described by classical comparative anatomists more than a century ago, long before a good understanding of the physics and physiology of vocal production was in place. Adding to this difficulty, many of the descriptions of anatomical peculiarities were published in non-English languages and often in hard-to-access journals. This chapter starts with a short review of the rise and fall of comparative anatomy as a leading branch of biology, focusing especially on vocal anatomy. It then provides a brief overview of the many known anatomical peculiarities that, although poorly understood, are thought to play some role in vocal production. Both morphology and possible function are considered, and any available empirical research is reviewed. The chapter covers most known vocal peculiarities including air sacs, vocal fold modifications, the syringeal bulla present in most ducks, or the elongated trachea seen in many bird species. Such unusual modifications of vocal anatomy will provide a rich and rewarding topic of future research in bioacoustics.