Peripheral Vocal Mechanisms in Birds: Are Songbirds Special?

Abstract

This paper reviews recent advances regarding the peripheral mechanisms for song production by oscine songbirds and compares the vocal mechanisms of songbirds with those of certain non-oscines. The tracheobronchial syrinx of songbirds has several pairs of intrinsic muscles specialized for controlling particular aspects of sound production. The syringeal and vocal tract anatomy of non-oscines is much more diverse than that of songbirds and has fewer or no intrinsic syringeal muscles. Often the same extrinsic tracheal muscles control both the temporal and spectral properties of vocalizations. Although the vocalizations and vocal anatomy of these two groups are quite different, a number of motor patterns important in oscine song are also used by non-oscines. These include special respiratory techniques, such as minibreaths and pulsatile expiration, for sustained rapid vocalization, as well as the ability to simultaneously produce two acoustically unrelated 'voices'. However, the complex syringeal musculature of songbirds with laterally independent motor control of each side of the syrinx provides a more versatile vocal system in which the left and right sound sources can be coordinated in different ways, by specialized song control nuclei capable of vocal learning, to achieve diverse vocal effects.