COMPARATIVE APPROACHES TO THE AVIAN SONG SYSTEM

There is extensive diversity among the 4000 species of songbirds in di fferent aspects of song behavior, including the timing of vocal learni ng, sex patterns of song production, number of songs that are learned (i.e., repertoire size), and seasonality of song behavior, This divers ity provides unparalleled opportunities for comparative studies of the relationship between the structure and function of brain regions and song behavior. The comparative approach has been used in two contexts: (a) to test hypotheses about mechanisms of song control, and (b) to s tudy the evolution of the control system in different groups of birds. In the first context, I review studies in which a comparative approac h has been used to investigate sex differences in the song system, the relationship between the number of song types a bird sings and the si ze of the song nuclei, and seasonal plasticity of the song control cir cuits. In the second context, I discuss ?whether the vocal control sys tems of parrots and songbirds were inherited from a common ancestor or independently evolved. I also consider at what stage in the phylogeny of songbirds the hormone-sensitive forebrain circuit found in modern birds first evolved. I conclude by identifying directions for future r esearch in which a comparative approach would be productive. (C) 1997 John Wiley & Sons, Inc.