Song syntax in bengalese finches: Proximate and ultimate analyses

Bengalese finch song has a unique type of complexity. We analyzed the syntactical rules underlying it by statistical methods and found that the songs of these birds could be expressed as finite state syntax. In general, two to five song notes are arranged in fixed order to form "chunks" and several chunks are arranged with probabilistic rules into variable song phrases. Our aim was to understand the song complexity of Bengalese finches in terms of the 'four questions' raised by Tinbergen and thus to show the strength of his integrative approach in the study of behavior. Through song development, we found that the phonological characteristics appeared first and syntactical characteristics were then established. In other words, song development follows the hierarchical path from song phonology to song syntax. To understand the evolution of the song complexity, we examined songs of the wild strain of the Bengalese finch, the white-backed munia. Their songs are linear strings of notes in a highly stereotyped order, neither hierarchical nor complex like those of Bengalese finches. Thus, song syntax must have been acquired at some point during the process of domestication. We then investigated the brain mechanisms by which this complex syntax was enabled. A series of lesion studies demonstrated that the behavioral hierarchy of the song is expressed in the anatomical hierarchy of the forebrain song control system. Auditory neurons in these hierarchical brain structures respond to the particular aspects of song structures that reflect the behavioral hierarchy. Finally, in a series of studies examining female preferences for song complexity, we found that complex songs would attract not only Bengalese finch females, but also white-backed munia females. On the basis of these data, we suggest that song complexity in Bengalese finches may have been initiated as a sexually selected trait in the wild, and then enhanced in a domesticated environment that relaxed several selection pressures in the wild. Further research is necessary to examine the hypotheses that have arisen from these studies so far. © 2004 Elsevier Inc. All rights reserved.