Meeting Abstract
Avian vocalizations are highly diverse, and arise from an interplay between morphology, aerodynamics and neuromuscular control. Although variation in the morphology of the vocal organ of birds, the syrinx, has been described, its functional role in generating vocal diversity is still poorly known for most bird taxa. Among Passseriformes, substantial differences in syrinx morphology exist between various suboscines, but their functional relevance has not been directly investigated. Here we illuminate the functional morphology of the syrinx in three “tracheophones”, which are thought to generate sound with a prominent pair of membranous windows located in the distal end of the trachea (e.g. Ames, 1971, Peabody Museum of Natural History, Bulletin 37; King 1989, Form and Function in Birds, Volume 4; Beddard, 1898, The Structure and Classification of Birds). Using a fine optic fiber system inserted into the trachea, we identified the vibratory structures in the syrinx during induced phonation and found three possible sound sources: one pair of membranes in the distal trachea and one pair in each bronchus. We then tested the respective roles of these putative sound sources during spontaneously produced distress calls and induced phonation before and after experimental disruption of the tracheal membrane pair. Although the membrane windows can oscillate, they typically are not the main sound source. However, vibrations of the intact membranes are of low frequency and their disruption results in reduced amplitude and frequency modulation patterns. These data provide strong evidence that “tracheophones” likely use 3 sound sources. However, the role of the postulated “main” sound source, the tracheal membranous windows, is primarily that of modulating vibrations generated by the labial sound sources located in each bronchus.
