MECHANISMS OF VOCAL PRODUCTION IN BUDGERIGARS (MELOPSITTACUS-UNDULATUS)

Songbirds vocalizing in helium show a change in the spectral quality o f their vocalizations. This effect is due to an increase in the speed of sound in helium that in turn alters the resonance properties of the vocal tract. Here, this approach is extended to a psittacine, the bud gerigar (Melopsittacus undulatus), whose syringeal anatomy and innerva tion differ from that of a songbird. Contact calls from birds vocalizi ng in heliox (70/30 helium/oxygen environment) showed an overall incre ase in the amount of energy at frequencies above the fundamental, slig ht changes in the frequency of the fundamental and harmonics, and some change in the level of harmonics. Calls produced by a syringeally den ervated bird showed more dramatic changes. Recordings from live birds were compared with sounds produced by various simple ''artificial'' tr acheal and syringeal models. Results suggest that budgerigars produce contact calls using the syringeal membranes as a unitary sound source which produces acoustic energy in a narrow frequency band whose fundam ental frequency is matched to the resonant frequency of the trachea. T he syrinx is not normally coupled to the tracheal resonator, and reson ances probably play only a minor role in shaping the spectrum of conta ct calls. (C) 1997 Acoustical Society of America.