The Function and Significance of Inter-Species Acoustic Cues in the Transformation of Budgerigar (<em>Melopsittacus Undulatus</em>) Sounds Into "Speech"

Abstract

Analysis of speech-imitation sounds produced by pet budgerigars (Melopsittacus imdulatus) reveals a consistent focus on acoustic components of speech which have counterparts in the species-specific vocalizations of budgerigars. These budgerigar vocalizations include whistle sequences (which, with their rapid glides in pitch contour, need only slight modification to constitute a second-formant representation of speech), the contact call (which is acoustically similar to the secondformant transition of high front vowels), and sounds with harmonic spectra (which can be modified to represent the formant structure of certain vowels). This transformation of species-specific sounds into speech-imitation sounds by focusing on shared acoustic features prompts the hypothesis that, with the appropriate social stimulation, pet budgerigars perceive human speech as modified budgerigar sounds. The hypothesis is supported by the fact that the shared acoustic features are particularly important cues in the perception of species-specific communication sounds by both humans and budgerigars. Such inter-species vocal communication cues, having a common origin somewhere in vertebrate phylogeny. would help to explain the many reported examples of human-like speech perception by nonhuman vertebrates. The shared neural mechanisms which correspond to these shared acoustic patterns could constitute a phylogenetically conservative level of auditory perception which is communication sound-specific but not species-specific.