The vocal repertoire of grey parrots (Psittacus erithacus) living in the Congo Basin

Abstract

This dissertation is a report on the investigation of the vocal behavior of free-living Grey Parrots (Psittacus erithacus) that inhabit the Congo Basin in Central Africa. I observed Grey Parrots in the Central African Republic and Cameroon and made audio recordings of their vocalizations. The results of spectrographic analysis of vocalizations lend support to the assertion that Grey Parrots produce calls that fall into four major acoustical classes--tonal, harmonic, noisy-harmonic, and noisy--and that these call classes may be subdivided into as many as 39 different acoustical types. A reliability study of this classification scheme demonstrated that both clustering of these acoustical types into aggregate categories and the combined method of visual inspection and basic spectrographic measurement enable reliable classification of calls into classes, types and also subtypes. The majority of calls in the observed repertoire belong to pure tonal call class, which may suggest that a large proportion of Grey Parrot calling behavior is adapted for tonal call production. Grey Parrots may also adjust the acoustic characteristics of their calls to better adapt them to their environment and communication needs. Both observations of Grey Parrots and analysis of the acoustic and production characteristics of their calls indicate that Grey Parrots may share functional call types of some New World and Australian parrot species. Some Grey Parrot calling vocal behavior parallels that of captive Grey Parrots in the laboratory. I conclude with an exploration of possible reasons why Grey Parrots possess such a diverse vocal repertoire.