Neuroethology of acquired English and conspecific vocalizations in the budgerigar (Melopsittacus undulatus)

Abstract

This dissertation is a report of neuroethological investigations of the vocal and cognitive behavior of the budgerigar (Melopsittacus undulatus). Budgerigars were trained, via an interactive modeling technique, to reproduce English words and phrases. Budgerigars' abilities to use their acquired English vocalizations were then assessed. Budgerigars produced English vocalizations in three main ways: (1) enmeshed in warble song; (2) in response to presented objects; and (3) alone, neither enmeshed in warble song nor in response to presented objects. Budgerigars also formed functional categories of their English vocalizations and used them in a context-dependent manner. Budgerigars' English vocalizations and contact calls were subjected to acoustic analyses and found to contain nonlinear amplitude modulation. A comparison with the sounds produced by humans and other speech-producing birds (Grey parrots, Psittacus erithacus, and mynahs, Gracula religiosa) revealed that budgerigars produce speech in a fundamentally different manner. Ibotenic acid lesions were placed in the vocal control nucleus, NLc, and the effects on budgerigars' contact calls and English vocalizations assessed. NLc lesions affected production of, but not memory for, budgerigar vocalizations. Specifically, the amplitude of the carrier signal of amplitude- modulated vocalizations was disrupted. No abnormalities were detected in the frequencies that budgerigars produced post-lesion. The implications of these findings regarding the presence of amplitude modulation and the effects of NLc lesions with respect to past and future studies of the acoustic, physical and neural mechanisms underlying budgerigar vocal production are discussed, and a working model for the function of the budgerigar syrinx presented.