The budgerigar brain enlarges and there is striking differentiation of brain nuclei during the nestling period (i.e. the first 5 weeks posthatch). Although brainstem vocal nuclei can be distinguished at hatching, telencephalic nuclei are either poorly developed (AAC) or non present. As vocal control nuclei differentiate and add neurons calls change. The sonograms below illustrate the qualitative changes in calls produced by nestlings during this period. It is notable that both auditory feedback (Heaton and Brauth, 2000) and functioning telencephalic vocal control nuclei (Heaton and Brauth, 2000) are needed for production of normal calls after 3 weeks but not for production of earlier calls.
|Call development in nestlings proceeds through five different phases or stages each marked by transitions which can be quantitated (Hall et al, 1999). The sonograms on the top row represent the normal stage transitions for a budgerigar while those on the lower row reflect those deprived of auditory feedback. In the absence of auditory feedback early calls are not affected by calls produced after 3 weeks are severely disrupted.|