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Vocal Behavior in Psitacids: Learning Processes in Nestling and Fledgling Communication
Acoustic communication represents a cornerstone for social behavior in most vertebrate social species. In this domain, vocal learning fosters complex communicative systems, and has been consolidated as a central topic of neuroethological research. Passerine birds, in which adult male song is learned from a social tutor during early stages of development, have provided a canonical model for these studies. An advanced understanding of the behavioral mechanisms and neural substrates involved in this complex behavior is currently available . Among birds, parrots (Order Psittacidae) represent another group of highly developed vocal learners. They show a remarkably extended sociality, and display a repertoire of vocal communicative behaviors, substantially more diverse than that of passerine songbirds . Surprisingly, vocal learning processes have not received enough attention in this group. In particular, few studies have investigated learning processes during early development. Parrots are highly altricial, and show intense socio-vocal interactions from the nestling phase onward. The begging calls of nestlings merge into mature contact calls during a continuous process of interactions with their parents and siblings . In the current study we explore the development of communicative behavior during the nestling and fledgling phases in the budgerigar (Melopsittacus undulatus). Our main interest is to determine the role of nestling socio-acoustical experience and learning mechanisms in this developmental process. Playback experiments performed during different phases of nestling growth revealed that mature contact calls arise through 3 main sequential stages in nestling's vocal development: (1) spontaneous begging vocalizations not related to acoustic stimulation (0-7 post-hatching days), (2) emergence of specificity of begging responses to contact call stimulation (8-21 p-h. days), and (3) onset of selectivity in responses to different conspecific contact calls (22-35 p-h. days). Additional social deprivation experiments, in which nestling birds are separated from their parents and hand-fed from their second week onward, show that socially deprived birds do not develop specificity or selectivity in their vocal responses. Finally, cross-foster experiments in which nestlings are raised by an unrelated breeding pair show that: (1) preferences for parental calls expressed by nestlings in playback tests in late phases of their development (stage 3) depend on their socio-acoustical experience with caregivers, and (2) the first contact calls emitted by fledgling once they leave the nest are acoustically derived from those of their caregivers. Our results indicate that psitacid vocal behavior develops through a sequential differentiation of perceptual, motor and social traits in which socio-acoustical experience has a preponderant role. We conclude that psitacids constitute a good model to study vocal learning in highly socio-vocal species. Parrots seem to be more advantageous than songbirds to study the diverse behavioral and social factors involved in the emergence of sound communication. Finally, the analogy between budgerigar “perceptual-before-vocal” contact call learning and human pre-grammatical phoneme learning is particularly remarkable .