| Summary: | Belugas (Delphinapterus leucas) are highly vocal cetaceans, but the function of their calls, repertoire ontogeny, and role of learning in vocal behavior are poorly understood. This dissertation examines these issues, focusing on a captive beluga group at the Vancouver Aquarium. First, I investigated vocal development in a beluga calf, longitudinally throughout his first year of life, and later opportunistically. The first sounds after birth were low energy, broadband pulse-trains, which increased in pulse repetition rate with age. He incorporated rudimentary whistles at two weeks. His mixed calls, which became consistent at four months, became progressively stereotyped, increasingly like his mother’s “Type-A” call, a presumed contact call. Six months after he was first exposed to his father’s calls, he developed a call type similar to one of his father’s. I discuss these findings in light of theories of sound production mechanisms, developmental stages of vocal acquisition, and vocal learning. Secondly, I examined context-specific use of call types recorded from the beluga group, with particular focus on the Type-A call. This signal constituted 24-97% of the vocalizations during isolation, births, deaths, presence of external stressors, and re-union of animals after separation. In contrast, it represented 4.4% of the vocalizations during regular sessions. I identified five Type-A variants subjectively and quantitatively. I used these findings to generate hypotheses about the usage of these signals by wild belugas, verified the existence of A-calls in the repertoire of St. Lawrence herds, and documented their usage by two wild individuals from different populations in contexts that supported their contact function. Finally, I investigated contextual vocal learning in trained tasks in adult belugas, focusing on the ability of a female beluga to respond to playbacks of two categories of beluga calls with matching vocalizations; pulse-trains are a natural category, and screams an artificial class shaped by training. The subject successfully matched only pulse-trains, the class that is part of this species’ natural repertoire. Her poor performance on matching screams might be partly explained by a difficulty to perceive categorically a signal that lacks a function in the natural repertoire of belugas. Science, Faculty of Zoology, Department of Graduate
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