Trajectories of Vocal Repertoire Development in Beluga (Delphinapterus leucas) Calves: Insights from Studies a Decade Apart

There has been only one published study of beluga vocal development, despite the value of ontogenetic research for our understanding of sound centered species. Findings from this seminal study were vital to understanding the beluga vocal repertoire, but further empirical study is necessary to determine if other calves follow similar trajectories in sound acquisition arid development. Herein, we compare the two-year vocal progression of an additional calf, "Kylu," to the previous research. Additionally, we report on changes in acoustic energy distribution and source, level of early calf sounds for the first time as part of a larger effort to understand the impacts of underwater noise on neonate vocalizations. From his day of birth, Kylu produced broadband pulse trains with upperfrequency limits above, the study's Nyquist cutoff (128 kHz) higher than what was reported by the previous study, which was limited by lower samplint! rates. Pulsed signals were his most common sound type during his first year as in the previous study. Over Kylu's first month of life, pulse repetition rate, source level, and third quartile frequencies of the calf's pulse trains increased significantly. First and third quartile, center, and peak frequencies increased significantly over the, first year as did pulse repetition rate arid call duration. Mixed calls and tonal sounds were infrequent and not regularly produced until later in the first year of life. Calf acquisition of adult-like mixed call production appeared similarly between studies, while tonal acquisition appeared more variable. Kylu developed a contact call that was most similar to his mother's as found in the previous study, although slight variation in contact call acquisition was evident. By comparing beluga calves and employing new technology, we reveal species-specific parallels in development and provide new information about beluga calves.