Acoustic communication in elephant seals (Mirounga leonina): structural and functional correlates of male vocalizations

Sanvito, Simona (2006) Acoustic communication in elephant seals (Mirounga leonina): structural and functional correlates of male vocalizations. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Southern elephant seals (SES, hereafter) show the most extremely polygynous mating system of all mammals, with a very intense competition among males for access to females. Vocalizations are the most important component of SES male agonistic behaviour. Notwithstanding this, the knowledge of SES vocalizations was scanty, and mostly anecdotal, before I started studying them. During my previous research, I focused on the acoustic structure and the individual variation of vocalizations. The goal of my PhD research project was to study the development of male vocalizations, to understand their functions, to explore their relationships with male phenotype, and to assess their potential use as honest signals. -- The first step was to analyze the male phenotypic traits that should be related to vocalizations. I studied body size and growth, as well as the development or the proboscis, a peculiar secondary sexual trait which role in vocalizations has always been controversial. I showed that the proboscis has indeed an active role in vocalization, and may serve as a way or elongating the vocal tract or the emitter, hence exaggerating the size information conveyed by acoustic signals with respect to the true size. -- I then focussed on the different acoustic features of vocalizations. I showed that the temporal macro-structure of vocalizations, which is not constrained by vocal tract length or shape, is probably learned by young males through imitation of the older, most successful, breeders. On the contrary, the frequency features or vocalizations (formants, in particular), which are constrained by the vocal tract length, have a predictable development pattern related to body growth. – Finally, I demonstrated that both source level and formant frequencies give reliable information about the phenotype of the emitter and, hence, are honest signals. But I also showed that the phenotypic information content of these signals is rather low. Vocalizations are, hence, a far from perfect assessment system, being very effective in settling contests between males when phenotypic differences are great, but not when interacting males have similar phenotypes.

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