BIOACOUSTICS OF SOUTHERN ELEPHANT SEALS. II. INDIVIDUAL AND GEOGRAPHICAL VARIATION IN MALE AGGRESSIVE VOCALISATIONS

ABSTRACT In traditional studies of animal communication, individual variability was sometimes considered less relevant than species specific aspects, mostly because the goal was the classifications of sounds in repertories. However, individual variability seems to have a significant role in signal function and evolution. In this paper, we analyse individual variation in the structure of aggressive vocalisations of male southern elephant seals and we compare sounds from our main study population, Sea Lion Island (Falkland Islands), with sounds recorded in the nearby population of the Valdés Peninsula (Patagonia, Argentina). We firstly analysed the repeatability of acoustic parameters at vocalisation and male level. Repeatability of bouts of the same vocalisation was extremely high and this confirmed that vocalisation is the fundamental level of organisation of male acoustic communication in this species. Also repeatability of vocalisations of individual males was very high and hence sounds may effectively convey information about identity of the individual who emits the sound. Male aggressive vocalisations were categorised into a small number of types and each male emitted always the same type of vocalisation. We compared the typology of sounds emitted by Sea Lion Island males with vocalisations by Valdés Peninsula males and we found striking differences. The two populations shared none of the sound types and, although similar in fundamental acoustics, sounds from the two populations had a different macrostructure. We conclude that these two populations show dialects in male acoustic communication, although the scarcity of recordings from other populations limits the scope of this conclusion.

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