Vocal signalling of male southern elephant seals is honest but imprecise

Abstract

In the most common models of communication, it is assumed that animals provide reliable information about phenotype, and hence can settle competitive contests without physical interactions like fights. This assumption has rarely been tested for wild mammals. Recent studies of mammals have revealed relationships of vocal attributes to age and body size. Here, we analyse relationships of frequency attributes of agonistic vocalizations to phenotype (age, body size, proboscis size and agonistic behaviour) in males of the southern elephant seal, Mirounga leonina, a species with intense male competition for access to females, and in which vocalizations are used frequently to settle male–male contests. We analysed formant structure and vocal tract size, and found that nasal and oral components of the vocal tract contribute separately to vocal formants; hence, the male's proboscis serves to elongate the vocal tract. We also found that formants in the upper part of the frequency spectrum (fourth and fifth in particular) and formant dispersion convey significant information about age, size and resource holding potential at large, and, therefore, can be honest signals of a vocalizer's phenotype. Explained variance was statistically significant in our study and in similar studies but was not high, so formant structure cannot serve as the sole basis of acoustic assessment. Other possible sources of information exchanged in elephant seal contests are nonvocal acoustic signals (e.g. vibrations) and optical displays.