The Role of Grunt Calls in the Social Dominance Hierarchy of the White-Lipped Peccary (Mammalia, Tayassuidae)

<div><p>Grunt-like calls are present in the vocal repertoire of many group-living mammals and seem to facilitate social interactions between lower and higher-ranking members. The white-lipped peccary (<i>Tayassu pecari</i>) lives in stable hierarchical mixed-sex groups and like non-human primates, usually emits grunt-like calls following aggressive interactions, mainly during feeding contexts. We investigated the possible functions of peccaries’ grunt-like calls and their relationship to the individuals’ social rank, identity, and sexual dimorphism. We observed that low-ranking individuals emitted grunt-like calls more often than high-ranking ones, and that the alpha male never emitted this vocalization. Moreover, the mean minimum frequency of grunt-like calls decreased as the peccary’s rank increased. The findings revealed differences among individual grunts, but the low accuracy of cross-validation (16%) suggests that individual recognition in peccaries may be less important than an honest signal of individual social status. In addition, the absence of differences in the acoustic parameters of grunt-like calls between males and females points to the lack of sexual dimorphism in this species. We verified that after hearing grunt calls, dominant opponents were more likely to cease attacking a victim, or at least delay the continuation of conflict, probably decreasing the severity of agonistic interactions. Our findings are particularly important to improve the current understanding of the role of grunt-like calls in herd-living mammals with linear dominant hierarchies, and strongly suggest that they are involved in the maintenance of herd social stability and cohesion.</p></div

Mean values (± standard deviation) of the acoustic parameters for grunts emitted by white-lipped peccaries according to the ranking position.

<p>Lower numbers correspond to higher positions in the dominance hierarchy. All measurements were taken from 50 samples from each individual. The percentage of correct cross-classified grunt calls for each individual based on the conventional (DFA) and permuted discriminant analysis (pDFA) is also presented, based on 37 calls for each individual.</p

Coefficients of the two main discriminant functions (DF) indicating the relative contribution of each acoustic parameter (variable) for discriminating between individuals’ grunt calls.

<p>The values in bold indicate the parameters with higher loading for the discriminant functions (DF1 and DF2).</p

Distribution of discriminant scores for each individual along the two canonical discriminant functions.

<p>Distribution of discriminant scores for each individual along the two canonical discriminant functions.</p

Grunt call emitted by a white-lipped peccary (<i>Tayassu pecari</i>).

<p>Grunt call emitted by a white-lipped peccary (<i>Tayassu pecari</i>).</p