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

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 (Tayassu pecari) 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.

Gestural communication in a new world parrot.

Male birds can use visual signals to provide information about their sexual status, via bright coloration, sophisticated sexual displays and elaborate tail and head crests. The majority of forest bird species use vocal communication as their main strategy to show their physiological status during breeding season. It is also used to keep contact between individuals in the same group, in agonistic contexts, and by chicks begging for food. We registered, for the very first time, gestural communication acting in the context of biparental care for the Orange-winged Amazon, Amazona amazonica. This parrot presents at least nine different sounds uttered in contexts of alarm, agonistic, foraging, contact flight and others. This finding suggests that despite being a vocal species, this parrot can perform gestural communication related to parental care. The gestures exhibited by this species represent a strategy for survival, a clever way to protect the nest, reducing the risk of attracting the attention of predators.

Influence of the nycthemeral cycle on the roosting behaviour of the Orange-winged Amazon.

Environmental stimuli exert important effects on the expression of the endogenous rhythms. Daily movements of groups of parrots in response to the light/dark cycle have been studied by several researchers. However, the factors modifying the intrinsic rhythmicity of this behaviour remain little known. This study describes how the nychthemeral/circadian periodicity of roost daily movements of the Orange-winged Amazon Amazona amazonica is modified by weather factors. Numbers of parrots arriving or leaving the roosting site Ilha dos Papagaios were determined on a minute by minute basis. More parrots have significantly arrived at the roost after sunset than before, while more parrots have significantly left the roost before sunrise than after. The peak exodus of parrots occurred at 23 ± 5.24 minutes before sunrise, when the average light intensity was 1 lux. The peak influx of parrots occurred at 6 ± 6.1 minutes after sunset, when the average light intensity was 50 lux. By altering ambient light intensity, weather conditions have significantly influenced the arrival and departure times, with parrots leaving later and arriving earlier when conditions were overcast at the roost site.