Vocal Communication of Wild Crested Macaque (Macaca nigra).

Abstract

Communication is an important aspect in the life of primates. In general, communication in primates involves the visual, auditory, and olfactory system. However, the vocal communication is an effective mode of communication since it may reach further than any other mode, especially for primates living in the forest habitat. Communication has important roles for the social life of primates such as individual or group identity, providing information of the presence of food and predators, and facilitating social interactions in primate social groups. This research was carried out on wild Macaca nigra, which is one of the seven macaque species endemic to Sulawesi. The species is characterised by a high level of social tolerance. Vocal communication studies on tolerant species are very limited compared to other, more despotic macaque species. The purpose of this study was to determine the variation of vocalizations of M. nigra and the social contexts in which the calls are issued. This study aims at providing a comprehensive overview of the complex social communication of these macaques and indirectly, contributes to the conservation and management of it, both in the wild and in captivity. A total of 1369 call units were generated from 328 sequences of calls. The calls were categorized based on their acoustic structure and the contexts in which they were uttered. Descriptive statistics of the acoustic parameter measurements are presented. This study found 11 call types emitted by M. nigra. Based on the physical structure of acoustics, the calls are categorized as tonal calls, non-tonal calls and complex calls (combination of tonal and non-tonal parts). M. nigra emitted the calls in all five main social contexts: affiliation, group cohesion (incl. group movement), agonism, predation and mating behaviour, whereas the loud call was uttered in several different contexts including non-social one. The calls were emitted by all individual, except the calls during mating behaviour and loud calls. Females and males had distinct call structure and calling time during mating behaviour. The loud call was issued only by adult males. One of the vocalizations can be considered as discrete signals while the others calls show high degrees of grading into each other. The discrete signals include calls in the group cohesion. The graded call signals were issued in the context of affiliation, agonism, the presence of predators and calls related to sexual behaviour. The ability of receiver to assess various clues and the usage of multimodal by the sender would influence the individual’s response to the graded signals. As a tolerant species, M. nigra showed high variation of calls compared to other monkey species. The call variation differences were likely influenced by various factors such as the character of species, behaviour and habitats. Vocal communication data on the species M. nigra can complement the data supporting the taxonomic determination and conservation activities of the species. The calls might give information regarding the emotional state of animals, which is important in ecotourism activities and captive animal management.