Wild-captive contrasts in non-vocal communicative repertoires and functional specificity in orang-utans

Abstract

The creation of novel communicative acts is an essential element of human language. Although some research suggests the presence of this ability in great apes, this claim remains controversial. Here, we use orang-utans (Pongo spp.) to systematically assess the effect of the wild-captive contrast on the repertoire size of communicative acts. We find that individual communicative repertoires are significantly larger in captive compared to wild settings, irrespective of species, age-sex class or sampling effort. Twenty percent of the orang-utan repertoire in captivity were not observed in the wild. In Sumatran orang-utans, the more sociable species, functional specificity was also higher in captive versus wild settings. We thus conclude that orang-utans, when exposed to a more sociable and terrestrial lifestyle, have the behavioural plasticity to invent new communicative behaviours that are highly functionally specific. This productive capacity by great apes is a major prerequisite for the evolution of language and seems to be ancestral in the hominid lineage.

A socio-ecological perspective on the gestural communication of great ape species, individuals, and social units

“…Orang-utans showed little variability in the types of gestures used within age classes, with mother-infant dyads using the same travel-initiation gestures as other members of their age group (but different from other age groups; Cartmill & Byrne 2010 ), while chimpanzee mothers living in the same community used different sets of gestures to initiate travel with their infants (Fröhlich et al 2016b ). However, here orang-utan data were limited to small numbers of captive individuals, and in other settings captivity appeared to increase diversity of gesture use in orang-utans (Fröhlich et al 2021 ).…”

“…The majority of these apparently novel “inventions” were gesture types typical in other ape species (e.g., cf. Fröhlich et al 2021 with Byrne et al 2017 ), suggesting that while immediate socio-ecology shapes local repertoires in particular ways, apes retain access to shared ape-typical sets of available signals.…”

“…Orang-utans were found to be highly responsive in their gesturing, typically responding before their partner’s gestures were completed, perhaps as a result of their familiarity (Knox et al 2019 ). Interestingly, in the unusual socio-ecological contexts of captivity where orang-utans are kept in atypically large social groups and experience a more terrestrial lifestyle, their repertoires of regularly used signals were larger (Fröhlich et al 2021 ). The majority of these apparently novel “inventions” were gesture types typical in other ape species (e.g., cf.…”