Orangutans have larger gestural repertoires in captivity than in the wild—A case of weak innovation?

Whether nonhuman species can change their communicative repertoire in response to socio-ecological environments has critical implications for communicative innovativeness prior to the emergence of human language, with its unparalleled productivity. Here, we use a comparative sample of wild and zoo-housed orangutans of two species (Pongo abelii, Pongo pygmaeus) to assess the effect of the wild-captive contrast on repertoires of gestures and facial expressions. We find that repertoires on both the individual and population levels are larger in captive than in wild settings, regardless of species, age class, or sampling effort. In the more sociable Sumatran species, dominant use of signals toward single outcomes was also higher in captive settings. We thus conclude that orangutans exposed to more sociable and terrestrial conditions evince behavioral plasticity, in that they produce additional innate or innovated signals that are highly functionally specific. These findings suggest a latent capacity for innovativeness in these apes' communicative repertoires

Call Cultures in Orang-Utans?

BACKGROUND: Several studies suggested great ape cultures, arguing that human cumulative culture presumably evolved from such a foundation. These focused on conspicuous behaviours, and showed rich geographic variation, which could not be attributed to known ecological or genetic differences. Although geographic variation within call types (accents) has previously been reported for orang-utans and other primate species, we examine geographic variation in the presence/absence of discrete call types (dialects). Because orang-utans have been shown to have geographic variation that is not completely explicable by genetic or ecological factors we hypothesized that this will be similar in the call domain and predict that discrete call type variation between populations will be found. METHODOLOGY/PRINCIPAL FINDINGS: We examined long-term behavioural data from five orang-utan populations and collected fecal samples for genetic analyses. We show that there is geographic variation in the presence of discrete types of calls. In exactly the same behavioural context (nest building and infant retrieval), individuals in different wild populations customarily emit either qualitatively different calls or calls in some but not in others. By comparing patterns in call-type and genetic similarity, we suggest that the observed variation is not likely to be explained by genetic or ecological differences. CONCLUSION/SIGNIFICANCE: These results are consistent with the potential presence of 'call cultures' and suggest that wild orang-utans possess the ability to invent arbitrary calls, which spread through social learning. These findings differ substantially from those that have been reported for primates before. First, the results reported here are on dialect and not on accent. Second, this study presents cases of production learning whereas most primate studies on vocal learning were cases of contextual learning. We conclude with speculating on how these findings might assist in bridging the gap between vocal communication in non-human primates and human speech

Monthly range of adolescent orangutans (Pongo pygmaeus wurmbii) based on fruit availability in Tuanan Orangutan Research Station, Central Kalimantan, Indonesia

Adolescent orangutans become competitors with mothers supporting newborn infants. Thus, adolescent orangutans must coordinate with other orangutans in order to find fruit. How adolescent orangutans respond is reflected in the size and utilization of their home range area. The aims of our research were to determine (i) fruit availability, as an important component of orangutan diet, (ii) and the effect of fruit availability on home range use by adolescent orangutan. This research was conducted from August 2013 to July 2014 in Tuanan Orangutan Research Station, Central Kalimantan. The fruit trail method was used to estimate abundance of fruits (both from trees and lianas).Fallen fruit on census trails was assessed once per month, while focal animal sampling was used to estimate the home range by tagging a GPS point every 30 minutes during the tracking of an orangutan. In total, 62 tree and 15 liana species included in the known orangutan diet were fruiting during this study period. The highest period of fruit abundance for orangutan food occurred in November until January. Adolescent orangutans responded by increasing their monthly ranging area during this time of high fruit availability and decreased their range when fruit vailability was low. Adolescent orangutans often used areas in their monthly range that had a high to medium abundance of fruit trees. When the number of trees bearing fruit decreased (low period), adolescent orangutans changed their monthly range to areas that consisted of mediu

Innovative behaviors in wild Bornean orangutans revealed by targeted population comparison

The aim of this study was to assess whether geographic variation in wild orangutan behavior reflected the presence of innovations or merely variation induced by genetic or environmental differences. We improved upon previous attempts to answer this question in three complementary ways. First, to minimize the possible effects of differences in genetic composition or the physical, biological and social environment, we compared a population of Bornean orangutans (Pongo pygmaeus wurmbii) at a new site (Sungai Lading) with that of an established site (Tuanan). These two populations were physically separated but showed high genetic similarity and occupied very similar habitats, leaving different innovation histories as the only plausible source of significant differences in their behavioral repertoires, if these were found. Second, we used identical observation methods and overlapping observers at both sites, deliberately attempting to record the full behavioral repertoire. Third, we introduced statistical techniques to reduce the likelihood of false absences. The results showed several behavior patterns unique to the new site, as well as the absence of several patterns observed at the established site, most of them satisfying the criteria previously proposed for recognizing innovations. We, thus, confirm that orangutans produce behavioral innovations, and conclude that the geographic method for identifying innovations in wild populations is a valid, albeit conservative, approach that can complement other techniques. Finally, the results also strongly support a cultural interpretation of geographic variation in orangutan behavior

Individual variation and plasticity in the infant-directed communication of orang-utan mothers

Between-individual variation in behavioural expression, such as social responsiveness, has been shown to have important eco-evolutionary consequences. However, most comparative research on non-human primate communication has focused on species- or population-level variation, while among- and within-individual variation has been largely ignored or considered as noise. Here, we apply a behavioural reaction norm framework to repeated observations of mother–offspring interactions in wild and zoo-housed orang-utans (Pongo abelii, P. pygmaeus) to tease apart variation on the individual level from population-level and species-level differences. Our results showed that mothers not only differed in the composition of their infant-directed gestural repertoires, but also in communicative tactics, such as gestural redoings (i.e. persistence) and responsiveness to infants' requests. These differences remained after controlling for essential moderators, including species, setting, parity and infant age. Importantly, mothers differed in how they adjusted their behaviour across social contexts, making a strong case for investigating within-individual variation. Our findings highlight that partitioning behavioural variation into its within-individual, between-individual and environmental sources allows us to estimate the extent of plastic responses to the immediate environment in great ape communication

Multicomponent and multisensory communicative acts in orang-utans may serve different functions

From early infancy, human face-to-face communication is multimodal, comprising a plethora of interlinked communicative and sensory modalities. Although there is also growing evidence for this in nonhuman primates, previous research rarely disentangled production from perception of signals. Consequently, the functions of integrating articulators (i.e. production organs involved in multicomponent acts) and sensory channels (i.e. modalities involved in multisensory acts) remain poorly understood. Here, we studied close-range social interactions within and beyond mother-infant pairs of Bornean and Sumatran orang-utans living in wild and captive settings, to examine use of and responses to multicomponent and multisensory communication. From the perspective of production, results showed that multicomponent acts were used more than the respective unicomponent acts when the presumed goal did not match the dominant outcome for a specific communicative act, and were more common among non-mother-infant dyads and Sumatran orang-utans. From the perception perspective, we found that multisensory acts were more effective than the respective unisensory acts, and were used more in wild compared to captive populations. We argue that multisensory acts primarily facilitate effectiveness, whereas multicomponent acts become relevant when interaction outcomes are less predictable. These different functions underscore the importance of distinguishing between production and perception in studies of communication