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.

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.

No abstract

As climate change continues to fundamentally alter resource landscapes, the ability to flexibly respond to spatio-temporal changes in the distribution of preferred food sources is increasingly important for the overall health and fitness of animals living in seasonal, variable, and/or changing environments. Here, we investigate the effects of an uncharacteristically long period of fruit scarcity, following widespread thick haze caused by peat and forest fires in 2015, on the behaviour and sociality of female Bornean orangutans (Pongo pygmaeus wurmbii). We collected data from 2010 to 2018 at Tuanan, Central Kalimantan, Indonesia, and compared the activity, diet, and association patterns of adult females during low-fruit periods before the fires, i.e., regular, seasonal periods of low fruit availability (“pre-fire”), and after the fires, i.e., during the extended period of low fruit availability (“post-fire”). First, we found that, post-fire, female orangutans adopted a more extreme energy-saving activity pattern and diet — resting more, travelling less, and diet-switching to less-preferred foods — compared to pre-fire. Second, we found that the probabilities of association between females and their weaned immature offspring, and between related and unrelated adult females were lower, and the probability of agonism between unrelated females was higher, post-fire than pre-fire. This change in energetic strategy, and the general reduction in gregariousness and social tolerance, demonstrates how forest fires can have lasting consequences for orangutans. Fission–fusion species such as orangutans can mitigate the effects of changes in resource landscapes by altering their (sub)grouping patterns; however, this may have long-term indirect consequences on their fitness.