Looking beyond the great apes

To date, research on gestural communication has been largely focused on great apes, owing to their close phylogenetic proximity to humans. Yet including a broader range of species is essential for identifying evolutionary patterns and for understanding how socio-ecological conditions shape the way primates communicate. Several macaque species —including the moor macaque, a socially tolerant primate endemic to the Indonesian island of Sulawesi— had so far received very little attention.

To help close that gap, the team carried out a five-month observational study of a wild, habituated group of 27 moor macaques in the Teaching Forest of South Sulawesi. Across 148 focal video samples, they documented a repertoire of 19 distinct gesture types — combining tactile, visual and multimodal signals —used across affiliative, agonistic, play and sexual interactions, and recorded close to 800 gestures in total.

"Most of what we know about primate gestures comes from great apes," explains Miquel Llorente, co-author of the study and researcher at the University of Girona. "Studying an Endangered Sulawesi macaque directly in the wild lets us test how widely these communicative abilities are shared across the primate family —and the moor macaque turned out to be a remarkably good model."

The social moment matters more than who you are

The core of the research examined what drives the way moor macaques gesture. The animals communicated predominantly in the visual modality, and — contrary to patterns reported in many other primates — neither age nor sex predicted variation in their gestural repertoire, their reliance on different modalities, their attention to the recipient, or their success in eliciting a response.

What did matter was the immediate context. Visual gestures were far more likely when the group was resting than when it was on the move, when stable spatial arrangements make eye contact easier. Signallers were also more likely to take the recipient's visual attention into account during calm, affiliative interactions than in higher-arousal contexts such as play, aggression or sex. And gestures were more likely to get a response during affiliative and agonistic exchanges than during sexual ones, with visual gestures proving more effective than tactile ones.

"What stands out is that neither age nor sex predicted how these macaques gestured —what mattered was the immediate social situation," says Miquel Llorente. "It suggests that, in this species, communication is shaped moment to moment by the context rather than by stable individual traits. That is a different picture from the developmental story we often see in great apes, and it points to social and ecological pressures as key drivers of how primates signal." — Miquel Llorente

This pattern fits the biology of the species. Moor macaques are highly socially tolerant and maintain richly differentiated relationships with relatively loose dominance hierarchies, so a flexible, context-sensitive communication system is exactly what one might expect.

Scientific impact and future directions

By documenting this behaviour, the Comparative Minds group expands the comparative database on primate gestural communication and reinforces macaques as valuable models for understanding how context shapes the way primates signal. The findings also carry a conservation message: the moor macaque is listed as Endangered by the IUCN, with a declining population, and this is among the first systematic descriptions of its communication.

The authors are careful to frame the results as preliminary, given the relatively small, single-group sample and the short study period. Future work — across multiple groups, over longer periods, and integrating gestures with vocalisations and facial behaviour — will be needed to build a fuller picture of how these primates communicate. Even so, the study takes a clear step towards mapping the communicative building blocks that, across the primate lineage, may underpin the social complexity that eventually gave rise to human language.

Reference: Martínez Rubio, V., Maulany, R. I., Ngakan, P. O., Liebal, K., Llorente, M., Serres Peralta, G., Majolo, B., & Amici, F. (2026). Gestural Communication in a Wild Population of Moor Macaques (Macaca maura) in South Sulawesi. International Journal of Primatology. https://doi.org/10.1007/s10764-026-00572-z