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Expressive Faces in Social Interactions Held Rhesus Macaques’ Attention Longer

Rhesus macaque at Punta Santiago, Puerto Rico
Research · Behaviour

An experiment with 81 rhesus macaques (Macaca mulatta) on Cayo Santiago, Puerto Rico, found that facial expression and social context jointly influenced how long the animals watched other macaques. The researchers presented pairs of male macaque avatars while the subjects were free to look at the images.

The two faces either looked towards one another, creating the appearance of a social interaction, or faced away from each other. They also showed either neutral expressions or social expressions — a threat face or a silent bared-teeth display. The researchers measured total looking time and how often the observing macaques shifted their gaze between the two faces.

The macaques looked significantly longer at expressive faces presented within an apparent social interaction than at neutral faces shown in a noninteracting configuration. Gaze-shift frequency did not differ significantly among conditions, although there was a tendency towards more shifts in trials with expressive faces.

The authors interpret the result as evidence that rhesus macaques attend not only to the expression on another individual’s face but also to the social setting in which that expression appears. Observing third-party facial interactions may therefore provide information about relationships and ongoing social events without the observer taking part directly.

Sources and image credit

  1. O’Callaghan, O., Whitehouse, J., Rees, K., & Waller, B. M. (2026). Direction and expressivity of faces impact third-party social attention in rhesus macaques. Animal Behaviour, 233, 123492. https://doi.org/10.1016/j.anbehav.2026.123492Primary peer-reviewed open-access article published online 19 February 2026 under CC BY 4.0. Eighty-one semi-free-ranging rhesus macaques on Cayo Santiago viewed paired male macaque avatars varying in direction and facial expressivity; looking time was significantly longer for expressive faces in an apparent interaction than for neutral, noninteracting faces.

Image: Geoff Gallice — rhesus macaque (Macaca mulatta) at Punta Santiago, Puerto Rico, 19 January 2012; representative Puerto Rico image, not an animal from the Cayo Santiago experiment. Source: Wikimedia Commons. · CC BY 2.0 — https://creativecommons.org/licenses/by/2.0/ · Source

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