# Social engagement modulates wild monkeys’ vocal expressions and the behavioral response to that of others

## TL;DR

Wild gelada monkeys change their yawn vocalizations based on social context, and their responses to others' yawns depend on their own social engagement.

## Contribution

The study reveals context-dependent modulation of gelada yawns and how social engagement influences their contagiousness.

## Key findings

- Gelada yawns vary acoustically depending on the social context in which they are produced.
- Monkeys pay more attention to yawns that occur in social contexts compared to non-social ones.
- Yawn contagion is higher when geladas are engaged in positive social behaviors like grooming.

## Abstract

Animal vocal communication relies on the dynamic interaction between emitter and receiver, with signals shaped within a social and embodied context. To fully understand how such interactive processes operate, we used yawn vocalizations of geladas (Theropithecus gelada), a species showing exceptional yawning variability. We first examined yawn calls produced in three contexts: high-intensity social, low-intensity social, and non-social context and found clear acoustic differences among them, revealing context-dependent modulation in a typically stereotyped behavior. We conducted field playback experiments exposing wild geladas to unfamiliar male yawn vocalizations emitted in the three contexts. During playbacks, monkeys gazed more at the loudspeaker when yawns originated from a social rather than a non-social context, indicating that animals perceive the stimuli’s differing nature. Although yawn responses did not vary across contexts, contagion was higher when geladas were grooming during test, suggesting that positive social engagement enhances, rather than reduces, susceptibility to contagion.

•Gelada yawns vary acoustically across contexts, challenging their fixed nature•Geladas show greater attention to yawns in social than in non-social contexts•Yawn contagion occurs regardless of the emitter’s behavioral context•Receiver context, such as grooming, increases susceptibility to yawn contagion

Gelada yawns vary acoustically across contexts, challenging their fixed nature

Geladas show greater attention to yawns in social than in non-social contexts

Yawn contagion occurs regardless of the emitter’s behavioral context

Receiver context, such as grooming, increases susceptibility to yawn contagion

Wildlife behavior; Biological sciences; Zoology; Evolutionary biology