For group-living animals, staying together is vital for survival. If members cannot agree on when or where to move the group may split, putting individuals at risk. To prevent this, group members typically reach a consensus before setting off. However, the process and the participants involved in these decisions vary across species.

We wanted to understand how such coordination unfolds in a highly intelligent species. Our focus was on wild western gorillas, one of our closest relatives. These gorillas live in stable family groups, usually led by a dominant silverback male and composed of several adult females and their offspring. Silverbacks are about twice the size of females and provide protection, leading to the assumption - supported by previous observations on mountain gorillas - that males dominate group decisions, particularly when it comes to initiating movement.

We revisited this assumption in western gorillas, a species more reliant on fruit than their mountain-dwelling relatives. Because fruit sources are patchy and variable, locating them requires considerable ecological knowledge. To explore how travel decisions are made, we studied three habituated groups in the Dzanga-Sangha Protected Areas, managed collaboratively by the government of the Central African Republic and the World Wide Fund for Nature.

Our research revealed that travel decisions were typically made collectively, with most or all adult group members participating. These decisions involved coordinating both the timing and direction of movement. Grunt-like vocalisations played a crucial role in the process. We found that while high-ranking individuals - regardless of sex - had more influence over the direction of travel, the timing of departures was shaped by any individual who signalled their intent using vocal cues.

Despite the significant size difference between males and females, our findings show that western gorillas use a consensus-based process to decide when and where to travel.

Lara Nellissen, Terence Fuh, Klaus Zuberbühler and Shelly Masi

Original publication
Nellissen, L., Fuh, T., Zuberbühler, K. & Masi, S. (2024): Vocal consensus building for collective departures in wild western gorillas. Proceedings of the Royal Society B 291: 20240597