Vocal consensus building for collective departures in wild western gorillas

The ability to coordinate actions is of vital importance for group-living animals, particularly in relation to travel. Groups can only remain cohesive if members possess a cooperative mechanism to overcome differences in individual priorities and social power when coordinating departures. To better understand how hominids achieve spatio-temporally coordinated group movements, we investigated vocally initiated group departures in three habituated groups of western gorillas ( Gorilla gorilla ) in the Central African Republic. The large sexual dimorphism of gorillas has led to the untested assumption that the silverback males are the sole decision-makers in gorilla groups, although there are also observations that suggest otherwise. To address this, we analysed the direction and timing of group departures and found that high-ranking individuals (silverbacks and high-ranking females) were more successful in indicating the direction of future travel than others, but that the timing of departure was the apparent result of a cumulative vocal voting process among all adult group members. Our findings illustrate that even in species with a large sexual size dimorphism, travel decisions can be taken collectively via a consensus-building process.