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
amongst 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.