A group may seemingly go far out of its way to avoid contact with another group. Intragroup relations seem to be much more cohesive in the gorilla than in the chimpanzees. In his study area in the Virunga Volcanoes region, group size ranged from 2 to 30 individuals. If there is more than a single adult male, one is dominant and is the leader of the group, and only that one normally breeds. There is a general rank order for the group, based mainly on size, with silverback males being dominant over all other animals.
Groups are highly stable, and the dominant male retains leadership for years.
Unlike the situation in most primates, nearly all female gorillas emigrate from their parental group at maturity. These include roars and growls of aggression, grunts and barks for group coordination, and loud hoots that can be heard 1 km away by people and may serve to space different groups. Schaller also described the elaborate chest-beating display that may be elicited by the presence of outsiders, either other gorillas or humans. It begins with a series of hoots, after which the animal stands on two legs and alternately slaps its chest with slightly cupped hands 2-20 times. The gorilla then runs about and breaks vegetation.