Introduction Crowding has been viewed as a cause of aggression in socially housed animals.
Severe aggression is limited but rates of mild aggression increase.
Chimpanzees in a well-established group also inhibit social behavior when crowded into a familiar area. All adult social activity, including allogrooming, submissive greeting, and various forms of agonistic behavior, decrease under high-density conditions. All social behaviors between adults, including aggression and social grooming, will decrease progressively as density increases. Tension will increase with increasing population density as reflected by rates of self-grooming. Other behaviors to be investigated included contact-sitting and juvenile play behavior.