Ecological and social factors affect the occurrence and outcomes of intergroup encounters in chimpanzees

► Male chimpanzees defend group territories and sometimes kill their neighbours. ► Food, not females, determined when intergroup encounters occurred. ► Chimpanzees travelled to danger zones when food was more abundant there. ► Chimpanzees responded more aggressively when they had more adult males. ► In decisions to escalate a contest, females, infants and food did not matter as much as strength in numbers.