Since the 1970s, researchers have known that male chimpanzees defend
group territories, and that fights between groups can be deadly.
But what triggers these fights? Do chimpanzees go looking for trouble? Do they get into fights over mates or over some other resource, such as food? And when they do meet the neighbors, what determines whether they fight or flee? Are they more likely to respond aggressively if they are defending mates, or young infants, or food? Or does strength in numbers matter more?
A study that appears in this month’s issue of the journal Animal Behaviour sought answers to these questions using 15 years of behavioral and ecological data collected on Kanyawara’s chimpanzees. The study, led by Michael Wilson, found that intergroup encounters occurred most often when key foods attracted chimpanzees into border areas. Once Kanyawara chimpanzees detected their neighbors, though, their response depended mainly on strength in numbers, rather than the presence of food resources or
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