Strategy, not habitat loss, leads chimps to kill rivals

Human impacts on the apes have not increased their violence

Chimpanzee male named Titan

BAD DUDE  Chimpanzee males, such as Titan shown here, kill stray members of nearby communities whom they perceive as rivals for food and mates, a new study finds.

Ian Gilby

Foraging chimpanzees gang up on and kill stray members of nearby chimp communities to eliminate competitors for food and mates, whether or not people have intruded on the animals’ territories, an international team of primatologists says.

Chimps have not killed each other over dwindling resources as loggers have cut down the apes’ forest homes, report anthropologist Michael Wilson of the University of Minnesota in Minneapolis and his colleagues in the Sept. 18 Nature. Neither have chimps turned homicidal when a few have chanced upon animals given bananas by human tourists, they find. 

chimp patrol in line
LETHAL WEAPONS Male chimps patrol their territory in single file. Chimps from other communities who encounter a patrol can end up dead if they’re seen as competitors for vital resources, field data suggest. John Mitani

The scientists examined information collected over the last 50 years from 18 communities of common chimps, Pan troglodytes, and four bonobo communities. Bonobos, Pan paniscus, are a generally peaceful chimp species. In 15 common chimp communities, Wilson’s group documented 152 killings that were observed, inferred from obvious wounds such as bites on dead bodies or suspected due to other wounds or an animal’s sudden disappearance. Just one suspected killing occurred among bonobos.

Killings clustered in communities with high numbers of males and relatively large populations. Males were the most frequent attackers and victims. The most violent community inhabited a largely undisturbed area, whereas another exposed to intense logging and tourism experienced no killings. The new study fits the idea that lethal clashes, along with social graces, have a long pedigree in chimps and humans (SN: 8/10/13, p. 10).

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