When it comes to territory, chimpanzees are ruthless. Chimp coalitions will kill and sometimes cannibalize their neighbors to expand their community’s real estate, according to a study published in the June 22 issue of Current Biology.
This study provides “the first clear-cut, direct evidence that killings in a particular area of the territory periphery lead to territory expansion,” study co-author Sylvia Amsler, an anthropology lecturer at the University of Arkansas at Little Rock, wrote in an e-mail.
For a decade, Amsler and her co-authors — John Mitani of the University of Michigan and David Watts of Yale University — observed the behaviors of a wild chimpanzee community living in Uganda’s Kibale National Park.
As part of their research, the scientists followed gangs of primarily male chimps on reconnaissance missions into neighboring territories. The chimps moved silently in single file along their neighbors’ borders. When they encountered rivals, they employed one of two options: retreat or attack. If they were not obviously more powerful, the patrollers would mouth off, calling loudly at their opponents, as they withdrew. If they had the upper hand, however, things often turned deadly.
Patrollers attacked by jumping on and beating the victims; they also bit and tore at the rival chimps as if they were prey. Protruding body parts, such as testes and ears, were particularly vulnerable, Amsler said. Sometimes infants were killed, then eaten after the battle. Males were the usual fighters, as the few female patrollers usually stood on the sidelines. Researchers witnessed 18 of these lethal attacks; they inferred three other violent deaths from circumstantial evidence.
Once chimps conquered their neighbors, they claimed the land, Amsler said. “Observations suggest that chimpanzees benefit from their territorial activities because they are able to acquire land from neighbors that they regularly and successfully defeat in intercommunity conflicts,” she wrote.
Findings also suggest that an enlarged chimp domain has reproductive benefits: more food and possibly more mates. Scientists still don’t have clear evidence, however, whether the size of the territory correlates with more opportunities for males to meet and attract females.