The Outlaw Chimps of Gishwati Forest

Slate’s animal blog.
June 17 2014 7:00 PM

The Outlaw Chimps of Gishwati Forest

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A baby chimp is not so adorable when its troop is raiding your crops.

Photo by MOHD RASFAN/AFP/Getty Images

On the edge of a forest in Rwanda, farmers have been battling thieves. These thieves often come under the cover of darkness to steal crops, so farmers play defense, standing guard all night in mosquito-infested fields and risking exposing themselves to malaria. Under normal circumstances, these thieves could be captured and made to stand trial for their crimes, but these thieves are protected by international law: They are chimpanzees.

The International Union for Conservation of Nature designates chimps as an endangered species; there are only 100,000-200,000 chimps left in the wild. Twenty of these live in the Gishwati Forest, and they have been munching on maize, beans, and peas from farmland on the perimeter of the forest for generations, according to a new paper in Human Dimensions of Wildlife. Chimps enjoy the same protein-rich foods as humans do, which leads them to seek out farmers’ crops. It makes sense that these foods would also appeal to our closest relatives; after all, humans have been working for centuries to domesticate these plants to make them tasty and highly nutritious.

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Convenience is also a factor. Why pass up an easy food source? As the study’s lead researcher, Shane McGuinness of Trinity College Dublin, puts it: “I would rather go to the supermarket than continue to hunt.” In fact, chimps aren’t the only animals that have been raiding farmers’ crops. In a series of interviews, farmers reported that Angola monkeys have also been spotted in fields, brazenly snacking until humans chase them away. Throwing stones or banging pots and pans is usually enough to scare off primates, but the chimps and monkeys are becoming desensitized to these tactics, so farmers will need to develop more extreme measures in the future.

Besides their thievery, the chimps have another interesting feature: extra fingers and toes. This is likely due to inbreeding, a byproduct of this troop’s small group size. “It’s a problem,” says McGuinness. “It’s a very small and isolated fragment of forest, and it’s a long way away from the next population of chimps.” Local conservation experts have considered planting crops between this troop of chimps and others as a bridge to encourage breeding between groups, but there’s no telling whether these crop-raiding chimps would bother making the trek when there’s a much more easily accessible food source nearby.

Meanwhile, farmers have discovered that chimps don’t like potatoes very much, so they have been planting more potato plants in place of the crops chimps love. McGuinness cites this as a triumph of community—people share this knowledge as a peaceful way to avoid further losses. Researchers are still working on estimates of just how much loot chimps are making away with, whether there may be repeat offenders, and how best to address crop-raiding. Until then, chimps are continuing to enjoy a free lunch.

Jane C. Hu has a Ph.D. in psychology from the University of California–Berkeley and is a 2014 AAAS Mass Media Fellow. Follow her on Twitter.