Chimpanzees at the Loango National Park in Gabon have recently become habituated to human researchers—a gradual process that can take several years. While gathering data on this newly accessible population, a team of scientists observed the chimps chowing down on an unusual snack: tortoises.
It was the first time that the animals had been documented eating any type of reptile. What’s more, in order to access their hard-shelled prey, the chimps would bash the tortoises against a tree—yet another sign that they use “percussive technology,” the researchers write in Scientific Reports.
Chimps have been know to crack other kinds of food—like nuts and snails—but this behavior is rare, reports Douglas Main of National Geographic. Among the chimps of Loango National Park, however, smashing open tortoises seems to be a relatively regular occurrence. The researchers documented 38 “prey events,” 34 of which were successful. After spotting and capturing a tortoise, the chimps would typically hit the underside of the shell against a tree trunk using one hand, and then climb into a tree to eat the exposed flesh.
For the most part, it was adult male chimpanzees that successfully cracked the tortoise shells, probably because a certain amount of strength is necessary for getting through the prey’s tough exterior. Interestingly, two females and one juvenile that were unable to get the shells open received help from another member of the group. The “successful openers” then shared the meet with their less fortunate buddies. Sharing was, in fact, a common occurrence; the researchers observed 23 instances of tortoise meat being passed around among members of the group.
The behavior of one adult male was particularly intriguing. After he cracked open his tortoise, he ate half of it while sitting in a tree, then stashed the other half in a tree fork. The next morning, he returned to the tree to finish his snack—suggesting that he was planning for the future. To date, signs of future planning have only been documented in captive animals, says Simone Pika, first author of the study and a cognitive scientist at the University of Osnabrück in Germany.
“Many scholars still believe that future-oriented cognition is a uniquely human ability,” Pika elaborates. “Our findings thus suggest that even after decades of research, we have not yet grasped the full complexity of chimpanzees’ intelligence and flexibility.”
The chimps were only seen eating tortoises in the dry season from May to October. It’s not entirely clear why because plenty of other food sources are available during this period, but Tobias Deschner, study co-author and primatologist at Max Planck Institute for Evolutionary Anthropology, thinks it might be easier for the chimps to hear the tortoises rustling around.
“During the dry season the leaves are really dry, and then it’s amazing how much noise a tortoise can make just by moving around,” he tells Michael Marshall of New Scientist.
Why tortoise consumption has never been seen among other chimpanzee groups is another interesting question. The two animals may not always overlap in habitat, the study authors note. And chimps in other communities may be able to get sufficient meat from non-tortoise sources. But it is also possible, according to the researchers, that tortoise-bashing behavior is cultural—meaning that it is population specific and acquired through social learning.
It has previously been shown, in fact, that chimpanzees have local traditions. Neighboring chimp communities in Uganda, for instance, rely on different tools to extract honey from fallen logs; some use sticks, while others use masticated leaves to sop up the tasty snack. But due to factors like population decline and climate change, chimp culture is in trouble. A recent study found that chimps living in areas with high degrees of human impact were 88 percent less likely to display socially learned behaviors than those that do not.
Researchers are keen to study chimp behavior not only to better understand these fascinating animals, but also to gain further insight into our own ancestors. "As one of our closest living relatives, the study of chimpanzee behaviour is a window into our own history and evolution," says Pika. "To prevent this window from closing once and for all, we need to do whatever we can to secure the survival of these fascinating animals in their natural habitats across Africa."