As omnivorous creatures, chimpanzees eat all sorts of things, including fruits, termites, tiny rodents and even fully grown monkeys. As for chimps eating reptiles, that’s completely unheard of – until now. Unprecedented observations have uncovered a community of chimps in Gabon that regularly consume tortoises.
New research published last week in Scientific Reports describes the first observations ever made of chimpanzees preying upon and eating tortoises. The previously unseen behaviour expands the known dietary repertoire of chimps, while casting new light onto chimpanzee intelligence and their remarkable capacity for prosocial behaviours.
Tortoises have a robust defence against predators in the form of their thick, hard shells. But these wild chimps, which were observed in Gabon’s Loango National Park, devised a rather ingenious solution. Armed with their primate brains and dextrous hands, the chimps smashed the tortoises against tree trunks until the shells broke. Once the tortoise was cracked open, the chimps consumed the exposed meat with relish.
The lead authors of the new study, Simone Pika from the University of Osnabrück and Tobias Deschner from the Max Planck Institute for Evolutionary Anthropology, described this shell-smashing behaviour as “percussive technology”.
“We have known for decades that chimpanzees feed on meat from a variety of animal species, but until now the consumption of reptiles has not been observed,” said Deschner in an Max Planck Institute release. “What is particularly interesting is that they use a percussive technique that they normally employ to open hard-shelled fruits to gain access to meat of an animal that is almost inaccessible for any other predator.”
Chimp with tortoise. Image: Nadia Balduccio
Chimps eat a surprising variety of prey, including several species of monkeys (even baboons), red duikers (a small antelope), bushpigs and various rodents. We can now add reptiles to the list, namely hinge-back tortoises (Kinixys erosa).
The scientists observed the Rekambo population of chimps from July 2016 to May 2018, but the tortoise-eating behaviour was only seen during the dry season. This dietary choice may have had something to do with the availability of food, but as the authors pointed out in the study, fruit is in abundance during the dry season. The specific timing of this behaviour remains a mystery, and something worthy of future research.
As to why tortoise-eating has only been seen in the Rekambo population and not others is another mystery to be solved. That said, the behaviour appears to be cultural (as opposed to instinctual), with the chimps learning from each other and retaining the practice over time.
“It is too early to claim this, but the fact that tortoises exist at several other field sites where chimpanzees have been observed for decades and predation on them has never been observed is a first hint that indeed this might be a cultural trait,” explained Deschner in an email to Gizmodo. “To prove that social learning is the source of [cultural] transmission is difficult to show, but again, given the absence of this behaviour in other populations suggests that most probably, this behaviour was once invented by one individual in this population and then spread via observation and copying of the behaviour, which is social learning.”
Two chimps feeding on a tortoise. Image: Nadia Balduccio
In total, 10 different chimps were seen consuming tortoise meat: seven adult males, one adult female, one adolescent male and one adolescent female. Of the 38 predation events observed, 34 were successful (a failed attempt was an inability to access tortoise meat). The majority of the male population engaged in this dietary practice, making it a normal or 'customary' behaviour in the words of the researchers.
Here’s what a typical feeding session looked like. After a chimp discovered and captured a tortoise, it repeatedly smashed its plastron, or shell, against a tree trunk. The chimp then climbed up into a tree to consume the meat.
As if eating tortoises wasn’t remarkable enough, the researchers documented several other intriguing behaviours associated with the practice.
First, the “percussive technology”, in which the tree trunk was used as an anvil, can be construed a precursor to tool use in primates. This behaviour, therefore, may be a glimpse into our ancient past.
Second, some chimps weren’t strong enough to break open the shells with their hands, so they handed the tortoises over to a stronger male. Remarkably, the male smashed the shells and willingly shared the meat with others. In total, 23 of the 38 events involved sharing of some sort. This prosocial behaviour demonstrates the emotional complexity of chimps, and possibly even the consideration of needs of others. That said, Deschner said that sharing doesn’t necessarily tell us anything interesting about the social intelligence of animals, but rather the quality of their social relationships.
“Although we still have not enough detailed data to analyse the sharing patterns in detail, it seems that the Loango chimpanzees share tortoise meat very frequently and without harassment,” Deschner said, “indicating that high-ranking individuals do not use their force to acquire the meat via aggression and that the possibility exists that meat is exchanged for other services, [such as] grooming, [and] support in conflicts with other group members.”
Finally, one male was observed to store his food – a behaviour typically ascribed to early hominins (humans and related species since the split from the last common ancestor shared with chimpanzees). This male, after eating about half of the tortoise meat, hid the remainder into the fork of a tree. The chimp then relocated to a different tree where he built a nest and called it a night. The next day he returned to the tree to retrieve and consume the remaining parts of the tortoise. This behaviour certainly appears like foresight, in which the chimpanzee established conditions in the present to help out his future self. As the authors noted in the study, this cognitive trait may have emerged in early primates prior to the evolutionary split of hominin and chimpanzee ancestors.
For Deschner, this finding was of special importance because it highlighted a previously unknown behaviour in a chimpanzee population that’s located quite far from any other group of well-studied chimps.
“We always find new behaviours – some of them cultural ones – that have never been observed before,” Deschner told Gizmodo. “This means though that when we lose chimpanzee populations due to habitat destruction and poaching, we do not only lose a number of individuals that might later on be replaced again, but we lose unique cultures which will be lost forever, and by this we close one window after the other that would allow us to study aspects of our own evolution.”
Featured image: Erwan Théleste