Dinner on the half-shell: chimps eat tortoises

Chimpanzees are handy with tools, but it appears they also resort to brute force when needed.

German researchers have discovered that they prey on tortoises, smashing them against a hard surface such as a tree to break the shell, or plastron, and get at the meat – which they then often share.

This sheds new light, the researchers say, on the “percussive technology” chimpanzees (Pan troglodytes) use to open food items such as nuts, hard-shelled fruit and snails, as well as on their large and flexible cognitive abilities.

The apes were previously known to hunt and consume the meat of various animals, but until now there have been no direct observations of tortoise predation.

Between July 2016 and May 2018, a team led Simone Pika from the University of Osnabrück in Germany watched a group of wild chimpanzees of the Rekambo community, living in the Loango National Park in Gabon, West Africa.

They observed 38 events involving 10 different chimpanzees preying on hinge-back tortoises (Kinixys erosa), 34 of which were successful. 

In 23 cases, the food was shared with other group members, including those who had previously attempted to open the tortoise shell but not succeeded. {%recommended 6028%}

“The behaviour is frequently shown by the majority of adult males of the Rekambo community, thereby qualifying as customary,” Pika and colleagues write in a paper in the journal Scientific Reports.

“In addition, we report on a single case of food storage, in which an adult male tucked a half-eaten tortoise in a tree fork and retrieved it the next day to continue feeding.” 

All predation events were observed in periods of high fruit availability and in the dry season.

The researchers, who included anthropologists and cognitive scientists, noted a distinct sequence of behaviours involving the discovery of the prey, followed by smashing the plastron with one hand against a hard surface, then climbing a tree to consume the meat.

It’s an adult activity, however. In the two cases where adolescents attempted to smash open a tortoise, they failed. 

“Similar to nut cracking in chimpanzees – a percussive technology which is only mastered at the age of approximately nine to 10 years – the acquisition of a successful tortoise smashing technique may rely on a certain amount of strength,” the authors write. 

“In addition, it may also involve a relatively long period of time to learn, practise and refine.”

Why tortoise predation has never been directly observed at any other long-term chimpanzee field site remains a puzzling question. 

One explanation may be lack of opportunity, the researchers suggest; the ecological niche of chimpanzees may only rarely overlap with that of hinge-back tortoises.

They also note that the site in Gabon is ecologically quite distinct from other sites, consisting of a mosaic of different habitat types varying from marine, coastal lagoons, mangrove swamps, coastal forest, secondary and primary forest to open savannah.

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