The apes were seen smashing hinge-back tortoises’ shells against tree trunks to kill them and to enable them to access the meat, which is high in protein, vitamins and fats.
The behaviour was recorded by a team of German scientists over a two year period in Gabon, west Africa. They also observed the chimps sharing the tortoise meat and one on occasion storing pieces of the carcass in a tree trunk for later consumption.
In some instances they transported the living tortoises for several minutes in order to bring them to a suitable tree upon which to crack them open.
“Storing food and later on retrieving it is an indication that the animals are able to plan into the future," said Tobias Deschner, a primatologist at the Max Planck Institute for Evolutionary Anthropology in Germany. “This is a trait that has long been claimed to exist only in humans [among primates].
He added: “The fact that we saw this happening exactly in a situation while feeding on a tortoise and while no other group member was close by, indicates to me that we may sometimes underestimate the mental capacities of certain animals species.”
Until the early 1960s it had always been thought chimpanzees only ate fruits, seeds, nuts, flowers and leaves.
But chimpanzees – the closest living relative of homo sapiens – are now known to be omnivorous like us.
Reporting the latest evidence in the journal Scientific Reports, the team said tortoise hunts happened regularly during the two years they observed the wild chimps.
Between July 2016 and May 2018, they witnessed 38 attacks by 10 different male individuals – of which 34 were successful.
The finding was described as “unprecedented” by another of the study’s authors, professor Simone Pika, a cognitive scientist at the University of Osnabruck.
She said: “Tortoise predation was observed frequently in most or all of the studied adult chimpanzee males. It consisted of a distinct sequence of behaviours involving the discovery of the prey, followed by smashing the tortoise shell with one hand against a hard surface, such as a tree trunk.
“The chimpanzees then climbed a tree to consume the meat. In one instance, they even stored it.”
She added: “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.”
In 23 of the cases, the food was shared with other group members, including those who had previously attempted to open the tortoise shell but not succeeded.
Professor Pika said: “The most frequent behavioural sequence consisted of discovering and capturing the prey, smashing the shell with one hand repeatedly against a tree trunk and climbing into a tree to consume the meat. In six cases, the chimpanzee first transported the tortoise between 10 to 50 metres on the ground, for a duration of one to eleven minutes, before smashing it.”
Chimpanzees are listed as an endangered species, and in west Africa where this population was observed they increasingly face threats to their long term survival.
These include risks from disease, habitat loss, illegal poaching, and conflict with people competing for resources.
West Africa already has one of the most fragmented tropical forest landscapes in the world due to high levels of deforestation. The majority of chimpanzees in this part of Africa remain particularly vulnerable as they live outside protected areas.
Hinge-back tortoises are native to Africa and are so-called because of a 90 degree hinge at the lower part of their shell, which when closed can protect the animals’ rear legs and tail from predators.
Animals known to prey upon hinge-backs include hawks, eagles and leopards. It is threatened by humans as shells are prized in illegal international trade, but it is not endangered.
Additional reporting by SWNS
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