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Tortoise meat is supposedly so delicious it has led people to eat some species to extinction. Evidently chimpanzees enjoy it too, as a group of these apes has figured out how to crack open tortoise shells to eat the meat within.

The chimps in question live in Loango National Park in Gabon, west Africa. They have only got used to humans within the last three years, so little is known about their behaviour.

Between 2016 and 2018, Tobias Deschner at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany and his colleagues observed 38 incidents of chimps trying to eat , all but four of them successful.

When a chimp found a tortoise, it picked it up and started hitting its underside – which is softer than the tough shell on its back – against a hard surface like a tree trunk. Once the tortoise had been cracked open, the chimp climbed into a tree to eat it.

On one occasion, the group’s alpha male ate half a tortoise, then wedged the remainder into the fork of a tree and slept overnight in a nearby nest. He then returned the next day and ate the rest.

The chimps only ate tortoises during the main dry season from May to October, when other food was plentiful. The tortoises may simply be easier to find then, says Deschner. “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 says.

Other groups of chimpanzees have devised other tools, such as using sticks to “fish” for termites and spear bush-babies, and using moss as a sponge to drink water.

It is not clear why chimps in other groups, some of them studied for decades, do not eat tortoises. The reptiles are widespread in Africa, so availability is not the issue.

Loango chimps already have a practice of breaking open hard nuts, which they could have adapted for the tortoises. “I think it’s just a cultural behaviour,” says Deschner. “At one point one individual comes up with a way to do it, and then others copy this behaviour, and then it spreads through the group, because it allows them access to meat that otherwise would not be available.”