Chimpanzees have been caught on camera tucking into an unusual snack, tortoises, whose hard shells they crack against tree trunks before scooping out the meat.
A new study, published in the journal Scientific Reports, describes how a group in Loango National Park in Gabon smashed the shells of the reptiles before climbing up trees to enjoy their snack.
The chimpanzees hunting tortoises were mainly male and used a "distinct smashing technique", according to the researchers.
They said the technique displayed by the chimpanzees provides "further support for their exceptionally large and flexible cognitive tool kits".
While chimpanzees are known to hunt other animals, it is believed to be the first time they have been observed preying on tortoises.
The researchers, from the University of Osnabruck and Max Planck Institute for Evolutionary Anthropology in Germany, spotted the behaviour in the Rekambo chimpanzee community between July 2016 and May 2018.
They observed 10 animals hunting hinge-back tortoises, which are native to Africa, on 38 occasions, 34 of which were successful.
The tortoise meat was shared with other chimpanzees, including those who had been unsuccessful in opening the shell, a total of 23 times.
"In the two cases where adolescent chimpanzees attempted to smash open a tortoise, they were unsuccessful," the authors wrote.
"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.
"In addition, it may also involve a relatively long period of time to learn, practise and refine."
Similar smashing techniques have been observed in the species to get into nuts and hard-shelled fruits.