Chimpanzees in Guinea and the forests of Liberia have been observed picking up stones and throwing them at a tree as well as placing them gently at the base - behaviour that appeared to serve no purpose and could be evidence of "ritualistic behaviour" in animals.
"What we saw on this camera was exhilarating – a large male chimp approaches our mystery tree and pauses for a second. He then quickly glances around, grabs a huge rock and flings it full force at the tree trunk," said Laura Kehoe, PhD researcher at Humboldt University of Berlin.
The German primatologist, whose team discovered the odd behaviour, said that the practice "could be a ritual ... This would be the first evidence of ritualistic behaviour in animals."
In a paper published in the journal Nature Scientific Reports the researchers suggested two possible explanations: "The behaviour could be part of a male display" or "it could be more symbolic than that."
In the first case the loud noise made by the rock hitting a tree could "add to the impressive nature of a display".
One of the other videos that were sent in by other groups working on the Pan African Programme, however, showed a chimp placing, rather than throwing stones inside the hollow tree.
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