Chimpanzees in Senegal have been observed making and using wooden spears to hunt other primates, according to a study in the journal Current Biology.
Researchers documented 22 cases of chimps fashioning tools to jab at smaller primates sheltering in cavities of hollow branches or tree trunks.
The report's authors, Jill Pruetz and Paco Bertolani, said the finding could have implications for human evolution.
Chimps had not been previously observed hunting other animals with tools.
Pruetz and Bertolani made the discovery at their research site in Fongoli, Senegal, between March 2005 and July 2006.
"There were hints that this behaviour might occur, but it was one time at a different site," said Jill Pruetz, assistant professor of anthropology at Iowa State University, US.
"While in Senegal for the spring semester, I saw about 13 different hunting bouts. So it really is habitual."
Chimpanzees were observed jabbing the spears into hollow trunks or branches, over and over again. After the chimp removed the tool, it would frequently smell or lick it.
In the vast majority of cases, the chimps used the tools in the manner of a spear, not as probes. The researchers say they were using enough force to injure an animal that may have been hiding inside.
However, they did not photograph the behaviour, or capture it on film.