Mandrill is the fifth species of monkeys that appear to modify the tool. Apes, including chimpanzees and orangutans, can adjust the basic tools for specific jobs.
"This is a capability, which until a few years ago considered uniquely human," said Dr. Riccardo Pansini, who led the research.
Pansini make a recording while studying the relation of pressure and mandrill's behavior at the zoo. In the tape, a big male mandrill takes twigs and modify it to scrape dirt from under fingernails.
"Mandrill also seen cleaning the ear with a modification in the wild. This is thought to help prevent ear infections," Pansini said.