In local parlance, the great apes of the Bili Forest fall into two distinct groups. There are the “tree beaters”, which disperse high into the trees to stay safe, and easily succumb to the poison arrows used by local hunters. Then there are the “lion killers”, which seldom climb trees, are bigger and darker, and are unaffected by the poison arrows.
When Karl Ammann, a Swiss photographer and anti-bushmeat campaigner, first visited the region in 1996, he was looking for gorillas, but instead discovered a skull that had dimensions like that of a chimpanzee, but with a prominent crest like that of a gorilla. Ammann purchased a photograph, taken by a motion-detecting sonar cone, from poachers that captured an image of what looked like immense chimpanzees. Ammann also measured a fecal dropping three times as big as chimp dung and footprints as large as or larger than a gorilla’s.
In 2000, Ammann returned to the area described by the bushmeat hunter with a group of ape researchers. Although they did not find a live Bili ape, they did find several well-worn ground nests, characteristic of gorillas rather than chimpanzees, in swampy river beds. ~Wiki