For the next several years civil war in the Democratic Republic of Congo made travel to the Bili forest difficult. Ammann recruited a bush meat hunter from Cameroon to visit and survey the area. The hunter returned with photographs and reports of gorilla ground nests in an area north of Bili.
In 2000, Ammann returned to the area described by the bush meat hunter with a group of ape researchers. Although they did not find a live ape, the group did stumble across several well-worn ground nests in swampy river beds.
Ground nests are characteristic of gorillas. Chimpanzees are thought to prefer to sleep in trees. However, an analysis of feces found in the nests suggests that whatever left them was eating a diet rich in fruits, a diet characteristic of chimpanzees, not gorillas.
Other evidence collected from the site includes hair samples, which have been sent out to various laboratories for DNA analysis. The initial results indicate they belong to a chimpanzee. All of this evidence is causing the researchers to believe that what Ammann has found is a chimpanzee that behaves like a gorilla.
"It is a chimpanzee," said Esteban Sarmiento, a functional anatomist at the American Museum of Natural History in New York who traveled to the region with Ammann in 2000. "There are presently three recognized subspecies of common chimpanzee Pan troglodytes and it could represent a fourth subspecies or change our present understanding of where to draw the divisions between subspecies."
Local hunters in the region added to the mystery when they told Ammann and his colleagues about two kinds of chimpanzees in the region. Normal chimps, so-called "tree-beaters," are easily killed with poisonous arrows when they feed in trees.
Another, large chimpanzee seldom climbs trees and does not succumb to the poison arrows shot by the hunters. Called "lion killers," these big chimpanzees flee through the thick forest and disappear when shot at by hunters.
Evidence for these giant chimpanzees collected by Ammann includes a photograph of a cadaver alongside the hunter that killed it and casts of some large footprints. The pronounced ridge, called a sagittal crest, on the skull that Ammann found in 1996 is thought to be formed to support large jaw muscles, an indication of large body size.
"Giant chimpanzees occasionally occur here and there in the central and eastern subspecies, but evidence so far indicates that Karl [Ammann] may have a population of giants in his area," said Groves. "Presumably their giantism is relevant to their ground nesting behavior."
This group of what appear to be a distinct culture of ground-nesting chimpanzees is the now focus of Ammann's research. "Work has started on habituating one of the ground nesting chimp groups. This is done by provisioning them with sugar cane," he said.
This habituation will allow the researchers to document this new culture of chimpanzee as the researchers await the results of nuclear DNA analysis to determine if what they have is indeed a new subspecies of chimpanzee or simply a unique culture. Either way, the scientists are intrigued.
"Discovering an isolated group of apes exhibiting unusual cultural behaviors is just as important as identifying new DNA profiles. That's why continuous observation, habituation, and surveying are so important," said Williams.
Additionally, researchers have not yet given up on the possibility of finding gorillas in the area.
"I would think there is a strong possibility that south of Bili on the other side of the Uele River there may be gorillas, and this would seem an important area to turn our attention to," said Sarmiento.
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