Bili ape

The Bili apes or Bondo mystery apes are large chimpanzees that inhabit Bili Forest in the Democratic Republic of the Congo.

"The apes nest on the ground like gorillas, but they have a diet and features characteristic of chimpanzees", according to a National Geographic report. While preliminary genetic testing with non-nuclear DNA indicates a close relationship with the eastern chimpanzee (Pan troglodytes schweinfurthii) subspecies of the common chimpanzee, a range of behaviors that are more closely related to those of gorillas have greatly intrigued primatologists from around the globe. Though their taxonomic classification has been clarified, the need for further information about these chimpanzees persists.

History of research
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.

In 2001, an international team of scientists, including George Schaller of the Wildlife Conservation Society and Mike Belliveau of Harvard University were recruited by Karl Ammann to search for the elusive Bili ape, but the venture came up empty.

After a five-year-long civil war ended in 2003, it was easier for scientists to conduct field research in the Congo. The first scientist to see the Bili apes, and also recruited by Ammann, was Shelly Williams, PhD, a specialist in primate behavior. Williams reported on her close and chilling encounter with Bili apes, "We could hear them in the trees, about 10 m away, and four suddenly came rushing through the brush towards me. If this had been a mock charge they would have been screaming to intimidate us. These guys were quiet, and they were huge. They were coming in for the kill – but as soon as they saw my face they stopped and disappeared."

"The unique characteristics they exhibit just don't fit into the other groups of apes", says Williams. The apes, she argues, could be a new species unknown to science, a new subspecies of chimpanzee, or a hybrid of the gorilla and the chimp. "At the very least, we have a unique, isolated chimp culture that's unlike any that's been studied", she says.

Scientists believe they are dealing with a very inbred population, in which even a large number of animals could share identical or near identical haplotypes. Bili ape reports have also been investigated by Esteban Sarmiento, who has said "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." Scientists working within these forests south of the Uele, however, have found no such evidence, nor heard any such reports from local communities. It remains an important region, however, based on the discovered presence of other flagship species, like chimpanzees and elephants.

In June 2006, British Science Weekly reported that Cleve Hicks and colleagues from the University of Amsterdam had completed a year-long hunt for these apes during which they were able to observe the creatures a total of 20 full hours. Hicks reported, "I see nothing gorilla about them. The females definitely have a chimp's sex swellings, they pant-hoot and tree-drum, and so on".DNA samples recovered from feces also reaffirmed the classification of these apes in the chimp subspecies Pan troglodytes schweinfurthii.

Hicks encountered a large community of the apes to the northwest of Bili that displayed interest in him and his colleagues reminiscent of previous reports (this was misreported in the New Scientistas being 18 km from Bili, but it was actually considerably farther from the village. This was the first group of Bili apes to be encountered where the adult males did not flee immediately upon seeing the humans). The apes, including adult males, would surround their human visitors and show curiosity towards them, but would not attack or become threatening.

Hicks has emphasized that there is little evidence suggesting that they are any more aggressive than other chimpanzees (predatory behavior being the norm for the species). However, he has been misquoted in the press about this.

Further study was undertaken by Hicks between July 2006 and February 2007, accompanied by Jeroen Swinkels of the University of Amsterdam. A new base camp was established in the Gangu Forest.

Behavioral characteristics
In some ways, the apes behave more like gorillas than chimpanzees. For example, they build ground nests as gorillas do, using interwoven branches and/or saplings, bent down into a central bowl. However, they frequently nest in the trees as well. Often ground nests will be found beneath or in proximity to tree nests. Their diet is decidedly chimpanzee-like, consisting mainly of fruits (fruiting trees such as strangler figs are visited often).

The Bili apes pant-hoot and tree-drum like other chimpanzees, and do not howl at the moon, contrary to initial reports.

Behavior toward humans has baffled and intrigued scientists. There is little to no aggression, yet no fear, either. "Gorilla males will always charge when they encounter a hunter, but there were no stories like that" about the Bili apes, according to Ammann. Instead, they would come face-to-face with their human cousins, stare intently in half-recognition, then slide away quietly. Hicks's group later confirmed and somewhat expanded those observations, saying that when they encountered a large group of Bili apes in the deep forests (far from the roads and villages), they not only approached the humans, but also would actually surround them with intent curiosity. Hicks clarifies the issue as follows: the apes within 20 km or so of the roads flee humans almost without exception. The adult males show the greatest fear. Further from the roads, however, the chimpanzees become progressively "naive".

Morphology and physiology
The Bili ape has been reported to be bipedal (meaning they walk upright) and stand 5 to 5.5 feet (1.5 meters) tall, with the looks of a giant chimpanzee; making them look more like the extinct australopithecine, Sahelanthropus or Toumaï. Their footprints, which range from 28 to 34 centimeters long, are longer than the largest common chimp and gorilla footprints, which average 26 cm and 29 cm, respectively.

According to Williams, "They have a very flat face, a wide muzzle and their brow-ridge runs straight across and overhangs. They seem to turn grey very early in life, but instead of turning grey-black like a gorilla, they turn grey all over." They develop uniform grey fur independently of age and sex, which suggests that greying takes place early in life (whereas in all known gorilla species, only males gray as they age and graying is restricted to their backs).

Bili ape skulls have the prominent brow ridge and may sometimes have a sagittal crest similar to that of a gorilla, but other morphological measurements are more like those of chimpanzees. Only one of the many skulls found at Bili had a sagittal crest, thus it cannot yet be considered typical for the population. Chimpanzee skulls are 190 to 210 millimeters long, but four out of five Bili ape skulls measured more than 220 millimeters, well beyond the end of the normal chimpanzee range

Female Bili apes have genital swellings similar to other chimpanzees.