ARE they a giant new species of great ape, or a hybrid of a chimp and a gorilla? The mysterious population of apes living in the remote north of the Democratic Republic of the Congo has been the subject of a heated debate. Now genetic evidence and a comprehensive survey suggest that, despite their size and unusual behaviour, the apes belong to a recognised subspecies of chimpanzee, Pan troglodytes schweinfurthii.
People living around the town of Bili, about 200 kilometres east of the Ebola river, have long swapped stories of ferocious apes with a penchant for killing lions (快猫短视频, 9 October 2004, p 32). The apes seemed too large to be chimps. From photographs, they were estimated to weigh up to about 100 kilograms, and their footprints at up to 34 centimetres long were bigger than a gorilla鈥檚.
To solve the mystery Cleve Hicks and colleagues at the University of Amsterdam, the Netherlands, spent a year in the field tracking the apes. During that time, Hicks logged an unprecedented 20 hours observation. 鈥淚 see nothing gorilla about them,鈥� he says. 鈥淭he females definitely have a chimp鈥檚 sex swellings, they pant-hoot and tree-drum, and so on.鈥�
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Analysis of mitochondrial DNA taken from faecal samples also puts the animals within the P. t. schweinfurthii group. Hicks is now analysing samples of nuclear DNA in the expectation that this will rule out a chimp-gorilla hybrid. 鈥淚 would say that possibility is negligible,鈥� he says.
The Bili apes are, nevertheless, unusual. Their skulls have a gorilla-like sagittal crest, but also many chimp-like features. Recordings reveal that they howl during the full moon. The apes live at high density. Hicks found 430 nests in a 160-kilometre trail system. 鈥淎t least some are definitely night nests,鈥� he says, which is atypical for a chimp. While gorillas nest on the ground, chimps usually bed down in trees.
Hicks says the animals regularly smashed up termite mounds, and used tree roots and rocks as anvils for breaking open fruit and, in one instance, a forest tortoise. They also use sticks up to 2 metres long to dip for driver ants, and shorter sticks to fish for other invertebrates.
Colin Groves of the Australian National University in Canberra has studied skulls collected from the region. He thinks that the Bili skulls are unusually large, but that morphologically they are a unique population of P. t. schweinfurthii.
About 18 kilometres north-west of Bili, Hicks discovered a large population in which the density of the animals is much greater. What鈥檚 more, they do not appear to have encountered humans before. 鈥淚t鈥檚 fantastic. They surround us and show curiosity 鈥� even the adult males,鈥� he says. 鈥淚t is these guys we want to study.鈥�
Hicks reported his findings at the annual conference of the International Primatological Society in Entebbe, Uganda, held from 25 to 30 June.
