Nigerian chimpanzees (Pan troglodytes vellerosus) at Gashaka: two years of habituation efforts.

Cross-population comparisons of chimpanzees can shed light on the pathways of hominid evolution. So far, no eco-ethological data exist for the recently recognized subspecies Pan troglodytes vellerosus. We report on the first 2 years of a new long-term study from what is perhaps their last remaining stronghold: the Gashaka Gumti National Park, Nigeria. The mosaic habitat (woodland, lowland and gallery forest) receives 1,826 mm rain/year, with 4-5 months being completely dry. Primates at Gashaka are not hunted, and the chimpanzees are therefore relatively tolerant of human observers. We focused on the Gashaka-Kwano community, investing 3,000 h of patrols. A total of 95 sightings were achieved which lasted for an average of 27 min (range 1-190 min). Party size averaged 3.7 animals (range 1-17) but was, similarly to encounter length, susceptible to a wide range of methodological, social and ecological factors. The Kwano community comprises at least 35 members which occupy a home range of at least 26 km(2), yielding a density of 1.3/km(2). The area represents the West African equivalent of a chimpanzee site similar to the forest-woodland habitat in which early humans might have evolved.