Chimpanzee research and conservation in Bossou and the Nimba Mountains: a long-term international collaborative effort in West Africa.

The Nimba Mountains are a West African Natural World Heritage site located in the range of the Guineo-equatorial evergreen rainforest, renowned for its rich biodiversity with a high level of endemism. In 1976, Yukimaru Sugiyama from Kyoto University initiated the long-term study of chimpanzees at Bossou, a Guinean village situated 5 km from the northern foothills of Nimba. This Japanese initiative has provided key discoveries and insights on our closest living evolutionary relatives over the 40 past years, and has grown to become an international collaboration with a research focus extended to adjacent chimpanzee communities. The present paper describes a mid-term behavioral and ecological study on wild chimpanzees populating the southern slope of the Nimba Mountains, conducted in the framework of this collaborative project. It aimed to assess the status and ecological requirements of chimpanzees in order to formulate purpose-built actions for their conservation. We estimated a density of 0.46 chimpanzee per km(2) using nest count methods from line transects. We used logistic and Poisson regressions to investigate basic ecological characteristics of chimpanzees in relation to habitat composition and structure, topography and seasonality. We performed an in-depth analysis of their nesting and feeding behaviors, and identified important components of their diet; we also recorded their year-round ranging patterns. Our findings highlight the importance of old secondary forest and high-altitude habitats for these chimpanzees. We discuss the results in the light of other studies from the perspective of the conservation of the species and its natural habitat.