Census and distribution of chimpanzees in Côte D’Ivoire

Abstract

Most methods of estimating chimpanzee population densities rely on nest counts. We tested the most frequently used techniques on a known chimpanzee community living in the rainforest of the Tai National Park, Cote d’Ivoire. The best density estimates are given by counts that assume groups of nests to be distributed randomly and that use the mean group size for homogenous habitat but the median for heterogenous habitats. Correction for real forest cover within the region should be made because chimpanzees make nests only in forested regions. This method gave the exact chimpanzee density for the Tai population, i.e. 1.7 nest builders/km2. For the nationwide survey, we first estimated the chimpanzee density for different types of habitat (e.g. intact primary forest: 1.64 chimpanzees/km2; degraded forests: 0.4 chimpanzees/km2; human encroached forests and mosaic habitats: 0.09 chimpanzees/km2). Second, we estimated the total forest cover of the country with satellite pictures. This gave an estimated chimpanzee population in Cote d’Ivoire of about 11,676 ± 1,168 individuals, which equals the number of spectators at a soccer game in an average European town. Sadly, only three National Parks may have chimpanzee populations large enough to be viable, whereas the rest are scattered and isolated small populations that are already threatened in their survival.