No abstract

Over 8 months we surveyed the Lake Tumba landscape, Democratic Republic of Congo, walking 86 km of transects and 324 km of reconnaissance, to document the distribution and estimate the abundance of great apes. Five separate groups of bonobo Pan paniscus were located in the areas of Bolombo-Losombo, Mbala-Donkese, Ngombe-Botuali, Botuali-Ilombe, and Mompulenge–Mbanzi-Malebo–Nguomi, and one population of chimpanzees Pan troglodytes in the Bosobele-Lubengo area. Mean bonobo densities ranged from 0.27 individuals km-2 in the vicinity of Lake Tumba to 2.2 individuals km-2 in the Malebo-Nguomi area. In the latter they appear to be living at a higher density than reported for any other site. This may be due to the area's forest-savannah mosaic habitat, which may provide year-round fruit sources, with bonobos falling back on savannah fruits when forest resources are scarce. The bonobos of the Bolombo-Losombo area and the Bosobele-Lubengo chimpanzees have low relative abundances and live in marginal habitats of islands of terra firma within inundated forests.

Data on food items were collected from the Lac Tumba Swampy Forests (LTSF) with the objective to gauge the effect of food type and availability on the distribution of the bonobos. Bonobos at the LTSF feed on at least 61 plant species and eat more Terrestrial Herbaceous Vegetation (THV) than at other sites (t = 0.676, df = 3, p = 0.548 > 0.05; insignificant). Fruits were available for most of the year at sites within the LTSF. At the Mbou-Mon-Tour (MMT), a site with higher bonobo density, the mean density of 1.42 fruits/m 2 per month (range 0.62 -3.82 fruits/m 2 per month) was recorded, higher than in other sites where bonobos occur (general univariate linear model = 0.422, t = 1.543, df = 11, p = 0.151, non-significant). In-site differences between MMT and other sub-sites in the LTSF were significant (t = 2.793, df = 12, p = 0.016 < 0.05). Fruit abundance in the LTSF ( X =138 fruits/km, SD = 13.80) was higher than in the Salonga National Park (SNP) ( X =83 fruits/km, SD = 6.49). There were five species of THV in the LTSF, with the most abundant being Megaphrynium macrostachyum (41.18%), which was scarce in the Lomako Forests. Comparisons between sites indicated that sites in SNP consistently had lower stem densities than sites in LTSF (t = -7.528, df = 3, p =0.005, significant). These results, in agreement with previous studies, concluded that the distribution of THV in different sites significantly determined the bonobo distribution.