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.
Knowing how habitat determines the distribution of great apes is essential for understanding their ecology and conservation requirements. Habitats in the northern Lac Tumba Landscape where this study was conducted are mostly swamp and flooded forests, which types have been overlooked in many great ape surveys. This study describes and discusses patterns of bonobo and chimpanzee nesting sites across these habitat types in the general scope of habitat use by great apes. Considerable efforts were deployed to survey forests of the Ngiri Triangle (186 km), Bomongo‐Lubengo (126 km) and Bolombo‐Losombo (112 km). Great ape nesting site encounter rates (r) were calculated for Bonobos (r = 0.21 nesting sites km−1; Bolombo‐Losombo), chimpanzees (r = 0.11 nesting sites km−1; Ngiri Triangle) and (r = 0.02 nesting sites km−1; Bomongo‐Lubengo). Swamps and flooded forests dominated the three zones. Nesting sites were at the highest encounter rates in flooded forests; both great ape species were significantly associated with swampy and flood forests. Human signs did not influence the occurrence of nesting sites in these forests. These results confirm findings from other sites where great apes were observed using swamps; they suggest that future surveys include these types of habitat to avoid under‐estimating population sizes.
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