Chimpanzee (Pan troglodytes troglodytes) and western gorilla (Gorilla gorilla gorilla) populations in central Africa are rapidly declining as a result of disease epidemics, commercial bushmeat hunting, and habitat destruction. Our main objective was to estimate the absolute abundance and habitat utilization of chimpanzees and gorillas in the intact forests of the Goualougo Triangle in the Republic of Congo, and in an adjacent area in which selective logging will take place in the near future. The estimates provide a unique baseline for apes inhabiting an undisturbed environment. A second objective was to compare estimates of abundance and patterns of habitat utilization generated by different techniques: 1) distance sampling of individual ape nests and nest sites along line transects, 2) direct observations of apes during reconnaissance surveys, and 3) observations of ape traces during reconnaissance surveys. We completed a total of 222 km of line transect surveys in 4 sampling areas, resulting in overall density estimates of 1.53 chimpanzees/km2 and 2.34 gorillas/km2 from nest sites. We generated a density estimate of 2.23 chimpanzees/km2 from direct observations during reconnaissance surveys of a semihabituated community in 1 of the 4 sampling areas. Habitat use profiles that nest surveys depicted on transects differed from those of direct observations and traces we encountered on reconnaissance surveys. We found the highest overall abundance of chimpanzee nests in monodominant Gilbertiodendron forest, whereas our direct observations showed that chimpanzees preferred mixed species forest. Transects that traversed the core area of the community range had the highest encounter rates of chimpanzee nests and nest sites. Gorilla nests on transects showed a preference only for mixed species forest with an open canopy, but direct observations and traces on reconnaissance surveys clearly indicated that gorillas use several habitat types. We conclude by evaluating the precision of these nest surveys and our ability to detect future trends in ape densities in the Goualougo Triangle.
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Notes
Used as the technical term in survey design and analysis.
Cross-validation refers to a specific technique where each case (nest) is classified with a model derived from all other cases in the sample other than the particular case being assigned.
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ACKNOWLEDGMENTS
We are deeply appreciative of the opportunity to work in the Nouabalé-Ndoki National Park and especially the Goualougo Triangle. This work would not be possible without the continued support of the Government of the Republic of Congo and the Wildlife Conservation Society, Congo. Special thanks are due to J. M. Fay, P. Elkan, S. Elkan, B. Curran, M. Gately, and B. Djoni. A dedicated team of tracking assistants from the village of Bomassa and Makao provided invaluable assistance in the field. We also greatly appreciate the improvements made to this manuscript by comments from E. Stokes, F. Maisels, B. Inogwabini, C. Boesch, P. Lee, and R. Sussman. We thank Peter Walsh for many thought-provoking discussions about ape conservation and survey methods. Grateful acknowledgment of funding is due to the U.S. Fish and Wildlife Service, National Geographic Society, Columbus Zoological Park, Brevard Zoological Park, Lowry Zoological Park, and the Wildlife Conservation Society. During the preparation of the manuscript, C. Sanz was supported by a Richard Carley Fellowship from the Wenner-Gren Foundation for Anthropological Research.
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Morgan, D., Sanz, C., Onononga, J.R. et al. Ape Abundance and Habitat Use in the Goualougo Triangle, Republic of Congo. Int J Primatol 27, 147–179 (2006). https://doi.org/10.1007/s10764-005-9013-0
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DOI: https://doi.org/10.1007/s10764-005-9013-0