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Survey of Grauer's Gorillas (Gorilla gorilla graueri) and Eastern Chimpanzees (Pan troglodytes schweinfurthi) in the Kahuzi-Biega National Park Lowland Sector and Adjacent Forest in Eastern Democratic Republic of Congo

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Abstract

We describe the distribution and estimate densities of Grauer's gorillas (Gorilla gorilla graueri) and eastern chimpanzees (Pan troglodytes schweinfurthi) in a 12,770-km 2 area of lowland forest between the Lowa, Luka, Lugulu, and Oku rivers in eastern Democratic Republic of Congo, the site of the largest continuous population of Grauer's gorillas. The survey included a total of 480 km of transects completed within seven sampling zones in the Kahuzi-Biega National Park lowland sector and adjacent Kasese region and approximately 1100 km of footpath and forest reconnaissance. We estimate total populations of 7670 (4180–10,830) weaned gorillas within the Kahuzi-Biega lowland sector and 3350 (1420–5950) individuals in the Kasese survey areas. Within the same area, we estimate a population of 2600 (1620–4500) chimpanzees. Ape nest site densities are significantly higher within the Kahuzi-Biega lowland sector than in the more remote Kasese survey area in spite of a significantly higher encounter rate of human sign within the lowland sector of the park. Comparison of our data with information obtained by Emlen and Schaller during the first rangewide survey of Grauer's gorillas in 1959 suggests that gorilla populations have remained stable in protected areas but declined in adjacent forest. These findings underscore the key role played by national parks in protecting biological resources in spite of the recent political and economic turmoil in the region. We also show that forest reconnaissance is a reliable and cost-effective method to assess gorilla densities in remote forested areas.

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Authors and Affiliations

  1. Wildlife Conservation Society, 185th Street and Southern Boulevard, Bronx, New York, 10460

    Jefferson S. Hall, Lee J. T. White, Bila-Isia Inogwabini, Hilary Simons Morland, Amy Vedder & Kathy Freeman

  2. Marsh Hall, School of Forestry and Environmental Studies, Yale University, New Haven, Connecticut, 06511

    Jefferson S. Hall, Ilambu Omari & Claude Sikubwabo

  3. Department of Psychology, University of Stirling, Stirling, U.K

    Elizabeth A. Williamson

  4. School of Forestry and Environmental Studies, Yale University, New Haven, Connecticut

    Kristin Saltonstall

  5. Department of Entomology, American Museum of Natural History, New York, New York

    Peter Walsh

  6. Laboratoire de Mammalogie, Departement de Biologie, Centre de Recherche des Sciences Naturelles, Lwiro, Democratic Republic of Congo

    Dumbo Bonny & Kaleme Prince Kiswele

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  1. Jefferson S. Hall
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  13. Kathy Freeman
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Hall, J.S., White, L.J.T., Inogwabini, BI. et al. Survey of Grauer's Gorillas (Gorilla gorilla graueri) and Eastern Chimpanzees (Pan troglodytes schweinfurthi) in the Kahuzi-Biega National Park Lowland Sector and Adjacent Forest in Eastern Democratic Republic of Congo. International Journal of Primatology 19, 207–235 (1998). https://doi.org/10.1023/A:1020375430965

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