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Estimating Orangutan Densities Using the Standing Crop and Marked Nest Count Methods: Lessons Learned for Conservation |
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| Authors: | Stephanie N Spehar Paul D Mathewson Serge A Wich Andrew J Marshall Hjalmar Kühl Erik Meijaard |
| Institution: | 1. Anthropology, Department of Religious Studies and Anthropology, University of Wisconsin-Oshkosh, 800 Algoma Blvd., Oshkosh, Wisconsin 54901, U.S.A.
1Corresponding author;2. e-mail: spehars@uwosh.edu;3. Nelson Institute for Environmental Studies, University of Wisconsin-Madison, 550 N. Park Street, 70 Science Hall, Madison, Wisconsin 53706, U.S.A.;4. Sumatran Orangutan Conservation Programme, Jl. K. H. Wahid Hasyim NO 51/74, Medan Baru, Medan 20154, Sumatera Utara, Indonesia;5. Anthropological Institute and Museum, University of Zurich, 8057 Zurich, Switzerland PanEco, Foundation for Sustainable Development and Intercultural Exchange, Berg am Irchel, Switzerland;6. Department of Anthropology and Graduate Group in Ecology, University of California at Davis, One Shields Avenue, Davis, California 95616, U.S.A.;7. Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, 04103 Leipzig, Germany;8. The Nature Conservancy, Indonesia Forest Program and Orangutan Conservation Services Program, Jalan Polantas No. 5, Markoni, Balikpapan, East Kalimantan, Indonesia;9. People and Nature Consulting International, Kerobokan, Badung 80361, Bali, Indonesia School of Archaeology and Anthropology, Building 14, Australian National University, Canberra, ACT 0200, Australia |
| Abstract: | Reliable estimates of great ape abundance are needed to assess distribution, monitor population status, evaluate conservation tactics, and identify priority populations for conservation. Rather than using direct counts, surveyors often count ape nests. The standing crop nest count (SCNC) method converts the standing stock of nests into animal densities using a set of parameters, including nest decay rate. Nest decay rates vary greatly over space and time, and it takes months to calculate a site-specific value. The marked nest count (MNC) method circumvents this issue and only counts new nests produced during a defined period. We compared orangutan densities calculated by the two methods using data from studies in Sumatra and Kalimantan, Indonesia. We show how animal densities calculated using nest counts should be cautiously interpreted when used to make decisions about management or budget allocation. Even with site-specific decay rates, short studies using the SCNC method may not accurately reflect the current population unless conducted at a scale sufficient to include wide-ranging orangutan movement. Density estimates from short studies using the MNC method were affected by small sample sizes and by orangutan movement. To produce reliable results, the MNC method may require a similar amount of effort as the SCNC method. We suggest a reduced reliance on the traditional line transect surveys in favor of feasible alternative methods when absolute abundance numbers are not necessary or when site-specific nest decay rates are not known. Given funding constraints, aerial surveys, reconnaissance walks, and interview techniques may be more cost-effective means of accomplishing some survey goals. |
| Keywords: | Borneo density estimate great ape Indonesia Pongo population census primate Sumatra |