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A simple alternative to line transects of nests for estimating orangutan densities

van Schaik, Carel ; Wich, Serge ; Utami, Sri ; Odom, Kisar

In: Primates, 2005, vol. 46, no. 4, p. 249-254

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    Titre
    • A simple alternative to line transects of nests for estimating orangutan densities
    Auteur
    • van Schaik, Carel. Anthropologisches Institut und Museum, Universität Zürich, Winterthurerstrasse 190, 8057, Zürich, Switzerland
    • Wich, Serge. Department of Behavioural Biology, Utrecht University, PO Box 80086, 3508TB, Utrecht, The Netherlands
    • Utami, Sri. Fakultas Biologi, Universitas Nasional, Jl Sawo Manila, Pejaten, Pasar Minggu, Jakarta, Indonesia
    • Odom, Kisar. Kantor Mawas, Jl Yos Sudarso 1A, 73112, Palangkaraya, Kalimantan Tengah, Indonesia
    Type de document
    • Postprint
    Langue
    • Anglais
    Publié dans
    • Primates, 2005, vol. 46, no. 4, p. 249-254. Springer-Verlag; http://www.springer.de
    Autre version électronique
    Identifiant OAI-PMH
    • oai:doc.rero.ch:314585
    Summary
    We conducted a validation of the line transect technique to estimate densities of orangutan (Pongo pygmaeus) nests in a Bornean swamp forest, and compared these results with density estimates based on nest counts in plots and on female home ranges. First, we examined the accuracy of the line transect method. We found that the densities based on a pass in both directions of two experienced pairs of observers was 27% below a combined sample based on transect walks by eight pairs of observers, suggesting that regular line-transect densities may seriously underestimate true densities. Second, we compared these results with those obtained by nest counts in 0.2-ha plots. This method produced an estimated 15.24nests/ha, as compared to 10.0 and 10.9, respectively, by two experienced pairs of observers who walked a line transect in both directions. Third, we estimated orangutan densities based on female home range size and overlap and the proportion of females in the population, which produced a density of 4.25-4.5 individuals/km2 . Converting nest densities into orangutan densities, using locally estimated parameters for nest production rate and proportion of nest builders in the population, we found that density estimates based on the line transect results of the most experienced pairs on a double pass were 2.82 and 3.08 orangutans/km2, based on the combined line transect data are 4.04, and based on plot counts are 4.30. In this swamp forest, plot counts therefore give more accurate estimates than do line transects. We recommend that this new method be evaluated in other forest types as well