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Terrestriality in the bornean orangutan (Pongo pygmaeus morio) and implications for their ecology and conservation


  • Brent Loken,

    Corresponding author
    1. School of Resource and Environmental Management, Simon Fraser University, Burnaby, British Columbia, Canada
    2. Integrated Conservation, Gig Harbor, Washington
    • Correspondence to: Brent Loken, School of Resource and Environmental Management, Simon Fraser University, PO Box 2932, Garibaldi Highlands, Burnaby, BC, Canada V0N 1T0. E-mail:

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  • Stephanie Spehar,

    1. Integrated Conservation, Gig Harbor, Washington
    2. Anthropology Program, University of Wisconsin Oshkosh, Oshkosh, Wisconsin
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  • Yaya Rayadin

    1. Forestry Faculty, Mulawarman University, Samarinda, East Kalimantan, Indonesia
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Aside from anecdotal evidence, terrestriality in orangutans (Pongo spp.) has not been quantified or subject to careful study and important questions remain about the extent and contexts of terrestrial behavior. Understanding the factors that influence orangutan terrestriality also has significant implications for their conservation. Here we report on a camera trapping study of terrestrial behavior in the northeastern Bornean orangutan, Pongo pygmaeus morio, in Wehea Forest, East Kalimantan, Indonesia. We used 78 non-baited camera traps set in 43 stations along roads, trails, and at mineral licks (sepans) to document the frequency of orangutan terrestriality. Habitat assessments were used to determine how terrestrial behavior was influenced by canopy connectivity. We compared camera trapping results for P. p. morio to those for a known terrestrial primate (Macaca nemestrina), and another largely arboreal species (Presbytis rubicunda) to assess the relative frequency of terrestrial behavior by P. p. morio. A combined sampling effort of 14,446 trap days resulted in photographs of at least 15 individual orangutans, with females being the most frequently recorded age sex class (N = 32) followed by flanged males (N = 26 records). P. p. morio represented the second most recorded primate (N = 110 total records) of seven primate species recorded. Capture scores for M. nemestrina (0.270) and P. p. morio (0.237) were similar and almost seven times higher than for the next most recorded primate, P. rubicunda (0.035). In addition, our results indicate that for orangutans, there was no clear relationship between canopy connectivity and terrestriality. Overall, our data suggest that terrestriality is relatively common for the orangutans in Wehea Forest and represents a regular strategy employed by individuals of all age−sex classes. As Borneo and Sumatra increasingly become characterized by mixed-use habitats, understanding the ecological requirements and resilience in orangutans is necessary for designing optimal conservation strategies. Am. J. Primatol. 75:1129–1138, 2013. © 2013 Wiley Periodicals, Inc.