RESEARCH ARTICLE Terrestriality in the Bornean Orangutan (Pongo pygmaeus morio) and Implications for Their Ecology and Conservation

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.Weused78non‐baited cameratrapssetin43stationsalongroads,trails, andatminerallicks (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 ¼ 32) followed by flanged males (N ¼ 26 records). P. p. morio represented the second most recorded primate (N ¼ 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 relationshipbetweencanopyconnectivityand terrestriality.Overall,ourdatasuggest thatterrestriality is relatively common for the orangutans in Wehea Forest and represents a regular strategy employed by