Diet traditions in wild orangutans

Authors

  • Meredith L. Bastian,

    1. Department of Evolutionary Anthropology, Duke University, Durham, NC 27708-0383
    2. Gunung Palung Orangutan Project, Ketapang 78851, Kalimantan Barat, Indonesia
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  • Nicole Zweifel,

    1. Anthropologisches Institut & Museum, Universität Zürich, CH-8057 Zürich, Switzerland
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  • Erin R. Vogel,

    1. Center for the Advanced Study of Hominid Paleobiology, Department of Anthropology, George Washington University, Washington, DC 20052
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  • Serge A. Wich,

    1. Great Ape Trust of Iowa, Des Moines, IA 50320
    2. Behavioural Biology, Utrecht University, 3508 Utrecht, The Netherlands
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  • Carel P. van Schaik

    Corresponding author
    1. Department of Evolutionary Anthropology, Duke University, Durham, NC 27708-0383
    2. Anthropologisches Institut & Museum, Universität Zürich, CH-8057 Zürich, Switzerland
    • Anthropologisches Institut & Museum, Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland
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Abstract

This study explores diet differences between two populations of wild Bornean orangutans (Pongo pygmaeus wurmbii) to assess whether a signal of social learning can be detected in the observed patterns. The populations live in close proximity and in similar habitats but are separated by a river barrier that is impassable to orangutans in the study region. We found a 60% between-site difference in diet at the level of plant food items (plant species–organ combinations). We also found that individuals at the same site were more likely to eat the same food items than expected by chance. These results suggest the presence of diet (food selection) traditions. Detailed tests of three predictions of three models of diet acquisition allowed us to reject a model based on exclusive social learning but could not clearly distinguish between the remaining two models: one positing individual exploration and learning of food item selection and the other one positing preferential social learning followed by individual fine tuning. We know that maturing orangutans acquire their initial diet through social learning and then supplement it by years of low-level, individual sampling. We, therefore, conclude that the preferential social learning model produces the best fit to the geographic patterns observed in this study. However, the very same taxa that socially acquire their diets as infants and show evidence for innovation-based traditions in the wild paradoxically may have diets that are not easily distinguished from those acquired exclusively through individual learning. Am J Phys Anthropol 143:175–187, 2010. © 2010 Wiley-Liss, Inc.

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