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Famished Frugivores or Choosy Consumers: A Generalist Frugivore (Wild Bornean Orangutans, Pongo pygmaeus wurmbii) Leaves Available Fruit for Nonfruit Foods

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Abstract

Research in primate nutritional ecology uses concepts of quality, preference, and energy content to explain food choice: a primate consumes high-quality, preferred, and/or high-energy foods when available, and moves to other foods when they are not. Many frugivorous primates are thought to maximize energy, suggesting that high-energy fruit is a quality/preferred resource. However, recent research suggests a more complicated picture, including nutrient balancing and state-dependent foraging decisions. This brings into question whether a food is inherently high- or low-quality or whether this depends on previous feeding choices of the consumer. We tested whether a frugivorous primate, Pongo pygmaeus wurmbii, selects nonfruit foods when fruit is available. To test selectivity, we looked for three behaviors: (1) orangutans leaving available fruit for nonfruit foods, (2) evidence of orangutans navigating to nonfruit foods, and (3) orangutans selecting nonfruit when fruit was available and nearby. We use data from 51 focal follows (611 feeding bouts, 15 animals) in Gunung Palung National Park, Indonesia. We found when orangutans leave available fruit, it often is for nonfruit foods. We found evidence of orangutans navigating for nonfruit foods. GPS data show that orangutans leave or pass by fruit to consume other foods. When orangutans consumed nonfruit resources, 26% of the time, there was at least one available fruit resource within a 50-m radius. These data suggest that orangutans select nonfruit foods, strengthening the argument that feeding choice is consumer state-dependent, and leading us to argue for a revision of the use of “quality” as a descriptor of primate foods.

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Acknowledgements

The authors conducted this research in collaboration with the Ministry of Research and Technology/National Research and Innovation Agency of the Republic of Indonesia (RISTEK/BRIN) and the Gunung Palung National Park Office (Balai Taman National Gunung Palung). The authors thank these organizations for sponsoring us and allowing us to conduct this research. The authors also thank the Universitas Tanjungpura (UNTAN), the National University of Indonesia (UNAS), the Directorate of Natural Resource Conservation and Ecosystems (KSDAE) – Ministry of Environment and Forestry, and the Indonesian Institute of Sciences (LIPI). Drs. Erin Vogel, Jessica Rothman, and Chris Schmitt provided valuable comments and suggestions that bettered this manuscript as a part of A. DiGiorgio’s doctoral committee.

The authors are grateful to the reviewers (including Dr. David Raubenheimer) and editor (Dr. Joann Setchell) who provided very valuable and insightful comments that improved this manuscript significantly. This work was supported by grants to A. DiGiorgio from the National Science Foundation (NSF GRFP Grant No. DGE-1247312) and from Boston University; to A. DiGiorgio and C. Knott from the National Science Foundation (NSF BCS-1540360); and to C. Knott from the National Science Foundation (BCS-0936199, BCS-1638823, 9414388); the US Fish and Wildlife Service (F15AP00812, F12AP00369, 98210-8-G66); the LSB Leakey Foundation; the National Geographic Society; the Disney Conservation Fund; Focused on Nature; the Conservation, Food and Health Foundation; the Orangutan Conservancy; and the Nacey Maggioncalda Foundation.

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Authors and Affiliations

  1. Princeton Writing Program, Princeton University, 2 New South, Room 307, Princeton, NJ, 08544, USA

    Andrea L. DiGiorgio

  2. Department of Anthropology, Princeton University, Princeton, NJ, 08544, USA

    Andrea L. DiGiorgio

  3. Department of Anthropology, Boston University, Boston, MA, 02215, USA

    Andrea L. DiGiorgio, Natalie J. Robinson & Cheryl D. Knott

  4. Department of Earth and Environment, Boston University, Boston, MA, 02215, USA

    Yaxiong Ma & Sucharita Gopal

  5. Mathematics and Statistics Department, Williams College, Williamstown, MA, 01267, USA

    Elizabeth M. Upton

  6. Department of Biology, National University, Jakarta, 12520, Indonesia

    TriWahyu Susanto

  7. Gunung Palung Orangutan Project, West Kalimantan, Indonesia

    TriWahyu Susanto & Cheryl D. Knott

  8. Department of Biology, Boston University, Boston, MA, 02215, USA

    Cheryl D. Knott

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Contributions

AD conceived of and designed experiments, collected and managed data, completed initial statistics, and wrote the manuscript. YM and SG assisted with movement ecology portions of data management and analysis and conceptualization of methods. EU completed final statistics, data management, conceptualization of final analyses, and revisions. NW assisted with editing manuscript and revisions. TS oversaw field site and permitting. CK supervised project and field site, assisted with conceptualization and edits.

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Correspondence to Andrea L. DiGiorgio.

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One or more of the authors of this paper self-identifies as an underrepresented ethnic minority in science. One or more of the authors of this paper self-identifies as living with a disability. While citing references scientifically relevant for this work, we also actively worked to promote gender balance in our reference list. The author list includes contributors from the location where the research was conducted, who participated in study conception, study design, data collection, analysis, and/or interpretation of the findings.

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DiGiorgio, A.L., Ma, Y., Upton, E.M. et al. Famished Frugivores or Choosy Consumers: A Generalist Frugivore (Wild Bornean Orangutans, Pongo pygmaeus wurmbii) Leaves Available Fruit for Nonfruit Foods. Int J Primatol 44, 377–398 (2023). https://doi.org/10.1007/s10764-022-00347-2

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