Are Male Orangutans a Threat to Infants? Evidence of Mother–Offspring Counterstrategies to Infanticide in Bornean Orangutans (Pongo pygmaeus wurmbii)

Abstract

Sexually selected infanticide by males is widespread in primates. Female primates employ a variety of strategies to reduce infanticide risk. While infanticide has never been directly observed in wild orangutans (Pongo spp.), their slow life history makes infants vulnerable to infanticide. The mating strategies of female orangutans include polyandrous and postconceptive mating that may serve to increase paternity confusion, an infanticide avoidance strategy. Here, we investigate whether female orangutans alter their social interactions with males as another infanticide avoidance strategy. We hypothesize that females with younger offspring avoid males and that the distance between mother and offspring decreases in the presence of males. We use long-term behavioral data collected between 1994 and 2016 from Bornean orangutans (Pongo pygmaeus wurmbii) in Gunung Palung National Park, Indonesia, to test whether the sexual selection hypothesis for infanticide helps explain aspects of orangutan social behavior. We found that mothers with offspring <6 yr. old both encountered fewer males and spent less time with males during social interactions than did mothers with offspring >6 yr. old and females without offspring. In addition, the distance between a mother–offspring dyad showed a statistically significant decrease in the presence of males, but not females. Our results are consistent with the hypothesis that female orangutans employ strategies to reduce infanticide risk in their social interactions. Because orangutans have a high fission–fusion dynamic, they have flexibility in manipulating social interactions as a counterinfanticide strategy. Our results suggest that infanticide by males is a selective pressure shaping female orangutan social behavior.

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Data Availability

The data sets generated during and/or analyzed during the current study are available from the authors on reasonable request.

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Acknowledgments

We thank the Universitas Nasional (UNAS), the Universitas Tanjungpura (UNTAN), the Eijkman Institute for Molecular Biology, the Directorate of Natural Resource Conservation and Ecosystems (KSDAE), the Gunung Palung National Park office (BTNGP), the Indonesian Institute of Sciences (LIPI), the Center for Research and Development in Biology (PPPB), and the Ministry of Research, Technology and Higher Education (RISTEKDIKTI) for their sponsorship and for granting permission to conduct research in Gunung Palung National Park. This research was supported by grants to CDK from the National Science Foundation (BCS-0936199, BCS-1638823, 9414388); the National Geographic Society; the L.S.B. Leakey Foundation; the Wenner-Gren Foundation; the US Fish and Wildlife Service (F15AP00812, F12AP00369, 98210-8-G661); the Conservation, Food and Health Foundation; Focused on Nature; the Orangutan Conservancy; Disney Wildlife Conservation Fund; and the Nacey Maggioncalda Foundation. AMS was supported by a National Science Foundation Graduate Research Fellowship under Grant DGE-1247312 and by a Boston University Graduate Research Abroad Fellowship. We also thank all the dedicated field assistants, research assistants, field managers, and students who assisted with data and sample collection. We would like to thank the editor, two anonymous reviewers, Erin Kane, and Caitlin O’Connell for constructive suggestions on the manuscript.

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AMS and CDK formulated the idea. CDK supported and supervised the collection of data and maintains the long-term database. TWS contributed to field supervision and data collection. CDK and AMS prepared data for analysis. AMS analyzed data and wrote the majority of the manuscript. CDK provided guidance and assisted with data analysis and writing of the manuscript.

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Correspondence to Amy M. Scott.

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Scott, A.M., Knott, C.D. & Susanto, T.W. Are Male Orangutans a Threat to Infants? Evidence of Mother–Offspring Counterstrategies to Infanticide in Bornean Orangutans (Pongo pygmaeus wurmbii). Int J Primatol 40, 435–455 (2019). https://doi.org/10.1007/s10764-019-00097-8

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Keywords

  • Great apes
  • Male avoidance
  • Male infanticide
  • Orangutan sociality
  • Sexual selection hypothesis