Abstract
Orangutans have a slow life history with one of the longest interbirth intervals and the lowest reported infant mortality rates among primates or even mammals. Breastfeeding is a key factor in their life history because it possibly promotes offspring health and increases maternal interbirth intervals. However, quantifying milk intake is difficult, and existing estimates for their weaning age are contradictory. Here, we use fecal proteomics to predict the breastfeeding and weaning patterns in wild Bornean orangutans in Danum Valley, Sabah, Malaysia. Age changes in milk-specific proteins identified from 20 feces of five immature individuals revealed that the orangutans in Danum Valley consistently consumed milk for ≥6.5 years after birth, consistent with the behavioral evidence as having one of the longest breastfeeding periods in mammals. Milk intake was significantly correlated with higher levels of biological defense and probiotic bacterial proteins. Mothers were not pregnant with their next offspring during the breastfeeding period. These results indicate that a continuous and long breastfeeding period is a key component of the slow life history of orangutans and shows that fecal proteomics can be applied to a wide range of wild animal populations, with the potentials to uncover novel aspects of behavior and physiology.
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Acknowledgements
We thank Sabah Biodiversity Centre, Danum Valley Management Committee, Universiti Malaysia Sabah (especially to Henry Bernard), Sabah Wildlife Department (especially to Peter T. Malim), and the Department of Agriculture Sabah. We are grateful to the various supporters of our research, especially Yayasan Sabah, Borneo Nature Tours, South East Asia Rainforest Research Partnership (SEARRP), Danum Valley Field Center, Danum Valley Management Committee, and Borneo Rainforest Lodge, as well as our research assistants in the field (Mike Bernadus, Eddy Boy, Kirimizi Bin Roseliu, Jaidi Bin Jolin, Lijor Bin John, and Elny Dencio). Rikai Sawafuji, editors, and reviewers gave constructive comments on this manuscript. This study was supported in part by Grants-in-Aid for Scientific Research from Japan Society for the Promotion of Science (KAKENHI: 24-785, 2540012, 2940025, 15J00464, 19K06100, 21K14867, 22KK0170, 24H01571, JPJSBP120249918, and Core-to-Core Program “International Network for Tropical Biodiversity Conservation focusing on the Studies on Large Animals”); AEON Environmental Foundation (29-4009, 30-4002); Environmental Restoration and Conservation Agency (ERCA) (2020-i-A2, 2021-i-B2, 2022-i-B4, 2023-i-0003, 2024-i-C6); Keidanren Nature Conservation Fund (2020-0238, 2021-0123, 2022-0002, 2023-0026, 2024-0029); Mitsui & Co. Environment Fund (R11-G4-1022); Taisei Corporation Public Trust of Funds for Natural and Historic Environments; Tokyo Zoological Park Society; Cooperative Research of Wildlife Research Center, Kyoto University; the Leading Graduate Program in Primatology and Wildlife Science (PWS); pre-research project in the Division of Evolutionary Studies of Complex Adaptive Systems, Research Center for Integrative Evolutionary Science, SOKENDAI; crowdfunding by JapanGiving “Continuing our long-term field research of wild orangutans in Borneo” and “Trying to observe wild orangutans during nighttime”; UMSGreat (GUG0605-1/2023).
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Makbul, N.S., Tajima, T., Kanamori, T. et al. Continuous and prolonged breastfeeding in wild Bornean orangutans verified with fecal proteomics.
Commun Biol (2026). https://doi.org/10.1038/s42003-026-09968-2
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DOI: https://doi.org/10.1038/s42003-026-09968-2
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