The dark side of the red ape: male-mediated lethal female competition in Bornean orangutans
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Female Bornean orangutans (Pongo pygmaeus wurmbii) are mainly solitary and philopatric, leading to adult female relatives sharing adjacent and overlapping home ranges. Females tend to be intolerant of unrelated females, with whom they also may have overlapping home ranges. However, fights that lead to injuries are extremely rare and lethal aggression had never been observed. Here, we report the first case of lethal female-female aggression during over 26,000 h of focal data collected on adult females at Tuanan, Central Kalimantan: A young female, who had recently lost her infant, attacked an old resident female. The interaction’s unique feature was that the attacking female was supported by an unflanged male, who had been in consort with her during the week preceding the attack and was responsible for the lethal injuries to the victim. The victim received protection from a flanged male who was probably attracted to the noise generated by the fight. We conclude that even in a species in which coercion is frequently observed in male-female interactions, female leverage over males can coax males into providing services, such as coalitionary support.
KeywordsOrangutan Lethal aggression Coalitionary attack Female-female competition Male support
We gratefully acknowledge the Indonesian Institute of Science (LIPI), the Indonesian State Ministry for Research and Technology (RISTEK), the Director General Departemen Kehutanan (PHKA), Departamen Dalam Negri, the local government in Central Kalimantan, the BKSDA Palangkaraya, the Bornean Orangutan Survival Foundation (BOSF), and the MAWAS in Palangkaraya for their permission and support to conduct this research. We also thank the Fakultas Biologi Universitas Nasional (UNAS) in Jakarta for their collaboration and support for the Tuanan project and in particular Dr. Tatang Mitra Setia. We are indebted to the Tuanan field team for their contribution to data collection, in particular Pak Rahmatd, Pak Yandi, Tono, Idun, Kumpo, Suwi, Abuk, and Wilhelm Osterman as well as many local and foreign students and their financial supporters. For major financial support, we thank the University of Zurich, the A.H. Schultz Stiftung, Philadelphia Zoo, as well as USAID (APS-497-11-000001 to E.R.V.). This research complied with the current national laws of Indonesia. We also thank the two anonymous reviewers for their helpful feedback.
Compliance with ethical standards
All applicable international, national, and/or institutional guidelines for the care and use of animals were followed. This article does not contain any studies with human participants performed by any of the authors.
This study was funded by the University of Zurich (grant number not available), A.H. Schultz-Stiftung zur Förderung Primatologischer Forschung (grant number not available), United States Agency for International Development (USA) (APS-497-11-000001), and Philadelphia Zoo (grant number not available).
Conflict of interest
The authors declare that they have no competing interests.
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