The first lethal incident among orangutans ever observed by scientists took place in a Borneo forest where a female orangutan and her male partner teamed up and killed an older female orangutan.
Anna Marzec, a primatologist at the University of Zurich in Switzerland, said that female orangutans rarely engage in fights and are usually solitary. What is even more surprising, the female sought help from a male orangutan to attack the victim, she added.
Aggression – in the form of a quick chance, or sometimes biting and hitting – is quite frequent among primates, but lethal attacks are very rare, according to the researchers. Those types of attacks have only been observed in: red colobus monkeys, spider monkeys, chimpanzees, muriquis, and capuchins.
For primates, aggression is an expression of competition when it comes to resources. Females compete over food, and males compete over females; these conflicts usually occur between the members of the same sex.
The new case – published Wednesday (Feb. 3) in the journal Behavioral Ecology and Sociobiology – involved an older female orangutan named Sidony, and a young female named Kondor. The two animals had a history of aggressive integration – they both lived in the Mawas Reserve in Indonesia.
Two weeks before the attack, Kondor was seen associating with a male orangutan named Ekko. At one point, Ekko sexually inspected Sidony, but then returned to mate with Kondor. The young female orangutan interrupted her mating and started to attack Sidony as she began to move away. Researchers said that soon after, Ekko joined the fight.
Guapo, another male orangutan saw the fight and approached to protect Sidony. He managed to drive the older female away from the fight. Unfortunately, the injuries that Sidony had suffered were too severe, leading to her death two weeks after the attack, according to the researchers.
John Mitani, a primate behavioural ecologist who studies chimpanzees at the University of Michigan in Ann Arbor, said that this is a really odd case. It is difficult to interpret what exactly went on and what started the fight.
Marzec said that the extreme competition for resources might have been responsible for the lethal attack. The orangutan habitats in the area were destroyed due to illegal logging and forest fires, which led to limited resources and crowded conditions among the animals, she explained.
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