Sidony is the first recorded orangutan to be killed by another female Anna Marzec

It was a deadly rumble in the jungle. A female orangutan was attacked and killed by another female and a male – the first time lethal aggression has been seen between females of the species.

Female orangutans are normally solitary, and very rarely engage in fights. It’s also unusual for females and males to form coalitions.


In this case, Kondor, a young female, and Ekko, her suitor, beat and bit an older female named Sidony in the swamp forests of Indonesia’s Mawas Reserve. Sidony sustained serious wounds that became infected, and she died two weeks later.

“It was very surprising,” says Anna Marzec at the University of Zurich, Switzerland, who observed the behaviour. “We had never seen anything like this before.”

Ekko (left) and Kondor (right) were behind the killing Anna Marzec

It’s unclear why Kondor showed such unusually aggressive behaviour. Female orangutans don’t defend their territory and the researchers saw no sign of any provocation. “We think the presence of the male had a lot to do with the fact that she was brave enough to attack and then was so persistent,” says Marzec.

Kondor had recently lost an infant. Just before the attack, she was in a courtship with Ekko. The pair encountered Sidony and Ekko inspected her before returning to mate with Kondor. Kondor then broke away from Ekko to attack Sidony, and Ekko joined in.

Another male, Guapo, came to Sidony’s defence, and chased Ekko away, but Sidony had already received severe injuries.

The area is becoming more crowded for orangutans because of habitat destruction, and this could have played a role in the unusual behaviour. “We want to see if it’s going to happen more often now,” says Marzec.

Journal reference: Behavioral Ecology and Sociobiology, DOI: 10.1007/s00265-015-2053-3

Correction:Since this article was first published we have updated the headline and story to make it clear that this is the first time lethal aggression has been seen between female orangutans