Males in a group of chimpanzees killed a deposed alpha male by beating him with rocks, before others in the group cannibalised his dead body.

Researchers studying a group of chimpanzees in Fongoli, Senegal were woken early in the morning by screeching from a nearby nest. They discovered the dead body of the former leader, known as Foudouko, bleeding from bite wounds in his foot, with a gash in his back, a ripped anus and broken ribs. A paper and a series of videos of the aftermath of the incident are published in the International Journal of Primatology.

Foudouko had been a tyrannical ruler of the clan about 13 years ago. He was ousted when his beta-male partner was injured and lost social status. He became an outcast and was rarely seen near the group.It was bad timing of an attempt to rejoin the group at a high social level that seriously backfired for Foudouko.

"We just happened to have at the time five young males all coming up in the hierarchy and those guys together didn't want to let Foudouko back in," study author Jill Pruetz of Iowa State University told the New Scientist. "He was trying to come back in at a high rank, which was ultimately a foolish thing to do on his part."

Many chimpanzees joined in the attack on his dead body. The most violent were a young male and an older female, who also ate the most of the body, the researchers say.

"Do chimpanzees understand death? It's not clear if they do," said primatologist Michael Wilson of the University of Minnesota, who was not involved in the study. "It seems unlikely that they know about using pulse or breath to make sure something's dead, so we do see them beating on individuals they've killed after they've expired. But the cannibalisation was unusual."

The body of the former leader of the clan, Foudouko, is pictured after he was killed by a group of males. Jill Pruetz / Iowa State University

Killing an adult male from within a group is rare in chimpanzees, with only nine cases ever recorded. The biologists suggest that an unusual gender imbalance in the group may have contributed to the attack.

Ordinarily there are more females than males in a group but in this community there were almost two males for each female, which led to intensified sexual competition. Poaching of female chimpanzees for their infants for the pet trade is the likely cause of the gender imbalance in the group, Pruetz said.

Foudouko grave
The body of Foudouko in a grave dug by researchers studying the chimpanzee group. Jill Pruetz / Iowa State University