Imoso is easily identified by his pinkish speckled face, relatively rare in adult chimpanzees of this subspecies. While this "baby face" makes him appear harmless, when suitably aroused, he can be a force to be reckoned with.

This is the 27-year old alpha male of the Kanyawara community and he has been at the top since 1998.

Martin Muller, now an assistant professor at Boston University,  was present to document the aggression and endocrine physiology of Kanyawara males when Imoso rose to power.

Martin's findings show that during this period of dominance instability, male rank was positively correlated with both testosterone and cortisol levels.

Thus, while Imoso may gain many advantages to being the top ranking chimpanzee, he also appears to suffer increased stress because of all the challenges of this role.

© Jean-Michel Krief

When Imoso arrives at a tree, he does a "display". He storms in with hair erected and lips pursed, making him look large and fierce. Banging on tree trunks to make lots of noise is also part of this display.

Other chimpanzees make "pant-grunt" noises to him as signs of greeting and deference.

Imoso and a few other males in the Kanyawara community are unique and infamous among primate males in having adopted the use of large branches to beat female chimpanzees in their own community.

In January 1999 Carole Hooven, lecturer in Anthropology at Harvard, saw a viscious attack that Imoso launched on Outamba, an adult female.

It seems the assault took place after the female tried to protect her infant from the alpha male. Here is how Carole's notes on this event read:

'Imoso first attacks Outamba with one stick for about 45 seconds, holding it with his right hand, near the middle.

Imoso (left) grooming with the female he battered in 1999, Outamba.
© Jean-Michel Krief

'She was hit about 5 times ... he beat her hard. The stick was brought down on her in a somewhat inefficient way ...

'Imoso seemed to start with the stick almost parallel to the body and bring it down in a parallel motion. There was a slight angle to his motion, but not the way a human would do it for maximum impact.'

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