Tabernanthe iboga used by Animals
Boars, porcupines, gorillas, and mandrills have been reported eating iboga roots in Gabon and the Congo. A Mitsogho shaman (nganga) in Gabon described to Giorgio Samorini the use of iboga roots by mandrills in dominance displays:
When a male mandrill must engage in combat with another, either to establish his claim to a female or to climb a rung of the hierarchical ladder, he does not begin the fight without forethought. Instead, he first finds and digs up an iboga bush, eating its root; next, he waits for its effects to hit him full force (which can take from one to two hours); and only then does he approach and attack the other male he wants to engage in battle. The fact that the mandrill waits like this to feel the full effect of the drug before attacking demonstrates a high level of premeditation and awareness of what he is doing. (Samorini, pp. 57 ff.)
Interesting as this hypothesis is, another explanation is possible. These mandrills may have accidentally intoxicated themselves. Upon feeling the powerful effects of iboga, they may have become disinhibited like a belligerent drunk in a bar.
Reference: Samorini G. Animals and Psychedelics; The Natural World and the Instinct to Alter Consciousness. Park Street Press. 2000.