The Tana River mangabey is a diurnal species that primarily feeds on seeds, leaves and fruit (4) (6). This monkey occupies multimale-multifemale groups (5) that range from 10 to 36 individuals (8). Mating behaviour is not fully understood, but a single offspring is known to be usual (6), after a gestation period of around 170 to 180 days (2) (8). Life-expectancy is thought to be between 19 and 21 years (9), but little else is known about the life history of this species.