This chapter broadly covers what we know of the natural history of the olive colobus monkey, the only monotypic African colobine that shows a suite of unique traits. Distributed in the upper Guinea forests of West Africa, these cryptic, drab-coloured monkeys tend to form long-term and often permanent polyspecific associations with guenon groups as part of their predation avoidance strategy. They carry their infants in their mouths and show several morphological and behavioural traits (e.g., sexual swellings, canine dimorphism, extra-group copulations) that indicate that sexual selection has been important in their evolutionary history. They are selective feeders that favour young leaves and often eat lianas. No long-term studies are currently being conducted on olive colobus monkeys and there is much remaining to be discovered about their behaviour and ecology.

This chapter reviews current knowledge of the red colobus, Piliocolobus, a polytypic widespread colobine living in sub-Saharan African forests, woodlands, mangroves, and riparian forests. The taxonomy of Piliocolobus has undergone many changes and is still unresolved, resulting in confusion and possibly hindering conservation efforts. Red colobus is known for being the favourite prey of chimpanzees in many locations, and in several populations red colobus associate with guenons to reduce predation risk. Less well-known are their sexual swellings, which vary greatly in size across the genus, and their graded vocal repertoire that lacks a long call, but in some cases includes female mating calls. Noisy, large multi-female multi-male groups, female dispersal, philopatric males that form coalitions, and lack of female allomothering are considered the norm for the genus but these are not universal. Red colobus is facing extirpation in many locations due to human hunting and forest destruction. Various serious diseases and parasites are also reported for many populations and are often associated with human encroachment into their habitat. Much about the social behaviour is yet to be studied, especially in the less-studied central African species assemblage.