Procolobus verus (van Beneden 1838)

Tree-dwelling olive colobus live in groups of 5 to 20 individuals with around half containing one adult male with several females and their young (2), and the remaining groups having multiple breeding males (6). Members of a group communicate infrequently with very quiet chirping or burring calls (2). Little is known about reproduction in the olive colobus, but it is believed to be the only Old World monkey in which the female carries the newborn in her mouth while she travels for the first month of life (5) (7). As the infant grows, it may wrap itself around the female's neck or cling to her body as she moves through the forest (2). The olive colobus is a shy and retiring monkey that prefers to move through dense growth below ten metres, but climbs higher when feeding amongst the protection of other species (2) (7), particularly Diana monkeys (Cercopithecus diana), with which they have a strong tendency to associate (8), as well as lesser spot-nosed guenons (Cercopithecus petaurista) and king colobus (Colobus polykomos) (5). By foraging with other primate species, the olive colobus benefits from extra eyes and ears to stay alert for predators (8). Males are also believed to use these associations to obtain mating partners; the Diana monkeys are a resource which the males can expect female olive colobus to visit (6). If a predator is spotted, the primary response of the timid olive colobus is to move in to dense foliage and freeze in a hunched or crouched position (2). The diet of the olive colobus is dominated by young leaves and flowers, with one study showing 27 percent of their diet acquired from lianas, in the tangles of which they spend much of their time (9). Fruit and seeds are also eaten, with the quantities varying seasonally (2), but mature leaves are rarely ingested (9). They eat the food directly off the plant using their mouth, and do not pick it by hand (2).

The olive colobus occurs in a number of protected areas (5), such as the Taï National Park in Cote d'Ivoire (11), and is listed on Appendix II of the Convention on International Trade in Endangered Species (CITES), meaning that any international trade in this species should be carefully monitored (3). Otherwise, there are no known conservation measures in place specifically aimed at the rarely seen olive colobus.

The olive colobus has the distinction of being the smallest colobus monkey (2), a group of primates that primarily consume leaves and possess an unusual stomach that enables them to digest this plant matter efficiently (4). The olive colobus has greenish-olive fur graduating to brown on the back, and dull grey undersides. The small, rounded head has a short, grey crest running down the crown with a swirl of light grey hair on each side of the forehead. A dull white ruff frames the hairless dark face (2)

Inhabits forest, including rainforest, dry semi-deciduous forest, palm forest, forest margins, swamps forest, and abandoned cultivated areas (2) (5).

The olive colobus occurs from southern Sierra Leone to Ghana, just east of the Volta River, and also in Nigeria, on the south bank of the River Benue (2) (5).

Classified as Near Threatened (NT) on the IUCN Red List (1) and listed on Appendix II of CITES (3).

Like many forest-dwelling primates, habitat loss and hunting pose the greatest threat to the existence of the olive colobus (1) (2), and populations may be declining as a result (2). However, a study revealed that the olive colobus may actually be very tolerant of hunting, but is greatly impacted by agriculture invading their natural habitat (10).