Colobus Monkeys

Thumbless Vegetarians - Colobus Monkeys

Africa has a rich diversity of primates, with the apes (gorillas, chimpanzees and us) and monkeys (guenons, baboons and colobus) forming the major diurnal groups. With one exception, all of these primate families are omnivorous, feeding on both plant and animal matter.

The 14 species of colobus monkeys are entirely vegetarian and have anatomical adaptations suited to this way of life. One trait which all of them share is the absence of a thumb, which prevents them from grasping moving objects. They also have a large complex stomach which can hold a third of their bodyweight in food, and possesses chemicals able to break down cellulose and detoxify plant compounds.

The spectacular Pied Colobus is the best-known member of the family, with five similar and closely related species. Two forms of the Black-and-white (or Guereza) Colobus occur in lowland rainforest and east African highlands respectively; the lowland form has a short coat and a distinctive white-tipped tail, whereas the highland form has a luxuriant long coat and a pure white tail.

The Black-and-white Colobus lives in family groups of up to twelve, with one or more dominant male and several related 'sisters' and their offspring. Each morning, the group climbs to a high point in the forest canopy to bark out their territorial chant - an evocative chorus to welcome the day. Home ranges are small and typically linear along forested watercourses. Leguminous trees such as Acacia and Albizia form the bulk of their diet with leaves, petioles and unripe seed pods being the favoured browse. Green figs and unripe fruits are sometimes eaten. The leaves of leguminous plants are well protected by chemicals such as tannins but the colobus have evolved to deal with this defence. In order to digest this plant material, the monkeys rest for long periods allowing for bacterial fermentation similar to that in cows and other ruminants.

These striking monkeys are common in gallery forest along the lower Grumeti River in the Serengeti where CC Africa guides based at Grumeti River Camp have been studying their diet and behaviour for several years. Several troop leaders are individually recognisable on the basis of their coat patterns. They are also abundant in the Kakamega Forest of western Kenya and in many other parts of East Africa.

The smaller Red Colobus is divided into eight species, five of which are confined to isolated forest patches and are correspondingly rare and endangered. The Zanzibar Red Colobus numbers fewer than 1500 individuals but is regularly seen in the Jozani Forest reserve where the healthiest population survives. This small reserve - a unique forest growing on coral rag - may be visited en route to CC Africa's tropical island retreat of Mnemba Island.

- Duncan Butchart -

Posted: Mammals by CC Africa, Date: 21 November 2006