Colobus monkeys and the closely related langurs and leaf monkeys are Old World monkeys in the subfamily Colobinae of the family Cercopithecidae. The primates in this subfamily share a common trait—they lack thumbs or have only small, useless thumbs. (The name colobus comes from a Greek word meaning mutilated.) However, lack of a thumb does not stop them from nimbly moving among the branches. They just grasp a branch between the palm of the hand and the other fingers. The Colobinae are distinguished from the other subfamily of Old World monkeys, the Cercopithecinae, by their lack of cheek pouches, their slender build, and their large salivary glands. They live throughout equatorial Africa, India, and Southeast Asia.
Unlike most monkeys—which are fairly omnivorous, eating both plant and animal foods—many colobus monkeys eat primarily leaves and shoots. In the tropical and subtropical regions in which these leaf-eaters live, they have an advantage over other monkeys in that they have a year-round supply of food. Leaf-eaters also have an advantage in that they can live in a wider variety of habitats than fruit-eaters, even in open savanna. Fruit-eaters, on the other hand, must keep on the move in forests to find a fruit supply in season. Most colobus monkeys also eat fruits, flowers, and seeds when they can find them.
Like all Old World monkeys, colobus monkeys have tough hairless pads, called ischial callosities, on
their rear ends. There are no nerves in these pads, a fact that allows them to sit for long periods of time on tree branches without their legs “going to sleep.” Some colobus monkeys have loud, raucous calls that they use particularly at dawn. Apparently these signals tell neighboring troops of monkeys where a particular group is going to be feeding that day.
Leaves do not have much nourishment, so colobus monkeys must eat almost continuously, up to a quarter of their body weight each day. Their leafy diet requires them to have stomachs specially adapted for handling hard-to-digest materials. The upper portion of the stomach contains anaerobic bacteria that break down the cellulose in the foliage. These bacteria are also capable of digesting chemicals in leaves that would be poisonous to other primates. Colobus monkeys have large salivary glands which send large amounts of saliva into the fermenting food to help its passage through the digestive system.
The black and white colobus monkeys of central Africa (genus Colobus ) have the least visible thumb of any genus in the subfamily Colobinae, although what little thumb remains has a nail on it. These monkeys have slender bodies, bare faces, and long tails with a puff of long fur on the end. Head and body length is 17.7–28.3 in (45–72 cm), tail length is 20.5–-39.3 in (52–100 cm), and weight is 11.9–31.9 lb (5.4–14.5 kg).
The five species in this genus are distinguished by the amount of white markings and by the placement of long silky strands of fur in different locations. The black colobus (C. satanus ) has a completely black, glossy coat. Colobus polykomos has a white chest and whiskers and a white, tuftless tail; C. vellerosus has white thigh patches, a white mane framing its face, and a white, tuftless tail; C. guereza has a flat black cap over a white beard and “hairline,” a long white mantle extending from the shoulders to the lower back, and a large white tuft on its tail; C. angolensis has long white hairs around the face and on the shoulders, and a white tuft on the end of its tail.
Black and white colobus monkeys are typically highly arboreal (tree-dwelling) inhabitants of deep forests, but some species feed and travel on the ground where the trees are more widely spaced. When they sit still in the trees, these monkeys are well camouflaged because their black and white color blends with the patches of sunlight and shadow. When moving in the trees, colobus monkeys tend to walk along branches, either upright or on all fours, instead of swinging beneath them, and they often make amazingly long leaps from tree to tree. Their long hair apparently acts as a parachute to slow them down.
Black and white colobus monkeys often live in small social groups, consisting of both males and females. For example, C. guereza lives in groups of three to 15 individuals; most groups have a single adult male and several adult females with their young. The female membership in these groups seems stable, but adult males are sometimes ousted by younger males. Relations among members of the same group are generally friendly and are reinforced by mutual grooming.
Black and white colobus monkeys can apparently breed at any time of the year. Females become sexually mature at about four years of age, while males reach sexual maturity at about six years of age. Each pregnancy results in a single offspring. Infants are born with all white fur, which is shed before the regular coloring comes in. Child rearing seems to be shared among the females in the group.
All species of black and white colobus monkeys have declined over the last 100 years due to hunting for meat and the fur trade, the rapid expansion of human populations, and habitat destruction by logging or agriculture. The skins of black-and-white colobus monkeys were often used for clothing in Europe during the nineteenth century. They were still available as rugs in the early 1970s. The pelts of as many as 50 animals might have been used to make a single rug. The black colobus (C. satanus ) and Geoffroy’s black and white colobus (C. vellerosus ) are classified as vulnerable by IUCN—The World Conservation Union. Their continued survival is threatened by hunting and habitat disturbance and destruction.
Red colobus monkeys (genus Procolobus or Piliocolobus ) live along the equator in Africa. They come in many different colors in addition to the reddish black that gives them their name. They often have whitish or grayish faces and chests, with the deep red color appearing only on their back, crown of the head, paws, and tip of the tail. This color variety has made these monkeys difficult to classify, and there is considerable disagreement in their grouping. Red colobus monkeys have a head and body length of 17.7–26.4 in (45–67 cm), a tail length of 20.5–31.5 in (52–80 cm), and weigh 11.2–24.9 lb (5.1–11.3 kg). These monkeys have no thumb at all, lacking even the small vestigial thumb seen in black and white colobus monkeys.
Red colobus monkeys are also arboreal. Most populations are found in rain forests, but they also inhabit savanna woodlands, mangrove swamps, and floodplains. Red colobus monkeys also form stable groups, but the groups are much larger than those formed by black and white colobus monkeys—ranging in size from 12 to 82 with an average size of 50. These groups usually include several adult males and 1.5–3 times as many adult females. There is a dominance hierarchy within the group maintained by aggressive behavior, but rarely by physical fighting. Higher ranking individuals have priority access to food, space, and grooming.
Red colobus monkeys also seem to breed throughout the year. A single offspring is born after a gestation period of 4.5–5.5 months. The infant is cared for by the mother alone until it reaches 1–3.5 months old.
Most red colobus species are coming under increased population pressure from timber harvesting. This activity not only destroys their rainforest habitat, but also makes them more accessible to hunters. At
Ischial callosity— A hard hairless pad of skin, or callus, located on the lower part of the buttocks, or ischium.
least one authority considers red colobus monkeys to be the easiest African monkeys to hunt. Several species and subspecies are considered endangered, vulnerable, or rare by international conservation organizations. For example, the Zanzibar red colobus (Procolobus kirkii ) is seriously endangered—in 2000 less than 1, 200 animals were estimated to survive.
Grouped with the red colobus monkeys because of its four-chambered stomach is the olive colobus, Procolobus verus, of Sierra Leone and central Nigeria. This monkey is actually more gray than olive or red. Its head and body length is 16.9–35.4 in (43–90 cm) and it weighs 6.4–9.7 lb (2.9–4.4 kg). This species is also arboreal and is restricted to rainforests. It forms small groups of 10–15 individuals, usually with more than one adult male in each group. In a practice unique among monkeys and apes, mothers of this species carry newborns in their mouths for the first several weeks of the infant’s life.
Davies, Glyn, and John Oates, eds. Colobine Monkeys: Their Ecology, Behaviour and Evolution. Cambridge: Cambridge University Press, 1995.
Dolhinow, P., and A. Fuentes, eds. The Nonhuman Primates. Mountain View, CA: Mayfield Pub. Co., 1999.
Napier, J.R., and P.H. Napier. The Natural History of the Primates. Cambridge, MA: The MIT Press, 1985.
Peterson, Dale. The Deluge and the Ark: A Journey Into Primate Worlds. Boston: Houghton Mifflin, 1989.
Preston-Mafham, Rod and Ken. Primates of the World. New York: Facts on File, 1992.
Jean F. Blashfield