Angolan Colobus, Colobus angolensis

ANGOLAN COLOBUS

Colobus angolensis

Angolan Colobus

Geographic Distribution and Habitat

More than any other African monkey, the Angolan colobus, Colobus angolensis, also called the Angolan black-and-white colobus, is exceptionally adapted to a life lived almost exclusively in the tree canopy. A leaf-loving primate with a body built for tree-hopping acrobatics, this Old World monkey thrives in a variety of forest types, including lowland, bamboo, coastal, gallery, and montane forests, although the species has also been observed in savannas and swamplands.

TAXONOMIC NOTES

The Angolan colobus is one of Central Africa’s five known species of black-and-white colobus and has a fragmented range that extends from Nigeria to Tanzania and Gabon to Ethiopia. Within the Angolan colobus species, researchers note at least eight subspecies (distinguished by various and sometimes minor differences in their coats), found in specific areas of the region:

  • Sclater’s Angolan colobus (C. a. angolensis), found in Angola and northward to the great bend in the Congo River;
  • Powell-Cotton’s Angolan colobus (C. a. cottoni), Adolf-Friedrichs’s Angolan colobus (C. a. ruwenzorii), Cordier’s Angolan colobus (C. a. cordieri), and Prigogine’s Angolan colobus ( C. a. prigoginei), in regions of the Democratic Republic of Congo, Rwanda, Uganda, and Tanzania;
  • Peter’s Angolan colobus (C. a. palliates), in discontinuous areas of southern and eastern Tanzania and southeastern Kenya.
  • Sharp’s Angolan colobus (Colobus angolensis ssp. sharpei)   has an extremely fragmented distribution in Malawi and possibly Mozambique.
  • Mahale Mountains Angolan colobus or Nkwunge Angolan colobus (Colobus angolensis ssp. nov) is only known from Mount Nkungwe in the Mahale Mountains, central western Tanzania. Its range is isolated and poorly understood and there may be fewer than 1,000 individuals.
Angolan colobus geographic range. Map credit: IUCN, 2020

Size, Weight, and Lifespan

Angolan colobuses are slender, medium-sized monkeys with long, elegant tails. A female will grow to about 19 inches (48 cm) with a 28-inch (71 cm) tail; males are slightly larger, growing to 27 inches (69 cm) with a 33-inch (84 cm) tail. Adult females weigh, on average, 13 lbs (6 kg) whereas males can weigh almost twice as much at 25 lbs (11.4 kg).

In the wild, Angolan colobus monkeys live about 20 years, though lifespans of up to 30 years in captivity are not uncommon. 

Appearance

Like their black-and-white mantled guereza (Colobus guereza) cousins, Angolan colobuses have striking black-and-white coats but are differentiated by long, silky white hair that frames their black faces and drapes their shoulders like regal epaulettes. Their long tails fade from black to white at the lower half.

As with other colobus monkeys, they have an opposable toe and a reduced thumb; their curved narrow fingers form a single flexible hook, an adaptation that helps them more easily navigate branches in the canopy. All colobuses also share flattened nails, hind legs that are longer than the forelimbs, and prominent pads on the buttocks.

Babies are born with tender pink faces and unmistakable pure white coats which, by three months of age, begin to change to the black-and-white coloration of adults. 

Diet

One of the most remarkable aspects of the arboreal (tree-dwelling) Angolan colobus is their food intake. Angolan colobus monkeys are primarily folivorous, eating as many as 46 different species of leaves. They also feed on stems, bark, buds, shoots, and insects. Much of their diet, however, has little nutritional value, so the Angolan colobus will feed in the canopy for hours, consuming as much as 7 lbs (3kg) of leaves in order to satisfy their daily dietary needs.

It’s worth noting that the Angolan colobus does not have cheek pouches, as is common with other Old World monkeys. Instead they have a complex ruminant-like digestive system that allows them to eat what other monkeys cannot, including unripe fruits, flowers, and cellulose-rich mature leaves, which are hard to digest and sometimes toxic. The stomach itself has three chambers that carry specific bacteria to help ferment and digest leaves. Colobus monkeys have been observed eating clay found in termite mounds, which researchers suggest may further help process toxins.  

With a leaf-rich diet only a colobus could love (most monkeys cannot digest what a colobus can) and a predilection for the safety of the tree canopy, the Angolan colobus fortunately faces less food competition than other African monkeys.

Behavior and Lifestyle

The Angolan colobus is one of the most arboreal of all monkeys in Africa. On any given day, this colobus rarely needs to touch ground. Except for the infrequent descent to nibble on stream-side plants, they spend their daytime hours grazing the canopy, bouncing and leaping from branch to branch. Their lightweight bone structure, balancing tail, and elongated limbs help them navigate among branches, sometimes making long leaps of up to 50 feet (15.2 meters) and then free-falling with outstretched limbs to catch a branch. Their shawl-like hair and tail are thought to act like a parachute during those daring leaps and drops.

Fun Facts

A lack of thumbs is what gives the Angolan colobus its name: the word “colobus” comes from the Greek word “kolobos,” which means “mutilated one.” For Angolan colobus monkeys, however, this seems a terrible misnomer, as the colobuses’ lack of thumbs is not a mutilation, but a powerful adaptation to arboreal life.

Daily Life and Group Dynamics 

Angolan colobuses tend to live in relatively small troops led by one adult male and up to six females and their young. When larger troop sizes occur, more than one resident male is typically present. Exceptionally large troops of over 300 members are rare but have been recorded in Rwanda’s Nyungwe forest, where researchers believe an abundance of mature leaves with unusually high nutritional value puts few restrictions on troop growth.

Groups will defend their home range from other troops of colobus monkeys, as well as band together to stave off predators. Their nimbleness and adeptness in the canopy also helps them avoid predators. Females lead the troop, but the dominant male takes responsibility for defending the troop’s territory and protecting the troop from predators.

Communication

Researchers have observed morning roaring contests between dominant Angolan colobus males, a behavior that may help the group maintain spacing in the canopy.

For his role as defender and protector of the troop, a male Angolan colobus will continuously roar and jump in the presence of a predator until his troop has fled to safety. Squealing, purring, tongue-clicking, and yawning may also signify threats or distress.

Reproduction and Family

In the Angolan colobuses’ polygynous society, the dominant male controls access to the reproducing females, who will signal to the male when she is ready for mating. Although there is no distinct birth season, most mating occurs during the rainy season with a peak in births seen in September and October. Average gestation periods range from 147 to 178 days. Females give birth every 20 months, usually to single offspring, although twins do occur.

A mother will carry her clinging infant on her abdomen. While researchers note that infant mortality rates remain relatively high for this species, it’s not from neglect. Many troop members share the work of caring for the young. Infants’ striking white coats are thought to promote “aunting” behavior among females so that nursing mothers have time to feed long enough to satisfy her nutritional needs.

By 15 months, infants will wean, and by two years of age, females reach sexual maturity. A male reaches sexual maturity by four years, when he’ll either be forced to leave the group or challenge the dominant male for control. Females remain with their birth troops for life.

​Ecological Role

Angolan colobus monkeys provide food for some large predators, such as eagles and large cats, and contribute to forest propagation as seed dispersers. ​Researchers also suggest Angolan colobus monkeys merit deeper study for their role as harbingers of overall forest health, given their high dependence on the tree canopy.

Conservation Status and Threats

The International Union for Conservation of Nature lists the Angolan colobus as Vulnerable (IUCN, 2016), appearing on the IUCN’s Red List of Threatened Species. Despite a very large geographic range, the species is threatened in most parts of its range by habitat loss, degradation and fragmentation caused mainly by collection of timber and fuelwood, conversion of forest to farmland, the expansion of human settlements and encroachment due to a fast growing human population.

Hunting is a major threat, particularly in Central Africa. The Angolan colobus is targeted for bushmeat because of its large size. Despite the existence of largely intact, suitable, and protected habitat in the Domaine de Chasse de Swa-Kibula, southwestern DRC, Sclater’s Angolan colobus (C. a. angolensis) became locally extinct before 1990 due to unsustainable hunting. Although hunting may be a particularly high threat in the Congo Basin, a number of other populations have already been eradicated from suitable habitats elsewhere due to unsustainable hunting levels. In the unprotected Udzungwa Scarp Nature Reserve in the Udzungwa Mountains, Tanzania, scientists documented declines to near local extinction of Sharpe’s Angolan colobus (C. a. sharpei) due to hunting in a span of less than 10 years.

The Angolan colobus is suspected to have undergone a population decline exceeding 30% during the past 33 years (three generations). The threats that caused population reductions in the past are not reversible and have not been eliminated, nor will they be in the foreseeable future.

Conservation Efforts

Angolan colobus monkeys are listed as an Appendix II species by CITES (the Convention on International Trade in Endangered Species of Wild Fauna and Flora), which means that although there’s no immediate threat of extinction, close monitoring is warranted.

Within DRC, they are the totally protected list and may not be hunted.

For the past 20 years, the Colobus Conservation not-for-profit in Kenya’s Diani Beach has been working to protect the Angolan colobus. The group has developed programs for human-primate conflicts, biological/ecological research, community development and education, forest protection and enrichment, and eco-tourism awareness. The organization is also lobbying to have the colobus palliatus subspecies status changed to vulnerable from its current designation as least concern.

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Written by Christine Regan Davi, November 2017. Conservation Status updated Jul 2020.