Geographic Distribution and Habitat
Also known as mantled colobus, eastern black-and-white colobus, magistrate colobus, and a several other variations on the common name, guereza colobus monkeys (Colobus guereza) are Old World monkeys with widespread distribution across Central Africa. The species’ range extends in an easterly direction from Nigeria, east and west of the Niger river and the upper Donga river tributaries; to the Yabassi District of Cameroon; to Equatorial Guinea; through Chad, Gabon, the Central African Republic, across the Oubangui River to the Republic of Congo; to northern Democratic Republic of the Congo; through southern Sudan to Ethiopia, Kenya, Uganda, Rwanda, and finally, south into northern Tanzania.
Seven subspecies are recognized, although there is some scientific squabble regarding the level of distinction qualifying each as its own subspecies. Each subspecies occupies a specific range and exhibit slight variations in appearance:
- Western guereza (C. g. occidentalis) is found from eastern Nigeria, Cameroon, south to Gabon, eastward to southwestern Sudan and into Uganda, west of the Nile river.
- Omo River guereza (C. g. guereza) is found in forested areas of the Ethiopian highlands, west of the Rift Valley and within the lowland areas along the Awash River, the Omo River, and in the Blue Nile gorge.
- Djaffa Mountains guereza, aka Neumann’s black-and-white colobus (C. g. gallarum), is found only in the Ethiopian highlands east of the Rift Valley.
- Dodinga Hills guereza (C. g. dodingae) is found only in the Didinga Hills of southeastern Sudan.
- Mau forest guereza (C. g. matschiei) is found in Kenya, west of the Rift Valley, inhabiting forestland within the rift, west to Mount Elgon (Kenya and Uganda), and south to the Ngorongoro Crater and the Grumeti River in Tanzania.
- Mt. Uaraguess guereza, aka Percival’s black-and-white colobus (C. g. percivali), is found the highest peak in the Matthews Range of central Kenya.
- Mt. Kenya guereza (C. g. kikuyuensis) is found in central Kenya, from the Ngong Escarpment, Mt. Kenya, and the Aberdare Mountain Range.
Guerezas reside in both deciduous and evergreen thicket forests, where the canopies of individual trees overlap to form a closed, continuous layer. Although found in both secondary and primary (or old growth) forests, they prefer disturbed, secondary forests. Scientists speculate that this predilection is due to the high diversity of food trees that secondary forests offer.
Additional habitats include swamp forests, wooded grasslands, wooded savannas (characterized by trees being widely spaced so that the canopy does not close), riparian forests (that is, forestland adjacent to a river, lake, or other body of water), gallery forests (small, lush forests that grow along waterways in an otherwise treeless area) dominated by acacia trees, moist lowland, medium-altitude rainforests, and high montane forests at altitudes up to 14,764 ft (4,500 m). Guerezas are also known to venture into agricultural tracts of land, such as eucalyptus plantations (likely to fulfill a nutritional need, scientists speculate).
Size, Weight, and Lifespan
Guerezas are sturdy, long-tailed monkeys. Males are slightly larger than the females. In the subspecies, males typically (but not always) have larger teeth than the females. Scientists attribute this dental differential to a natural response to habitat and to social dynamics between the sexes.
Head-to-body length in males is between 21.4 and 27.5 in (54.3 to 70 cm), averaging about 24 in (61.5 cm). Average weight is between 20.5 and 29.8 lb (9.3 and 13.5 kg). Head-to-body length in females is between 20.5 and 26.5 in (52 and 67.3 cm), averaging about 22.7 in (57.6 cm). Average weight is between 17 and 20 lb (7.8 and 9.2 kg). Tail length is greater than head-to-body length, to varying degrees depending on the subspecies.
A glossy, black coat covers most of the guereza’s body. Adding contrast, and likely the thought behind this primate’s nickname as “magistrate,” is a long, white mantle (or cape) draped over the shoulders that extends the length of the back, reaching the hips. White whiskers and a full white beard frame a gray, hairless face that is characterized by a long, flat, wide muzzle and an underbite. (The guereza’s white beard distinguishes it from its cousin, the Angolan colobus, whose dark face is framed by silky white strands of hair.) Imagination might suggest that the guereza’s brown eyes evoke a pensive mien (fitting for a magistrate, perhaps?) A long, thin mostly black tail ends in a fluffy, white plume.
At birth, the coats of guerezas are completely white and remain so for the first few weeks of the young primates’ lives.
But at high altitudes on the west side of Mt. Kenya, sightings of all-white adult guerezas have been reported. No scientific explanation for this albinism has been proffered, however.
The seven subspecies of guerezas are differentiated by the coloring of their mantles, which can vary from whitish-yellow to creamy white. Tail length and the degree of fluffiness of the plume further distinguish one subspecies from another.
Like most members of the colobus family, the guereza has no thumbs. Scientific thought is that this adaptation allows for quick movement through the trees. The species also lacks the cheek pouches that are common in many Old World monkeys.
Generous pads on their rump (known as “ischial callosities”) provide guerezas with a bit of comfort while they are sitting in their treetop perches.
Guereza colobus monkeys are folivorous, that is, they eat a whole lot of leaves. Leaves of the hackberry tree (a kind of nettle tree) are their favorite, and unripe leaves comprise a larger portion of their diet than mature leaves. Fruits, leaf buds, bark, seeds, and blossoms complement their diet. The monkeys’ geographic distribution and seasonal fluctuations impact food availability and thus may cause related fluctuations in their diet. To lessen changes in their menu, guerezas select leaves that are less susceptible to seasonal change. Drops of dew provide their daily water requirement, and they will also drink rainwater that has collected inside tree trunk hollows.
Nature has fitted guerezas with a multichambered stomach that allows for the digestion of large amounts of foliage. Microbes in the gut work with fluids secreted by the monkeys’ salivary glands to efficiently break down leaf cellulose. This morphological adaptation allows the monkeys to obtain the necessary nutrition from their leafy diet.
Behavior and Lifestyle
Although they are diurnal creatures, meaning that they are active during daylight hours, guerezas are late risers, as compared to other diurnal primates—leaving their sleeping trees one to several hours after sunrise. Then they spend about half their day resting. Foraging and feeding occupy most of their remaining daylight hours. Before sunset, they once again retire to their sleeping trees.
A group usually occupies up to four nearby trees that offer food sources and avoid sleeping in proximity to other guereza groups. The monkeys take turns sleeping so that at least one individual can act as “lookout” for potential predators, who include crowned hawks, chimpanzees, and leopards.
Mostly arboreal (living in the trees), guerezas reside deep within the forest where they glide through the connecting tree canopies quadrupedally (on all fours), bounding and leaping through gaps from one tree to another. When trees are not densely spaced, providing no arboreal passageways, these monkeys are known to descend to the ground to forage and travel.
In contrast to their exploitation as animal research models by western medicine, Colobus guereza is one of many monkey species sacred to the Hindu and Buddhist religions. Guerezas play a major role in these religions as icons of sacred gods.
Daily Life and Group Dynamics
Guereza colobus monkeys are social animals who live in cohesive, mixed-gender groups averaging 3 to 15 individuals; however, groups as large as 23 have been reported. A group is typically comprised of one adult male, several adult (reproducing) females, juveniles, and infants. Occasionally, a group might hold several adult males; however, this is a temporary situation and the superfluous males eventually wear out their welcome and exit the group.
A group’s adult male most often assumes leadership duties. Females, however, form the group’s core. They remain with their birth group for life, so they are likely to be close relatives. Females engage in mutual grooming and support one another with infant care. Males typically leave their birth group before they are considered fully mature so they can create, or overtake, a group (a harem) of their own.
Guerezas live in well-demarcated territories of about 32 to 40 acres (13 to 16.2 hectares), but sometimes territories marginally overlap. Encounters with outside guereza groups are not friendly, and the dominant male of a group strenuously defends his group’s territory through intimidation tactics that include screams, roars, displays of flapping his white fur fringe up and down, leaping, chasing, and actual combat. Guerezas exhibit more tolerance for certain primate species who share their habitat, including mangabeys (cercocebus) and guenons (cercopithecus), with whom they share habitat without rancor. Scientists have observed infant guerezas playing with infant vervet monkeys.
Guerezas are vocal creatures. Their most impressive vocalization is their signature roar, most often sounded by a group’s dominant adult male. Male guerezas from neighboring groups will return the roar. Scientists believe that these loud roaring sessions, which occur during the night and at dawn, play a role in male competition, with guereza males trying to out-roar one another. Their roars also help to maintain territorial distance between groups.
Other vocalizations include snorts, purrs, honks, and screams.
Besides vocalizations, guerezas use body language to communicate. Flapping their white fringe in a spectacle of intimidation is likely the most dramatic. Facial expression and body postures are also used in aggressive communication between groups.
Tactile communication includes grooming (which helps to strengthen social bonds), playing, and fighting.
Reproduction and Family
Female guerezas reach reproductive maturity at about 4 years old. Males are a little slower in attaining their maturity, at about 6 years old. They make up for this lag time by embracing their polygynous culture: the dominant male gets to breed with all the females in his harem. The female initiates sex, however. By coquettishly tongue-smacking, she indicates to the male that she is interested.
Breeding occurs year-round, but births are timed so that weaning occurs at the time of greatest food availability.
After a gestation period of nearly 6 months, a female gives birth to a single infant. All members of a group pay attention to the newborn, particularly the females of the group. In a phenomenon known as “infant transfer,” several females handle the infant soon after its birth, carrying the infant as far as 82 ft (25 m) from her or his mother. A mother might suckle the infant of another female while simultaneously allowing her own to suckle. Females give birth every 20 months.
An infant clings to her mother’s chest through her first 20 weeks of life, at which time she begins to grow more independent. At about a year old, she no longer clings to her mother, nor does she suckle. Because females remain with their birth group, mothers and daughters forge life-long bonds.
Guerezas play an important, but unwitting, role in the food web of their ecosystems: they are prey to other species who also live there.
Conservation Status and Threats
Because of their widespread distribution and large populations in certain areas, guerezas are classified as Least Concern by the International Union for Conservation of Nature (IUCN, 2016). Nevertheless, their populations are declining in many localities.
Hunting poses a significant threat to the species. In what is a lucrative business for the trade and fur industries, these monkeys are killed, skinned, and their pelts sold to be turned into “fashionable” fur coats for human primates to wear.
Habitat loss is another looming threat, as it is for many wildlife species. Forestland is routinely razed and transformed into agricultural tracts of land. Should the guerezas venture onto these new farmlands, they are regarded as crop pests. Of the subspecies, the Mt. Kilimanjaro guereza, Mt. Kenya guereza, Omo River guereza, and the Western guereza are also classified as Least Concern. The Djaffa Mountains guereza, Dodinga Hills guereza, and Mau Forest guereza are classified as Data Deficient. Only the Mt. Uarges guereza is classified as Endangered.
The biomedical research community places importance on guerezas for their use in animal research. Animal protection advocates dispute the necessity of animal experimentation, however. Organizations such as New England Anti-Vivisection Society (NEAVS) advocate for superior, humane science to cure human diseases—without the use of animal models.
Guerezas are listed in Appendix II of the Convention on International Trade in Endangered Species (CITES), an international agreement between governments whose goal is to ensure that international trade in specimens of wild animals and plants does not threaten their survival. The species also appears as Class B of the African Convention on the Conservation of Nature and Natural Resources.
Protected areas, such as national parks, offer a modicum of safety to those guerezas residing within the parks’ boundaries.
Scientists agree that further taxonomic study is needed to determine the validity of the eight subspecies and to accurately determine the conservation status of those classified as Data Deficient. Research is currently underway in Kenya to collect baseline data on the Endangered Mt. Uarges guereza for the purpose of establishing appropriate conservation initiatives.
African Wildlife Foundation (AWF) is one organization working to protect the guereza. Projects include using technology, such as Geographic Information System (GIS), to identify key threats to conservation and pinpoint areas with the most potential for wildlife. Working with local livestock farmers to develop sustainable agricultural practices while conserving guereza habitat is another AWF initiative.
Written by Kathleen Downey, December 2017