MOUSTACHED GUENON

Cercopithecus cephus

Geographic Distribution and Habitat
Moustached guenons, also known as moustache monkeys (Cercopithecus cephus), are native to western Africa. Their geographic distribution begins south and east of the Sanaga River and extends to the banks of the Congo/Ubangi river system. The region where the Congo River empties into the Atlantic Ocean was once thought to be a natural blockade to the species’ range. But the monkeys’ presence here—how or when these intrepid primates crossed this river barrier is unknown—have led researchers to acknowledge the species’ wider distribution. Accordingly, moustached guenons are known to reside within southern Cameroon, southwestern Central African Republic (CAR), northwestern Angola, Equatorial Guinea, Gabon, eastern Democratic Republic of the Congo (DRC), and the neighboring Republic of the Congo.

Primary, lowland tropical rainforests are their favored habitat. Secondary rainforests, along with gallery forests, flooded forests, and mangrove forests provide alternate habitats.

Researchers recognize three subspecies, or “children,” of the moustached guenon “parent” species. (Note the interchangeable spelling/nomenclature for the species and subspecies: “mustached” instead of “moustached”; “monkey” instead of “guenon.”)

  • Red-tailed mustached monkey (Cercopithecus cephus cephus): the nominate subspecies, shares about 70 percent of the parent species’ range, occupying the African countries of Cameroon, Gabon, Equatorial Guinea, Republic of the Congo, and the Central African Republic (CAR). The Sanaga River in the north and the Ogooué River in the south serve as geographic boundaries. (This monkey is not to be confused with the red-tailed monkey, also known as, Schmidt’s guenon (Cercopithecus ascanius schmidti)and also known as the black-cheeked white-nosed monkey).
  • Gray-tailed mustached monkey (Cercopithecus cephus cephodes): found in the Angolan province and exclave of Cabinda; in the southern region of the Republic of Congo; in Gabon (south of the Ogooué River); and in a small coastal area of the Democratic Republic of Congo (DRC), where the Congo River serves as the southern geographic boundary.
  • White-nosed mustached monkey (Cercopithecus cephus ngottoensis): resides in the prefecture of Mambéré-Kadéï within Central African Republic (CAR), east of the Ubangui River; as far north as the capital city of Bangui; and in the northern region of the Democratic Republic of the Congo.
Moustached guenon range, IUCN 2019

Size, Weight, and Lifespan
Males are a bit larger than the females (an example of sexual dimorphism), carrying a bit more girth on their frames and standing a bit taller.

Average weight for an adult male is 8.8 lb (4 kg); average weight for an adult female is 7.9 lb (3.6 kg).

Head-to-body length for adult male moustached guenons is 23 in (58 cm); head-to-body length for adult female moustached guenons is 19.3 in (49 cm). Tail length adds another 31 in (78 cm) to the male’s physique and another 27.4 in (69.5 cm) to the female’s physique.

Lifespan for the species is uncertain. A wild-born female who was captured as a child lived in captivity for 31 years; at her death she was thought to be as old as 36 years. Average lifespan in the wild for close cousins within the genus Cercopithecus is about 22 years.

Appearance
This monkey may have one of the most alluring faces in the primate world. Mother Nature has powdered the cheekbones, the skin surrounding the copper-colored eyes, and narrow muzzle in shades of bluish-gray with whispers of violet undertones for a sublimely beautiful mask. A crescent-shaped white strip of fur between the nostrils and upper lip—the monkeys so-called “mustache”—adds décor. Giving further contrast are yellow-orange tufts of fur that fan out from either side of the face, bordering long, black hairs that tickle just beneath the mustache.

A pronounced brow line demarcates the face from a black and reddish-gold speckled fur cap that hugs the forehead. Dark, scalloped ears sit demurely and are evenly aligned.

Both males and females are cloaked in the same color pelage.

The fur covering the monkeys’ back and limbs matches the black and reddish-gold color pattern of their fur cap, while the fur on their underside is an ashen gray color. Reddish fur adorns their long, nonprehensile tail.

Hairless, callused areas on either side of their rump—scientifically known as ischial callosities, more casually known as rump pads and characteristic of Old World monkeys—provide comfort to the guenons while they sit.

What Does It Mean?

Anthropogenic:
Environmental disturbance or environmental pollution originating in human activity. ​

Commensalism:
An association between two organisms in which one benefits and the other derives neither benefit nor harm.

Exclave:
A territory (or a part of one) that is entirely surrounded by the territory of one other state.

Nominate subspecies:
In zoological nomenclature, when a species is split into subspecies, the originally described population is retained as the “nominotypical subspecies,” which repeats the same name as the species.
Denoting a race or subspecies that is given the same epithet (the part of a taxonomic name identifying a subordinate unit within a genus) as the species to which it belongs; for example, Cercopithecus cephus cephus.
 
Pelage:
The fur, hair, or wool of a mammal.
 
Sexual dimorphism:
Distinct difference in size or appearance between the sexes of an animal in addition to difference between the reproductive organs themselves.

Subadult
An animal who is not fully adult.

Visit the Glossary for more definitions

Diet
Moustached guenons are omnivores, meaning that they eat foods of both plant and animal origin. The bulk of their diet, however, consists of fruits. One essential dietary staple is the fruit, or rather the nut, of the oil palm (Elaeis guineensis). In fact, these “frugivorous omnivores” have adapted to subsist on the fruity pulp of these nuts. So crucial is this sustenance to their survival, the guenons reside only in regions where oil palms are abundant.

Seeds and leaves provide the “croutons” of their plant-based diet. The occasional insect, nestling, and bird’s egg provide foods of animal origin.

Behavior and Lifestyle
These monkeys are both diurnal (active during daylight hours) and arboreal (spending most their time in trees). They travel through their treed environment quadrupedally (on all four limbs), their long nonprehensile tails providing balance and their opposable thumbs helping them to grip (both are physical attributes characteristic of Old World monkeys). Graced with impressive agility, moustached guenons easily leap from tree to tree. These impressive acrobats have been known to leap an astounding 65 ft (20 m) between trees when escaping a predator

Their day of foraging begins before dawn has broken. Following one another along the same routes each day, the guenons arrive at lush fruit trees and lay claim to their bounty before any other primates arrive. But they might not be able to consume such ample amounts in one sitting. Not to worry. Like all guenon species, moustached guenons are fitted with ginormous cheek pouches, which they stuff with fruits for later eating—preferably in a secluded area away from predators. And if they are still hungry at end of day? These guenons are known to return to fruiting trees in the early evening hours to eat whatever leftovers might remain from other primates. They then go to bed with full stomachs, choosing sleeping sites within tangles of vegetation in the lower to middle levels of the forest.

Fun Facts

Moustached guenons’ ginormous cheek pouches hold as much food as their stomach!

There are at least 26 guenon species in the genus Cercopithecus.

Daily Life and Group Dynamics 
A group (or “troop”) of moustached guenons might be led by an adult alpha male with 10 to 40 females in his harem along with their young offspring. (One study puts average group size at 22 individuals.) Occasionally, an outsider adult male (one or several) may infiltrate the troop to try his luck with the ovulating females, particularly when the harem is large (does he think the alpha male won’t notice because there are so many females? Or perhaps the alpha male turns a blind eye, a kind of tacit permission, because he is unable to “service” all his ladies himself?). These randy male interlopers are sexual opportunists who hope to quickly copulate and leave; they might pass on their genes in the act. However, females are not always receptive to an outsider male’s advances. If they are disinterested in the “Wham bam, thank you, ma’am” interloper, females will rebuff his advances and chase him away.

Another troop composition consists solely of males in what is colloquially known as a “bachelor group.” Of course, at some point these bachelors must venture out of their testosterone-imbued brotherhood if they wish to find a female with whom they can copulate—and perhaps procreate.

Among primate societies, moustached guenons hold the distinction for forming “polyspecific associations”; that is, a troop may include multiple species, including other guenons and mangabeys. These mixed-species members commonly forage with one another.

Home range has not been documented in the species; however, moustached guenons are known for their wanderlust. Their explorations often take them to the edge of the forest and to tracts of forest where trees are being cut down (maybe their presence is to show their consternation—or heartache—for this anthropogenic activity?). Researchers posit that the species’ home range is likely about 296 ac (120 ha), similar to that of the closely related black-cheeked white-nosed monkey, aka, Schmidt’s guenon.

Natural predators include leopards, snakes, birds of prey—and chimpanzees. Moustached guenons must also be fearful of humans, who kill the monkeys for their flesh or kidnap them to keep or sell as pets.

Communication
Vocalizations, visual cues, tactile activity, and possibly chemical cues serve moustached guenons in communicating with others.

More than 20 distinct vocalizations—including alarm calls, chirps, whistles, low croaking noises, and loud sneezing sounds—have been attributed to the genus Cercopithecus. Each guenon species puts a unique “accent” on these vocalizations. However, all the guenons across the genus learn one another’s warning calls—so they are better able to avoid danger and keep one another safe.

Subadult moustached guenons emit a soft, trill-like call, deferential in its nature, that oscillates in a descending pitch when they are approached by an adult.

A sharp, staccato-sounding, rhythmically repeated bark is emitted by males when they wish to send a warning.

Both males and females emit a “ke-ke-ke” call when frightened.

Visual cues convey important messages through specific body posturing. “Stare-downs” indicate a threat. With his eyes focused on the individual he wishes to intimidate, a moustached guenon raises his eyebrows, thereby retracting his scalp, and contorts his face into a grimace. He might also hang open his mouth, keeping his teeth covered, while he bobs his head up and down.

A friendlier, tactile exchange is the nose-to-nose greeting used by moustached guenons when approaching one another. This “Eskimo greeting” is often followed by play or grooming sessions—important activities that help to establish social bonds with one another.

Chemical communication has not been documented in the species. However, researchers posit that moustached guenons practice this scent-based method, as do most Old World primate species.

Reproduction and Family
The mating system in moustached guenon societies is mostly polygnous; that is, one male (the troop’s alpha) mates with all the females in his harem. But when his harem is particularly large, the mating pattern may become polygynandrous; that is, both males and females have multiple mating partners during a breeding season. This scenario occurs in moustached guenon societies when those randy outsider opportunistic males temporarily join a group with the sole purpose of having sex with the females.

Males and females attain sexual maturity between 4 and 5 years old, with females reaching this milestone a bit earlier than males. To initiate copulation, a female presents her rump to a male.

Like other nonhuman primate species, moustached guenons take environmental cues when it comes to breeding and giving birth. Infants born at the end of the rainy season, when food is most plentiful, have the best chance of survival.

The breeding season for the majority of this guenon population is from July through September, with births occurring from December through February. In the equatorial countries, however, where rainfall is year-round, mating and births occur year-round.

Because these highly social animals spend so much time in the company of other monkeys and guenon species, researchers speculate that they may rely on their distinctive pelage patterns to prevent interbreeding. Should they mate across species, their offspring would likely be prone to poor health ramifications. Wild guenons rarely interbreed; however, captive (zoo) guenons are known to do so.

After a pregnancy of nearly six months (172 days), a female gives birth to a single infant. This tiny newborn, who weighs a mere 340 g (11.99 oz), is able to cling to the fur on its mother’s stomach. A mother nurses her baby for a full year, at which time the infant is considered weaned. Birth interval in the species is 821 days.

Mothers are the primary caregivers and protectors. An alpha male may protect his troop against rival males and from predators, indirectly protecting his offspring, but he has little to do with their daily care or upbringing.

Photo credit: Peggy Motsch/Creative Commons

Ecological Role
​Thanks to their largely frugivorous diet, moustached guenons help to regenerate their forest habitat by dispersing seeds, via their feces. Certain native birds benefit as well, particularly a subspecies of the long-tailed hornbill (Tropicranus albocristatus cassini), who picks and eats the seeds and insects (drawn to the poop piles). These avian opportunists know where and how to find a meal, a classic example of commensalism.

Conservation Status and Threats
The moustached guenon is classified as Least Concern by the International Union for Conservation of Nature (IUCN, April 2017), appearing on the IUCN Red List of Threatened Species. Although the species is common and widespread through some sections of its geographic range, these monkeys are routinely hunted—very much a concern for their survival. In fact, moustached guenons are one of the most frequently, and illegally, “harvested” monkeys; their flesh is sold for local consumption at bushmeat markets. Though wildlife biologists agree that the species is in decline, population numbers cannot be quantified due to a lack of data.

Only in northern Congo and most of Gabon are the monkeys considered common. They are extremely rare in DRC, in central and southern Congo, and in the forests of coastal Congo outside of protected areas. A survey conducted in 2011 found only a few individuals in all of Equatorial Guinea.

Deforestation is another threat to the species survival. Infrastructure and human settlements have razed much of the moustached guenons’ habitat.

Palm oil expansion may not be a current threat, as it is to Critically Endangered orangutans who live about 7,000 miles away (more than 11,000 km) in Borneo, where palm trees are planted and cultivated in tracts of razed, once-pristine forestland. But the companies driving these activities—harvesting oil from palm nut trees to become ingredients in soaps, cosmetics, and biofuels—are looking to expand their operations into Africa (according to an August 2018 article in BBC News).

Oil palm trees are native to western Africa. And moustached guenons rely on the fruity pulp of the palm nuts for their crucial sustenance. So the potential of a threat exists. Wildlife biologists have sounded the alarm that Africa’s primates are already in steep decline due to poaching and habitat loss. They stress that the possibility of oil palm expansion and African primate conservation are two disparate undertakings that cannot be reconciled.

Of the three subspecies, the white-nosed mustached monkey faces the greatest survival threat. Classified as Endangered by the IUCN, the species is heavily hunted. These monkeys also find themselves casualties of civil unrest and political conflict in their small geographic range. Both the red-tailed mustached monkey and the gray-tailed mustached monkey are classified as Near Threatened by the IUCN.

Conservation Efforts
Moustached guenons 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 is also listed in Class B of the African Convention on the Conservation of Nature and Natural Resources and in Annex B of the EU Wildlife Trade Regulations.

Protected areas where populations of moustached guenons reside include most of its geographic range. However, as is too often the case, these protections are not always enforced—or rather, they are routinely violated. Hence, even in national parks and reserves, the monkeys are hunted and killed.

Wildlife biologists assert that additional surveys are necessary to make effective conservation decisions. They call on government and conservation agencies to do more—and to work together—for the sake of preserving Africa’s tropical forests and wildlife.

The creation of educational programs and employment opportunities for local citizens must also be a part of primate conservation efforts. Bushmeat hunting is linked to survival for those who earn little to no income otherwise. An October 2019 Reuters article profiled one bushmeat hunter who earned a meager $75 monthly paycheck, supplemented by another $7 to $60 for the number of monkeys he killed and sold at market (keeping just enough flesh to feed his family). “This is Congo: we try to do whatever we can to make it,” he stated.

Are you on Facebook? “Like” the Guenon Conservation Community Facebook page. Most recent activity appears to be from 2019; however, you will find enlightening articles and conversations: https://www.facebook.com/GuenonConservationCommunity.

References:

  • https://www.iucnredlist.org/species/4214/166614362  2020
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Written by Kathleen Downey, September 2021