Agile Mangabey, Cercocebus agilis
AGILE MANGABEY
Cercocebus agilis
Geographic Distribution and Habitat
The agile mangabey (Cercocebus agilis) is a primate species native to several countries on the African continent: the Democratic Republic of the Congo, the Republic of Congo, Cameroon, Central African Republic, and Gabon. Although they have different geographical boundaries in each direction, agile mangabeys can be found throughout the Congo Basin, which is the largest tropical forest in Africa and the second-largest tropical forest in the world.
In totality, the Congo rainforest covers over 741.32 million acres (300 million hectares). The Congo Basin experiences two rainy seasons, one from March to May and another from September to November. In contrast, the driest season is from June to August. Rainfall is common year-round, and the average annual rainfall is around 60 inches (152 centimeters). Additionally, the average year-round temperature is about 70 degrees Fahrenheit ( 26 degrees Celsius).
Agile mangabeys have a home range that is estimated to be around 1.16 square miles (3 square kilometers). Throughout their range, they can be found living in many different habitats, including seasonally inundated forests, riparian forests, and terra firma forests. Geographic boundaries within this range include the Dja Biosphere Reserve and the Ubangui River, which are found in Cameroon, and the Congo River, also known as the Zaire River, which flows through the Democratic Republic of the Congo, the Republic of Congo, and Angola.
They are most active in the lower portion of their habitat, preferring elevations under 32 feet (10 meters), although their upper elevation limit is 3,359.6 feet (1,024 meters).
Size, Weight, and Lifespan
Agile mangabeys are sexually dimorphic, meaning there are noticeable size differences between males and females. Male agile mangabeys are typically larger and heavier than their female counterparts and have an average body length of 20 to 26 inches (50.8 to 66.04 centimeters). Males weigh between 15 to 29 pounds (6.8 to 13.15 kilograms). Comparatively, being smaller than males, females have a body length of roughly 17 to 22 inches (43.18 to 55.88 centimeters) and weigh between 11 to 15 pounds (5.0 to 6.8 kilograms), on average.
Both males and females have tails that are longer than their bodies. Although the exact size is unknown, other primates in this genus have tails that range between 20 to 39 inches (50.8 to 99.06 centimeters). Just as with their size and weight, the tails of males tend to be longer than those of females.
Although the exact life expectancy for wild agile mangabeys is unknown, when considering other mangabey species, it is hypothesized that agile mangabeys live until about 20 years old.
Appearance
Agile mangabeys are characterized by their dusty-olive, brown, or gray hair, caramel-brown colored eyes, and white skin. As identified on most of the body, the skin of an agile mangabey is predominantly white, or light pink, and can be seen under a layer of thick fur. Other body parts, such as the muzzle or hands and feet, differ. The muzzle, which is the projecting part of the face that includes the nose and mouth of a primate, is black or gray. Their hands and feet are also this color.
Agile mangabeys are characterized by their white eyelids, which happen to be bare of any hair or fur. Evolutionarily speaking, the benefit of primates having bare, or lightly-colored eyelids is likely so that they can utilize this feature as a way to enhance their visual communication skills. White eyelids may play a significant role in an individual’s ability to socially interact with other primate species, especially during confrontations. Besides agile mangabeys, other primates that share this feature includes: collared mangabeys (Cercocebus torquatus), golden-bellied mangabeys (Cercocebus chrysogaster), sanje mangabeys (Cercocebus sanjei), sooty mangabeys (Cercocebus atys), Tana River mangabeys (Cercocebus galeritus), and white-naped mangabeys (Cercocebus lunulatus).
Unlike some of Latin America’s arboreal primate species, agile mangabeys do not have prehensile tails, which means that they cannot use their tails to hold or grasp objects. Instead, their tails are used to assist individuals with balance, especially as they climb and run on tree branches within the forest. In color, the tail of an agile mangabey is light-brown.
Diet
Agile mangabeys are omnivorous monkeys, meaning they eat food from both plants and animals. Their diet mainly consists of fruit, seeds, grasses, mushrooms, insects, bird eggs, and some vertebrate prey. Having a unique dental formula, mangabeys are also able to bite through the hard shells of some fruits and other food resources. These food types, also known as fallback foods, often have low nutritional value and are challenging to consume. Fortunately, fallback foods do not make up a significant portion of an agile mangabey’s diet, and they are really only consumed when an individual’s preferred resources are not readily available.
Throughout their geographic range, agile mangabeys are known to eat at least 42 different species of fruits, some of which include dika nuts (Irvingia gabonensis), sugar plums (Uapaca kirkiana), kola nuts (Cola acuminata), figs (Ficus cyathistipula), bananas (Musa acuminata Colla), and jackfruit (Artocarpus heterophyllus). Insect species include termites (Isoptera), ants (Dorylus), African honeybees (Apis mellifera), and potter wasps (Delta lepeleterii ). Additionally, the most notable vertebrates that agile mangabeys consume are infant Peter’s duikers (Cephalophorus callipygus), which are small, reddish brown antelope-like creatures.
To assist with the large amount of food they consume in a day, mangabeys have large cheek pouches in which they store their food. These pouches extend down the sides of their necks and can hold large quantities. Not only do they assist with storage, but these pouches allow agile mangabeys to efficiently forage and quickly transport food away from predators.
Behavior and Lifestyle
Agile mangabeys are named for their ability to move quickly and nimbly with ease and speed across an arboreal environment. That is, they are agile! As quadrupedal primates, they use all four of their limbs for locomotion, which includes walking, running, and jumping. In fact, agile mangabeys are capable of jumping up to 30 feet from one branch to the next! With long arms, legs, tails, and opposable thumbs, they use their adaptations to rummage through trees, deftly navigating the forest. Much of their days are spent foraging for food, exploring their home range, or socially engaging with other troop members.
Although they are mostly arboreal, agile mangabeys spend up to 22% of their daytime on the ground, especially during the dry season. During the dry season, they spend more time on the ground due to factors like water availability, food scarcity, and temperature changes. During this time, trees typically have less fruit and water sources, which forces primates to seek alternatives. Additionally, because temperatures during the drier season tend to increase, mangabeys may also seek water sources as a way to regulate their internal temperatures. Swimming, or wading, can prove very beneficial under these circumstances and will set agile mangabeys up for success!
As diurnal primates, after a long day spent traveling and foraging, once the sun has set, agile mangabeys retreat to their sleeping sites. Such sites, or nests, are constructed in the forest canopy and are typically located in trees at least 88.58 to 121.4 feet (27 to 37 meters) in height. The height and location of these sites are strategically positioned by mangabeys to help them avoid predators, both aerial and terrestrial.
The natural predators of agile mangabeys include forest leopards (Panthera pardus pardus), African rock pythons (Python sebae), African crowned hawk eagles (Stephanoaetus coronatus), and humans.
Did you know nonhuman primates can get cancer? While cancer is less common in many non-human primates compared to humans, they can still develop tumors and certain cancers. In fact, agile mangabeys are known to contract T-cell leukemia virus, which is similar to the leukemia virus that spreads through the human body.
T-cell leukemia virus, specifically Simian T-Lymphotropic Virus 1 (STLV-1), is associated with various symptoms. For nonhumn primates, biological symptoms of this disease include regional or generalized lymph node enlargement, the enlargement of both the liver and spleen, and red blood cell deficiencies. This disease may occur spontaneously through environmental exposures, viral infection, or through genetics.
As of today, there are no established methods for treating cancer in wild primates.
Mangabeys are highly social primates, and they live in groups called “troops”. The average troop of agile mangabeys consists of anywhere between 7 to 20 members, and each troop is made up of a variety of males, females, juveniles, and infants. These individuals are all led by one adult male. This male, the most dominant member of a troop, acts as the leader and protector to all other individuals.
Females stay with the troops that they were born into from birth to death. In contrast, juvenile males, once they reach sexual maturity, at about five years old, leave the natal troop. While away from their birth troop, these males will explore their environment in search of another troop to join. They will remain alone until they can find a troop, or establish a new troop in which they will serve as alpha male.
To become a troop’s dominant male, or gain rank in the troop’s social hierarchy, juvenile male mangabeys engage in four types of behavioral patterns to create change. These patterns include: directly challenging a high-ranking male; joining with an aggressor against a higher-ranking opponent; challenging a higher-ranking individual, while in the area of an even higher-ranking individual, and enlisting their support against the former; and challenging a higher-ranking monkey when an adult male is in the area, enlisting the support of the adult. Without the support of females, if a juvenile is able to defeat his opponent, he will move up in rank. Contrarily, if he loses, his ranking will fall.
Unfortunately, those with low rank have an increased likelihood of facing neglect and abuse from their superiors. For example, an individual at the bottom of the social ladder may have less access to preferred food sources, fewer mating opportunities, and is likely to be the target of aggression, harassment, or displacement.
When it comes to communication, agile mangabeys are typically heard before they are seen. In fact, agile mangabeys can be quite noisy! Each individual has specialized throat sacs that enhance their vocal resonance, allowing for a strong, booming call. The sac, which is often larger in males than in females, enables individuals to produce calls such as shrieking, barking, and shouting.
Interestingly, adult mangabeys also produce a sound that biologists refer to as a “whoop-gooble”. This call is used to attract the attention of nearby mangabeys and can be heard from up to 0.62 miles (1 kilometer) away. This particular call is particularly useful for agile mangabeys to avoid geographical overlap with other species.
In addition to vocal communication, agile mangabeys also communicate through bodily gestures. This includes facial expressions and facial displays. For example, as previously mentioned, agile mangabeys have white eyelids, which can be flashed to emphasize messages they wish to convey. Moreover, behaviors such as head bobbing or open-mouthed staring can serve as social signals to troop members, but they may also indicate aggression to outsiders.
Female agile mangabeys experience a gestation period of about 170 days, which is the time it takes for a fetus to develop inside the mother’s womb. Once the gestation period is complete, mothers give birth to one infant. On rare occasions, she may give birth to twins.
Infant agile mangabeys are born with light-colored hair and soft fur, typically weighing around 1 pound (453.59 grams)—approximately the same weight as one can of soup! For the first couple of months, infants cling to their mother’s abdomen before transitioning onto her back. They are usually weaned at around 7 to 10 months of age, but will remain close to their mother for grooming, protection, and care. As they mature, aunts or siblings may step up to assist the mother with infant care. This process, also known as allomothering, is a behavior common in many social species. One of the advantages of allomothering is that it can provide the mother with additional support, enabling her to focus on other tasks, particularly if she has other children to care for.
Agile mangabeys, both male and female, reach sexual maturity between the ages of 4 and 5 years old. In males, sexual maturity is marked by an increased rate of penile erections, thrusting, and mounting. A female’s sexual maturity is marked by the swell of her buttocks, or perineal area, which swells when she is sexually receptive and ready to mate.
Like many primates, agile mangabeys are seed dispersers and play a crucial role in promoting forest regeneration and biodiversity. Seed dispersal is the process by which seeds are moved away from their parent plant to new locations, which enables them to colonize new areas and adapt to changing environments. So, when mangabeys eat or excrete seeds, a new plant may germinate in a new location. By dispersing seeds, this process allows plants to avoid overcrowding and competition with other species, especially for resources like sunlight and nutrients. Mangabeys contribute to the regeneration of forest ecosystems, especially in fragmented areas that lack species diversity.
The International Union for Conservation of Nature lists agile mangabeys as Least Concern (IUCN, March 2018), appearing on the IUCN Red List of Threatened Species.
Agile mangabeys are hunted throughout their range for bushmeat. They are also sometimes persecuted for crop raiding. Because they spend a fair proportion of time on the ground, they are vulnerable to snaring—a method of hunting used throughout their geographic range. Snares are usually set for forest antelopes and rodents, but can catch any terrestrial animal.
According to the IUCN, agile mangabeys occur at a low density, meaning that the areas where individuals live, per unit of land, are very small. Because it is hard to identify them within their small environment, a low density and a significant population decrease are expected. More data is needed to properly quantify the threats to this species.
That being said, considering their geographic range, primates in the Congo Basin are vulnerable to hunting pressures, snaring, and habitat loss due to deforestation.
The agile mangabey is 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.
Agile mangabeys have been recorded in various protected areas throughout their geographic range. Examples of such protected areas include: Mengame Gorilla Sanctuary, Dja Biosphere Reserve, Chinko Reserve, Zemongo Reserve, Lac Télé Community Reserve, Okapi Wildlife Reserve, etc.
Nationally, agile mangabeys are partially protected in Cameroon, the Democratic Republic of the Congo, and the Republic of Congo. Unfortunately, they are not listed in Gabon’s protected species list, although their list is currently being revised. Furthermore, by Presidential Decree, the hunting, sale, and consumption of primates is forbidden in Equatorial Guinea.
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Written by Brooklynne Mitchell-Arno, May 2025