AGILE MANGABEY

Cercocebus agilis

Geographic Distribution and Habitat
Agile mangabeys are Old World monkeys found north of the Congo River to Garamba and the Semliki River. They are present in Cameroon, northeast Gabon, northern Congo, and the Democratic Republic of the Congo, the Central African Republic, and possible Equatorial Guinea.

Agile mangabeys are found primarily in forested areas such as flooded forests, swamp forests, or forests near bodies of fresh water. Some populations live in non-flooded mixed forests away from bodies of water. Agile mangabeys prefer the understory of the forest and are terrestrial when traveling and feeding.

Agile mangabey range, IUCN 2019

Size, Weight, and Lifespan
The size of agile mangabeys can vary, with western populations being slightly larger than eastern agile mangabeys. Sexual dimorphism is present, with adult females attaining about 60 percent of the mass of adult males. On average, agile male mangabeys are 20–26 in (51–65 cm) in length and weigh about 15–29 lbs (7–13 kg), while females are smaller than males measuring 17–22 in (44–55 cm) and weighing 11–15 lbs (5–7 kg).

Agile mangabeys can live up to 20 years in the wild.

Appearance
The pelage of agile mangabeys is brownish-gray agouti. (Agouti is a hair pattern that has a few alternating bands of color.) The long non-prehensile tail is also brownish-gray, but only agouti at the base of the tail. The tips of the hair are usually black on the dorsal side. Their coat is light tan on their underside. The hands, feet, upper eyelids, and skin of the ears and face are all black. Infants are born with lighter colored faces, which darken as they age.

The skulls of agile mangabeys are rather broad like many members of the Cercocebus genus. The upper molars are wider than they are long, which aids in cracking open nuts and ripping open tough fruits.

Agile mangabeys are members of the white-eyelid group of mangabeys that are characterized by bare upper eyelids that are lighter than their facial skin coloring. They share this unique feature with five other mangabey species: sooty mangabey (Cercocebus atys)red-capped mangabey (Cercocebus torquatus)Sanje mangabey (Cercocebus sanjei), Tana River mangabey (Cercocebus galeritus), and the Golden-bellied mangabey (Cercocebus chrysogaster). White-eyelid mangabeys are more closely related to mandrills and drills than any of the other mangabey species.

Photo credit: leamaimone/Flickr/Creative Commons

What Does It Mean?

Dominance hierarchy:
A type of social hierarchy that arises when members of a social group interact, often aggressively, to create a ranking system. In social living groups, member are likely to compete for access to limited resources and mating opportunities. 

Forest floor:
The fourth and bottom layer of the forest. It’s very dark and almost no plants grow in this area as a result.

Old World monkey:
Monkeys native to Africa and Asia.

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.

Terrestrial:
Living on the ground.

Understory layer (of a forest):
The third layer of the forest, above the forest floor. Little sunshine reaches this area, so plants must grow larger leaves to reach the sunlight. These plants seldom grow to 12 feet.

Visit the Glossary for more definitions

​Diet
Agile monkeys have cheek pouches in which they gather food for later consumption. They are omnivores who feed on plants, fungi, and animal material, eating both ripe and unripe fruit, as well as nuts and seeds. They have large incisors and strong jaw muscles that they use to crack open fruits, pods, and nuts that are too tough for other monkey species to eat. They particularly like old hard nuts that they open with their large and robust molars. In addition, they consume the tips of herbs and grasses, roots, fungi, insects, and bird eggs.

Behavior and Lifestyle
Like other mangabey species, agile mangabeys are diurnal, being active during daylight hours. They are primarily arboreal (live in trees), but spend a significant amount of time on the ground, especially during the dry season. Males tend to spend more time on the forest floor than females. They travel using quadrupedal locomotion (walking and running on all fours).

Grooming is common in agile mangabeys; however, the receiver almost never reciprocates. Females typically groom only juveniles.

Unfortunately, there are few in-depth studies on the behaviors and lifestyle of agile mangabeys in the wild.

Daily Life and Group Dynamics 
Groups consist of 7 to 22 individuals, which include one or multiple males and multiple females and are led by a single male. If multiple males are present in the group they tend to avoid each other. Adult males not in groups tend to travel singly. During the peak of the rainy season and at the start of the dry season, smaller groups sometimes come together to form larger groups.

In the dry season, groups travel up to 2 miles (3.2 km) a day in search of food. When fruit is absent, the group ranges further. These seasonal patterns increase their total home range size. 

There is a dominance hierarchy in agile mangabey groups in which group members create a ranking system. The most dominant individuals usually get first choice in mates and food sources.

Fun Facts

Agile mangabeys are known to contract the T-cell leukemia virus that is similar to the leukemia virus that infects humans.

Like all “cheek pouched” monkeys, agile mangabeys gather food in the pouches of their cheeks to save food for later consumption.

Known predators of the agile mangabey are leopards, pythons, crowned-eagles, and humans.

Communication
One of the primary communication methods between group members is vocal signals. It is important for agile mangabeys to emit danger calls to group members when danger is present. A danger call is also known as a “chuckle” call.

Agile mangabeys utter loud calls to locate a group’s position in regard to other neighboring groups in dense foliage.

When greeting one another, greeting grunts are emitted. This is mainly used by males when juveniles approach them. It is also used to reassure them.

Olfactory communication is used by males when determining whether females are in estrus. Usually the male sniffs the female in response to her presenting to him.

Agile mangabeys communicate through visual cues such as staring, head bobbing, pouting, and social presenting. Staring and head bobbing are used as threat displays. Females pout to communicate sexual receptivity or when ready to mate. Social presenting is often used to conciliate aggression and is used by a subordinate toward a more dominant group member.

Reproduction and Family
Agile mangabeys reach sexual maturity at 4 to 5 years of age. Although not much is known about them in the wild it is assumed that they are either polygynous or promiscuous, which means that both males and females have multiple mates during breeding season.

Females develop sexual swellings when they are in estrus or when they are ovulating. This lasts just under two weeks and attracts the attention of mature males. Sometimes conflict occurs between males who are interested in mating with the same female.

Agile mangabeys breed year-round and typically birth one offspring at a time. Their gestation period, or the period of development in the womb, lasts 165 to 175 days (5.5 to just under 6 months). A group of well-studied agile mangabeys at the Bai Hokou research site in the Dzanga Sangha Protected Areas in the southwestern region of the Central African Republic, where agile mangabeys are habituated to the presence of human scientists, have an established birthing season from July to August during which most of the females give birth. Scientists speculate that this simultaneous birthing might be a biological tactic that obscures paternity, increasing male protection of the offspring and reducing risks of infanticide.

Newborns are mostly hairless and cling to their mothers’ underbellies for safety. The mother is the primary caregiver, nursing and carrying her infant. Occasionally, males hold and carry infants too. In general, not much is known about behaviors related to paternity; however, the habituated males at Bai Hokou tend to guard their mates, and females have shown preference for association with certain males. Biologists speculate that these behaviors could indicate awareness of who sired the infant.

Offspring become fully independent around 3–6 years old.

Young agile mangabey. Photo credit: David Schenfeld/Flickr/Creative Commons

Ecological Role
Agile mangabeys play a primary role in dispersing seeds throughout the forest. Since they specialize in breaking open and eating tough seed pods, nuts, and fruits, it is likely that they play a role in reproduction of the plant species they consume. Thus, they regenerate their forests.

Conservation Status and Threats
The agile mangabey is categorized as Least Concern by the International Union for Conservation of Nature (IUCN, 2018). However, their populations are decreasing due to hunting for bushmeat, as well as retaliatory killings that result from the monkeys raiding farmer’s crops. In addition, since agile mangabeys spend a good amount of time on the forest floor, they are vulnerable to snaring, a hunting method used throughout their range. Snares are usually set out for animals such as forest antelopes or rodents, but they often capture any terrestrial animals in their path, killing or maiming them.

On the western, northern, and eastern edges of their geographic range, agile mangabeys are threatened by a substantial amount of habitat loss caused by deforestation for firewood and timber. Mining and quarrying are additional threats. The ongoing disturbances to the home of the agile mangabey not only causes stress on this species, but stress on the entire ecosystem, thereby threatening their survival.

Conservation Efforts
The agile mangabey is listed on Appendix II of the Convention on International Trade in Endangered Species (CITES) and on Class B of the African Convention on the Conservation of Nature and Natural resources. It is listed as partially protected in Cameroon, Congo, and DRC. In Equatorial Guinea the hunting, sale, and consumption of primates is forbidden by Presidential Decree. They are also on List C of Annex 2 Ordinance 84.045 of 1984 in Central African Republic (CAR). Cameroon, Gabon, and Congo are currently revising their protection species list.

Agile mangabeys have been recorded in a number of protected areas including: 

  • Cameroon: Lobéké NP, Boumba Bek NP and Nki NP, and Mengame Gorilla Sanctuary.
  • CAR: Dzanga-Ndoki NP, Mbaéré-Bodingué NP, and Zemongo Reserve.
  • Congo: Nouabalé-Ndoki NP, Lac Télé Community Reserve, and Odzala-Kokoua NP.
  • DRC: Bili-Uéré Hunting Domain (Hicks 2014), Garamba NP, and Okapi Wildlife Reserve.
  • Gabon: In 1975 a study (Quris 1975) recorded the agile mangabey present south of the Ivindo River (just to the east of what is now the north of Ivindo NP). It has not been recorded in protected areas of Gabon since. However, in 2013 it some scientist suggest that they may still occur in Invindo NP, Minkébé NP, and Mwagna NP.

Research is recommended to determine the western limits of agile mangabey distribution. Additional conservation actions are needed, such as education and awareness, land and water management, research on population trends and behavior, as well as monitoring harvest trends versus population size in agile mangabeys. To ensure protection of the agile mangabey and its habitat, more efficient laws and policies are needed on both the sub-national and national level.

​References:

  • ​https://www.iucnredlist.org/ja/species/136615/17955862
  • https://animaldiversity.org/accounts/Cercocebus_agilis/#fe80017cb90d7d3a60af0a9df97af011
  • http://www.theprimata.com/cercocebus_agilis/
  • Devreese L, Huynen M,-C, Stevens JMG, Todd A. 2013. Group Size of a Permanent Large Group of Agile Mangabeys at Bai Hokou, Central African Republic. Folia Primatol. 84:67-73.
  • https://wwf.panda.org/wwf_offices/wwf_offices_in_africa.cfm?329359/The-Agile-Mangabey-group-at-Bai-Hokou
  • Fleagle JG. 2013. Old World Monkeys. Primate Adaptation and Evolution. 119-150.​

Written by Tara Covert, December 2019