Dent’s Monkey, Cercopithecus denti
DENT'S MONKEY
Cercopithecus denti
Geographic Distribution and Habitat
Dent’s monkeys (Cercopithecus denti), also called Dent’s mona monkeys, are Afro-Eurasian monkeys native to the Democratic Republic of the Congo, Rwanda, Uganda, and possibly Burundi, though populations here have yet to be confirmed. They are bounded to the north by the Uélé River, to the west by the lower Itimbiri River, to the east by the Albertine Rift, and to the south by the forest and savannah ecosystems of Kindu. There have been unconfirmed reports of populations along the Ruzizi Plain in Burundi, but this has not been substantiated. Dent’s monkeys prefer low- to mid-elevation tropical forests. They tolerate elevations up to 7,900 feet (2,400 m) in the eastern part of their range.
Dent’s monkeys are classified in the genus Cercopithecus, members of which are known as guenons, though, as evidenced by Dent’s monkeys, not all members have the word “guenon” in their common name. Historically, the Dent’s monkey was considered a subspecies of the Wolf’s guenon (Cercopithecus wolfi), or sometimes, both the Wolf’s guenon and the Dent’s monkey were considered subspecies of the crowned monkey (C. pogonias). More recently, the Dent’s monkey was elevated to the species level and this is currently the most widely accepted classification, though it is subject to some debate.
Size, Weight, and Lifespan
Female Dent’s monkeys range in weight from 5.3 to 6.8 pounds (2.4 to 3.1 kg), while males are larger, at 8.4 to 9.3 pounds (3.8 to 4.2 kg). They range in head and body length from 17.5 to 20.1 inches (44.5 to 51.1 cm). Their tail adds about another 19 inches (49 cm) to their total length. They are believed to live to an age of about 20 years.
Appearance
Dent’s monkeys are rather small guenons and have a long, lithe body type. Their limbs are long and flexible, with their arms about the same length as their legs. They have a long tail that is invaluable for navigating their canopy homes. Though their tail is nonprehensile, meaning that it cannot tightly grasp, it is extremely important for helping the monkeys maintain their balance. Most of their body is covered in hair that ranges in colors such as brown, tan, gray, and red. Their belly and inner limbs are ivory white. They have a grayish-white beard that frames their black face. Like other members of their genus, they have cheek pouches—handy features that can store nearly as much food as their stomachs. Common for many Afro-Eurasian species, Dent’s monkeys possess ischial callosities—thick, callus-like skin on their buttocks that makes sitting more comfortable. As with many other guenons, males’ scrotums are blue, and this interesting coloration may be an important consideration for mate selection. In addition to their larger size and colorful genitals, males also possess larger canine teeth than females. These differences between the sexes are what make the Dent’s monkey sexually dimorphic.
Diet
Although guenons are typically classified as frugivores, or fruit eaters, studies show that Dent’s monkeys have an extremely varied diet that consists of fruit, arthropods such as caterpillars, flowers, shoots, and leaves. One study found the diet of one population consisted of 58% leaves and 18% fruits over the course of the study period– challenging the standard assumption that all guenons are primarily frugivores.
Behavior and Lifestyle
Dent’s monkeys are diurnal, meaning that, like most humans, they are awake during the day and sleep at night. They are also arboreal, meaning they live in trees, and they move about quadrupedally—on all fours. Dent’s monkeys tend to be most active in the early morning and in the evening.
Dent’s monkeys are pinnacles of interspecies cooperation, forming groups with other monkey species to forage and keep watch for predators together. They have even been known to hybridize with Doggett’s silver monkeys (C. mitis doggetti) and red-tailed monkeys (C. ascanius).
Dent’s monkeys live in groups ranging in size from seven to 21 individuals. Groups may be composed of a single male with multiple females, a small numbers of males with females, or entirely males in the case of bachelor groups. Sometimes, groups temporarily split into smaller groups and spread out to forage. Their home range sizes are not well known, nor is it understood what degree of territoriality they exhibit.
Dent’s monkeys are known to form loose inter-species groups with red-tailed monkeys (C. arcanius), blue monkeys (C. mitis stuhlmanni), silver monkeys (C. mitis doggetti), gray-cheeked mangabeys (Lophocebus albigena), mantled guerezas (Colobus guereza), and Oustalet’s red colobus (Piliocolobus oustaleti). Studies of such interspecies groups have shown that different species within the group carry out unique roles. For example, species that tend to inhabit the lower levels of the forest watch for terrestrial predators, while those in the upper canopy stay alert for birds of prey. Studies also show that foraging is actually more efficient when different species come together.
Dent’s monkeys use a wide array of communication tactics. Though they tend to be on the quiet side, they emit several types of calls. Contact calls are short, and are used while foraging to maintain cohesion in a group and ensure that no one individual strays too far. Alarm calls are used to alert groupmates to the presence of a potential predator. Males also emit calls to claim their territory. These can be heard from a long distance so all monkeys in the area know that there is a dominant male nearby. Visual communication includes body posturing and facial expressions that can convey threats, aggression, fear, or tension. Tactile communication includes grooming, which is important not only for the monkeys’ hygiene and health, but also for group bonding. Finally, olfactory communication is not documented in Dent’s monkeys, but it likely occurs through the use of pheromones.
Dent’s monkeys have a single-male, multi-female mating system. The top-ranking males get a near-monopoly on mating opportunities. When a group has too few males for the number of females, bachelor groups of males sometimes infiltrate a group to mate. Females do the bulk of the initiating, presenting their rear ends to males when they are receptive to mating.
Though specifics about Dent’s monkey reproduction are not well documented, based on closely related species, it is likely that their gestation length is about 165 days, or about five and a half months. Births are likely concentrated from June to December, when food is abundant. They give birth to a single baby at a time, or to twins rarely. Parenting among Dent’s monkeys is not well understood, but babies are known to ride on their mother’s backs for their first few months of life. Other females in a group may help to raise the baby, a behavior known as alloparenting. The young reach sexual maturity at around four to five years of age. At this time, females stay with their natal group—the one they were born into—while males leave to form bachelor groups.
Dent’s monkeys are preyed upon by animals such as birds of prey and leopards. As fruit-eaters, they likely also serve important ecological roles as seed dispersers as they drop or excrete seeds in their travels.
The International Union for Conservation of Nature lists the Dent’s monkey as Least Concern (IUCN, 2019) appearing on the IUCN’s Red List of Threatened Species. Although they are threatened by habitat loss and hunting, Dent’s monkeys fortunately remain widespread. However, their population is believed to be in decline.
Dent’s monkeys are threatened by encroachment from small-scale mining operations, hunting, and human settlement in the protected areas they inhabit, such as in Kahuzi-Biega National Park. Small mining sites are becoming more common in their range, and illegal operations are even set up in protected areas like national parks and wildlife reserves. In addition to the habitat disturbance caused by these sites, they are also operated by people who hunt Dent’s monkeys for food. Dent’s monkeys are commonly targeted by subsistence hunters because they are diurnal and widespread throughout their range. When the mothers are hunted, their babies are sometimes raised as pets and may enter the pet trade.
Expanding human settlement in their range also means that forests are cut to make room for agriculture and villages, which have a negative impact on the monkeys.
Additionally, Dent’s monkey habitat is faced with impacts from climate change, including increased temperatures, more frequent and extreme weather events, and changes in rainfall patterns. These changes cause widespread and unpredictable ecosystem changes that put stress on species. Even widespread species with healthy populations, like Dent’s monkeys, are experiencing impacts from climate change that will likely make survival more difficult.
Dent’s monkeys 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. They are also listed in Class B of the African Convention on the Conservation of Nature and Natural Resources, a landmark continent-wide agreement enacted to protect Africa’s diverse natural resources. Animals in Class B are protected and can only be hunted or captured under special authorization.
Dent’s monkeys live in a variety of protected areas, including Kahuzi-Biega National Park, Maiko National Park, Semuliki National Park, Nyungwe National Park, Okapi Wildlife Reserve, and Rubi-Télé Hunting Reserve.
Clark, A., & Kaplin, B. A. 2023. Preliminary study of Dent’s monkey (Cercopithecus denti) living in a forest fragment in Rwanda, highlighting dietary flexibility in guenons. African Journal of Ecology, 62. https://doi.org/10.1111/aje.13228
Gautier-Hion, A., Quris, R. & Gautier, JP. 1983. Monospecific vs polyspecific life: A comparative study of foraging and antipredatory tactics in a community of Cercopithecus monkeys. Behav Ecol Sociobiol 12, 325–335. https://doi.org/10.1007/BF00302901
- https://www.iucnredlist.org/species/136885/92413658
- https://animaldiversity.org/accounts/Cercopithecus_wolfi/
- https://animals.sandiegozoo.org/animals/guenon
- https://www.britannica.com/animal/guenon
- https://nationalzoo.si.edu/animals/news/guenon-qa
- https://www.usaid.gov/climate/country-profiles/democratic-republic-congo
Written by K. Clare Quinlan, March 2024