Cercopithecus ascanius

Geographic Distribution and Habitat
The red-tailed monkey is a species of guenon native to central Africa. Other common names include the black-cheeked white-nosed monkey and the red-tailed guenon. Their home range extends throughout the Central African Republic and the Congo, with southern Sudan as the northern boundary and northern Zambia as the southern limit. Populations are found in Kenya to the east and occur in Angola in the west.

Within this species there are five recognized subspecies, which possess distinguishing markings and occupy different areas within the home range. The zones where these subspecies are found are separated generally by major rivers in the region.

Red-tailed monkeys are mostly tree-dwellers with populations densest in undisturbed Afrotropical forest. Other populations may live in fragmented forested habitats, open woodlands, or grasslands. In west Tanzania, groups of red-tailed monkeys occupy open valleys with some tree growth present near rivers. Within this species, there is substantial habitat variation of vegetation, rainfall, and seasonal changes. Red-tailed monkeys are versatile primates, and group behaviors and ecology differ depending on their particular habitat.

Red-tail monkey geographic range. Map: IUCN, 2019

Size, Weight, and Lifespan
​The red-tailed guenon is a relatively small and agile primate with long limbs and an even longer non-prehensile tail, which helps with balance when traveling in the trees. Males reach their adult size around age six. Once fully mature, they weigh 8.2 lbs (3.7 kg) and are 18 in (46 cm) long from the top of their head to the base of their tail. Males are noticeably larger than adult females, which are on average 6.2 lbs (2.8 kg) and 15 in (38 cm) long in body length. Females reach maturity earlier, between four and five years of age. Other than size differences between the sexes, males and females appear similar. While the longevity of this species has not been studied extensively in the wild, existing documentation shows red-tailed monkeys aging to 25–30 years.

These colorful primates possess bold markings on their face and tail. The skin on their face is black, which contrasts with the white cheek fur and the white spot on their nose. Red-tailed monkeys have a soft, dense haircoat that is yellowish-brown and appears speckled due to alteration of two hues along each hair shaft. Their under-side is white, and limbs are either black or gray depending on the subspecies. Subspecies possess slight variations in color and markings, mostly on the face, tail, and shoulders. These monkeys are named for their long, red-colored tails, which have an increasingly vibrant chestnut-tone from base to tip. Infants are darker in color with gray-brown fur and have no visibly red tail or colored facial markings until about 4 months old.

While it may seem these striking colors make the red-tailed monkey conspicuous, these features surprisingly serve a camouflaging function in the forest. Their speckled fur blends in with the similarly speckled appearance of sunlight passing through the leaves. When light is coming from above and predators below look upwards at the white underbelly of the red-tailed guenon, their shadow is minimized, and the outline of their darker bodies is concealed. Similarly, the contrasting white and black on the monkey’s face may disrupt predators’ perception, misleading a predator into thinking the white and black tones belong to different objects in the canopy instead of a red-tailed monkey’s face. In dense Afrotropical forests, these small primates face many predation threats from all areas. They make a tasty meal for crowned-hawk eagles from above, for wild-cats and raptors from below, or even for other primate species, like chimpanzees, who share similar spaces in the trees.

What Does It Mean?

Of, relating to, or being aggressive, or defensive social interaction (such as fighting, fleeing, or submitting) between individuals usually of the same species.

Active during daylight hours.

Visit the Glossary for more definitions

Photo credit: Rod Waddington/Creative Commons

These primates are frugivore-insectivores, meaning that most of the foods they eat are either fruits or insects. Leaves, leaf-buds, flowers, seeds, and gums are also common in their diet. Studies of red-tailed monkeys in the wild show that the composition of their meals largely depends on the habitat they occupy. Red-tailed monkeys have flexibility in the foods they eat and are able to adjust to living in different habitats while still meeting their energy needs. While ripe fruit is a preferred food item because of the high energy yield, these monkeys eat unripe-fruit frequently, which other primates like ape-species avoid.

Insects and leaves are an important staple of protein in a red-tailed monkey’s diet. When foraging for food, red-tailed monkeys seek out leaves that have a high protein content relative to fiber and will carefully turn and unfold individual leaves in search of insects to catch with their mouths or hands. Types of insects consumed are those like caterpillars, grasshoppers, and cicadas who live alone, instead of insects who live in colonies. Studies examining feeding ecology in this species show that fruits comprise around 25% of their diet, insects satisfy just under 50%, leaves and flowers make up about 18%, and other items like bark, seeds, and gums account for the rest. Furthermore, adult males typically eat more fruit and fewer leaves than females, and juveniles eat fruits more so than adults. These differences suggest that these monkeys have slightly different nutritional requirements depending on sex and age and that their food preferences reflect these needs.

While red-tailed guenons can live in different habitats because they readily consume a wide range of foods, they are also very versatile and efficient eaters because of their large cheek pouches. In forests, fruits are typically found in patches and at the ends of tree branches. Accessing fruits often requires feeding in open places with less tree cover and among other fruit-eating primate species who use the same tree routes. The red-tailed monkey’s small size makes them vulnerable to predation in these open areas and less likely to secure good fruits when larger primate competitors are simultaneously feeding at the site. Red-tailed monkeys use their large cheek pouches as temporary storage for harvested fruits so that they avoid food theft by other monkeys and can retreat to a more protected area to eat. 

Red-tailed monkeys eat insects rapidly by swallowing, but fruit eating is a more time consuming and careful process that requires the fruit pulp to be separated from the seeds, which are spat out, before the pulp is ingested. Cheek pouches contain enzymes that break down the starches in forest fruits, aiding in digestion, and also allowing greener, less ripe fruits to be rapidly converted into energy when consumed.

Water intake comes from fruits, nearby streams, and water holes that form in trees.

Behavior and Lifestyle
Red-tailed guenons living in dense forests with a high abundance of plant and animal species feed on many food types in a smaller area. Typically, their home range is small and unchanging. Populations living in open zones like woodlands or fragmented forest spend more effort searching for food throughout the day. This foraging behavior extends the boundaries of their home range, which may change depending on resource abundance. The red-tailed monkey is diurnal and is mostly found in trees. Red-tailed guenons are highly active in the early morning and at dusk, resting during higher temperatures at midday. Most of the time, they leap and climb in the middle tree layer, at 33–60 ft (10–20 m) above the forest floor, and occasionally forage on the ground. Their smaller body size allows for foraging along the outside of the forest and on thinner branches where larger primates cannot secure supports.

Within living groups, members reinforce affiliation when sitting closely, nuzzling, or grooming one another. Youngsters may engage in play and play-chasing. Aggressive signs and actions, like shaking of the head and fore-quarters, stare-threats, growls, and contact fights with biting and slapping are less frequent in red-tailed monkeys. Agonistic behaviors arise when males defend home boundaries and occasionally in conflict between inter-group females. During mating periods, females lip-pucker and males head-flag, with either partner persistently following the other until mating occurs.

Certain movement behaviors seen in these monkeys likely help with predator avoidance. Though locations of food sources in a home range are well known to a red-tailed group, individuals seldom take a direct route to a feeding patch and instead travel to their destination by threading through the trees. Additionally, while some group members may search for food on the ground, females nursing infants are not observed foraging on the forest floor. Mothers with babies may feel more protected in the trees where they climb easily compared to toting an infant on all fours on the ground, an exceptionally difficult and dangerous task when raptors and wild felines are present.

Fun Facts

Cercopithecus ascanius cheek pouches have high concentrations of enzymes called amylases, which break down starches. Their cheek pouches are so high in these enzymes that when unripe fruit is temporarily stored there and then swallowed, 50% of the fruit is digested after just 5 minutes. 

Daily Life and Group Dynamics 
These animals feed, live, and raise offspring in groups. Typically, one adult male lives with a core of females and youngsters. While males will leave the birth group once mature, a female lives in the birth group her entire life, often in the same home range. Groups studied vary in size but average 25 members, with red-tailed monkeys in open habitats forming smaller groups and those living in dense forests forming larger ones.

Living groups are not fixed, since other transient red-tailed males may displace the resident male or temporarily join the group for periods of time to mate with adult females. Additionally, red-tailed monkeys are highly social. Those in close proximity to other primate species may form mixed-species groups, which is seen in some places with red colobus and blue monkeys. Living in single- or mixed-species communities may serve to mitigate predation risk while increasing competition over food and mates between group members and associated members of other species.

Communication is paramount for maintaining cohesion of red-tailed monkey groups as they move throughout the day. During these periods, individuals may be close to other group members, physically distant but visible to one another, or distant to and hidden from associated individuals by trees and plants. Signaling between monkeys is important for coordinating movement, and red-tailed monkeys use combinations of tactile, visual, and auditory cues to do so.

Vocalizations are a nuanced form of signaling in red-tailed monkeys, as their calls must carry through noisy environments to reach other group members who are not visually apparent. Auditory signals are specific, are accurate, and may be quite loud. Like other cercopithecines, red-tailed guenons have a set of calls used specifically by adult males. Distinctly male vocalizations are used during male-male fights, as with the “hack” train, and group disturbances, where males may elicit a “waa” nasal scream. Male-specific calls are usually louder than those of females and juveniles, who vocalize softly in phased “grunts” during group movement and reserve high-pitched “chirps,” “trills,” or shrill screams to raise alarm. While the vocalizations of red-tailed monkeys are unique to their species, researchers have noted substantial overlap with closely associated primate species occupying the same areas. For example, blue monkeys use similar types of calls, which may indicate mutual influence.

Reproduction and Family
Females mate with the resident adult male or new males traveling into the group. Takeover males may try to kill a group’s infants to hasten the mother’s reproductive ability, but his actions are met with counter-aggression by other group members. Females give birth to one infant a year, usually during times of fruit and insect abundance. Gestation periods last about 7 months, and higher birth rates occur in populations with stable male membership. Adult females outnumber adult males (by a 3:1 ratio). Assuming that both sexes are born at equal rates, significantly fewer males in this species survive to adulthood. This marked sex difference in mortality rate is not well accounted for in existing research.

Newborns are very vulnerable and seldom leave their mothers until they reach 1–2 months and can eat some solid foods. By the time they are one year old, they acquire most of their own food. Other females and juveniles in the group help transport, feed, and raise offspring. Involvement of other adult females in co-parenting solidifies group cohesion and social learning of younger group females.

Kibale National Park, Uganda. © c perry & r sayers jr. Used with permission

Ecological Role
These small monkeys promote plant growth through seed dispersal. Contrary to other frugivorous primates that swallow fruit whole and defecate clumps of seeds far away from their place of origin, red-tailed monkeys spit out single seeds near their parent trees. These two dispersal types are referred to respectively as “far-clumped” and “close-single” methods. While it is difficult to quantify how much this “close-single” species contributes to plant growth and diversity in habitats they occupy, studies show that spit-out seeds are more likely to germinate successfully relative to those contained in undisturbed fallen fruits.

Conservation Status and Threats
The International Union for Conservation of Nature categorizes red-tailed monkeys as Least Concern (IUCN, 2018), appearing on the IUCN’s Red List of Threatened Species. Their wide geographic range and habitat flexibility allows for survival in areas with some ecological disturbance. However, wild living populations are decreasing as dense forest is replaced by farms and fragmented by industrial clearing and logging. In central Africa, human population growth is currently the highest in the world. The corresponding demand for natural resources and acceleration of habitat destruction poses a substantial and unabating threat to species survival.

Although their small size and nimble climbing makes them a difficult target for hunters, red-tailed monkeys are killed for the bushmeat trade and for encroachment into local agricultural zones. The “Least Concern” label granted by the IUCN accounts for the species overall, while further distinctions in threatened status are not provided or known for the five subspecies. And population sizes and stability are not well-documented. Some restrictions exist on international trading, killing, and capturing of Cercopithecus ascanius. Yet the enforcement and efficacy of these restrictions is unclear, since these measures have been in place for many years and widespread hunting and trading continue.

Conservation Efforts
Some countries have designated areas as protected zones where land-clearing and other human ecological interference is prohibited. In Kenya, the Mount Elgon Game reserve and Kakamega forest reserve were created for species preservation. Other national parks in Tanzania, Uganda, and Democratic Republic of the Congo are similarly protected by their country’s government. Red-tailed monkey populations are present in some of these sites and presumably fare better than groups in unprotected habitats. However, due to the paucity of documentation on population size and stability in Cercopithecus ascanius and its subspecies, conservation status is currently unknown.


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Written by Cookie Koch, November 2020