Bouvier’s Red Colobus, Piliocolobus bouvieri
BOUVIER'S RED COLOBUS
Piliocolobus bouvieri
Geographic Distribution and Habitat
Bouvier’s red colobus monkeys are endemic to the forests along the Congo River, spanning the Democratic Republic of the Congo and the Republic of the Congo. The species was considered extinct because no one had seen one in decades, since the 1970s. In 2015, some intrepid researchers ventured into some of the remotest parts of the Congo forest, where they rediscovered and took the first photographs of Bouvier’s red colobus monkeys. This was the first live record of the species in about thirty years. They were seen in Ntokou-Pikounda National Park, in the Republic of Congo. As a result of the sighting, they realized that the species could thrive in landscapes unaffected by humans and that hunting pressures had contributed to their near extinction in other parts of their distribution.
They are found in dense riparian forests along rivers. These forests have high rainfall and are adapted to flooded conditions. As a result, these red colobus monkeys spend most of their time in the higher levels of the forest canopy.
Locally, they are known as Inia or Ingon.
Red colobus taxonomy is highly debated, and the classification of the rare and poorly studied Bouvier’s red colobus adds to the complexity of their relationships with other members of the genus. Some researchers consider the Bouvier’s red colobus a subspecies of Pennant’s colobus (Procolobus pennantii). We follow the Groves (2007) classification, which treats the Bouvier’s red colobus as a separate species.
Size, Weight, and Lifespan
Bouvier’s red colobus monkeys appear to be a smaller species within the genus, although they have relatively long tails. Their body length is about 23 inches (58 cm), and their tail is approximately 30 inches (76 cm) long. Based on closely related species, they most likely weigh between 15 and 22 pounds (7 to 10 kg) and live to be a maximum of 30 years old.
Most estimates are from recent sightings or old records where the Bouvier’s red colobus may have been confused with other red colobus species. Metrics around lifespan are lacking.
Appearance
Like other members of the genus, the Bouvier’s red colobus monkey is mainly covered in reddish fur with white fur on their cheeks and chest. They also have short thumbs and long fingers, which are standard for red colobus monkeys. They resemble the closely related Pennant’s red colobus (Procolobus pennantii) and Tshuapa red colobus (Piliocolobus tholloni). The primary differentiation of Bouvier’s red colobus is that the red fur on their head is broken up by black superciliary (eyebrow) bands that run to their ears.
Their face has a unique, light-colored appearance with large pink eye-rings, light-colored noses and lips, and prominently dark cheekbones, which prompted the initial description of their face as “rosy flesh.” A black band down their back fades to a broad gray patch at the base of their spine. Their tail is usually black at the base and turns bright red towards the tip. Their large feet and hands are dark in color.
Diet
Red colobus monkeys specialize in eating leaves (folivores) and, occasionally, seeds. These foods are notoriously low in energy-rich sugars, high in fiber, and can be tough to digest. They prefer younger leaves that are higher in protein and sugars. Folivores have to eat a lot of leaves to get enough energy and often have to spend most of their time eating.
These primates have a large, multichambered stomach that helps hold a large quantity of leaves long enough to break down the tough cellulose and release the sugars that provide energy for their activities. This digestive system has two main advantages. One is that having a large stomach allows the red colobus monkey to eat a lot of leaves in one sitting. Another benefit is that their stomach chambers can divide digestion into different stages, including a section with complex gut bacteria that help break down the tough leaf fiber or cellulose. This makes it possible for their stomachs to extract the maximum nutrition from the leaves before excreting the fiber.
You might wonder why some primates feed primarily on leaves when fruits, a more nutrient-dense food, are available. Fruits are seasonal and are a desired food source for many species, including insects, birds, rodents, and other primates. Therefore, there is a lot of competition for fruits. Leaves are an abundant food source in the forests, and there is almost no competition for them as a food source. Adapting to eating and extracting energy from leaves is a survival advantage that allows large families of red colobus monkeys to thrive without running out of food.
Behavior and Lifestyle
As a poorly studied and recently rediscovered species, little is known about the specific behaviors of Bouvier’s red colobuses. Here, we describe behaviors that are common to the biology of red colobus monkeys of the region and tend not to vary between species of the genus.
Red colobus monkeys are arboreal (tree-dwelling) and built to move quickly through the tree canopy. Their short thumb and long fingers act like a grappling hook as they swing and throw themselves to latch on to the next branch. They repeat the long swinging and catching motion in a behavior called “brachiation.” Their shoulder blades (scapulas) are also more flexible than other primates, which helps them hyperextend their arms to reach long distances between branches. Additionally, their long tail helps balance and steady them as they leap through the trees. These adaptations allow the red colobus monkeys to quickly travel long distances without wasting much energy.
They can walk on all fours (quadrupedally) and mainly use this method when walking along branches within a tree or, on rare occasions, on the ground.
These primates are diurnal (active during the day) and spend most of their day foraging for food. Nighttime is usually a time of danger for these monkeys, as they are not adapted to seeing well in low-light conditions, and many of their predators are nocturnal (active at night).
The Bouvier’s red colobus was considered extinct for forty years until two researchers rediscovered a population deep in the Congo rainforest in 2015.
They have a unique black eyebrow band that runs from their crown to their ears.
They do not run from strangers, but instead stay where they are to confront them.
Their tendency to hold their ground during encounters makes them an easy target for human hunters.
Red colobus monkeys in the hot, humid rainforest of the Congo River are most active in the cooler mornings, just after sunrise. They wake up, vocalize to gather everyone, and start their morning foraging, looking for trees with young palatable leaves. The first three to four hours are spent traveling and eating as much as possible. As the day gets hotter, the monkeys rest in the cool shade. It is during this rest time that their digestive system is most active. The resting phase allows stomach acids to break down the quickly chewed leaves and send the partially digested leaves to the bacteria fermentation chamber, where most of the protein and sugar are extracted. So, resting is an essential part of the red colobus monkey’s day. Some estimates suggest that they can spend 30-58% of their active time resting, compared to 20-46% of their time actively feeding.
These social monkeys are generally not aggressive and resolve most disputes through vocalizations and posturing. They live in large, multi-female, multi-male groups with separate dominance hierarchies among males and females. Males form coalitions that work to protect the troops from intruders and predators. Males exhibit the most aggressive behaviors while fighting for top mating rights with females. Young males often find themselves on the receiving end of this aggression as they mature and test their dominance.
Red colobus monkeys are known for their complex vocalizations. Vocalizations are the most efficient communication method in dense rainforests, where maintaining visual contact with each other through the foliage is difficult. Some red colobus species have more than 25 different recorded call types. Communication sounds and meanings vary between the species, and no studies have been done on the Bouvier’s red colobus calls. For all red colobus monkeys, males are the loudest and most frequent vocalizers.
Females commonly make copulation calls and sounds when mating, which trigger other troop members to mate. These copulation calls have not been recorded for Bouvier’s red colobus. Still, they could vary from soft quivering sounds to louder yowls heard in closely related species.
Recent video footage of Bouvier’s red colobus monkeys shows they frequently use high-pitched chirp sounds as they move through the forest.
Red colobus families are large, consisting of many adult males, adult females, and their offspring. Mating season varies among many red colobus species, and it likely depends on the quality of available food and rainfall.
Female red colobus monkeys advertise their readiness to mate (or when they are hormonally ready to mate, a condition called estrus) with sexual swelling where their genitals are visibly enlarged. Females sometimes approach males to entice them to mate. Males are more often triggered by the female’s sexual swelling to approach them for copulation or mating. Mating is also associated with copulation calls from the female, which may encourage other ovulating females to mate with the other males.
In a multi-male society, most mature males will mate with the females in the troop. Males try to compete with each other, mate with a female multiple times, and sometimes even try to prevent other males from mating with her. The male’s reproductive goal is to pass on his genes and actively prevent another male’s genes from being passed on to the offspring.
By comparison, the female’s reproductive goal is to successfully birth and rear offspring to adulthood. Male colobus monkeys can harm monkeys they haven’t fathered, a situation the mothers would prefer to avoid. It is in the female’s best interest not to let the males know if they have successfully fathered a child and to prevent any aggression toward her infants. Therefore, she will mate with multiple males and even encourage copulation after she is pregnant and her genital swelling has reduced.
Infants depend entirely on their mothers for nutrition and protection as they travel through the forest. Although multiple adult females are in the troop, they rarely help take care of each other’s infants as occurs with some primate species. This practice of related or non-related females helping to raise the young is called “allomothering.”
Sub-adult females disperse from their natal troop (the family where she was born) and find another troop to join. This prevents inbreeding between her and closely related males. Sub-adult males tend to stay in the troop (they are philopatric) and spend time moving through the ranks of males. By the time these subadult males become ready to mate, mature females in the troop are unlikely to be related to them.
It is suspected that the Bouvier’s red colobus monkey has a long development period and interbirth interval, given that their numbers were reduced to near extinction in such a short time. So, the red colobus monkeys must spend a lot of time (about 4-5 years) and energy to help an infant monkey reach adulthood. Disruptions, such as not having enough food or a drastic reduction in the family size or number of males that protect the infants from predators, can have devastating effects on the entire population. This makes them particularly vulnerable to environmental changes and human activities, such as deforestation or hunting.
Folivores like Bouvier’s red colobus monkeys are essential in controlling the canopy size and sunlight reaching the forest floor. Trees are the climax species in rainforests, meaning they are the ecosystem’s largest and most complex structures. They maintain that status by spreading out as much as possible to get the most sunlight for photosynthesis, the process by which plants make food. This means that canopies block out the sun for many smaller plant species, which prevents these shorter, less established plants from taking root or growing. Folivores eat a lot of leaves and create light gaps in the canopy that allow sunlight to reach the forest floor. The shorter plants can photosynthesize in these gaps.
The Bouvier’s red colobus’s survival is closely tied to the quality of the rainforest. Their adaptation to high canopies and a more leaf-eating diet allows them to share the forest resources, in terms of space and food, without competition. This resource-sharing increases the complexity of an ecosystem and makes the rainforest better suited to adapting to changes in weather, climate, and human disturbances. So even when the number of Bouvier’s red colobus monkeys dropped drastically, there were enough other herbivore species that the forest system could survive. In this case, the Bouvier’s red colobus is an extra layer of protection for the forest species. Similar to adding a layer of bubble wrap to a fragile package. Removing this outer layer would not destroy the package. Still, it would expose it to more damage, which can eventually ruin it.
These red colobus monkeys are also part of the rainforest food chain, where they are preyed on by African crown eagles, leopards, crocodiles, and pythons.
The International Union for Conservation of Nature lists Bouvier’s red colobus as Endangered (IUCN, 2019), appearing on the IUCN Red List of Threatened Species.
Hunting is the main threat to the Bouvier’s red colobus monkey’s survival. These primates are often curious or aggressive towards humans. Instead of running away from hunters, large family units confront the humans to chase the threat off. Unfortunately, this makes the monkeys an easy target, and hunters can successfully kill dozens of monkeys in one site. These monkeys were commonly traded in commercial bush markets before their numbers were depleted to near extinction.
The drastic habitat destruction in this region makes hunting these primates through dense vegetation possible. Logging, mining, agriculture, and other development projects have led to deforestation and fragmentation of the rainforest, which exposes red colobus monkeys to human settlements and hunting.
Habitat loss degrades the quality of food available to them, putting pressure on all the wildlife with the same survival space.
The Bouvier’s red colobus 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.
One of the main reasons Bouvier’s red colobuses still survive today is that they inhabit inaccessible, thick forests along the Congo, where humans cannot travel easily. Active protection in parks like the Lesio-Louna Reserve maintains undeveloped areas where hunters cannot traverse, which are vital to the species’ continued survival.
They are protected from trade and hunting on a regional scale; however, local enforcement of hunting regulations is not practiced. Therefore, maintaining an undeveloped core of pristine habitat would be the best effort to preserve existing populations of Bouvier’s red colobus monkeys.
- Butynski, T.M., Oates, J.F., Struhsaker, T.T. and de Jong, Y.A., RED COLOBUS PROCOLOBUS, subgenus PILIOCOLOBUS de Rochebrune 1887 Peter Grubb.
- Hance, J. (2015). Expedition in the Congo rediscovers lost primate. Mongabay Environmental News. https://news.mongabay.com/2015/04/expedition-in-the-congo-rediscovers-lost-primate/
- Korstjens, A.H., Hillyer, A.P. and Koné, I., 2022. 9 Red Colobus Natural History. The Colobines: Natural History, Behaviour and Ecological Diversity, 89, p.108.
- Maisels, F. & Devreese, L. 2022. Piliocolobus bouvieri (amended version of 2020 assessment). The IUCN Red List of Threatened Species 2022: e.T18250A210339606. https://dx.doi.org/10.2305/IUCN.UK.2022-1.RLTS.T18250A210339606.en. Accessed on 28 April 2025.
- Ndzai, Christian & Malonga, Phael & Maisels, Fiona. (2019). Rediscovery of Bouvier’s Red Colobus in the Southern Republic of Congo. Primate Conservation. 33. 43-46.
- Oates, J. and Ting, N., 2015. 15. Conservation consequences of unstable taxonomies: The case of the red colobus monkeys. Taxonomic tapestries, p.321.
- Struhsaker, T. T., & Leland, L. (1985). Infanticide in a patrilineal society of red colobus monkeys. Zeitschrift für Tierpsychologie, 69(2), 89–132. https://doi.org/10.1111/j.1439-0310.1985.tb00139.x
- Struhsaker, Thomas T.. The Red Colobus Monkeys: Variation in Demography, Behavior, and Ecology of Endangered Species. United Kingdom: OUP Oxford, 2010.
- World Wildlife Fund. (n.d.). This rare monkey species was caught on video for the first time!. YouTube. https://youtu.be/pBL4Aui55kk?si=7vHqmU_wVQnFQHxY
Written by Acima Cherian, April 2025