TSHUAPA RED COLOBUS

Piliocolobus tholloni

Geographic Distribution and Habitat

The Tshuapa red colobus is endemic to the African nation of the Democratic Republic of Congo, or DRC. There is little known about their true range. Their distribution is broken up across the Congo basin, where the habitat is mostly continuous tropical rainforest. It would seem that the Congo and Lomela rivers form boundaries of their distribution, but many expeditions to locate Tshuapa red colobus populations in expected habitats have failed to find them. The patchy distribution is peculiar because Tshuapa red colobuses have been detected on the right bank of the Lomela river, but not on the left. Almost everything we know about the species comes from populations in the Salonga National Park, where they occur in higher numbers. 

Researchers have suggested that perhaps forest age or floristic composition and human pressure are important factors that affect their distribution. The limited sightings of Tshuapa red colobus suggest that they prefer closed-canopy forests, utilizing the middle canopy layer, and are sometimes found in seasonally flooded forests.

TAXONOMY IN TRANSITION

The genus Piliocolobus, or red colobus, is classified into different species based on their coat coloration and pattern. However, pelage color can have a lot of overlap and this can be a superficial distinguishing feature, which is why taxonomists have debated on whether there are 18 species of red colobus or only one. Currently, the general consensus is there are 16–18 forms or species of red colobus.

Prior to 1974, the Tshuapa red colobus was considered a subspecies of the Western red colobus (Piliocolobus badius) that are endemic to the western coastal regions of Senegal, Guinea, and Côte d’Ivoire. The taxonomic confusion for the Tshuapa red colobus is especially prominent because they live in the DRC with six other red colobus species and cross-breeding between these species can blur the genetic lines for taxonomic classification. One region of the DRC is called the “Hybrid Zone” because there is a high probability of hybridization or cross-breeding between red colobus species in that area.

Tshuapa red colobus range, IUCN 2018

Size, Weight, and Lifespan

Tshuapa red colobus are comparatively larger than other members of their genus. Only a few specimens have been measured and, from what has been documented, their head-and-body length is 25.2  inches (64 cm) in males, and 23–24 inches (58–60 cm) in females. Their tails are almost as long as their bodies, ranging from 16 to 27 inches (41–69 cm) in length. It is estimated that their weight ranges from 15 to 22 lbs (7–10 kg).

Their skulls have a large developed saggital crest and lower jaw, which are large points of muscle attachments that indicate the large amount of chewing they have to do as mostly foliovores.

We do not have any data on the life span of the Tshuapa red colobus, but from closely related taxa we assume that they may live up to 22 years old.

Appearance

These russet-colored primates have a deep brown forehead without hair whorls and white cheeks, chest, and belly. The base of their tales has long dark hair tufts. Distal ends including hands, feet, and the last third of their tails are darker brown and almost black.

What Does It Mean?
Distal end:
Situated away from the point of attachment or origin or a central point.

Folivore:

An animal who primarily eats leaves.

Florisitic:
Of or relating to flowers, a flora, or the study of plants and plant groups.
 
Hybridization:
The act or process of mating organisms of different varieties or species to create a hybrid.
 

Sagittal crest:
A ridge of bone along the middle of the skull. Primates with large jaws have a sagittal crest.

Visit the Glossary for more definitions

Photo credit: violettederozier/iNaturalist/Creative Commons

Diet

Their diet consists of mostly leaves (about 60%), seeds, and legumes (about 30%), followed by fruits and flowers. These types of food are high in fiber and difficult to digest, and therefore Tshuapa red colobuses have to consume a lot of food, which is then processed through a specialized digestive system to extract nutrients. Mother Nature has outfitted colobus monkeys with multichambered stomachs that allow for the digestion of large amounts of foliage. Microbes in the gut work with fluids secreted by the monkeys’ salivary glands to efficiently break down leaf cellulose. This morphological adaptation allows the monkeys to obtain the necessary nutrition from their leafy diet.

Behavior and Lifestyle

Tshuapa red colobuses are diurnal and arboreal. They use their long tails and hind legs to leap through the forest canopy. Their low-calorie diet requires them to spend much of their day foraging for food and conserving their energy as their body digests the food slowly. As a results Tshuapa red colobuses are often slow to move, making them easy prey for hunters and predators.

Fun Facts
  • Tshuapa red colobuses feed mostly on leaves and have a specialized digestive system to process the high-fiber foods.
  • Adult males are the prominent vocalizers and use various “chirps” and “honks” to warn against predators.
  • Their predators include African crowned eagles, leopards, and, in some areas, chimpanzees. 
Daily Life and Group Dynamics

Groups size of the Tshuapa red colobus is between 31 and 42 individuals (average of 12.6 individuals), which is relatively large compared to other red colobus species. However, there is variation between populations. Studies, as mentioned, are limited. Obtaining accurate ranges of group dynamics data would require long-term studies.

Group sizes are generally determined by the quality of the habitat, the presence of predators, and sociological conditions within the group. Habitats that can provide consistent food sources, such as forests that do not flood seasonally, can support larger group sizes of red colobuses because individuals do not have to compete with each other for food. African crowned eagles and leopards are the main predators of red colobus monkeys and larger groups sizes can help defend against these predators because there are more eyes to keep a look-out for danger. If there are no predators and food is consistent, then the number of adult males is what makes the group size larger. Male red colobuses do not leave the natal group and the more males that survive to adulthood the larger the group size gets. Males actively defend the group from other red colobus monkeys and so having more males means the group can stay and feed at sites with high-quality food sources for a longer time than groups with fewer males and less protection. Adult female red colobuses have to compete with other members within their group for food sources and some studies have found that having more female members in the group can increase juvenile mortality. So while more males in a group can result in larger group sizes, more females can lead to smaller group sizes.

Experts think that in almost all species of red colobuses, it is the female that disperses from the natal group. The process of dispersal and joining of new groups have yet to be studied in Tshuapa red colobuses. Males tend to stay in the group they were born in and eventually become part of a male coalition. We do know that dispersal from natal groups decreases competition for food and therefore can increase survival for both members of the natal group and juveniles. Additionally, the movement of related individuals allows genetic flow between groups and prevents inbreeding.

Communication

As there are only limited studies of behavior and ecology of Tshuapa red colobuses, experts have had to compile and compare data from all red colobus taxa in order to develop inferences on communication systems in the genera. Vocalizations among red colobuses are mostly emitted by males of the species. Females and juveniles are capable of communicating vocally but they often do not. In Tshuapa red colobuses, vocalizations include “chirps,” “honks,” “wheets,” and “chists,” the latter of which is a quick ascending pitch sound. These vocalizations seem to be emitted by different red colobus species for various inter-group communications, aggression, and alarm calls (which mostly warn group members of predatory birds and venomous snakes).

Female Tshuapa red colobuses emit rapid “quaver” sounds (similar to loud rapid inhalations) during copulation. This vocalization and the accompanied swelling of their external reproductive organs signals their estrus status and willingness to mate.

Reproduction and Family

Families consist of adult males, adult females, and juveniles. Males most likely reach sexual maturity in 5 years, and females in 4–5 years of age. Females display a swollen perineum when in estrus and ready to mate.

Male red colobuses form coalitions, a tight-knit group of males that forage and work together to protect the group. All adult males of the coalition will have mating access to females, but a few males may exhibit “copulation dominance,” where these males will get most mating opportunities with the females. This dominance usually lasts for 1–2 years, after which other males will get the advantage of copulation dominance. Females will copulate with multiple males in the group. On average, females reproduce every two years. There does not appear to be a breeding season for red colobuses, but, as found in the few studied groups, there may be birthing peaks that coincide with the hormonal cycles of the females. Females spend a lot of time on maternal care, including grooming and feeding, which greatly improves the chances of infant colobuses surviving to adulthood.

Photo credit: violettederozier/iNaturalist/Creative Commons
Ecological Role

As Tshuapa red colobuses consume fruits, they disperse seeds and assist in forest regeneration. Their leaf consumption also results in opening of canopy layers to allow sunlight to penetrate the lower layers of the rainforest. This promotes growth of new trees and smaller shrubs that do not have access to adequate sunlight with a full canopy.

Tshuapa red colobuses form a part of the food chain where they are an important prey source for African crowned eagles and leopards. In areas where their habitat overlaps, red colobuses are also potential prey for chimpanzees.

Conservation Status and Threats

The International Union for Conservation of Nature lists the Tshuapa red colobus as Vulnerable (IUCN, 2019), appearing on the IUCN Red List of Threatened Species. Populations are decreasing. It is estimated that between 2000 and 2017 Tshuapa red colobus populations decreased by more than 30% and they are expected to continue decreasing into the future.

There have not been population studies conducted on the species but, per the IUCN’s Red Colobus Action Plan 2021–2026 (published in 2021), expedition data suggest that there may be more than 30,000 Tshuapa red colobuses remaining in the wild. Tshuapa red colobuses are highly susceptible to hunting pressures because they are larger and slower to flee than some other primates. Additionally some cultures prefer Tshuapa red colobus meat and they believe that its consumption holds a divine quality. If it weren’t for hunting pressures these primates could be locally abundant. 

Political instability and war generally have a devastating effect on wildlife species as habitat gets destroyed and people have to depend on bushmeat for sustenance. The Congo wars between 1996 and 2003 increased hunting of Tshuapa red colobuses (as with other wildlife species), thus accelerating the decline of the species. Current concerns of declassifying the protection status of areas of the Salonga National Park for oil exploration have raised concerns for the inevitable habitat loss for the species.

Conservation Efforts

The Tshuapa 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.

All red colobus species are completely protected by the national laws in the Democratic Republic of Congo. The Tshuapa red colobus is listed as a Class B species in the African Convention on the Conservation of Nature and Natural Resources, which means that the species is protected from hunting unless a special permit is issued by authorized government organization. Practically, the enforcement of these laws falls short, which results in a declining population of Tshuapa red colobuses.

References:
  • Detwiler, K.M., Hart, J.A., Maisels, F., Thompson, J., Reinartz, G. & Struhsaker, T.T. 2019.
    Piliocolobus tholloni. The IUCN Red List of Threatened Species 2019: e.T18257A92662288.
  • GBIF Backbone Taxonomy. Piliocolobus tholloni A.Milne-Edwards, 1886 in GBIF Secretariat (2021).  Checklist dataset https://doi.org/10.15468/39omei accessed via GBIF.org on 2022-08-24.
  • Korstjens, A. H., Hillyer, A. P., & Koné, I. (2022). 9 Red Colobus Natural History. The Colobines: Natural History, Behaviour and Ecological Diversity, 108.
  • Linder, J.M., Cronin, D.T., Ting, N., Abwe, E.E., Davenport, T.R., Detwiler, K.M., Galat, G., Galat-Luong, A., Hart, J.A., Ikemeh, R.A. and Kivai, S.M., 2021. Red colobus (Piliocolobus) conservation action plan 2021-2026. Gland: IUCN. doi10.
  • Struhsaker, T. T. (2005). Conservation of red colobus and their habitats. International Journal of Primatology26(3), 525-538.
  • Struhsaker, T. T. (2010). The red colobus monkeys: variation in demography, behavior, and ecology of endangered species. Oxford University Press

Written by Acima Cherian, August 2022