Semliki red colobus, Piliocolobus semlikiensis
SEMLIKI RED COLOBUS
Piliocolobus semlikiensis
Geographic Distribution and Habitat
The Semliki red colobus is restricted to the northeastern part of the Democratic Republic of Congo (DRC) and western Uganda. In DRC, their geographical range extends from the Lowa River in the southwest to the Oso River in the East, the Ituri River in the northeast, and the Aruwimi River in the west. Semiliki red colobus distribution in the East extendd past the DRC border into the Semuliki National Park in western Uganda.
Their habitat is dense rainforests that are often flooded, but these monkeys usually live in hardwood forests that remain above the forest’s flood lines.
Four species of red colobus monkeys have overlapping distributions in DRC, and differentiating between them has been difficult. This has complicated the taxonomic classification of this group of monkeys, collectively called “Eastern DRC red colobus monkeys.” Adding to the taxonomic confusion is that these species can mate between them and produce hybrids of these four colobuses.
All red colobus species were once considered subspecies of the western red colobus, Colobus badius. The Semiliki red colobus has undergone multiple taxonomic naming transitions, from their initial Latin name of Colobus ellioti to Colobus badius semlikiensis in 1991.
Limited monetary, political, and research resources may be dedicated to conserving a species. However, when we cannot taxonomically define a species, forming conservation plans, laws, and budgets is challenging. Though the Semlikli red colobus classification is still being debated, the scientific community accepts them as an independent species (Piliocolobus semlikiensis) with possible hybrid variants.
Size, Weight, and Lifespan
Red colobuses are large monkeys that are conspicuous or easy to see in the forest. Most available measurements for this particular species come from older museum specimens. In general, red colobus males are larger and more robust than females. Males’ body length (head to the base of their tail) is 19 to 22.3 inches (48-54 cm), and females’ bodies measure 19.7 to 22.3 inches (50 -54 cm). Their tails are longer than their bodies, measuring 22.3 to 29.5 inches (54-75 cm).
Similar species weigh 15 to 20 pounds (7- 9 kg). We assume the lifespan of Semliki red colobus is comparable to that of other red colobus species and is probably between 8 and 12 years.
Appearance
These large monkeys have dark, hairless faces and bright brown-orange eyes that peer through shocks of reddish fur. Red colobus monkeys are distinguished by their coat colors of varying shades of red and gray on different parts of their bodies. Semliki red colobuses have a reddish tuft of fur on the crown of their heads, contrasting with their blackish face. Their throat, whiskers, and side of their head are also red. The dark fur on their shoulders, referred to as a mantle, and upper body parts fade to a gray-orange color on the lower back and legs. Their arms are brick-red on the outside and dark grey on the inside from their elbow to wrist. Their hands, feet, and tail are blackish. On either side of their tail base, there is a prominent tuft of reddish hair called a panache. They have shortened thumbs and long fingers, allowing them to quickly grab onto branches as they travel through the forest canopy. They also have long hind feet that help make long leaps between canopies.
Though the coloration of males and females is similar, males tend to be larger, so there is some degree of sexual dimorphism (different appearance between genders). Females have perineal swellings during mating, but field observers have noted that differentiating males and females is difficult in a large group of red colobuses with adult and juvenile monkeys.
Diet
Red colobuses are mainly folivorous (leaf-eating) monkeys who occasionally feed on flowers and fruits. Leaves have a lot of fiber and are lower in sugar than fruits, which means that folivores have to eat a lot of leaves to get enough energy to engage in their daily activities. The advantage of feeding mainly on leaves is that they are an abundant food source in a forest, and folivores do not have to travel far to forage.
These monkeys generally prefer younger leaves that have more sugar and protein. Some trees also have tannins and other toxins in their leaves that can build up in their body. Red colobuses have been observed eating clay, dirt, and charcoal (a phenomenon called geophagy) to help neutralize these poisons.
Their digestive system is complex, with a multi-chambered stomach and special bacteria that digest cellulose (the fiber part of leaves), which helps red colobuses digest the large number of leaves they must eat.
Behavior and Lifestyle
Research on the species’ behavior or ecology is limited due to its low numbers, rugged habitat, and political unrest in DRC. This makes conducting surveys and scientific studies difficult. Their behaviors, especially foraging and moving through the rainforest, would be similar to those of other red colobus species in the region.
We know they are arboreal (tree-dwelling) and diurnal (active during the day). Red colobus behaviors are affected by the quality of their environment. In fragmented forests with lower food availability and higher chances of being spotted by predators, red colobuses travel smaller distances and settle for lower-quality, more mature leaves (which are harder to digest). This results in smaller home ranges in forests affected by deforestation.
Behaviors also change seasonally. During fruiting season, red colobuses opt to eat more fruit even though most of their diet still consists of leaves. During the rainy season, they move less and stay under the canopy for shelter.
These social monkeys rely on the safety provided by the large numbers in their troop, as many eyes can spot potential predators and trouble better than an individual. This sense of security makes them more likely to observe the threat rather than run away. Often, alarm calling will deter a predator, or observing the predator’s behavior can help determine the best path to escape. Unfortunately, this tactic does not work with humans, who use the red colobuses “wait and observe” behavior as an opportunity to shoot as many monkeys as they can.
Semiliki red colobuses can be distinguished by reddish hair tufts at the base of their tail (called a panache), darker grey chest, and inner arms.
Their taxonomy is uncertain, and they have hybrid offspring with other red colobus species.
They rely on safety in numbers and live in large social groups of more than 40 individuals.
They have a polygynandrous mating system where males and females have multiple mating partners.
They often wait and observe potential threats, which makes them an easy target for hunters.
These monkeys live in multi-male, multi-female groups with more than 40 individuals. Larger groups tend to form when food sources are abundant; even then, groups can split up to forage in smaller groups (fission-fusion social system).
Red colobuses go foraging for food as soon as they wake up. They spend 20-46% of their active time feeding, 5-22% traveling to food patches, and 30-58% resting, mainly in the middle of the day. During these rest periods, they spend 2-12% of their time socializing, which includes playing and grooming each other.
Most competition between groups of the same red colobus species is for space and mates. Leaves are an abundant food source, so competition for food is not typical. Groups usually avoid violent interactions. However, when one group feels threatened by another, the male interactions tend to be agonistic or aggressive, and they are associated with loud vocalizations, bared teeth, and some chasing.
Polygynandry is common in red colobus, where one female can mate with multiple males, and one male can mate with multiple females. Often, it is difficult to tell which male is the father of her offspring.
Female red colobuses have visibly swollen perineal tissue (near the reproductive organs) when they are hormonally ready to mate. This signals to males that she will likely be receptive to male attention. Female red colobuses have been observed making copulation calls that further attract males to them. However, females can also reject males they are not interested in.
The gestation period (time she is pregnant) is estimated to be 4-6 months. Red colobuses have a slow population growth rate, with only one offspring every two years. Females can have more than one infant per birth. Still, their reproductive rate is reduced in degraded habitats, and fewer infants are born per female.
The female primarily cares for infants, but as they become more independent, other troop members will be involved in feeding, playing, and protecting young red colobuses. Juvenile red colobuses become sexually mature adults when they reach 2-5 years old.
Through limited observations, it is assumed that females and males disperse from natal troops (the family they were born in)
Red colobuses are the most endangered primate genus in Africa. They are considered flagship species that indicate good forest health. They are also one of the more poorly studied groups of monkeys in Africa.
As folivores, red colobuses help maintain plant diversity by predating on trees that can over-crowd the forest and prevent other plant species from establishing themselves. In tropical forests, large trees dominate the access to sunlight for photosynthesis, limiting how much smaller plants (with less access to sunlight) can grow. By feeding on such many leaves, red colobuses create more light gaps that can reach the forest floor.
As a larger primate in their habitat, they are predated on by many species, including crowned eagles, leopards, hyenas, and, famously, chimpanzees (Pan troglodytes). Though predation by chimpanzees has not been confirmed for Semiliki red colobuses, chimpanzees occupy the same habitat and have been observed hunting other red colobus species regularly. Chimpanzee troops often violently chase and kill red colobuses.
Red colobuses can peacefully coexist with other frugivorous primates, forming large groups that can warn each other of potential predators.
The International Union for Conservation of Nature lists Semliki red colobus as Vulnerable (IUCN, 2020), appearing on the IUCN Red List of Threatened Species.
Like many species living in rainforests, deforestation and habitat loss are the main threats to the survival of the Semiliki red colobus. People have converted forests into farmland to support the growing population in the Congo region. The increasing number of farms results in forest removal and the introduction of chemical fertilizers and pesticides into the environment, negatively affecting soil and water quality.
The DRC has experienced political changes and war. Often, people have to rely on whatever natural resources they can find to survive, especially wood for fuel and hunting wildlife for food. As a result, wildlife conservation has not been a national priority for many years. The forests in this region are highly fragmented and patchy, so there is less food available for red colobuses, and they have to travel further to find enough food and shelter.
Red colobuses are large monkeys hunted for bushmeat because they are easily seen and provide a family with a meal. These monkeys also live in social groups and often wait and observe potential threats rather than run away. This behavior makes these monkeys even easier targets, allowing hunters to catch multiple individuals simultaneously.
Studies have revealed that certain viruses have co-evolved with red colobuses, and infections such as herpes are common in some species. They also have common gut parasites. Red colobuses can usually live with this microbial presence, but when the quality of their habitat and food is poor, their immunity or ability to withstand these infections is reduced. So, fragmented habitats have multiple negative effects on the red colobus population.
The Semliki 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.
The Semliki red colobus is protected from international trade on the continent through CITES and the African Convention on the Conservation of Nature and Natural Resources. Nationally, they are also illegal to kill. Still, implementing these laws is complex, with insufficient law enforcement and infrastructure to deter hunters.
An action plan published in 2020 set priority conservation areas and potential actions the government could take to improve the population of red colobuses. Many of these actions include prioritizing improving local people’s living and health conditions to decrease their dependence on hunting these primates.
- Groves, C.P., 2007. The taxonomic diversity of the Colobinae of Africa. Journal of Anthropological Sciences, 85, pp.7-34.
- Linder, J.M., Cronin, D.T., Ting, N., Abwe, E.E., Davenport, T.R., Detwiler, K., Galat, G., Galat-Luong, A., Hart, J., Ikemeh, R.A. and Kivai, S., 2021. Red colobus (Piliocolobus) conservation action plan 2021–2026. IUCN: Gland, Switzerland.
- Maisels, F. & Ting, N. 2020. Piliocolobus semlikiensis. The IUCN Red List of Threatened Species 2020: e.T92657343A92657454. https://dx.doi.org/10.2305/IUCN.UK.2020-1.RLTS.T92657343A92657454.en. Accessed on 15 October 2024.
- Butynski, T.M., Oates, J.F., Struhsaker, T.T. and de Jong, Y.A., RED COLOBUS PROCOLOBUS, subgenus PILIOCOLOBUS de Rochebrune 1887 Peter Grubb.
- Korstjens AH, Hillyer AP, Koné I. Red Colobus Natural History. In: Matsuda I, Grueter CC, Teichroeb JA, eds. The Colobines: Natural History, Behaviour and Ecological Diversity. Cambridge Studies in Biological and Evolutionary Anthropology. Cambridge University Press; 2022:108-127.
- Struhsaker, T.T., 2010. The red colobus monkeys: variation in demography, behavior, and ecology of endangered species. Oxford University Press.
- Sussman, R.W., Hart, D. and Colquhoun, I.C. eds., 2022. The natural history of primates: A systematic survey of ecology and behavior. Rowman & Littlefield.
- Tim Davenport, via Instagram, confirms that the Semliki red colobus is still active in the Semliki Forest of western Uganda, November 2024
Written by Acima Cherian, October 2024