Geographic Distribution and Habitat
Black colobus monkeys are endemic to the forests of Equatorial Guinea, southwest Cameroon, Congo and northwestern Gabon. Some are also found on Bioko, a small island off the coast of Cameroon in the Gulf of Guinea. There are two subspecies, the Bioko black colobus (Colobus satanas satanas), only found on Bioko island, and the Gabon black colobus (Colobus satanas anthracinus).
Size, Weight, and Lifespan
Black colobus monkeys are between 20 and 27 inches (50–68 cm) tall and weigh between 15 and 33 pounds (7–15 kgs). Their tails are longer than their bodies and can measure between 24 and 33 inches (60–84 cm). The males are a little bigger than the females and have much more impressive upper canines–up to 7 inches (18 cm) in males vs. only 4 inches (10 cm) in females.
They live up to 20 years.
These large-bodied primates are entirely covered in black hair. The individuals born on Bioko island have longer and fluffier hair. Their bodies and limbs are thin; their legs are longer than their arms. Their thumbs are underdeveloped and hardly noticeable. Their thin and long fingers serve as hooks to hold on to branches. The leathery patch of skin (or ischial callosities) on the rump allows the monkeys to sleep sitting up on thin branches without falling.
The eyes of all colobus monkeys are set further apart than those of monkeys in the Cercopithecidea family, which means they have better depth perception. This is very useful in tree dwellers.
Their molars are flat and well adapted to seed crushing. They rely on them to crack open hard shells and they use their sharp canines to open soft pods.
What Does It Mean?
A thickened piece of skin found on the buttocks of animals.
Refers to phenol, an organic compound, like resin, found in some plants.
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Black colobus monkeys feed on foliage, seeds, and buds. When the seasons change and there aren’t enough young leaves, seeds, or buds, they feed on mature leaves. Nonetheless, there are dietary differences between black colobus monkey groups depending on where they live. Although the exact reasons behind the differences in feeding strategies are not completely understood, it is likely a good example of how species adapt to their environment.
The forest in Douala-Edea in Cameroon, for instance, grows on a marine sedimentary basin; the soil is sandy and plants are low in nutrients, so the vegetation contains large quantities of tannin and phenolics—making foliage less desirable. This is probably why black colobus monkeys in that region eat a lot more seeds than leaves (a good choice because seeds are more nutritious than foliage). They also avoid the tannin- and fiber-rich leaves of common trees, favoring those of deciduous trees instead because they are more easily digested.
Although there are more plant species in the Réserve de la Lopé-Okanda in Central Gabon, foliage available may be of lower quality because the local black colobus monkeys eat even more seeds than those in Douala-Edea.
The soil of the Kibale forest in Uganda, on the other hand, is rich in nutrients; the vegetation has low levels of chemicals that make digestibility of foliage problematic. Therefore, black colobus monkeys there predominantly consume young leaves.
Another surprising factor influencing black colobus monkey feeding habits is the presence of frugivorous primate species in their groups. Observations seem to indicate that when mangabeys and Cercopithecus monkeys are present, black colobus monkeys tend to eat more seeds.
Eating seeds is time consuming. Because they lack an opposable thumb, black colobus monkeys must crack a pod open while holding it with four fingers; they then retrieve the contents with their mouth. Just accessing the seeds of one shell can keep them busy for 15 minutes.
These monkeys also occasionally eat flowers, such as those of the Kola tree, or the occasional moth larvae, if it happens to be rolled in Okoume tree leaves that they pick. Finally, they have been observed descending to the ground to ingest some sandy earth, as is common in other colobine monkeys. This is thought to aid in digestion.
Behavior and Lifestyle
Black colobus monkeys’ activity levels are pretty low. They spend half of their waking hours resting. In fact, they lie down, sit, or groom each other in their sleeping quarters until mid-morning. Then they move to the lower canopy, where they pluck some edibles here and there before resting some more. They start traveling to feeding sites in the late morning and spend a quarter of their day eating. They visit the same foraging sites a few days in a row and it is not unusual for the entire group to eat all at once from the same tree.
Their daily range is small—between 900 and 1300 feet (300–400 m). On rainy days, they travel shorter distances. They are only forced to travel a little further when food is scarce. Such is the case in La Forêt des Abeilles in Gabon, where the vegetation mix and a harsh dry season force the small groups living there to travel much longer distances than black colobus monkey groups in other areas.
Every day at around 6 PM, the monkeys select trees with a large crown and settle down for the night.
Daily Life and Group Dynamics
Black colobus monkeys are diurnal and live in multi-male, multi-female groups of 10 to 20 individuals—although in Monte Alén National Park, groups of 50 individuals were observed. These groups can include up to three adult males.
These monkeys are quadrupedal, semi-brachiators, and skilled leapers. They spend most of their day socializing and grooming in the upper canopy of primary or secondary forests. Adult males groom one another, as do juvenile males; females, on the other hand, groom across generations and gender, with adult males getting the most attention.
Like all other primates, black colobus monkeys use a series of vocalizations—including alarm calls, which sound like snorts. Males defending their territory emit roar-like calls. If both males and females start tongue clicking, a fight is imminent. Females and infants snuffle when in distress. A purr is used to rally the troop before group travel.
Postures are also used as forms of communication. Yawns, open mouth gapes, and stares are threat displays. Touching, embracing, and grooming are friendly gestures.
Colobus monkeys have a digestive system similar to that of ruminants. They have an enlarged fore-stomach in which food breaks down through bacterial fermentation; this is why they are able to digest cellulose, which is the main component of leaves. Their diet consists of 40% foliage.
The black colobus monkey is the oldest of the colobus monkeys. Genetic studies indicate that it appeared between 3 and 4 million years ago.
The word colobus comes from ancient Greek and means “mutilated.” It was probably chosen because colobus monkeys have an underdeveloped thumb. The Latin word satanas means “satanic.”
Single adult male crested mona monkeys were observed joining groups of black colobus monkeys. They probably did so for protection and were able to fully participate in grooming sessions with black colobus monkeys and integrate the groups without any issues. When part of a group of colobus monkeys, single male crested mona guenons vocalize. When they are alone in the forest they remain silent.
Observations indicate that black colobus monkeys correctly recognize the alarm calls emitted by the crowned guenons.
Reproduction and Family
Males reach sexual maturity at 6 years and females at 4 years of age. Most colobine females don’t exhibit sexual swellings; however, Colobus satanas females do. Both males and females leave their natal groups to go join a new group when they are ready to mate. There is no definite breeding period, but all black colobus monkeys tend to mate during the rainy season. Females give birth to one infant.
Babies are born after a gestation of about 195 days. They are brown and change color a few months after birth until they achieve their black pelage. There is no data on inter-birth intervals for this species, but it is likely that there is a two-year period between pregnancies—as is the case for most colobine monkeys. The length of these intervals may be longer or shorter depending on nutritional value of the food available, seasonal extremes, stress due to habitat deterioration, or the loss of an infant.
Black colobus monkeys are seed dispersers. By eating foliage and cutting branches, they also thin trees.
Conservation Status and Threats
The International Union for Conservation of Nature categorizes the black colobus monkey (Colobus satanas) as Vulnerable (IUCN, 2019); it appears on the Red List of Threatened Species.
The Gabon black colobus monkey (Colobus satanas ssp. anthracinus) is also classified as Vulnerable (IUCN, 2016) because their population has declined by over 30% in the last 30 years. Although actual numbers are not known, studies show that the largest groups are found in Réserve de la Lopé-Okanda in Gabon, Forêt des Abeilles in central Gabon, and Douala-Edea forest in Cameroon.
The Bioko black colobus (Colobus satanas ssp. satanas) found on Bioko island, on the other hand, is considered Critically Endangered (IUCN, 2016) as its population declined by over 80% in the last 30 years.
Habitat loss due to deforestation for agriculture and logging is the primary cause of the population decline in the species. Bushmeat hunting has taken its toll on primates all over Africa and black colobus monkeys are no exception. While present in relatively large groups in the forested areas of the Monte Alén National Park, in continental Equatorial Guinea these monkeys seem completely absent near villages where gun hunting has long been practiced. This does not mean that all of them were killed in those areas, but that they likely have learned to be less visible around villages. The price of black colobus meat is one of the cheapest on the markets, indicating that they are sold in larger quantities than other species. Because these monkeys are relatively large and move slowly, they are an easy target. Although gun hunting had decreased thanks to a ban in the 1970s, it is now easy to acquire firearms. In 1995, the discovery of oil off the coast of Rio Muni (continental Equatorial Guinea) created and economic boom and therefore an increase in the human population in the region. Although reportedly dry and bitter, the meat of black colobus monkeys is an easy source of protein for the growing human population.
The main predators of colobus monkeys are leopards, large eagles, chimpanzees, and humans.
Because the species is included in Appendix II of the Convention on International Trade in Endangered Species (CITES), the trade of black colobus monkeys is restricted. However, presently there are no laws against hunting these animals.
There is little enforcement of laws and regulations intended to protect national forests and national reserves. This makes habitat conservation difficult and affects the plight of black colobus monkeys as they don’t fair well in degraded forests. Fortunately, devoted organizations are trying to make a difference. The Rainforest Trust is one them. The non-profit just raised over $400,000 for the “Greater Protection for Cameroon’s Atlantic Rainforest” project. The trust is working with Cameroon Wildlife Conservation Society to elevate the protected status of Douala-Edea Wildlife Reserve to that of a national park, while simultaneously increasing the size of the protected area by over 300,000 acres. The additional acreage consists of mangrove forests, rivers, wetlands, and marine habitat. This will be beneficial to many local species, including the black colobus monkey. It will also benefit local people by creating jobs and other opportunities.
The Bioko Biodiversity Protection Program is another devoted organization. This program is the result of a collaboration between Drexel University in Philadelphia, USA, Universidad Nacional de Guinea Ecuatorial in Malabo, and the Wildlife Conservation Society. It focuses on research, ecotourism, and community programs. The artisan collective, for instance, is a way to help rural communities by facilitating sustainable and eco-friendly micro-entreprise. The Bioko Island Book Series is another project. It helps children develop knowledge about the incredible biodiversity their homeland exhibits.
- Ranging Behavior of a Group of Black Colobus (Colobus satanas) in the Douala-Edea Reserve, Cameroon – Doyle McKey, PeterG Waterman
- Body Measurements for the Monkeys of Bioko Island, Equatorial Guinea – Thomas M. Butynski, Yvonne A de Jong, Gail W, Hearn
- Feeding Ecology of Black Colobus, Colobus satanas, in Central Gabon – M J S Harrison
- Impact of Gun-Hunting on Diurnal Primates in Continental Equatorial Guinea – Noëlle F Kümpel, EJ Milner-Gulland, J Marcus Rowcliffe, Guy Cowlishaw
- Seminomadic Ranging in a Population of Black Colobus (Colobus satanas) in Gabon and its Ecological Correlates – Marie-Claire Fleury, Annie Gautier-Hion
- Better to Live with Allogenerics Than to Live Alone? The Case of a Single Male Cercopithecus pogonia in Troops of Colobus satanas – Marie-Claire Fleury, Annie Gautier-Hion
- Do black colobus in mixed-species groups benefit from increases foraging efficiency? – Annie Gautier-Hion, Jean-Pierre Gautier, Augustin Moungazi
- Primate Behaviorial Ecology – Karen B. Strier
- Primate Societies – edited by Barbara B Smuts, Dorothy L Cheney, Robert M Seyfarth, Richard W Wrangham, Thomas T Struhsaker
- Un primate granivore : le colosse noir dans la forêt du Gabon ; potentialité d’évolution du comportement alimentaire – M.J.S. Harrison et C.M. Hladik
- www.rainforesttrust.org – Greater Protection for Cameroon’s Atlantic Rainforest
Written by Sylvie Abrams, December 2019