White-Thighed Colobus, Colobus vellerosus
WHITE-THIGHED COLOBUS
Colobus vellerosus
Geographic Distribution and Habitat
The white-thighed colobus monkey can be found in several African countries, namely Benin, Côte d’Ivoire, Ghana, and Togo. Some believe that this monkey can also be found in Nigeria, though that is unconfirmed. It is also believed that they have possibly vanished from Burkina Faso. They inhabit lowland rainforests, riparian forests, and have been spotted in semi-deciduous forests in places like Benin. Their home range, which is the area of land they frequently travel for food or sleep, varies between 27 to 119 acres (11 to 48 hectares). The white-thighed colobus shows a strong preference for particular types of sleeping trees, specifically Celtis intergrifolia, Cola cordifolia, and Holoptelea grandis. These trees are tall, and have a large trunk, which gives the monkeys a feeling of safety when they are high in the canopy. This strong preference for tree type and characteristics is important to note, as the countries this monkey lives in are being affected by habitat loss, much like other primate host countries.
The white-thighed colobus received its species status relatively recently in 2005. It was once thought to be a subspecies of the king colobus (Colobus polykomos) but was determined to be morphologically and genetically distinct. The white-thighed colobus is also known by the common names Geoffroy’s black-and-white colobus, ursine colobus, and the white-thighed black-and-white colobus.
Size, Weight, and Lifespan
The white-thighed colobus shows mild sexual dimorphism, which is the difference in body size or physical characteristics depending on the animal’s sex. Males weigh 22 to 23 pounds (9.9 to 10.3 kg), and females weigh 18 to 19 pounds (8.3 to 8.7 kg). Males are 24 to 26 inches (61 to 66 cm) in length, while females are on average just an inch shorter in length, between 24 to 25 inches (61 to 63 cm). Their tails range from 29 to 36 inches (75 to 93 cm).
In nature, the life expectancy of the white-thighed colobus is around 20 years.
Appearance
The white-thighed colobus is a stunning monkey. Sporting black and white fur, their coloration helps them to blend with their surroundings, while also allowing them to impress potential mates. Their backs and arms are a rich black, which is amplified by the medium hair length in these areas. Their thighs are, as the name might suggest, a while-silver color. Their tails are white as well. Their faces are haloed with pure white that wraps around their cheeks, chin, and up to but not including the crown of their head. Their crown is black, giving them a regal appearance.
Infants are born stark white, and as they mature they lose this natal coat and the distinguished black coloring comes in.
Like all colobus monkeys, the white-thighed colobus has a greatly reduced thumb. It is so reduced that it appears as though they are missing the digit entirely, and indeed they only utilize their remaining four fingers. This physical trait is thought to be an advantage for this highly arboreal species as they swing through the canopy. A thumb might get in the way!
Diet
The white-thighed colobus is a folivorous monkey, meaning their primary food is leaves. One group in Benin was found to have a diet that consisted of 60.3% leaves, 33.3% fruits, and 6.4% miscellaneous foods, such as seeds and flowers. They prefer young leaves that are light green and frequently dine on the greenery that comes from lianas, a type of woody vine. Being able to eat such great amounts of leaves is no small feat on an animal’s digestive system. Because of this, the white-thighed colobus, as well as all other colobines, have a special digestive system that allows them to process the cellulose found in the cell walls of the leaves. This adaptation, a sacculated foregut, aids in digestion by fermenting the leaves in microbial colonies and a high concentration of acid.
Due to the relative abundance of leaves, folivorous primates rarely deal with feeding competition. When the white-thighed colobus does find itself clashing for a meal, it is usually over unripe fruit or coveted flowers.
Behavior and Lifestyle
The white-thighed colobus is a diurnal primate, meaning they are awake during the day and sleep at night. They spend much of their time feeding and resting. Specifically, 22% of their day is spent eating and foraging, and 68.6% is spent resting. Since white-thighed colobus has an energy-expensive digestive system, rest is a vital part of their life and health maintenance. They are social monkeys, and 2.6% of their day is spent engaging in social activities, such as allogrooming and playing — however, this may vary depending on the size and compilation of the group.
White-thighed colobus are highly arboreal, spending the majority of their lives high in the canopy.
The taxonomic subfamily name for all colobus monkeys is Colobinae. The word Colobinae can be traced back to a Greek word that means “mutilated”, a reference to the colobus monkeys’ reduced thumb.
A white-thighed colobus group can vary significantly in size and composition. Groups as small as five and as large as thirty have been observed. Though, the most common group size is somewhere around 10 to 15 individuals. The composition of these groups is often composed of one male and several females, or multi-male and multi-female groups — though the latter tends to have a distinct social hierarchy among the males. All male groups also occur as a result of males not forming a family group yet, or when a male is ousted from his existing family group.
Females are the philopatric sex, meaning they stay in their natal group and do not migrate out. Males do migrate out, however, usually around the time of maturity. They may spend this time visiting other groups, and deciding which one may provide the best opportunity for mating selection later on.
While many females within the group may be related, they are not known to form alliances the way that some other monkeys do. They are not known to bond with one another or socialize in any significant way. However, the exception to this rule is when there are new or many mothers in the group — they may form a coalition to better protect the infants.
The white-thighed colobus has a host of verbal and nonverbal communication methods. Like many other primates, males often produce a guttural roar to denote their territory and location. All white-thighed colobuses will participate in an alarm call if necessary, which sounds like quick snorts.
White-thighed colobuses rely heavily on body language when socializing. Like most monkeys, open mouths and direct eye contact indicate aggression or a challenging posture. This will often lead to displays which is a behavior in which dominant males make a mess of their surroundings by shaking branches and vocalizing loudly.
White-thighed colobuses are a polygynous species, meaning that males may copulate with multiple females within the group. Females become sexually mature at 4 years old, with males following at 6 years. Upon maturity, males will disperse to new groups in the hopes of maximizing their chances of mating with available females. This dispersal method is also useful in avoiding inbreeding.
Females do not show any outward signs of their fertility, a phenomenon called concealed ovulation. This is thought to occur as a defense against infanticide since the return of ovulation is often what spurs a male to commit such an unsavory act. By concealing this biological occurrence, a male is left in the dark regarding the female’s receptiveness. While this seems to be an effective strategy against infanticide sometimes, it does not help if the dominant male is usurped. Once a new dominant male is present in the group, they will often kill all infants in the group.
Males are not subtle in their pursuit of females. They often chase, slap, grab the rear of, and generally annoy a female whom they are interested in. If the copulation is desired by the female, she will eventually present herself to the male and he will mount. Females are pregnant for 5 to 6 months, and give birth to one infant at a time. White-thighed colobuses do not have a breeding or birthing season but rather are able to reproduce throughout the year.
Once an infant is born, mothers and other females will care for the baby, a behavior known as allomothering. Mothers nurse their infants for one year, and at the beginning of motherhood, they rely on other females to care for the infant so they can feed themselves.
White-thighed colobuses act as seed dispersers in their environment, because of the inclusion of fruit in their diet. They also act as prey for large animals such as eagles and leopards.
The International Union for Conservation of Nature lists the white-thighed colobus as Critically Endangered (IUCN, 2020), appearing on the IUCN Red List of Threatened Species.
The white-thighed colobus’s population numbers are astonishingly low. At just an estimated 975 mature individuals left in the wild, this monkey is primarily threatened by hunting and habitat loss. The areas that the white-thighed colobus lives in have been affected by increasing human settlement. The land, particularly in places like Ghana and Côte d’Ivoire, is often cleared for farmland or plantations. Animals once hunted have migrated out or become extinct from the area altogether, leaving the white-thighed colobus as one of the largest animals to hunt.
Though they are protected under international legislation, the enforcement of these laws isn’t always a reality.
According to recent surveys, the white-thighed colobus has all but been extirpated from the protected areas in Côte d’Ivoire, except for one location in the northeast. In Ghana, the encounter rate of seeing these monkeys in their protected areas is down 87% compared to 30 years ago. There are some locations where there are populations that seem to be going strong, namely the Boabeng-Fiema Monkey Sanctuary in Ghana, where an estimated 350 individuals live.
There are some traditions and taboos that exist around this monkey, and they are largely positive. It is considered sacred in many cultures and it is extremely frowned upon to kill it. However, this cultural belief is reduced with each generation.
The white-thighed 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 white-thighed colobus is protected by the African Convention on the Conservation of Nature and Natural Resources under Class A. It is suggested that countries that still have these monkeys do more to protect them. That includes enacting more stringent laws and increasing the consequences for breaking them.
The IUCN Red List suggests that the European Association of Zoos and Aquariums develop a captive breeding program for these monkeys in order to preserve and potentially grow their dwindling numbers. Additionally, more surveys are needed to better understand their population numbers and where they are occurring. Côte d’Ivoire, Ghana, and Togo are all involved in conservation efforts that help to engage and educate the public about these wonderful and unique animals.
- https://www.cambridge.org/core/journals/journal-of-tropical-ecology/article/abs/growing-population-of-the-critically-endangered-whitethighed-colobus-monkey-colobus-vellerosus-from-forest-fragments-in-ghana/EF5EB4FE268ECBF644FCE41BAB00FC02
- https://www.inaturalist.org/taxa/74201-Colobus-vellerosus
- https://animalia.bio/index.php/ursine-colobus
- https://www.speciesconservation.org/case-studies-projects/white-thighed-colobus/16022
- https://www.iucnredlist.org/species/5146/169472127
- https://neprimateconservancy.org/king-colobus/
- https://bioone.org/journals/primate-conservation/volume-2015/issue-29/052.029.0106/Habitat-Use-by-White-Thighed-Colobus-in-the-Kik%C3%A9l%C3%A9-Sacred/10.1896/052.029.0106.full
Written by Robyn Scott, August 2024