WHITE-THIGHED COLOBUS

Colobus vellerosus

Geographic Distribution and Habitat
The white-thighed colobus, also known as Geoffroy’s black-and-white colobus monkeys and ursine colobus monkeys, is one of the world’s 25 most endangered primates and is endemic to West Africa—specifically Benin, Ivory Coast, Ghana, Nigeria, and Togo. Previously found in Burkina Faso, it is now thought to have been eradicated from this country. Their distribution is fragmented.

White-thighed colobus monkeys thrive in the upper canopy of lowland rainforests, swamp forests, semi-deciduous forests, savanna-woodlands, and gallery forests.

White-thighed colobus range, IUCN 2019

Size, Weight, and Lifespan
There is some gender dimorphism between males and females. Both sexes can be 24-26 in (61-67 cm) tall, but males are a little heavier, averaging a weight of 18-22 lbs (8.5-10 kg), whereas females average a weight of 15-17 lbs (7-8 kg). The tail is 29-35 in (75-90 cm) long for females and 32-36 in (83-93 cm) long for males.

White-thighted colobus monkeys can live up to 20 years in the wild.

Appearance
White-thighed colobus monkeys have muscular bodies covered in long, shiny black fur, except for their silvery thighs. Their black faces are elongated with two beady eyes, a flat nose, and slender black lips. Black ears sit at the top of their head. White hair frames the face, giving this monkey the appearance of a sage. The band of white hair above their eyes is differently shaped for each monkey, and is a handy characteristic trait to recognize individuals in a group.

They have smaller incisors than other colobines. Their teeth have high cusps with cutting crests, and their molars have high and sharp cusps linked by transverse crests.

Their hands are perfectly adapted to brachiation, with an underdeveloped thumb and long fingers with shiny black finger nails. Their feet have long digits and an opposable “big toe.”

Rump callosities are prevalent on white-thighed colobus monkeys and provide a cushion for sitting on hard tree branches. Their long white, slightly tufted tail is useful for balance when in the trees.

Infants are born completely white, except for their face, ears, and fingers. They change to adult coloring at three or four months old.

Photo credit: © ONG ODDB/iNaturalist/Creative Commons

What Does It Mean?

Agonistic:
Of, relating to, or being aggressive or defensive social interaction (such as fighting, fleeing, or submitting) between individuals usually of the same species.

Arboreal:
Physically adapted to living primarily or exclusively in trees, such as arboreal-dwelling (tree-dwelling) monkeys.

Brachiation:
Also called arm swinging, this is a form of arboreal locomotion in which primates swing from tree limb to tree limb using only their arms.

Endemic:
Native or restricted to a certain area or country.

Gallery forest: 
A forest that serves as a corridor along rivers or wetlands and projects into landscapes that are otherwise sparsely treed, such as savannas, grasslands, or deserts.

Gender dimorphism:
When the two sexes of the same species have differences in body structure, or anything beyond their sexual organs.

Lowland rainforest:
A forest found at elevations of up to 1,000 meters within the tropical belt. Because it rains a lot and temperatures are high, these forests promote great plant and animal diversity.

Savanna forest:
A mixed woodland grassland ecosystem characterized by the trees being widely spaced so that the canopy does not close. Usually found in tropical or subtropical regions with seasonal rainfall.

Visit the Glossary for more definitions

Diet
The white-thighed colobus diet is highly folivorous (79% leaves) but also includes fruit (10%), flowers and buds (6%), seedpods (4%), and sap, as well as the occasional insect and clay.

Like all colobines, their digestive system is adapted to the ingestion and processing of leaves and seeds that are rich in cellulose, poor in nutrition, and may be toxic to other primates. Their salivary glands are unusually developed and produce high quantities of saliva. Their large sacculated stomach is divided into four chambers. The saliva acts as a buffer to lower acidity in the first two stomach chambers, so the bacteria contained there can survive and break down cellulose. The bacteria are then digested in the third and fourth chambers by various enzymes.

Feeding competition is rare, but when it occurs, surprisingly, it is over unripe fruit and flowers.

Behavior and Lifestyle
White-thighed colobus monkeys are diurnal and mostly arboreal (although they may occasionally travel on the ground between food patches in the savanna). 

They spend a great deal of time resting in trees. It would not be fair to call them “lazy,” even though they spend 68% of their time at rest. There’s good reason for their apparently inactive lifestyle. They are leaf-eaters. Digesting leaves requires more energy than digesting other food items. Much of the leaf matter that they consume is nutrient-poor and they must, therefore, expend their calories wisely. A more active lifestyle would interfer with the energy required for cellulose digestion in their complex digestive system. External factors such as weather or habitat quality do not seem to play a role in extending or shortening the length of resting periods.

They use different sleeping sites every night, some near feeding areas. These can be nests of leaves, holes, or branches in a tree, usually selected where the chances of predation are lowest. In the Kikélé Sacred Forest in Benin, white-thighed colobus seem to prefer the African Hackberry tree, Celtis integrifolia, because it has well-spread rigid stems and branches.

They spend 22% of their time feeding, about 6% traveling, and the rest of the time socializing. Larger groups spend more time feeding and socializing than smaller groups.

It would seem that adult females spend more time grooming each other than they do with adult males. However, neither females nor males are very cuddly; in fact, they spend less time grooming than most Old World monkey species do.

Daily Life and Group Dynamics 
White-thighed colobus live in groups that vary greatly in size from five or seven to over thirty individuals. These groups can be mixed (multi-male and multi-female), uni-male (one male and multiple females and juveniles), or all-male bands.

Males tend to leave their natal group around the age of 5. They usually participate in several short and aggressive incursions into neighboring groups to assess the situation and decide which group they want to integrate with. They usually migrate into a group with a more favorable ratio of adult females to adult males, thereby increasing their rank and reproduction chances. Migration is facilitated if they already have allies in the new group. It is not unusual for several males of the same group (some of which may be kin) to migrate to the same new group.

Alpha males rarely leave, but can opt to participate in neighboring group incursions to demonstrate their strength by fantastic displays and, as a result, seduce and attract new females to their own group.

Competition is higher and takeovers are more frequent in all-male groups than in mixed groups.

There are very few dominant agonistic interactions between females. Females rarely participate in inter-group encounters. They do not form coalitions over food and do not affiliate with each other as readily as females of other monkey species do. They may occasionally form short-term coalitions to protect infants. They also seem to use infant handling as a way to bond with other females, although mothers are somewhat hesitant to leave their offspring in the hands of non-kin sub adult females.

Fun Facts

White-thighed colobus are colobine monkeys. The word colobine comes from the Latin (Colobinae), which derives from the Greek (kolobos), which means “mutilated.” This is in reference to their unformed thumb.

The white-thighed colobus is one of four black-and-white colobus monkeys in Africa and was recognized as a separate species from Colobus polylomos in 1983. Each species is black and white, but the pelage patterns differ.

During and before the 19th century, skins of the white-thighed colobus was in high demand by the kings and chiefs of West African kingdoms for ceremonies, international trade, ornaments, and clothes. In the 1890s, an estimated 190,000 skins were exported from Ghana. In the early 20th century, the trade averaged 17,000 per year.

Communication
Adult male white-thighed colobus monkeys use loud roars to call out their territory and location. The roars can be multiple and in chorus with other groups, especially in the morning. If several members of a group (except infants) start snorting, danger is imminent and a predator is near. If males produce slow, low-pitch roars, on the other hand, they are simply trying to stay in touch with other members of the group over a long distance.

When trying to establish contact, an individual can approach another member of the group at approximately 3 arms length. If the targeted individual does not move, this means they can be friends. If they both start producing short burst roars, it means they are not getting along and are being aggressive toward each other. Jumping displays, stiff legs, and open mouths (accompanied or not by loud calls) are also signs of aggression and conflict. High ranking males display more than anyone else, probably to advertise their fighting ability and discourage any wannabe newcomer to attempt a takeover.

Although there is no ritualized submissive signals, a subordinate male usually grimaces and pant-grunts when approached by a dominant male.

When in a romantic mood, males are not very subtle, nor are they gentlemanly. They touch females on the hips, face, or back, sniff the genitalia of the female, grab her hips, push her, mount her, or lick her face. Receptive females reciprocate with similar moves directed at the males. Non-receptive females, on the other hand, stubbornly sit and refuse to present. Disgruntled males may then chase and slap them. When feeling jealous and possessive, males guard the females by sitting next to them, herd females away from another group of males, or simply become aggressive.

Reproduction and Family
Females reach maturity at around 4 years old and males at around 6 years of age. There is no mating or birth season, although breeding occurs in 20-month intervals. Females do not show external signs of ovulation and give birth to one offspring after a gestation period of 5 to 6 months.

Infants are handled by the mother and other females so the mother can go foraging.

Females nurse and protect their offspring until she can be independent, however, this is not an easy task. The situation for females and infants is different, depending on the group they live in. In groups with a larger number of males, infanticide is high (38% of infant mortality). Indeed, when a new dominant male takes over, he kills infants in the group. This probably explains why white-thighed colobus females seem to prefer groups with one dominant male (uni-male) over multi-male/multi-female groups. They do nonetheless use the same practice as other monkey species—i.e. they copulate with several males to blur paternity lines—independent of the group they live in.

Infants are born white and their coat color changes by four months of age, although the coloring changes faster when the infant is born in a multi-male group. A strategy of nature that allows them to survive potential infanticide.

Photo credit: © ONG ODDB/iNaturalist/Creative Commons

Ecological Role
White-thigh colobus monkeys are prey to raptors like the crowned hawk eagles, and leopards. They may help the forest ecosystem by dispersing seeds of the tree species they feed on.

Conservation Status and Threats
The white-thighed colobus is classified as Critically Endangered (IUCN, 2020), appearing on the International Union for Conservation of Nature’s Red List of Threatened Species. It was listed as one of the world’s 25 most endangered primate species in the IUCN’s Primates in Peril 2018-2020 report.

The Critically Endangered assessment is based on a suspected population reduction of more than 80% over the past three generations (1992-2019) due to the combination of intensive hunting and decline in habitat quality across its geographic range. The species has very likely been extirpated in two countries, is close to being lost in a third, and continues to hang on in only two others despite already severe population declines.

Unregulated hunting and habitat loss due to deforestation are major threats to the survival of the species. Habitat has decreased in extensively over the last 30 years. In Ghana, logging (especially illegal logging) increased by 600% between 1995 and 2008. More than 50% of protected areas and forest reserves that contained white-thight colobus in the 1970s no longer sustain it. More than 50% of protected forests in Ivory Coast, Togo, and Benin have been logged or have been converted to plantations for oil palm, cocoa, and rubber in the last 50 years. Other factors contributing to the demise of primate populations, including this one, are a dramatic increase in human population (50% in the last 15 years in Ivory Coast alone) and civil unrest in several countries. Despite community conservation initiatives, hunting continues as well.

There has not been any systematic population survey of the species. However, we know that the species is now rare in Benin, Ivory Coast, Nigeria, Togo, and Ghana, and seems to have disappeared in Burkina Faso. In fact, the species only survives in community forests in Ivory Coast. It is almost gone in Ghana, except in Boabeng-Fiema Monkey Sanctuary, where the population grew since the 1990s, but recent population data are lacking. 

There are still some groups in Lama Forest Reserve and Kikélé Sacred Forest and Bonou swamp forest in Benin.  It is not clear whether the species is still present in Pénéssoulou Forest Reserve. There are claims that the species is still present in Old Oyo National Park and Kainji Lake National Park in Nigeria, but recent surveys did not confirm the claim.

Conservation Efforts
Despite its rapid disappearance, the white-thighed colobus monkey is not as protected as other primates. The survival of the species is strongly dependent on small sanctuaries and forest reserves, local initiatives and in some cases cultural traditions and local taboos—like in Ghana where, in the 1830s, a local oracle instructed villagers to take care of the monkeys.

Better enforcement of hunting laws, better habitat protection, and reduction in logging need to be implemented.

References:

  • Dr Pascale Sicotte – University of Calgary website.
  • Primates in Peril – The World’s 25 Most Endangered Primates – 2016-2018
  • The effect of female kinship and relatedness on natal attraction and infant handling – Iulia Badescu
  • Geoffroy’s black-and-white colobus fact file – Arkive website
  • Conservation Status of Geoffrey’s pied Colobus Monkey Colobus vellerosus Geoffrey 1834 has Dramatically Declined in Côte d’Ivoire – S. Gonedelé, A. Bitty, G. Gnangbé, J. C. Bené, I. Koné & D. Zinner.
  • Controversy Over the Application of Current Socioecological Models to Folivorous Primates:Colobus vellerosus Fits the Predictions – Tnia L. Saj, Sarah Marteinson, Colin A. Chapman, Pascale Sicotte
  • Dispersal in male ursine colobus monkeys (Colobus vellerosus): influence of age, rank and contact with other groups on dispersal decisions -Julie A. Teichroeb, Eva C. Wikberg & Pascale Sicotte
  • Habitat Use by White-Thighed Colobus in the Kikélé Sacred Forest: Activity Budget, Feeding Ecology and Selection of Sleeping Trees – S. Djègo-Djossou, I. Koné, A. B. Fandohan, J. G. Djègo, M. C. Huynen and B. Sinsin
  • Infanticide risk and quality influence optimal group composition for Colobus vellerosus – Julie A.  Teichroeb, Eva C. Wikberg, Iulia Badescu, Lisa J. Macdonald and Pascale Sicotte.
  • The Function of Male Agonistic Displays in Ursine Colobus Monkeys (Colobus vellerosus): Male Competition, Female Mate Choice or Sexual Coercion? – Julie A. Teichroeb and Pascale Sicotte
  • Animal Diversity website.
  • ​IUCN Red List

Written by Sylvie Abrams, May 2018