MT. KILIMANJARO GUEREZA

Colobus caudatus

Geographic Distribution and Habitat

The Mount Kilimanjaro guereza (Colobus Caudatus) is a species of Old World monkey endemic to northern Tanzania and southern Kenya. In Tanzania, they reside in and near the slopes of Mount Kilimanjaro (Kilimanjaro National Park) and Mount Meru (Arusha National Park). In Kenya, they are known to occur only in two small and degraded forests: Kitobo Forest Reserve and Loitokitok Forest Reserve. Overall, about 98% of their range is in Tanzania and 2% is in southern Kenya.

Mt. Kilimanjaro guerezas are primarily arboreal (tree-dwelling) and reside in low to highly mountainous, evergreen, and closed-canopy forests. In Tanzania, they can live in forests at elevations as low as 2,165 ft above sea level (asl) (660 meters) and as high as at least 9,843 ft (3,000 meters) asl. However, they are commonly found between 5,906 ft (1,800 meters) asl and 7,546 ft (2,300 meters) asl.

TAXONOMY IN TRANSITION

The genus Colobus comprises five species: black colobus (Colobus satanas), Ursine colobus (Colobus vellerosus), king colobus (Colobus polykomos), Angola colobus (Colobus angolensis), and mantled guereza (Colobus guereza). The mantled guereza further consisted of eight subspecies. Prior to 2018, the Mt. Kilimanjaro guereza was considered to be one of these eight subspecies of mantled guereza and was referred to as “Colobus guereza caudatus Thomas 1885.

However, a study by Butynski and De Jong in 2018 revealed that there are geographic and genetic differences between the Mount Kilimanjaro guereza and the other subspecies of mantled guereza, and they should therefore be considered a separate species. For example, geographically the Mt. Kilimanjaro guereza is isolated from the other mantled guereza subspecies by at least 124 miles (200 km) of arid country, making interspecies movement almost impossible. Additionally, notable differences between the length, shape, and percentage of white in their tails allow them to be distinguished from the other subspecies.

Since Mt. Kilimanjaro guerezas were only recently recognized as a separate species, a majority of the accounts and research are based on mantled guereza colobus monkeys. While the recent study by Butynski and De Jong provides a starting point for establishing the Mt. Kilimanjaro guereza as a distinct species, additional research on physiology, behavior, and various other characteristics is needed to reveal features and enhance our understanding.

Mt. Kilimanjaro guereza range, IUCN 2020

Size, Weight, and Lifespan

While specific information regarding the weight and size for Mt. Kilimanjaro guerezas is lacking at present, one may draw insights from the fellow mantled guereza species. Guerezas are sexually dimorphic with males weighing up to 1.19 times more than females. On average, male’s weigh between 20.5 and 29.8 lbs (9.3–13.5 kg) and females weigh between 17.2 and 20.3 lbs (7.8–9.2 kg). Additionally, there is dental sexual dimorphism, with males having a larger set of teeth than females, which may be attributed to socio-sexual factors. The head-to-body length averages 24.2 in (61.5 cm) for males and 22.7 in (57.6 cm) for females.

The lifespan of the mantled guereza is thought to be about 29 years in captivity and about 20 years in the wild.

What Does It Mean?

Diurnal
Active during daylight hours.

Ovulation
The release of the ripe egg (ovum) from the ovary.

Visit the Glossary for more definitions

Appearance

Mt. Kilimanjaro guerezas are one of the most distinguished looking primates with a turban of black hair on the head and a cape of white hair cascading on the side, which might make celebrities jealous. Underneath the turban of black hair, the face is gray framed by white hair. Their noses are stubby rather than pointed. The body is covered in glossy black hair, with the white cape-like mantle extending from the shoulder to the hip. The tail is black with a white tuft resembling a duster. One characteristic that helps distinguish the Mt. Kilimanjaro guereza from other guereza subspecies is the percentage of white fur on the tail and the size of the tail bush. In Mt. Kilimanjaro guerezas, 71–88% of the tail is white with the tail tuft being very full, whereas in the other studied subspecies of guerezas, the whiteness of the tail may range anywhere from 36 to 81%.

Diet

Mt. Kilimanjaro guerezas are highly folivorous and they can be found munching primarily on leaves with high protein-to-fiber ratio. When available, they don’t mind changing up the palate to consume flowers and fruits.

The folivorous nature of their diet is supported by their stomach anatomy. These primates are termed “foregut fermenters” and display a diverse array of digestive adaptions, one of which is the presence of a multi-chambered stomach. The complex, microbiome rich stomach allows them to digest plant fiber and detoxify plant chemicals, possibly allowing them to ingest leaves in greater quantities compared to other simple-stomached primates such as gibbons.

Behavior and Lifestyle

Mt. Kilimanjaro guerezas are arboreal, spending most of their time in trees and, when active, bound through canopies, leaping from tree to tree. They descend to the ground in order to move locations, when trees are not densely spaced for them to swing, and sometimes to forage for food.

Despite being a diurnal species, the adults spend more than half the day resting, followed by feeding, while comparatively less time is spent traveling and on social activities. Infants, like all babies, spend more time in social activities, such as playing, and less on resting. All age groups prefer to forage and feed during the cooler parts of the day, such as the morning or evening. These monkeys may be hitting the snooze button more frequently during the day to either regulate temperatures and conserve energy to beat the African afternoon heat, or to digest the cellulose-rich food in their diet. Come nightfall, the members of a single group occupy several adjacent trees, close to a source of food.

Fun Facts

Males are significantly more vocal than females and emit distinct roars to maintain distance between groups or intimidate predators and competition.

Roars are contagious, with males from across the jungle joining in when one male starts roaring.

Daily Life and Group Dynamics

These monkeys live in highly cohesive social groups ranging in size from three to fifteen individuals. The groups normally comprise one adult male, accompanied by several females, juveniles, and infants. In some cases, multiple adult males may be observed in the same group; however, one of the males is dominant over the other males and may force the other males out if they do not behave.

Males are rowdier and spend more time on vocalization tactics and inter-group aggression, while females are the gentler of the two sexes and partake in grooming one another significantly more than the males do. The males groom others the least and receive little in return. In these instances, the key to keeping one’s hair looking luscious is to self-groom, which is observed particularly in adult males.

Communication

Mt. Kilimanjaro guereza colobus monkeys communicate by vocalizations and exhibit many different sounds, which may indicate alarm calls, socialization, or male-male competition. A distinctive sound that males in particular emit is a high-volume, low-frequency loud call termed a “roar,” described as a “rurr rurr rurr rurr” sound that can be heard for more than a mile. Research has shown that the frequency of a roar by Mt. Kilimanjaro guerezas is significantly different from some other subspecies of guereza studied. For example, male Mt. Kilimanjaro guerezas emit a higher-pitched roar compared to the western guereza (Colobus guerza occidentalis).

While these loud calls may be used in different contexts by different species, it is believed that the main function of the roaring is to communicate with other groups over long distances. These vocal displays thus function effectively in increasing intergroup distances. A chorus of these loud calls occurs most frequently during the night and early morning, which may indicate that they are uttered close to sleeping sites and to help maintain space between groups.

Apart from roaring, the other vocal sounds emitted are snorts in response to predators (such as leopards) or tongue clicking during intergroup conflicts.

In addition to vocal sounds, Mt. Kilimanjaro guerezas also communicate through non-vocal gestures, which may either occur separately or in association with loud calls. These consist of shaking trees or branches while jumping around and may indicate threats to members of adjacent groups.

Reproduction and Family

Reproductive information specifically to the Mt. Kilimanjaro guereza is not well-studied in the wild. However, research in mantled guerezas can shed some light on their ovulation.

Groups of four to ten individuals generally consist of one male and the number of adult females per group can be between one and three. Some groups may consist of two males, but this is rare. In the wild, the mantled guereza ovulates for approximately 24 days, during which the female can conceive and is receptive towards copulation. Females initiate sexual behavior towards the males through lip smacking or display of the genital region. The median gestation length is 158 days and median interval between birth is 22 months, which is shorter compared to other species of similarly sized Old World monkey.

Immediately after birth, the infant becomes the center of attention with the group huddling around the mother to get a closer look at the newborn. Mt. Kilimanjaro guerezas make excellent babysitters, with females of all ages looking after the infant and carrying the baby around from the very first day. While all females may share childcare responsibilities, an infant is primarily nursed only by their own mother.

Ecological Role

Since Mt. Kilimanjaro guerezas are primarily herbivores, they serve as a food source to other species living in the forest, thus inadvertently playing a part in the food chain.

While folivorous primates such as Mt. Kilimanjaro guerezas have the potential to strip trees of their leaves and exert considerable pressure on the trees, particularly in areas where these leaf-eating monkeys are highly abundant, these primates are in fact engineers of the ecosystem they live in.

When consuming fruit, the Mt. Kilimanjaro guerezas act as seed dispersers. By transporting the seeds away from the parent tree, the primates increase the likelihood of seed survival and germination, since the chances of seed consumption by beetles and other insects decrease. Through seed dispersal, primates play an important role in the distribution and composition of plant communities.  

Furthermore, plant-eating monkeys such as the Mt. Kilimanjaro guerezas can make the trees they feed on more productive. Through foraging and removal of terminal buds, the tree is stimulated to produce more young leaves and promote branch formation, which in turn increases foliage. Lastly, folivorous primates provide essential nutrients to the forest ecosystem and can improve the soil quality through the large amounts of dung they produce. Nutrients that would have been locked in leaves, taking months or years to fall to the forest floor and decompose, are liberated for use through consumption, digestion, and defecation. In fact, the soil under folivorous monkey bathrooms has been shown to have increased seedling growth, microbial and earthworm activity, and improved soil fertility.   

Conservation Status and Threats

The International Union for Conservation of Nature lists Mt. Kilimanjaro guereza as Vulnerable (IUCN, 2018), appearing on the IUCN’s Red List of Threatened Species.

While overall the Mt. Kilimanjaro guereza may be considered a Vulnerable species, locally in Kenya it would be considered Critically Endangered. The number of Mt. Kilimanjaro guerezas in Tanzania is likely well over 10,000; however, Kenya is a different story. Research has indicated that the Mt. Kilimanjaro guereza is Kenya’s most threatened species of primate, with the total number of individuals likely to be fewer than 200—and may even be fewer than 100.

The lower slopes of Mount Kilimanjaro and Mount Meru are one of the most populous regions in Tanzania and continue to rapidly grow. However, human population growth comes at the price of forest loss, including forests that Mt. Kilimanjaro guerezas call home. Large areas of the forests have been degraded and continue to be cleared for timber extraction, exotic tree plantations, and agriculture, all of which negatively impact the relatively small habitat these monkeys have in East Africa. Additionally, with great beauty comes great pain, which is evidenced by the mantled colobus (Colobus guereza) being exploited for its skins to be used for rugs and hunted for its meat.

Naturally in the wild, the Mt. Kilimanjaro guereza can fall prey to crowned hawk eagles and leopards. However, this is nothing compared to the negative impact human activities have on their habitat degradation and population decline.

Conservation Efforts

In Tanzania, Mt. Kilimanjaro guerezas are relatively well protected in the two national parks where they are found: Mount Kilimanjaro National Park and Arusha National Park. In Kenya however, if this species is to survive, it needs to be actively protected. The Kenyan Wildlife and Forest Service, and more importantly the people living around the Kitobo Forest Reserve and Loitokitok Forest Reserve, should limit the degradation and loss of habitat, critical to the survival of these primates.

One ray of hope is the work by Global Wildlife Conservation, which is supporting local communities and the Kenya Forest Service in efforts to save the Kitobo Forest Reserve and halt biodiversity loss. The primary activities of this project are reforestation, conservation training, and education.

References:
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Written by Divya Pawar, May 2022