Piliocolobus kirkii

Geographic Distribution and Habitat

The Zanzibar red colobus, also called the Kirk’s red colobus monkey, is endemic to Ungula, the main island of the Zanzibar archipelago, off the coast of Tanzania.

This mainly arboreal (tree-dwelling) species is found in three forests within the island and prefers drier areas over wetter ones. The habitats of Zanzibar red colobuses include coastal rag scrub and coastal thickets, but they can also be found in mangrove swamps and agricultural areas. Those found in agricultural areas (known as shambas—Swahili for “farmland”) are more used to human presence, and thus, come closer to ground level.

Zanzibar red colobus monkey range. Map: IUCN, 2018.

Size, Weight, and Lifespan

Adult Zanzibar red colobuses range in size from a head-to-body length of 18–30 inches (45–70 cm). Their average tail length is 2–2.5 feet (55–77 cm). Males can weigh over 26 pounds (12 kg), and females, 22 pounds (10 kg). Sexual dimorphism is not readily visible to the naked eye in the Zanzibar red colobus, meaning both sexes have little difference in body color and size. However, there are subtle differences, including that females are more slender than males, while males have broader shoulders, bigger skulls, and longer canine teeth. 

The average lifespan of the Zanzibar red colobus is unknown. However, other colobus species are reported to have a lifespan of around 20 years in the wild.


The coat of Zanzibar red colobuses ranges from dark red to black, and is accented with a black stripe along the shoulders and arms. The underside is pale. Their faces are black, and crowned with long white hair, and the nose and lips feature a distinguishing pink mark. They have a long non-prehensile tail, used for balance, and long hind legs for leaping through the trees. Highly differentiated facial features help individuals distinguish one another in their group.

The coat of infants is black and white, with red and brown pigments appearing at around 3 to 5 months of age. Full coloration of adults is achieved in 6 to 11 months of age.

Zanzibar red colobuses, like other colobus monkeys, have a significantly reduced opposable thumb. This lack of a thumb is so they can easily brachiate through the trees and achieve the acrobatic nature of their movement through their habitat. “Brachiation” is swinging between tree limbs, in this case, with their four long fingers forming a strong hook to easily grasp branches. It’s like swinging on the (appropriately named) monkey bars in a playground. While the tail of the Zanzibar red colobus is incapable of grasping, it instead acts as a rudder, providing balance as the monkey maneuvers in the trees.


Zanzibar red colobuses have a large, sacculated, four-chambered stomach specific for breaking down certain plant material, giving them a pot-belly. Their stomach is filled with beneficial bacteria, which allows Zanzibar red colobuses to ferment and break down the cellulose-filled, highly fibrous leaves they regularly consume. The Zanzibar red colobus is mainly a folivore (leaf-eater), and typically half of the leaves they consume are young. Due to their heavy diet of young leaves, there are times when the Zanzibar red colobus consumes charcoal, which is believed to aid in the digestion of toxins found in mango and Indian almond treestoxins that other animals cannot consume. This charcoal-consumption habit is thought to be a learned behavior, passed down from mother to offspring. It should be noted, however, that not all populations carry out this behavior; rather, it is mostly done by those who consume more perennial and exotic plant matter. They also eat flowers, seeds, leaf shoots, unripe fruit, bark, dead wood, and soil.

Since some small populations use mangroves as a food source, these individuals naturally consume more salt. As a result, these individuals have been observed drinking water directly from tree holes or licking rainwater or dew off of leaves. 

The Zanzibar red colobus is one of the few primate species unable to digest the sugars found in ripe fruit.

Due to their slow digestive tract, Zanzibar red colobuses are the slowest-moving of all colobus species.

Behavior and Lifestyle

Zanzibar red colobuses are diurnal (most active during daylight hours) and arboreal. They move around their habitat by leaping through the trees.

In terms of activity budget, analyses of groups in Jozani Chwaka Bay National Park and farmland groups revealed no difference in time spent feeding or resting; however, forest groups spent significantly more time moving around, and had longer daily travel distances compared to farmland groups. 

Zanzibar red colobuses have long periods of inactivity during the day (7 hours of the 10 they are awake), due to the buildup of both carbon dioxide and methane gases during digestion stemming from their diet. Digesting and fermenting highly fibrous foods in a four-chambered stomach is a long process. During these periods of downtime, individuals groom and play with one another, and burp! Luckily for the Zanzibar red colobus, though, like all species of red colobus, burping is considered a friendly gesture. During downtime, Zanzibar red colobuses make good use of their ischial callosities, which are pads on their buttocks that enable them to sit comfortably on tree branches for long periods of time. (For specifics, “ischial” relates to the ischium, the curved bone at the base of the pelvis that forms the lower and back part of the hip bone; “callosities” refers to the hardened skin that encloses these butt pads.) 

Like other colobus species, the Zanzibar red colobus sleeps in the trees and does not construct nests.

Since the extinction of the Zanzibar leopard in the mid-1990s, humans are their main predator, with carcasses being fed to domestic dogs and sometimes consumed by humans. It is possible that young individuals may be taken by large snakes and raptors.

Fun Facts

Locals call the Zanzibar red colobus “kima punju,” meaning “poison monkey” in Swahili, due to their distinct, pungent smell.

The Zanzibar red colobus is also called Kirk’s red colobus, after Sir John Kirk, the British Resident of Zanzibar who first brought it to the attention of zoological science.

The Zanzibar red colobus’ leaps between trees can cover as much as 25 feet (7.6 meters)! 

Daily Life and Group Dynamics

Zanzibar red colobuses are very social, with groups consisting of up to four adult males and many more females. Group size ranges between 30 and 50 individuals. There is a dominance hierarchy among only the males in a group. Two forms of social presenting have been observed relating to male dominance: submissive presenting by adult females and juveniles to adult males, and another form in which dominant males show their backsides primarily to subordinate males to reinforce the dominance hierarchy.

Zanzibar red colobus societies additionally exhibit fission-fusion, in which socially integrated groups will regularly divide into temporarily smaller foraging groups. This particular system appears to be related to food distribution and availability and is thought of by researchers as a way of uniting cost-effective foraging strategies alongside the social benefits of living in a group.

Solitary males have been observed, and are believed to represent dispersal and potential immigration into new groups. This solitary behavior is higher in the Zanzibar red colobus compared to mainland red colobus species, possibly due to the lack of predators in the Zanzibar archipelago.

With regard to intergroup relations (i.e., relations between two or more groups), groups are generally tolerant of one another. However, intergroup conflict rates increase with higher population density. Among Zanzibar red colobuses, both males and females can exhibit aggression towards rival groups in agricultural areas, as population density is higher in these areas, creating greater competition for food. In terms of intragroup relations (i.e., those within a singular group), adult males are the more common aggressors, with both adult and subadult males being aggressive towards one another over both food and mates. Rates of aggression that involve physical contact, such as biting and grabbing, are generally low, except for high-density populations in agricultural areas.

In terms of grooming, adult females perform the majority of the grooming, and adult males are groomed most often. Infants are rarely groomed; however, adult female Zanzibar red colobuses groom infants and juveniles more often than other red colobus species. Males have never been seen grooming each other, and this may have to do with frequent emigration and immigration of males between groups.

Play behavior is primarily among infants and juveniles. Studies have shown that young members in farmland groups play significantly more than their forest-dwelling counterparts, which is likely due to the farmland groups’ shorter daily travel times, spatial cohesiveness, and tendency to spend more time on the ground.

Finally, with regard to home range, there is significant variation in home range size. Home ranges vary between 1.2–21.8 acres (0.5–8.8 hectares) for populations living in different habitats and sites. Instead of group size, habitat quality and type appear to be the main determinants in home range size. There has also been observed extensive overlap in the home ranges of neighboring groups; in one study of several populations at different sites, the mean percentage of home range overlap between groups varied between 6.9% and 42.9%.


Zanzibar red colobuses are non-territorial in nature, and thus, do not make loud territorial threat calls. Their distress and warning calls are known as the “bark,” “chist,” or “wheet.” One of their loudest and longest callsconsisting of howls and high-pitched criesis heard when a male expresses his dominance over the group, as well as when checking the sexual status of group females. When there are changes in the surrounding environment (e.g., weather, animal movement in proximity to the group), grunts and chirps are made. Young may make alerting calls when seeing the shadow of what they perceive to be a predator.

Due to their sociable nature, Zanzibar red colobuses have a specific call for when an individual is alone for a certain amount of time upon which the individual feels threatened or vulnerable. Typically, those making this call (which sounds like a loud scream) are the young, but adults occasionally make a variation of this call as well when necessary.

Red colobus species have a smaller larynx compared to other members of the subfamily Colobinae. Compared to the low bass call of a male black-and-white colobus, the Zanzibar red colobus male sounds more like an alto or soprano. Visual communication is also important among all red colobus species, and it is thought that they have distinct facial features, coat color, postures, and movements for this purpose. 

Reproduction and Family

Both sexes are promiscuous, and during estrus, females may mate with multiple males. Males reach sexual maturity at about three to three-and-a-half years old, while females reach it at about two years of age.

During estrus, the female’s anogenital area will swell and redden. Just before mating, males will probe the female’s vaginal area with their fingers, followed by sniffing the area. This routine helps the male determine if the female is truly ready to breed, by detecting certain hormones. Gestation is about six months, resulting in a single offspring, though twin births have occasionally been reported. Parental care is shared between female members of a group. Weaning age ranges between one to three years. Young Zanzibar red colobuses will cling to their mother’s belly for their first six months, after which they become more locomotive on their own, but may continue to be carried by their mother for more than a year. Juveniles begin to eat exclusively adult foods at two to three years of age.

Both sexes leave their natal groups starting at around three or four years of age to breed with members of other groups. There is no defined breeding season, but most births occur during the rainy season (September–December).

Ecological Role

Being folivores and frugivores, the Zanzibar red colobus might, like other colobus monkeys, play a role in seed dispersal. No official studies have been conducted regarding this, however. Since Zanzibar red colobuses heavily rely on the resources provided by the forest habitat, they play a crucial role being an indicator of overall forest health. In addition, by feeding extensively on young leaves, the Zanzibar red colobus, like other red colobuses, largely strip trees of their young leaves. This stimulates the trees to recover by producing a new set of young leaves within a week, thereby increasing their productivity and growth rate.

Finally, the Zanzibar red colobus is a great flagship species, one whose presence and health act as an indicator for that of other species living in the same habitat.

Conservation Status and Threats

The International Union for Conservation of Nature lists the Zanzibar red colobus as Endangered (IUCN, 2018), appearing on the IUCN Red List of Threatened Species.

Zanzibar red colobuses face multiple threats to their survival, and fewer than 6,000 individuals remain. Mainly, they are threatened by habitat destruction due to logging, wood harvesting, and charcoal production. Their habitats are also destroyed to construct and expand housing, roads, railroads, and urban/recreation areas. Residential and tourism-based developments in villages such as Fumba, Nungwi, Uroa, and Kiwengwa have completely destroyed the Zanzibar red colobuses’ habitat. The construction of roads has also led to fatal motor vehicle collisions. In addition, the habitats of the Zanzibar red colobus have shifted and altered as a result of global climate change.

They are also illegally killed as retribution for raiding crops, and legitimization of forest removal for human development. Killings are done by guns, domestic dogs, and sometimes poison. The resulting carcasses are fed to dogs and sometimes consumed by humans. This is despite the traditional belief that the Zanzibar red colobus—the “poison monkey”—is unfit for consumption. As bushmeat, carcasses are also sold for $3–6 dollars (USD) each. From 2007–2013, poisoned water was routinely left out to kill Zanzibar red colobuses in the mangroves on Uzi. The use of such poison can also spell a threat to other native wildlife in the area.

The red colobus monkey genus as a whole—Piliocolobus—is the most endangered primate species on the African continent.

Conservation Efforts

The Zanzibar red colobus is listed in Appendix I 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 Zanzibar red colobus is found in various protected areas in Ungula, including Jozani-Chwaka Bay National Park, and Kiwengwa-Pongwe Forest Reserve. Even in these areas, deforestation for the use of firewood and charcoal fuel (which is less costly than electricity) persists. To ensure the survival of the Zanzibar red colobus, all remaining forest patches must be identified, protected, and integrated into a Protected Area network, like the one designed by the Wildlife Conservation Society (WCS). Along with the Protected Area network, the WCS has also worked with the Zanzibar government and 29 communities around the two protected forest areas to establish and strengthen law enforcement by training, equipping, and deploying government and community “forest guardians.” Speed bumps along roads have also reduced, but not completely eliminated, collisions with vehicles. These actions, coupled with environmental education programs and activities to protect the local forest habitat are the key to saving the Zanzibar red colobus from extinction.

Update per Instagram post on February 1, 2024: A new protected area has been established to safeguard the Endangered Zanzibar red colobus. Conservationists have worked for 7+ years on the archipelago of Zanzibar to make the Kidikotundu-Nongwe-Vundwe Reserve a reality. This protected area now protects roughly 500 individuals of this Endangered primate – representing over 10% of their entire global population.

Total population surveys, led by Re:wild Africa Director Dr Tim Davenport over a number of years, assessed the abundance and distribution of the Zanzibar Red Colobus. This allowed the conservationists to understand the need for additional protected areas and their locations. In addition to protecting primates, this reserve is home to the Critically Endangered Hawksbill Sea Turtle, Endangered Aders’ Duiker, Zanzibar Slender Mongoose, and Rufous Elephant Shrew.

Considered the most threatened group of monkeys across mainland Africa, red colobuses are in dire need of conservation action. Re:wild has worked with over 160 conservationists to develop a comprehensive Red Colobus Conservation Action Plan that addresses the most urgent needs for red colobus to ensure their survival. We are dedicated to preserving these primates and their forest habitats, helping shine a spotlight on efforts to protect them.

The creation of Kidikotundu-Nongwe-Vundwe Reserve was funded in part by @rainforesttrust, Margot Marsh, and @rewild.


Written by Sienna Weinstein, December 2023