ZANZIBAR RED COLOBUS
Geographic Distribution and Habitat
Red colobuses are Old World monkeys that are indigenous to Unguja—the main island of the Zanzibar Archipelago, off the coast of Tanzania—as well as the islands of Uzi and Vundwe. The species has been extirpated from Bambi, Jendele, Kichwele, and Nungwi forests in the last 35 years. They may have once lived on the African mainland, but are now restricted to the islands of the Zanzibar Archipelago.
Habitats for this predominantly arboreal species include coastal thickets or bushes, coral-rag scrubs, mangrove swamps, farmlands, and secondary forests.
Size, Weight, and Lifespan
Average head-to-body length range for both sexes is between 17.7 and 25.5 in (45-65 cm), with average tail length ranging from 1.9-2.5 ft (58–77 cm). Both males and females weigh between 11.5 and 24.9 lbs (5.2–11.3 kg).
Sexual dimorphism—or the differences in body shape or size between the two genders—is more pronounced in their cranial sizes and canine length. Adult males have stronger skulls and longer canines, and their tails are generally thicker than their female counterparts.
While scientists have been able to determine the lifespan of other colobus, the average lifespan of a Zanzibar red colobus is unknown, mainly because they have not ever successfully been held in captivity.
These medium-sized monkeys have little potbellies, as is typical of leaf-eating monkeys. Their pelage (or coat) ranges in color from dark red to black and is sometimes accented with a black stripe on the shoulders and arms. The middle and lower back coloring varies from red-brown to orange. They have black hands, feet, and faces, topped with long white hair. Their lips and noses are a pinkish hue. The ventrum, or underbelly region, is white to a light-greyish hue.
Infants have black and white coats only, with the introduction of red and brown pigments appearing around 3 to 5 months of age. Full adult coloration isn’t achieved until the 6-to-11-month age range.
All species of the colobus monkeys have a stumped thumb, as well as long tails, which are used for balance and posture purposes.
Their notably long hind limbs help facilitate large leaps between trees, as do their long digits, or fingers, that form a hook-like grip, allowing them to grasp branches with ease.
What Does It Mean?
A finger (including the thumb) or toe.
To root out and destroy completely. Biologists use the term “extirpated” to describe species that no longer exist in a specific region.
The fur, hair, or wool of a mammal.
Distinct difference in size or appearance between the sexes of an animal in addition to difference between the reproductive organs themselves.
The stomach or belly area, the outside lower surface of the torso.
Visit the Glossary for more definitions
Like all colobus monkeys, the Zanzibar red colobus is considered to be a folivore, or an herbivore that specializes in eating leaves. Younger leaves are preferred and account for 60% of their daily diet, with unripe fruit and seeds comprising 10-31% of their diet. Fruit is consumed un-ripened, due to their inability to digest the sugars formed during the fruit’s aging process. The rest of their diet consists of flowers, flower buds, soil, bark, and petioles, or stalks that connect plants leaves to stems.
Since their leaf-heavy diet provides little nutritional value and has high levels of difficult-to-digest cellulose, they had to evolve to adapt by developing long digestive tracts and a slow metabolism. They also sometimes consume charcoal to rid their digestive tracts of toxins found in leaves—a behavior thought to be learned and passed on from mothers to their offspring. Sources of charcoal include logs, branches, and charred tree stumps. Charcoal is believed to combat the toxins found in leaves by absorbing organic materials that can potentially be toxic.
Because of their slow digestive tracts, they are the most sluggish of all colobus monkey types.
Behavior and Lifestyle
Zanzibar red colobus monkeys are diurnal and arboreal, which means they are most active during daylight hours and spend most of their time in the trees. Their lightweight bodies allow them to leap around the canopy. They tend to have long periods of inactivity, which could be a result of the buildup of methane and carbon dioxide gases stemming from their diets. Burping in each other’s faces is common behavior during play.
Feeding is a group activity that begins in the early morning hours. Individuals have been observed using different strategies to drink water, including drinking from tree-holes and licking dew or licking rain off of leaves, as well as from crevices in coral rock formations. This behavior is learned among troops with limited resources that are movement-restricted due to forest and species fragmentation.
Daily Life and Group Dynamics
Zanzibar red colobus troops are typically comprised of four adult males and several adult females, and can range anywhere from 30 to 50 individuals.
They are highly social and often play or groom between meals. Males in a group tend to have closer bonds among each other compared to females in the same group.
The Zanzibar red colobus, often referred to as Kirk’s red colobus, is named after Sir John Kirk, the British Resident to Zanzibar who first identified these creatures.
The word “colobus” means “he cut short” in Greek, and refers to the significantly small, or complete lack of an opposable thumb in comparison to other primates.
Locals refer to them as “kima punju,” which means “poison monkey” in Swahili, because of their distinct and pungent smell.
Predominant communication tactics involve different types of vocalizations. These primary vocalizations are used to indicate distress, warnings, and threats, and include “barks,” “chists,” and “wheets.” Since they have a smaller larynx than other colobuses, the males’ sound is closer to an alto or soprano.
Long calls consisting of yelps and shrill squeals are given out to express dominance and sexual interest in females. Locals have also noted that they become quiet when gloomy weather is approaching.
Because they are highly social creatures, they have a distinct call to indicate when they are alone for extended periods of time, and begin to feel threatened.
Reproduction and Family
Both sexes are considered promiscuous and females copulate with multiple males when in estrous. Often, a copulating couple will be harassed by other members in a group. Methods of harassment include grabbing, twisting the males head, or slapping and climbing on the male, and can be seen as a form of competition.
Both sexes leave their natal groups to engage in sexual activity with members of different groups. This period usually begins during the age of 3 to 4 years, with full sexual maturity being reached at the age of 5.
While there is typically no defined breeding season, most births occur during the wet season, and usually result in a single offspring. An occasional twin birth has been reported. The average gestation period lasts between 5 to 6 months.
Since they rely heavily on resources provided by their forest habitats, they continue to be a good indication of the health of the forest. Being one of the main folivores and frugivores in the region, they may also help to disperse seeds throughout the forest.
Conservation Status and Threats
The Zanzibar red colobus is classified as Endangered by the International Union for Conservation of Nature (IUCN, 2018) Red List.
A 2017 census conducted by the Wildlife Conservation Society (WCS) Tanzania Program reveals that just under 6,000 individuals remain in varying group sizes throughout their habitat. A good portion of these populations live outside of protected zones, which increases endangerment to these groups.
Zanzibar red colobuses are mainly threatened by habitat destruction due to timber cutting, bush burning, charcoal production, and human development. Hunting of primates, including Zanzibar red colobus monkeys, for consumption by humans and dogs, and in retribution for crop damage is widespread across Zanzibar. Tourism and residential developments have destroyed their habitat in parts of their geographic range. Over the past 35 years, the species has become locally extinct in several regions of Zanzibar.
Since the eradication of the Zanzibar leopard, humans have been their main predator. They have few non-human predators, which include chimpanzees and crowned eagles.
These creatures are listed as “Class A” by the African Convention. Tanzanian laws also protect them under the Forest Resource Management and Conservation Act of 1996.
The Tanzania Forest Conservation Group (TFCG) is implementing environmental education programs and activities to help make people aware of the need to protect the local forests.
Speed bumps installed at the Jozani Chwaka Bay National Park have also helped reduce the number of road kill related deaths.
Many thanks to Tim Davenport, Country Director for the Wildlife Conservation Society (WCS) Tanzania Program, for providing the most current census information for the Zanzibar red colobus monkey. We are grateful.
- Tim Davenport, Country Director for the Wildlife Conservation Society (WCS) Tanzania Program
Written by Nina Shangari, May 2018