Zanzibar red colobuses belong to the Old World monkey family. They have dark red to black fur, accented with a black stripe along the shoulders and arms, and a pale underside. Their black face is crowned with long, white hair, and features a distinguishing pink mark on lips and nose. Zanzibar red colobuses have a long tail used only for balancing - it is not prehensile.
Zanzibar red colobuses are native to Unguja, the main island of the Zanzibar Archipelago, off the coast of Tanzania. They prefer drier areas over wet ones and inhabit coastal thickets and coastal rag scrub. They can also be found in agricultural areas and in mangrove swamps.
Zanzibar red colobuses are arboreal and social animals. They live in groups that consist of up to 4 adult males and many adult females with their young. The number of monkeys in a group can range from 30 to 50 individuals. These colobuses like to spend their time playing and grooming during the rest periods between meals. Unlike females, in a group, males actually maintain close bonds, acting together in defense of their group and even in grooming each other. Feeding is also a group activity. They begin foraging in the morning, and are more active during the cooler parts of the day. Loud calls from males indicate the group is ready to move to another tree to feed. When threatened Zanzibar red colobuses produce "bark", "chist", or "wheet". These are distress and warning calls. The call heard most often is the 'alerting signal'. This is an attention-getting call. Because Zanzibar red colobuses are extremely social, they have a specific call for when they are alone for a long time upon and feel vulnerable or threatened. The young are typically the ones who make such a call that sounds like a loud scream.
Zanzibar red colobuses are polygynandrous (promiscuous). This means that both females and males have multiple partners during the breeding season. Females give birth to 1 or 2 babies every two years mainly in September-December. The gestation period is about 6 months. Infants are born naked with their eyes closed and are nursed until two years of age. They are carried by their mother, clinging to her belly for 6 months. After that, infants can locomote independently but still may be carried by the mother for more than a year. The young are almost independent at around 24-36 months of age and become fully independent when leaving the natal group, at around 37-52 months of age. Females reach reproductive maturity when they are 4 to 5 years old and males usually become mature at 5 years of age.
The loss of the habitat and hunting for meat and pet market are main threats to Zanzibar red colobuses. Deforestation because of charcoal production, timber felling, clearance for cultivation, and bush-burning is the biggest threat at this time. On Uzi and Vundwe Islands, these animals are in decline due to habitat destruction, particularly with coral rag forests. They also suffer from poisoning, netting, and disappearance of monkeys.
According to the IUCN Red List, the total population size of Zanzibar red colobus is less than 2,000 individuals. This species’ numbers are decreasing and it is currently classified as Endangered (EN) on the IUCN Red List.
Due to their diet, Zanzibar red colobuses play an important role as seed dispersers of plants that they consume.