UDZUNGWA RED COLOBUS
Geographic Distribution and Habitat
As the name suggests, the Udzungwa red colobus is found exclusively in the Udzungwa Mountains in central Tanzania, a country in eastern Africa. Other common names for this species include Uzungwa red colobus and Irinea red colobus. This monkey is just one of many species endemic to the isolated mountain range, which is covered by a rich tropical rainforest, rivers, and bordering grasslands.
Size, Weight, and Lifespan
The average Udzungwa red colobus is about 24 inches (61 cm) tall and weighs about 24 pounds (11 kg). Their tail lengths generally match the individual’s height. Males are slightly larger than females.
The lifespan of the Udzungwa red colobus is unknown. Their closest relatives have lifespans ranging between 20 and 30 years old.
The most distinct feature of the Udzungwa red colobus is the red cap on their heads. The auburn tuft of hair provides a stark contrast to the rest of the monkey’s body, which is often white on the ventral side (belly) and black on the dorsal side (back). Their faces are covered by mostly black skin and patches of pink scattered on the muzzle.
All colobus monkeys lack true thumbs. There is only a small nub where their thumb would be. In fact, the name colobus comes from the Greek word meaning “cut short” or “maimed,” in reference to their lack of a thumb. However, colobus monkeys make up for this with their four hook-like fingers. This hand structure actually makes it easier for the colobus to leap from branch to branch in quick succession.
Their long tails are non-prehensile and are used primarily to maintain balance when walking across branches.
Leaves are the most important part of the Udzungwa red colobus’s diet. Studies show that leaves make up anywhere between 70% and 90% of their diet. Their remaining diet is filled out by fruits and flowers. Many of the plants red colobuses eat are highly toxic containing chemicals such as cyanide, but these monkeys have physically adapted to eating these toxins by developing larger salivary glands and a larger, multi-chambered “sacculated” stomach. Mothers have also been observed teaching their offspring to eat soil, which helps neutralize the toxins.
Behavior and Lifestyle
Colobus monkeys are said to be the most arboreal (tree-dwelling) of all African primates, only leaving the comfort of the trees when it is absolutely necessary. Like most primates, they are diurnal.
Red colobus monkeys are often suspicious of newcomers. Before joining a new group, a lone monkey may spend several months following and spying on the target group to see if they will accept him.
Udzungwa red colobus monkeys live in groups of 20 to 40 individuals. Some groups number as high as 81 while other monkeys wander alone. The monkey troop wakes around sunrise and forages during the early morning. They rest for most of the day and spend much of their downtime grooming each other and building social bonds. They forage again in the evening before retiring for the night. Red colobuses often sleep in the same trees where they were feeding that day, preferring to stay in the tallest trees they can find.
Male red colobuses tend to stay in their natal group for life and develop strong social bonds with one another. They will only usually leave to form a group of their own. Females in the main group often form smaller associations and will move from group to group several times in their lives.
All red colobus species are fiercely territorial and they often engage in violent battles with neighboring troops. Most of this fighting is left to the males, who also fight within their own troop to rise up the dominance hierarchy. When a predator is nearby, the males will gather together to defend the group while the females, infants, and juveniles escape to safety.
Udzungwa red colobuses make several vocalizations, but researchers have not yet deciphered their meanings. When these colobuses see a human, adults and juveniles make a “chist” call. Other calls include barks, yelps, squeals, shrieks, and quavers.
Mating for red colobus monkeys occurs year-round and is most frequent between March and June. Males compete with each other for mating opportunities, but no male holds exclusive mating rights. When a female enters estrus and is sexually receptive for mating, her anogenital region swells up. After mating, the female has a pregnancy that lasts about six months.
Because females move between groups several times in their life, most females in a group are unrelated to each other. Scientists speculate that this is why red colobus mothers do not generally practice allomothering, where all females work together to raise their offspring. Instead, mothers are highly protective of their young from all males and females in the group. On average, females give birth to a new offspring every three years.
Females reach sexual maturity at two years of age. At that point, they may go off on their own to find a new group, or they may stay close to their mother and aunts and leave only when they do. Males reach sexual maturity some time between 3 and 4 years old.
The Udzungwa red colobus is sympatric with several species of primates and has often been seen forming short-term groups with other species. These monkeys have formed friendly relationships with yellow baboons, Sanje mangabeys, and Angola colobuses. Such inter-specific associations provide extra protections against predators.
Many red colobus monkeys are being seriously threatened by rising hunting rates from chimpanzees ;however, the isolated Udzungwa red colobus lives well outside the chimpanzee’s current range.
The International Union for Conservation of Nature rates the Udzungwa red colobus as Vulnerable (IUCN, 2016), stating that the biggest threat to the species is habitat destruction, which has severely fragmented the population. Habitats are destroyed for the sake of logging, charcoal production, and agriculture. It is unlikely that these activities will slow down in Tanzania, which has the world’s 11th fastest growing population and 18th fastest growing economy.
Over 90% of the Udzungwa red colobus’s population lives on legally protected lands. A majority live in Udzungwa Mountains National Park, which is well protected; however, the remaining individuals live in forests that are either not protected or their protections are not well-enforced. Conservation groups are looking to expand the park to cover adjacent forests that are poorly protected. Another strategy attempts to tackle forest fragmentation by planting and establishing forest corridors to connect isolated patches of forest. This not only requires the planting of new trees but also prevention of bush fires, which often prevent forests from recovering.
- Marshall, Andrew. Piliocolobus gordonorum. © All the World’s Primates. N Rowe, M Myers, eds. (alltheworldsprimates.org).
- Cardini, A., Elton S. The radiation of red colobus monkeys (Primates, Colobinae): morphological evolution in a clade of endangered African primates. Zoological Journal of the Linnean Society, Volume 157, Issue 1, September 2009, Pages 197–224.
Written by Eric Starr, September 2019