Black and white colobus monkeys: lazy, leaf eating loudmouths of the forest

By Tara R. Harris, Ph.D.

If you haven’t noticed yet, black and white colobus monkeys (Colobus guereza, a.k.a. “guerezas;” local name: “engeya”) can be found in Uganda almost anywhere there is forest. I have been studying them in Kibale National Park since 2000, after one nearly scared me to death one night, roaring loudly at me and jumping up and down in the trees while I was in the latrine. At first glance, guerezas are strangely beautiful creatures that seemingly lead rather dull lives. As is often the case with people who possess such qualities, though, if you take the time to get to know them a little better, they turn out to be quite interesting. Guerezas are medium to large-sized monkeys - the males average about 12kg - that inhabit equatorial forest, mainly in East Africa. Unlike many other arboreal monkeys, they are most abundant on forest edges and in somewhat disturbed forest. They are one of five species in the genus Colobus, and undoubtedly the most common in Uganda.

Guerezas are visually striking animals with black bodies and flowing white capes of hair down their backs and sides, as well as long black tails with a white poof at the end that looks a bit like an artist’s paintbrush. Beauty comes at a price, however - guerezas and other black and white colobus monkeys have been hunted throughout history for their unusual skins. They have been used in numerous East African cultures as adornments for warriors and weapons: the beautiful pelts were formerly worn at the feudal courts in Mengo and Busoga. Overseas trade in guereza skins is also quite ancient, with reports from the days of Marco Polo (late 13th century) of guereza-skin capes being worn in Central Asia. Unfortunately for the monkeys, they also came into fashion in Europe in the late 1800s, as well as in the early 1970s, and it is reported that over 2 million skins were imported from Africa and made into coats. Most of these were skins of Colobus polykomos, but guereza skins were also highly prized. In addition, guereza skin rugs have often been spotted for sale in tourist shops, particularly in Kenya during the 1970s.

Despite the locally intensive hunting pressure guerezas have sometimes faced, they have managed to survive and reproduce successfully, at least in protected areas where there is a constant supply of leaves. Guerezas are one of the most folivorous monkeys, with 50-90% of their diet made up of leaves. Like other colobus monkeys, they have a large 4-chambered stomach and special bacteria to help them digest their high-fiber diet. They also feed on a number of unusual items, where they are available. Guerezas often travel long distances, for example, to feed on the bark of eucalyptus, a non-native tree that happens to be high in sodium. Low-lying ponds or swamps may also contain high-sodium plants and guerezas can sometimes be observed wading through the water to get at them. Guerezas also sometimes enter peoples’ kitchens, but unlike baboons and vervets, they are not there to steal food but to eat any leftover charcoal or ash, and to lick the concrete. These strange habits may provide them with necessary minerals, regulate their stomach pH, or help neutralize toxins. Most of the time when guerezas aren’t feeding, they are resting, digesting their meal. In fact, they are among the most inactive of all primates and typically travel only about 350m/day. Like other primates, though, they often groom one another to remove parasites and debris, as well as to reinforce social bonds.

Juveniles also play with together, wrestling and chasing one another in the trees or hopping around like rabbits after each other on the ground.

Guereza groups are small, with typically 1-3 adult males, 2-4 adult females, and their offspring. Females give birth to a single infant about once every two years, after a gestation period of close to 5.5 months. When a new infant is born, it is a big deal. At birth, they are completely white, except for a pink face, and usually all the group’s females – even little juveniles – want to hold them. Sometimes, this allows the mother to gain valuable feeding or resting time, but there are a lot of incompetent babysitters - infants sometimes get held upside down by their tails or even dropped from high in the trees. Such negligent behavior is actually a major source of infant mortality.

Crowned hawk eagles are one of the main predators guerezas face, but leopards may also prey on them where they coexist. Their primate relatives, chimpanzees, also occasionally hunt guerezas but seem to prefer red colobus monkeys instead. Guerezas are often found in small forest fragments – many of which are disappearing quickly - and there, they often fall prey to dogs.

Guerezas produce quiet grunts if they have spotted a predator which is not an immediate threat. If the predator is close, though, and has likely seen the monkeys, the adult males of the group snort at it and roar loudly, sometimes running and jumping through the treetops. Adult males produce these same roars, as intergroup communication, nearly every morning between midnight and dawn during choruses. The roaring typically starts somewhere off in the distance, and spreads like a wave throughout the forest until nearly all the males are roaring. The roars are not like those of a lion, but sound a bit like a motorcycle or like your stomach rumbling at 75 decibels. The length of a male’s roars are indicative of his fighting ability and the auditory frequencies of a male’s roars also contain information about his body size, relative to other guerezas. Guerezas’ roars (made using an unusually large larynx and air sac) however, exaggerate their body size relative to other species – a trait that may have initially functioned in intimidating predators … and still functions in intimidating new researchers and tourists.

Where guereza densities are high, like in Kibale National Park, which has one of the highest primate densities of any forest ever surveyed, groups and especially adult males fight each other frequently. When groups approach, males threaten one another by clicking their tongues and sticking out their legs, a display called “stiff legs.” If groups don’t back off, males often chase one another, sometimes all over the forest, and occasionally one falls from high in the treetops. When a winner is not easily decided and the contest drags on for hours, sometimes these lazy monkeys simply decide to take naps near one another and resume fighting when they wake up. The point of all of this aggression seems to be access to high quality food, the males securing feeding areas for their mates and offspring.

Scientists have been studying guerezas in Uganda since the 1960s. One of my current projects examines how forest fragmentation in western Uganda affects dispersal and gene flow in guerezas. My main research project, however, is located in Kibale National Park, and uses genetic, hormonal and behavioral data from eight guereza groups to examine how and why males defend food resources against other groups. In case you are wondering where the genetic and hormone data comes from – well, my field assistants and I are in the rather unfortunate business of collecting pee and poop. It’s not exactly what most young girls dream of doing when they grow up, but in the end – when the results come in - it’s rewarding.

Guerezas can be a bit shy and difficult to observe, but there are several tourist spots in Uganda where they are very used to people and even come down to the ground. Lake Nkuruba is a community-managed forest fragment/campsite with bandas that is home to three such guereza groups, as well as other monkey species and a beautiful, reportedly bilharzia-free crater lake. It is about an hour drive south of Fort Portal, close to Ndali Lodge. Sebitoli, a small tourist camp (also with bandas) located at the northern end of Kibale National Park, also has a very well-habituated group of guerezas that regularly hang out in camp. It is also easily accessible, being about a 15-minute drive from Fort Portal on the road to Kampala. You may also be able to see habituated guerezas in Queen Elizabeth National Park, at Ishasha Wilderness Camp or Jacana Lodge. Undoubtedly, there are other places as well, so keep a look out for them – or listen for them – whenever you are near the forest.