TANA RIVER RED COLOBUS
Geographic Distribution and Habitat
The Tana River red colobus (Piliocolobus rufomitratus) is a species of red colobus monkey endemic to the evergreen forests growing along the lower Tana River and Tana River Delta in Kenya.
This region’s more arid climate supports significantly less biodiversity of plants and trees than the wet rainforests of East and Central Africa that all other red colobus species call home. Less rain means fewer trees, making the forests and their canopies along the Tana River more sparse. Their differing habitat has sent the Tana River red colobus down a unique evolutionary path from all other species.
With less rainfall, the lives of Tana River red colobuses are tied to the river for which they are named, and they are highly susceptible to its degradation and destruction. As of 2019, this species has one of the smallest ranges of any primate in the world. Its available habitat currently stretches less than 40 miles (a mere 60 km) along the lower portion of the Tana River and into the upper delta. Small, isolated bands of Tana River red colobuses are known to occupy a total of 34 riverine and flood-plain forests between the town of Kipende in the north and Mitipani in the south. It may also be possible, though unlikely, that even smaller, more isolated populations subsist further south within the lower delta’s heavily degraded forest patches.
Size, Weight, and Lifespan
Tana River red colobuses are medium-sized monkeys weighing, on average, around 20 pounds (9 kg). From head to tail, they measure around 1.6 feet (50 cm). Their long tails add another two feet to their overall length.
The lifespan of red colobus monkeys in the wild is not well researched, being that most field studies are short. In captivity, other colobine monkeys rarely live past 30 years. It can be assumed that this is significantly shorter in the wild.
There are 18 species of red colobus monkeys currently known to science. All of them are somewhat similar in appearance. Though their colorations are also quite similar, each has its own striking patterning that, to the trained eye, makes it easily distinguishable from the rest.
Tana River red colobuses sport gray fur coats, darker on their backs than their chests. This gray patterning continues down the length of their tails. On their feet, hands, and face their fur gives way to dark gray skin. Tufts of gray fur frame their rounded faces. Their rounded, inset eyes look especially dark. The identifying red for which they are named sits like a blob of paint on the top of their heads.
Tana River red colobuses are specially adapted to process a diet rich in leaves. High cusped ridge molars grind the leafy fibers down, breaking down cell walls to ensure more nutrients are absorbed during digestion. Fibrous plant materials are no match for their large four-chambered stomachs. Special bacteria live in their forestomachs, where the contents of their meal is fermented.
Young leaves, which tend to be higher in protein—not to mention easier to digest—are preferable to mature ones. Groups of Tana River red colobuses have shown particular liking for three species of plants’ leaves: Ficus syocmorus, Sorindeia obtusifolioata, and Acacia robusta. Surprisingly, they are rarely seen eating the leaves of the most common tree in their habitat, Diopyros mespiliformis. This might be because the leaves of this species are toxic to them.
When young leaves are not available, mature ones will do. Additionally, Tana River red colobuses occasionally eat fruits and certain types of flowers.
Behavior and Lifestyle
Tana River red colobuses spend all their time in the trees, only venturing to the ground when they need to reach another patch of forest. As such, they are dextrous climbers and acrobatic leapers. Their long tails give them exceptional balance as they navigate the canopy on all-fours in search of food. Though diurnal, they take long rests during the day, lounging in the branches after meals to digest their leafy bounty. Long rests give these social animals tons of time to interact. Adults might take turns grooming each other while the little ones in the group play.
Young red colobus monkeys spend a significant amount of their time playing. They chase, wrestle, and generally just enjoy clambering and leaping about the canopy for no ostensible reason. These activities are important practice for real life scenarios they may experience as adults: fleeing predators, defending themselves, or just navigating the canopy.
Researchers theorize that red colobuses’ significantly playful natures may be an evolutionary consequence of their diet. Having to rest for such long periods while they digest their fibrous meals affords them, and other folivorous species, tons of free time during which rigorous play routines can develop. Play prepares its participants for the dangers of living in an unpredictable world—so, the more the better.
Though play behaviors have not been studied in Tana River red colobus groups, it is likely that their lifestyles are not so different from their relatives in other habitats. In fact, this species tends to rest for even longer periods than any other. Does their overall playtime increase along with it? Researchers may one day know the answer!
Red colobus monkeys are social and gregarious, with some species living in large groups of 30–50 members. Their groups are composed of multiple males and multiple females, with generally a single male playing a more dominant role.
Tana River red colobuses, however, are the only red colobus species to not live in lush, wet rainforests where the resources to support such large groups are more likely to be available. For this reason, their own groups tend to be smaller, ranging from 12–30 members. Unfortunately, this statistic is shrinking as the overall population plunges toward extinction.
Tana River red colobus groups do not function according to the strict dominance hierarchies observed in their rainforest relatives. Instead, their smaller-sized groups have only a single male—or occasionally a small exclusive group of males—who drive other males from their territory. Though not thoroughly studied, some researchers hypothesize that this behavior better serves a species living in a habitat where protecting one’s access to mates and resources has important implications for one’s survival and passing on one’s genes.
Living in such a unique habitat also influences the the daily routines of Tana River red colobuses. Leaf-eating monkeys are well-known for spending a large portion of their days resting. Rainforest varieties of red colobus, like Preuss’s red colobuses and ashy red colobuses, spend a whopping 1/3 at rest in the canopy, allowing their fibrous meals time to digest. By contrast, Tana River red colobuses rest for half the day! The remaining half is largely given to munching down the meals that take so long to properly digest. Less than 10% of their day is spent traveling to find food. Grooming, play, and other forms of socializing make up the remaining 10% of their daily activities.
A group of Tana River red colobuses wakes in the early hours of the morning and begins feeding. Stomachs filled with leaves, they rest. A few hours later, the group slowly begins to rouse. A few adults groom each other; infants and juveniles scamper about, playing alone or with their mates. By the late afternoon, the pangs of hunger revive. The group may choose to stay where they are or collectively travel to another spot—perhaps a tastier patch of foliage. Satisfied once more, they settled down again for the evening. As the daylight wanes, they find comfortable spots in the canopy to sleep for the night.
As social creatures, primate species have evolved to develop unique ways to communicate with each other. The most conspicuous signals primates use to communicate are vocalizations. Tana River red colobuses are known to make loud barks, possibly to warn each other of approaching threats. Females make copulation calls when they are ready to mate, attracting the dominant male to her location. Though they most certainly make other sorts of sounds, their potential meanings have yet to be explored by researchers.
Somatic gestures, such as facial expressions, hand signals, and other forms of body language, have also been observed in Tana River red colobuses. Long controlled stares, slaps, and grimaces are used by males during agonistic encounters. In a particularly heated argument, a male may try to intimidate his adversary by lunging or shaking branchings at him. In general, these signals are used to encourage his adversary to vacate the area, thereby avoiding physically violent altercations.
While the communication methods of Tana River red colobuses are not well-studied at this time, everything about their lifestyle suggests that they use a variety of complex signals to share important information about the world around them and about their emotional inner states. The importance of play in red colobus species development possibly suggests that they spend a great time learning a vast repertoire of vocalizations, body postures, facial gestures, and hand signals that eagerly awaits thorough study.
Tana River red colobuses are the only species of red colobus, out of 18, who do not live in wet rainforest.
Living in an arid climate makes Tana River red colobuses survival tied directly to the healthy and well-being of the Tana River and, indirectly, the entire Tana River Basin.
Tana River red colobuses are the only species of red colobus living outside the range of chimpanzees and are, therefore, not hunted by them.
Tana River red colobus groups often comprise several females and a single male with whom they exclusively mate. The lone male asserts his dominance over the group by warding off all other potential rivals. Such a polygynous mating system is different from that of the rainforest varieties of red colobuses found in central and eastern Africa living in larger groups with multiple males whose abilities to mate are determined by a dominance hierarchy.
A female initiates copulation by making specialized calls that attract the dominant male to her location. A swelling near her anus marks that she is currently ovulating—ready to mate. In other red colobus species, the couple is often harassed by rival males during the mating process. But this behavior has never been observed in Tana River red colobuses, most likely due to there being only one male per group.
Following copulation, a red colobus female experiences a gestation period lasting 4.5 to 5.5 months. She gives birth to a single infant. Infants are born with silky black and gray coats, and the exposed skin on their faces, ears, hands, and feet is pink. They are born without the signature red crown of Tana River red colobuses. This feature doesn’t begin to develop for a least two months after their births. Around the same period, the fur on their torsos begins to lighten as well and their skin darkens.
At first, infants are completely reliant on their mother, clinging to her fur at all times. Sometime between two and four months of age, they begin getting a bit of distance but never venture more than a few feet (about a meter) away from her. Within a month or two, they start playing on their own and with other monkeys. As they develop their skills through play, they become more and more independent.
At 18 months of age, a female has matured and leaves her natal group to join another. Depending on her situation, she may emigrate to new groups regularly and throughout her entire life, bearing offspring for multiple males along the way. The fluid nature of female group membership keeps females from bonding deeply. Mothers are the sole caretakers, nursing, carrying, and generally looking out for their own offspring.
The dominant male provides little more than protection to his progeny, both from predators as well as from rival males outside the group who would seek to supplant him. Like females, fully grown males also leave their natal groups, but a male cannot simply join a new group. Instead, he must vie for dominance over an already established group by intimidating, or sometimes killing, its current dominant male. If he is successful, he kills the infants of his former rival thereby ensuring that his new harem of females re-enter their estrus cycle sooner. It also means he won’t expend his precious time and energy caring for offspring that do not carry his own genes.
Endemic to the riverine and floodplain forests of Kenya along the Tana River, Tana River red colobuses primarily eat leaves, influencing overall foliage coverage in this arid region. As merely occasional fruit eaters, they likely do not play a significant role in seed dispersal. However, the relationships these monkeys have formed with their environment are not well-researched at this time.
Tana River red colobuses have few natural predators. Interestingly, as they are the only members of this genus to live outside the rainforests of central and eastern Africa, their range does not overlap with that of chimpanzees. This makes them the only red colobus species not regularly hunted by these great apes. The ways that this influences their lives are not well understood at this time.
Red colobuses are generally seen as an indicator species. This means that their abundance, or lack of abundance, indicates the overall health of the ecosystems in which they live. They tend to be vulnerable to even slight ecological changes, and they are usually one of the first species to disappear in highly disturbed habitats.
As the only species of red colobus not living in a rainforest, Tana River red colobus represent a unique opportunity to learn more about the genus, Piliocolobus. By comparing and contrasting their lifestyles and habits with that of their rainforest relatives, researchers may begin to understand the roles each red colobus species plays in its particular ecosystem with more nuance than if only those rainforest species existed. Unfortunately, as time is running out for Tana River red colobuses in the wild, such research will hopefully come sooner rather than later.
The Tana River red colobus is classified as Critically Endangered by the International Union for Conservation of Nature (IUCN, 2019), appearing on the IUCN Red List of Threatened Species. As one of the 25 most endangered primates in the world, this species faces a multitude of threats, all while it teeters on the edge of extinction.
Tana River red colobuses are confined to a small range of riverine and flood-plain forests along the Tana River. Here, the usual anthropogenic projects, such as local agriculture and timber processing, which countless primates face all over the world, regularly contribute to the loss of their habitat.
At this point, the declining wild populations of Tana River red colobuses mete out their existence within a handful of fragmented forest patches throughout the river basin. These patches are not only heavily degraded, their isolation is likely to create genetic bottlenecks for the species. When groups of a species can not easily access each other, gene flow slows to a halt. Under these conditions, inbreeding becomes likely. Lack of genetic diversity makes each succeeding generation prone to diseases and morphological deformities, and vulnerable to parasites. Offspring, therefore, become less and less viable over time.
In such an arid region, regular access to the river is essential to Tana River red colobuses’ survival. This relationship introduces a host of other, unique threats posed by projects relating to humans’ water consumption in the region. Countless dams and irrigation projects upstream, and locally within their range, re-direct water away from delta’s floodplains. The growing number of such projects jeopardizes the entire Tana River ecoregion and, with it, the dwindling population of Tana River red colobuses who still call it home.
Though Tana River red colobuses only live along the lower portion of Kenya’s longest river, their survival is tied to the health of the region’s entire water table. This means threats that directly affect habitats upstream, even though they are outside the red colobuses’ physical range, indirectly affect them as well. Unfortunately, once damage to these ecosystems is done, it cannot be undone—and evidence suggests that the Tana River is likely be drastically affected by the effects of climate change in the coming years.
Tana River red colobuses survival as a species is also linked to the survival of other species living within their range as well as upstream. Elephants once roamed the Tana River Basin freely and widely. Now, following years of uncontrolled poaching and habitat destruction, the elephants’ numbers are dwindling. The migration routes long established by the elephants have also been destroyed, meaning that the few remaining herds now trample the remaining forest fragments during their long migrations, further degrading the habitats that Tana River red colobuses call home.
As they play crucial roles in their ecosystems as seed dispersers, elephants are often called the “Gardeners of the Forest.” Seeds from the food they eat are expelled in their dung, far from the tree that bore the fruit. In a well-established ecosystem, this way of propagating species far and wide keeps the ecosystem healthy and biologically diverse. But in a habitat already ravaged by other factors, like that of the Tana River red colobus, this process takes too long and cannot keep up with the damage inflicted by human activities. Plants, especially trees, play crucial roles in how water moves through an ecosystem. This means that Tana River red colobuses are even linked to the elephant herds living outside their range but further upstream.
A number of smaller issues further compound the already dire situation of Tana River red colobuses. Wildfires are not uncommon occurrence in the area. The invasion of new plant species, spurred by the disruptions to the water table, further upsets the already unbalanced ecosystem. Though Tana River red colobuses are not known to raid crops, some farmers may kill them anyway—just to be safe. Civil unrest in the area is also a factor that effects wildlife in this region. Protecting wildlife may often seem frivolous to local peoples struggling through poverty and political upheaval, making it more difficult to rally them behind conservation causes.
Lack of research also threatens the Tana River red colobus, not for this species alone but for all 18 members of the Piliocolobus genus. As the only red colobus species not living in a rainforest, the very existence of Tana River red colobuses offers a unique opportunity for researchers to compare and contrast such closely related species in order to find out how different ecosystems have effected their development and evolution.
Tana River red colobuses live in very few protected areas. The only significant conservation area where they are found, dubbed the Tana River Primate National Reserve, was established specifically to protect this species. Unfortunately, it has a history of being poorly managed. Illegal clearing of forests and the settlement of humans within in the reserve largely goes unpunished. The establishment of the reserve was also called into question in 2007 by the High Court of Kenya, which argued it had not been created with adequate feedback from local peoples. Though the Wildlife Act of 2013 states that changes to the reserve’s boundaries can only be published by the Cabinet Secretary and approved by Parliament, the High Court’s decision has obscured the reserve’s official status. So long the gazettement of the reserve remains unclear, it only further complicates the enormous task conservationists have before them to save the Tana River red colobus from extinction.
Tana River red colobus populations have been in steady decline now for decades, and this species has maintained a spot on Primate in Peril’s biennial list of the 25 most endangered primate species in the world since 2002. Today, less than 1,000 are estimated to exist in the wild, and their numbers continue to decline along with their available habitat.
Legally, this species has been given multiple protections, both national and international. It is listed on the Convention on International Trade in Endangered Species (CITES) Appendix I and as a Class B species of the African Convention on the Conservation of Nature and Natural Resources. Unfortunately, the protections these afford Tana River red colobuses and their habitats are inconsistently enforced.
This pattern is seen with the general mismanagement of the Tana River Primate National Reserve. While the reserve technically still exists, local communities continue to clear its forests in order to build their farms and settlements with little or no repercussions. This pattern was only worsened following the High Court of Kenya’s decision to degazette the reserve, obscuring the area’s very right to these protections. If, in the end, the reserve loses its protections, researchers estimate that the current population of Tana River red colobuses will likely decline by at least 80% by 2050.
The Tana River Delta was deemed a Ramsar site in 2012 but is otherwise completely unprotected. Like the Tana River Primate National Reserve, the protections the delta’s Ramsar status affords it have done little to stop locals from continuing to settle there. While no colobuses are actually known to live within the delta at this time, the survival of the species is tied to the entire Tana River watershed. The well-being of one region affects all others.
Civil unrest in the region often makes conservation seem frivolous to local peoples who feel they are already struggling just to keep themselves alive and out of harm’s way. Persuading people in dire straits to care about wildlife and ecosystems is an ongoing challenge for conservationists, especially when such unrest makes it difficult to sustain any meaningful, long-term conservation projects in a region. Unfortunately, it is a problem conservationists will have to solve if the Tana River red colobus is to survive.
One way to encourage community support may be to tie the region’s economy to conservation by creating jobs through ecotourism and opening new parks that need people to manage and maintain them. When people are able to take active roles in conservation that simultaneously enhance their own livelihoods, they are more likely to feel connected to, and willing to protect, ecosystems they may have once destroyed.
For now, the future of the Tana River red colobus looks bleak, but hope has not dissipated completely yet. Recently, various plans to develop the Tana River Basin have been abandoned by commercial enterprises. Furthermore, the Kenyan government has begun to support new community-led efforts to conserve the ecoregion. One such project, Ndera Community Conservancy, is already under way. Another, the Nwango Community Conservancy, is in the process of being established. Projects like these are hopefully the beginning of a new era for the region that, in turn, is renewed hope for Tana River red colobuses.
Written by Zachery Lussier, August 2021