FOA’S RED COLOBUS
Geographic Distribution and Habitat
The Foa’s red colobus (Piliocolobus foai), also known as the Central African red colobus monkey, is endemic to the Democratic Republic of Congo. They prefer rain and mountainous forest habitats and can be found at altitudes ranging from 2,953 to 9,186 feet (900–2,800 m) above sea level. Historically, their range started from Kahuzi-Biega National Park, which lies adjacent to Rwanda, and stretched to Kabobo National Reserve, adjacent to Lake Tanganyika. However, in the present day, they are known to occur only in two separate locations: Kabobo Massif Protected Area Complex, which comprises Kabobo and Ngandja National Reserve complex, and, to its north, the Itombwe Nature Reserve.
Foa’s red colobuses belong to the genus Piliocolobus and family Cercopithecidae. In some reports, the red colobus is placed under the genus Procolobus; however, the International Union for Conservation of Nature (IUCN) places them under the Piliocolobus genus. Piliocolobus includes all other red colobus monkeys, distributed across central Africa in patches from Senegal in West Africa to Zanzibar in the East. While the taxonomy of red colobus monkeys is debated and there is no current consensus on the number of species, the most recent study suggests that Piliocolobus consists of 17 full species (1 sub-species) of red colobus, including the Foa’s red colobus. Lack of consensus on how many species should be recognized and difficulty to access some war-torn habitats has made research on Foa’s red colobus difficult, and limited records for them exist. However, reports for the other red colobus species provide some insights into their behavior and lifestyle.
Size, Weight, and Lifespan
On average, male Foa’s red colobus monkeys can weigh between 20 and 29 pounds (9–13 kg) and females can weigh between 15 and 20 pounds (7–9 kg). Their head-to-body length ranges between 6 and 9 inches (15.5–24.0 cm), and their tail length is between 8 and 12 inches (20.5–30.0 cm).
Although some reports suggest that these monkeys live up to 12 years in captivity, individuals typically live up to 8 years in the wild.
Troops of monkeys belonging to different species.
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Foa’s red colobuses are characterized by a red crown framing a face with black-gray features. Their back is black with a whitish chest. The arms and legs are red-brown and resemble a shirt with red sleeves and red pants. After birth, red colobus babies are black-grayish and lack red or brown colors, making them very distinct from the older monkeys. They develop their red coloration as they grow older. The nonprehensile tail is very long and is used for balance while climbing and helps determine the trajectory of their leaps. The hind feet are also very long, approximately 1/3 of the length of the entire hindlimb, and facilitate leaps between the trees.
Red colobuses are primarily folivorous, with a preference for young leaves. In times of food scarcity, they can switch to eating lower-quality mature leaves. This selection makes sense since young leaves contain significantly less cellulose material, making them easier to digest, and contain higher levels of digestible carbohydrates and other nutrients. Depending on availability, fruits, seeds, or flowers may also be a part of the menu. Red colobuses have a large and specialized digestive system to support their largely leaf-based diet, including a four-chambered sacculated stomach with bacteria in the forestomach that allows them to digest cellulose, thus permitting the efficient digestion of large quantities of leaves and seeds. Most of their water intake is derived from the leaves they consume.
Behavior and Lifestyle
Due to limited research, little to no detailed behavioral data are available for Foa’s red colobuses. However, records for other red colobus species may provide some insights. Arboreal in nature, they tend to spend most of their time in the upper and middle forest canopy, although they may occasionally descend to the ground to cross forest gaps or feed. Red colobuses most commonly use quadrupedal walking (on all fours) (53%), leaping (17.8%), and climbing (17%) during locomotion. Red colobuses are notorious for their lethargic lifestyles and spend up to 47% of their time resting followed by feeding.
The gender of juvenile males is deliberately obscured by the presence of a unique bright red and swollen genitalia “perineal organ,” which mimics that of adult females during estrous.
Due to lack of bonding between females, allomothering is rarely tolerated and females do not let other females handle their infants.
Red colobuses live in large social groups that may typically include between 25 and 40 individuals. Groups usually contain 3–4 adult males and many adult females outnumbering males. An exception to this is when red colobuses co-occur with chimpanzees; ratios of adult males to females tend to be much higher than at sites where chimpanzees are absent, which may have to do with predator protection since chimpanzees prey on red colobus monkeys. Within the groups, males are more permanent members than females, who tend to transfer memberships between groups. As a result, female members of a group are not closely related and do not form bonds with other females.
Males often participate in aggressive interactions with the males of other groups but within their own group, adult males often groom each other. This may be because males in a particular group spend much of their lives with the same fellow male compatriots, and therefore form tight bonds leading to mutual or allogrooming of other males. Allogrooming behavior between females is rarely observed. Some individuals also exhibit food-based feeding competition, wherein individuals compete with other groups by depleting resources such as leaves before others can encounter them.
When under threat by predators, such as chimpanzees, red colobuses engage in long bouts of alarm calling, and males group together to counterattack the chimpanzee hunters that approach the group. The greater the number of red colobus males that counterattack, the less likely a chimpanzee hunt is successful. If the canopy is dense, the males will not attack. Instead, they will retreat quietly along with the other group members to avoid detection. Some red colobus species form strong polyspecific associations with other species such as guenons and follow their range patterns as an anti-predation strategy.
Limited studies and accounts of red colobus vocalizations exist. However, these few accounts indicate that the vocal repertoires of red colobuses are complex and may contain a diverse variety of calls. In fact, they are considered chatterboxes and are notable for their inability to remain silent for any length of time. Adult males are the primary vocalizers even though they represent a small proportion of the total population. However, during copulation and intra- and intergroup aggressive encounters, adult females appear to be more vocal.
The most common call types are chirp, chist, wheet, bark, yelp, wa, and quaver. The chirp is characterized by an abrupt drop in pitch whereas the chist is characterized by an abrupt increase in pitch. The presence of a potential predator, or another troop of colobuses, elicits an aggressive or threatened response which is met with one of three calls, the bark, chist, or wheet. Before and during copulation, females produce a series of wa sounds that result in intense quavers and are accompanied by yelps from males. In some cases, individuals also produce rapid quaver calls when harassing other copulating pairs of monkeys.
A unique form of communication occurs in the form of physical display in red colobuses. The perineal organ in young males resembles the bright red and swollen genitalia that develops in adult females during estrous. This mimicry of the female structure in juveniles makes it difficult to determine the sex and may serve to reduce the intolerance of adult males toward young males. Harassment starts when this organ begins fading to the gray color of males and may be circumvented by the subordinate males performing submissive displays.
Estrus in females may peak in the rainy season. The length of gestation, or pregnancy, is around 5–6 months. Births may occur throughout the year, and there is generally a 25–30 month interval between births. Adult females, especially those in or approaching estrus, display auditory and visual signals. They are distinguished by a very apparent swelling and vivid red coloration of the genital area. These highly visual signals serve to notify the males of the group that the female is ready for copulation. These visual signals are accompanied by loud quaver calls and leaping to convey information about her reproductive state to the males. After birth, unlike many other primate species, females do not generally allow other group members to handle their infants and allomothering behavior is rarely tolerated.
As seed dispersers, red colobus monkeys play an important role in maintaining the health of the forests they live in. Secondly, by feeding extensively on young leaves, red colobuses largely denude a tree of young leaves. This stimulates the tree to recover by producing a new set of young leaves within a week, thereby increasing its productivity and growth rate. Thirdly, the home range of the red colobus overlaps with other African primates, meaning that effective protection for red colobuses simultaneously helps protect many other species.
The International Union for Conservation of Nature lists the Foa’s red colobus monkey as Endangered (IUCN, 2020), appearing on the IUCN Red List of Threatened Species.
Natural threats include predation by chimpanzees, crowned-hawk eagles, leopards, and hyenas.
Red colobus monkeys throughout Africa are considered to be the most threatened group of African monkeys with 13 of the 17 species (>75%) listed as Critically Endangered or Endangered. The primary threats facing red colobuses are poaching for the commercial bushmeat trade, and habitat loss due to mining, logging, and agriculture. Due to their noisy nature and large group size, they easily attract hunters’ attention. Once they see a hunter they typically do not flee, but rather just watch the humans below. Due to habitat loss, there is very little remaining suitable habitat for this species and numbers have drastically declined, so much so that in Itombwe Nature Reserve, one of the two last reserves where the Foa’s red colobus monkeys currently occur, only one sighting has been reported since 2003. Habitat loss leads to a loss of trees, which serve as an important food source, leading to a decline in monkey populations.
Despite their conservation status, only a few red colobus populations have been studied in detail, partly because their distribution is in areas that have not been politically stable for long periods. Additionally, instability in the taxonomic classification of the red colobus has been one factor that has led these monkeys to be relatively neglected in conservation planning compared to some other primates. Unstable classifications can cause confusion, and lead to less focused conservation action to reduce the decline and possible extinction of some distinctive populations.
The Foa’s red colobus (Piliocolobus foai) is listed in Appendix I of the Convention on International Trade in Endangered Species (CITES), an international agreement between governments whose goal is to ensure that international trade in specimens of wild animals and plants does not threaten their survival.
The IUCN has partnered with numerous organizations such as the African Primatological Society and the International Primatological Society to establish a conservation plan from 2021–2026 whose primary objectives are to establish a red colobus monitoring program in the Kabobo massif complex, conduct forest surveys, and genetic analysis to elucidate taxonomic features and work with the local Democratic Republic of Congo authorities to improve enforcement of wildlife laws in areas where the species occurs.
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Written by Divya Pawar, October 2022