Geographic Distribution and Habitat
The sooty mangabey (Cercocebus atys), also called the spectacled mangabey (an alias sanctioned by the International Union for Conservation of Nature, replacing previous nicknames of white-crowned and white-collared), is native to West Africa. The geographic range includes the coastal countries of Senegal, Guinea-Bissau, Guinea, Sierra Leone, Liberia, and Côte d’Ivoire (Ivory Coast) west of the Nzo-Sassandra River system.
Sadly, this species has drastically declined throughout much of its natural range. Some reports put the Senegal, Guinea-Bissau, and Guinea populations at nearly extinct. And those sooty mangabeys residing in Côte d’Ivoire have been all but eradicated; only Taï National Park and the sacred forest grove of Gbepleu in western Côte d’Ivoire provide sooty mangabeys with safe haven. Sierra Leone populations within Gola Forest National Park may be more stable, though “robust” would be an overly optimistic descriptor, particularly since population counts are from 2007 and habitat destruction continues at an alarming rate.
Primary (old growth or virgin) and secondary forests (those that have regrown after a major disturbance), along with flooded, dry, swamp, mangrove, and gallery forests provide sooty mangabeys with their habitat. These monkeys reside in valleys at elevations from sea level to 3,281 feet (1,000 m) above sea level, and likely at higher elevations in Sierra Leone’s Loma Mountains. They are also known to inhabit farmland, where they have a reputation as crop pests.
The climate throughout the species’ six-country geographic distribution is characterized by subtle variations in temperature and annual rainfall amounts.
Parenthood rescinded. The sooty mangabey had been considered a parent species to one child (or subspecies): the white-naped mangabey (Cecrocebus atys lunulatus). Then, in 2016, researchers declared the white-naped mangabey a distinct species (giving it the updated Latin name of Cecrocebus lunulatus).
Of course, the sooty mangabey is not the first primate species to “lose a child.” What makes this family breakup especially confusing is the continued practice of using the same nicknames (or aliases) when referring to these two estranged species. As example, the alias “white-collared mangabey” is often used, interchangeably, to refer to both the sooty and the white-naped mangabey. It gets murkier. Some scientific accounts still refer to the white-naped by its previous Latin subspecies name, despite this primate’s distinct species status.
There’s even more muck: originally, both the sooty and the white-naped mangabeys were considered subspecies of the red-capped mangabey (Cercocebus torquatus), who has the nickname (you guessed it!): white-collared (or collared) mangabey. Talk about a family history quagmire. But we won’t go further. To mitigate the risk of losing readers in this nomenclature quicksand, this Primate Species Profile will endeavor to focus on the attributes of the sooty mangabey—and, hopefully, untangle its taxonomic association with the white-naped mangabey.
Size, Weight, and Lifespan
Sooty mangabeys are large monkeys, with the male of the species being larger than the female (an example of sexual dimorphism). Males weigh between 19 and 31 pounds (8.5–14 kg) with an average weight of 23 pounds (10.2 kg); females weigh between 11 and 20 pounds (5–9 kg) with an average weight of 12 pounds (5.5 kg). Males also have larger heads, and their canine teeth are larger than those of females.
Head-to-body length for males is 18.5–26.5 inches (47–67 cm) and 16–24 inches (40–60 cm) for females. A nonprehensile tail adds another 16–32 inches (40–80 cm) to the frame of both sexes.
The species’ lifespan in the wild has been documented at 18 years. The average lifespan for captive males has been documented at 26.8 years.
Members of the genus Cercocebus, including sooty mangabeys, are characterized by white upper eyelids, leading some locals to refer to them as “four-eyed monkeys.” They don’t have four eyes, of course, but the bare, white skin above their deep brown eyes allows one to playfully imagine this trait—and likely led to the sooty mangabey’s nickname of spectacled mangabey. White-eyelid mangabeys are most closely related to mandrills and drills.
You have likely guessed that sooty mangabeys take their name for the soot-colored pelage (fur coat) that drapes their sturdy bodies. Coat coloring ranges from ashen gray to brownish gray with lighter coloring on the monkeys’ ventral surfaces (underparts), which can appear light blue. Darker fur covers the arms, legs, hands, feet, and tail.
The facial skin of sooty mangabeys is a mottled, pinkish-gray contrasted by a band of dark fur that envelopes the forehead and buries their ears. Light-colored whiskers shoot out from a dark-colored muzzle that is flat and narrow. Tufts of light gray fur feather out from the cheeks.
Distinct from the whorl of fur that graces the crown of the head of white-naped mangabeys (who have retained the alternate name of white-collared mangabey), sooty mangabeys have a flat, unpretentious hairdo. It’s as if Mother Nature took a comb to the sooty’s head and combed the hair straight back. Then, realizing her work might be construed as lazy, she painted a few straw-colored tips on the heads of some individuals.
Webbing between their fingers and toes allows mangabeys to swim, an adaptation that helps these monkeys navigate swamp forests and perhaps grab a frog egg or crab from swampy waters for a meal. Another adaption in this species is specialized nerve fibers beneath their skin and at the base of their fingertips.
Nuts and seeds make up most of the sooty mangabey’s diet. Fruits, grains, leaves, tree bark, fungi, insects, invertebrates (including crabs and worms), and frog eggs complete their meal plan.
Many of the nuts consumed have hard shells, making these foods inaccessible and therefore impossible for most animals to eat. But not for sooty mangabeys. Mother Nature has pragmatically fitted these monkeys with powerful jaws and large incisor teeth that enable them to crack open hard nuts. They then crush the flesh with their large premolars, aided by thick dental enamel. Their specialized dentition also allows them to tear bark from trees. Wildlife biologists laud this evolutionary adaptation as a crucial means for ensuring the species’ viability.
Perhaps the most common food in their diet with the hardest shell is the nut from the bitterbark tree, aka cherry mahogany (Sacoglottis gabonensis). Other plant foods that provide nourishment include the boleko nut (Ongokea gore), Chinese banyan (Ficus thonningii), sacred garlic pear (Crateva religiosa), hairy rock fig (Ficus glumosa), Raphia palm (Raphia africana), African nutmeg (Pycnanthus angolensis), leaf flower (Phyllanthus), and China laurel (Antidesma). Large cheek pouches allow the mangabeys to store food for later snacking.
Males and females exhibit different dietary behaviors. Males tend to eat more hard nuts, seeds, and crunchy invertebrates; as such, they rely on their incisors and molars to crack open and crush the flesh. Females typically choose softer seeds and fruits. Young sooty mangabeys favor Irvingia gabonensis seeds, from a tree that bears fruit similar to a mango. (Sidebar: Irvingia gabonensis seeds are cultivated and marketed to human primates, who ingest the seeds for medicinal purposes, including cholesterol reduction, diabetes control, and weight loss—though effectiveness is largely anecdotal.)
Behavior and Lifestyle
Sooty mangabeys are primarily terrestrial—meaning that they spend most of their time on the ground, rather than in the trees. If they must venture into the trees (to evade a predator, as an example), they stick to the lower levels of the forest strata. Most of their movement (whether on the ground or in the trees) is quadrupedal; that is, they use all four limbs to advance. But if a situation warrants, they will climb or leap through the forest understory, shrub layer, or on the ground. Their long tail helps them to balance.
Diurnal creatures, sooty mangabeys are active during daylight hours; they engage in activities as a group. About 75 percent of their day is spent foraging and eating. They find most of their food by foraging through leaf litter on the forest floor. While they are capable of cracking open hard nuts, they aren’t above scavenging for nut remains cracked open and discarded by chimpanzees and red river hogs, who share mangabey habitat. According to wildlife biologists, sooty mangabeys show evidence of spatial memory skills: these monkeys remember the location of fallen fruit and are able to discern whether or not a tree is bearing fruit. And to the ire of local farmers, sooty mangabeys are known to be crop raiders.
Travel time and rest periods make up the remainder of their day. When traveling, individuals remain within 3.3 feet (1 m) of one another. When resting, they choose an object such as a fallen tree limb to sit upon, rather than place their tushes directly on the forest floor. Younger individuals engage in play sessions with one another. Occasionally, adults join the fun.
Even though sooty mangabeys are primarily terrestrial in their daily activities, they choose to sleep overnight in trees, according to researchers’ observations. During harsh weather conditions (such as a monsoon event), they may huddle together.
Sooty mangabeys’ many predators include humans (Homo sapiens), crowned hawk eagles (Stephanoaetus coronatus), chimpanzees (Pan troglodytes), gaboon vipers (Bitis gabonica), and leopards (Panthera pardus). Fortunately, these monkeys are exceptionally savvy at spotting predators. By acting as a sentry, upon spotting a predator a sooty mangabey sounds an alarm call to his group. Depending on the type of predator (terrestrial or arboreal), the monkeys will either ascend to the trees or descend to the ground to evade capture.
The name “mangabey” is taken from the district of Mangabe (Manongabe) in Madagascar, mistakenly applied to these primates by early explorers who erroneously believed these primates were from Madagascar, a large island country 249 miles (400 km) off the coast of east Africa. Though these explorers later realized they were incorrect—mangabeys are not from Madagascar—the name stuck.
Sooty mangabeys live in large multimale/multifemale groups (also known as “troops”) composed of 30 to 120 individuals. An alpha (dominant) male leads a troop, followed by all other males over the age of 5 or 6, then an alpha female, followed by the remaining females. Both sexes form linear dominance hierarchies and coalitions. Higher-ranking males and females are centrally located within their troop and spend more time eating, while lower-ranking individuals spend more time foraging.
Juveniles engage in social ranking “contest competitions,” where females establish matrilineal dominance-based lines; that is, at birth, they resemble the hierarchal ranking of their mothers and their ranking remains stable. Male ranking also resembles that of their mothers at birth; however, around the age of 4 when these juveniles begin to grow larger canine teeth and as they approach their sexual maturity, their hierarchal ranking rises above that of their mothers. As such, brothers and sisters do not occupy similar ranks. Juvenile males are more likely than juvenile females to approach adult males, but juvenile female offspring of the alpha female interact more with males than with other females. In fact, these young females often groom the troop’s oldest male. When females choose to interact with other females, their relationships are not based on rank. Similarly, they show no preference for related kin when interacting with members of their troop.
While female sooty mangabeys remain with their birth (natal) group, most males immigrate into other groups upon reaching adulthood. Some stay behind, however, and others leave for several months before returning. Others remain solitary for a period of time until they find a suitable group to join—or return home. Occasionally, a wandering solitary male commits infanticide in an attempt to instill himself as a troop’s new leader, so he can sire his own offspring.
Apart from those murderous solitary male outliers, sooty mangabeys are reported to have extremely low rates of agonistic behavior, exhibiting little contact aggression. As example, bites issued to other individuals are typically no more than a gentle nip to the tail or rump. Wildlife biologists posit that because alliances and strong matrilineal lineage are relatively unimportant in this species, a controlled form of aggression prevails. (Agonistic behaviors, particularly rank challenges by females, are more commonly observed in captive sooty mangabey groups.)
Home range for the species is estimated at 1.54–2.32 sq miles (4–6 sq km), but a range of 2.5 sq miles (6.5 sq km) or larger is not unusual. Though neighboring groups typically set up residence about 2 miles (3 km) from one another, home ranges often overlap. These intergroup encounters are most often uneventful.
Sooty mangabeys share their wide-ranging habitat with a wide variety of animals, though individual niches within a habitat can be different from one another. Lions (Panthera leo), leopards (Panthera pardus), African wild dogs (Lycaon pictus), African forest buffalo (Syncerus caffer nanus), African forest elephant (Loxodonta cyclotis), red river hogs (Potamochoerus porcus), warthogs (Phacochoerus africanus), hippopotamus (Hippopotamus amphibius), mongoose (Herpestidae), duikers (antelopes), and anteaters make up some of the impressive array of non-primate mammals across the sooty mangabey’s geographic range. Primates include baboons, western chimpanzees (Pan troglodytes verus), and a variety of monkey species.
Within the Taï National Park in Côte d’Ivoire, sooty mangabeys intermingle with groups of western black-and-white colobus monkeys (Colobus polykomos), red colobus (Piliocolobus sp.), olive colobus (Procolobus verus), Diana monkeys (Cercopithecus diana), Campbell’s guenon (Cercopithecus campbelli), and other primates.
Red colobus and Diana monkeys, who are arboreal species, benefit from sooty mangabeys’ ability to detect predators approaching from the ground. Alerted by the sooty’s loud alarm call, these monkeys escape higher in the trees. Not only are they able to evade capture, they are also able to safely expand their feeding niche thanks to the watchful behavior of the terrestrial sooty mangabeys. But sootys also benefit from this interspecies, affiliative relationship, retrieving fruit from the forest floor that their arboreal primate cousins have dropped.
Alarm calls of sooty mangabeys have evolved acoustically, and each alarm call signifies a specific predator.
Both males and females produce alarm calls. Females are able to distinguish between group and nongroup calls, which may help prevent infanticide attacks by outsider males.
In addition to their loud alarm calls, sooty mangabeys possess a full repertoire of vocalizations used for different situations:
- Grunts are low-frequency sounds frequently emitted by males while foraging. The soft grunt, also known as a staccato bark, is most common and consists of a multitude of rapid grunts and a whoop, ending with a multi-syllabled rumble.
- Twitters, which can contain up to 23 syllables, range from soft and melodic to harsh. They are emitted by adult females and by juveniles of both sexes during social interactions and to locate one another while foraging over wide areas.
- Screams are loud, noisy agonistic vocalizations, emitted mostly from juvenile and adult females during contact aggression.
- Growls are multisyllabic, emitted during agonistic situations, and often accompanied by a raised eyebrow.
- Grumbles, hoos, intense threats, and waus and random other vocalization are emitted during agonistic interactions.
- Copulation calls are composed of a complex phrase structure and last up to 10 seconds. These calls are emitted by females during copulation and occasionally during defecation, and emitted by males after ejaculation.
- Whoop gobbles are low-frequency, high-volume long calls that can be heard for a distance of up to 0.6 mile (1 km). They are emitted only by adult males for contacting other mangabey groups or to alert troop members of a predator.
In addition to their many vocalizations, sooty mangabeys communicate with one another through other methods. As example, raising and lowering their bright eyelids in repetition signals a potential threat. Their many facial expressions include a lip grin while sticking out their tongue. While researchers have not discerned the meaning of this expression, grins in nonhuman primates are known to indicate fear (the mangabeys themselves surely know why they are sticking out their tongue!).
When it comes to the tactile activity of social grooming, adult males avoid one another. Instead, they direct their grooming toward females. Sooty mangabey mothers have been observed using a stone for grooming their infants. Researchers are hesitant to state that this stone action represents tool use. But . . . we use grooming stones on our domesticated animal companions—including dogs, cats, horses, and any other furred family ones—to remove dander, dried mud, and excess hair, and to bring out the natural oils in our animal’s coat. So we will comfortably state that the sooty mangabeys know what they’re doing.
The species follows a polygynandrous (promiscuous) mating system in which both males and females have multiple partners. Sexual activity occurs early in males; at 1 year old, they begin mounting sexually mature females. Curiously, juvenile males are more likely than adult males to try to have sex with mature females. No matter. Until the age of 4 when they finally reach the edge of sexual maturity (able to sire young), males are shooting blanks. Females reach reproductive maturity (able to conceive and bear young) at about 4.5 years old.
During her estrous (reproductive) cycle, a female’s genitals swell, an indication to males that she is ready to mate. Females initiate copulation. She presents herself to a potential mating partner who then grasps the female by her ankles and mounts her from behind. In a troop’s linear dominance hierarchy, higher-ranking males mate more frequently than lower-ranking males.
Mating season is from May through September, peaking in July and August though births can occur year-round. After a gestation period of about 5.5 months, a single infant is born. Average time between births is 13 to 16 months; a longer interbirth interval is associated with lower infant mortality.
A mother is the primary caregiver for the first 2 to 7 months of her infant’s life. Young infants cling to mom’s abdomen as she travels, transferring to her back when they are a few months old. Occasionally, males carry infants they have sired. A mother nurses her infant anywhere from 4 to 10 months and continues to keep a close eye on her child for the first year of life. Aunts of the infant help out mom by grooming the little one from age 10 to 12 months. An infant’s siblings (both male and female) also lend grooming assistance.
While most promiscuous primate mating systems are typically characterized by female-to-female aggression as they compete for male partners, this behavior is not true for sooty mangabeys. Rather, females are more likely to receive a slap from a randy (sexually aroused) male.
Should a mother’s infant die within six months after her giving birth, she immediately re-enters estrus (the period of sexual receptivity and fertility). Hence, an outsider male who has successfully infiltrated a group and committed infanticide (murdering a mother’s baby) within this six-month period has the opportunity to breed with the female and sire his own lineage.
Sooty mangabeys are ecological ambassadors. Thanks to the many seeds they eat—and then poop throughout their range—they help to regenerate forest growth. Sometimes they discard, rather than consume, certain seeds while foraging. These seeds, too, nourish their ecosystem and lead to new life on the forest floor.
Sooty mangabeys are classified as Vulnerable by the International Union for Conservation of Nature (IUCN, June 2019), appearing on the IUCN Red List of Threatened Species. This assessment is an escalation from these primates’ previous classification of Near Threatened. A population decline of at least 30 percent over the previous 27 years (the equivalent of three generations) led to this heightened threat status. And if anthropogenic (human-caused disturbances) continue, the sooty mangabey’s declining population trend is predicted to continue at the same or at an accelerated rate. The Red List has not provided a current estimated overall population count for the species.
Intensive hunting across the species’ range—including within protected areas—is a paramount threat. The animals are killed and their flesh sold as “bushmeat.” In coastal Guinea, bordering Sierra Leone, and in central Liberia, sooty mangabeys are the most hunted primates. They are the most common primates found in bushmeat markets, with the price of a freshly killed adult male in areas bordering the Cavally River (Côte d’Ivoire and Liberia) selling for the equivalent of approximately $5 U.S.
Loss of habitat and degradation of habitat also threaten the species’ existence in our world. Tracts of pristine forest are razed and transformed into agricultural land and commercial human enterprises, including logging and mining—as well as human settlements. This habitat destruction conspires with the bushmeat trade: As woodlands continue to be lost, the monkeys are forced into small forest fragments, where they are more easily spotted and killed by hunters.
Sooty mangabeys also fall victim to the illicit pet trade. To kidnap a young sooty mangabey for a pet, the mother is always killed. Both the bushmeat market and the practice of keeping these wild animals as pets increase the risk of transmission of zoonotic diseases from monkey to human. In March 2012, a sooty mangabey found dead in Taï National Park, Côte d’Ivoire was discovered to have been infected with monkeypox virus, which is pathogenic (causing disease) to humans. Sooty mangabeys are the only primates other than humans known to acquire leprosy from their own species. Mangabeys are also susceptible to contracting Type 2 diabetes.
When it comes to studying AIDS (acquired immunodeficiency syndrome) in human primates, sooty mangabeys are favored biomedical research subjects. Scientists have discovered that the sooty mangabey is a natural host of the simian immunodeficiency virus (SIV), the disease from which the human immunodeficiency virus (HIV) is derived. Because it is a natural host, if infected with the virus, the sooty mangabey does not get sick. A team of scientists at Yerkes Regional Primate Research Center at Emory University in Georgia did just that: they deliberately infected a colony of captive sooty mangabeys with the virus; and yet, none developed the disease. To learn how the primates achieved this feat, the team sequenced the sooty mangabey genome. The scientists concluded that several genetically based mechanisms naturally enhanced the mangabeys’ immune systems.
But testing on nonhuman animals is controversial. And once their “utility” has ended, these animals are routinely killed.
Yerkes has been cited on numerous occasions, going back decades, for cruelty and negligence resulting in death. In 2020 alone, Yerkes scientists experimented on 1,485 monkeys, with another 2,270 housed in dismal conditions. Hundreds of millions of taxpayer dollars funded these experiments.
The U.S. Department of Agriculture (USDA) denied two requests from Emory University to remove animal safety citations from federal inspection reports of the Emory-affiliated Yerkes National Primate Research Center laboratories, according to a March 21, 2022 People for the Ethical Treatment of Animals (PETA) press release.
To the further dismay of Yerkes scientists, the U.S. Fish & Wildlife Service (USFWS) invoked restrictions that make continued research on captive sooty mangabeys and SIV challenging. So Yerkes has been working with other institutions in the hopes of persuading USFWS to ease these restrictions.
We find it sad that these primates are primarily regarded as laboratory subjects—and not as sentient beings who have their own place in our world.
Sooty mangabeys are listed in Appendix II 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 species is also listed as Class B of the African Convention on the Conservation of Nature and Natural Resources.
The species occurs in the following protected areas:
- Taï National Park (Côte d’Ivoire) and within Gbepleu sacred grove in western Côte d’Ivoire near the town of Man
- Sapo National Park, Grebo-Krahn National Park, and Gola National Park (Liberia)
- Tiwai Island Wildlife Sanctuary, Gola Forest National Park, and Loma Mountains National Park (Sierra Leone)
- Cantanhez Forest National Park (Guinea-Bissau)
Unfortunately, laws intended to protect the species are routinely flouted and these animals are hunted and killed in “protected” areas.
Sooty mangabeys, like their Endangered cousins the white-naped mangabeys, need conservation advocates and angels. West African Primate Conservation Action (WAPCA), an organization based in Ghana, has adopted the white-naped mangabey as one of its focal primates. WAPCA seeks to safeguard the future of endangered primates and their habitats in West Africa through the “development of management strategies and conservation actions by all responsible parties for all populations of a species, whether inside or outside their natural range.” Education is regarded as crucial in ensuring positive attitudes toward the environment. As such, WAPCA educates local the Ghanaian people on the importance of the forest and its primate citizens, highlighting the white-naped mangabey.
Written by Kathleen Downey, March 2023