Geographic Distribution and Habitat
The red-eared guenon (Cercopithecus erythrotis), also known as the russet-eared guenon or red-eared monkey, is a denizen of Africa. This shy primate’s restricted range extends from the Cross River in southeastern Nigeria to south of the Sanaga River in Cameroon. The species also inhabits the island of Bioko, 20 mi (32 k) off of Africa’s west coast, in northernmost Equatorial Guinea. Considered a biodiversity “hot spot” for Africa’s primates, Bioko Island is home to 11 primate species, with red-eared guenons being the most prevalent. Unfortunately, their population is steadily declining.
Subtropical/submontane and tropical moist lowland forests provide the environment conducive to red-eared guenon habitat. These monkeys inhabit both primary and secondary forest types. On the island of Bioko, red-eared guenons reside at elevations up to 3,281 ft (1,000 m) above sea level; groups are also known to live nearby human settlements.
Size, Weight, and Lifespan
Red-eared guenons are Old World monkeys and among the smaller of the forest guenons.
Males are slightly larger than females, averaging about 16.5 in (42 cm) in head-to-body length. A long, partially prehensile tail adds another 24 in (60.9 cm). Average weight for adult males is 7.9 lb (3.6 kg).
Average head-to-body length for females is just over 15 in (38.4 cm); their long, partially prehensile tail adds another 22 in (55.3 cm). Average weight for adult females is 6.4 lb (2.9 kg).
Lifespan for red-eared guenons has been documented as 16 years.
Pockets on the side of the head between the jaw and the cheek that some animals have to store food.
The tail of an animal that has adapted to be able to grasp or hold objects.
Visit the Glossary for more definitions
While this monkey takes its name from the wispy, reddish (or russet) tufts of hair decorating the tips of its ears, its expressive, colorful face—among the cutest of all monkeys—has the power to bewitch all those who look upon it. Okay, literary hyperbole aside, it’s hard to deny the red-eared guenon’s cute countenance.
A prominent reddish triangle (the same shade of red as the monkey’s ear tufts) paints the bridge of the nose, extending downward to meet pale pink nostrils. Narrow lips sit above a humble chin accented by long, random strands of hair (like those sometimes seen on an elderly grandparent), with a white chinny underside that melts into a furry white fur collar.
Yellow and white hairs that feather out from the monkey’s cheeks are like expensive salon highlights, made more distinct by black fur tufts decorating the lower half of the face. Blueish-black fur encircles the red-eared guenon’s round brown eyes, completing the facial features for an overall effect that reflects personality . . . and sentience.
Wildlife biologists have discovered correlations between monkeys’ colorful facial patterns and their social structure and environment. In the case of red-eared guenons, their colorful faces allow individuals to recognize one another so they can defend their territories.
The furry cap atop the red-earned guenon’s round head and the silky fur adorning the back appear glittered with gold in what is called an agouti pattern, a fancy way of saying that each hair has alternate dark and light bands, for a grizzled appearance. Dark-to-pale gray hair covers the legs and arms, and the belly is pale gray. Its long red tail (the same shade as the ear tufts and nose triangle) is punctuated by a black furry tip.
About 85 percent of the red-eared guenon’s diet consists of fruits, followed by seeds, young leaves, flowers, shoots, and insects. (Wildlife biologists have counted 38 plants in this species’s diet.) Insects provide important nutrition, particularly for pregnant and lactating females. The consumption of both plants and animals (insects) characterizes red-eared guenons as omnivores.
Guenons are fitted with generous cheek pouches that allow the monkeys to store extra food (for later snacking!) as they forage.
Behavior and Lifestyle
Little research data are available about this species, attributed, perhaps, to the red-eared guenon’s nature, described as “secretive,” “shy,” and “unobtrusive.” Compared to other guenon species, red-eared guenons are much quieter as they go about their daily activities, drawing less attention to themselves. They are active during daylight hours, making them diurnal, and they spend most their time in the trees, making them arboreal. Sleeping sites are in trees.
Scientific studies have found that most guenon species move primarily by quadrupedal locomotion (that is, they advance forward by using all four limbs), followed by climbing and leaping. They leap only 10 percent of the time. Climbing and leaping are associated with limb proportion, and not the size of the monkey.
Red-eared guenons’ long, partially prehensile tails assist in agility and balance as the monkeys move through the forest. Infants use their tails to cling to their mothers.
Arboreal guenons are known to travel to the lower branches to forage; occasionally, they venture to the forest floor to search for insects. Red-eared guenons adhere to this behavior. On Bioko Island, they are most often found in the lower levels of the canopy, but they have been observed foraging for food in upper grasslands and on beaches too. On rarer occasions, these monkeys have been found in the forest’s emergent layer. In the past, red-eared guenons were known to frequently raid native plantations.
Both Bioko Island’s red-eared guenons and those on the African mainland appear to prefer the forest’s lower canopy. However, those residing on Bioko Island are more adaptive to varied habitats in their environment.
“Guenon” is the French word for a female monkey.
Sclater’s guenon (Cercopithecus sclateri), Nigeria’s only endemic primate species, had been considered a subspecies of the red-eared guenon until it was reclassified as its own species in 1980.
Red-eared guenons live in family groups (known as troops) of 4 to 30 individuals. Group size varies, depending on habitat quality and availability of food sources. A typical troop consists of 1 adult male and 10 adult females with their young offspring. In other guenon societies, groups of “outsider” males drift in and out of an established territory. It is not unusual for males to sometimes live alone for a period of time or live in small bachelor groups. However, this phenomenon has not been remarked upon concerning red-eared guenons. Red-eared guenons are reportedly less hierarchal than some primate societies. Although they are territorial, they do their best to avoid conflicts with other guenon troops. They are frequently found in mixed-species groups, particularly with putty nose guenons (Cercopithecus nictitans). These different guenon groups appear to understand one another’s alarm calls, sounded when a predator is nearby. Natural predators to red-eared guenons include eagles and snakes.
Two threatened species who share habitat with red-eared guenons are the Critically Endangered Cross River gorilla (Gorilla gorilla diehli), found in Cameroon and Nigeria, and the Endangered drill monkey (Mandrillus leucophaeus), found in Cameroon and Nigeria and on Bioko Island.
Biologists regard Bioko Island as a “living laboratory for studying how plants and animals evolve in isolation.” One of four islands in an archipelago, Bioko is an ecosystem unto itself. Up until 12,000 years ago, Bioko had been connected to Africa’s mainland. Described as an “exclusive ark,” the island is home to select species who have evolved separately from those on the mainland.
Besides the Endangered drill monkey, red-eared guenons share their island home with six other species of monkeys, including the Endangered Pennant’s red colobus (Piliocolobus pennantii), two antelope species (duikers), a porcupine species, three species of scaly-tailed squirrels, one species of pouched rat, one species of tree hyrax (a plump, furry, small nocturnal animal that looks like a rodent but is, in actuality, distantly related to elephants), and carnivorous, tree-dwelling cat-like linsangs. Forest buffalo once roamed this Bioko Island, too, but they were hunted to extinction more than a century ago.
A wildlife expedition to Bioko Island, written about in National Geographic magazine in 2008, reports on the team’s encounters with the island’s red-eared guenons. In the first instance, the guenons immediately began sounding hack calls and chirps, and mothers clutched their babies as they desperately attempted to escape this human intrusion. A lead primatologist on the team described the monkey’s eyes as being “wide with terror.” Over the course of their 10-day study, the team came across another red-eared guenon troop, sheltering in the forest’s leafy canopy within the Gran Caldera Scientific Reserve. The experience was the same. Upon seeing the humans approaching, the monkeys warned one another with alarm calls and fled deeper into the forest.
Males emit nasally hack alarm calls in response to predator threats. Females tend to chirp. To further communicate with one another, red-eared guenons sound quiet, trill-like contact calls. These contact calls are quite unlike the loud, long-distance contact calls of other guenon species. Like other guenon species, however, red-eared guenons contort their face into a grimace—mouth parted, sharp teeth bared—when they are angry or excited. They might also close their eyes, tilt their head, or flick their tail to send a message or convey their mood. Males are reported to engage in an activity described as “stone clapping” to get attention.
Most of the information about red-eared guenon reproduction and family life is promulgated, and conjectured, from other guenon species.
Breeding season varies between species. Some species breed at the end of the dry season, so that births occur during the peak fruiting season. Other guenon species breed throughout the year.
Guenon species usually give birth to a single infant every one to three years, after a gestation period (pregnancy) of five or six months. Red-eared guenon mothers nurse their babies for six months, at which time the infants are considered weaned (weaning time in other guenon species varies from 9 to 18 months).
Although mothers are the primary caregivers to their infants, other adult females in the troop might assist with child care. Initially, mothers carry their babies. But by the time they are two weeks old, infant guenons are climbing. By the time they are three months of age, young guenons have attained their adult coloration.
With most guenon species, a daughter’s social status depends on her mother’s ranking within the troop. (As noted earlier, however, red-eared guenons do not appear to abide by as strict a hierarchy as other guenon species.) Related females usually remain together for life, while young males leave a troop upon reaching sexual maturity to seek a new troop to join.
Thanks to all the fruits they eat, red-eared guenons are important habitat regenerators. Every time they defecate, they help to disperse seeds and encourage new plant growth in their forest ecosystem.
The red-eared guenon is listed as Vulnerable by the International Union for Conservation of Nature (IUCN 2020), appearing on the IUCN Red List of Threatened Species.
Even the red-eared guenon’s two subspecies share the ignominious distinction of possible extinction in the wild. Both the Cameroon red-eared monkey (C. e. camerunensis), found from the Cross River in southeastern Nigeria to just north of the Sanaga River in southwestern Cameroon, and the Bioko red-eared guenon (C. e. erythrotis), found on Bioko Island, are listed as Vulnerable by the IUCN.
Habitat loss combined with the illicit bushmeat trade has had a detrimental effect on the species. Wildlife biologists estimate that more than 30 percent of the overall red-eared guenon population has been lost. Red-eared guenons are not usually seen as pets. Those who fall victim to the illegal pet trade, however, have extremely poor survival rates.
Trees have been wantonly felled to supply the timber industry and pristine forests have been transformed into farmland, essentially leaving the monkeys homeless.
Rampant hunting has taken a grim toll on red-eared guenons, throughout their range. Wildlife biologists estimated, back in 2006, that about 3,400 red-eared guenons were being killed annually. On Bioko Island, their flayed corpses were commonly found for sale at the Malabo bushmeat market.
A study ten years later, in 2016, found that red-eared guenons (along with putty-nosed guenons) had become somewhat more “tolerant” of heavy hunting; that is, hunters were having less success killing these monkeys as compared to other hunted species. Biologists attribute the red-eared guenons’ preservation to adaptive behavioral changes: the monkeys have become less vocal and are quieter in their calls, and they have become more “cryptic” in their movements through the forest. Nevertheless, red-eared guenons remain vulnerable to extinction.
The red-eared guenon is 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 on Class B of the African Convention on the Conservation of Nature and Natural Resources and is protected by national legislation in Cameroon and Nigeria. And the species resides in the following protected areas: Cross-River National Park in Nigeria; Korup National Park and several forest reserves in Cameroon; and Pico Basile National Park and Southern Highlands Scientific Reserve, both on Bioko Island.
Additionally, red-eared guenons are found at the following research sites: Rhoko Research and Education Centre, Nigeria (a field site of the Centre for Education, Research and Conservation of Primates and Nature [CERCOPAN], a government agency established in 1995); and the Gran Caldera and Southern Highlands Scientific Reserve on Bioko Island. The Limbe Wildlife Center in Cameroon, established in 1993, cares for a small population of red-eared guenons.
All of these protections sound good. Unfortunately, as is often the case with endangered species, laws created to protect them are largely ignored and difficult to enforce. A case in point: In October 2007, the conservation/activist group Bioko Biodiversity Protection Program (BBPP) convinced Equatorial Guinea’s president, Teodoro Obiang Nguema Mbasogo, to issue a ban against the hunting, selling, and consumption of primate meat. Disappointingly, this ban was short lived. Furthermore, with flagrant disregard for the law, hunters have killed these monkeys within protected areas—using access roads created by the BBPP to reach and kill their prey.
Journalist Virginia Morell eloquently wrote: “It is clear that all seven monkey species are in danger of becoming extinct, and that the Equatorial Guineans could well eat their way through the island’s fabled biodiversity.” (“Island Ark: a threatened African treasure,” National Geographic, August 2008.)
Despite the associated challenges, BBPP remains undeterred in its commitment to save red-eared guenons (along with other threatened wildlife species) from extinction. Since 2011, the U.S. Fish and Wildlife Services (USFWS) has supported BBPP through grants, important funding that has allowed BBPP to implement and continue protection its efforts. Red-eared guenon protection measures include: organizing patrol teams that deter hunters; enlisting local citizens to help monitor monkey populations; creating community awareness and educational programs; cultivating a national appreciation of the red-eared guenon; and promoting ecotourism to reframe red-eared guenons from bushmeat to precious island inhabitants and attractions.
Written by Kathleen Downey, September 2019