Red-Eared Guenon, Cercopithecus erythrotis
RED-EARED GUENON
Cercopithecus erythrotis
Geographic Distribution and Habitat
Red-eared guenons are Afro-Eurasian monkeys that live in a relatively small range along the Gulf of Guinea. On the mainland, their habitat spans from the Cross River in southeast Nigeria to the Sanaga River in northwest Cameroon. They also live on Bioko Island, which is part of Equatorial Guinea.
Red-eared guenons live in primary and secondary forest environments. They’re more frequently seen in the lower canopy of the trees, but can also be spotted in the emergent layer, at the top of the tree line. Though they are found in both lowland forests and montane forests, they are more prevalent in lowland forests. On Bioko, they’ve been spotted at sea level on the beaches and on Mount Basile at elevations up to 10,170 feet (3,100 meters) above sea level.
Bioko Island provides a unique habitat where these guenons share space with six other primate species, including the critically endangered Pennant’s red colobus and black colobus, and two other guenon species. On the mainland, red-eared guenons share habitats with endangered Cross River gorillas and drill monkeys.
There are two subspecies: The Cameroon red-eared guenon, Cercopithecus erythrotis camerunensis, on the mainland, and the Bioko red-eared monkey, Cercopithecus erythrotis erythrotis, on Bioko. Evidence shows that Bioko Island split from the mainland at least 10,000 years ago, and many of its animals and plants have been evolving separately from their mainland counterparts.
Size, Weight, and Lifespan
Red-eared guenons are fairly small compared to other forest guenons. Their nonprehensile tails are longer than the rest of their body. Males are, on average, 16.5 inches (42 cm) long from head to body, with tails around 24 inches (60.9 cm). The females are slightly smaller, with an average head-to-body length of 15 inches (38.4 cm) and tails around 22 inches (55.3 cm) long. Adult males weigh 7.9 pounds (3.6 kg) on average, and females 6.4 pounds (2.9 kg).
The lifespan of red-eared guenons is around 16 years in the wild.
Appearance
The name red-eared guenon comes from the distinctive tufts of reddish fur found on the tips of their ears. A triangle of fur along the bridge of their nose is the same red color. Their cheeks feature distinctive triangles of fur in shades of cream and dark grey. Pale fur surrounds their pink chins.
These unique facial features may help the guenons tell each other apart and discern members of their own species from other types of guenons, which is particularly important when different species live in close proximity to one another, like on Bioko Island. Dark color patterns may also help camouflage guenons from predators like snakes and eagles.
Red-eared guenons have expressive, close-set eyes. Patches of blue-grey skin are visible around the eyes and ears. They have large cheek pouches for storing extra food for later—red-eared guenons can fit enough food in their cheek pouches to completely fill their stomachs!
The rest of their fur is in an “agouti pattern,” where individual hairs have bands of different colors. In the red-eared guenon, this results in dark gray fur that appears almost speckled with white or gold. They have pale grey bellies, and their tails are mostly red with a black tip.
Diet
The majority of the red-eared guenon’s diet is fruit, but they also eat seeds, flowers, shoots, and young leaves. They are categorized as omnivores because they also eat insects, which are particularly important sources of nutrition for pregnant and lactating females.
Behavior and Lifestyle
There is little information on the red-eared guenon’s behavior, perhaps because they are often characterized as shy, quiet, and unobtrusive. They are diurnal—active during the day—and spend most of their time in trees, including when they sleep. On Bioko, they have been found at ground level, foraging for insects and other treats on grasslands and beaches. In the past, they were known for raiding plantations.
In Cameroon and Nigeria, the red-eared guenon is found primarily in the lowest parts of the tree canopy. This behavior may be helpful to avoid predators like the crowned hawk eagle. But on Bioko, where there are much fewer natural predators, red-eared guenons spend more time in the emergent layer of the forest. This behavior may help them evade hunters.
Research shows that guenons generally use all four limbs to move (quadrupedal locomotion) but they also climb and, occasionally, leap. They leap only about 10 percent of the time. Their long tails assist with balance, and young guenons use their tails to cling to their mothers.
“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, usually consisting of 1 adult male, around 10 adult females, and young offspring. These groups, also called troops, can vary in size with the habitat and food availability. In other guenons, unattached young males will often live together in small groups of bachelors, but this has not been recorded in red-eared guenons.
Red-eared guenons are territorial, but they are often found in mixed-species groups. This is particularly common with putty-nose guenons (Cercopithecus nictitans), but they’ve also been seen with the Preuss’s red colobus (Piliocolobus preussi).
Though other guenon species tend to make loud “boom calls” to warn of predators, the red-eared guenon is fairly quiet. Male red-eared guenons do make a nasally hack sound when they sense a threat. The females tend to chirp. Red-eared guenons also make trilling noises.
There is some evidence that different guenon groups can understand each other’s vocalizations. Guenons from one species may benefit from the proximity of another species with louder alarm calls, such as the crowned monkey (Cercopithecus pogonias). Once an alarm call sounds, the troop escapes deeper into the forest canopy to avoid a threat.
Guenons also communicate with expressive body language. They can grimace by opening their mouths and baring their teeth when angry or excited. They use head tilts and tail movement to communicate their mood as well.
There is little direct information about the red-eared guenon’s family life, but scientists conjecture that it is similar to other guenons.
Different species of guenon have different breeding seasons. Some breed at the end of the dry season, so that births occur during peak fruit season; others breed throughout the year.
Guenons generally give birth to a single infant every one to three years. Gestation (pregnancy) lasts five or six months, and the mother will nurse the infant for around six months before the infant is weaned. Though mothers are the primary caregivers for infants, other adult females in the troop might assist with care.
Infant guenons can climb on their own by the time they are two weeks old and gain their adult coloration by three months. Once young guenons reach sexual maturity, related females usually stay in the same troop for life. Young males, on the other hand, leave to seek out a new troop.
Thanks to all the fruits they eat, red-eared guenons are important habitat regenerators. They eat the fruit and then wander away into new areas. Every time they defecate, that helps to disperse seeds and encourage new plant growth in their forest ecosystem.
Both subspecies of the red-eared guenon are classified as Vulnerable by the International Union for Conservation of Nature (IUCN, 2020), appearing on the IUCN Red List of Threatened Species.
A primary threat red-eared guenons face is the illegal bushmeat trade. Primate hunting and consumption are banned in all the countries where the red-eared guenon lives, but the bans are largely ignored. In fact, on Bioko, primate hunting has increased substantially since the ban in 2007. In urban areas, where cheaper protein sources are available, wild meat is in demand as a luxury item. Urban meat markets regularly contain species that are (in theory) protected by national and international laws. A 23-year study of Bioko’s wild meat markets estimated up to 67,000 primate carcasses were sold on the island from 1997 to 2021.
Another threat to the species on the mainland is habitat loss from the logging industry. Infrastructure projects also disturb and remove primary forest habitats. In some cases, newly constructed roads on Bioko made it easier for hunters to access the animals, even in protected areas.
Some estimates indicate a population decline of approximately 70 percent in red-eared guenons on Bioko between 1986 and 2016.
Red-eared guenons 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 protected by national legislation. However, as discussed, these laws have little effect without regular enforcement.
Red-eared guenons live in the following protected areas: Cross River National Park in Nigeria, Korup National Park and forest reserves in Cameroon, and, on Bioko, Pico Basilé National Park and Gran Caldera de Luba Scientific Reserve. Unfortunately, hunting is widespread inside and outside the protected areas.
On Bioko, conservation projects have had some success in curbing the wild meat trade. For instance, the Bioko Biodiversity Protection Program conducts surveys of the meat markets in Bioko, promotes conservation through community engagement, encourages ecotourism, and operates patrols in protected areas.
Cameroon passed a new forestry law in 2024 that imposes tougher penalties for poaching activities; seeks to limit deforestation; and bolsters the protection of some protected species. The law also strengthens community involvement in conservation by encouraging ecotourism as an economic alternative to bushmeat trading and implementing measures to lessen human-wildlife conflicts.
Cameroon and Nigeria also signed an agreement in 2024 to cooperate in handling wildlife crime along their border—a border along which the red-eared guenon lives. These are hopeful signs, but the effectiveness of these measures remains to be seen.
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Written by Courtney Daniels, Jul 2025