GREEN MONKEY

Chlorocebus sabaeus

Geographic Distribution and Habitat
The green monkey, also known as the sabaeus monkey, is native to West Africa, ranging 386,102 square miles (over one million square kilometers) across 11 countries. Their ranges stretches from southern Mauritiana in the north, down the coast to Sierra Leon, and as far west as Ghana and Burkina-Faso.

These monkeys inhabit a wide range of habitat types, including riverine gallery woodland, acacia savanna, Sahel savanna, Guinea savannas, savanna-forest mosaic, mangrove forest, and lowland tropical moist forest. Unsurprisingly, given the variation in habitats that they occupy, home range sizes for groups of green monkeys can vary across their range. 

Aside from their native range, green monkeys were introduced to Barbados and Saint Kitts and Nevis in the Caribbean several centuries ago by ships carrying slaves from West Africa. Additionally, they have also been introduced to Cape Verde and a small wild population exists in Diana Beach, Florida, descended from monkeys that escaped from a research and entertainment facility.

TAXONOMIC NOTE

Until fairly recently, green monkeys were categorized as a subspecies vervet monkeys. However, they are now considered a separate species under the genus Chlorocebus, the five other species of which are found across sub-Saharan Africa.

Green monkey range, IUCN 2020

Size, Weight, and Lifespan
While the coloration of male and female green monkeys is similar, this species does show sexual dimorphism in terms of size. Male head and body length ranges from 16.5 to 23.6 in (42–60 cm), considerably larger than the female range of 8 to 20 in (20–50 cm). Tail length adds an additional 18–30 in (46–76 cm) in males and 16–26 in (41–66 cm) in females. On average females weigh 9.7 lb (4.4 kg) and males weigh 13 lb (5.9 kg).  

These monkeys are relatively long-lived and can reach up to 30 years in captivity. It has been estimated that they may live up to 27 years in the wild, although the increasing threats posed by a changing climate and hunting by humans may mean fewer monkeys are able to reach this age.

Appearance
Green monkeys look very similar to the other species that make up the Chlorocebus genus; however, there are some key differences that make them easily distinguishable from these other species. Most notably their pelage is more yellowish than other Chlorocebus species, giving them an almost golden-green appearance, particularly across their heads and backs. The whiskers around their chin are also heavily set with yellow. They do not have a particularly distinct white brow, but a paler and more yellow brow than other Chlorocebus members. They have black faces with deep red-brown eyes and dark, square ears. The backs of their hands and feet are gray and their tails a yellowish-gray with a golden tip. Males are easily identified by their pale blue scrotums, the shade of which may change with the male’s age and rank in the group.

What Does It Mean?

Bushmeat:
Meat from wildlife species that are hunted for human consumption, generally in tropical forests.

Crop feeding:
The feeding on human-cultivated crops by wild animals, often primates.

Dispersal: 
When an individual leaves a social group in order to move to another social group. Often occurs at sexual maturity, but can occur throughout an individual’s lifespan.

Dominance hierarchy:
A type of social hierarchy that arises when members of a social group interact, often aggressively, to create a ranking system. In social living groups, member are likely to compete for access to limited resources and mating opportunities. 

Sexual maturity:
The age that an animal is able to reproduce successfully. 

Sexual dimorphism:
Distinct difference in size or appearance between the sexes of an animal in addition to difference between the reproductive organs themselves.

Visit the Glossary for more definitions

Diet
Green monkeys are generalist omnivores and their diet can comprise a wide range of food items, including fruits, leaves, seeds, gum, insects, birds, eggs, lizards, and more. Fruits, leaves, and seeds tend to make up the bulk of their diets, although this can change depending on season and location. In many places, acacia trees provide a large part of their diet and enable to them to inhabit otherwise resource-poor areas. They are very opportunistic, even digging lungfish out of their subterranean burrows to eat them, as well as preying on fiddler crabs among mangroves.

This opportunistic, generalist diet has allowed this species to inhabit a wide range of areas across a large swathe of West Africa and beyond, but it sometimes also leads to conflict with humans. In tourist areas, they are well known for “stealing” food (and even alcoholic drinks) from humans. This usually begins when people feed the monkeys for entertainment, or when food is left out in the open for the monkeys to eat, and can lead to tense relationships between humans and monkeys in these areas. Green monkeys also engage in crop feeding behaviors in some locations, which can lead to retaliatory killings by farmers looking to protect their crops.

Behavior and Lifestyle
Green monkeys are diurnal, meaning that they are active during the day and at night they sleep in tall trees, close to a river if they can, and in close proximity to one another. In some places, members of different troops will share the same sleeping trees.

In order to survive in sometimes harsh environments, green monkeys can spend much of the day searching for food and water. They can spend up to 60% of their waking time on the ground, usually when traveling or foraging. They are also accomplished swimmers and can cross rivers, or simply play in the water when it gets too hot. 

Social bonds are important for this species, particularly for females who stay in the same groups throughout their lives. These bonds are strengthened by social grooming, which the monkeys often engage in when they have time to rest.

Fun Facts

Beyond their native range of West Africa, green monkeys have also been introduced to the Caribbean and Florida by humans.

They are opportunistic, generalist feeders and even dig lungfish out of their burrows to feed on.

Daily Life and Group Dynamics 
Like other members of the Chlorocebus genus, green monkeys live in multi-male/multi-female groups. Their wide distribution across a number of different habitat types means that their behavior and group size can vary widely, depending on the type and amount of resources available. These monkeys thus provide a perfect example of why a species’ behavior and demographics should never be determined from just one study population. 

Group sizes can vary from eight to a whopping 174 individuals in Senegal, although these larger troops will split into smaller one-male groups during some seasons. In Côte d’Ivoire, smaller groups of up to nine individuals have been observed. Interestingly, in resource-rich environments, these monkeys will live in small groups with small home ranges (around 74–123 acres/30–50 ha) and show terrestrial behavior. However, in resource-poor environments, larger groups will form, and they will have a larger home range (up to 346 acres/140 ha), allowing them to search further afield to find enough food to sustain the group. In these poorer environments, the home ranges of several groups may overlap extensively, but the groups don’t show much territoriality when encountering other groups. In fact, researchers have witnessed up to 300 individuals of different groups sharing a large food source without displaying aggression.

Communication
Like other members of the Chlorobecus genus, green monkeys display a wide range of communicative behaviors, using a diverse vocal repertoire, body gestures, and facial expressions to communicate with one another. Most well-studied are their vocalizations, which include grunts, screams, contact calls and alarm calls. These monkeys have different alarm calls for different predators, allowing the rest of the group to respond appropriately. For example, a bark in response to a leopard sighting will cause the monkeys to run to the relative safety of the trees, whereas a chirp in response to a snake sighting may cause the monkeys to stand bipedally and search for the snake in the grass.

Researchers have also found that green monkeys seem to change their vocal behavior in response to hunting pressure. Usually, they will emit territorial loud calls at dawn and sunset, alerting other groups to their presence. However, this also alerts human hunters to their presence and leads the hunters directly to the sleeping site of the group. In areas of high hunting pressure and lower density of monkeys, the monkeys become quieter, making them harder to locate. While it’s unclear whether this is a response to the hunters or a way to avoid competition with larger groups, it is certainly adaptive in shielding the monkeys from human hunters.

Reproduction and Family
Females will generally give birth to one infant at a time, who they will carry dorsally for the first few months of life. Inter-birth intervals can vary depending on the habitat, and may be every year, or every two years depending on the availability of food and water. Birthing season generally coincides with the rainy season and plentiful food for the mother and infant. Infants stay close to their mother initially, but then begin to venture further and further away from her as they grow, interacting with other infants and group members and learning the social rules of the group. They are usually weaned at around six months of age, though may still suckle in times of stress for comfort. Females reach sexual maturity at around three years of age, although they can give birth as young as three, whereas males tend to be later at five years. 

Females will usually stay in their natal group for their whole lives, with their place in the social hierarchy largely dependent upon their mother’s rank. Males, on the other hand, leave their natal group at sexual maturity and seek to join other groups, where they will have mating opportunities. Males must integrate into these new groups by forming bonds with the resident females and competing with the current group males for their place in the hierarchy. Males who become dominant generally have better access to females during the mating season, although non-dominant males are still usually able to father offspring. 

Ecological Role
​​Given their wide range across many countries and habitats, green monkeys likely play a diverse range of ecological roles depending upon their behavior and diet. They may be central to the seed dispersal of certain species of tree, such as acacia in some areas, whereas in other habitats they may play a more prominent role in the pruning of young trees as they eat leaves. 

Conservation Status and Threats
As with most primates, the primary threat to green monkeys comes not from leopards or eagles, but from humans. Green monkeys are hunted both as a source of bushmeat and for the live pet trade. Furthermore, they are also often killed in an attempt to protect crops. Increasing hunting pressure and the bushmeat trade is causing population decline in Burkina Faso, Côte d’Ivoire, Ghana, Guinea, and Sierra Leone. Habitat loss caused by mining, agriculture, and human settlements is also causing declines for many populations. While their International Union for Conservation of Nature conservation status is Least Concern (IUCN, 2020), many conservationists feel that this gives a false sense of security for a species that is currently in decline across most of its range.

In addition to humans, green monkeys are also prey for a range of animals, including chimpanzees, leopards, pythons, caracals, and eagles. It is likely that domestic dogs also prey on these monkeys when possible.

Conservation Efforts
Green monkeys are listed on Appendix II of the Convention on International Trade in Endangered Species (CITES) and on Class B of the African Convention on the Conservation of Nature and Natural Resources. 

The green monkey is present in many protected areas, including: Niokolo-Koba and Delta du Saloum national parks in Senegal; Comoé National Park in Côte d’Ivoire; Comoé-Leraba Hunting Reserve, Mare aux hippopotames de Bala MaB Biosphere Reserve, Bontioli and Deux Balé forêts classées in Burkina Faso; River Gambia National Park in Gambia; Badiar and Haut Niger national parks in Guinea; and Boucle du Baoulé National Park in Mali. 

However, many populations exist outside of protected areas and stronger conservation actions need to be taken to protect this species from the threats of habitat loss and hunting.

References:

  • Bi, S. G., Bené, J. K., Bitty, E. A., Koné, I., & Zinner, D. (2009). Distribution of the green monkey (Chlorocebus sabaeus) in the coastal zone of Côte d’Ivoire. Primate Conservation, 24(1), 91-97.
  • Galat, G. 1983. Socio-ecology of the Green Monkey (Cercopithecus aethiops sabaeus), with reference to four sympatric forest Cercopithecines (Cercocebus atys, Cercopithecus campbelli, C. diana, C. petaurista) from West Africa. State Doctorate thesis. Pierre and Marie Curie University.
  • Anh Galat-Luong, Karin Jaffe, Gérard Galat, 2016, Green Monkey, Alltheworldsprimates.org 
  • Gonedelé Bi, S., Galat, G., Galat-Luong, A., Koné, I., Osei, D., Wallis, J., Wiafe, E. & Zinner, D. 2020. Chlorocebus sabaeus. The IUCN Red List of Threatened Species 2020: e.T136265A17958099. 
  • Price, T., Ndiaye, O., Hammerschmidt, K., & Fischer, J. (2014). Limited geographic variation in the acoustic structure of and responses to adult male alarm barks of African green monkeys. Behavioral ecology and sociobiology, 68(5), 815-825.
  • Wiafe, E. D. (2019). Primates crop raiding situation on farmlands adjacent to South-West of Mole National Park, Ghana. Ghana Journal of Agricultural Science, 54(2), 58-67.

Written by Jennifer Botting, PhD, January 2022