VERVET

Chlorocebus pygerythrus

Geographic Distribution and Habitat

Vervets (Chlorocebus pygerythrus) are native to eastern and southern Africa. They make their homes in the forests, savannas, and shrublands of Botswana, Burundi, Eswatini, Ethiopia, Kenya, Malawi, Mozambique, Rwanda, Somalia, South Africa, United Republic of Tanzania, Uganda, Zambia, and Zimbabwe.

They like to live near rivers, lakes, or other bodies of water where they can drink daily, and they prefer to sleep in tall trees. While vervets inhabit a wide area, it is not a continuous range; rather, groups may be small and isolated from each other.

The miombo woodland make up much of the vervets’ home range, but they have also adapted to be able to survive and even thrive in a range of environments including secondary and disturbed forests, plantations, rural gardens, and urban areas.

TAXONOMY IN TRANSITION
Until fairly recently, “vervet” referred to all members of the genus Chlorocebus, including grivets, green monkeys, tantalus monkeys, malbroucks, and vervets themselves. ​There is still a great deal of overlap in data, and resulting confusion. The species within the Chlorocebus genus are quite similar yet have some distinguishing characteristics, especially as relates to their geographic ranges, food sources, threats, and life spans. As of this writing, six Chlorocebus species are recognized. The vervet species includes four vervet subspecies:
  • The Hilgert’s vervet monkey (Chlorocebus pygerythrus hilgerti) ranges in Ethiopia, Kenya, South Sudan, Tanzania, and Uganda.
  • The Pemba vervet monkey (Chlorocebus pygerythrus nesiotes) ranges in Tanzania. This subspecies is listed as Vulnerable.
  • The Southern vervet monkey (Chlorocebus pygerythrus pygerythrus) ranges in Botswana, Mozambique, South Africa, and Zimbabwe.
  • The reddish-green vervet monkey (Chlorocebus pygerythrus rufoviridis) ranges in Burundi, Congo, Mozambique, Rwanda, Tanzania, Uganda, and Zambia.​
Vervet range, IUCN 2019

Size, Weight, and Lifespan

Vervets are sexually dimorphic. Males are larger than females and are easily differentiated by their bright blue scrotum. Males weigh between 8.6 and 18 lb (3.9–8 kg), with a head-to-toe length of 19 in (49 cm) and a tail longer than their body at 24–30 in (60–75 cm).

Females weigh between 7.5 and 12 lb (3.4–5.3 kg), are 18 in (44.6 cm) long, and have a tail length of 19–26 in (48.5–65.3 cm).

They can live up to 18 years in the wild and up to 30 years in captivity.

Appearance

These medium-sized monkeys have a long tail and whitish-gray fur. They have patches of color on their heads, backs, and sides. The color of these patches vary with subspecies in hip and trendy Mother Nature balayage—from olive-green and reddish-brown to a mottled black and gray.

They have black feet, hands, and ears. Their winsome faces are black, highlighted with white hair on their eyebrow ridges and white cheek whiskers. They have dark brown eyes that invite connection.

Vervets have gray sitting pads. Sitting pads (found in all Old World monkeys and gibbons) allow the vervet to comfortably sit and sleep upright. They have long arms and legs that they use to walk on quadrupedally.

Males have bold and distinctive coloring on their genitals of red, white, and blue—red penis, white perineal stripe, and bright blue scrotum. Females have a blue vulva, pink perineal, and no stripe. 

Infants are born with a pink face and black or brown hair; by the third month their face darkens, contrasting their white cheek whiskers. They have their adult coloration by six months.—

Diet

While most of their diet is plant-based, vervets, like humans, are opportunistic omnivores. Vervets will eat what is available! They eat primarily from the acacia tree—eating leaves, stems, flowers, pods, and bark. They eat these hand to mouth. 

Seasonal changes affect the diet of vervet monkeys. When fruit, seeds, and flowers are available, vervets dine well on the bounty. Wildfires occur during the dry season and can disrupt the food supply so that during the rainy season—which normally provides their most favored foods—the vervets might not have enough. 

During the dry season, when food and water are scarce, vervets have been observed eating anything possible, such as lizards, rodents, insects, invertebrates, shoots, roots, bird eggs, birds, fungi, bark, and grass. They can catch flying insects by leaping and catching them between two hands.

The gum from the acacia tree is available year round. They also eat gum from the fever tree, or gum from other trees, and gum makes up an important part of their diet. They scrape the gum off the bark directly with their mouths. 

They like to clean their food by rubbing it on an object, or even just between their hands.

Where habitat loss has left vervets living in greater proximity with human primates, they have adapted to eating some human food. In more highly populated suburban areas, vervets may raid the crops of local farmers. They have also been known to raid trash cans and break into houses and help themselves to food.

Behavior and Lifestyle

Vervets are active in the day (diurnal) and spend most of their day foraging for food, climbing trees, and loping along the ground. They are quadrupeds on the ground—traveling via their hands and feet. They may spend as much time on the ground as they do in the trees, or in some cases, more. They are described as both semi-terrestrial and terrestrial by researchers, as the amount of time they spend on the ground depends on the particulars of their location.

The distinctive acacia trees of east and south Africa are vital to the animal kingdom, and the vervet lifestyle is very connected to the acacia tree. The acacia tree is their preferred tree for feeding, protection, and sleeping. The tree also gives some protection against predators, of which they have many—from raptors and big cats to pythons and even baboons.

With so many predators, it stands to reason that vervets spend as much time visually scanning the area as they do anything else in a day. As much time is spent on the lookout as is spent foraging for food.

Fun Facts

In addition to skillfully navigating the treetops, vervet monkeys are also adept at swimming.

Vervet infants are known to form special connections to their grandmothers, preferring them to everyone else (with the exception of mom).

Excavations suggest that there were vervets in households in ancient Egypt.

Daily Life and Group Dynamics 

Vervets are very social, and live in hierarchical multi-female and multi-male groups. Group sizes vary based on environmental factors, and on average, the smaller groups are around 10, larger groups around 40.

A day in the life of a vervet finds them up and active in the morning, foraging first in the tree in which they are sleeping. If it is the acacia tree, they will forage everything from the flower to the gum. 

Then they move to the ground and spread out, with no apparent leader, as they look for food. They can be seen turning over logs and branches, scratching dirt, leaping for insects. 

Brunch time is spent looking for food in shrubs (or eating the shrubs themselves) or other plants. Then, as is appropriate for having such a busy morning, they take a nap. After a nap, they will forage in trees or on the ground for food. Of course, all this time is also time spent with their group, and dynamics are always part of the day.

Males and females both have clear hierarchies within their group. Females have more consistent, stable hierarchies, with daughters often inheriting status from their mother. Individuals who are not closely related to the high-ranking members will vie for attention and grooming from those in a higher position. They may form coalitions or alliances. 

Females stay in their natal group for life, but there have been cases where two groups will fuse together. Males leave their natal groups when they become sexually mature and join a new neighboring or adjacent group. 

As males do not stay within their natal groups, this means they need to prove themselves to their adopted group, and there is more instability about rank. Males assert their dominance with their voices and with performative displays. Males may even transfer between groups a number of times in their lives.

They are territorial and will defend their space making vocal calls and shaking tree branches at would-be intruders. They live in boundaries that are between 0.02–0.04 square miles (5–103 ha). The area of a group depends on available space and number of competing groups, and there can be some territorial overlap.

Adults and older adolescents (over 3 years of age) of both sexes may participate in aggressive displays with those outside the group when conflict arises. This usually occurs when members of another group enter their territory. Domestic spats within groups occur occasionally, as well as members fussing over more grooming time. 

Allogrooming, meaning everyone participates in grooming the others, is key to helping groups maintain cohesion. Members of the group take turns having others pull parasites and debris from their fur. Sometimes, as they are grooming, they find themselves muzzle to muzzle in a way that observers have called a “kiss.” (Awww…)

When the sun starts to set, they will climb back into their sleeping trees. They sleep in the taller trees, in the highest limb that can securely hold their weight. They like to sleep in the same trees again and again. Smaller groups may share a tree while larger groups will split into smaller groups and sleep in neighboring trees.

Communication

Vervets use a great deal of verbal and visual communication in their group interactions. They are very vocally expressive. They often use lip smacks and teeth chatters–possibly to let each other know they are friends. Their calls are described as squeals, barks, purrs, and “chutters.” Scientists have so far determined that the vervets can understand and respond to 36 different vocalizations.

Different alarm calls designate different types of predators. These are used to warn the group about large cat, eagle, and snake predators. When a leopard, for instance, is seen, a short call is given and the monkeys scatter into the trees. If an eagle is spotted, one of the group will emit a series of short grunts. Others in the group have been observed to run toward nearby bushes and to look up to gather more information on the possible predator. Upon seeing a snake, short “chutter chutter” sounds are vocalized and monkeys will look around at the ground for the predator. There is also a vocalized warning for baboons and humans that the group members know—they respond by heading for cover.

The most common noise within group communication is low “grunts” to greet others or to warn that an unknown primate is moving into their territory. 

Vervets also communicate with visual and performative displays, many of these around asserting dominance. One such display scientists call the “red white and blue”—a dominant male holds up his tail and circles back and forth around a subordinate showing off the full color of his genitalia. This shows he means business!

Reproduction and Family

While there may be notable performative displays around dominance, courtship seems to be a more simple affair. Males initiate interest, but females decide whether or not they will mate—or she may just move away from him. Or bite! But if she is interested, she may be interested all year long. Females continue mating even after they are pregnant. Higher-ranked males mate more than subordinate males, but rank matters less during peak times of the breeding season.

Breeding season varies from country to country, depending on rainfall and food availability. After about 5 and a half months, babies are born at the end of the rainy season when food is more abundant and there is a better chance of survival for mother and infant. Babies weigh less than a pound (300–400 g). A baby clings to the front of its mother’s body. As the mother walks on all fours, the baby must hold on tight!

In the first two months, babies feed at different times than their mothers, but after three months they eat at the same times as their mothers and the same food. Males and females eat the same things.

Males do not participate in the raising of the young, but all the females of a group do. Vervets are raised through allomothering. After the first three weeks all females–aunties, grandmothers, sisters, and adolescent females–will start to help care for the infant. Juvenile females are especially interested in helping, and will seek out mothers with infants and groom the mothers just for a chance to hold and cuddle the infant. Adolescent females will dote on the younger vervets and carry the infant against their chest, walking on three limbs, or hold the infant in their arms and run on both legs. This caretaking helps the younger females learn how to carry and take care of their first infant. It may also increase their social standing, and they form relationships with the infants that last a lifetime. A regular vervet babysitting club!

At 3 to 6 months of age, babies begin to be weaned and mothers carry them only in emergencies. Meanwhile, the babies start to form play groups with other young vervets. Babies are fully weaned after a year to 18 months, and play is an important part of their socialization.

Both males and females are able to reproduce around the age of 5. A female vervet in her reproductive prime can have one baby every one to two years.

Males transfer to other groups right before they reach sexual maturity, and may leave with other members of their peer group. These transfers happen rather quickly, and no males remain solitary for more than 2 months. Males may transfer groups several times during their life. Most of these transfers are during mating season, when the females in the new group are open to their advances.

Females generally stay with their natal group for life—only when there are great losses in group numbers will they fuse with other groups.

Ecological Role

​Vervets play an extremely important role in the ecology of the African continent. Many animals rely on the availability of vervets as a food source. Vervets repopulate the trees in the environment through dropping excrement, which contains seeds from the many fruits in their diet.

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Vervets are listed as Least Concern on the International Union for Conservation of Nature Red List of Threatened Species (IUCN, 2016).

Vervets, while still abundant, are declining overall in population and need protection from humans in particular. Because vervets do not live in continuous areas, local groups may decline or even go extinct in certain areas. Habitat loss is the greatest threat to vervets. Vervet conservation organizations report that vervet groups were more than double in their sizes a century ago.

Vervets may be persecuted as pests in tourist areas or farms. The ongoing feud between landowners and monkeys usually results in vervet monkeys being killed or captured and sold for medical research. Vervets are also hunted for bushmeat in certain rural areas. Baby vervets are highly susceptible to predation from pythons, leopards, raptors, and baboons. Extreme distress and death from lack of food and water during the dry season also impacts vervet mortality.

Vervets are used in biomedical research and human behavioral research because of their similarity to humans, both genetically and socially. In experiments they will suffer from anxiety, hypertension, and alcoholism. 

Conservation Efforts

Vervets are listed on 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. They are listed on Class B of the African Convention on the Conservation of Nature and Natural Resources.

Some of the conservation efforts intended to assist the vervet monkey are land and water protection, education, international legislation, research, and monitoring. 

Several organizations and individuals rehabilitate monkeys who are found injured or orphaned. Educators go to villages to raise awareness of the need to conserve wildlife, and primates in particular. The Vervet Monkey Foundation in South Africa and the Pan African Sanctuary Alliance (with 22 members in 13 African states) are two of these organizations. These groups are working with governments to step up patrols of wildlife areas, educate the next generation, give medical treatment and long-term care, and assist in apprehending wildlife poachers.

References:
  • ​​​Acacia. (n.d.) In San Diego Zoo Wildlife Alliance Animals & Plants. Retrieved December, 2021. https://animals.sandiegozoo.org/plants/acacia
  • Birmingham, D. (2020). Central Africa. In Encyclopedia Britannica, Retrieved December 27, 2021, from https://www.britannica.com/place/central-Africa.
  • Butynski, T.M. & de Jong, Y.A. (2019). Chlorocebus pygerythrus. The IUCN Red List of Threatened Species 2019: e.T136271A17957823. Retrieved December, 2021, from  https://dx.doi.org/10.2305/IUCN.UK.2019-3.RLTS.T136271A17957823.en
  • Isbell, L.A. and Jaffe, K.E. 2013. Chlorocebus pygerythrus Vervet Monkey. In: T.M. Butynski, J. Kingdon and J. Kalina (eds), The Mammals of Africa. Volume II: Primates, pp. 277–283. Bloomsbury Publishing, London.
  • Jaffe, K. (n.d). Chlorocebus, pygerythrus. In All the World’s Primates. Rowe N, Myers M. eds. Retrieved December, 2021 from https://alltheworldsprimates.org/Members/Home.aspx  
  • Miombo Woodland (n.d.) In World Wildlife Fund for Nature. Retrieved December, 2021 from  https://wwf.panda.org/discover/knowledge_hub/where_we_work/miombo_woodlands/
  • Vervet Monkey (Chlorocebus pygerythrus) Fact Sheet. (c2014-2020). In San Diego (CA): San Diego Zoo Wildlife Alliance. Retrieved December, 2021 from http://ielc.libguides.com/sdzg/factsheets/vervet 
  • Vervet monkey (n.d.) In A-Z animals. Retrieved December, 2021 fromhttps://a-z-animals.com/animals/vervet-monkey/
  • Vervet Monkey. (n.d.) In Animal Spot. Retrieved December, 2021 from https://www.animalspot.net/vervet-monkey/
  • Vervet Monkey (n.d.) In African Wildlife Foundation. Retrieved December, 2021 from https://www.awf.org/wildlife-conservation/vervet-monkey
  • Vervet Monkey. (2021, November 19). In Wikipedia. Retrieved December 2021 from https://en.wikipedia.org/wiki/Vervet_monkey
  • Vervet Monkey Foundation. In Vervet Monkey Foundation. Retrieved December 2021 from https://vervet.za.org/

Written Laura Lee Bahr, December 2021