Vervet Monkeys
Vervet monkeys are the only species at Monkeyland to swim in the dam. They can dive for special treats such as frogs and small water snakes. Swimming is a rare behaviour for a non-human primate! Other swimming primates are crab-eating macaques, Japanese snow monkeys and humans.

Physical Description: Vervet monkeys have a greyish-brown coat with white on their stomachs and on the undersides of their arms and legs. Their faces are black with white skin around their eyes and on their eyelids. Males have brightly coloured genitals. The scrotum is blue and the penis is red. Vervet males and females are very different in size. Males range from 420–600mm in height and 3.9–8kg in weight. Females are smaller, measuring 300–495mm and weighing around 3.4–5.3kg.

Habitat: Vervet monkeys are found in sub-Saharan Africa in 39 countries ranging from Angola to Zimbabwe and including South Africa. Exact distributions according to genetic differentiations are unknown, but the range is likely to be smaller than indicated by the IUCN and in this map. Extensive field studies on vervet monkeys have been conducted in Kenya.

They are quadrupedal and semi-terrestrial/semi-arboreal. Vervet monkeys can live in almost any area with water and sleeping trees available. They are found in a variety of habitats including humid rainforests, semi-desert environments and even in swamps.

Diet: Vervets are omnivores and will eat basically anything! They have cheek pouches like hamsters for storing food. Their diet includes such items as leaves, fungi, nuts and small vertebrates. Their favourite types of foods are fruit and flowers, which are seasonal. At the Monkeyland feeding platforms they are particularly fond of corn, sweet potatoes, cucumbers and guavas. In some areas, vervet monkeys are seen as pests because they are very good at stealing crops.

Life History: Gestation in the vervet monkey is around 165 days. Slightly over half of all infants born in the wild die, either from poor nutrition or predation. When vervets are first born, they are all black in colour with pink faces. By 3 months of age, they are greyish-brown like adults and only their faces are black.

Infants spend 90% of these first 3 months within 2m of their mother. Later on, siblings and other females will help care for the infant. They may be weaned by 3 months, but may also continue to nurse for up to 2 years if their mother does not have another infant to care for. By the time infants are 1 year old, they spend only 10% of their time with their mother.

The range of vervet monkeys and the distance travelled per day varies across geographical regions, season and resource availability. Vervets are preyed upon by large cats like cheetahs and lions and also other primates such as baboons and humans, as well as jackals and raptors. The lifespan of wild vervets is unknown because of high predation at field study sites. In captivity health begins to decline around 12 years of age.

Social Structure: Vervet monkeys live in mutli-male/multi-female groups of 7–76 individuals. The average group size is 25. Females remain in the group they were born into and have a dominance hierarchy based on matriline (female ancestry; mothers, daughters, sisters). This means that the daughter of a high-ranking female will automatically be high-ranking and the daughter of a low-ranking female will automatically be low-ranking.

Unlike females, males leave their natal group when they become sexually mature. When they leave their group for the first time, they often partner up with another male or join a group where they have a relative to facilitate their transfer. When they change groups again after this initial transfer, they move on their own and pick a group with no family relations. They will change groups many times over their lifetime and usually do so during the mating season. Within males there is also a dominance hierarchy which is determined by age and by interactions and fighting with the other males.

The top male is called the alpha male. The alpha male has access to the high-ranking females. A single male is dominant over a single female, but when females form a group, they can dominate individual males. Territoriality in vervet monkeys is facultative, which means it varies depending on environmental condition. Factors that affect territoriality include habitat, season, the number of predators, the number of vervets, and the number of resources. For example, when resources are easily found within a small area or when resources are seasonal, the group will defend a territory by chasing other groups away.

However when resources are broadly distributed, vervets are not territorial. Energy is spent foraging rather than protecting a large area.

Communication: Communicative behaviours have been well documented in wild vervets. They have distinctive alarm calls for certain types of predators. For example, vervet monkeys will run for the trees after a leopard alarm call, but look to the air and hide in thick brush when the eagle alarm call is given. If they hear the snake alarm call, vervets will look about in the grass to locate the predator and mob it as a group. It takes some time to learn about these alarm calls and make the appropriate response.

Young vervets often make errors. Vervets in the West Indies have also been observed to use silent visual signals to alert other vervets to a predator (usually a dog or human). The group will appoint one male to keep guard during foraging. If a predator is seen, the “guard” will take cover which is the group’s cue to hide as well. One other interesting form of visual communication is the “splaylegged red, white and blue display” used by males. They expose their genitalia to warn males from other troops and also to display dominance over males in their own troop.

Mating: Vervet monkeys mate during a specific time period of the year. The mating season varies somewhat with geographic location but is roughly April–June in wild African vervets. This allows for infants to be born after the rainy season when more food is typically available. Females are sexually mature at the age of 4 and begin to produce offspring about a year later. Females give birth every 1–2 years.

They cycle every 32.5 days and menstruate like women. Cycles are regular during the breeding season and usually irregular the rest of the year. Males are sexually mature at the age of 5 but are more likely to mate when they are a bit older and fully-grown.

Other Behaviour: Both older brothers and older sisters defend their younger siblings. Like other primates, vervet monkeys sleep in trees at night. They prefer trees in wooded areas that are around 7–8m in height. Female vervets are particularly attracted to males with a very blue scrotum, since this is a sign of good health and high dominance rank within the group.

Conservation: Vervet monkeys are classified as Lower Risk/Least Concern by the IUCN due to their wide range. Numbers are declining however. International trade of vervets is regulated by CITES. Ghana is the only vervet range country that has not signed the CITES agreement. Ghana nevertheless tries to limit how many vervets are exported or killed. Vervets are killed in some regions for the bushmeat trade.

They are also popularly kept as pets. In South Africa, infant vervets can sell for R500 to R1500. Very quickly however, owners come to realize that their “pet” is highly destructive and the vervet is abandoned, sold or killed. For wild vervets the situation is just as dismal. Vervet monkeys unfortunately do well living around agriculture and urban areas. When the natural areas where wild vervets normally find food disappear due to growing human populations, these versatile monkeys manage to survive by stealing food from people in agricultural or urban areas.

For this reason, they are commonly viewed as pests and killed after they raid crops and dustbins. Currently vervet monkeys can be killed without a permit and by any means in South Africa. Vervet monkeys are also frequently used in biomedical research worldwide.

They are often in blood pressure studies as they naturally develop high blood pressure. In addition, SIV (simian immunodeficiency virus) has been found in wild vervet populations, making the vervet monkey the subject of many HIV/AIDS studies.

The Vervet Monkey Foundation in the Letaba District protects and rehabilitates vervet monkeys and you can find out more about their work at www.enviro.co.za/vervet. There are a number of other organisations which support vervet conservation worldwide that can be found on the web. Please consider supporting a primate conservation organisation of your choice.

Did You Know? Vervet monkeys are the most prevalent African monkey. There are at least 6 species of vervet monkeys. Vervets were formerly classified in the genus Ceropithecus but are now grouped under the genus Chlorocebus.