MONKEY

Facts

The Vervet Monkey (Chlorocebus Pygerythrus), or simply Vervet, is an Old World Monkey of the family Ceropithecidae native to Africa. The term “Vervet” is also used to refer to all the members of the genus Chlorocebus. The five distinct subspecies can be found mostly throughout Southern Africa, as well as some of the eastern countries. These mostly herbivorous Monkey have black faces and grey body hair colour, ranging in body length from about 40 cm (16 in) for females, to about 50 cm (20 in) for males.

In addition to behavioural research on natural populations, Vervet Monkey serve as a nonhuman primate model for understanding genetic and social behaviours of humans. They have been noted for having human-like characteristics, such as hypertension, anxiety, and social and dependent alcohol use. Vervets live in social groups ranging from 10 to 70 individuals, with males moving to other groups at the time of sexual maturity. Studies done on Vervet Monkey involve their communication and alarm calls, specifically in regard to kin and group recognition, and particular predator sightings.

The Vervet Monkey very much resembles a Grey Langur, having a black face with a white fringe of hair, while its overall hair colour is mostly grizzled-grey. The species exhibits sexual dimorphism; the males are larger in weight and body length and may be recognized by a turquoise-blue scrotum. Adult males weigh between 3.9 and 8.0 kg (8.6 and 17.6 lb), averaging 5.5 kg (12 lb), and have a body length between 420 and 600 mm (17 and 24 in), averaging 490 mm (19 in) from the top of the head to the base of the tail. Adult females weigh between 3.4 and 5.3 kg (7.5 and 11.7 lb) and average 4.1 kg (9.0 lb), and measure between 300 and 495 mm (11.8 and 19.5 in), averaging 426 mm (16.8 in).

When males reach sexual maturity, they move to a neighbouring group. Often, males move with a brother or peer, presumably for protection against aggression by males and females of the resident group. Groups that had previously transferred males show significantly less aggression upon the arrival of another male. In almost every case, males migrate to adjacent groups. This obviously increases benefits in regard to distance travelled, but also reduces the amount of genetic variance, increasing the likelihood of inbreeding.

Females remain in their groups throughout life. Separate dominance hierarchies are found for each sex. Male hierarchies are determined by age, tenure in the group, fighting abilities, and allies, while female hierarchies are dependent on maternal social status. A large proportion of interactions occurs between individuals that are similarly ranked and closely related. Between unrelated individuals, female competition exists for grooming members of high-ranking families, presumably to gain more access to resources. These observations suggest individual recognition is possible and enables discrimination of genetic relatedness and social status. Interactions between different groups are variable, ranging from highly aggressive to friendly. Furthermore, individuals seem to be able to recognise cross-group vocalisations, and identify from and to which Monkey, each call is intended, even if the call is made by a subadult male, which is likely to transfer groups. This suggests the members within a group are actively monitoring the activity of other groups, including the movement of individuals within a group.

Within groups, aggression is directed primarily at individuals that are lower on the hierarchy. Once an individual is three years or older, it is considerably more likely to be involved in conflict. Conflict often arises when one group member shows aggression toward a close relative of another. Further, both males and females may redirect aggression towards individuals in which both had close relatives that were previously involved in a conflict. This suggests complex recognition not only of individuals, but also of associations between individuals. This does not suggest recognition of other’s individual kinship bonds is possible, but rather that discrimination of social relationships does occur.

Vervet Monkey have four confirmed predators: Leopard, Eagle, Python, and Baboon. The sighting of each predator elicits an acoustically distinct alarm call. As infants, Vervets learn to make the variety of calls from observation alone, without explicit tutelage. In experimentation with unreliable signallers, individuals became habituated to incorrect calls from a specific individual. Though the response was lessened for a specific predator, if an unreliable individual gives an alarm call for a different predator, group members respond as if the alarm caller is, in fact, reliable. This suggests Vervet Monkey are able to recognize and to respond to not only the individual calling, but also to the semantics of what the individual is communicating. Vervet Monkey are thought to have up to 30 different alarm calls. In the wild, they have been seen giving a different call when seeing a human being approaching, leading researchers to believe that Vervet Monkey may have a way of distinguishing between different land and flight predators.

Mothers can recognise their offspring by a scream alone. A juvenile scream elicits a reaction from all mothers, yet the juvenile’s own mother has a shorter latency in looking in the direction of the scream, as well as an increased duration in her look. Further, mothers have been observed to help their offspring in conflict, yet rarely aid other juveniles. Other mothers evidently can determine to which mother the offspring belongs. Individuals have been observed to look towards the mother whose offspring is creating the scream.

Siblings likely provide the prevailing social relationships during development. Within social groups, mother-offspring and sibling interactive units are distinct groups. The sibling interactions are heavily supportive and friendly, but do have some competition. Contests primarily involve postweaning resource allocation by the common mother. For example, siblings have conflict over grooming time allocated by their mother. Offspring are usually not born in extremely close time proximity due to the interbirth period of the mother. This time can be reduced by use of an allomother. The clarity of the familial and sibships within a group may act as a form of alliance, which would come at relatively low cost in regards to grooming. Other alliances are shown through conflict with aggressive individuals that have acted against a closely related sibling.

Allomothering is the process when another individual besides the mother cares for an infant. In groups of Vervet Monkey, infants are the target of a tremendous amount of attention. Days after an infant is born, every member of the group inspects the infant at least once by touching or sniffing. While all group members participate in infant caretaking, juvenile females that cannot yet menstruate are responsible for the majority of allomothering. The benefit is mutual for the mother and allomother. Mothers that use allomothers are able to shorten their interbirth periods, the time between successive births. At the same time, allomothers gain experience in rearing infants, and had more success in raising their own offspring. Juvenile females discriminate in preference for the infant they choose to allomother, and usually choose siblings or infants of high-ranking individuals. When a mother allows her juvenile daughter to become an allomother for a newborn sibling, the mother decreases her own investment in the infant, while increasing the chances of successful rearing of her immature daughter.

Grandmothers and grandchildren share one-quarter of their genes, so they should be more likely to form affiliative relationships than unrelated members in a group. Not only do infants approach their grandmothers more often than unrelated members, but they also prefer their grandmothers compared to other adult female kin, not including their own mothers. Additional research has shown grandmothers show no preference over the sex of their grandchild. Interest in the grandchild spurred from the rank of the grandmother within a group. Higher-ranking grandmothers showed more interest in caring for their grandchildren when compared to low-ranking grandmothers. The presence of grandmothers has been associated with a decrease in mortality of infants.

Spiteful actions are extremely rare in the animal kingdom. Often, an indirect benefit is gained by the individual acting ‘spitefully’, or by a close relative of that individual. Vervet Monkey have been observed to destroy a competitor’s food source rather than consume or steal it themselves. While energy is being lost on destroying the food, an advantage is obtained by the individual due to an increase in competitive gain. This would be pertinent for a male that could be displaced within his group by immigrating males.

Female Vervets do not have external signs indicating oestrus, thus elaborate social behaviours involving reproduction do not occur. Typically, a female gives birth once a year, between September and February, after a gestation period around 165 days. Usually, only one infant is born at a time, though twins can occur rarely. A normal infant weighs 300–400 grams (11–14 oz).

The Vervet Monkey eats a primarily herbivorous diet, living mostly on wild fruits, flowers, leaves, seeds, and seed pods. In agricultural areas, Vervets become problem animals, as they raid bean, pea, young tobacco, vegetable, fruit, and grain crops. Animal foods of their diet include grasshoppers and termites. Raids of cattle egrets and weaver bird nests have been observed where the Vervets eat the eggs and chicks.