The Green Monkeys of St Kitts and Nevis

Within the context of the twin island federation of St Kitts and Nevis and other Caribbean countries, a dynamic conflict is unfolding between humans and ‘alien invasive’ Green vervet monkeys (Chlorocebus aethiops sabaeus). In order to fully apply management interventions which may alleviate this conflict, one needs to understand the social, economic and political complexities pertaining to this dynamic human-nonhuman primate interface.

Humans are literal and figurative kin to other primates, with whom many of us coexist in diverse social, ecological, symbolic, conflictual, and even hopeful contexts. Anthropogenic action is changing globally. With their adaptability, intelligence, agility, dexterity, and high levels of sociality and cooperation nonhuman primates present one of the greatest and most complex challenges to human non human primate conflict mitigation. In particular, vervet monkeys exhibit unrivalled levels of contact with humans, are considered one of the most troublesome nonhuman primate genus and are reported as throughout Africa and countries where they were historically introduced. Although vervet monkeys are not currently listed as threatened or endangered (IUCN 2010), yet a Protected Species in South Africa, the high levels of human non human primate co-existence and the associated conflict seen throughout Africa (Strum 1994, Hill 2005, Strum 2010) are likely to increase as human populations continue to expand and land development proliferates. 

Ethnoprimatology, the combining of primatological and anthropological practice and the viewing of humans and other primates as living in integrated and shared ecological and social spaces, is becoming an increasingly popular approach to primate studies in the twenty-first century. This approach plays a core linking role between anthropology and primate studies and may enable us to more effectively assess, and better understand, the complex ecologies and potential for sustainability in human–other primate communities. The last two decades have witnessed a drive towards finding innovative and effective solutions to the complex management difficulties associated with HWC. Organisational innovation in wildlife management has increasingly centred on the engagement of stakeholders in decision-making and implementation of wildlife management actions (Raik et al, 2005:110).

In their natural range Chlorocebus aethiops sabaeus (the green vervet monkey) is found almost exclusively in West Africa. It ranges from Senegal to the White Volta River in Ghana and can be found in many other African nations. Chlorocebus aethiops sabaeus was introduced to the Caribbean islands during extensive slave trading in the 1600s. These islands include St. Kitts, Nevis, and Barbados. (Cawthorn Lang, 2001; Zinner, et al., 2009).

Although Green vervet monkeys prefer specific environmental conditions, they easily adapt to a wide range of habitats. In Africa, Green vervet monkeys live south of the Sahara Desert in forests that border woody grasslands. These areas are normally characterized by low, bushy foliage and tall grasses. Green vervet monkeys live near the edges of these transitional forests and can be found crossing savannas between forest edges. They avoid the interior of dense, wet forests. Green vervet monkeys also have colonized coastal regions of West Africa, although this is a deviation from habitat norms. Recent habitat destruction and deforestation are thought to have contributed to these recent migrations. In the Caribbean, Green vervet monkeys occupy a variety of habitats including mangrove swamps, agricultural sectors, and highly populated urban settings. (Cawthorn Lang, 2001; Dunbar, 1974; Wolfheim, 1983; Zinner, et al., 2009).

These medium-sized monkeys are covered in thick golden fur with a green tint, which is how they get their common name, Green vervet monkeys. The face is hairless, but is covered with dark blue skin outlined by a soft line of white fur. Like other monkeys, they have long, slender, semi-prehensile tails. Males and females are sexually dimorphic. Males can weigh between 4 and 8 kg and measure an average of 500 mm in length. Adult females normally weigh between 3.5 and 5 kg and measure approximately 450 mm in length. Males have blue scrotal regions and distinctly red penises. The combination of colours is said to present a distinctive “red, white, and blue” display.

Green vervet monkey locomotion varies little, regardless of habitat or substrate. In almost all circumstances, they travel quadrupedally on the ground or in tree canopies. Being relatively light, Green vervet monkeys are able to nimbly travel on the tops of branches using all four limbs. (Cawthorn Lang, 2001; Skinner and Smithers, 1990; Young, 1998).

Green vervet monkey social structure revolves around alpha males. These males control interactions and contact of males and females. The alpha male dictates which males mate with females in this polygymous mating system and dominate most of the mating. (Cawthorn Lang, 2001). In their natural home range Green vervet monkeys are seasonal breeders, breeding between April and June. In the area typically inhabited by Green vervet monkeys, these months are characterized by heavy rainfall. Abundant rainfall results in an exponential increase in available food and nutritional resources. It is thought that this particular breeding season is an adaptation to take advantage of abundant resources. Green vervet monkeys breed approximately once a year. The time interval between each breeding attempt depends on the success or failure of the previous pregnancy. Females reach sexual maturity in 2 years and males in 5 years. Infant mortality is high, resulting in a loss of about 57% of all newborns. (Cawthorn Lang, 2001; Cheney, et al., 1988; Fairbanks and McGuire, 1985; Young, 1998). Observations of monkeys by Nevisian farmers indicate that birthing occurs all year round and is “rampant”. It can be hypothesized that the hunting of alpha males has altered the social dynamics and hierarchical structure of troops leading to higher birthing rates.

Green vervet monkeys are highly social. Grooming behaviours and gender relationships suggest underlying social hierarchies. Total group number can vary greatly, from 7 to 80. Male and female Green vervet monkeys partake in inter-group emigration. After reaching sexual maturity, adults move from group to group with closely related family members. This helps to avoid predation, reduce inbreeding, and increase the spread of desired genes. Small overlaps of Green vervet monkey territory exist in many habitats. Alpha males establish dominance through physical fighting or scrotal displays. Dominance rank determines access to mates and resources. Green vervet monkey alpha males limit the proximity of other males to females and defend their territory with physical aggression against alien males. Such encounters typically are limited by environmental conditions and resource availability. It is only when food or habitat becomes scarce that territorial encroachment occurs. (Cawthorn Lang, 2001; Cheney, et al., 1988).

Green vervet monkeys are very vocal primates. Vocalizations serve mainly to alert local members to danger. Using distinct vocalizations, Green vervet monkeys are able to differentiate among various predators and levels of danger. Green vervet monkeys have evolved a unique call for each predator. Vocalizations may be altered outside of their natural range where no natural predators exist and in the case of St Kitts and Nevis may be limited only to the presence of humans and dogs. Males are also capable of communicating through body language. Using brightly coloured genitalia, Green vervet monkeys can signal danger to other monkeys without vocalizations. This form of non-verbal communication is also a method of establishing social hierarchies and male dominance. A more subtle mode of communication is through facial expressions. Research demonstrates that facial expression is correlated with emotional state. Feelings of anger, elation, and even frustration are manifested in distinct facial expressions. It is possible that Green vervet monkeys use facial expressions to indicate danger or satisfaction, depending on the circumstances. (Cawthorn Lang, 2001; Cheney, et al., 1988; Peters and Ploog, 1973; Skinner and Smithers, 1990).

Green vervet monkeys are both frugivorous and folivorous depending on the availability of leaves and fruit. Green vervet monkeys adapt to available resources depending on the time of year and environmental conditions. During the dry season or after a fire, little fruit is available. In their natural home range Green vervet monkeys forage across short expanses of grassland eating available plants. Nonetheless, fruits are preferred to leaves and less nutritious grasses commonly found in natural home ranges, like savannas. When rain is plentiful, fruits become more abundant. Fruits typically are collected in the trees and common fruit species eaten include wild bananas, papayas, and mangos. In the wild, Green vervet monkeys commonly use a mouth pouch to store and carry food as it is found. This behaviour protects valuable food from other consumers and allows Green vervet monkeys to continue collecting food for extended periods. (Dunbar, 1974; Young, 1998; Dunbar, 1974; Young, 1998). Like elsewhere in the world, primates are opportunistic feeders when living in close proximity to human habitation and this has led to an extensive negative impact on the agricultural production of Nevis.