Geographic Distribution and Habitat
The Diana monkey (Ceropithecus diana) is an Old World monkey that is found in West Africa, from Sierra Leon to Ghana. They are primarily arboreal, meaning they spend most of their time in trees, and they live in primary tropical and terrestrial forests. Diana monkeys dwell in the upper canopy of the forest; however, they rarely make nests to sleep in.
Size, Weight, and Lifespan
From head to rump the male Diana monkey is 20-24 in (51-62 cm) long and their tails measure 30-35 in (76-90 cm) long. Males can weigh 11-12 lbs (5-5.4 kg). Females are slightly smaller than males. They are 16.5-17.7 in (42-45 cm) long with tails from 20.5-29 in (52-73 cm) long, and weigh 9-11 lbs (4-5 kg).
The average lifespan for both male and female Diana monkeys in the wild is about 20 years of age.
To remove or destroy totally; do away with; exterminate.
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The Diana monkey is a medium-sized primate with a slender build, long legs, and a long tail. Males and females are similar in appearance, though males are slightly larger in size. Their faces are black and outlined with white cheeks and a white beard. Their bodies are mainly black, but the front of their chest and inner arms are covered with white fur. A white stripe tends to run down the outer thighs and the rump appears to be covered with red and cream-colored fur.
Diana monkeys are omnivorous, meaning they eat a wide variety of foods such as fruits, flowers, leaves, insects, and invertebrates.
Behavior and Lifestyle
The behaviors and activities of the Diana monkey mainly take place in trees. They are not necessarily frequent leapers, since they are mainly arboreal (tree-dwelling) quadrupeds (traveling on all fours) and often climb while foraging for food. Diana monkeys are active during the day and make quite a noisy presence in the forest. These monkeys communicate with each other with vocal calls and visual cues in response to a predator or another troop of monkeys. Their calls are used as a warning signal as well as a threat to the source of danger to their group, though not usually aggressive.
Diana monkeys are named for the crescent-shaped white brow-band that resembles the crescent on the brow of the Roman goddess Diana, the protector of wildlife and woodlands.
Diana monkeys store food in their cheek pouches as they forage in the forest.
Diana monkeys’ tails are often carried in a question-mark-like curve.
Diana monkeys are dirunal, which means they are mainly active during the day. They have a unimale social structure, where only one male is found in each group. They live in groups of 15 to 50 individuals. Males tend to disperse from their natal group (the group in which the individual was born), while females remain in their natal group through adulthood.
The group size in many primate species, including Diana monkeys, can affect the group dynamics and social system. For example, Diana monkeys have a ranking system within their social group, and members are likely to compete for mates and resources. This is known as a dominance hierarchy, and arises when members of a social group interact with each other (often aggressively), causing both males and females to vary in their social rank. The maternal position in the group affects the position of her offspring, whether daughter or son. A female with a high social rank gives birth to high-ranking offspring. High-ranking females may have more foraging success or greater access to resources and mates. High-ranking males may have more mating opportunities. Lower ranking individuals have fewer mating opportunities and limited access to resources.
Diana monkeys use visual cues like facial expressions and body postures to communicate. Tactile communication, such as touch, is also very important for bonding and maintaining social relationships. This would include grooming, caring for offspring, and even mating. They also use vocalizations, especially to warn their troop if there is nearby danger. They often have distinct alarm calls for specific predators like leopards or eagles.
Other species also benefit when Diana monkeys use their alarm calls. Red and olive colobus monkeys often live near Diana monkeys and respond to these warnings. This relationship is successful because these species are not in competition since colobus monkeys have a slightly different niche and food resources. Colobus monkeys live in all levels of forests (including rainforests, gallery forests, and mature forests), while Diana monkeys stay high in the tree tops. However, their paths may overlap, as herbivores colobus monkeys mainly seek leaves and foliage.
Reproduction and Family
Diana monkeys have a polygynous mating system—one male mates with multiple females. They breed seasonally and give birth to one (and very rarely two) offspring at a time. Females nurse and care for their offspring for about six months. It takes the young about three years to reach sexual maturity. Daughters stay in their mother’s group up until they die, but males leave once they have matured.
The females will provision their young, meaning they will supply them with food and protection until they are mature enough to do so themselves.
Fruit eaters, such as Diana monkeys, have a large impact on seed dispersal throughout their forest habitat.
Previously assessed as Vulnerable, the Diana monkey is now listed by the International Union for Conservation of Nature as Endangered (IUCN, 2019), appearing on their Red List of Endangered species. Based on deforestation rates in Sierra Leone, Liberia, Guinea, and Ivory Coast, this species has lost at least 30% of its primary habitat over the past three generations (from approximately 1990-2018). Due to the combined negative impacts of hunting, which has resulted in the extirpation of a number of subpopulations and reduced others to levels that may not be viable over the long-term, Diana monkey numbers are suspected to have undergone a decline of 50% or more over this time period.
Due to the larger size of the Diana monkey, it makes them a target for hunting and it increases the demand for their meat. In Liberia, it is estimated that 50% of Diana monkey populations could have been lost in the last three generations due to hunting. The availability of firearms and limited wildlife protection contribute to the suffering of this primate. Subspecies of the Diana monkey, such as the roloway monkey (Cercopithecus roloway) are even more impacted by hunting and habitat loss than the Diana monkey. The roloway monkey is classified as Endangered (IUCN, 2016) and has lost an estimated 80 percent of their forested lands in Ghana.
In addition, to accommodate growing populations, human settlements in forested areas are increasing. Both the Diana monkey and the roloway monkey have lost a considerable amount of their land and a considerable amount of their populations. They are frequent targets for the bushmeat trade. Large forests are cleared for conversion to agriculture land, logging, and charcoal production. As the forest becomes more fragmented, this species is less able to establish home ranges, forage widely, and move safely through the forest.
The Diana monkey is listed in Appendix I in the Convention on International Trade in Endangered Species (CITES). CITES is an international agreement between governments that ensures that international trade in specimens of wildlife and plants does not threaten their survival. The Diana monkey is also listed on Class A of the African Convention on Conservation of Nature and Natural Resources. This also ensures environmental protection and sustainable use of natural resources.
The Diana monkey is also found on Mt. Nimba, which is a designated World Heritage Site, where they are protected and preserved.
It is often difficult to enforce the laws created for vulnerable and endangered species. With a growing human population, the need for more usable land tends to overlap into forested areas. In order to protect this species, large areas of mature forest need to be protected. With logging and agriculture still on the rise, it is difficult for a plan to be in full effect.
Written by Tara Covert, June 2018