GRIVET

Chlorocebus aethiops

Geographic Distribution and Habitat

Grivets are endemic to the savannas of eastern Africa in the countries of Ethiopia, Sudan, South Sudan, Eritrea, and Djibouti. They have adapted to thrive in both urban and natural environments. Their territories are usually based around rivers, as they need a dependable water supply during the dry season.

TAXONOMIC NOTE

Until fairly recently, grivets were generally categorized with and were often referred to as vervets. “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. 

Grivet range, IUCN 2008

Size, Weight, and Lifespan

Grivets can have a body and head length of anywhere between 16 and 32.5 inches (40–83 cm). Males are significantly larger than females, weighing in at 6.8–14 pounds (3–6.4 kg), while females have a weight range of 3.3–11 pounds (1.5–5 kg). Males are also have very long tails that can be up to 45 inches (114 cm) long.

Grivets can live to be 31 years old in both captivity and the wild. Although other sources list their lifespans as being 11–13 years in both captivity and the wild. The larger number is more likely accurate, as it comes from direct studies of the grivet; the smaller number comes from studies of the Chlorocebus genus as a whole.

Appearance

The grivet has a narrow black face with thick white sideburns and red eyes. The crown of their head and their backs can be red, brown, or gray. Mature males have bright blue genitals. Their tails, which are often longer than their own body, are used to maintain balance while walking on all four limbs. They have opposable thumbs as well as opposable big toes.

Photo credit: Charles J Sharp/Creative Commons
Diet

The most common foods in the grivet’s diet are figs and other fruits. They will often hurriedly stuff fruits into their cheek pouches so they may eat them at safer locations. They also eat acacia seeds, flowers, leaves, and bark. Grivets are omnivores and will eat insects as well as other small animals if given the opportunity.

Behavior and Lifestyle

Grivets are quadrupedal, meaning they walk on all fours to get around. They spend most of their lives on the ground and are adept swimmers, too, but they are still comfortable in the trees as well.

Fun Facts

Grivets were one of the animal species highly revered by ancient Egyptians.

Daily Life and Group Dynamics 

Grivets awake near sunrise and forage throughout the early morning. They rest midday and forage again in the late afternoon and evening. At sunset, they return to the trees to sleep for the night.

These Old World monkeys live in multi-male/multi-female groups that can range from 3 to 50 individuals, with most groups featuring about 25 monkeys. A group typically controls around 60 acres of territory. Females tend to stay with their natal group for life, while males are forced to leave the group after reaching puberty. Both males and females have their dominance hierarchies, which establish who gets first access to food sources, which in turn increases their reproductive success and benefits the health of their offspring. Grooming is an important part of building social bonds and females will often take care of the babies of high-ranking mothers, likely to build trust with them.

Communication

Grivets have a rich repertoire of vocal and visual communication. Their calls include: grunts, which represent aggression; barks from males that can either call for peace or show submission; and shrieks from females to call for help. Infants and juveniles give off purring noises when they are playing. There are also various chirping calls used to warn others of a nearby predator.

The grivet’s tail seems to be a good indicator of an individual’s attitude. When a monkey has a rigid and upright tail, it shows he is confident and is ready to show off his dominance. A monkey who lowers his tail as if trying to hide it is showing his submission and his wish to avoid conflict.

Their are several facial displays that are similar to those of most monkeys. These displays, which most often signify aggression, include staring, head-bobbing, and stretching one’s face by moving the ears and scalp back.

Reproduction and Family

Grivets usually mate during the dry season, between the months of July and November. With a gestation period of about 6 months, babies are often born around the start of the wet season in April and May. Babies are born with pink skin, which turns black after about 12 weeks. The young are weaned after 6 months as they gradually grow more independent.

Female grivets reach sexual maturity at about 4 years. Although not monogamous, females tend to only mate with a small number of males over the course of their life. They will stay with their natal group for life and will take part in allomothering, helping raise the offspring of other females in the group.

Male grivets reach maturity at 5 years of age, at which point the alpha males will force them to leave the group. After finding a new group, new males will start at the bottom of the hierarchy and work their way up the social ladder. Unlike females, male grivets will mate with as many females as they can. They show little to no interest in the babies; it is hard to say if they can even tell which babies are their own.

​Ecological Role

Because grivets often ingest seeds, they perform the crucial ecological role of seed dispersal. While the seed travels through the monkey’s digestive system, the monkey travels to other areas, where the seed will be defecated. There, the seed will sprout and be able to grow without having to compete for sunlight and other resources with its parent plant.

Conservation Status and Threats

The International Union for Conservation of Nature classifies the grivet as Least Concern (IUCN, 2018), stating that their population is numerous, widespread, and stable, with no major threats. Grivets are durable generalists who can easily adapt to changing environments.

Still, habitat destruction has forced grivets into less than ideal environments. There are numerous reports of grivets being killed by humans and preyed upon by feral dogs.

Conservation Efforts

The grivet is listed in Appendix II of the Convention on International Trade in Endangered Species (CITES), indicating that while the species is not threatened, trade must still be controlled. The species lives on legally protected habitats such as Awash National Park in Ethiopia. The IUCN states that their assessment of the grivet does need updating, as the least concern listing was last made in 2008. Since then, countries like Ethiopia have rapidly grown, meaning that habitat destruction may become a more pressing threat in the near future.

References:
  • https://www.iucnredlist.org/species/4233/10695029
  • http://pin.primate.wisc.edu/factsheets/entry/vervet/taxon
  • https://animaldiversity.org/accounts/Chlorocebus_aethiops/
  • [Karin Jaffe]. [Chlorocebus, aethiops, ]. © All the World’s Primates. N Rowe, M Myers, eds. (alltheworldsprimates.org).
  • Zinner, D., Pelaez, F., & Torkler, F. (2002). Distribution and habitat of grivet monkeys (Cercopithecus aethiops aethiops) in eastern and central Eritrea. African Journal of Ecology, 40, 151– 158.
  • Alelign, Aschalew and Yonas, Meheretu (2017) “Community Perceptions of Grivet Monkey Crop Depredation in the Ethiopian Highlands: Implications for Primate Conservation,” Human–Wildlife Interactions: Vol. 11 : Iss. 2 , Article 8.
  • https://animalcorner.co.uk/animals/grivet-monkeys/
  • http://www.theprimata.com/cercopithecus_aethiops/

Written by Eric Starr, November 2019