TANTALUS MONKEY

Chlorocebus tantalus

Geographic Distribution and Habitat
The tantalus monkey (Chlorocebus tantalus), a type of Old Word monkey, inhabits various geographical regions of sub-Saharan Africa between Ghana and Sudan and as far south as Uganda.

The tantalus monkey is one of six similar—but ultimately distinct—monkey species in the genus Chlorocebus. Not too long ago, all six species were commonly grouped together as “vervets.” Until quite recently, as the species were being distinguished, the tantalus monkey was considered to be a subspecies of grivet (Chlorocebus aethiops). More recent study using molecular and morphological data supports the treatment of tantalus as its own species.

Just like others in the Chlorocebus genus, tantalus monkeys are extremely adaptable primates, capable of living in many types of habitat including degraded forests and urban areas. Tailored for both ground and tree life, they thrive particularly well at the edge of forests or in areas of savanna where trees are abundant, never straying far from a fresh source of water.

Tantalus monkey range, IUCN 2020

Size, Weight, and Lifespan
Tantalus monkeys are a bit smaller than their other Chlorocebus cousins, with the average female tantalus weighing 7 pounds (3.36 kg). As a sexually dimorphic species, males are slightly larger than females, weighing approximately 10 pounds (4.6 kg).

Data describing the tantalus’ lifespan does not exist at this time. If they are at all like their vervet cousins, heavy predation would mean that wild monkeys’ lives are typically cut short, suggesting few live to old age.

Appearance
Tantalus monkeys closely resemble vervet monkeys but are smaller in stature. Their dark eyes are hardly distinguishable from their black faces. Long white hairs flare outward from their cheeks and temples, partially covering their ears. A half-crown of shorter white hair ridges their brows. Yellowish brown fur extends from the top of their heads, down their shoulders and backsides, all the way to the tip of their long tails. The fur on their arms and legs is grayer in hue than on the rest of their bodies. The skin on their hands and feet matches their faces. Females are noticeably smaller than males, and have plain white fur covering their abdomen. Males’ undersides are also mostly white, except for the orange hairs around their bright blue scrotums.

Photo credit: Bernard DUPONT/Creative Commons

Diet
Tantalus monkeys are eclectic eaters. Their omnivorous diet consists of almost anything—leaves, gums, seeds, nuts, grasses, fungi, berries, flowers, buds, shoots, invertebrates, bird eggs, birds, lizards, rodents, and other types of vertebrate prey—though they have a strong preference for fruit.

Their diet depends on what a season provides—and vary from one habitat to the next. For instance, in certain areas, troops of tantalus monkeys consume animal prey at a notably higher rate than tantalus troops in other areas.

What Does It Mean?

Alarm call:
Specific calls that individuals in a troop make to warn other members of their group of imminent danger – such as predators.

Alloparent: 
An individual other than the biological parent of an offspring that performs the functions of a parent (as by temporarily caring for an infant).

Cheek Pouches:
Pockets on the side of the head between the jaw and the cheek that some animals have to store food.

Dominance hierarchy:
A type of social hierarchy that arises when members of a social group interact, often aggressively, to create a ranking system. In social living groups, member are likely to compete for access to limited resources and mating opportunities. 

Hierarchy:
A system of organization in members of a group who are ranked one above the other according to status or authority.

​​Natal group:
The group into which an animal is born.

Omnivorous:
Having a diet that consists of food of both plant and animal origin.

Semi-terrestrial:
Living partially, but not wholly, on the ground.

Subspecies:
A population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.

Visit the Glossary for more definitions

Behavior and Lifestyle
Tantalus monkeys are diurnal primates. They spend portions of their day both on the ground and in trees, where they forage for whatever happens to be in season. Their semi-terrestrial lifestyle means they exclusively live at forest edges or in parts of savannah where trees are plentiful. At night, troops clamber up into trees, where they sleep in relative safety from predators.

Tantalus monkeys routinely travel up to 2 miles (3 km) a day. When on the ground, they walk on all four limbs. Their cheeks are equipped with special pouches where they store snacks—convenient for when they are on the move between foraging spots. In trees, their movements are quite a bit more limited compared to other monkey species. They never leap or jump between branches.

Due in part to their ability to exploit both ground and tree resources, tantalus monkeys are notoriously adaptable creatures. Capable of living in a wide variety of habitats (including cities), their main caveat for survival seems to be direct access to fresh water, which they must drink regularly or risk dehydration. Like others in their genus, tantalus monkeys never stray far from rivers and lakes. Perhaps it is this special relationship with water that has made Chlorocebus one of the few primate genera capable of swimming!

While genetic research has established tantalus as a distinct species, its behaviors as distinct from others in its genus have yet to be determined. To some extent, the tantalus lifestyle is probably quite similar to that of their cousin, the vervet, who has been more thoroughly studied.

Like vervets, tantalus monkeys may benefit from color vision, an adaptation that helps them in a number of substantial ways such as differentiating between ripe and unripe fruit.

Fun Facts

The tantalus monkey has a complicated taxonomy that needs to be further researched.

Tantalus monkeys spend most of their day on the ground, foraging for food and traveling up to 2 mile (3 km) a day.

Their habit of wandering between forest patches makes tantalus monkeys important seed dispersers.

Daily Life and Group Dynamics 
Tantalus monkeys live in troops of 11 to 70 individuals. A troop spends the majority of its day on the ground foraging for food. When resources run low, the monkeys migrate together to a new feeding ground.

Since tantalus monkeys are not a well-studied species on their own, we can glean from what we know of vervets, their better-studied cousins, to obtain some of their story.

A vervet troop is socially dynamic and functions according to a strict hierarchy. Rank is passed to a monkey through his or her mother. The highest ranking members are always males. These monkeys are responsible for protecting the group. While the rest of his troop forages, a dominant male monkey assumes his position atop a conspicuous perch. In his role as sentinel, he watches for predators. When he spots a threat, he raises an alarm. His alarms are often vocalizations that specify what type of threat is nearby. In this way, he not only warns his subjects of danger, but lets them know how they can best get out of harm’s way.

Within their troops, peace and order is kept according to a strict hierarchical structure. Aggression moves down the ranks, meaning that monkeys only lash out at members of the troop who hold a lower status than themselves. Instead of retaliating against their aggressor, offended monkeys find others who are lower in status than themselves at whom to lash out. This chain of aggression makes the lowest in the troop’s ranks easily identifiable by the bite marks at the base of individuals’ tails. Generally, however, relations are friendly and upbeat. Relatives hold especially close bonds with each other and show it with physical affection. Sometimes families within a troop rally together in order to win larger political disputes. Vervets sometimes use deception as a strategy to gain access to food or to achieve higher ranking.

Within a troop, some vervets make up family-like units. Family members are exceptionally affectionate with each other and show their bonds through physical affection, grooming, and allo-parenting. Occasionally, family units will form alliances in order to settle injustices against their kin.

Most socializing takes place during the warmest part of the day. When the troop clambers into the trees to sleep for the night, monkeys of similar rank huddle together along the same branches.

Other troops of vervets are generally considered outsiders and, therefore, threats. Dominant males define their territorial boundaries by rubbing their cheeks or chest on branches in order to leave behind their scent and warn rival troops who come too close. That being said, meetings between different troops are not always antagonistic. The results are facultative, meaning that they depend on a number of environmental and social factors. For instance, troops are more likely to be cordial, and even keep each other company, where and when resources are plentiful and if the two troops have gotten along in the past.

More research needs to be done to describe the daily life and group dynamics specific to troops of tantalus monkeys.

Communication
As social creatures, tantalus monkeys have developed multifaceted ways to communicate. Based on what we know about the communication habits of vervets, their better-studied cousins, one can assume that tantalus’ methods are, if not altogether alike, at least similarly sophisticated.

Vervets make at least 36 distinct vocalizations. Of these, six are alarm calls. A monkey chooses which alarm vocalization to make depending on the type of threat he perceives. In this way, his fellow monkeys know their best course of action to get out of harm’s way. Other vocalizations are used to reinforce bonds and when aggressively disciplining lower-ranking troop members.

As guardians for their troop, a dominant male vervet warns rival troops to stay away by marking the boundaries of their territory with his scent. Dominant male vervets have clever ways of communicating with their own subjects, particularly concerning predators. While his troop forages, a male finds a conspicuous perch. From here, he watches for threats. When he spots danger, he lets the rest of the troop know by vocalizing. Each alarm call warns his troop of a particular predator, allowing its members to take the most effective course of action.

Vervets also use body language and facial expressions to communicate. A monkey that bares his teeth at another, for instance, is signalling that he is potentially aggressive.

Vervets use grooming as a means to form and develop bonds with each other. Females, especially, exploit this practice as a means of currying favor with higher ranking troop members.

The highest ranking males are notorious for flaunting their exceptionally flamboyant genitals for all of his troop to see. By drawing everyone’s attention to his bright blue scrotum and red penis, the dominant male constantly reminds his subjects that he is the boss. If he ever feels challenged by a lower ranking male, he might emasculate his rival by rising up on his hind legs and flourishing his fully erect penis directly in front of his rival’s face.

Tantalus monkeys may have unique ways of communicating that their vervet cousins do not. Until more research has been performed, we can at least use our knowledge of vervets to imagine how tantalus monkeys might be communicating with each other.

Reproduction and Family
The reproductive habits and family dynamics of tantalus monkeys are not well studied, but are probably similar to their vervet cousins.

When the breeding season begins, only the highest ranking males in a vervet troop get the chance to mate. Their paternal link to so many in their troop makes dominant males invested in its protection. As sentinels, they raise the alarm more reliably and more frequently than any other troop members. Beyond this protective role, their fatherly duties cease.

A female comes to term between five and six months of pregnancy. Her single infant is born with black fur and a pink face. For the first week of his life, he clings to his mother’s underside, where he has consistent and convenient access to her milk.

His special coloration ensures that other members of the troop will look out for him as he learns to navigate through the world. As he grows, he becomes bonded to relatives—especially female ones—other than his mother. Playing and mimicking the behaviors of adult monkeys around him, he learns the social and survival skills necessary for negotiating the complexities of vervet culture.

After about 12 weeks, his fur and face begin to change color. He spends the next five years learning the rules of vervet society. By that time, he leaves his troop to join another. Sometimes, several related males leave their troop together. His sisters and other female relatives reach maturity at about four years of age and remain with their natal group throughout their lives.

A female usually bears her first infant within her first year of maturity. By that time, she has gained considerable practice caring for infants, having played the babysitter to many of her younger siblings and relatives while growing up. With a baby of her own, other females in the troop are likely to vie for her infant’s attention. This is especially so if the mother is of a high rank, as females like to curry favor with higher ranking females by caring for their infants.

Often, vervet siblings form a tight social web, supporting and defending each other during upheavals within their troop. Older offspring of either sex pointedly protect their younger siblings from unfriendly monkeys. Such bonds are nurtured and kept strong even as vervets age.

Females remain within the troop they were born in for their whole lives. Males leave their natal groups to join another troop almost as soon as they reach sexual maturity. By joining another troop as a new member, a male vervet has more opportunity to rise in rank. In turn, he has a better chance of mating. It is not uncommon for two males—usually brothers—to depart together at the beginning of the breeding season.

Vervets, with their many natural predators, have established their social hierarchies and relationships to better protect each other and their infants. In spite of them, infant mortality rates are considerably high in the wild, and few individuals live to an old age.

While vervet monkeys can provide a general framework for how tantalus monkeys might behave, more research needs to be done to determined exactly how reproduction and family relationships play out in tantalus troops.

Photo credit: Bernard DUPONT/Creative Commons

Ecological Role
Tantalus monkeys play a vital role in dispersing the seeds of they fruit they eat—possibly more so than any other species in their genus. By habitually roaming grasslands in search of fresh foraging grounds, the seeds from the fruit that a tantalus monkey recently ate are distributed to brand new areas via his or her feces. A monkey also carries snacks in his or her handy cheek pouches, giving seeds another means by which to be transported. By saving these snacks for later, seeds are likely to be brought even further from their source than if had they been digested alone.

Tantalus monkeys generally seem to have a preference for fruit, but also eat a particularly varied diet compared to other primates. Some troops of tantalus monkeys have exhibited a uniquely strong taste for animal prey.

As semi-terrestrial primates, tantalus monkeys are targeted by many meat-eating savanna predators.

The roles that tantalus monkeys play vary from site to site. How they effect their ecosystems needs to be better researched.

Conservation Status and Threats
The tantalus monkey is classified as Least Concern by the International Union for Conservation of Nature (IUCN 2008), appearing on the IUCN Red List of Threatened Species.

Unlike many other primates, the number of tantalus monkeys in the wild is apparently increasing. The clearing of forest for farming often creates more widespread areas of the type of habitat in which the tantalus thrives. The issue is more complicated, however, and threats that may not affect the general population do greatly affect the well-being of certain troops and individual monkeys.

While tantalus monkey populations typically increase wherever forest is converted to farmland, there are many instances where entire troops have been wiped out due to other factors. In Amboseli National Park in Kenya, for instance, human development negatively affected the native elephant population, which, in turn, affected the troops living there. By building fences around the park, humans drastically shrank the area in which the elephants could roam. With all their movements now confined to just the park, the elephants destroyed the saplings and other plants that tantalus monkeys depend on for food and shelter. As of 1990, more than half the Amboseli population had been wiped out.

In other cases, humans have become pointedly hostile toward tantalus monkeys, perceiving them as nuisances. Farmers unapologetically trap, poison, shoot, and kill monkeys who they catch raiding their crops. In extreme instances, farmers have even hired other humans to round up entire troops to exterminate them all at once. Besides being cruel, the extermination of entire troops is likely to have negative effects on genetic diversity in the future.

Historically, tantalus monkeys have also been hunted for bushmeat; it is not uncommon for the offspring of slain adults to be harvested and kept as pets—a cruel fate for any primate.

Like other members of their genus, tantalus monkeys are commonly used as subjects in bio-medical research.

Conservation Efforts
Efforts to conserve the tantalus monkey are currently nonexistent. Though the tantalus population does appear to be increasing, there is a great need for research in order to better understand the species taxonomy and ecological roles as they are distinct from other members of their genus.

​References:

  • ​https://www.iucnredlist.org/species/136208/4259825
  • https://www.researchgate.net/publication/230237731_Seed_dispersal_by_tantalus_monkeys_Chlorocebus_tantalus_tantalus_in_a_Nigerian_montane_forest
  • https://www.ajol.info/index.php/jrfwe/article/view/125064
  • http://pin.primate.wisc.edu/factsheets/entry/vervet
  • http://ielc.libguides.com/sdzg/factsheets/vervet/taxonomy
  • https://www.nikela.org/vervet-monkeys/
  • http://southafrica.co.za/vervet-monkey/
  • https://vervet.za.org/tantalus-monkey-chlorocebus-tantalus/
  • ​http://www.departments.bucknell.edu/biology/resources/msw3/browse.asp?id=12100515
  • https://pdfs.semanticscholar.org/358c/a99404c78ae11c87b5f053e342d6d72b13d9.pdf

Written by Zachary Lussier, October 2019