OLIVE BABOON

Papio anubis

Geographic Distribution and Habitat
Olive baboons live in central sub-Saharan Africa, spreading over 25 countries, from east to west with a few pockets of isolated populations in the Saharan region. Although usually referred to as savanna monkeys, they are extremely adaptable and thrive in a wide variety of habitats, ranging from open grasslands and riverine forests to valleys separated by rocky cliffs, evergreen forests, and agricultural areas. 

At Giligil, Kenya, where temperatures are mild (51.1° to 78° F/10.6° to 26° C), rainfalls can be abundant, averaging 1.95/2.48 feet (595 mm/756 mm) in the fall and spring. In the lava fields around Mount Fantale, Ethiopia, on the other hand, rainfalls can either be dramatic or non-existent. In the savanna woodland of Benin, where thickets and dry forests intersperse, temperatures often reach up to 104° F (40° C) with severe droughts. Yet, populations of olive baboons are found in all those regions as well as in the woodlands, savanna and evergreen tropical forests of Uganda, and the dense forests and sandy areas of the Democratic Republic of the Congo.  

One of the reasons the species is so adaptable is its ability to extract nutrients from anything in its environment.

Olive baboon range, IUCN 2020

Size, Weight, and Lifespan
With a height of 2.3 ft (70 cm) and an average weight of 53 lb (24 kg), males are twice the size of females. In captivity, both males and females are a little heavier (up to 63 and 37 lb respectively).

Olive baboons can live up to 30 years in the wild but, because of predators, injuries, and infant mortality, few reach such an old age. They can live longer in captivity.

Appearance
Olive baboons have a long square muzzle with large nostrils pointing forward. The top of the head appears flat. The skull has a sagittal crest indicative of strong jaw muscles. The fur is grey with speckles of black and yellowish color; it is coarse and short. Adult males have a mane of long hair from the top of the head to the shoulders. The skin of the face and ears is black. The face is covered with very fine hair. The eyes are sunken under the eyebrow bone and are an orange-brown color. The tail is long (1.25 to 1.9 ft (380 to 584 mm) and at its base, on each side of the buttocks, two rough patches of skin, called ischial callosities, allow baboons to sit upright on branches without falling. Females have a separation between the two ischial callosities, but the two sides fuse in males.

They have 32 teeth. The upper canines are longer than the bottom ones and are larger in males than in females. Much like humans, olive baboons can have tooth decay and gum disease. Older males especially can have worn, chipped and stained canines. The cheek pouches inside the mouth allow these baboons to store food while on the go. The feet and hands have black fingernails and opposable thumbs and toes. The fingers are short compared to the palm. The top of the hand and fingers is covered with fur, and the palm of the hand is black skin with ridges.

Infants are black and skinny with large ears. The wrinkled skin on the face, ears, and inside of the hands and feet is pink. Babies become peppery grey at seven months old, and their coat turns olive around their first birthday.

When walking slowly, they use hand digitigrade posture and feet semi-digitigrade posture. This means that only a small area of the palm of the hand or sole of the foot touches the ground. In general, primates put more weight on their hind limbs than on their forelimbs. Experiments have shown that olive baboons switch between palmigrade hand posture on branches to digitigrade posture during terrestrial locomotion. The pressure on the fingers, however, does not change with speed.

What Does It Mean?

Corm:
A rounded underground storage organ present in plants such as crocuses, gladioli, and cyclamens, consisting of a swollen stem base covered with scale leaves.

Digitigrade:
Term used to indicate a mammal walks on its toes and its heels do not touch the ground – like dogs.

Palmigrade:
Term used to indicate an animal puts the whole foot – with the sole – on the ground to walk.

Sagittal crest:
A ridge of bone along the middle of the skull. Primates with large jaws have a sagittal crest.  

Visit the Glossary for more definitions

Diet
Olive baboons are omnivores. They use foraging methods that enable them to survive in different environments—from forests to deserts—gathering food on the ground and in trees and digging for food. Their diet varies depending on where they live. Except in Uganda, where food plants are available all year long, the species’ feeding habits change with the season. During rainfalls, olive baboons pick and gorge on fruit, young leaves, and flowers—especially abundant in forested areas; they feed on fresh grasses in the savanna, grewia berries, and star grass. During the dry season, they dig out roots, tubers, corms, and seeds. They also consume cacti, insects, birds, eggs and vertebrates—such as Thompson gazelles, rabbits, and even other primates.  However, since they are not true carnivores, hunting is only occasional, and they only feed on a carcass if they witnessed the kill.

They are experts at selecting the most nutritious part from each of the food items they find, in any season. They have developed techniques that allow them to take advantage of difficult food resources—like opuntia, also referred to as prickly pear. They knock it down and rub it back and forth on the ground to remove the prickers that would make the consumption of the fruit very painful.

Where human population is nearby, olive baboons feed on crops as well as garbage.

Behavior and Lifestyle
Olive baboons live in large multi-male, multi-female troops of 15 to 150 individuals.

They share territory with Guinea baboons in Guinea and Mali, but the two species do not interbreed; whereas interbreeding occurs in Ethiopia, where they share territory with hamadryas baboons.

Olive baboons form a hierarchical society, in which adult males continuously compete for dominance. A male rises to power through aggression by toppling the current male in charge. Once he has ascended to power, and as long as everybody fears his stares, a dominant male does not necessarily need to resort to aggression but very rarely retains his tenure for more than one year.  

Despite constant turmoil and political plays for dominance, males are pretty good at avoiding direct confrontation whenever possible—a good strategy, since males can inflict severe wounds on each other with their sharp canines. In some cases, alpha males seem to voluntarily step down once they have fathered infants. 

Females remain in their native troop their entire lives, but males depart when they reach maturity.  The new-comer approaches the troop he wants to integrate into by first trying to befriend females. At the five-year mark, he will leave for another troop. This makes sense from an evolutionary standpoint, because the daughters he may have fathered reach sexual maturity at age five; thus, incestuous mating is avoided. 

When encountering outside olive baboon troops, adolescent males from both troops first approach each other with curiosity. Younger males may sometimes even play together for a short time.  However, conflict may arise if an adult female in estrus gets too close to the outside troop.

Daily Life and Group Dynamics:
Olive baboons are diurnal and spend approximately sixty percent of their time walking and foraging.  

They spend the early hours of the morning resting until mid-morning when they start traveling to feeding sites, keeping track of each member through contact calls—i.e., loud barks that can be heard 0.3 miles away (500 m). Who decides to go where is not a one-baboon decision. Since females are permanent members of the group, they have the advantage of knowing the territory very well; whereas males may be useful in leading the troop to better feeding grounds outside the home range, which can be a life-saver in times of drought. They usually walk as a group for a mile or two (1.6 km to 3.2 km), longer distances when food is scarce; then they rest, feed, and groom. When the troop is on-the-move, the dominant males are at the center, around them are the females with babies and youngsters; the other females, juveniles, and low-ranking males are at the periphery and provide protection from predators to those in the center. The troop continues foraging until sunset. It is then time to socialize and retire for the night.

As with many primates, grooming is the glue that holds baboon society together. It helps establish and maintain relationships; it provides relaxation as well as hygiene and health benefits. By keeping hair out of wounds, they heal faster. Vermin are kept out of the animals’ fur by preventing it from getting matted. Self-grooming is a regular activity, but getting help from a friend is better, and it is not unusual for an individual to extend an arm or present a side that needs special attention to a friend.

While male relationships are unstable, female relationships last a long time—although a female’s allegiance is first to her family. 

Hierarchy not only rules the troop, but also the family. The mother is dominant, the baby is in second position, then the baby’s siblings in reverse age order.

Female-male friendships may form outside the mating season. Much like her male counterpart, a low-ranking female is at the mercy of higher-ranking females. If she has adolescent sons or a consort, she can rely on them for protection, even if her rank does not change. Another strategy is for her to use avoidance behavior.

Alpha females play an important role in keeping the peace, not only in their own family but also between families.

Fun Facts

It is unusual for primates to swim, but olive baboons in Nigeria can swim with their faces under water and have been seen diving from tree branches hanging over the river.

In 1972, sixty baboons escaped from a safari park in Spain and established a free-ranging colony. They were subsequently re-captured and transferred to various zoos.

Visitors to the Sacrarium of the Temple of Isis in Pompeii can admire a painting of a primate that looks very much like an olive baboon, sitting on a rock and holding a cobra in its hands.

Communication
Olive baboons use many ways to communicate: facial expressions, body posture, touch, and vocalizations. 

The male vocabulary is rich and colorful. Often engaged in dominance contests, the “tension yawn” (full mouth open) or the “canine display” are efficient ways for adult males to show their power to intruders, mating rivals, or predators. Very often, the canine display is accompanied by eyebrow flashing which is anything but nice. However, if the recipient is a female and the eyebrow flashing is accompanied by friendly “rhythmic grunts,” this is a pickup line.

When an adult male wants to let other males know they should not mess around while he is guarding the troop, he may sit with an erection. This is known as the “penile display.” 

Two males in close vicinity may grind their teeth with the mouth closed to threaten each other. The “stare” with eyebrows raised and the face skin pulled back by moving the ears is another variant on this display.

Gentle touch of the penis and genitals, on the other hand, is a very intimate, yet dangerous way to affirm bonds of friendship between two males. This is a language only the males can use with each other.

When there is too much tension in the air, “rapid glancing” may be a way to diffuse it. One baboon simply turns her head away to look opposite the threatening individual. If, unfortunately, the spirits do not calm down, males may puff up their manes to appear twice their size, lunge at each other open-mouthed, and flail their razor-sharp canines at each other.

Or, they may decide to engage in “wahoo contests.” This is a loud low-pitched two-phase bark. Rivals can assess their dominance without a physical fight simply by competing in the equivalent of a shouting match. Only fully adult males in their prime can participate, as they have to bark while racing through trees, which requires extraordinary stamina. The “wahoo” can also signify that a predator is nearby—especially if it is a big cat. Grunts and roars are also used before and during conflicts or male arousal. The “grating roar” is a way for the dominant adult male to claim victory and declare the fight is over. Adult males also use it to indicate the cause of a disturbance is gone.

Individuals of all ages and sexes may resort to “screeching” or high-pitched screams to inhibit aggression. When withdrawing from an aggression, individuals may “yak” and “fear grimace” (the lips are pulled, revealing clenched teeth). 

When danger is spotted, one individual alerts the troop with a “shrill bark’. Not to be confused with the “doglike bark” that baboons emit when individuals are separated from the troop.

If an olive baboon likes another baboon and wants to be friends, she will use “lipsmacking”, sometimes accompanied by “social presenting” – a submissive display of the buttocks, indicating good intentions towards the recipient.

Social grooming, “nose to nose greeting”, and “social mounting” are other ways to communicate friendliness and reassurance to others.

Reproduction and Family
Females are sexually mature at five years old and usually give birth for the first time a year later. Adult males prefer females that have already given birth and raised young, as it indicates better survival for their progeny.  

Males reach adolescence at six years old and become adults at ten. During the transition period, the canines develop, the testicles descend and the mantle hair grows out fully.  

Females develop swelling and present their rear with the tail up to males, when in estrus, to indicate they are sexually receptive. 

When a baby is born, after a gestation period of 180 days, females in the troop are automatically attracted to the little bundle of joy. They present, lip-smack at the mother and, if permitted, approach. They then proceed to groom the infant. The ritual is the same, no matter the mother’s position in the hierarchy.

Changing environmental conditions and stress-inducing group interactions affect primates physiologically and thereby influence their chances at reproduction. In stable hierarchies, for instance, low-ranking olive baboons (more susceptible to be picked on) have elevated basal glucocorticoids (a class of natural steroid hormones) and lower testosterone (male hormone) concentrations in their bloodstream than high-ranking baboons. Similarly, during droughts, basal testosterone concentrations in adult and sub-adult males drop considerably, independent of their rank within the group. 

However, even if dominance is a sure way to get female partners and secure reproductive rights, lower ranking males can create opportunities for themselves–by surreptitiously getting close to a female, while her suitors are fighting, for instance, and sneaking away with the object of his affection. It would also seem that males with female friendships are more successful than bullies.

Ecological Role
Olive baboons play an important ecological role as seed dispersers. In Ivory Coast alone, they harvest fruit from at least seventy-nine plant species and studies of scat samples reveal that most seeds pass through their digestive system undamaged. In Nigeria, out of twelve species of trees visited by olive baboons, seeds of eight species are dispersed regularly, either by passing through a baboon’s digestive system or by attaching to her fur and dropping a few miles away.

Conservation Status and Threats

The olive baboon is listed as Least Concern on the International Union for Conservation of Nature Red List of Threatened Species (IUCN, 2020).

The populations of olive baboons everywhere in Africa, however, are impacted by habitat loss due to agricultural expansion. Proximity to humans means they are being shot or trapped when they raid crops, so humans and domestic dogs are becoming a threat to them. 

Natural predators of the olive baboon include big cats, wild dogs, hyenas, chimpanzees, crocodiles, and raptors.

Conservation Efforts
​Most conservation efforts focus on educating local communities on crop diversification and methods to deter baboons from raiding crops (like the introduction of domestic dogs near farms, or planting crops that are not nutritionally attractive to baboons).

References:

  • Primate Info Network – Wisconsin University
  • Almost Human – A Journey Into the World of Baboons – Shirley Strum
  • Styles of male social behavior and their endocrine correlates among low-ranking baboons –  Charles E. Virgin Jr., Robert M. Sapolsky (1997)
  • Endocrine and behavior correlates of drought in wild olive baboons (Papio Anubis) – Robert M. Sapolsky (1986)
  • Laboratory Animal Medicine – edited by Lynn C. Anderson, Glen Otto, Kathleen R. Prittchett-Coming, Mark T. Whary
  • Dynamic Pressure Patterns in the Hands of Olive Baboons (Papio Anubis) During Terrestrial Locomotion: Implications for Cercopithecoid Primate Hand Morphology – Biren A.Patel and Roshna E. Wunderlich
  • The role of olive baboon (Papio Anubis, Cercopithecidae) as seed disperser in a savanna-forest mosaic of West Africa – Britta Kerstin Kunz and Karl Eduard Linsenmair
  • Re-assessment of Seed Acquision and Dispersal by Olive Baboon (Papio Anubis) in Gashaka-Gumpti National Park, Nigeria – Forestry Research Institute of Nigeria.

Written by Sylvie Abrahms, January 2018