Hamadryas Baboon, Papio hamadryas
Geographic Distribution and Habitat
Most people imagine baboons foraging among lush trees in forests, but the hamadryas baboon thrives in shrubby habitats with few large trees and they often take refuge in rocky cliffs. Hamadryas baboons live in dry, arid (almost desert-like) regions in the southern peninsula of Arabia and north-eastern Africa. Currently, the highest population of hamadryas baboons can be found in Ethiopia. Smaller populations are found in Eritrea, Djibouti, Somalia, Sudan (in Africa), and South Arabia and Yemen (In Arabia).
This baboon is the only species in its genus (Papio) known to extend beyond the African continent. Researchers think that a Red Sea land-bridge connecting the Mediterranean and African land masses allowed movement of baboons and other animals between the two regions before the land-bridge was submerged 35,000 years ago.
Papio means baboon and Hamadryas is a Greek reference to a spirit or nymph that lives in trees—or an oak tree, to be specific. Perhaps the stature and color of the hamadryas baboon evoke imagery of a sturdy, woody oak tree.
The Hamadryas baboon has been a distinct species from other Papio species since about 350,000 years ago and is the first in the genus to be described. However, in Africa, where there is geographical overlap, hamadryas baboons naturally hybridize with olive baboons (Papio anubis) resulting in fertile offspring. It appears that this hybridization zone is growing larger, and this could change the taxonomical landscape in the future as more baboon hybrids survive and reproduce. Studies have shown that the genetic variation is small between hybrids of hamadryas baboons and other Papio species. This is one reason why many taxonomists think that all the current Papio species should be classified as subspecies of the hamadryas baboon. As genetic studies become more sophisticated, the taxonomy and our understanding of baboon evolution become hotly debated. Currently, we follow the system of baboons classified as separate species.
Size, Weight, and Lifespan
Larger than a medium-sized dog, hamadryas baboons carry most of their weight in their powerful shoulders and large skulls. Females are smaller than males and, in general, hamadryas baboons stand about 1.6–3.1 feet (50–70 cm) tall, with a tail that is slightly shorter than their body. Tail length varies between 1.2 and 2 feet (37–60 cm). Females weigh between 22 and 33 pounds (10–15 kg) and males weigh 33–46 pounds (15–21 kg).
Hamadryas baboons have been known to live for about 20 years (maximum of 27 years) in the wild, but in captivity one male lived for 37.5 years.
Hamadryas baboons are impressive-looking, with their strong upper body and thick hair. Males are almost twice as large as females and have long silvery hair and a large mane and cape down their backs. Females tend to be more brownish. Youngsters start out with black hair that changes as they grow older.
Their reddish-brown faces, deep-set eyes, and extended muzzles impart an alert and serious gaze. Their extended muzzles also have cheek pouches that can store food temporarily. Finding food in a dry environment takes a lot of time and so hamadryas baboons will stuff the food they find into their cheek pouches and continue searching for food. When they collect a good amount of food, they will settle and eat their food or even eat on the go. This is an efficient way to eat when you are not sure where your next meal will come from. The base of the baboon’s tail is stiff and held at a characteristic arch that curves down away from its body. Tails are rarely dragged on the floor as the baboons walk.
Males and females are easy to tell apart (they are sexually dimorphic), and not only because the males are considerably larger than females. Males have a fierce-looking mane of hair on their head and shoulders, which reaches all the way to their hips. Females lack this mane and have much shorter hair. Both males and females do not have fur on their hind quarters; instead, their backside is covered in red skin. Males also have larger canine teeth. You may wonder why a baboon that rarely hunts need such large teeth. Well, in primates, the large canines have evolved as a display of size and aggression, especially in societies where males have to fight each other for resources like mating access or food access. Male hamadryas baboons bear their teeth, exposing the sharp canines, to show rivals what they will have to deal with. Most conflicts are resolved without actual fighting because the baboon with smaller canines will accept that he will be defeated by the larger male and he backs off. Physical fighting can be costly for both baboons—the larger one can get injured and the smaller baboon could die. So, in nature we often see displays of strength, such as large canines, that can be used as a way to show strength without causing life-threatening injuries.
Notably, hamadryas baboons feed on fruit from Acacia species, which are trees that have evolved to conserve water by having small leaves, bean-like fruits, and thorns. Hamadryas baboons are also dietary generalists, feeding on flowers, seeds, and small invertebrates such as insects. They are even capable of finding underground water sources, using puddles of water that seep through to get enough water. In areas where they live close to cities, they will supplement their diet by foraging at garbage dumps. In an environment where water sources and plant diversity is low, hamadryas baboons have evolved to take advantage of every available food source, which is why they have been successful in these arid regions.
Some scientists have reported instances of hamadryas baboons preying on hares and small antelope, but this is rare. These baboons are opportunistic and will not turn down an easy meal. When locusts swarm in the millions (these grasshopper species fly from field to field feeding on plants, and devastating crops), hamadryas baboons and almost every animal in the area will feed on the locusts, taking advantage of the sudden surplus of protein-rich food.
Behavior and Lifestyle
Hamadryas baboons are considered one of the most adaptable baboons in the world. This means they have the amazing ability to change their behaviors depending on their resources or challenges in their environment. Ecologists often refer to this ability as “plasticity” because the animals are flexible and can mold their behaviors to whatever is suited for the environment, just like melted plastic can be molded. This is why hamadryas baboons are seen in a variety of habitats, from mountains to low-lying coastal wetlands. One outcome of this plasticity is their omnivorous diet, which does not limit them to just one type of food. They can even eat from landfills if needed.
All baboons are extremely dependent on water and need to drink almost every day, especially when fruits and green leaves are not available. Therefore, most Papio species live close to rivers and open water sources. Hamadryas baboons are relatively more tolerant of low-water conditions and can be found more than 3.5 miles (6 km) away from rivers, unlike other species that often live less than half a mile away from water.
Like other baboons, hamadryas baboons are diurnal (active during daylight hours) and quadrupedal. They spend a lot of time walking on their hands and feet in their rocky, grassy habitat. These baboons have to work to find food in a low-resource environment, and often have long foraging excursions to find enough food. They can travel 2–8 miles (3–13 km) a day while foraging and travel further from their sleeping sites to find trees during fruiting season.
Though tool-use in primates has been documented with many species, in hamadryas baboons tool-use has been recorded mostly in captive individuals. In one study, researchers reported one individual sharing a tool and teaching another how to use it. Given how hamadryas baboons live such social lives, it seems reasonable that such tool use and learning through interaction and cooperation would occur in the wild as well.
Unlike most baboons, hamadryas baboons almost exclusively select cliffs as sleeping sites. Baboons often chose sleeping sites based on how protected the sites are from predators, as well as proximity to food sites and water sources. In most cases, baboons choose to sleep in trees or use forest cover for protection. But in the hamadryas baboon’s habitat, trees are scarce and cliffs provide protection where land predators (like leopards) can approach from only one side, and aerial predators (like eagles) can easily be detected. But even in this case, hamadryas baboons are flexible; in Ethiopia, researchers have reported some hamadryas baboons using doum palm trees (Hyphaene thebaic) as sleeping sites, probably because there are not enough prime cliff sites and there was too much competition for them with other individuals.
Aggressive behaviors in hamadryas baboons are generally seen in male leaders when they threaten and bite females that stray away from the family unit or get close to other males. This is called herding behavior. Males display similar behavior when they want to take or coerce females from one group into their own family unit.
The social bonds within groups are strengthened through grooming. The act of touching and removing pests is valuable for the physical health of the individual being groomed, and also for reducing stress. Grooming in many species is associated with dominance gradients, where the more dominant individual gets the benefits of being groomed. In wild hamadryas baboons, researchers have mostly reported male leaders being groomed by females in their family unit (one-male unit or OMU), and to a lesser degree males returning the favor with the females. Females grooming each other within an OMU were largely considered unimportant for social bonds in hamadryas baboons. However, recent studies with captive OMUs have shown that female-female grooming occurs more commonly but may be a more subtle way of maintaining group bonds in the OMU.
Hamadryas baboons are the only baboons to be endemic to the Arabian Peninsula.
They are the only baboons species that thrive in arid desert-like habitats.
Hamadryas baboons sleep on rocky cliffs in groups of up to 200 individuals.
They live in complex societies with four layers of organizations with family units being lead by one male leader.
The have “discussions” first thing in the morning to decide which direction to start foraging in.
Female baboons have more influence on social structure than previously thought.
Hamadryas baboons are famous for their complex, multi-level social system, which is unique among primates. Hundreds of hamadryas baboons gather at sleeping sites in large groups called “troops.” Troops do not interact socially for any other reason than gathering for protection during resting times.
Within each troop, there are smaller groups called “bands” that often travel and forage together. Most social interactions occur within a band. The terminology may seem confusing at first, especially if you have been reading about other primates. To simplify, what we think of as a troop for other primates is a band in the hamadryas baboon.
In hamadryas baboon society, there is another layer of grouping called “one-male units” or OMUs, which occur within a band. OMUs consist of a male leader, several females, and their offspring, and sometimes a few “follower” or non-dominant males. Most social interactions between individuals take place within an OMU. Within a band, there are also solitary males that tend to hang out with other solitary males.
These three levels are the most stable and established understanding of hamadryas baboons’ complex social groups. Recently, another level of society has been investigated. In the 1980s, it was noted that some OMUs routinely traveled with groups of solitary males and/or other OMUs. This social structure was called a “clan.” Some researchers suggest that clans form when the adult males are closely related and there are abundant food sources that can support a larger number of individuals foraging together.
This multi-level social structure is another example of their ecological plasticity or flexibility. More baboons mean more eyes and ears to detect predators, but it also means that less food is available in one area for all of them. By living in these different social levels, the baboons can split up to find more food and avoid competition in their resource-scarce environment. And at night, they can come together for protection while they rest. In this way, they maximize their chances of survival.
The arid habitat of hamadryas baboons means that they have to journey longer than most non-human primate species to find enough food. They can travel an average of 8 miles (~13 km) a day foraging. The direction and pathways they use can change daily and will depend on fruiting trees, rainy seasons, and group dynamics and communication, especially between male leaders.
Bands of hamadryas baboons can occur in group sizes of 9 to more than 200 individuals. Larger food resources can support larger group sizes. Additionally, how long bands stay together is also dependent on predator risk. If predator presence is detected (e.g., they hear a leopard vocalizing nearby), bands will delay their departure for foraging. Adults from different bands are generally not social and any interaction is usually aggressive and competitive.
One-male units allow a dominant male to have access to females for mating for a long period of time. This strategy increases his chances of reproductive success—that is, fathering offspring. In many primate species, males lose mating access when another male takes over the dominant position in a group. Once again, the hamadryas baboons are different in this regard. In hamadryas baboon society, a male-leader loses mating rights when a female leaves his OMU for another male’s OMU. Males are aggressive when they try to herd females into their own OMUs, often biting and snarling to intimidate them. This is called “coercion” and is the equivalent of takeovers seen in other primate societies. Early studies of hamadryas baboons viewed the female’s role as passive during these coercion events. More recent studies have revealed that females actually influence the likelihood of a male’s attempts to herd her into his OMU. If she shows any preference for her present male-leader, other males are unlikely to take the risk of herding her only to lose her again to the original male-leader later. These contests and herding behaviors are energy-expensive, after all. However, if a female communicates that she is willing to leave her present male-leader, the likelihood increases that a rival male will herd her into his own. The social dynamics in OMUs and the influence of females in hamadryas baboon societies are difficult to tease out in the wild and most studies have been conducted in captive settings. Nonetheless, it is a fascinating insight into the complex behavioral and communication structure of these primates, and despite being one of the best-studied baboon species in the world, there is so much we still have to learn.
Females tend to stay with male leaders of their OMU for at least three years. In her lifetime, a female may change OMUs two or three times. When a female transfers into another OMU, the rate of interaction between her and the new male-leader is high and he engages in more herding behavior with her. Most transfers of females occur within a clan, and socialization with members of a previous OMU is prevented by the new male-leader.
If a female has an infant when she is coerced into another OMU, the new male-leader will often kill the child to eliminate a rival’s genetic material. This phenomenon is seen in many mammals and is called “infanticide.” It most likely occurs because the new male-leader does not want to expend energy in protecting another individual’s offspring. In captive hamadryas females that were taken over, females went into estrus (the reproductive state where she is ready to mate) and displayed perineal swelling within two weeks.
When animals live in social settings, communication is vital for organization, maintaining access to resources, and even more complex decisions such as where to travel to find food. Because hamadryas baboons live within many social structures, communication happens between different levels of society. Hamadryas baboons may sleep as a troop of hundreds of individuals, but they forage for food as a smaller band of baboons. The decision of where they should forage has important outcomes for their survival and researchers have observed that it can take the baboons over an hour to communicate and jointly agree on a travel direction. Older males in the band are mainly involved in this communication, but it is the male-leaders of OMUs that have the most influence on the decision. They do this in a behavior called “notifying,” where one male walks up to another and immediately presents his hind quarters while turning to look at the other male. Both males may vocalize with grunts during this process. When a male wants to suggest a direction of travel he will walk stiffly in the direction he wants to go. And if the other male rejects this suggestion, he will abruptly sit down and bend his head to his chest for about two minutes.
With bright pink faces and prominent muzzles, facial features are an important part of how hamadryas baboons communicate with each other. These types of communication can be difficult for scientists to understand because humans may not be perceptive to little changes in the baboon’s expression. Just like a dog may not know that humans communicate the feeling of surprise with each other by raising eyebrows. Scientists have tried to study the importance of facial features using responses of captive hamadryas baboons to pictures of facial parts. It turns out that viewing different pictures of the dominant male’s eyes got the most response from the hamadryas baboons, indicating the importance of expressions that include the eyes.
Other types of communication that use facial expressions in hamadryas baboons include lip-smacking, ear-flattening, grimacing, and eye-narrowing. These expressions are associated with greeting interactions, particularly between males during foraging. Much like baring of the large canines (as discussed in the section about “Appearance”), facial expressions allow communication without touch or conflict.
The one-male unit (OMU) is the main reproductive and family unit because the male-leader will mate with multiple females and these females are not allowed to engage with other males outside of the OMU. Male-leaders are known to be aggressive when they herd females from other males into their own OMUs. The more females he has in his OMU, the more offspring a male-leader is likely to have, and therefore the more successful he is. Other males, whether “followers” or solitary males in a clan, do not try to mate with females in an OMU. In this regard, researchers have made an interesting observation. Hamadryas baboons have smaller testes (male reproductive organs) compared to other baboon species. This seems to suggest that hamadryas baboons do not need to produce as much sperm as other species to be reproductively successful. Most primate males that have to compete with other males for mating rights have to try and mate with females as many times as they can. So, the ability to produce more sperm can increase their chances of fathering offspring. In hamadryas baboons, the solitary or follower males do not challenge the leader-males by mating with the females in the OMU. This means that leader-males do not need to waste energy by producing excess sperm in order to pass their genes to the next generation.
Females become sexually mature when they are 4–5 years old and males when they are 5–6 years old. When females are ready to mate, their perineal region swells and becomes bright red. This is a visual signal for males that females will most likely become pregnant if mated during this time. Also during this time, females tend to spend more time grooming the male-leader. In the wild, females tend to become pregnant at least a year after they first become sexually mature.
Gestation lasts 5–6 months and young are weaned or dependent on mothers for food for almost a year (average of 9 months). Females are responsible for most of the parental care, including grooming and playing, while males may tolerate young for short periods of time. There is no seasonality for the births. Females spend 18–22 months weaning and taking care of an infant before giving birth to their next infant.
Once juvenile hamadryas baboons become 2–3 years old, they tend to leave the OMU. Juvenile males will join solitary males without an affiliated OMU, or they will become “follower” males in another OMU. Juvenile females usually disperse and become part of another OMU.
Hamadryas baboons are an important link in the food chain where there are only a few producers (plants, which are the source of energy for other living beings in an ecosystem). These baboons control invertebrate populations, particularly during locust swarms when the locusts can destroy entire fields of plants. Hamadryas baboons also help disperse seeds of a few trees that thrive in those arid habitats.
Lions, leopards, spotted hyenas, jackals, crocodiles, and avian species like Verreaux’s eagles are potential predators of hamadryas baboons. However, in some places, human presence has reduced the number of predators, which has caused an increase in hamadryas baboon populations in these areas. This overpopulation of hamadryas baboons causes increased competition for food, increased human-wildlife conflicts, and ultimately poorer quality of health for the baboons. This shows how delicate the balance is in nature and how an upset in this balance can have cascading effects.
Hamadryas baboons are abundant in their current range and are listed as a species of Least Concern by the International Union for Conservation of Nature (IUCN, 2016). However, their current distribution is smaller than their historical range. For example, hamadryas baboons used to be abundant in Egypt, but are no longer found there now. This is likely due to a combination of reasons including agricultural expansion into the hamadryas habitat, hunting for bushmeat, and conflicts between farmers who want to protect their crops and kill baboons that come close to their farms. These threats to their populations also exist in areas where the populations are more stable.
In Saudi Arabia, people sometimes feed wild hamadryas baboon populations. Feeding wildlife can cause harmful effects that usually end with animals being worse off. Feeding wild baboons can make them lose their fear of humans and baboons become aggressive when getting food. Some individual baboons can become problem animals and harass humans. With baboons being stronger, they can cause serious harm. This eventually leads to a need to manage these individuals and often results in the death of the baboon.
The hamadryas baboon is protected under the APPENDIX II Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), which means that populations are not extinct but trade should be controlled.
Hamadryas baboons have been culturally important for humans, particularly for ancient Egyptians who considered these baboons as avatars of the god of learning, Thoth. Egyptians have even mummified them in tombs similar to how they would mummify revered cats in tombs of pharaohs.
Hamadryas baboons have been kept in captivity for many years, both in zoos and laboratories for research. They have been a model organism to study genetics and evolutionary linkages to understand primate diseases, including those diseases that affect humans. Additionally, captive studies on hamadryas baboon groups are used to develop a human understanding of how learning and culture develop in societies.
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Written by Acima Cherian, October 2022