Animal Diversity Web

Geographic Range

Papio hamadryas is found on the African continent in the area of the southern Red Sea, in Ethiopia, Somalia, and Eritrea. This species also occurs in the Palearctic region, in Saudi Arabia and Yemen. The latter populations often occur in close association with humans, and, although considered endemic to the region, were probably introduced there accidentally at some point during the height of the ancient Egyptian Empire.

This species is part of a complex of closely related African baboon species. We have an account of the whole genus under Papio. (Groves, 2001; Jolly, 1993; Nowak, 1999; Primate Info Net, 2002)

• Biogeographic Regions
• palearctic
  • introduced
  • native
• ethiopian
  • native

Habitat

Hamadryas baboons are found in subdesert, steppe, alpine grass meadows, plains, and shortgrass savannahs. Their distribution is limited by the availability of watering holes and appropriate sleeping rocks or cliffs. In parts of Ethiopia, they are found in agricultural areas and are considered crop pests. (Jolly, 1993; Napier and Napier, 1985; Nowak, 1999; Primate Info Net, 2002; Stammbach, 1987)

• Habitat Regions
• tropical
• terrestrial

• Terrestrial Biomes
• desert or dune
• savanna or grassland
• mountains

• Other Habitat Features
• suburban
• agricultural

Physical Description

These monkeys are highly sexually dimorphic in size and pelage characters. Adult males weigh around 21.5 kg and females around 9.4 kg. Male pelage is basically grayish-brown in color, with the ventrum colored like the back or darker. Hairs on the cheeks are lighter, forming "whiskers" which grade into a very pronounced, bushy, silver-colored mane. The long back hairs are wavey. Females are a plain olive-brown color. The skin may be very colorful in some animals. In both males and females, the skin surrounding the ischial callosities is pink or bright red. Males have skin of a similar color on their muzzle and face, whereas females possess a muted, grayish-brown face. The tail is long, and curved, with a graceful arch at the base. The natal pelage is black, although this is lost by approximately six months of age, when it is replaced by an olive-brown coat like that of the adult female.

The head and body length has been reported as 610 to 762 mm, with the tail adding an additional 382 to 610 mm. (Groves, 2001; Napier and Napier, 1985; Nowak, 1999; Primate Info Net, 2002)

• Other Physical Features
• endothermic
• homoiothermic
• bilateral symmetry

• Sexual Dimorphism
• male larger
• sexes colored or patterned differently
• male more colorful
• ornamentation

• Range mass

  9.2 to 21.5 kg

  20.26 to 47.36 lb

• Range length

  610 to 762 mm

  24.02 to 30.00 in

• Average basal metabolic rate

  21.095 W

  AnAge

Reproduction

The basic social and reproductive unit in hamadryas baboons is the one male unit (OMU). Within this OMU, there is a single adult male who mates with one or more females. (Kummer, 1968; Primate Info Net, 2002; Stammbach, 1987)

Reproductive behavior in P. hamadryas is closely tied to social organization. The basic breeding unit is the OMU, in which the leader male aggressively herds females, keeping them from straggling during the foraging march, and preventing them from socializing with other males. Females typically spend most of their social time in proximity to the leader male. Most social grooming within the OMU is focused on the leader male, with females grooming him, especially his mane, face, and buttocks. The pelage characters of males can therefore be thought of as strong mate attractants, and seem to function in the maintenance of the OMU. (Kummer, 1968; Stammbach, 1987)

Because of the division into OMUs, most females have only opportunities to mate with the OMU leader. However, males may follow a number of reproductive strategies, and females may at times "sneak" copulations with males other than their unit leader. (Jolly and Phillips-Conroy, 2003; Kummer, 1968; Swedell, 2002; Zinner and Deschner, 2000)

For males without an OMU, reproductive behavior is limited, and effort seems to be expended in attempts to establish an OMU. Establishment of an OMU can occur in one of two ways. First, a subadult male may attach himself to an already established OMU as a follower. In general, a follower male remains separated from the females of the OMU, although he travels with the OMU on the daily foraging march, and sleeps near the OMU at night. There may be some potential for such follower males to mate with females, if such copulations can be conducted without detection by the leader of the OMU. Evidence for such copulations comes from the pattern of testicular development in this species, as well as a limited number of observations of such "trysts." However, the principle goal of followers seems to be to either steal females from the OMU leader, having become familiar to these females through association with the OMU, or to depose the OMU leader and commandeer his entire harem of females. (Jolly and Phillips-Conroy, 2003; Kummer, 1968; Stammbach, 1987)

Because OMU leaders actively restrict the interactions between their females and other males, chasing, biting, or otherwise punishing females who appear to be straying, one might wonder why a female would risk incurring his wrath by engaging in copulations with other males. One might speculate that such interactions might confuse paternity if there is a turnover in leadership of the OMU, and thereby inhibit tendencies toward infanticidal behavior on the part of the new leader male. (Jolly and Phillips-Conroy, 2003; Stammbach, 1987; Zinner and Deschner, 2000)

In general, hamadryas males "respect" the social bond between other males and their female affiliates. However, rarely within a band, there is intense physical competition between males. This seems to be associated with turnover of male OMU leaders. (Kummer, 1968; Stammbach, 1987)

The second strategy utilized by males to establish a OMU is to "adopt" a juvenile or subadult female. This strategy entails much less risk to the male, because there is no overt competition for the female in question. The male will care for the little female, grooming her, carrying her if necessary, and providing what would appear to many to be parental care. When the female reaches reproductive maturity, he will breed with her. This strategy seems especially effective because females hamadryas baboons do not readily consort with single males. Once a male has established a OMU with his "adopted" female, he may become much more attractive to other females. (Kummer, 1968; Stammbach, 1987; Kummer, 1968; Stammbach, 1987)

Females exercise some choice in their mates. Females typically disperse from their natal group between 1.5 and 3.5 years of age. About 70% of females will change affiliation to a new OMU within a period of 3 years, often choosing to join OMUs that contain other females with whom they are already familiar. Through this type of transfer, it is possible for females to maintain bonds with one another throughout their lives. (Stammbach, 1987; Swedell, 2002)

• Mating System
• polygynous

Hamadryas baboons breed aseasonally. Mating is based on the occurence of estrus in females, and the reproductive condition of females is generally independent of season. However, Kummer (1968) did report a peak of births in May/June and November/December.

Females characteristically have an estrous cycle of 31 to 35 days in length. There is a noticeable menstrual flow for approximately three days per cycle if the female does not conceive. During the period around ovulation, the perineal skin of the female swells, alerting the male to her potentially fertile condition. During mating, there is generally a pattern of serial mounting initiated by the female, who presents her hindquarters to the male. The male mounts the female and thrusts several times. This mounting is followed by other mount/thrust episodes until the male ejaculates. Mating frequencies can be from 7 to 12.2 per hour while the female is receptive. (Hrdy and Whitten, 1987; Kummer, 1968; Stammbach, 1987)

Gestation lasts about 172 days, after which the female gives birth to a single offspring. The neonate, weighing from 600 to 900 g, has a black coat, making it readily identifiable from older infants. Infants are completely dependent upon their mother for the first few months, until they begin to eat solid food and are able to walk on their own. (Jolly, 1993; Kummer, 1968; Nowak, 1999; Stammbach, 1987)

Puberty occurs between the ages of 4.8 and 6.8 years in males, and around the age of 4.3 years in females. Full size is attained in males around 10.3 years of age. Females, which are significantly smaller than males, reach adult size around 6.1 years of age. (Jolly and Phillips-Conroy, 2003; Stammbach, 1987; Walters, 1987)

Puberty in males is a lengthy process, and the timing of different developmental events reveals interesting details about the reproduction of these animals. Testicular development does not closely follow male growth in this species. Testes develop rapidly between the ages of 3.8 and 6 years, reaching full size prior to attainment of full adult body size. In contrast, body mass doubles between the ages of 7 and 8 years, after the testicles are fully developed. This pattern of development may indicate that subadult males, who do not possess OMUs of their own, may yet achieve some "sneak" copulations. Interestingly, the remainder of adult male secondary sexual characteristics, including the silver mane, white cheeks, and pink hindquarters, do not develop until after full adult size is reached. These characteristics are thought to function in the maintenance of the OMU, as they are very attractive to the females of the OMU and elicit large amounts of female grooming. (Jolly and Phillips-Conroy, 2003; Kummer, 1968; Stammbach, 1987)

Females have an average interbirth interval of 24 months, although individual females have been known to have offspring as close together as 12 months. Some females have not given birth until 36 months after the birth of their previous offspring. It is likely, that as in anubis baboons, differences between females in the length of the interbirth interval are related to differences in nutritional status or social stress levels. (Bercovitch, 1987; Hrdy and Whitten, 1987)

The average length of lactation is 239 days, but the timing of weaning may vary according to maternal condition, ecological variables, and social circumstances. Lactation can last from 6 to 15 months. The period of infant dependence is difficult to assess. Because this species is social, juveniles may continue to associate with their mothers until they disperse at or near adulthood. Also, because young females may be "kidnapped" by males wishing to establish an OMU, it is even more difficult to assess whether or not these individuals could survive without the quazi-parental care provided by the kidnapping male. In short, it would be reasonable to put the upper limit of the period of juvenile dependence at the mean interbirth interval (24 months), but to realize that this type of estimation is imprecise. (Kummer, 1968; Nowak, 1999; Stammbach, 1987; Walters, 1987)

• Key Reproductive Features
• iteroparous
• year-round breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual
• fertilization
• viviparous

• Breeding interval

  Male hamadryas baboons can breed continuously, if females in their OMU are in reproductive condition. Females can produce offspring annually, but are more likely to produce an offspring every two years.annually

• Breeding season

  Hamadryas baboons are not seasonal breeders, and can mate throughout the year, provided females are in estrus.

• Range number of offspring

  1 (low)

• Average number of offspring

  1

• Average number of offspring

  1

  AnAge

• Average gestation period

  172 days

• Average gestation period

  171 days

  AnAge

• Range weaning age

  6 to 15 months

• Average time to independence

  24 months

• Average age at sexual or reproductive maturity (female)

  4.3 years

• Average age at sexual or reproductive maturity (female)
  Sex: female

  1514 days

  AnAge

• Range age at sexual or reproductive maturity (male)

  4.8 to 6.8 years

Most parental behavior is performed by the female. Females nurse and groom their offspring. There does not seem to be cooperative care of offspring among females, although it is not uncommon for one female in an OMU to groom the offspring of another female. As is the case for all baboons, infants are very attractive to other members of the social group, and are the focus of a great deal of investigation and attention, especially while they are still displaying their black natal coat. (Nicolson, 1987; Stammbach, 1987; Swedell, 2002)

Females can experience deceptive estrous cycles when a new male takes control of the OMU. This may be an adaptive parental behavior with an anti-infanticidal effect. (Zinner and Deschner, 2000)

Males offer protection to infants by keeping control of the OMU. Males exclude other males from contact with their females and offspring, potentially inhibiting infanticide. Also, adult males maintain vigilance over the group, and are therefore likely to spot potential predators, protecting their offspring from that particular threat. Males are typically very tolerant of infants and juveniles within the OMU, and will often play with them or carry them. (Kummer, 1968; Whitten, 1987)

The caretaking behavior of males toward to juvenile females during the formation of an OMU is quazi parental. Although from the perspective of the male this behavior is reproductive, it is parental from the perspective of the juvenile female. She obtains food, protection, warmth, and is often carried by the male, much as she would be by her own father or mother. (Kummer, 1968; Stammbach, 1987)

• Parental Investment
• altricial
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female
• pre-weaning/fledging
  • provisioning
    • female
  • protecting
    • male
    • female
• pre-independence
  • provisioning
    • female
  • protecting
    • male
    • female
• post-independence association with parents
• extended period of juvenile learning

Lifespan/Longevity

The maximum lifespan of a captive hamadryas baboon is measured at 37.6 years. It is likely that the maximum is slightly lower in the wild (Nowak, 1999)

• Range lifespan
  Status: captivity

  37.6 (high) years

• Average lifespan
  Sex: male
  Status: captivity

  37.5 years

  Max Planck Institute for Demographic Research

• Average lifespan
  Status: captivity

  35.6 years

  Max Planck Institute for Demographic Research

• Average lifespan
  Status: wild

  37.0 years

  Max Planck Institute for Demographic Research

• Average lifespan
  Status: captivity

  28.8 years

  Max Planck Institute for Demographic Research

Behavior

Hamadryas baboons are quadrupedal, mainly terrestrial primates. They are highly social animals, which display a complex, multi-level social structure. The basic unit of social organization is the OMU, or one male unit, in which a central male, the leader, aggressively herds and controls from one to nine females and their offspring. Members of a OMU forage together, travel together, and sleep together. Males typically restrict the social interactions of females and juveniles within their OMU, suppressing aggression between females, and maintaining nearly exclusive reproductive access to the mature females. A single OMU may be comprised of from 2 to 23 animals, although the average is 7.3 animals per OMU. In addition to the leader male, there may be a subordinate "follower" male. This "follower" is thought usually to be related to the leader in some fashion. (Kummer, 1968; Stammbach, 1987)

Two to three OMUs come together to form clans. The males found in a clan are thought to be close genetic relatives of one another, based both on phenotypic resemblance and genetic similarity. Social interactions occur with greater frequency within than between clans. Also, clans form a cohesive foraging groups, often separating themselves from other clans during foraging. (Kummer, 1968; Primate Info Net, 2002; Stammbach, 1987)

Two or three clans form a single band. Bands exhibit stable membership, even if membership in lower levels of social organization is not stable. Males and females typically do not disperse beyond the boundaries of the band. Male OMU leaders suppress any attempts of infants or juveniles to interact with like-aged animals in different bands. When conflicts occur between different bands, such as those that have been induced at sleeping rocks by provisioning food, OMU leader males are the primary combatants. (Kummer, 1968; Stammbach, 1987)

Bands of hamadryas baboons appear to have an important function in allowing the baboons to compete for sleeping sites and for access to water holes. Male OMU leaders begin each day by "coordinating" with one another regarding the location of the specific watering hole at which the band will reunite at midday. An OMU leader will take several steps in the direction of a particular water hole. Other OMU leaders may signal "agreement" with the choice by taking a few steps in the same direction, or they may signal that they wish to visit a different water source by taking some steps in the direction of the other water hole. Members of the same clan tend to support one another in this debate. When a majority of OMU leaders agree, the baboons will begin their daily foraging march. The band will break up into separate clans or OMUs during the morning in order to make use of the sparse and patchy food resources. These sub-groups are out of visual and vocal communication most of the time, yet they manage to converge at the specified water hole at midday. Since other animals and other baboons may utilize the same water hole, it is important for hamadryas baboons to have adequate numbers of individuals present when they appear at the water source to secure access to the water. A similar pattern of behavior is expressed in the designation of sleeping sites for the night. (Stammbach, 1987)

Troops of hamadryas baboons may contain several bands. Troops are aggregations of baboons which utilize the same sleeping cliffs or rocks. It is unlikely that the troop has any social significance to the animals themselves. This level of organization appears to be an artifact not of the affiliative tendencies of the species, but the limited number of sleeping sites available in the habitat. (Kummer, 1968; Stammbach, 1987)

Males appear, then, to affiliate with kin throughout their lives. In this respect, hamadryas baboons differ from other members of the genus Papio. In other baboons, males transfer from their natal groups into other troops, where they establish themselves in the male dominance hierarchy, and pursue their reproductive agendas accordingly. In P. hamadryas, although both males and females transfer to new social groups, or OMUs, the males maintain active bonds with their male kin, remaining in their natal clans and usually their natal bands. These groups of related males are united against other groups of male kin. (Kummer, 1968; Pusey and Packer, 1987; Stammbach, 1987)

It may be this close association of male kin that has led to the peculiar tendency of male hamadryas baboons to "respect" the social bonds between other males and their mates. Studies of male hamadryas baboons in captivity suggest that if two males are placed into an enclosure with a strange female, they will compete aggressively for access to her, in much the same fashion as other baboons. However, if one of the males is allowed to view the other male with the female before he is placed into the enclosure with them, he will avoid the female, and will not instigate a fight with the "resident" male for access to the female. The integrity of the OMU as the basis of hamadryas baboon society, in some measure, depends upon this "agreement" between males to respect the proprietary access of their male kin to certain females. (Stammbach, 1987)

Interestingly, it is quite likely that female baboons retain close associations with their female kin throughout their lives, also. Female hamadryas baboons prefer to affiliate themselves with OMUs in which past female associates already reside. It is not uncommon for females from the same natal group to end up in the same OMU as adults. Such females are likely to be half-sisters or full sisters. Within the OMU, some females spend as much time with other females as they do with the OMU leader, a pattern of association which may be a product of female relatedness. The amount of time which females spend in proximity with one another or interacting socially with one another is greater in OMUs with more females. The relatedness between females in hamadryas OMUs is higher than is seen in other species of primates in which females transfer into new groups. Although many of the interactions between female hamadryas baboons are controlled by OMU leader males, the females still have some ability to associate with, and help, their extended families. (Swedell, 2002; Swedell, 2002; Swedell, 2002)

Within an OMU, females do not display the consistent dominance relationships which are seen in other species of baboons. That the females of this species are capable of such dominance relationships is demonstrated by their presence in captive groups of female hamadryas baboons. However, in wild groups, OMU leader males suppress the aggression between females that could lead to social stratification (Kummer, 1968; Stammbach, 1987)

In spite of the lack of typical baboon dominance hierarchies, female hamadryas baboons do exhibit social differences. Some females, called central females, spend more time in proximity with the OMU leader, have a stronger social bond with him, and are more socially active. Females who spend less time in proximity with the OMU leader are called peripheral females. Peripheral females may incur greater risks of predation than central females. These females are often the first to enter a new foraging area, or first to attempt to use a water hole, and, as a result, are more likely to be surprised by a lurking predator than are central females. (Stammbach, 1987)

Perhaps because of this difference, females of an OMU compete amongst themselves to have stronger bonds with the OMU leader. This competition may play a role in "deceptive" sexual cycles exhibited by females when a new OMU leader takes over control of a social group. Females who are lactating may develop sexual swellings and exhibit estrous behavior immediately upon OMU takeover. These females do not become pregnant any sooner than they would have had the leadership of the OMU remained stable, however, copulations with the new leader male may place them higher in his favor. (Kummer, 1968; Stammbach, 1987; Zinner and Deschner, 2000)

An alternative explanation for these "deceptive" sexual cycles is that the females are preventing the new leader male from killing their infants. In primates, it is not uncommon for males to kill the dependent offspring of a female when they take over control of a harem unit. This will shorten the period of lactational ammenorhea, and bring the female more quickly into sexual cycling. If the female can mimic this effect, making herself appear fertile even though she might not be, there is no reason for the male to kill her infant. (Zinner and Deschner, 2000)

• Key Behaviors
• terricolous
• diurnal
• motile
• sedentary
• territorial
• social
• colonial
• dominance hierarchies

• Range territory size

  40 (high) km^2

Home Range

The home range size for hamadryas baboons varies depending upon the habitat quality and the location of sleeping cliffs. The maximum home range size for baboons is approximately 40 square km. The daily range of hamadryas baboons varies from 6.5 to 19.6 km. (Nowak, 1999)

Communication and Perception

As in all highly social species, communication is varied and complex. Hamadryas baboons utilize visual signals and gestures, vocalizations, and tactile communication. Visual signals include social presenting, in which a females or juveniles display their hind quarters to the male. This submissive signal differs from sexual presenting (which females do to elicit copulation) in that the hindquarters are much lower to the ground. Staring is a threat behavior, the effect of which is enhanced by the differently colored fur in the region of the eye which is revealed when the baboon stares. The mouth may be opened during this type of staring, although the canine teeth typically remain covered. Bobbing the head up and down is also considered a threatening behavior among hamadryas baboons. Canine teeth are displayed by a tension yawn, as another threatening gesture. This last behavior is performed only by males toward their rivals or toward predators. (Primate Info Net, 2002)

Teeth chattering and lipsmacking, although not technically vocalizations, are auditory cues of reassurance, often performed by a dominant animal when another is presenting to him. Vocalizations made by these animals include a two-phase bark, or "wahoo" call, which adult males direct toward feline predators or toward other males. It is thought to communicate the presence of the male and his arousal. All hamadryas baboons, except infants, make rhythmic grunting vocalizations when approaching another animal to signal affiliative intentions. A shrill bark is produced by all except adult males to indicate alarm, especially due to sudden disturbances. (Primate Info Net, 2002)

Although chemical communication has not been reported for these animals, anubis baboon females are known to produce aliphatic acids when they are sexually receptive. These acids are thought to enhance a female’s sexual attractiveness. It is possible that similar olfactory cues may exist in P. hamadryas. (Hrdy and Whitten, 1987)

As in all primates, P. hamadryas can spend a significant amount of time engaged in social grooming. Social grooming is thought to help develop and maintain social bonds between animals. Within hamadryas baboons, most social grooming is performed by females and is directed toward the leader of the OMU. Other forms of tactile communication in this species include reassuring touches and embraces, as well as a variety of agonistic bites and slaps. (Kummer, 1968)

• Communication Channels
• visual
• tactile
• acoustic

• Perception Channels
• visual
• tactile
• acoustic
• chemical

Food Habits

Papio hamadryas is omnivorous. They have been known to eat a variety of foods, including, but not limited to: fruits, tree gums, insects, eggs, acacia seeds, acacia flowers, grass seeds, grass, rhizomes, corms, roots tubers, small vertebrates. Because of the aridity of their habitat, these baboons must subsist on whatever edible items they can find.

One feeding adaptation thought to be shared by all baboons is the ability to subsist on a relatively low quality diet. Baboons can subsist on grasses for extended periods of time. This allows them to exploit dry terrestrial habitats, like deserts, semideserts, steppes, and grasslands. (Kummer, 1968; Nowak, 1999; Oates, 1987; Primate Info Net, 2002)

• Primary Diet
• omnivore

• Animal Foods
• birds
• mammals
• reptiles
• eggs
• carrion
• insects
• terrestrial non-insect arthropods

• Plant Foods
• leaves
• roots and tubers
• seeds, grains, and nuts
• fruit

Predation

Natural predators have been virtually eliminated from most of the range of P. hamadryas. However, it is thought that the higher levels of social organization seen in hamadryas baboons are a response to past predation. Bands undoubtedly help the baboons to defend themselves against predators, by increasing the number of adult animals to ward off attacks. Because bands and clans tend to congregate at just before reaching watering locations, a place where predators are likely to hide, such a function seems plausible. Also, troops seem to be a side effect of the desire of these animals to sleep on elevated rocks or cliffs. On explanation for this sleeping arrangement is that it inhibits access of predators to the animals. The availability of sleeping sites appears to be the principle limitation on the range of these animals. (Kummer, 1968; Nowak, 1999; Stammbach, 1987)

• Known Predators

  • leopards (Panthera pardus)
  • Verreaux's eagles (Aquila verreauxi)

Ecosystem Roles

Because hamadryas baboons are prey items, they form an important link in local food webs, making nutrients they obtain from plants and small animals available to larger animals. They dig for tubers, roots, rhizomes and corms, so it is likely that these animals help to aerate the soil where they forage. Also, it is likely that they play some role in dispersing seeds they eat.

• Ecosystem Impact
• disperses seeds
• soil aeration

Economic Importance for Humans: Positive

Hamadryas baboons are very interersting animals, and provide a great deal of entertainment to people who visit them in zoos. There are also populations of hamadryas baboons, especially on the Arabian peninsula, which attract visitors and tourists to view them. Some of these animals have been used in medical research. (Nowak, 1999; Williams-Blangero, et al., 1990)

• Positive Impacts
• research and education

Economic Importance for Humans: Negative

Hamadryas baboons are common in irrigated agricultural areas and can be terrible crop pests. They are large animals which can be aggressive when confronted. (Nowak, 1999)

• Negative Impacts
• injures humans
  • bites or stings
• crop pest

Conservation Status

IUCN lists P. hamadryas as lower risk/ near threatened. These primates are threatened by habitat loss, harvesting for food and for research, as well as outright persecution. CITES does not list Papio on any appendix.

• IUCN Red List

  Least Concern
  More information

• IUCN Red List

  Least Concern
  More information

• US Federal List

  No special status

• CITES

  No special status

Other Comments

Hybridization between P. hamadryas and P. anubis occurs along the Awash river valley in Ethiopia. The area of hybridization appears to be stable, without noticeable introgression of P. hamadryas phenotypes into anubis baboon populations or of P. anubis phenotypes into hamadryas baboon populations. The reasons for this stability are probably very complex. However, it is worth discussing two contributors to this stability in this forum. (Nowak, 1999)

In hamadryas baboons, the basic social unit, or OMU, is maintained as a cohesive entity through the activity of the adult male leader of the OMU. He herds females and juveniles, regulates their interactions, and prevents them from straying. Although anubis baboon males possess the same basic behaviors that would allow the males of this species to form one-male-units, there are significant differences in expression between the two species which make it impossible for male anubis baboons migrating into hamadryas territory to successfully maintain a harem of females. (Kummer, 1968; Nowak, 1999; Stammbach, 1987)

For example, although male anubis baboons aggressively herd females and exclude rival males, they tend to do so only when the females are in estrus. This would prevent a male anubis baboon from maintaining a cohesive OMU in the hamadryas fashion. Also, although they form close social ties with females, they do not exhibit the "respect" of the relationship between other males and their females which is typical of hamadryas baboons. This may be related to differences in the kin associations of hamadryas and anubis baboons. Correlated with this, an anubis male trying to "steal" a sexually attractive female from a male hamadryas, would incur not just the wrath of that male, but likely the wrath of that male’s kin within the clan. (Melnick and Pearl, 1987; Stammbach, 1987)

Hybrid males are known to show behavior intermediate between the two parental species. Anubis-like hybrids form lasting social bonds with anestrous females, and assume a consort-like status when the females are in estrus. However, they are unable to herd them efficiently because they do not express this behavior when the females are anestrous. The more hamadryas-like hybrids are capable of forming OMUS. (Jolly and Phillips-Conroy, 2003; Melnick and Pearl, 1987; Phillips-Conroy, et al., 1992; Stammbach, 1987)

Interestingly, hamadryas males have been known to effectively integrate into anubis baboon troops. Although females mate with them, these males may still be at a reproductive disadvantage relative to anubis males. Because the mating system of the hamadryas baboon characteristically involves only one male, there has been little selection for sperm competition in this species. Hamadryas males have both relatively and absolutely smaller testicles than do anubis males. This likely results in lower production of sperm. Since female anubis baboons may mate with a number of males during their estrus cycle, lower sperm production by hamadryas males may lessen their chances for siring offspring (Jolly and Phillips-Conroy, 2003; Phillips-Conroy, et al., 1992)

Contributors

Nancy Shefferly (author), Animal Diversity Web.

References

Alberts, S., J. Altmann. 2001. Immigration and hybridization patterns of yellow and anubis baboons in and around Amboseli, Kenya. American Journal of Primatology, `53: 139-154.

Altmann, J. 1980. Baboon Mothers and Infants. Chicago: The University of Chicago Press.

Bentley-Condit, V., T. Moore, E. Smith. 2001. Analysis of infant handling and the effects of female rank among Tana River adult female yellow baboons (Papio cynocephalus cynocepahlys) using permutation/randomization tests. American Journal of Primatology, 55: 117-130.

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