Animal Diversity Web

Geographic Range

Papio anubis is the most broadly distributed baboon species, ranging through most of central sub-Saharan Africa. Isolated populations occur within the Saharan region.

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, 2000)

• Biogeographic Regions
• ethiopian
  • native

Habitat

Anubis baboons are found in savannah, grassland steppe, and rainforest habitats. (Jolly, 1993; Melnick and Pearl, 1987; Nowak, 1999; Primate Info Net, 2000)

• Habitat Regions
• tropical
• terrestrial

• Terrestrial Biomes
• desert or dune
• savanna or grassland
• forest
• rainforest
• scrub forest

• Other Habitat Features
• agricultural

Physical Description

These monkeys are highly sexually dimorphic in size and pelage characters. Males weigh around 25 kg and females around 14 kg, with some geographic variation in average size. The head and body of the average male measures 760 mm, with the tail adding an additional 560 mm. Females are smaller, with an average head and body measurement of 600 mm and an average tail length of 480 mm. Males have large canine teeth, whereas the teeth of the females are much smaller. Pelage is characteristically a dark, olive-gray. This overall color is produced by hairs with 1 to 2 alternating pairs of black and yellow-brown rings. Males possess a large mane, restricted to the anterior portion of the body, and grading into the shorter body hair toward the rear. Females lack a mane. (Groves, 2001; Jolly, 1993; Melnick and Pearl, 1987; Napier and Napier, 1985; Nowak, 1999; Primate Info Net, 2000)

The skin of the face and around the ischial callosities is dark gray to black in both sexes. The bare area of the rump is much smaller in this species than in Papio hamadryas or Papio papio. Unlike some species of baboons, the nostrils of P. anubis point forward. The head is flat on top, helping to distinguish this species from Papio cynocephalus which has a prominent crest on the top of the head. The first quarter of the tail is carried erect, being held straight upward, with the remainder of the tail falling down limp, giving the tail a broken appearance. The natal pelage is black, but this fur is replaced by the typical olive-gray by about 6 months of age. (Groves, 2001; Jolly, 1993; Napier and Napier, 1985; Nowak, 1999)

The skull of males has heavy ridges of bone on both sides of the nose, and a prominent rounded bar above the orbits. There is a sagittal crest and often a nuchal crest. Molars are large, and the first lower premolar has been modified into a hone for the upper canine. These primates have 32 teeth. (Alberts and Altmann, 2001; Groves, 2001; Jolly, 1993; Melnick and Pearl, 1987; Nowak, 1999)

• Other Physical Features
• endothermic
• homoiothermic
• bilateral symmetry

• Sexual Dimorphism
• male larger
• ornamentation

• Range mass

  14 to 25 kg

  30.84 to 55.07 lb

• Range length

  480 to 760 mm

  18.90 to 29.92 in

Reproduction

Reproductive behavior in P. anubis is closely tied to social organization. Because these animals live in multi-male, multi-female troops, there is the potential for any male to mate with any female. This results in fierce competition between males for access to sexually receptive females. In general, a male’s ability to consort with a female and exclude other males from access to her is related to the male’s ability to compete with other males. There is therefore a correlation between male dominance rank within the troop and mating success. Larger, younger, and stronger males have a distinct advantage in this type of competition. (Smuts, 1987a)

However, as in many social animals, there are other factors which affect a male’s mating success. For example, males may form alliances with other males, which can subvert the normal dominance hierarchy. Two males, neither of whom can dominate a third male alone, may join forces and together, as a coalition, these males may succeed in securing access to a sexually receptive female. Such coalitions are reciprocal, and typically occur between pairs of older males who are well acquainted with one another through mutual tenure in a troop. (Melnick and Pearl, 1987; Smuts, 1987a)

Males also follow a strategy of developing "friendships" with females, which enhances their opportunities to mate. In these friendships, males groom, share food, and have strong affiliative ties with particular females and their offspring. It is common for males to defend their female friends during agonistic encounters with other females, and with other males. These associations are not confined to the period during which females are sexually receptive, but span the entire gamut of the female’s reproductive life—including pregnancy, lactation, and time spent cycling. Females tend to exhibit a preference for mating with their male friends, and therefore make consortships with their male friends more likely. In addition, because females prefer their friends as mates, they are more likely to cooperate with them in the maintenance of a consortship than they are to cooperate with other, less favored, males. (Melnick and Pearl, 1987; Smuts, 1987a)

The prolonged period of sexual receptivity of females in this species is typical of primates living in multi-male, multi-female social groups. Females in monogamous or polygynous species are typically receptive for a very short time around ovulation. In P. anubis, females mate with a variety of males over a period of 15 to 20 days. Such multiple matings are not necessary to ensure fertilization, and may function to confuse the actual paternity of the female’s offspring. This may help to mitigate infanticidal tendencies of males. (Hrdy and Whitten, 1987; Melnick and Pearl, 1987)

Females exert some mate choice in this species. By making consortships easier or more difficult for males, females can exert some control over whom they mate with. Also, females can make it easier or more difficult for a given male to immigrate into the troop, influencing the pool of males from which they may choose mates.

Mating is initiated by the female, who presents her hindquarters to the male. The male mounts the female and thrusts about 6 times, then ejaculates. Matings are probably quick because of the intense intermale competition for access to sexually receptive females. (Hrdy and Whitten, 1987; Melnick and Pearl, 1987; Smuts, 1987b; Smuts, 1987a)

• Mating System
• polygynandrous (promiscuous)

Reproduction in P. anubis is related to the social structure of this species. Anubis baboons live in multi-male, multi-female troops. Mating is polygynandrous, with both males and females mating with multiple partners. Most matings occur during consortships. Consortships arise when a male, through aggression toward potential rivals, is able to maintain exclusive sexual access to a female. Females may consort with multiple males while they are sexually receptive, although they consort with only one male at a time. Because it is apparently easier for a male to maintain exclusive access to a female if the female is cooperative, there is a significant amount of female mate choice, with females preferring some partners over others. (Hamilton III and Bulger, 1992; Hrdy and Whitten, 1987; Melnick and Pearl, 1987; Smuts, 1987a)

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, and aliphatic acids are produced, alerting the males to her potentially fertile condition, and enhancing her attractiveness to them. Females are typically receptive for 15 to 20 days per cycle. (Hrdy and Whitten, 1987; Melnick and Pearl, 1987)

Gestation lasts about 180 days, after which the female gives birth to a single offspring, weighing approximately 1068 g. The neonate has a black coat, making it easy to distinguish from older infants. An infant is completely dependent upon its mother for the first few months, until it begins to eat solid food and is able to walk on its own. Females have an interbirth interval ranging from 12 to 34 months. This interval varies according to a number of factors. Females who are older or have a higher rank tend to have shorter interbirth intervals. Interbirth interval is also shorter if an infant dies before weaning. (Bercovitch, 1987; Hrdy and Whitten, 1987; Melnick and Pearl, 1987; Smuts and Nicolson, 1989; Strum, 1991)

Weaning typically occurs around 420 days of age. Lactation is a huge cost for adult females, and typically causes a reduction in female weight. Lower ranking and younger females probably take longer to recover adequate body weight to reproduce than do older, dominant females, explaining their longer interbirth intervals. (Bercovitch, 1987; Melnick and Pearl, 1987; Smuts and Nicolson, 1989)

The onset of puberty and attainment of adult size is highly variable and is associated with nutrition levels. In populations where baboons are known to raid human crops, and to thereby secure greater access to nutrients than naturally foraging animals, puberty can occur much earlier. In such food-supplemented populations, males attain adult body weight between 7 and 8 years. Females reach full size by 6.5 years. In contrast, in naturally foraging populations, males do not reach full adult size until they are 7 to 10 years old, and females do not reach adult weight until they are 7 to 8 years old. The effect of nutrition on growth is so strong that as little as 15 to 16 weeks of dietary variation in newborns can have lasting effects on overall rates of female growth, absolute adult weight, and age at menarche. (Strum, 1991)

In naturally foraging populations, puberty occurs between the ages of 5 and 6 years in females, and is signaled by menarche, or in some cases, first pregnancy. In males, puberty begins around 6.6 years of age, when body size begins to increase rapidly, third molars erupt, and canine teeth fully erupt. Changes in male body size include increases in muscularity, which give these animals a broader profile. The mane of males also begins to develop, contributing to the increase in shoulder size. Correlated with these changes in body size, male anubis baboons undergo an increase in testicular volume. Like human males undergoing puberty, male anubis baboons are also reported to undergo a break in their voices around this time, eventually leading to a deeper sounding alarm-bark. Males typically emigrate from their natal troop just after these changes are completed. (Jolly and Phillips-Conroy, 2003; Melnick and Pearl, 1987; Strum, 1991; Walters, 1987)

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

• Breeding interval

  Female anubis baboons with ample food and health can breed annually. However the interbirth interval ranges between 12 and 34 months, because female condition and food supply vary.

• Breeding season

  Mating can occur throughout the year.

• Average number of offspring

  1

• Average gestation period

  180 days

• Average weaning age

  420 days

• Average time to independence

  420 days

• Range age at sexual or reproductive maturity (female)

  7 to 8 years

• Range age at sexual or reproductive maturity (male)

  7 to 10 years

Most parental behavior is performed by the female. Females nurse, groom, and play with their offspring. Females express different patterns of infant care, often associated with rank and age. In yellow baboons, higher-ranking females tend to be more "permissive" in their parenting than lower ranking females, who tend to me more nervous and "restrictive," preventing their offspring from moving away from them. This difference has been reported in anubis baboons only up to the age of 8 weeks of infant life, but may be longer for some females or in some troops. Another difference seen in maternal behavior in this species is that older mothers are known to spend more time in contact or close to their infants and are less likely to terminate bouts of nursing than are younger females. First-time mothers are also likely to reject infants sooner than are experienced mothers. These differences may affect interbirth intervals. (Altmann, 1980; Melnick and Pearl, 1987; Nicolson, 1987; Smuts and Nicolson, 1989)

There does not seem to be cooperative care of offspring among females in P. anubis, but it is not uncommon for females other than the mother to groom an infant, sometimes providing allomaternal care to the infant. Subadult and juvenile females who have not yet reproduced themselves are most likely to exhibit allomaternal behavior. 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. In extreme cases, females may kidnap the offspring of other females. Lower-ranking females are more often subject to this extreme form of harassment than are higher-ranking females. Other factors known to affect the incidence of allomaternal behavior in other species include the infant’s age, and relatedness of the allomother to the mother and infant. (Melnick and Pearl, 1987; Nicolson, 1987)

Males have complex relationships with infants and juveniles, which in some cases may be a form of parental care. Males are known to carry, protect, share food (especially meat), groom, and play with, the offspring of their female friends. Because they are more likely to mate with their female friends than they are with other females, these infants and juveniles are more likely to be their own offspring than are other immature animals within the troop. This behavior, therefore, can be interpreted as paternal. (Melnick and Pearl, 1987; Stein, 1984; Whitten, 1987)

However, it should be noted that the relationship between adult males and these immature animals may be more complex than this. There may be some form of reciprocity involved. Adult males will often carry infants during tense interactions with other adult males. This carrying can be initiated either by the adult male or by the infant. Such contact with an infant during agonistic encounters may have the effect of inhibiting aggression by other males. The favors bestowed upon an infant used as a buffer may therefore be a form a "payback" from the adult male. However, since the tendency to use an infant as an agonistic buffer is related to familiarity with the infant and the probability of paternity, it is impossible to separate the nepotism from the reciprocity of such interactions. (Stein, 1984)

• Parental Investment
• altricial
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female
• pre-weaning/fledging
  • provisioning
    • male
    • female
  • protecting
    • male
    • female
• pre-independence
  • provisioning
    • male
    • female
  • protecting
    • male
    • female
• post-independence association with parents
• extended period of juvenile learning
• inherits maternal/paternal territory
• maternal position in the dominance hierarchy affects status of young

Lifespan/Longevity

The maximum lifespan of a captive hamadryas baboon is measured at 37.5 years. A captive chacma baboon is reported to have lived 45 years in captivity. Although the lifespan of P. anubis has not been reported, it is likely to be similar to these two species, although somewhat shorter than these in the wild. (Nowak, 1999)

• Average lifespan
  Sex: male
  Status: captivity

  25.2 years

  Max Planck Institute for Demographic Research

Behavior

Baboons are quadrupedal, mainly terrestrial primates. They are highly social animals, with a complex multi-male, multi-female social structure. Members of a troop travel, forage, and sleep together. An average troop may be comprised of 39 to 97 animals. The movements of a troop may be limited by the availability of appropriate sleeping locations. Because the troop beds down in trees, or on rocks/cliffs, activity of the troop must be coordinated so that one of a set number of sleeping sites can be reached by nightfall. (Melnick and Pearl, 1987; Nowak, 1999)

All males emigrate from their natal troops, with 85 per cent of males emigrating prior to the time that they reach full adult size. Upon settling in a new troop, males must establish themselves in the male dominance hierarchy of that troop. This typically involves aggressive behavior between males, with the "winner" of an encounter establishing dominance over the "loser." Some males may emigrate into new groups in pairs. These male pairs may be half - or full- siblings from the same natal troop. Aside from such occasional life-long affiliations, males do not maintain long-term bonds with their male kin, as is seen in hamadryas baboons. (Melnick and Pearl, 1987; Pusey and Packer, 1987)

An interesting phenomenon in P. anubis is the secondary transfer of aged adult males from their troops. Because the ability of a male to compete for mates is related to youth and vigor, or to long-term social relationships with females, transfer to a new troop in old age can only reduce a male’s opportunities to mate. In addition, transferring to a new group exposes a male to a great number of hazards, including increased risk of predation, and dangers from aggression while integrating into the male dominance hierarchy of the new group. However, it appears that aged males who once had high dominance ranks are the subjects of constant harassment by younger males, who seem to remember the former "greatness" of such older males. It seems that males with larger numbers of female "friends" are more likely to stay in their troop in spite of harrassment. Males without many female friends are more likely to transfer to new troops, thereby avoiding the costs of such harassment. (Sapolsky, 1996)

Because males do not maintain life-long social ties with their kin, it is female kinship that forms the core and stability of P. anubis society. Because females of this species do not emigrate from their natal groups, female kin have life-long associations. Within a troop of anubis baboons, there is a dominance hierarchy of matrilines which is very stable over time. In general, an individual female occupies a place in the dominance hierarchy immediately below her mother and her younger sisters. Dominance relationships appear to develop from infancy, when maternal kin intervene in encounters with other baboons, and through the differential treatment of the young of higher-ranking females by unrelated animals. Within a matriline, the dominance relationships of sisters are the inverse of birth order. (Melnick and Pearl, 1987)

Female kin behave differently toward one another than do unrelated animals. Females are more likely to aid their kin during disputes than they are to become involved in disputes of unrelated individuals. These relationship can extend over multiple generations, with females aiding not only their own offspring, and aunts aiding neices, but grandmothers aiding their granddaughters. (Melnick and Pearl, 1987)

The female dominance hierarchy is not continually challenged by the arrival of new females in the troop, which probably allows for the stability of female dominance relationships over time. Perhaps because relatedness of females within troops is inherently higher than the relatedness of females between troops, female baboons are likely to take the lead in aggressive encounters with other troops of baboons. Females are apparently acting to defend their food resources in such encounters. (Melnick and Pearl, 1987)

Within socially similar cercopithecines, females have been known to establish relationships across matrilines. Females may befriend others who are of similar rank. Also, low ranking females may attempt to gain favor with higher ranking females by providing grooming and other affiliate behaviors. An ally with higher rank may provide a low ranking female with preferential access to scarce food resources, or support during some aggressive encounters. (Bentley-Condit and Smith, 1999; Melnick and Pearl, 1987; Smuts, 1987b)

Because the dominance position of baboons is so important in their society, a great deal of investigation of potential physiological causes of dominance has been conducted. Most investigated have been levels of those hormones thought to be important in aggressive behavior and stress response. Some interesting correlations between endocrine profiles and behavioral patterns have emerged. (Sapolsky and Ray, 1989; Virgin, Jr. and Sapolsky, 1997; Sapolsky and Ray, 1989; Virgin, Jr. and Sapolsky, 1997)

In general, subordinate males who initiated fights with other males had higher testosterone levels than males who did not initiate fights. They also had lower base levels of glucocorticoids (hormones associated with stress and stimulation of the adrenal glands). When subordinate males were involved frequently in consortships, they were more likely to move into the top half of the male dominance hierarchy within 3 years than were males without frequent consortships. Like dominant males, they had reduced basal glucocorticoid levels and a larger glucocorticoid response to stressors. (Sapolsky and Ray, 1989; Virgin, Jr. and Sapolsky, 1997)

Major behavioral traits that seemed to contribute to lowered levels of glucocorticoid hormones were associated with the social "skillfulness" of the animals. Males with low basal levels of glucocorticoids were better able to distinguish between neutral and threatening interactions with their rivals. They also were more likely to initiate aggression against rivals in threatening interactions than were males with higher basal glucocorticoid levels. The males with lower glucocorticoid levels showed the greatest skill in determining whether they had won or lost an aggressive encounter, and also showed the greatest incidence of "displacement aggression" (aggression at something other than the rival or situation that was really upsetting them). (Sapolsky and Ray, 1989; Virgin, Jr. and Sapolsky, 1997)

Although it is not currently known whether the glucocorticoid levels of individuals lead to the behaviors, or visa versa, clearly, there are measurable differences between individuals which may allow prediction of their future reproductive success. Further research in this area promises to help us to better understand the genetic and physiological underpinnings of social behavior and success in this species. (Sapolsky and Ray, 1989; Virgin, Jr. and Sapolsky, 1997)

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

• Range territory size

  0.39 to 1.968 km^2

Home Range

Home ranges between 390 and 1,968 ha have been reported. The daily range of a troop averages 5,800 m. (Melnick and Pearl, 1987)

Communication and Perception

As in all highly social species, communication is varied and complex. Anubis baboons utilize visual signals and gestures, vocalizations, and tactile communication. (Primate Info Net, 2000)

Visual signals include social presenting, in which a female or juvenile displays its hind quarters to a male. It can also be done by a female who has approached another female with her black infant. This submissive signal differs from sexual presenting (which females do to elicit copulation), and is often accompanied by lip smacking. 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. Canine tooth display through a tension yawn is another threatening gesture. It is performed by lower-raking males toward higher-ranking males who are consorting with estrus females or who possess meat. Male baboons who are close to one another can use tooth grinding to threaten one another. Baboons retreating from high-tension situations use rapid glances to break tension. Adult males who are guarding mates sometimes sit with their erect penis in plain view. This penile display communicates the male’s presence to other males. (Primate Info Net, 2000)

Teeth chattering and lipsmacking, although not technically vocalizations, are auditory cues of reassurance, often performed by a dominant animal when another is presenting to it. (Primate Info Net, 2000)

Vocalizations made by anubis baboons 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. Adult male anubis baboons make grunting vocalizations as a threat, and are known to "roar" during fights. A grating roar, which is a deep, resonating call, is given by a dominant male after a fight, and is sometimes made by adult males when there is a night-time disturbance. Screeching is common during aggressive encounters, and can be made by any age or sex class. Subadult and adult olive baboons produce a yakking call when retreating from a threatening animal. This call is often accompanied by a grimace of fear. A shrill bark is produced by all except adult males to indicate alarm, especially due to sudden disturbances. Finally, rhythmic grunting may be produced by all anubis baboons except infants when they wish to signal reassurance to another animal. (Primate Info Net, 2000)

Juveniles and infants produce some vocalizations unique to their age class. These include clicking, which is a chirp-like noise which is analogous to yakking of adults. They also produce an ick-ooer sound which communicates a low level of distress. (Primate Info Net, 2000)

Tactile communication is common in cercopithecines. Social grooming is used to reinforce social bonds, as well as to remove parasites and debris from the fur. Social mounting is a reassurance behavior. Anubis baboons also perform a friendly nose-to-nose greeting. (Primate Info Net, 2000)

Chemical communication has also been reported for this species. Female anubis baboons are known to produce aliphatic acids when they are sexually receptive. These acids are thought to enhance a female’s sexual attractiveness. (Hrdy and Whitten, 1987)

• Communication Channels
• visual
• tactile
• acoustic
• chemical

• Perception Channels
• visual
• tactile
• acoustic
• chemical

Food Habits

Anubis baboons are known to eat a wide variety of foods. They consume fruits, tree gums, insects, eggs, seeds, flowers, grass, rhizomes, corms, roots, tubers and small vertebrates. (Melnick and Pearl, 1987; Primate Info Net, 2000; Strum, 1991)

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. (Melnick and Pearl, 1987; Oates, 1987)

• 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

Two predator species are known for anubis baboons. Leopards and chimpanzees have been known to kill these animals. Anubis baboons have been reported to mob leopards, often with adult males leading the attack. In the Gombe preserve in Tanzania, an estimated one percent of the population falls victim to predators annually. Of these, about 3/4 are infants, and 1/4 are juveniles. (Cheney and Wrangham, 1987; Melnick and Pearl, 1987; Nowak, 1999)

• Known Predators

  • chimpanzees (Pan troglodytes)
  • leopards (Panthera pardus)

Ecosystem Roles

Baboons likely play a role in aerating the soil through the digging of corms, roots, and tubers. They also are likely to disperse seeds of the fruits and grains that they eat. Baboons provide food for their predators, and also exert some affect on populations of small animals on which they feed. (Melnick and Pearl, 1987; Primate Info Net, 2000)

• Ecosystem Impact
• disperses seeds
• soil aeration

Economic Importance for Humans: Positive

Anubis baboons are used in medical and behavioral research. They are socially active animals which provide entertainment for zoo visitors and ecotourists. (Nowak, 1999)

• Positive Impacts
• ecotourism
• research and education

Economic Importance for Humans: Negative

Baboons are large animals, and not particularly timid of humans. They are known to raid crops, and can attack and injure humans if provoked. (Melnick and Pearl, 1987; Nowak, 1999; Strum, 1991)

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

Conservation Status

Anubis baboons are not considered threatened or endangered. The IUCN Redlist rates them "Lower Risk, Least Concern." Like most primates, they are included in Appendix II of the CITES, so international trade in the animals or their parts requires government approval.

• IUCN Red List

  Least Concern
  More information

• IUCN Red List

  Least Concern
  More information

• CITES

  Appendix II

Other Comments

Hybridization between Papio 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. (Melnick and Pearl, 1987; Nowak, 1999; Phillips-Conroy, et al., 1992)

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; Phillips-Conroy, et al., 1992)

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. (Kummer, 1968; Melnick and Pearl, 1987; Nowak, 1999; Phillips-Conroy, et al., 1992)

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. (Phillips-Conroy, et al., 1992)

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. This may contribute to the stability of the hybrid zone. (Jolly and Phillips-Conroy, 2003; Melnick and Pearl, 1987; Phillips-Conroy, et al., 1992)

Anubis baboons are also known to hybridize freely in the wild with yellow baboons,. In the Amboseli National Park in Kenya, the amount of reported hybridization between these two species has increased over time. Researchers think that the increasing immigration of anubis males into yellow baboon troops is responsible for the increase noted in hybrid characters. Because the slopes of Mount Kilamanjaro are under increasing agricultural pressure, it is likely that anubis males have no alternative areas into which to emigrate. (Alberts and Altmann, 2001; Jolly, 1993)

The only differences noted in behavior of hybrid animals is that males with anubis-like features (e.g. coarser hair, longer manes, darker coloration, broader chests, and more sharply "broken" tails) tend to emigrate from their natal group as juveniles or subadults, rather than as full adults. This behavior has been seen occasionally in the anubis baboons of the Gombe preserve in Tanzania, but is not known in yellow baboons. (Alberts and Altmann, 2001; Pusey and Packer, 1987)

The hybridization between anubis and yellow baboons seems to have a long history. Interesting, the Ibean form of yellow baboon, which has coarser hair than the typical yellow baboon, a more pronounced mane, and other somewhat "anubis-like" features, is thought by some researchers to be evidence of the historical influx of anubis genes into yellow baboon populations. (Alberts and Altmann, 2001; Jolly, 1993)

Contributors

Nancy Shefferly (author), Animal Diversity Web, George Hammond (editor), 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., E. Smith. 1999. Female dominance and female social relationships among yellow baboons (Papio hamadryas cynocephalus). American Journal of Primatology, 47: 321-334.

Bercovitch, F. 1987. Female weight and reproductive condition in a population of olive baboons (Papio anubis). American Journal of Primatology, 12: 189-195.

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