Primate Info Net Banner Wisconsin PRC Logo

Yellow baboon
Papio cynocephalus

SOCIAL ORGANIZATION AND BEHAVIOR

Like many other cercopithecines, yellow baboons live in multi-male/multi-female groups in which the females remain in their natal groups for their entire lives and males emigrate into a new social group to breed when they reach adult size (Samuels et al. 1987; Bentley-Condit & Smith 1999; Combes & Altmann 2001; Silk et al. 2004). Group size varies from 17 to 77, with the average group size at Amboseli National Park being 39 individuals (Samuels & Altmann 1991). There are slightly more adult females in the group than adult males. At Amboseli, baboon density is about 1.15 individuals per square kilometer (.715 individuals per square mile) (Samuels & Altmann 1991). In areas where food availability, including agricultural foods and human refuse, is high, group size is larger and grows more quickly compared to wild-feeding groups. Group size increases through recruitment and immigration of adult males (Samuels & Altmann 1991).

Females remain in their natal groups with their close female relatives. Dominance hierarchies exist among matrilines and young female baboons inherit the rank of their mothers (Bentley-Condit & Smith 1999). Dominant females assert their rank over submissive females by threats, mild aggression, biting, chasing, displacing at feeding sites, and fighting. Submissive animals respond by averting their head and body, avoiding the dominant animal, crouching, and screaming (Bentley-Condit & Smith 1999). Once dominance has been established between animals, though, the dominant individuals do not have to constantly behave aggressively to maintain their status as lower-ranking individuals respect the dominance hierarchy without being threatened (Altmann pers. comm.). When two females are involved in an agonistic dispute, another female will sometimes intervene and lend support to one of the females. These coalitions between female yellow baboons are primarily based on kinship and relative dominance rank (Silk et al. 2004). For example, young females are supported by their mothers and siblings while closely related adult females support one another during agonistic encounters. A female will not lend support to her relative during a dispute when both females involved are higher-ranking (Silk et al. 2004). Higher-ranking females accrue more benefits from maintaining their rank and mediating conflict between lower-ranking females than vice versa. Given priority access to scarce resources and enjoying higher reproductive success, high-ranking females protect their dominance status through the interactions of lower-ranking females (Samuels et al. 1987; Bentley-Condit & Smith 1999). Female rank remains stable for long periods but is very occasionally punctuated by rapid periods of change in which low-ranking females assume high-ranking positions. Some of the conditions under which this may occur includes the death or disappearance of a dominant female who can no longer can support her daughters or sisters in agonistic interactions and therefore the lower-ranking female wins, the increase in size of a subordinate matriline such that the lower-ranking females outnumber the higher-ranking females and can dominate in physical interactions, or when a large number of juvenile females reach adolescence and displace or outcompete older, higher-ranking adult females (Samuels et al. 1987).

Males disperse from their natal groups around 8.5 years of age (Alberts & Altmann 1995a). It is at this age that they have reached their full size and fighting ability even though they are capable of reproducing long before this age (Altmann et al. 1988). Male yellow baboons also exhibit a dominance hierarchy in which the largest, most capable fighters, usually the youngest immigrants, are the most dominant. Subordinate males flinch or move out of the way of a dominant male, jump back when approached, grimace, and scream (Noë & Sluijter 1995). Adult and subadult males are dominant over juvenile males and females and adult females, regardless of rank (Hausfater 1975; Bentley-Condit & Smith 1999). One benefit of high rank among males is higher levels of reproductive success, on average, than lower-ranking males (Alberts et al. 2003).

Before joining a new group, an emigrating male spends a period of time alone, usually lasting two months (Alberts & Altmann 1995a). This is a dangerous time for a young male because when moving solitarily on the savanna, yellow baboons are subject to higher levels of predation. When a male attempts to enter a new group, he immediately begins challenging other adult males in agonistic encounters in order to obtain reproductive opportunities with adult females (Drews 1996; Alberts & Altmann 2001). These fights can lead to serious injuries in males including cuts, punctures, and scratches from the opponent's formidable canine teeth as well as broken bones. Indirect injuries include loss of eyesight, bacterial infection, increased vulnerability to parasites, decreased ability to forage, and increased vulnerability to predators (Drews 1996). At one site, it was observed that when males are injured, they drop approximately one step from their previous rank and if the newcomer does not win a fight with an established adult male, he may be evicted from the group (Drews 1996). Like females, yellow baboon males form coalitions and support each other during fights. These coalitions are not based on kinship, however, as males within a group are not likely to be related, but rather are based on fighting ability. Middle-ranked males with average individual fighting abilities form alliances with similarly ranked males in order to dominate in interactions with higher-ranked males (Noë & Sluijter 1995). Once they have achieved top rank within the group, male yellow baboons maintain it for an average of two years before being displaced by a younger male, but tenure can be as short as one month and as long as 11.5 years (Alberts & Altmann 1995a). Males transfer groups throughout their lives and the average residency duration is 2.8 to 4.25 years (Altmann et al. 1988).

REPRODUCTION

Females reach reproductive maturity around 4.5 to five years of age in the wild, and a female first gives birth around six to 6.5 years of age. In captivity, yellow baboons reach adolescence earlier, around three to 3.5 years of age and can give birth within a year after puberty (Altmann et al. 1988; Rhine et al. 2000). The average ovarian cycle lasts about 33 days in yellow baboons and is characterized by anogenital tumescence and menstruation (Hausfater 1975). The peak of swelling is concurrent with ovulation and is a reliable sign to adult males and other females of the reproductive state of the female (Hausfater 1975). One advantage of being a daughter in a high-ranking matriline is that high-ranking daughters reach sexual maturity and reproduce at a younger age, almost an entire year earlier, than low-ranking daughters, increasing their overall potential fitness. Once they reach sexual maturity, female yellow baboons reproduce consistently until old age and associated problems prevent them from reproducing (Rhine et al. 2000). Yellow baboons do not exhibit birth seasonality as females mate and give birth throughout the year. Because of the somewhat marginal habitat in which they live, nutritional stress plays an important part on the regularity of ovarian cycling among females. Female yellow baboons are more likely to cycle during the rainy season, when resources are readily available, compared to the dry season (Altmann et al. 1988). Gestation lasts 180 days and the average interbirth interval is 1.78 years (Altmann 1970; Rhine et al. 2000). Females experience lactational amenorrhea and the ovarian cycle returns as the infant begins to be weaned (Altmann et al. 1988).

Physical development in males is slower than in females so that when young yellow baboon females are first conceiving, around age six, their male counterparts are only about half the adult size and are too low-ranking to mate within the group (Altmann et al 1988). When males reach their full size, they usually leave their natal group. Males that do not leave their natal group will stay and reproduce for several years before emigrating, potentially breeding with close relatives. One reason a young male risks inbreeding is the high cost of immigrating into a new group; when males disperse they spend a period of time alone and are subject to predation. Additionally, time spent alone translates into lost mating opportunities (Alberts & Altmann 1995a). Males experience their first sexual consortship around eight years of age (Alberts & Altmann 1995b).

Because baboons mate throughout the year, and females are not likely to be fertile at the same time of year, males are able to monopolize mating opportunities with a single female through consortship behavior and mate guarding. High-ranking adult males persistently follow estrous females and repeatedly mate with them during the most fertile phase of their cycle. These consortships often result in the pair lagging behind the rest of the group during traveling and foraging, peripheralization of the couple while the female is most receptive, and intense fights as the dominant male prevents other males from mating with the female (Rasmussen 1986; Alberts et al. 1996). Females exercise mate choice in the formation of these consortships; they can be eager to form a bond with a male, approaching and following him, sexually presenting, and allowing copulations or they can avoid an approaching male by walking away, rarely presenting, and not tolerating copulations (Altmann et al. 1988). When two yellow baboons form a consortship, it may last a morning, an afternoon, or an entire day, and females can have multiple mates during the estrus period (Hausfater 1975). Females do not always choose males based on rank but on mutual cooperation or "friendship" formed by grooming, maintaining close proximity, and infant handling (Rasmussen 1986; Altmann et al. 1988). Because the highest-ranking males in a group are likely to be new immigrants, females that have not established relationships with new males avoid them, especially if they have young offspring. Lower-ranking males form alliances and can harass newly immigrated but dominant males and protect adult females with which they have bonds. Overall, though, dominance rank of a male indicates reproductive success so that high-ranking males have more mating opportunities, more offspring, and increased fitness compared to lower-ranking males (Alberts et al. 2003).

PARENTAL CARE

Females are the primary caregivers to their dependent offspring, but males contribute to the survival of infants in direct and indirect manners (Altmann 1980; Altmann et al. 1988; Stein 1984). At Amboseli National Park, survival rates of the first year are around 79%, and maternal effects such as rank influence the survival of individual infants (Altmann & Alberts 2005). Shortly after birth, baboon infants cling to their mothers largely unaided and begin to nurse. For about the first week of life, the mother offers a supportive embrace to the infant to ensure that it does not lose its grip when she is moving (Altmann 1980). For the first two weeks of life, the infant will not move from the mother, but will increasingly begin to move around on her ventrum. They have poor motor control in the early weeks of life, and any locomotory attempts usually end with the infant falling over after the first few steps. By the end of the second week, the infant attempts to break contact with its mother, but the mother is extremely attentive and at any sign of distress or any change in the surroundings, including approaching group members, the mother immediately retrieves her offspring (Altmann 1980). Generally speaking, higher-ranking mothers are more permissive with their infants than lower-ranking females. High-ranking females allow their infants to be handled by other group members and groomed by others more frequently compared to low-ranking ones (Altmann 1980). A new infant attracts the attention of all group members, regardless of the mother's rank, and this is one reason that permissiveness and protectiveness are correlated with rank. Yellow baboon infants of low-ranking mothers are occasionally stolen or kidnapped by higher-ranking females. The mother is helpless to retrieve her infant because she is comparatively lower in the dominance hierarchy and is not likely to have female support to fight with higher-ranking females (Altmann 1980).

The infant rides ventrally for two to three months but then begins to move around to ride on the mother's dorsal side. At around two months of age, the mother begins to initiate breaks in contact with her infant, and by three or four months of age, infants spend increasing amounts of time in peer interactions, including play. Their locomotor skills have increased greatly by this point and they are able to climb some trees. They are still highly dependent on their mothers for food and transportation, especially if the group is traveling quickly, but they become increasingly independent as they age (Altmann 1980). They increase the amount of solid food consumed around four months of age, and within one year most yellow baboon infants can survive without their mother, though they continue to nurse occasionally and sleep in the mother's sleeping tree until a younger sibling is born (Altmann 1980; Rhine et al. 1985). The amount of time in contact with the mother begins at 100% in the first week of life and decreases by eight or nine percent each consecutive month of life. The mother increasingly resists an infant's attempts to be carried and nurse as the infant ages such that by six to eight months of age, she often dislodges the infant while walking and ignores the infant when it attempts to make contact (Altmann 1980). Weaning is almost completed by the end of the first year, but until another sibling is born, a young yellow baboon will nurse during times of extreme stress or alarm, as a form of comfort (Altmann 1980; Rhine et al. 1985).

COMMUNICATION

Visual communication among yellow baboons is important as a measure to deter agonistic interactions involving physical fighting, especially among males. Fighting is often very costly in terms of injuries that can lead to a host of other secondary problems such as infections, permanent injury, inability to forage, and inability to travel with the group, leading to higher likelihood of predation. Baboons therefore have highly ritualized signals which communicate threat without escalating to physical fighting (Drews 1996). These include intense staring, eyelid displays where one male blinks slowly, exposing his whitish eyelids to his potential competitor, ground slapping, audible chewing or teeth grinding, yawning (which displays the formidable canine teeth), eyebrow-raising, ear flattening, jerking of the head down and forward, piloerection, rearing onto the hind legs, and shaking of rocks and branches (Hall & DeVore 1965; Altmann 1967; Drews 1996). Females also use the yawn display during times of social tension (Hall & DeVore 1965). Some friendly signals seen in baboons include lipsmacking, grinning, looking over one shoulder, presenting any body part for grooming, and ear-flattening (Hall & DeVore 1965).

Vocalizations among yellow baboons include those given only by adult males, those heard from any adult baboon, and juvenile calls. Some calls given only by adult males include "barks," loud calls that can be heard for distances over.8 km (.5 mi) and which are given as a reaction to dangerous situations such as the presence of predators, "grunts," heard as males begins to threat display, "roars," loud vocalizations that are heard during physical confrontations, and "grating roars," resonant vocalizations with low intensity given by dominant adult males (Hall & DeVore 1965). Calls that can be given by any adult yellow baboon include "screeching," heard as a submissive animal retreats from a more dominant group member; "shrill barks," given in response to the sudden appearance of animals of different species, including predators; "dog barks," heard when one animal is separated from the rest of the group, and "grunts," heard when the group feeds together and as they gather in the sleeping grove at night (Hall & DeVore 1965). One vocalization given only by adult females in estrus is the "muffled growl," a sound made as the female inhales and exhales with her mouth almost closed and puffing out her cheeks. This is also called a "copulation call" as it is heard during and after copulation (Hall & DeVore 1965; Semple et al. 2002). Juveniles, including infants, also make vocalizations unique to their age-class, including "chirplike clicking," heard when the young baboon is separated from its mother or when it is frustrated and "ick-ooers," heard in similar situations (Hall & DeVore 1965).

Content last modified: January 6, 2006

Written by Kristina Cawthon Lang. Reviewed by Jeanne Altmann.

Cite this page as:
Cawthon Lang KA. 2006 January 6. Primate Factsheets: Yellow baboon (Papio cynocephalus) Behavior . <http://pin.primate.wisc.edu/factsheets/entry/yellow_baboon/behav>. Accessed 2014 April 24.