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Bonobo
Pan paniscus

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SOCIAL ORGANIZATION AND BEHAVIOR

Bonobos live in fission-fusion social groups where a large community of individuals separate into smaller groups, or parties, of variable size and composition. These "unit-groups" range from lone individuals to groups of 20 or more bonobos (Badrian et al. 1984; White 1988, 1996). These groups are patrilineal and the unit group is multi-male/multi-female, though the ratio of males to females is variable. At seven to nine years old, females emigrate from their natal groups to another group where they spend much time trying to initiate social interactions with dominant older adult females (Furuichi 1989). It is important for young, immigrant females to develop relationships with other females in their new groups because this is one of the strongest relationships in bonobo society. Unlike chimpanzees, females tend to have more cohesion with other females than with males, though there is evidence that as group size increases, cohesion between males and females increases (White 1988; 1996). Females obtain rank as they age and have offspring, especially males. Their sons often have corroborating rank as they mature and as the adult female becomes more central to the group (White 1996).


Photo: Joris Jacobs

Because females within the community are unlikely to be related, it is unusual that female bonobos show such strong affiliation with one another in parties and within communities. Paradoxically, males in bonobo communities are related to one another and show little affiliative behavior (White 1996). The duration and intensity of relationships that develop between male and female bonobos are not simply based on sexual attraction. Adult males and females associate for reasons besides mating that include kinship and rank acquisition (White 1996; Hohmann et al. 1999). Though females emigrate from their natal groups, molecular analyses of the genetic relatedness between community members at the Lomako field site recognized mother-son pairs and adult half-siblings associated more frequently than unrelated mixed-sex dyads (Hohmann et al. 1999). Males also associate with females for rank acquisition because females dominate the social environment. Females that have strong bonds keep males away from food and often attack males, biting off their fingers and toes (de Waal 1997). If a male is to achieve alpha status in a bonobo group, he must be accepted by the alpha female.

One of the most significant and defining characteristics of bonobo societies is sexual behavior. Sex serves purposes other than reproduction such as appeasement, affection, social status, erotic games, reconciliation, excitement, and stress reduction (de Waal 1997). Sex occurs in virtually all partner combinations and in a variety of positions. Sex, particularly genito-genital rubbing (G-G rubbing), facilitates and strengthens the bond between female bonobos (de Waal 1997). It is used in food-sharing interactions between females. Nonreproductive copulation is often seen between males and females as well. While males rarely share food, when subordinate females beg for food from dominant males, the likelihood that the male will share is greatly increased if they first copulate (Blount 1990). It is important to remember, though, that sex is primarily a function of stress reduction at feeding sites not as currency for food (Blount 1990).

REPRODUCTION


Photo: Max Planck Institut

Menarche occurs in female bonobos between ages six and eleven years (Vervaecke et al. 1999). Female bonobos exhibit obvious sexual swellings throughout their adult lives and the swelling of the sex skin is an external indicator of endocrinological processes. Only juveniles and mothers of very young infants exhibit truly flat sex skins. The swelling can be categorized into four stages over the menstrual cycle: preswelling, swelling, postswelling, and menses. Ovulation, though, is not perfectly correlated with swelling size (Thompson-Handler et al. 1984; Reichert et al. 2002). This extended period of swelling coupled with ambiguity in peak receptivity may have significance in the evolution of such promiscuous sexual behavior (de Waal 1997; Reichert et al. 2002). In males, it is difficult to determine pubertal onset and fertility onset is largely unknown (Watts & Pusey 1993). It is estimated that males reach sexual maturity around nine years when body size and testes greatly enlarge (Kuroda 1989).

As a tactic to avoid inbreeding, adolescent female bonobos emigrate from their natal groups at around seven years-old and join another group where they will produce their first offspring by the age of 13 or 14 (Rowe 1996; de Waal 1997). After their first offspring, the interbirth interval is four to six years (Kano 1992; Rowe 1996; de Waal 1997). Bonobos resume swelling cycles within one year after parturition and though they rarely become pregnant, have been seen nursing two infants of different ages (Kano 1996; de Waal 1997; Furuichi et al. 1998).

Data suggest that there is a birth peak during the light rainy season between March and May of each year (Furuichi et al. 1998). This timing is significant because it is directly after the driest part of the year and may have an influence on infant survival. In fact, immature bonobo mortality rates at Wamba are lower than for chimpanzees in sparser environments. With only 18.2% of the bonobos dying by age five and only 27.3% dying by age six, there may be a link between relative abundance of fruits and herbaceous foods and infant survival rates (Furuichi et al. 1998)

PARENTAL CARE


Photo: Joris Jacobs

Because of the promiscuous mating behavior of female bonobos, there is a great deal of paternal uncertainty. If a male cannot be sure which offspring are his, he is less likely to invest any time or energy caring for them. It is because of this lack of certainty that the entirety of parental care in bonobos is assumed by the mothers (de Waal 1997). That is not to say that adult males are not attentive to infants in the unit-group, in fact, there is very little aggression directed towards bonobo infants by adult males in the group and infanticide has never been recorded (Kuroda 1989; de Waal 1997).

Like all primates, bonobos exhibit a prolonged maturation period that is necessary for behavioral plasticity, strong mother-offspring relationship, and social development (Kuroda 1989). Bonobos, though, when compared to chimpanzees, have a particularly slow rate of development, and it is reported that bonobo mothers are more attentive to their offspring than chimpanzee mothers. In their first years, bonobos maintain close proximity to their mothers as they ride ventrally. Never before three months of age do they leave their mother and even at six months, they are rarely seen more than one meter away from her (Kuroda 1989). By 10 months the bonobo infant ventures about three to four meters (9.84 to 13.1 ft) from its mother, but any further and the mother will bring the infant back to her side. At one year, bonobo infants are still unsure as quadrupeds, but can locomote for a few meters. Play develops around two years of age but bonobos are still not a mobile as adults. Not until three years of age do bonobos move as gracefully as adults, and at this age they move more than 10 meters (32.9 ft) from their mothers, but are still close enough to return immediately if frightened or threatened. It is at this age that bonobo infants begin to ride dorsally rather than ventrally on their mothers (Kuroda 1989). Bonobos are not weaned until four or five years of age. They are sustained by nursing for the first year of life, and though they may mouth food, they never consume it in the first year (Kuroda 1989).

As bonobos age, the extent of the bond between mothers and offspring is sex-dependent. Subadult female bonobos begin to distance themselves from their mothers around six to seven years, though they are usually still in the same foraging party. Eventually they will emigrate from their natal group and the bond between mother and daughter is severed (Kuroda 1989). Male bonobos, on the other hand, remain quite close with their mothers through adulthood and a mother's rank within the group determines her son's rank as he reaches adulthood (Kuroda 1989; White 1996).

COMMUNICATION

Visual cues are important in primates, especially in the catarrhines, that lack a vomeronasal system. Bonobos have a remarkably expressive face and have a plethora of facial communications. Some of the predominant expressions include: "silent teeth baring," "tense mouth," "silent pout," "duck face," and "play face," though these represent only a percentage of the facial expressions seen in bonobos (de Waal 1988). Similar to visual communication, vocal communication is also important in bonobo society. Bonobos have higher pitched voices than chimpanzees and are easily distinguished based solely on sound. The two species do, however, have some overlap in their vocal repertoire (de Waal 1988). Some of the vocal displays noted in bonobos include: "low hooting," "high hooting," "contest hooting," "wieew-bark," and "greeting grunts" (de Waal 1988). An interesting vocalization that is characteristic of play is the "panting laugh." This jerky breathing that sounds like laughter and is always accompanied by a "play face" is usually heard during play and tickling (de Waal 1988).


Photo: Max Planck Institut

LISTEN TO VOCALIZATIONS

In trying to understand the context of human language evolution, much research has been conducted on bonobos. As a result, scientists have been successful in teaching bonobos the use of lexigrams as a way to communicate with humans. This work was first done with chimpanzees in Georgia at the Yerkes National Primate Research Center, but was made famous by a bonobo named Kanzi. With the help of language researcher Sue Savage-Rumbaugh, Kanzi can understand spoken word and can respond appropriately by using a lexigram. Researchers have not been able to teach apes spoken language because of physiological barriers; mainly the inability to accomplish velopharyngeal closure to produce consonant sounds (Savage-Rumbaugh & Lewin 1994).

SPECIAL NOTES

Bonobos have not traditionally been acknowledged for their use of tools, but they have been noted to self-medicate by leaf swallowing during the peak occurrence of intestinal parasites. Studies during the rainy season, at Iyema and Lomako show an increase in Oesophagostomum infections due to the lifecycle of these parasitic nematodes. This peak is correlated with leaf-swallowing, a behavior not often seen throughout the year (Dupain et al. 2002). This behavior is considered self-medication because bonobos generally chew leaves that they consume as food rather than swallow them whole. The physical action of swallowing leaves with rough surfaces facilitates expulsion of tapeworm fragments (Dupain et al. 2002).

Other interesting behaviors seen in bonobos include cultural differences in play and grooming among captive bonobos. Local variations of behavior in captive settings can be thought of as cultural differences; they are not seen in every captive population and new individuals introduced to groups that practice these diverse behaviors learn them and practice them. For example, at the San Diego Zoo, during grooming sessions between two animals, the bonobo that is grooming stops grooming at regular intervals and claps his or her hands, feet, or hand and foot together making an audible clapping noise. This behavior is the only place in the world where bonobos clap while grooming, and new individuals introduced to the group learn this behavior (de Waal 2001). Another behavior seen only among the San Diego bonobos are play behaviors such as "blind man's bluff" and "funny faces," two games played by the young bonobos of the group. In "blind man's bluff," a juvenile places an arm over his face or covers his eyes in some way and proceeds to walk along the play structures within the enclosure, often losing his balance or bumping into obstacles. This is a solitary game to begin with, but once a juvenile begins to play, other young bonobos in the group will begin to play (de Waal 2001). Finally, another cultural behavior seen among captive bonobos is a game called "funny faces" in which a solitary young bonobo makes faces for no obvious reason and which are directed at no member of the group (de Waal 2001). These behaviors are seen nowhere outside of the San Diego group of bonobos.

Content last modified: December 1, 2010

Written by Kristina Cawthon Lang. Reviewed by Frans de Waal.

Cite this page as:
Cawthon Lang KA. 2010 December 1. Primate Factsheets: Bonobo (Pan paniscus) Behavior . <http://pin.primate.wisc.edu/factsheets/entry/bonobo/behav>. Accessed 2014 April 16.