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
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).
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.
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
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).
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 &
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
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 September 1.