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Bonobos’ Sexual Receptivity and Social Behaviour


The Pan group of non human primates resembles the human beings the most. They are the chimpanzees of the Pan Troglodytes and the bonobo ape of the Pan Paniscus. Their sociosexual behaviors resemble hominoids. Their lives in the wild gave them special characteristics which were modified when they moved into captivity (Hohmann, 2003, p 563). Behaviors underwent changes when they moved from the dense forest to the captive environment. Adaptation has helped the chimpanzees hunt water in drought and use nests repeatedly while in the wild tropical rain forest, they had no dearth of water and nests could be changed daily from site to site. Bonobos came to the limelight after chimpanzees and had many of the behavior patterns of chimpanzees. Bonobos had the branch drag, branch clasp, branch shake, buttress beat, branch slap, leaf clip by mouth, leaf clip by fingers, leaf strip, hand clasp, leaf sponge, vegetation seat, fly whisk, aimed throw and branch din of the chimpanzees (Hohmann, 2003, p 565). The similarities between the two species could be due to the similar behavior patterns being those of the Pan group which have not been noticed by researchers previously or they could have evolved independently or they could have been attained through imitation (Hohmann, 2003, p 567).

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The behaviors of bonobos have been found to differ from site to site. Bonobos at Lomako did not eat duikers and the meat was equally divided among the mature members. Bonobos at Salonga National Park ate duikers. At Wamba they ate small animals (Hohmann, 2003, p 568). The bonobos sometimes catch small monkeys but do not eat them. They are used as playthings. Bonobos at Wamba drum using their feet while at Lomako, it is with hands or feet. Mutual grooming is a common behavior. At Wamba grooming is simultaneous while at Lomako, it is unidirectional. Leaves have been used for rain hats, toothpicks or napkins at Wamba while at Lomako the bonobos cover themselves with leaves during rain. Wading in water has shown differences. Bonobos at Lomako are quadripedal while those at Wamba are bipedal (Hohmann, 2003, p 569). Bonobos exhibit many characteristics previously thought to be cultural traits of chimpanzees.

Statement of purpose

This researcher intends to confirm the behavior patterns of the bonobos in a game reserve at …………. The behaviors in relationship to sociosexual patterns are being assessed in comparison to research studies done earlier. The dominance of the female,

the sexual receptivity of the female, the role of the male, the conflict management strategies and the egalitarian nature of the bonobos are variously pictured by different researchers. This researcher hopes to clarify the behavior patterns of the bonobos.

Significance of the study

This study hopes to provide more information on the various socio-sexual behavior patterns of the bonobos. Primates are believed to have been evolved from primitive insectivores which later became fruit eating or leaf eating animals. Consequently changes in dentition and digestion took place. The phylogenetic proximity to homo sapiens makes the non human primates important targets of research. Bonobos are apes belonging to the group of non human primates Pan Paniscus. This researcher intends to highlight various behavioral patterns pertaining to the bonobos.

Research Hypotheses

  1. Female dominance exists as an exclusive behavior in bonobos.
  2. The males are attracted to all females whether in the receptivity state or not and initiate courtship behaviors which may or may not end in successful reproduction.
  3. Bonobos are more playful during feeding time.
  4. Sexual activity is increased during feeding time.
  5. The more food, the more the sexual activity.
  6. Conflict management is well dealt with by bonobos.
  7. The bonobos are despotic in nature, not tolerant or egalitarian.
  8. Agonistic interactions are not just indicative of sexual selection and fleeing upon aggression is a sign of submission.

This researcher now intends to present the chapter on methodology and the various techniques used for assessing the behaviors in relation to the hypotheses mentioned above.


Statement of purpose

The behaviors of bonobos have been variously described by different researchers. Some have described the bonobo as a peaceful egalitarian ape with strong female dominance and female bonding. Others have claimed that this picture must be the result of adaptation to captivity. Captivity affects behavior in species with fission fusion systems like chimpanzees and bonobos (Stevens, 2008, p. 19). Changing the camp sites or zoos further makes modifications. The effect of captivity on bonobos has not yet been thoroughly studied. This study intends to elaborate the socio sexual behaviors of the bonobos focusing on the play, feeding time behaviors, sexual activity, grooming, agonistic behavior and affiliative behavior. The research would touch on the following thoughts and hopefully clarify present ideas which are ambiguous in nature.

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Research Hypotheses

  1. Female dominance exists as an exclusive behavior in bonobos.
  2. The males are attracted to all females whether in the receptivity state or not. and initiate courtship behaviors which may or may not end in successful reproduction.
  3. Bonobos are more playful during feeding time.
  4. Sexual activity is increased during feeding time.
  5. The more food, the more the sexual activity.
  6. Conflict management is well dealt with by bonobos.
  7. The bonobos are despotic in nature, not tolerant or egalitarian.
  8. Agonistic interactions are not just indicative of sexual selection and fleeing upon aggression is a sign of submission.

The ranging area is made up of primary forest, secondary forest swamp and agricultural fields. The annual rainfall is? The first phase involved the labeling of the bonobos at the site and understanding the number of adult males, adult females, young males and females. The children of adult females were also noted. We found…members:

…adult males,adult females,..adolescent female,..juvenile females,..infant males,.. and..infant females. We are planning observations from ……(date)……….. to ………Date Direct observations are to be done on………..days. We are following the bonobos from one sleeping area to another while they are moving around in the forest area. A GPS tracking system would help us to follow the bonobos on their trail and keep track every half hour. When we can not track them using the GPS, we would follow their tracks or vocal calls. The ranging rate is to be calculated by dividing the total ranging distance by the time taken for the tracking. We would be tracking parties by starting at a particular time and noting all bonobos seen within one hour.


All agonistic encounters are counted for this. The fleeing from aggression is to be taken as a marker of dominance. The directional consistency index (DCI) gives the frequency with which the behavior occurred in its more frequent direction relative to the total number of times the behavior occurred (van Hooff and Wensing 1987). The total number of times the behavior occurred in the direction of the higher frequency (H) minus the number of times in the less frequent direction (L) is divided by the total frequency. DCI = (H – L)/ (H + L) (Stevens, 2007, p 1420).

A David’s score uses dyadic dominance proportions to calculate dominance scores or cardinal rank for each individual, depending on the proportions of wins and lossess in agonistic encounters. A dominance value is obtained for each individual. The dyadic dominance index measures the degree of dominance of individual i over individual j, defined as the proportion of wins (s) relative to the total number of dominance interactions (n) between i and j Pij = sij/nij (Stevens, 2007, p.1421). The correction of index for chance under the assumption that the n + 1 possible outcomes of s, i.e., 0, 1, 2,…and n, are equally likely. The normalized dyadic dominance index corrected for chance is then: Dij = (sij + 0.5)/(nij + 1) (de Vries et al. 2006). DS can be then calculated.

The dominance may be classified into exclusive, non exclusive, matrifocal and co-dominance. The numbers of aggressions of the male and the female causing a fleeing from aggressions or a submission is compared. If they are almost equal, co- dominance would be concluded. If the aggressions are focused on the young adults for keeping them in line, it would be called matrifocal dominance. If the females are the only deciders or dominant ones, the dominance would be exclusive. If they share the honors with their children, it would be non-exclusive dominance. Intersexual dominance is to be assessed using Mann-Whitney U test. The success in evoking submissions is determined.

All females cannot evoke submission all the time. Some males would respond with more aggression or ignore it.

Courtship behaviors and reproductive success

The courtship behaviors start with a bonobo walking towards or following another. Courtship behaviors are recognized by the swaying of the upper part of the body backward standing on two feet, touching the female with the hands or penis, walking away while looking back hoping to lead the other, dropping branches and presenting (Furuichi, 2004, p 60). The picture of the perineum is noted as seen, swollen or shrunken, and recorded. A wrinkled perineum would sway while walking.

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The distances at which courtship is initiated are to be noted for the female and male. The number of successful copulations in both the oestrus and anoestrus cycles is to be noted for comparison of the male preference for either.

The sexual behaviors of the bonobos can be noted as in Appendix A which is just right for getting maximum information about the sexual acts and the initiation behaviors. The initiation behaviors can end successfully or get aborted. The behaviors have various entities which are the sway back, bipedal stand, raising the arms, touching the body, leading or dropping or shaking branches which could be assessed as initiation behaviors. Sometimes all are seen. Some initiation behaviors end in successful copulations.

Comparison of food abundance with the sexual acts

Food abundance is to be estimated by walking round the ranging area twice a month and noting the sites of abundant food (Furuichi, 2008, p 138). We would be recording the type of food, whether ripe or not. We would compare the number of detected sexual copulations with the food abundance each month to notice the impact of food abundance on the sexual activity.

Aggressive and submissive behavior

Agonistic aggressions between adult males and females for food and non food would be recorded. All forms of sudden movement without a playful face, a lunge and any physical attack would be considered under agonistic aggression. Fleeing upon aggression would be taken as submissive behavior. Observations would be made daily till the bonobos made their nests after stopping their activities. The intersexual aggression and intersexual submission would be both calculated (Stevens, 2007, p 1420). The individual percentage of submission evoked would be calculated by dividing the total intersexual submission by the total frequency of aggression.

Feeding Time activities

The grooming and sexual activities during the hour of feeding would be noted. Whether it is a simultaneous grooming or one sided grooming is to be especially noted.

The successful copulations are to be taken note of. The numbers of activities during the rest of the time are to be compared to the activities during feeding time.

BONOBO: Egalitarian, despot or tolerant?

The female bonobos would be observed for their role of dominance by noting the number of aggressive behaviors they demonstrate in restraining the others including young adults. Whether all their attempts are successful is noted. Reconciliations and sharing of food are to be noted. Any rallying against the dominant is noted. If the dominance is strong and there is no occurrence of reconciliations or sharing of food, the relationship is despotic. If the relationship is close with reconciliations and greater sharing of resources and the subordinates hardly rally against the dominant, the society is tolerant. In an egalitarian population, the tolerant characteristics are evident and the resources are equally distributed and there would be rallying against the dominant males.

Literature review

Non-human primates like the chimpanzees and bonobo apes are accorded a special place in anthropology as they are our closest hominoid relatives and can provide insights into the life of a human being. First wild primates and now captive ones are being studied frequently with the intention of deciphering the complex human nature (Strier, 2003, p 16). Evolutionary relationships justify our investigations. Ecology-stimulated field studies dwelt on the savanna baboons and then the chimpanzees.

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The sexual selection theory which raises a salute to Charles Darwin (1871) helped us understand why we as males and females behaved differently (Strier, 2003, p 19). Feminist behaviors have been evaluated in animals and found to strongly influence the males through their subtle tactics which ensure reproductive success. Female primates proved that they were not just silent witnesses of competing males. Primatology grew to study behaviors of animals with regard to ecology. Adaptations, social and sexual behaviors modified through ecological considerations and changes of natural habitat have triggered more studies with new questions and agendas. The bonobos or the Pan family which are Africa’s most endangered species (Lacambra et al, 2005) are very close evolutionary relatives of humans in the taxonomic classification and occupy a place of pride in recent studies (Strier, 2003, p 21).

Bonobos were believed to occupy dense tropical rain forest but have been found recently in gallery forests (Thompson, 2002). The studies of chimpanzees have shown different social behaviors in different sites. This is also expected from this study with bonobos though only one site has been selected. The flexibility of bonobos is evident from the research in the wild. This researcher aims to investigate the sexual receptivity and family social behavior of bonobos in captivity and whether the female domination, egalitarian concept, female bonding and peace loving nature really describe the bonobos in this site.

The sexual selection theory and calls

Adult male primates produce long distance vocalizations which are received by females. The loud calls may have subtle variations which the receiver identifies. Sexual selection theory has inter and intra selection components (Delgado, 2006, p 6). The dominant frequency, intensity of sound, rate and duration of call could also be relaying information about the body size, genetic quality and present condition of health and vigor (Delgado, 2006, p 6). Females recognize them as potential mates for reproductive success or as males with which they had previous social interactions. Other males may use this information to recognize potential rivals. Laryngeal sacs and specializations could account for these calls.

Socio-sexual behaviors

Vehrencamp (1983) defined despotism as complete exploitation of subordinates by dominant individuals. In despotism, the dominant would exploit the subordinates and punish them for transgressions. Reconciliations and the sharing of resources are not common. Tolerance sees a close relationship between the dominant and subordinates with little violence, frequent reconciliations and greater tolerance over contested resources and

subordinates hardly rally against the dominant (Stevens, 2007, p 1427). Egalitarian species have the characteristics of tolerant species and in addition, subordinates are capable of coming together to fight the dominant males. The resources are equally distributed.


Play has been a misinterpreted behavior. Different researchers have interpreted this in different ways. Play has been thought of as a means of physical training (Byers and Walker, 1995), developing skills both motor and cognitive (Dolhinow, 1999) and performing social assessment (Pellis and Iwaniuk, 2000). Social play and grooming are important in social cohesion as they allow prolonged physical contact (Palagi, 2006, p1258). Grooming reduces tension and allows appeasement. Grooming is more commonly seen in adult primates than play. Playful interactions are seen in the wild too.

Conflict management strategies may be expressed in the form of communicative displays, relationships of dominance and greeting gestures (Palagi, 2006, p 1259). Bonobos have shown increased grooming during the pre-feeding phases probably for relieving tension and an increased rate of sexual interactions in the presence of plenty of food. Play has been observed in bonobos where an adult male and an older female had a playful bout while aggressively competing over food. The play could also be a means of preventing future competitions. Bonobos probably use play to help in making food foraging peaceful (Palagi, 2006, p 1266). Reconciliation efforts are less seen in bonobos (Stevens, 2007, p 1428). There is no fission-fusion in captivity (Stevens, 2007, p 1428).

Chimpanzees too seeming to predict some competition at feeding time and the captive ones do more grooming. The bonobos meanwhile achieve the same purpose through more play, not grooming. They exhibit maximum play during the feeding. Bonobos can be thereby understood to deal actively with conflicts and tension by anticipation and celebration at short term level in pre-feeding and socio-sexual behaviors and appeasement and reassurance tactics at intermediate level as in feeding. (Palagi, 2006, p 1268). Frequency of sex also peaks at feeding time just like grooming. 97% of Copulation attempts were initiated by the approach or courtship of males from a distance (Furuichi, 2003, p1). Female bonobos usually showed their perineal swellings in the initiation. They were more receptive to sexual activity and complied for more copulations than those females without those swellings. Males thereby sought the females with swelling two thirds of the times and those without one third of the times. The second group of females only accepted copulation in half of the attempts. A difference seen in the chimpanzees is that only females with swellings (oestrus phase) participated in the acts (Furuichi, 2003, p 1). The perineum of female bonobos in the non swollen phase is wrinkled and soft but fairly large, enough to still attract males. Evolution must have done this to make the females still attractive to control sexual competition and put the female in a higher position. However the perineum is firmer in the oestrus phase. Dominant males obtain more copulations (Stevens, 2007, p 1428). However dominance and mating success do not always have a relationship (Marvan et al, 2006). The oestrus sex ratio (number of adult males per oestrus female) is less in bonobos (Furuichi, 2004, p 62). So male competition is controlled. Agonistic interactions are limited. The sexual attractiveness and receptivity during the anoestrus cycle would simulate the effects of prolonged oestrus. The high ranking of females could be due to the prolonged attractiveness.

Female dominance

Research by the 1990s saw the evolution of an egalitarian bonobo ape with strong female dominance and bonding (Stevens, 2008, p 19). Natural habitats saw the female as a ‘domineering matron’ who kept her males and children on their toes. Captivity made her more docile by adaptive potential but not forgetting her role (Stevens, 2008, p 20). Males were found to behave the same in natural and captive states (de Waal, 1994, p 248). The main reason for the different social behavior could be that the wild had temporary subgroups which kept changing in composition while the captive groups remained the same. Behaviors differ between camps in captivity. Relationship of bonobos in captivity has not been studied fully yet in the range achieved for chimpanzees. Females were not found to evoke submission from all males on all occasions (Stevens, 2007, p 1417). Males and females have despotic relationships. The bonobos can thereby be better described as semi despotic rather than egalitarian. A bonobo dominance system has been described as codominance (Fruth et al, 1999), female dominance (Parish and de Waal, 2000), matrifocal dominance (Furuichi, 1997), and non-exclusive female dominance. (Vervaecke et al, 2000a). Dominant males have more access to food and fertile females.


Fruit abundance increased the party size (Furuichi, 2008, p 144). Female bonobos are more likely to join mixed parties than males (Mulavwa et al, 2008). The higher social status of bonobos reduces the scramble competition for food in whatever parties they join. They also control the ranging area for food. Even if the males wish to forage further, they refrain from doing so if the females do not want to.


The research is a study into the sociosexual behaviors of captive bonobos. Though much literature is available for chimpanzees both in the wild and captivity, bonobos have only a limited literature giving information on their behavior patterns and their social lives. This researcher is attempting to study captive bonobos and their sexual behaviors, the agonistic interactions, play, grooming, feeding attitudes, dominance behaviors and the type of society whether despotic or tolerant or egalitarian. The behaviors that have been modified due to captivity are being evaluated here. The Pan Paniscus bonobo resembles the human being in many aspects of their sociosexual behaviors. The kind of dominance that is existing and the female dominance in relationship to the males’, the feeding patterns and the association with the increased grooming and sexual activity, the management of conflicts are all being addressed here. Following the bonobos on their trails is a task but interesting in that some activity would be up which needed recording. Watching animals behave is interesting in that we see ourselves many a time.


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