Observations on the meat-eating behavior of wild bonobos (Pan paniscus) at Wamba,Republic of Zaire

Meat-eating behavior of wild bonobos (Pan paniscus) was witnessed on two occasions at Wamba, Republic of Zaire. Only flying squirrels were observed to be eaten by the bonobos. Several bonobos gathered around the possessor of the meat and showed interest in the meat on all occasions. Begging behavior was noted on one of the two occasions, but the possessor of the meat ignored it. No sharing of meat was seen on either occasion. The exclusive targets of hunting by bonobos are apparently small mammals, such as flying squirrels and infant duikers, since evidence of meat eating by wild bonobos, which have been studied for more than fifteen years, has been restricted to these mammals. The bonobos at Wamba may have a specialized “prey image”, as in the case of the chimpanzees (Pan troglodytes) of the Tai forest, and certain medium-sized or small mammals may not conform to this image.     

Function of peering behavior among bonobos (Pan paniscus) at Wamba,Zaire

Peering behavior (prolonged gazing within 30 cm by an animal toward another) in wild bonobos (Pan paniscus) at Wamba, Zaire, was studied. A total of 230 peering episodes were observed in various social contexts. Peering behavior was often directed from younger animals toward older ones. In particular, adult females were most frequently involved in peering, with individuals of all age-sex classes. On the other hand, male bonobos seldom took part in peering behavior. Four types of behavior patterns followed the peering behavior: (1) the peerer left; (2) the peeree left; (3) both peerer and peeree stayed but had no further social interaction; and (4) some other social interaction followed. Type (1) was the most frequent. Peering usually led to tolerance by older (dominant) animals of a younger (subordinate) animal’s subsequent actions directed towards the former. Peering was thus concluded to be a unilateral action for initiating affinitive interactions by the peerer.     

Observations of physical abnormalities among the wild bonobos (Pan paniscus) of Wamba,Zaire

The wild bonobos (Pan paniscus) of Wamba, Zaire have an extremely high frequency of external abnormal traits. Out of 96 animals in a sample comprising all age and sex classes from two different natural groups, 46 individuals had at least one limb defect. The frequency of abnormalities was greater in males than in females, and increased directly with age. Almost all infants and juveniles had completely normal limbs, but virtually all males and over half the females which had reached their prime were found to have one or more limb defects. These findings indicate that congenital factors contribute little to the frequency of abnormalities in this sample. Survival rate is the same in individuals with defects as in those without defects. It appears that individual social status is far more important in procuring foods than locomotor ability. Thus, the operation of such abnormalities as a selective factor in intraspecific competition is minimized in the network of their social relations.     

Context and Development of Sexual Behavior of Wild Bonobos (Pan paniscus) at Wamba, Zaire

I studied sexual behavior of immature bonobos (Pan paniscus) in a wild group living at Wamba, Zaire, with special reference to its development. Even immature individuals under 1 year old performed sexual behavior. Sexual behavior occurred in almost all age–sex combinations, except between immature and mature females. Based on analyses of behavioral pattern and context, I classified sexual behavior involving immature individuals into three categories. (1) Genital contact between immature individuals was observed during play, and was performed by males more frequently than by females. This sexual behavior shared many traits with that of other great apes. (2) Copulation-like genital contact was observed between immature males and mature females. Its frequency increased with the immature male's age; it developed into copulation in adulthood. (3) Genital contact used to regulate interindividual relationships. This behavior, which is unique to bonobos, was absent among infants. It developed between late juvenile and early adolescent periods in association with changes in social circumstances.     

Population Dynamics of Wild Bonobos (Pan paniscus) at Wamba

We analyzed population dynamics and birth seasonality of wild bonobos at Wamba, Democratic Republic of the Congo, based on 20 years of observations (1976–1996). Wamba Bonobo infant mortality is much lower than that reported for chimpanzees. This seemes to be related to several socioecological characteristics of bonobos: the use of abundant fruit and herbaceous foods, larger food patch size, female feeding priority, and the absence of infanticide. The mean interval between live births of 4.8 years is shorter than those reported for chimpanzees, and some females simultaneously carried and nursed two successive offspring. Mother–offspring conflicts, such as refusal of suckling attempts and interference with mothers' copulation, which are common in chimpanzees, are rare in Wamba bonobos. A birth peak seems to occur during the light rainy season from March to May, just after the season with the least rainfall. This timing of births is similar to those reported for chimpanzee populations, and might benefit both mother and offspring by maximizing the amount of time before the next dry season.     

Structure and use of distance calls in wild bonobos (Pan paniscus)

We report the physical structure and use of a distance call (high-hoot) by wild bonobos (Pan paniscus).Although spectrographic analyses reveal high structural variability, the total sample can be subdivided according to the composition of units—the presence or absence of an initial segment—and the range of the lowest harmonic. Analyses of samples from male—female pairs,vocalizing simultaneously and in close proximity, reveal that both animals utter calls in more or less precise temporal alternation but with different spectral ranges. Whether these differences are gender-specific or related to other factors, such as age or the social relations between particular individuals, is not clear. We suggest that (a) individuals of the same party may coordinate their vocal activity on both the temporal and the spectral level and (b) high hootings stimulate emission of equal vocalizations by members of other parties and may increase cohesion among community members. Comparison of a restricted number of spectrograms from known individuals indicates that bonobos may be able to adjust spectral parameters of one type of distance calls (high- hoot) according to corresponding calls of conspecifics.     

Behavior of bonobos (Pan paniscus) following their capture of monkeys in Zaire

For the first time, three cases of capture and forced interaction were observed between bonobos (Pan paniscus)and two other species of primates (Colobus angolensisand Cercopithecus ascanius)in the Lilungu (Ikela) region, Republic of Zaire. The bonobos interacted with the captured primates as if they were dealing with individuals of their own species. They sought cooperation in their interactions with the captured young primates without scccess. There is no evidence that they ate the captives.     

Peering in mature, captive bonobos (Pan paniscus)

“Peering”—close-proximity staring at the mouth of another—was observed in ten (three males and seven females) mature (at least 7 years old) bonobos (Pan paniscus) living in three social groups at the San Diego Zoo and Wild Animal Park. Instantaneous scan samples, taken at 2-min intervals, over a three-and-a-half year period, yielded 617 observations of peering (1.4 per observation hour). Food was exchanged in only 15 of these scans. Peering was most often performed by younger animals and was primarily directed toward older females (“matrons”). In a given dyad, the animal more likely to peer at the other was also more like to both peer and be peered at if they frequently groomed and infrequently displayed aggression at a given female. An adolescent male showed the highest frequency of peering when living with two older females, but dropped to adult male levels when later housed with two younger (albeit mature) females. A reversal in which animal was more likely to peer, follow, and groom occurred in one female dyad, after the birth of the younger animal's first infant. After a similar birth in the other group, no such changes were observed. We discuss how these and related findings, in conjunction with what is known of the social structure of this species, suggest that one possible function of peering in bonobos may be as a signal acknowledging female status.     

Sex differences in copulation attempts in wild bonobos at Wamba

We examined sex differences in copulation attempts in a group of wild bonobos at Wamba, Congo, by analyzing the behavioral sequence. Most copulation attempts were initiated by approach or courtship behaviors by males. Males showed these behaviors when they were more than 5 m from females, whereas females did so only when males solicited them from within 5 m. Most copulations involved females showing perineal swelling, because males solicited those females more frequently and those females accepted copulation more frequently than did females in the non-swelling phase. Nevertheless, males solicited females in the non-swelling phase in one-third of copulation attempts, and those females accepted copulation in half of those attempts. This is markedly different from chimpanzees, in which sexual behaviors almost exclusively involve females in the swelling phase. The perineum of female bonobos during the non-swelling phase is soft and wrinkled but fairly large, which may attract males to some extent. The low, but existing, attractiveness and receptivity of female bonobos during the non-swelling phase might have evolved to control sexual competition among males and provide higher social status for females.     

Sexual competition in a group of captive bonobos (Pan paniscus)

We describe the occurrence of sexual competition, expressed as harassment of sexual interactions in a captive group of bonobos. We monitored all aggressive and pestering interventions during sexual interactions of three captive adult females, one adolescent, and three adult males. The study period covered two complete menstrual cycles for each female, with continuous daily observations. There was relatively little overt sexual competition by the males, in analogy with other studies. Most male interventions occurred towards interactions with the alfa female. The alfa female performed the most intense and the highest number of interventions towards the sexual interactions of the other females. The data provide evidence for female intra-sexual competition in this female dominant species.     

Habitat Use and Ranging of Wild Bonobos (Pan paniscus) at Wamba

The relationship between vegetation and ranging patterns of wild bonobos at Wamba, Democratic Republic of the Congo, was examined. Via Landsat data, we distinguished three types of vegetation—dry forest, swamp forest, and disturbed forest—at Wamba. The home ranges of the study groups changed considerably from year to year, due mainly to intergroup relationships. The population density of each group varied between 1.4 and 2.5 individuals per km ² and was lowest during a period of population increase. Home ranges consisted mainly of dry forest. The bonobos used dry forest more frequently than the other forest types, though they also used swamp and disturbed forest almost every day. The latter types of forest seemed to be important resources for the bonobos, owing to the abundant herbaceous plants that are rich in protein and constantly available. The bonobos tended to use dry forest more frequently in the rainy season than in the relatively dry season, probably because the favored fruits in the dry forest were mostly available in the rainy season. There was no seasonal difference in the size of the daily ranging area.     

Utilization patterns of a marsh grassland within the tropical rain forest by the bonobos (Pan paniscus) of Yalosidi,Republic of Zaire

The bonobos of Yalosidi, Ikela zone, near the southeastern limit of the range of this species, make regular visits to a marsh grassland known locally as Iyoko (or Yoku) within the tropical rain forest. They come to the marsh to feed on the fibrous vegetative organs of particular species of aquatic or amphibious herbs and grasses, especially those of the families Alismataceae and Cyperaceae. During fixed point observations at Iyoko between September 1975 and January 1976, seasonal changes were recognized in the party size, attendance rate, and arrival time of the bonobos, while no conspicuous change was observed in the composition and phenology of their food plants. The size of the bonobo parties appeared to be an important factor in determining the duration of stay at the marsh per visit. Throughout the study period with the exception of January, they intensively utilized a particular portion of Iyoko, in which their preferred food was scattered. Iyoko was also utilized frequently as a stable feeding place by other large forest herbivores such as elephants, buffalos, bongos, sitatungas, and duikers. In contrast, various species of cercopithecid monkeys commonly seen in the surrounding forest were never observed to enter Iyoko for foraging. This suggests a comprehensive use of the habitat by the Yalosidi bonobos compared with the more limited ecological niches of other sympatric non-human primates.     

Function and distribution of coalitions in captive bonobos (Pan paniscus)

We examined the distribution of support behaviour within a captive group of bonobos. Most support was evoked by inter-sexual conflicts with the two highest ranking females. Within a dyad, the usual winner was most often supported. Individuals that challenged the rank order by aggressions and pestering were aggressed more often by their targets in the company of an ally. The two lowest ranking males served as scapegoats, receiving 80% of the contra-support. In coalitions, inviduals did not aggress victims they would not dare to attack without supporters. However, the victims of coalitions reacted more strongly with fear and rarely counteraggressed than when being attacked alone, indicative of the high impact of aggression in support. The alpha female showed some control behaviour when intervening in conflicts. The data fitted with several functional hypotheses: coalitions functioned to maintain existing ranks, to acquire ranks, to reduce tension, and to test or strengthen the bond. We suggest that support behaviour fulfilled a crucial role in the maintenance of the power of the two highest ranking females over the males. Among the females themselves the dominance relationships were not based on coalitions, but on individual attributes.     

Agonistic Interactions and Matrifocal Dominance Rank of Wild Bonobos (Pan paniscus) at Wamba

I studied dominance relations in a wild group of bonobos at Wamba, Democratic Republic of Congo. Although agonistic interactions between males occurred frequently, most of them consisted only of display, and physical attacks were infrequent. Dominance rank order seemed to exist among males, but its linearity is unclear. Dominant males rarely disturbed copulatory behavior by subordinate males. However, high-ranking males usually stayed in the central position of the mixed party and, so, would have more chance of access to estrous females. Among females, older individuals tended to be dominant over younger individuals. However, agonistic interactions between females occurred rather infrequently, and most consisted of displacement without any overt aggressive behavior. Dominance between males and females is unclear, but females tended to have priority of access to food. The close social status between males and females may be related to the prolonged estrus of females and their close aggregation during ranging. Existence of a male's mother in the group and her dominance status among females seemed to influence his dominance rank among males. Young adult males whose mothers were alive in the group tended to have high status. In some cases, change in dominance between high-ranking males was preceded by a corresponding change in dominance between their mothers. As the dominance status of females is similar to that of males, mothers may be able to support their sons to achieve high status, stay in the center of the mixed party, and so have greater access to females, which may maximize the number of descendants of the mothers.     

Food calling by captive bonobos (Pan paniscus): An experiment

We examined (i) whether bonobos display a specific food-calling behavior when discovering a hidden food resource, (ii) whether the presence of competitors affects this behavior, and (iii) whether food quantity or gender influences its appearance. We carried out experiments (n = 108) within a captive group of eight bonobos at the Animal Park Planckendael (Mechelen,Belgium). We hid highly preferred food items (n = 7 or 25) in their enclosure and recorded vocal behavior and interactions between discoverer and group members. As a control, we gave the same number of items to the individuals when isolated from the group, a situation without potential food competition (n = 38). The only vocalization frequently uttered by the discoverer was the food peep. They uttered food peeps significantly more often when no food competition was possible. The amount of food had no significant influence on whether food peeps were uttered. The same applies to the individuals’ identity or gender. Although the costs of food calling behavior seemed much higher for males, both sexes uttered food calls to the same extent. We hypothesize thai males signal food presence in order to attract potential mates and are willing to give up the discovered food resource in return for sex: sex for food exchange. In contrast, females may vocalize to attract coalition partners. Through these coalitions, they can monopolize food resources vis-à-vis males. It is also possible that females have less reason to suppress food calk, since they are dominant to males. This study suggests that bonobos are able to give shaded signals about their environment and have the potential to communicate this information in order to promote their sexual strategy.     

Association and social interactions between strangers and residents in bonobos (Pan paniscus)

This study reports on close spatial association and repeated behavioural interactions between two strange adult male bonobos with residents of another community. Over a period of 12 months one of the two males developed friendly social relations to some of the females and other residents, which were indistinguishable from those existing between co-residents. Aggression by resident males against the strangers decreased but the former remained intolerant. The strange males appeared at a time when the number of adult resident males was lower as in the years before and when the adult sex ratio (number of adult females per male) was higher as in the years before. Using definitions from studies on dispersal patterns of male gorillas (Harcourt, 1978) and female bonobos (Furuichi, 1989) the spatial association between the two strange males and residents could be described as male transfer.     

Comparing infant and juvenile behavior in bonobos (Pan paniscus) and chimpanzees (Pan troglodytes): a preliminary study

The dichotomy between the two Pan species, the bonobo (Pan paniscus) and chimpanzee (Pan troglodytes) has been strongly emphasized until very recently. Given that most studies were primarily based on adult individuals, we shifted the “continuity versus discontinuity” discussion to the infant and juvenile stage. Our aim was to test quantitatively, some conflicting statements made in literature considering species differences between immature bonobos and chimpanzees. On one hand it is suggested that infant bonobos show retardation in motor and social development when compared with chimpanzees. Additionally it is expected that the weaning process is more traumatic to chimpanzee than bonobo infants. But on the other hand the development of behaviors is expected to be very similar in both species. We observed eight mother–infant pairs of each species in several European zoos. Our preliminary research partially confirms that immature chimpanzees seem spatially more independent, spending more time at a larger distance from their mother than immature bonobos. However, the other data do not seem to support the hypothesis that bonobo infants show retardation of motor or social development. The development of solitary play, environmental exploration, social play, non-copulatory mounts and aggressive interactions do not differ between the species. Bonobo infants in general even groom other group members more than chimpanzee infants. We also found that older bonobo infants have more nipple contact than same aged chimpanzees and that the weaning process seems to end later for bonobos than for immature chimpanzee. Additionally, although immature bonobos show in general more signs of distress, our data suggest that the weaning period itself is more traumatic for chimpanzees.     

Female relationships in bonobos(Pan paniscus)

The popular belief that women are not naturally able to bond with each other is often supported by theoretical and empirical evidence that unrelated females do not bond in nonhuman primate species. Bonobos (rare and endangered African apes, also known as pygmy chimpanzees) are (with their congener, chimpanzees) the closest living relatives of humans and appear to be an exception to this characterization. Data collected on individuals representing half of the world’s captive population reveal that bonobo females are remarkably skillful in establishing and maintaining strong affiliative bonds with each other despite being unrelated. Moreover, they control access to highly desirable food, share it with each other more often than with males, engage in same-sex sexual interactions in order to reduce tension, and form alliances in which they cooperatively attack males and inflict injuries. Their power does not stem from a size equality with or advantage over males (in fact, females average 82.5% of male size), but rather from cooperation and coalition formation. The immediate advantage to female alliances is increased control over food, the main resource on which their reproductive success depends, as well as a reduction in other costs typically associated with a female-biased dispersal system, such as male agonism in the contexts of feeding competition and sexual coercion. The ultimate advantage of friendly relationships among females is an earlier age at first reproduction, which results in a large increase in lifetime reproductive success. Analysis of this bonding phenomenon sheds light on when, where, and how we should expect unrelated human females to bond with one another by demonstrating that bonding is not dependent on access to one’s relatives but rather on an environmental situation in which female aggregation is possible, coupled with an incentive for cooperation.     

The responses of bonobos (Pan paniscus) to their mirror images: Evidence of selfrecognition

This research examined the responses of bonobos (Pan paniscus) to their mirror images. Nine bonobos were presented alternately with the reflective and non-reflective sides of a mirror. The apes exhibited considerable interest in the mirror, and immature animals exhibited higher frequencies of contingent action and inactive looking than did adults. four animals used the mirror to inspect parts of their bodies that were otherwise not visible to them, indicating that bonobos are capable of self-recognition.     

Social interactions and the life history of femalePan paniscus in Wamba,Zaire

The unit-group of Pan paniscustends to form one large mixed party consisting of most of its members. Females usually stay in the party irrespective of their estrous state. They aggregate in the center of the party; and, older females stay in the most central part. Adult and adolescent sons of the old adult females stay in the central part more than males without mothers in the unit-group do. Females leave their natal unit-groups as older juveniles or in early adolescence and. settle in another unit-group after visiting several. Newly immigrated young females are eager to have social interactions with senior females to improve their social positions. Females become less eager to interact socially with other females when they have their own offspring. The strong bond between mother and son continues into his adulthood; and, females in old age become important members of the unit-group, both as the targets of association for younger females and as the mothers of highranking males. High social status of females seems related to their cohesive grouping tendency. The consistency of the multimale/multifemale party and the existence of prominent mother-offspring subunits are unique characteristics of P. paniscusamong the Pongidae. This social structure may provide a feasible model of the basic society from which human society evolved.