Reconciliation and consolation in captive bonobos (Pan paniscus)

Although reconciliation in bonobos (Pan paniscus) has previously been described, it has not been analyzed heretofore by the postconflict (PC) match-control (MC) method. Furthermore, although reconciliation has been investigated before in this species, consolation has not. In this study we analyzed agonistic and affiliative contacts in all sex-class combinations to clarify and reevaluate the occurrence of reconciliation in bonobos via the PC-MC method. We also investigated the occurrence of consolation by analyzing the victims' triadic contact tendency (TCT), the influence of the sex of victims, and the relative occurrence of consolation and reconciliation. We collected 167 pairs of PC-MC observations in a captive group of bonobos (in Apeldoorn, The Netherlands). The conciliatory tendency (CCT) we obtained was tendentially lower than the mean value previously found for Yerkes captive chimpanzees. Close relationships, which were present in all female-female (FF) and some male-female (MF) dyads, positively affected reconciliation rates. When only adult PC-MC pairs (157) were considered, the mean TCTs and CCTs did not differ significantly. When we focused on types of PC affiliative contact, in the case of consolation we found a striking preference for sociosexual patterns. As to the relative occurrence of consolation and reconciliation, the highest level of the former was found in the absence of the latter. When reconciliation took place, consolation generally preceded it, suggesting that consolation may be a substitutive behavior. Our findings suggest that even if reconciliation remains the best option, consolation may be an alternative substitute for reconciliation that is used to buffer the tension originating from an unresolved conflict. Reconciliation and consolation are complex phenomena that are probably related to the life history of a group. Given that few studies have been conducted on this subject, we can not at this time make any generalizations regarding conflict resolution in certain species by comparing results among studies.     

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.     

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.     

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.     

Pan paniscus and human evolution

Detailed comparisons of the postcranium, cranium, and dentition of Pan paniscus, Pan troglodytes, and Homo reveal that except for slight differences in fore- and hindlimb proportions and the morphology of the shoulder, the postcranium of the two species of Pan are allometrically scaled variants of the same animal and one does not resemble Homo more than the other. Nor does the postcranium of one species of Pan resemble Australopithecus more closely than the other when the effects of body size are controlled. The over all morphological pattern of the skull and teeth of the two chimpanzees is clearly different, however, but both are about equally distinct from the earliest known members of the family Hominidae.     

Locomotor behavior of Pan paniscus in Zaire

The locomotor behavior of Pan paniscus was studied over a four-week period in Equateur, Republic of Zaire. Bonobos were found to be both arboreal and terrestrial in their daily activities. In the trees adult bonobos are basically quadrupedal, but they also have significant components of armswinging, diving, leaping, and bipedalism in their locomotor repertoire.     

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.     

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.     

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.     

A brief note on the effects of novel enrichment on an unwanted behaviour of captive bonobos

Animals in captivity may show undesirable behaviour when they are not sufficiently challenged, making it essential for their well-being to provide daily enrichment to zoo animals. Primates need a regular replacement with novel enrichment objects to prevent them from getting bored and look for challenging situations which might be even more undesirable. A socially housed group of bonobos showed behavioural problems such as stealing and rough handling and playing with a newborn infant in the group. To study whether providing novel environmental enrichment has an effect on this phenomenon we performed an experiment where we observed the change in behaviour in the presence of familiar and novel enrichment devices. When provided with novel enrichments, the general activity of the group increased. Simultaneously, these novel behavioural challenges significantly decreased the frequency of taking the newborn infant from its mother. Our results confirm previous findings that continuous application of new enrichments is necessary for providing sensory stimulation to primates as it promotes their well-being and indirectly might influence breeding success as well.     

Evidence for the consumption of arboreal,diurnal primates by bonobos (Pan paniscus)

We present evidence for the consumption of a diurnal, arboreal, group living primate by bonobos. The digit of an immature black mangabey (Lophocebus aterrimus) was found in the fresh feces of a bonobo (Pan paniscus) at the Lui Kotale study site, Democratic Republic of Congo. In close proximity to the fecal sample containing the remains of the digit, we also found a large part of the pelt of a black mangabey. Evidence suggests that the Lui Kotale bonobos consume more meat than other bonobo populations and have greater variation in the mammalian species exploited than previously thought [Hohmann & Fruth, Folia primatologica 79:103–110]. The current finding supports Stanford's argument [Current Anthropology 39:399–420] that some differences in the diet and behavior between chimpanzees (P. troglodytes) and bonobos are an artefact of the limited number of bonobo study populations. If bonobos did obtain the monkey by active hunting, this would challenge current evolutionary models relating the intra‐specific aggression and violence seen in chimpanzees and humans to hunting and meat consumption [Wrangham, Yearbook of Physical Anthropology 42:1–30]. Am. J. Primatol. 71:171–174, 2009. © 2008 Wiley‐Liss, Inc.     

A comparative study of the variety and complexity of object manipulation in captive chimpanzees (Pan troglodytes) and bonobos (Pan paniscus)

Four types of specific objects: wooden spoons, metal bowls, plastic boxes, and cotton towels were introduced in a similar setting to two captive groups of different species in the genusPan, the bonobo and the chimpanzee. In total, 582 unique manipulation forms were distinguished by a set of variables: types of objects, motor patterns, body-parts used, the number of objects manipulated, and types of orienting manipulation. In sum, chimpanzees and bonobos were not so different in the variety and the complexity of object manipulation forms. However, comparison of the two species revealed significant differences as follows: (1) chimpanzees preferred to use only one hand during manipulation of both single- and multiple-objects, whereas in the case of multiple-objects bonobos used both hands significantly more often; (2) chimpanzees performed more orienting manipulations in single-object manipulations than did bonobos, whereas the reverse was the case in multiple-object manipulations; and (3) chimpanzees' object manipulations were overall more substrate-oriented than were bonobos'. The factors producing these differences are discussed in relation to positional behaviors and habitual tool use in the two species.     

Handedness in captive bonobos (Pan paniscus)

Species level right-handedness is often considered to be unique to humans. Handedness is held to be interrelated to our language ability and has been used as a means of tracing the evolution of language. Here we examine handedness in 3 captive groups of bonobos (Pan paniscus) comprising 22 individuals. We found no evidence for species level handedness. Conclusions that can be drawn from these findings are: (1) species level handedness evolved after the divergence of the Pan and Homo lineages; (2) inconsistent preferences may represent precursors to human handedness, and (3) Pan may have language abilities but these cannot be measured using handedness.     

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.     

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.     

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.     

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.     

Behavioral laterality in captive bonobos (Pan paniscus): Replication and extension

We report observational data on behavioral laterality in 10 captive bonobos (Pan paniscus)at the San Diego Zoo. The unimanual measures include carrying, leading limb in locomotion, self-touching, face-touching, reaching, and gestures. We also recorded bimanual feeding in these subjects. A significant population level left-hand bias exists for carrying. Right-hand biases occur for leading limb in locomotion and gestures. During bimanual feeding, the bonobos hold food items with the left hand while feeding with the right hand. Overall, bonobos exhibit behavioral asymmetries that are similar to previous findings in other pongid ape species. The asymmetries in gestures and bimanual feeding represent novel findings with theoretical implications for the origins of tool use and language.     

Epidermal patterns of the hands and feet of the pygmy chimpanzee (Pan paniscus)

The characteristics of the epidermal ridge system were studied in a series of eighteen lesser or pygmy chimpanzees (Pan paniscus). The general ridge alignments are very similar to those of the chimpanzee (Pan troglodytes); Biegert ('61). On the average the pattern intensity (P.I.) of the palm configurations is considerably higher in the pygmy chimpanzee than in the chimpanzee, thus representing the highest total palm pattern intensity of all species of the Hominoidea. The sole configurations show parallel main results to those of the palm; however, the decreased sole pattern frequency of the pygmy chimpanzee is of a smaller predominance only as compared to the values of the other species of this superfamily. The preliminary data on the finger tip patterns, translated into P.I. values, are much higher than in chimpanzees and within the range of the mean values of gorillas (Brehme, '73), while those of the toes of pygmy chimpanzees seem to possess the lowest P.I. values of the African apes.