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.     

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.     

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.     

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.     

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 structures in Pan paniscus: testing the female bonding hypothesis

Based on previous research in captivity, bonobos, Pan paniscus, have been called a female-bonded species. However, genetic and behavioural data indicate that wild females migrate. Bonding between these unrelated females would then be in contradiction with socio-ecological models. It has been argued that female bonding has been overemphasized in captive bonobos. We examine patterns of proximity, grooming and support behaviour in six well established captive groups of bonobos. We find that female bonding was not a typical characteristic of all captive bonobo groups. In only two groups there was a trend for females to prefer proximity with other females over association with males. We found no evidence that following or grooming between females was more frequent than between males and unrelated females or between males. Only in coalitions, females supported each other more than male–female or male–male dyads. We also investigated five mother–son pairs. Grooming was more frequent among mothers and sons than in any other dyad, but sons did not groom their mothers more than males groomed unrelated females. Mothers groomed their sons, or provided more support to them than females groomed or supported unrelated males. Thus, while bonds between females were clearly present, intersexual relations between males and either unrelated females or their mothers are of more, or equal importance.     

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.     

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.     

Reactions of a group of pygmy chimpanzees (Pan paniscus) to their mirror-images: Evidence of self-recognition

A group of seven pygmy chimpanzees (Pan paniscus) was tested for their mirror-image reactions during a ten-day experiment. The time spent viewing the mirror waned quickly. Little social responses directed towards the mirror were observed. Self-directed behaviors were shown from testday one on. It was concluded that four out of seven animals could correctly identify their mirror-image, one infant was not (yet) able to do so, and for two other individuals the results were inconclusive.     

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.     

Beiträge zur Menschenaffenhaltung im Zoo Berlin nach 1945.: 2. Mitteilung: Bonobos oder Zwergschimpansen (Pan paniscus) Keeping and breeding of Great apes in Berlin Zoo after 1945. 2. Bonobos or Pigmy chimpanzees (Pan paniscus)

The first Bonobo arrived 1987 in Berlin Zoo, the first birth occurred 1995. Up to now four Bonobos were born in Berlin Zoo.     

Comparison of behavioral sequence of copulation between chimpanzees and bonobos

We compared sex differences in behaviors leading to copulation of chimpanzees (Pan troglodytes) in the Kalinzu Forest, Uganda with those of bonobos (Pan paniscus) at Wamba, D.R. Congo, using the same definition. Female chimpanzees were more likely to initiate copulation than female bonobos. While most of copulations (96%) were initiated by males in bonobos, among chimpanzees only 63% of copulations were initiated by males. Female bonobos initiated an interaction leading to copulation when males approached them within a short distance. On the other hand, both male and female chimpanzees initiated behavior at a longer distance. Higher proceptivity and a higher copulation rate during the maximal swelling period of female chimpanzees might suggest that they gain greater benefits from a high frequency of copulations than do female bonobos.     

A case of offspring desertion by a female chimpanzee and the behavioral changes of the abandoned offspring

In the Mahale Mountains National Park, Tanzania, a chimpanzee mother moved to a neighboring unit-group leaving her 5-year-old son behind in the original group. The mother remained in the new group for ten months and then after conceiving, returned to the original group. The mother and son were reunited again but the son died of illness two months later. The mother gave birth to a baby in the original group but eventually transferred to the neighboring group after that baby disappeared. This is the first record of an immature chimpanzee abandoned by its emigrating mother, although a similar phenomenon has been reported for gorillas and Hanuman langurs. The abandoned offspring followed an adult male of the unit-group and the male was the individual who gave most of the care to the offspring. The offspring's time spent on grooming others increased, the time spent on being groomed decreased, and the rate of aggression toward him increased after his mother's desertion. This report will occasion to reconsider the previous notion of all-powerful mother-offspring bond in chimpanzees.     

Influence of group size on reproductive success of female ring-tailed lemurs: distinguishing between IGFC and PFC hypotheses

Based on data obtained over a period of 11 years from female ring-tailed lemurs (Lemur catta), we analyzed the correlation between group size and female reproductive parameters. The birth rate and mean number of surviving infants 1 year after birth per adult female generated an inverted U-shaped curve when plotted against group size (although not significant) and number of adult female members. Infant mortality rate did not have a consistent correlation with group size and number of adult female members. Thus, our findings were similar to the predictions of Wrangham’s inter-group feeding competition hypothesis.     

Reproductive Parameters of Female<Emphasis Type="Italic">Pan paniscus</Emphasis> and <Emphasis Type="Italic">P. troglodytes</Emphasis>: Quality versus Quantity

We investigated intra- and interspecific differences in life history and reproductive parameters in bonobos (Pan paniscus) and chimpanzees (Pan troglodytes). We compare the parameters of wild and captive females in order to shed light on the influence of habitat or specific differences or both on reproduction. We present new and additional information on reproductive parameters from captive bonobos and chimpanzees. Captive chimpanzees birth more live offspring and have a shorter interbirth interval, but experience higher infant mortality than captive bonobos. Although captive bonobo females tend to start reproduction at a younger age than chimpanzees, this is effectively only so for wild-born females of both species. Ultimately both species reach the same rate of production of offspring surviving to 5 yr. These results contrast with data from the wild. Wild bonobos tend to have higher reproductive success, a higher fertility rate and a shorter interbirth interval than wild chimpanzees. Reproduction is similar for wild and captive bonobos, which suggests that they are producing at their maximum under both conditions. Overall captive chimpanzees perform better than their wild conspecifics, probably because of lower feeding competition. Infant survival is the only specific difference not affected by captivity. Bonobo infants survive better, which suggests that chimpanzee infants are more at risk. We argue that the interspecific variation in reproductive parameters in captivity is related to the different influence of captivity on reproduction and different pressures of external sources of infant and juvenile mortality.     

Social behaviour and infant carrying in a group of moustached tamarins,Saguinus mystax (primates: Platyrrhini: Callitrichidae), on Padre Isla,Peruvian Amazonia

The social behaviour of a group of eight moustached tamarins,Saguinus mystax, (five males, three females) was studied on Padre Isla in northeastern Peru. About 60% of all allogrooming was done by the two adult males in the group, and about 11% by a young adult female. All other group members groomed very little. The adult breeding female received more grooming than any other group member. After the death of the adult female (preyed upon by an anaconda) the amount of active allogrooming remained constant for all group members except for the young adult female, who increased her contribution to about 30%. Her preferred grooming partner was the subadult female, which generally screamed when being groomed by the young adult female and terminated grooming by going away. This kind of grooming relation is termed “forced grooming” and is interpreted as a possible social control mechanism. The young adult female groomed the adult males more often after the death of the adult female than before. This might have had the function of strengthening the social bond with the adult males and in obtaining the breeding position in the group. After the death of the adult female, the vulva of the young adult female grew to full adult size. Agonistic behaviour was less frequent than allogrooming. Most aggressive interactions (50%) originated from the subadult male of the group. The young adult female was the target of most of these aggressions. Extremely little aggression occurred between the three females. The young adult female was the only individual who tried to emigrate from the group during the study period. Her attempt to join a neighbour group failed due to rejection by all four members of this group. All group members participated in carrying an infant, but the adult males and the young adult female carried most frequently. Contribution to infant carrying varied with the infant's age.     

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.     

Responses of foster-mothers and troop members to adopted newborns in a captive group of rhesus monkeys

Two rhesus monkey males and two females, born to females caged singly, were exchanged with same-sex infants born to females in a large troop which was held in an enclosure in a different building. The ages of the infants were between 24 and 120 hr. The selected foster mothers (FMs) immediately accepted the foreign infants, allowed them to suckle and treated them as their own offspring. Compared with interactions with previous offspring, the FMs initially tended to be more possessive and restrictive of their foster infants: generally they took longer before they allowed the infants to sit at a distance from them and more readily retrieved them. The foster infants tended to be more active (‘fidgety’) than natural (control) offspring born to the troop. Non-related members of the troop, differentiated between foster and control groups. These troop animals more frequently approached and sat in proximity, often in fur-contact with, touched, groomed, and lipsmacked to, foster infants than control infants. The attractiveness of the fostered infants seemed to be slightly associated with the FMs' dominance rank. The foster infants were therefore viewed by others as having assumed the role afforded by the FMs' rank. Thus both FMs and other troop members recognized the unfamiliarity and novelty of the foster infant but the infants were still accepted into the group. We suggest that the different treatment of the foster infants by the troop may have consequences on the infants' future social development.     

Bonobo (Pan paniscus) Spatial Memory and Communication in a 20-hectare Forest

We used an artificial language as a tool for the study of spatial memory organization in a young Pan paniscus. In the first experiment, we showed the bonobo a road sign just outside its indoor sleeping area. The sign indicated, by means of arbitrarily designated geometrical shapes (lexigrams), where food was hidden. Only 2 of the 15 locations were visible from the sign. Distances ranged up to 170 m from the sign. In 99 of 127 test trials the bonobo went directly to the designated location on its first move. In a second experiment, we presented the road sign at varied points in the woods rather than at the original fixed place. In these trials the goal was a preferred toy. The bonobo's human companions were never told the location of the goal and distances were up to 650 m. In all 12 trials the bonobo led its companions to the designated place via an efficient path. The bonobo appeared to be able to move, based on the information provided by a lexigram, from almost any arbitrary starting location in its 20-ha environment to any one of the numerous goal locations.