Non-antagonistic relations between wild bonobos and two species of guenons

Interspecific relations between wild bonobos (Pan paniscus) and two species of guenons (Cercopithecus wolfi andC. ascanius) were studied at Wamba in the Central Zaire Basin from September 1989 to January 1990. Data on the guenons were collected while following parties of bonobos or when searching for them. The guenons were observed directly 59 times during the study period. In about half of these observations, the guenons were found within 20 m from the bonobo parties. The encounters between the bonobos and the guenons sometimes lasted over an hour. The guenons mainly initiated the encounters by approaching the bonobos. During the encounters, no aggressive interactions were observed between the bonobos and the guenons. Evidence of hunting by wild bonobos has been restricted to small mammals, and there has been no evidence of hunting of primates by wild bonobos. These findings and the results of the present study strongly suggest that wild bonobos do not hunt sympatric primates.     

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.     

Do bonobos copulate more frequently and promiscuously than chimpanzees?

The copulatory activities of bonobos (Pan paniscus) of Wamba, Zaire, were compared with those of chimpanzees (P. troglodytes schweinfurthii) of Mahale, Tanzania. The copulation rates of adult male bonobos were equal to or lower than those of adult male chimpanzees. The copulation rates of adult female bonobos were approximately equal to those of adult female chimpanzees who were in maximal genital swelling, but it should be much higher than those of the adult female chimpanzees throughout the birth interval. The copulation rates of adolescent male bonobos were lower than those of adolescent male chimpanzees, whereas the copulation rates of adolescent female bonobos were much higher than those of adolescent female chimpanzees. It was suggested that the bonobos of Wamba did not copulate more promiscuously than did the chimpanzees of Mahale. The female bonobos may show “receptivity”, whereas female chimpanzees may show rather “proceptivity”.     

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.     

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.     

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.     

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.     

Prospects for Bonobo Insectivory: Lui Kotal, Democratic Republic of Congo

Chimpanzees (Pan troglodytes) are well-known to eat invertebrates, especially social insects, across Africa, but allopatric bonobos (P. paniscus) are not. Bonobo insectivory is sparsely documented and apparently sporadic. However, the availability to bonobos of social insect prey and raw materials with which to make tools to exploit them is unknown. Here, we test a set of hypotheses that relates to questions of presence, abundance, density, and distribution of taxa that Pan consume and of vegetation suitable for making extractive foraging tools. We worked at Lui Kotal, Democratic Republic of Congo, where unprovisioned bonobos live in intact forest, far from villages. We collected insect and fecal specimens, transected for prey and assessed raw materials, and monitored mounds of Macrotermes. All but 1 of the major taxa of relevant termites, ants, and (stinging) honey bees were present. The 3 main taxa of insects that chimpanzees elsewhere eat —Macrotermes (fungus-growing termites), Dorylus (Anomma; army or driver ants), and Apis (honey bees)— were abundant and widespread, and usually at densities exceeding those at well-known chimpanzee study-sites. Similarly, woody and nonwoody vegetation suitable for making fishing probes was common at mounds of Macrotermes. There is no obvious ecological reason why bonobos should not use elementary technology in extractive foraging, e.g., termite-fish, ant-fish, ant-dip, honey-dip, to obtain social insects.     

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.     

Tolerance allows bonobos to outperform chimpanzees on a cooperative task

To understand constraints on the evolution of cooperation, we compared the ability of bonobos and chimpanzees to cooperatively solve a food-retrieval problem. We addressed two hypotheses. The "emotional-reactivity hypothesis" predicts that bonobos will cooperate more successfully because tolerance levels are higher in bonobos. This prediction is inspired by studies of domesticated animals; such studies suggest that selection on emotional reactivity can influence the ability to solve social problems [1, 2]. In contrast, the "hunting hypothesis" predicts that chimpanzees will cooperate more successfully because only chimpanzees have been reported to cooperatively hunt in the wild [3-5]. We indexed emotional reactivity by measuring social tolerance while the animals were cofeeding and found that bonobos were more tolerant of cofeeding than chimpanzees. In addition, during cofeeding tests only bonobos exhibited socio-sexual behavior, and they played more. When presented with a task of retrieving food that was difficult to monopolize, bonobos and chimpanzees were equally cooperative. However, when the food reward was highly monopolizable, bonobos were more successful than chimpanzees at cooperating to retrieve it. These results support the emotional-reactivity hypothesis. Selection on temperament may in part explain the variance in cooperative ability across species, including hominoids.     

Mirror inspection varies with age and tool-using ability in tufted capuchin monkeys (Cebus apella)

We examined mirror inspection in tufted capuchin monkeys (Cebus apella). Capuchins were presented with a non-reflective surface for 30 minutes and then a mirror for 3 hours. Inspection of the non-reflective surface did not vary significantly as a function of tool-using ability, age, or sex. Mirror inspection was lowest in older animals, and was greater in animals that used tools than in animals that did not use tools. Mirror-aided self-inspection was not observed. These results indicate that mirror inspection varies with age and tool-using ability in tufted capuchin monkeys. We hypothesize that psychological capacities associated with mirror inspection correspond with those related to the use of tools, and that these capacities facilitate the emergence of self-recognition in some primate species.     

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.     

Male-male relationships among wild bonobos (Pan paniscus) at Wamba,Republic of Zaire

Male-male relationships among wild bonobos (Pan paniscus) in two adjacent unitgroups (E1 and E2 groups), which were formed by division of the E group, were studied at Wamba, in the Central Zaire Basin, by analyzing the proximity and social interactions among males. Dominant-subordinate relationships between a male-male dyad were easily recognized from the directions of individual agonistic interactions. Male bonobos rarely joined forces in aggression. Clear differences in social status existed between adult and adolescent male bonobos in both groups, as reported in the case of chimpanzees (Pan troglodytes). The presence of mothers in the unit-group greatly influenced the dominant-subordinate relationships among males through strong mother-son bonds in both groups. However, the extent of the mother-son bonds differed between the groups. Males in the E2 group participated more frequently in agonistic or affinitive interactions than did males in the E1 group. Males in the E1 group were divided spatially into several clusters, while there were cohesive relationships among the adult males in the E2 group. The difference in intensities of mother-son bonds between the groups may be explained by the distribution of males at the time of the division of the E group. Differences in male-male relationships between bonobos and chimpanzees seem to be related to differences in intra- and inter-unit-group competition among males between the two species. Male chimpanzees may achieve coexistence by manipulating ambivalent relationships that are caused by intra- and inter-unit-group competition among them, while male bonobos may achieve coexistence by decreasing intra- and inter-unit-group competition among them.     

Factors underlying party size differences between chimpanzees and bonobos: a review and hypotheses for future study

Differences in party size and cohesiveness among females have been primary topics in socio-ecological comparisons of chimpanzees (Pan troglodytes) and bonobos (Pan paniscus). This paper aims to review previous studies that attempted to explain these differences and propose some hypotheses to be tested in future studies. Comparisons of recent data show that relative party size (expressed as a percentage of total group size) is significantly larger for bonobos than chimpanzees. Although the prolonged estrus of females, close association between mother and adult sons, female social relationships including unique homosexual behavior, and high female social status might be related to the increased party size and female cohesiveness of bonobos, these social and behavioral factors alone do not appear to explain the differences between the two species. Differences in ecological factors, including fruit-patch size, density of terrestrial herbs, and the availability of scattered foods that animals forage as they travel between large fruit patches could also contribute to the differences between chimpanzees and bonobos. However, these factors cannot fully account for the increased party size and female cohesiveness of bonobos. The higher female cohesiveness in bonobos may be explained by socio-ecological systems that reduce the cost in feeding efficiency incurred by attending mixed-sex parties. These systems may include female initiatives for party ranging movements as well as the factors mentioned above. Because of their geographical isolation, the two species probably evolved different social systems. Chimpanzees, whose habitats became very dry during some periods in the Pleistocene, likely evolved more flexible fission–fusion social systems to cope with seasonal and annual variation in food availability. On the other hand, bonobos had a large refugia forest in the middle of their range even during the driest periods in the Pleistocene. Therefore bonobos, whose habitats had more abundant food and smaller variation in food availability, probably evolved systems that help females stay in mixed parties without incurring large costs from contest and scramble competition.     

A new mark test for mirror self-recognition in non-human primates

For 30 years Gallups (Science 167:86–87, 1970) mark test, which consists of confronting a mirror-experienced test animal with its own previously altered mirror image, usually a color mark on forehead, eyebrow or ear, has delivered valuable results about the distribution of visual self-recognition in non-human primates. Chimpanzees, bonobos, orangutans and, less frequently, gorillas can learn to correctly understand the reflection of their body in a mirror. However, the standard version of the mark test is good only for positively proving the existence of self-recognition. Conclusive statements about the lack of self-recognition are more difficult because of the methodological constraints of the test. This situation has led to a persistent controversy about the power of Gallups original technique. We devised a new variant of the test which permits more unequivocal decisions about both the presence and absence of self-recognition. This new procedure was tested with marmoset monkeys (Callithrix jacchus), following extensive training with mirror-related tasks to facilitate performance in the standard mark test. The results show that a slightly altered mark test with a new marking substance (chocolate cream) can help to reliably discriminate between true negative results, indicating a real lack of ability to recognize oneself in a mirror, from false negative results that are due to methodological particularities of the standard test. Finally, an evolutionary hypothesis is put forward as to why many primates can use a mirror instrumentally – i.e. know how to use it for grasping at hidden objects – while failing in the decisive mark test.To see a video sequence of the instrumental use of mirror by Callithrix jacchus as described in this study, please go to     

Mirror responses in a Japanese macaque troop (Arashiyama West)

Behavior toward two mirrors in the field was observed in the Arashiyama West troop ofMacaca fuscata. Counts of visits to the mirrors, plus scan and focal animal sampling were used. Some animals were marked with fluorescent paint to test informally for self-recognition. A relatively high mean frequency of visits to the reflecting side of both mirrors by all age classes, ranks, and sexes was recorded. There was no age difference in frequency of mirror visits per sample but adults spent more time per visit than subadults who in turn spent more time than juveniles. There was no indication of self-recognition by paint-marked animals. Mirrors appeared to be used to monitor the reflected scene and to look at the self-image. Social behavior in the mirror zone that was not directed toward the mirror was common to all age classes. Species-typical behavior directed toward the mirror was seen in younger animals but very seldom in adults. No threat displays by any animal were observed. We suggest that for adults the mirror image was not seen simply as another monkey.     

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.     

Nonconceptive Sexual Behavior in Bonobos and Capuchins

Sexual behavior by infecundable females, and by same-sex and adult-immature dyads, occurs in wild and captive bonobos (Pan paniscus). Proposed functions of these behaviors, in social primates generally, include practice, paternity confusion, exchange, and communication as well as appeasement. We used this framework to interpret and to compare observations of sexual behavior in a captive bonobo group and a wild white-faced capuchin (Cebus capucinus) group. In both species, (a) sexual behavior was no more frequent in cycling females than in pregnant or lactating females and (b) same-sex and adult-immature dyads engaged in as much mounting or genitogenital contact as adult heterosexual dyads did. The species differed in that (a) bonobos engaged in sexual behavior 65 times as frequently as capuchins, (b) only bonobos engaged in sexual contact other than ventrodorsal mounting during focal observation, and (c) bonobo sexual contact was concentrated most heavily in socially tense situations in adult female–female dyads, whereas capuchin sexual contact was concentrated most heavily in socially tense situations in adult male–male dyads. These data and published literature indicate that (a) practice sex occurs in both species, (b) paternity confusion may be a current function of C. capucinus nonconceptive sex, (c) exchange sex remains undemonstrated in capuchins, and (d) communication sex is more important to members of the transferring sex—female bonobos and male capuchins—than to members of the philopatric sex.