Behavioral and functional strategies during tool use tasks in bonobos

Different primate species have developed extensive capacities for grasping and manipulating objects. However, the manual abilities of primates remain poorly known from a dynamic point of view. The aim of the present study was to quantify the functional and behavioral strategies used by captive bonobos (Pan paniscus) during tool use tasks. The study was conducted on eight captive bonobos which we observed during two tool use tasks: food extraction from a large piece of wood and food recovery from a maze. We focused on grasping postures, in‐hand movements, the sequences of grasp postures used that have not been studied in bonobos, and the kind of tools selected. Bonobos used a great variety of grasping postures during both tool use tasks. They were capable of in‐hand movement, demonstrated complex sequences of contacts, and showed more dynamic manipulation during the maze task than during the extraction task. They arrived on the location of the task with the tool already modified and used different kinds of tools according to the task. We also observed individual manual strategies. Bonobos were thus able to develop in‐hand movements similar to humans and chimpanzees, demonstrated dynamic manipulation, and they responded to task constraints by selecting and modifying tools appropriately, usually before they started the tasks. These results show the necessity to quantify object manipulation in different species to better understand their real manual specificities, which is essential to reconstruct the evolution of primate manual abilities.     

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.     

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.     

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.     

Female feeding priority in bonobos, Pan paniscus, and the question of female dominance

The question of whether bonobos show feeding priority and female dominance has been proposed and examined, both in the wild and in captive studies, with differing results. The relationship between female dominance and female feeding priority has been best studied in prosimian primates. These studies use established criteria of females consistently evoking submissive behavior from males in dyadic encounters for determining female dominance. Although the relationship is complex, female dominance in prosimians is associated with preferential access to food. Data from studies of wild habituated bonobos in the Lomako Forest, Democratic Republic of the Congo, are examined for evidence of both female feeding priority and female social dominance using similar criteria as used for prosimians. Bonobos showed evidence of female feeding priority in small, but not in large, food patches. Male-male competition for mating opportunities at the start of the food bout was related to some, but not all, differences in time spent feeding between the sexes. Female dominance similar to that seen in prosimians was not observed in these bonobos. Males were consistently dominant in dyadic interactions. Female feeding priority with male dyadic social dominance implies that male deference during feeding cannot be excluded as one explanation of interpretations of female dominance in bonobos. Additionally, dominance of male bonobos by females appears to require the presence of female coalition partners. As in other primates with female feeding priority, bonobo females express this trait where food is economically defendable. Unlike prosimians, however, bonobo female feeding priority may result from male deference and the importance of female coalitions in nondyadic interactions.     

Molecular paternity determination in captive bonobos and the impact of inbreeding on infant mortality

Inbreeding and the loss of genetic diversity may lower fitness and reduce the potential for a population to adapt to changing environments. In small populations, for example in captive populations or populations of endangered species, this can have considerable consequences for their survival. We investigated the effects of inbreeding on infant mortality in the world captive population of bonobos Pan paniscus . Using a combination of studbook data and high-quality pedigree data from genotyped individuals, inbreeding information was available for 142 captive-born individuals. For the determination of paternities that were unresolved in the studbook, nuclear microsatellite DNA was amplified from hair and blood samples using the Great Ape Kit and PowerPlex^® 16 System. In total, 54 bonobos (17 offspring and their putative parents) were genotyped at eight tetranucleotide repeat microsatellite loci. Inbreeding coefficients were calculated for each individual for whom paternity was confirmed by either studbook data or DNA analysis. We found significantly higher infant mortality in inbred offspring compared with non-inbred offspring, suggesting that inbreeding reduces infant survival in captive bonobos. In addition, we argue that the total magnitude of inbreeding depression is probably underestimated in this captive population. In conclusion, even though the breeding programme of captive bonobos is aimed at avoiding inbreeding, closely related individuals do occasionally produce offspring that do show inbreeding depression. There is, however, no indication that this currently threatens the long-time survival of the captive population of bonobos.     

Why preen others? Predictors of allopreening in parrots and corvids and comparisons to grooming in great apes

Allogrooming in primates serves not only a hygienic function, but also plays a crucial role in maintaining strong affiliative bonds between group members, which in turn, underpin the emergence of cooperative behavior. In contrast, although allopreening occurs in many avian species, we know little about its social functions. Our study addresses this issue by investigating allopreening in a broad comparative data set including six corvid and nine parrot species. We assessed whether rates of allopreening initiations, proportion of time spent allopreening, and the number of grooming partners in captive group-housed birds were comparable to patterns observed in captive chimpanzees and bonobos. While parrots and corvids were found to have similar rates of social grooming to bonobos and chimpanzees, Pan species dedicated significantly more time to social grooming. Animals in larger groups had more grooming partners, but when controlling for the number of potential partners, birds tended to have fewer grooming interaction partners than Pan species. We then investigated whether allopreening in parrots and corvids was predicted by behavioral markers of affiliative social bonds (close physical proximity, active feeding, and low levels of agonistic behavior). Results revealed that providing allopreening to a partner was significantly predicted by often being in close proximity, but not engagement in active feeding or agonistic behavior. We examined the region allopreened in a subset of species and found that preening a partner's head was predicted by both close physical proximity and active feeding, while body allopreening was only predicted by close physical proximity. Head preening may confer more hygienic benefits to recipients, and thus, may be more selectively provided to valued partners. Results support the hypothesis that allopreening in corvids and parrots helps maintain social bonds with an individual's most important social partners, showing some similarities to allogrooming in primates.     

A survey of entodiniomorphid ciliates in chimpanzees and bonobos

Intestinal entodiniomorphid ciliates are commonly diagnosed in the feces of wild apes of the genera Pan and Gorilla. Although some authors previously considered entodiniomorphid ciliates as possible pathogens, a symbiotic function within the intestinal ecosystem and their participation in fiber fermentation has been proposed. Previous studies have suggested that these ciliates gradually disappear under captive conditions. We studied entodiniomorphid ciliates in 23 captive groups of chimpanzees, three groups of captive bonobos and six populations of wild chimpanzees. Fecal samples were examined using Sheather's flotation and Merthiolate‐Iodine‐Formaldehyde Concentration (MIFC) methods. We quantified the number of ciliates per gram of feces. The MIFC method was more sensitive for ciliate detection than the flotation method. Ciliates of genus Troglodytella were detected in 13 groups of captive chimpanzees, two groups of bonobos and in all wild chimpanzee populations studied. The absence of entodiniomorphids in some captive groups might be because of the extensive administration of chemotherapeutics in the past or a side‐effect of the causative or prophylactic administration of antiparasitic or antibiotic drugs. The infection intensities of ciliates in captive chimpanzees were higher than in wild ones. We suppose that the over‐supply of starch, typical in captive primate diets, might induce an increase in the number of ciliates. In vitro studies on metabolism and biochemical activities of entodiniomorphids are needed to clarify their role in ape digestion. Am J Phys Anthropol 2010. © 2009 Wiley‐Liss, Inc.     

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.     

Comparative chemical analysis of body odor in great apes

Olfaction is important across the animal kingdom for transferring information on, for example, species, sex, group membership, or reproductive parameters. Its relevance has been established in primates including humans, yet research on great apes still is fragmentary. Observational evidence indicates that great apes use their sense of smell in various contexts, but the information content of their body odor has not been analyzed. Our aim was therefore to compare the chemical composition of body odor in great ape species, namely Sumatran orangutans (Pongo abelii (Lesson, 1827), one adult male, five adult females, four nonadults), Western lowland gorillas (Gorilla gorilla gorilla (Savage, 1847), one adult male, two adult females, one nonadult), common chimpanzees (Pan troglodytes (Blumenbach, 1775), four adult males, nine adult females, four nonadults), and bonobos (Pan paniscus (Schwarz, 1929), two adult males, four adult females, two nonadults). We collected 195 samples (five per individual) of 39 captive individuals using cotton swabs and analyzed them using gas chromatography mass spectrometry. We compared the sample richness and intensity, similarity of chemical composition, and relative abundance of compounds. Results show that species, age, and potentially sex have an impact on the variance between odor profiles. Richness and intensity varied significantly between species (gorillas having the highest, bonobos the lowest richness and intensity), and with age (both increasing with age). Richness and intensity did not vary between sexes. Odor samples of the same species were more similar to each other than samples of different species. Among all compounds identified some were associated with age (N = 7), sex (N = 6), and species‐related (N = 37) variance. Our study contributes to the basic understanding of olfactory communication in hominids by showing that the chemical composition of body odor varies across species and individuals, containing potentially important information for social communication.     

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.     

Interactions between zoo‐housed great apes and local wildlife

Although there are published reports of wild chimpanzees, bonobos, and orangutans hunting and consuming vertebrate prey, data pertaining to captive apes remain sparse. In this survey‐based study, we evaluate the prevalence and nature of interactions between captive great apes and various indigenous wildlife species that range into their enclosures in North America. Our hypotheses were threefold: (a) facilities housing chimpanzees will report the most frequent and most aggressive interactions with local wildlife; (b) facilities housing orangutans and bonobos will report intermediate frequencies of these interactions with low levels of aggression and killing; and (c) facilities housing gorillas will report the lowest frequency of interactions and no reports of killing local wildlife. Chimpanzees and bonobos demonstrated the most aggressive behavior toward wildlife, which matched our predictions for chimpanzees, but not bonobos. This fits well with expectations for chimpanzees based on their natural history of hunting and consuming prey in wild settings, and also supports new field data on bonobos. Captive gorillas and orangutans were reported to be much less likely to chase, catch and kill wildlife than chimpanzees and bonobos. Gorillas were the least likely to engage in aggressive interactions with local wildlife, matching our predictions based on natural history. However unlike wild gorillas, captive gorillas were reported to kill (and in one case, eat) local wildlife. These results suggest that some behavioral patterns seen in captive groups of apes may be useful for modeling corresponding activities in the wild that may not be as easily observed and quantified. Furthermore, the data highlight the potential for disease transmission in some captive settings, and we outline the associated implications for ape health and safety. Am. J. Primatol. 71:458–465, 2009. © 2009 Wiley‐Liss, Inc.     

Arboreal Postures Elicit Hand Preference when Accessing a Hard-to-Reach Foraging Device in Captive Bonobos (<Emphasis Type="Italic">Pan paniscus</Emphasis>)

Arboreal, and in particular suspensory, postures may elicit a preference for the strongest limb to be used in postural support in large bodied primates. However, selection may have favored ambilaterality rather than a preference for a particular hand in chimpanzees (Pan troglodytes) fishing arboreally for ants. To investigate the influence of arboreality on hand preference we recorded handedness in seven captive bonobos (Pan paniscus) manipulating a foraging device during terrestrial and arboreal postures in a symmetrical environment, observing 2726 bouts of manipulation. When accessing the foraging device in the arboreal position the bonobos adopted predominantly suspensory postures. There was no population level hand preference for manipulating the foraging device in either the terrestrial or arboreal positions. However, four of seven individuals that interacted with the foraging devices showed a significant preference for one hand (two were left handed, two were right handed) when manipulating the foraging device in the arboreal position whereas only one individual (left handed) showed a preference in the terrestrial position. This suggests that individuals may have a preferred or strongest limb for postural support in a symmetrical arboreal environment, resulting in a bias to use the opposite hand for manipulation. However, the hand that is preferred for postural support differs between individuals. Although our sample is for two captive groups at the same zoo, our findings suggest that the demand of maintaining arboreal postures and environmental complexity influence hand preference.     

Using the Tools at Hand: Manual Laterality and Elementary Technology in Cebus spp. and Pan spp.

Cebus and Pan appear to be a remarkable example of evolutionary convergence in behavioral ecology. We examine their apparently analogous solutions to problems posed by laterality of hand function and elementary technology. We scrutinize appropriate published data in a meta-analysis, focusing on Cebus apella and C. capucinus and on Pan paniscus and P. troglodytes. We compare behavioral data in terms of captive versus wild, and tool use versus non-tool use, but notable gaps exist in the data, especially for bonobos. Cebus and Pan spp. are equivalent tool users in captivity, but chimpanzees are notably more extensively so in nature. For hand preference, captive bonobos and wild and captive chimpanzees show ambipreference for non-tool-use patterns. For both Cebus spp. and Pan spp., there is a tendency for individuals to be committed exclusively to one hand or the other for tool use. The data for laterality of hand function fit consistently into the five-level model proposed by McGrew and Marchant (1996).     

Increased Frequency of Intergroup Encounters in Wild Bonobos (<Emphasis Type="Italic">Pan paniscus</Emphasis>) Around the Yearly Peak in Fruit Abundance at Wamba

Intergroup interactions in primates vary from nonagonistic to severely aggressive. Food resources and fertile females cause intergroup aggression when groups defend resources and mates from other groups. Peaceful intermingling during intergroup encounters is rare but has been reported in several primates, including bonobos (Pan paniscus). Although intergroup encounters in bonobos occur at both nonprovisioned and provisioned sites, provisioning may be one factor responsible for frequent intergroup encounters. We studied intergroup encounters between one bonobo group (PE) and its neighboring groups, one semihabituated and two habituated groups, under nonprovisioned conditions in 2010–2015 at Wamba, Democratic Republic of Congo. We examined whether fruit abundance and females with sexual swellings influenced encounter frequency. PE group encountered the other groups on 7.1 days (mean, range: 0–19) per month. Up to four different groups met simultaneously at one location. Encounter frequency was highest around the yearly peak in fruit abundance, suggesting that reduced food competition is linked to increased encounter frequency. During periods of relatively low fruit abundance, the probability of an encounter was higher when a higher number of adult females with maximum sexual swellings were present, suggesting that the attractiveness of females with sexual swellings promoted group encounters during periods of relatively low fruit abundance. These findings suggest that both competition for food and the availability of females with sexual swellings influence encounter frequency in bonobos.     

Co–Residence between Males and Their Mothers and Grandmothers Is More Frequent in Bonobos Than Chimpanzees

In long–lived social mammals such as primates, individuals can benefit from social bonds with close kin, including their mothers. In the patrilocal chimpanzee (Pan troglodytes spp.) and bonobo (Pan paniscus), sexually mature males reside and reproduce in their natal groups and can retain post-dependency bonds with their mothers, while immatures of both sexes might also have their paternal grandmothers available. However, quantitative information on the proportion of males and immatures that co-reside with both types of these close female relatives is limited for both species. Combining genetic parentage determination and group composition data from five communities of wild chimpanzees and three communities of wild bonobos, we estimated the frequency of co-residence between (1) mature males and their mothers, and (2) immature males and females and their paternal grandmothers. We found that adult males resided twice as frequently with their mothers in bonobos than in chimpanzees, and that immature bonobos were three times more likely to possess a living paternal grandmother than were immature chimpanzees. Patterns of female and male survivorship from studbook records of captive individuals of both species suggest that mature bonobo females survive longer than their chimpanzee counterparts, possibly contributing to the differences observed in mother–son and grandmother–immature co-residency levels. Taking into account reports of bonobo mothers supporting their sons'' mating efforts and females sharing food with immatures other than their own offspring, our findings suggest that life history traits may facilitate maternal and grandmaternal support more in bonobos than in chimpanzees.     

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.     

Inter-menstrual intervals in captive bonobosPan paniscus

In this study we provide new data on the duration of the inter-menstrual intervals of six captive female bonobos (Pan paniscus). We found that the mean duration of the inter-menstrual interval was about 34 days. This lies close to the average value of 37 days that has been reported for common chimpanzees (Pan troglodytes).     

Bonobo but not chimpanzee infants use socio-sexual contact with peers

Bonobos have been observed to use socio-sexual behavior at higher frequency than chimpanzees. Little is known about the developmental influences that shape this behavior in bonobos. We compared the social sexual behavior of wild-born bonobo (n = 8) and chimpanzee (n = 16) infants in an experimental feeding test. Subjects of both species were orphans of the bushmeat trade living at sanctuaries in peer groups. During the experiment, chimpanzee infants never had socio-sexual interactions with one another. In contrast, bonobo infants had socio-sexual interactions significantly more than the chimpanzee infants and more often when food was presented. During these socio-sexual interactions, bonobo infants did not show a preference for heterosexual partners or genital–genital positioning that is reproductive in adults (e.g. a dorso–ventral posture). These findings suggest that the socio-sexual behavior previously observed in various captive and wild bonobos is species-typical. Wild-born bonobos originating from a large geographical range develop this behavior long before puberty and without the need for adults initiating such behavior or acting as models for observational learning. Meanwhile, chimpanzee infants of the same age with similar rearing history show no signs of the same socio-sexual behavior. Results are interpreted regarding hypotheses for the evolution of bonobo psychology.