Chimpanzee Communities Research Articles

Oil Palm Use by Adjacent Communities of Chimpanzees at Bossou and Nimba Mountains, West Africa

We investigated oil palm (Elaeis guineensis) use for feeding in 3 chimpanzee communities: Bossou and Seringbara in Guinea and Yeale in Cote d'Ivoire. Bossou was used as the benchmark for comparison. Bossou chimpanzees (Pan troglodytes verus) exhibit a wide range of oil palm targeted behaviors. We used direct observations of their two tool use, i.e., nut-cracking and pestle pounding, to establish strict and reliable criteria to ascertain the presence of comparable behaviors at the two adjacent Nimba sites. Based on monthly surveys of oil palms across the three sites, significant differences in patterns of use emerged. Bossou chimpanzees demonstrated the greatest frequency of oil palm use, while Seringbara chimpanzees, 6 km away, failed to exhibit any use and Yeale chimpanzees, 12 km away, showed all uses comparable to Bossou chimpanzees except pestle pounding and mature leaf pith-feeding. We examined the density and distribution of oil palms, tool availability for nut-cracking and pestle pounding, fruit, flower and nut availability, competition with sympatric species for fruit and nuts and the diversity of fruit species in the diet across the 3 sites. We found no clear difference in proximate environmental variables underlying observed variations in oil palm use among the 3 sites, yielding the conclusion that the differences are cultural. Assuming individual interchange between communities and the involvement of social learning in the intracommunity transmission and maintenance of oil palm uses, the result raises interesting questions about diffusion of behavior between neighboring chimpanzee communities.

Sex differences in learning in chimpanzees

The wild chimpanzees in Gombe National Park, Tanzania, fish for termites with flexible tools that they make out of vegetation, inserting them into the termite mound and then extracting and eating the termites that cling to the tool. Tools may be used in different ways by different chimpanzee communities according to the local chimpanzee culture. Here we describe the results of a four-year longitudinal field study in which we investigated how this cultural behaviour is learned by the community's offspring. We find that there are distinct sex-based differences, akin to those found in human children, in the way in which young chimpanzees develop their termite-fishing skills.

To fission or to fusion: effects of community size on wild chimpanzee (Pan troglodytes verus) social organisation

To balance advantages and disadvantages of group living, some species have fission-fusion social systems in which members of the same group form frequently changing subgroups. This allows flexible responses of group size to external conditions while at the same time retaining group stability. In chimpanzees, subgroup (party) size and composition depend mainly on the presence of receptive females, food availability and the activity of the party. Here we analyse the extent to which fission-fusion parameters are influenced by changes of demographic variables like community size and composition. Data were collected from a habituated West African chimpanzee community (Tai forest, Cote d’Ivoire) over 10 years, during which total community size decreased from 51 to 21, and the number of adult males decreased from 9 to 2. Tai chimpanzees are highly gregarious, as they spend more than 80% of their time with unrelated conspecifics. With decreasing community size, party size, party duration and male-female association increased. Neither activity nor the presence of receptive females or feeding competition could explain the observed changes in grouping patterns. Thus, the decrease in community size led to an increase of party cohesion and also enhanced cohesiveness between the sexes, while general sociality remained unchanged. Therefore, our data support the notion that small communities are more cohesive and have a less flexible fission-fusion system.

Cultural innovation and transmission of tool use in wild chimpanzees: evidence from field experiments.

Chimpanzees (Pan troglodytes) are the most proficient and versatile users of tools in the wild. How such skills become integrated into the behavioural repertoire of wild chimpanzee communities is investigated here by drawing together evidence from three complementary approaches in a group of oil-palm nut- ( Elaeis guineensis) cracking chimpanzees at Bossou, Guinea. First, extensive surveys of communities adjacent to Bossou have shown that population-specific details of tool use, such as the selection of species of nuts as targets for cracking, cannot be explained purely on the basis of ecological differences. Second, a 16-year longitudinal record tracing the development of nut-cracking in individual chimpanzees has highlighted the importance of a critical period for learning (3-5 years of age), while the similar learning contexts experienced by siblings have been found to result in near-perfect (13 out of 14 dyads) inter-sibling correspondence in laterality. Third, novel data from field experiments involving the introduction of unfamiliar species of nuts to the Bossou group illuminates key aspects of both cultural innovation and transmission. We show that responses of individuals toward the novel items differ markedly with age, with juveniles being the most likely to explore. Furthermore, subjects are highly specific in their selection of conspecifics as models for observation, attending to the nut-cracking activities of individuals in the same age group or older, but not younger than themselves. Together with the phenomenon of inter-community migration, these results demonstrate a mechanism for the emergence of culture in wild chimpanzees.

?Decision-making? in conflicts of wild chimpanzees (Pan troglodytes): an extension of the Relational Model

>We examined the “decision-making” process of aggressive interactions within a community of wild chimpanzees (Pan troglodytes verus) in the Tai National Park, Cote d’Ivoire (West Africa). Costs and benefits were investigated for 876 dyadic aggressive interactions among 18 adults (including 4 independent adolescents) of either sex. An extended version of the Relational Model was developed to describe the dynamics of the “decision-making” process in Tai chimpanzees, which suggests that the net benefit determines the occurrence of conflicts. Both sexes fought more frequently for the resources that were most important to them, food for females and social contexts for males. Individuals used two different strategies according to their likelihood of winning the aggressive interaction, determined by the dominance relationship of the conflict partners. Dominant initiators had longer and more intense aggressive interactions, but they limited their social disadvantages by fighting non-cooperative partners. Subordinate initiators had shorter and less intense aggressive interactions, but risked more social costs, which they could reduce afterwards by reconciliation. Both strategies included a positive overall net benefit. The extended Relational Model fits the complexity of wild chimpanzee conflicts and allows for more flexibility in the “decision-making” compared to the original version.

The home range of the Sonso community of chimpanzees from the Budongo Forest, Uganda

AbstractEarly studies of chimpanzees in the Budongo Forest, Uganda, reported only rough estimates for home range size. This study aimed to quantify home range size and habitat composition for chimpanzees of the Sonso community in this forest. Home range is the habitually used portion of the total area over which an animal travels, and for chimpanzees the home range is shared by the community. From data collected in 1994 and 1995, the home range for this community was estimated to cover an area of 6.78 km2 using the minimum convex polygon analysis technique and 6.89 km2 using fixed kernel analysis. Habitat was highly heterogeneous. The small home range and consequent high local population density (approximately 6.8 individuals km−1) suggests that the Sonso region is highly productive in chimpanzee foods, possibly in contrast to other parts of the forest. This estimate of home range size is among the smallest reported for habituated chimpanzees, but comparisons with other sites are confounded by methodological and analytical differences. Future studies of chimpanzee ranging patterns should endeavour to use precise locations and the latest analytical techniques to ensure accurate estimation of range size and structure, and intersite comparability.

Technical challenges in the microsatellite genotyping of a wild chimpanzee population using feces

Noninvasive collection of samples from wild mammal populations presents an extraordinary opportunity to conduct genetic analysis without necessarily capturing or even directly observing the subjects of interest. Unfortunately, the hair or feces samples typically collected present formidable challenges in the laboratory. The investment of time and expense required makes careful experimental design a necessity. Researchers who want to examine the genetics of wild mammal populations have great interest in the use of noninvasively collected sample materials. Questions that can potentially be answered range from population-level inquiries into such topics as population size, sex composition, individual relationship, and dispersal, to comparisons between populations providing information on geographic differentiation, comparative levels of genetic diversity, and phylogenetic relationships.1 Effective investigation of these matters relies on an ability to examine genetic variation from the nuclear genome as well as the maternally transmitted mitochondrial DNA (mtDNA). A typical approach to examining the genetic structure of a population involves the assessment of variation at multiple nuclear microsatellite loci. Alleles of these microsatellite loci vary in the length of simple repeat elements, hence allowing for the potential assemblage, when enough loci are examined, of individually distinctive genotypes.2 I will therefore focus here on microsatellite analyses. Numerous studies have employed microsatellite analysis of noninvasive samples in the form of feces or shed hair.3–8 But, as Taberlet et al.9 recently noted, to date there have been relatively few “comprehensive” studies using nuclear DNA from noninvasive samples. This is surprising in view of the existence of the large body of literature on the topic, and the subjective impression that many field researchers are equipped with collection materials and a plan or at least a hope of arranging for later genetic analysis. The indication is thus that, years after it was heralded as representing a revolution in field studies of primates,10 noninvasive sampling for genetic analysis either has not yet reached its potential or has proved disappointing. Ironically, the simplicity and low costs of the polymerase chain reaction (PCR) that have led to its ubiquitous use in molecular analysis laboratories may have led to an underestimation by laboratory and field researchers alike of the difficulties inherent in the use of noninvasive samples. Such analyses in fact present considerable technical challenges that can only be overcome by investing a great deal of time, expense, and laboratory expertise. Most technical considerations involved in the production of accurate genotypes from noninvasive samples have been thoroughly addressed elsewhere.9,11 In this contribution, I will present some preliminary results from a study of habituated communities of chimpanzees (Pan troglodytes verus) in the Tai National Forest, Ivory Coast. The necessary investment, particularly in terms of time and expense, of generating reliable genotypes from a large number of individuals will be described.

Grooming Interactions Among the Chimpanzees of the Budongo Forest, Uganda: Tests of Five Explanatory Models

AbstractPatterns of allogrooming among the Sonso community of chimpanzees of the Budongo Forest, Uganda, were examined and found to closely resemble those at other study sites. Strong affiliative bonds among males were reflected in high levels of grooming compared with other sex combinations. Adult males groomed, and received grooming most often from, other adult males and also adolescent females which were the only females with regular oestrous cycles during the study. Males had a wider diversity of grooming partners than females and groomed more equitably. However, males concentrated the majority of their effort on a very small number of partners compared with other sites. Grooming reciprocity was found among all age/sex combinations with the exception of adult male-female dyads once immediate reciprocation in the form of synchronous mutual grooming was removed from the analysis. Since grooming among males is thought to play a major role in servicing relationships and agonistic coalitions that can improve dominance status, competition for high-ranking grooming partners was predicted to influence the distribution of grooming among males. Grooming was indeed directed up the male hierarchy and closely ranked males groomed each other more often than those that were distantly ranked. However, when only adult males were considered, rank had little effect on grooming distributions. High rank appeared to influence access to females, but did not attract more female grooming partners. Grooming distributions in this average-sized community did not fit a number of alternative priority of access models which assume competition for high-ranking grooming partners that Watts (2000b) found to have some explanatory value in one very large community of chimpanzees, but not in a smaller, more representative one. Although rank is highly likely to influence coalition partner choice, whether such relationships depend upon strategic grooming partner choices in wild chimpanzees is presently unclear.

Social and spatial aspects of male subgrouping in a community of wild chimpanzees

AbstractStrong social bonds typically develop between dyadic pairs of male chimpanzees. These bonds are manifest in several contexts, including association, grooming, and proximity. Here we demonstrate that social bonds exist at a higher level of organization among males living in an extremely large community at Ngogo, Kibale National Park, Uganda. An analysis of over 2,500 hours of observation of 35 individuals revealed two distinct subgroups of male chimpanzees. Males that composed each subgroup can be identified on the basis of their tendency to associate in temporary parties. Matrix permutation tests indicated that subgroup members tended to maintain spatial proximity to each other and participate together in territorial boundary patrols. Subgroups formed along the lines of age and rank; members of a small subgroup were younger and lower ranking than individuals in a larger subgroup. Despite this social clustering of males, community integrity remained intact with low levels of aggression between individuals of different subgroups. After controlling for the effect of association, significantly more aggression occurred within compared to between subgroups. In addition, males of the different subgroups displayed significant overlap in their use of the community territory and thus showed no tendency to divide spatially. We compare our findings with those from other animal species and chimpanzee populations and discuss them in the context of the unusual demography of the Ngogo community.

Demographic and social constraints on male chimpanzee behaviour

Male chimpanzees, Pan troglodytes, are well known for affiliating and cooperating in a variety of behavioural contexts. Prior field research indicates that maternal kinship does not affect patterns of affiliation and cooperation by males in the same social group. Two questions remain unclear from this finding. First, why do male chimpanzees not bias their behaviour towards maternal kin? Second, what factors account for who affiliates and cooperates with whom? We conducted behavioural observations of an unusually large community of chimpanzees at Ngogo, Kibale National Park, Uganda, to test the hypothesis that demographic constraints limit the number of maternal kin with whom male chimpanzees can cooperate, and thereby lead them to form selective bonds with nonkin of similar age and status. Results indicated that male age and rank are significantly associated with four measures of social behaviour. Members of the same age class and individuals close in rank were more likely to affiliate and cooperate than males that belonged to different age and rank classes. Additional analyses replicate earlier findings and show that males who affiliated and cooperated were not closely related through the maternal line, as assayed by mtDNA haplotype sharing. These results add to our growing understanding of the important role demographic and social constraints play in animal behaviour.

Reciprocity and interchange in the social relationships of wild male chimpanzees

Social relationships in nonhuman primates result from investments that individuals make while pursuing fitness-maximizing strategies. These strategies sometimes include social exchange, either reciprocity (exchange of the same acts) or interchange (exchange of different acts). Individuals in many species may negotiate for services in biological markets, particularly grooming and agonistic support. They also may compete for access to valuable social partners. Abundant evidence for reciprocity in grooming and in support and for competition over partners exists, notably for females in some cercopithecines. However, evidence for interchange of grooming and support is scarcer, and apparent interchange may be a byproduct of correlations between grooming or support and some third variable (e.g. dominance rank). Chimpanzees have been prominent in discussions of social exchange, especially because male chimpanzees cooperate in many ways. Most analyses of interchange have used data on captive chimpanzees; these provide good evidence for reciprocity, but ambiguity with regard to interchange. Data on an unusually large chimpanzee community at Ngogo, Kibale National Park, Uganda, strongly support the argument that social exchange is prominent in social relationships among males. Males at Ngogo show reciprocity in grooming and support. They also interchange grooming given and support received, as well as grooming received and support given, independently of reciprocity in grooming and support and of correlations of support and grooming with dominance rank. However, most cooperation in contests with third parties took low risk forms (e.g. both participants outranked their opponent). In this, males at Ngogo resemble captive chimpanzees and female cercopithecines. Reciprocity and interchange in this context may be important in the maintenance of social bonds between males, and in attainment and maintenance of high dominance rank, but probably represent mutualism, not reciprocal altruism.

Paternity and relatedness in wild chimpanzee communities.

The genetic structure of three contiguous wild chimpanzee communities in West Africa was examined to determine the extent to which the community, the mixed-sex social unit of chimpanzees, represents a closed reproductive unit. An analysis of paternity for 41 offspring resulted in 34 cases of paternity assignment to an adult male belonging to the same community. Among the 14 offspring for which all potential within-community fathers have been tested, one likely case of extra-group paternity (EGP) has been identified, suggesting an incidence of EGP of 7%. This more extensive analysis contradicts a previous genetic study of the Tai chimpanzees that inferred 50% extra-group fathers. We suggest, based on direct comparison of results for 33 individuals at 1 microsatellite locus and direct comparison of paternity assignments for 11 offspring, that the error rate in the previous study was too high to produce accurate genotypes and assignments of paternity and hence caused the false inference of a high rate of EGP. Thus, the community is the primary but not exclusive unit for reproduction in wild chimpanzees, and females do not typically reproduce with outside males. Despite the inferred low level of gene flow from extra-community males, relatedness levels among the community males are not significantly higher than among community females, and the distribution of genetic relationships within the group suggests that, rather than a primarily male-bonded social structure, the group is bonded through relationships between males and females. Kinship may explain cooperative behaviors directed against other communities, but is unlikely to explain the high levels of affiliation and cooperation seen for male within-community interactions.

Sources of variation in the nesting behavior of chimpanzees (Pan troglodytes schweinfurthii) in the Budongo forest, Uganda.

Data on nesting behavior and nests of the Sonso community of chimpanzees (Pan troglodytes schweinfurthii) living in the Budongo Forest, Uganda, were collected between October 1995 and December 1996. Analysis of the selection of nests shows a preference for particular tree species, especially Cynometra alexandri. Male chimpanzees nested lower than females. Day nests were found to be structurally simpler than night nests and were built in tree species used for feeding, at the same height as feeding activity. Day and night nests serve different functions, and should be clearly distinguished in studies of nesting behavior.

Cognitive capacities for behavioural flexibility in wild chimpanzees ( Pan troglodytes ): the effect of snare injury on complex manual food processing

In chimpanzees, it is only in the restricted context of tool use that manual and cognitive skills have been described, comparable to those that gorillas and orang-utans display in obtaining plant foods. We report the complex food preparation skills used to eat, without tools, the leaves of the tree Broussonettia papyrifera in the Sonso community of chimpanzees at Budongo Forest, Uganda. Able-bodied individuals used multi-stage techniques that required bimanual role differentiation at several stages, and were hierarchical in organisation. A total repertoire of 14 techniques was found, with strong preference in all individuals for either of two of these; 6 additional techniques were found when flowers and leaves were eaten together. However, in this community over 20% of individuals suffer from some form of upper- or lower-limb injury as a result of snares. We investigated the manner of compensation for upper-limb injury. Only the most severely injured showed reduced feeding efficiency. Injured individuals were found to use the same repertoire of techniques as able-bodied chimpanzees. We found no evidence to suggest that injured individuals were able to develop wholly novel techniques optimal for their specific injuries, although shifts in preference for particular techniques did occur. Rather, injured individuals used novel ways of achieving particular steps in the process; by "working around" their impairments; in this way, they managed to use the same techniques as the able-bodied. Since snare injuries generally befall young animals, these results suggest that chimpanzees learn techniques partly through observational learning (of, necessarily, able-bodied individuals).

Does participation in intergroup conflict depend on numerical assessment, range location, or rank for wild chimpanzees?

Male chimpanzees, Pan troglodytes, engage in cooperative territorial defence and sometimes kill members of neighbouring communities. Observations of intergroup interactions suggest that escalation of aggression depends on numerical assessment, with lethal attacks occurring when numerical advantage reduces the costs of attacking. To gain a better understanding of the factors guiding participation in intergroup conflict, we conducted a series of playback experiments with the Kanyawara chimpanzee community of the Kibale National Park, Uganda. We tested whether the response to the playback of the ‘pant-hoot’ call of a single extragroup male depended on the number of adult males in the listening party, the location of the speaker relative to the territory edge, and each male's agonistic rank. These playbacks elicited cooperative responses, with the nature of the response depending on the number of adult males in the party. Parties with three or more males consistently joined in a chorus of loud vocalizations and approached the speaker together. Parties with fewer adult males usually stayed silent, approached the speaker less often, and travelled more slowly if they did approach. In contrast to many territorial species, the location of the simulated intruder did not affect the response. Although high-ranking males might be expected to benefit more from repelling outside males, both high- and low-ranking males showed a similar pattern of response. Each male responded as if he benefited from repelling intruders, but only if he had strength in numbers. This pattern of response is consistent with cooperation based on mutualism.

Why do chimpanzees hunt and share meat?

Wild chimpanzees, Pan troglodytes, frequently hunt and share meat. Despite widespread interest and considerable study, continued controversy exists regarding the factors that influence chimpanzee hunting decisions and meat sharing. Three hypotheses invoke the importance of ecological, reproductive and social factors. A nutritional shortfall hypothesis suggests that chimpanzees hunt to compensate for seasonal shortages in food availability. A second hypothesis argues that male chimpanzees hunt to obtain meat that they swap for matings. A third hypothesis proposes that males use meat as a social tool to develop and maintain alliances with other males. We tested these hypotheses using observations of an unusually large community of chimpanzees at Ngogo in Kibale National Park, Uganda. Results did not support the nutritional shortfall or meat-for-sex hypotheses. The Ngogo chimpanzees hunted primarily during times of food abundance rather than scarcity. The presence of oestrous females did not predict the tendency of chimpanzees to hunt. Furthermore, meat-for-sex exchanges occurred infrequently, and males did not gain a mating advantage through sharing meat. Additional observations were consistent with the male social bonding hypothesis. At Ngogo, male chimpanzees were likely to hunt when accompanied by other males. Males shared meat nonrandomly and reciprocally among themselves, and males exchanged meat for agonistic support. Although several factors are likely to affect chimpanzee hunting decisions and meat sharing, these results indicate that primary causes will not be found through invoking simple energetic or reproductive considerations.

Territory Characteristics among Three Neighboring Chimpanzee Communities in the Taï National Park, Côte d'Ivoire

We studied territory characteristics among three neighboring chimpanzee communities in the Tai National Park, Cote d'Ivoire, and compared them with other chimpanzee populations. We characterized territories and ranging patterns by analyzing six variables:, (1) territory size, (2) overlap zone, (3) territory utilization, (4) core area, (5) territory shift, and (6) travel distance. Data collection covered a period of 10 mo, during which we simultaneously sampled the local positions of mostly large parties, including males in each community, in 30-min intervals. In Tai, chimpanzees used territories in a clumped way, with small central core areas being used preferentially over large peripheral areas. Although overlap zones between study communities mainly represented infrequently visited peripheral areas, overlap zones with all neighboring communities also included intensively used central areas. Territory utilization was not strongly seasonal, with no major shift of activity center or shift of areas used over consecutive months. However, we observed shorter daily travel distances in times of low food availability. Territory sizes of Tai chimpanzees tended to be larger than territories in other chimpanzee communities, presumably because high food availability allows for economical defense of territorial borders and time investment in territorial activities. Therefore we suggest, that use of territory in Tai chimpanzees is strongly influenced by intercommunity relations. To understand differences in territory characteristics between various populations, it is of major importance to consider not only the intracommunity but also the intercommunity context.

CHARTING CULTURAL VARIATION IN CHIMPANZEES

Abstract Cultural variation among chimpanzee communities or unit-groups at nine long-term study sites was charted through a systematic, collaborative procedure in which the directors of the sites first agreed a candidate list of 65 behaviour patterns (here fully defined), then classified each pattern in relation to its local frequency of occurrence. Thirty-nine of the candidate behaviour patterns were discriminated as cultural variants, sufficiently frequent at one or more sites to be consistent with social transmission, yet absent at one or more others where environmental explanations were rejected. Each community exhibited a unique and substantial profile of such variants, far exceeding cultural variation reported before for any other non-human species. Evaluation of these pan-African distributions against three models for the diffusion of traditions identified multiple cases consistent with cultural evolution involving differentiation in form, function and targets of behaviour patterns.

Intergroup Differences in a Social Custom of Wild Chimpanzees: The Grooming Hand-Clasp of the Mahale Mountains

Intergroup Differences in a Social Custom of Wild Chimpanzees: The Grooming Hand-Clasp of the Mahale Mountains

POST-CONFLICT BEHAVIOUR OF WILD CHIMPANZEES (PAN TROGLODYTES SCHWEINFURTHII) IN THE BUDONGO FOREST, UGANDA

AbstractSince de Waal & van Roosmalen (1979) first documented the occurrence of reconciliation between former opponents in captive chimpanzees, the study of the post-conflict behaviour of primates has provided valuable information about some of the details of primate social organisation. The vast majority of these studies have been carried out on captive subjects and it has been assumed that these findings are representative of wild primates. We set out to investigate whether this was true for the Sonso community of wild chimpanzees (Pan troglodytes schweinfurthii) of the Budongo Forest, Uganda, using controlled procedures comparable with those used in captive studies. We found that these chimpanzees were much less likely to reconcile than their captive counterparts. Only one dimension of relationship quality had an effect on the likelihood of reconciliation. Individuals which were highly compatible, in terms of time spent affiliating, reconciled conflicts more often than those with weak relationships. Captive chimpanzees have also been shown to 'console' one another (de Waal & van Roosmalen, 1979; de Waal & Aureli, 1996), where uninvolved bystanders initiate affiliative contacts with victims of aggression. This study did not confirm that consolatory behaviour was characteristic of wild chimpanzee post-conflict behaviour. Nor did these chimpanzees use explicit gestures during post-conflict interactions as they have been shown to do in two out of three captive studies. We conclude that the post-conflict behaviour of chimpanzees is more variable than has previously been thought and is likely to be dependent on the prevailing social environment.