Demographic influences on the behavior of chimpanzees

Recent research has revealed substantial diversity in the behavior of wild chimpanzees. Understanding the sources of this variation has become a central focus of investigation. While genetic, ecological, and cultural factors are often invoked to explain behavioral variation in chimpanzees, the demographic context is sometimes overlooked as a contributing factor. Observations of chimpanzees at Ngogo, Kibale National Park, Uganda, reveal that the size and structure of the unit group or community can both facilitate and constrain the manifestation of behavior. With approximately 150 individuals, the Ngogo community is much larger than others that have been studied in the wild. We have taken advantage of the unusual demographic structure of this community to document new and intriguing patterns of chimpanzee behavior with respect to hunting, territoriality, and male social relationships. Chimpanzees at Ngogo hunt often and with a considerable degree of success. In addition, male chimpanzees there frequently patrol the boundary of their territory and engage in repeated bouts of lethal intergroup aggression. By forming two distinct subgroups, male chimpanzees at Ngogo also develop social bonds above the level of dyadic pairs. While the sheer number of chimpanzees contributes to differences in hunting, patrolling, mating, and subgrouping at Ngogo, the demographic situation may also constrain behavioral interactions. At Ngogo, male chimpanzees who are closely related genetically through the maternal line do not appear to affiliate or cooperate with each other. Demographic constraints may be responsible for this finding. In this paper, I use these examples to illustrate how the demographic context affects the possible range of behavioral options open to individuals and ultimately contributes to the explanation of behavioral diversity in chimpanzees.     

Procedures for improving maternal behavior in captive chimpanzees

Captive female chimpanzees who have had no opportunity to observe mothers with infants or to interact with infants often show inappropriate maternal behavior, particularly with their first-born infant, and this usually results in the removal of the infant to be human-reared. The present study used two techniques to encourage appropriate maternal behavior in ten pregnant female chimpanzees. These females were housed together with unrelated infant chimpanzees to adopt, or with lactating female chimpanzees and infants to observe. In five cases both techniques were used, in two cases only the first technique was used, and in three cases only the second technique was used. All ten female chimpanzees showed appropriate maternal behavior when their infants were born, in contrast to a group of eight female chimpanzees who had no such experience whose infants had to be removed for human-rearing. It is suggested that these techniques, or adaptations of them, could be applied to many other captive female chimpanzees with similar results.     

Comparative locomotor behavior of chimpanzees and bonobos: The influence of morphology on locomotion

Results from a 10 month study of adult male and female bonobos (Pan paniscus) in the Lomako Forest, Zaire, and those from a 7 month study of adult male and female chimpanzees in the Tai Forest, Ivory Coast (Pan troglodytes verus), were compared in order to determine whether there are species differences in locomotor behavior and substrate use and, if so, whether these differences support predictions made on the basis of interspecific morphological differences. Results indicate that bonobos are more arboreal than chimpanzees and that male bonobos are more suspensory than their chimpanzee counterpart. This would be predicted on the basis of male bonobo's longer and more narrow scapula. This particular finding is contrary to the prediction that the bonobo is a “scaled reduced version of a chimpanzee” with little or no positional behavior difference as had been suggested. This study provides the behavioral data necessary to untangle contradictory interpretations of the morphological differences between chimpanzees and bonobos, and raises a previously discussed (Fleagle: Size and Scaling in Primate Biology, pp. 1–19, 1985) but frequently overlooked point–that isometry in allometric studies does not necessarily equate with behavioral equivalence. Several researchers have demonstrated that bonobos and chimpanzees follow the same scaling trends for many features, and are in some sense functionally equivalent, since they manage to feed and reproduce. However, as reflected in their morphologies, they do so through different types and frequencies of locomotor behaviors. © 1993 Wiley-Liss, Inc.     

Nutritional composition of actual and potential insect prey for the Kasekela chimpanzees of Gombe National Park,Tanzania

Humans, all great ape species, and some lesser apes consume insects. Insects can provide comparable nutritional yields to meat on a gram‐for‐gram basis and may serve as an important source of energy, fat, protein, minerals, and vitamins for hominoids. Although potential insect prey are abundant in ape habitats, patterns of insectivory are not consistent across species or populations. Efforts to understand these patterns are complicated by a lack of nutritional data. We collected samples of insects consumed by the Kasekela chimpanzee community of Gombe National Park, Tanzania, as well as of some insects found within the community range and ignored by these chimpanzees but known to be preyed upon by Pan elsewhere. We determined the gross energy (GE), estimated metabolizable energy (ME), fat, protein, fiber, and ash content of these samples following standard methodologies. We use these data to test the hypothesis that Kasekela chimpanzees choose insect prey (at least in part) based on energy and/or macronutrient content. On a fresh‐weight, per‐gram basis, the insect prey consumed by Kasekela chimpanzees had significantly higher fat and lower ash content than other assayed insects, and on a fresh‐weight, per‐foraging‐unit (“per‐insect,” “per‐dip,” or “per‐nest”) basis were significantly higher in GE, fat, and protein. On a per‐gram basis, the assayed insects were generally comparable in energy and macronutrients to wild vertebrate meat. We conclude that Kasekela chimpanzees do favor insects that are high in energy, fat, and protein, and that the potential macronutrient yields from some forms of insectivory are not trivial. © 2012 Wiley Periodicals, Inc.     

Innovation in chimpanzees

The study of innovation in non‐human animals (henceforth: animals) has recently gained momentum across fields including primatology, animal behaviour and cultural evolution. Examining the rate of innovations, and the cognitive mechanisms driving these innovations across species, can provide insights into the evolution of human culture. Especially relevant to the study of human culture is one of our closest living relatives, the chimpanzee (Pan troglodytes). Both wild and captive chimpanzees demonstrate an impressive ability to innovate solutions to novel problems, but also a striking level of conservatism in some contexts, creating a unique and at times puzzling, picture of animal innovation. Whilst the animal innovation field is rife with potential for expanding our knowledge of human and non‐human cognition and problem‐solving, it is undermined by a lack of consistency across studies. The field is yet to settle on a definition of the term ‘innovation’, leading to studies being incomparable across and even within the same species. Here, we fill two gaps in the literature. First, we discuss some of the most prevalent definitions of ‘innovation’ from different fields, highlighting similarities and differences between them. Secondly, we provide an up‐to‐date review of accounts of innovations in both wild and captive chimpanzees. We hope this review will provide a resource for researchers interested in the study of innovation in chimpanzees and other animals, as well as emphasising the need for consistency in the way in which innovations are reported.     

Inhibition of social behavior in chimpanzees under high-density conditions

This is the first study to investigate the short-term effects of high population density on captive chimpanzees (Pan troglodytes). Subjects of the study were 45 chimpanzees living in five different groups at the Yerkes Regional Primate Research Center. The groups were observed under two conditions: 1) when they had access to both the indoor and outdoor sections of their enclosures; 2) during cold days when they were locked into the indoor runs, which reduced the available space by more than half. Under the high-density condition, allogrooming and submissive greetings decreased, but juvenile play increased. Remarkably, the rate of various forms of agonistic behavior, such as aggression, bluff charge, bluff display, and hooting, occurred less frequently under the high-density condition. This general decrease in adult social activity, including agonistic behavior, can be interpreted as an inhibition strategy to reduce opportunities for conflict when interindividual distances are reduced. This strategy is probably effective only in the short run, however. Behavioral indicators of anxiety, such as rough scratching and yawning, showed elevated rates, suggesting increased social tension under the high-density condition. Am. J. Primatol. 41:213–228, 1997. © 1997 Wiley-Liss, Inc.     

Propagation of handclasp grooming among captive chimpanzees

A grooming posture previously reported for two wild chimpanzee (Pan troglodytes) communities developed spontaneously in a captive group of the same species. This offered a unique opportunity to follow the propagation of a new social custom. The posture consists of two partners grasping hands—either both right hands or both left hands—and raising the arms in an A-frame above their heads while mutually grooming with their free hands. The propagation of this pattern was followed over a 5 year period. In the beginning, handclasps were always initiated by the same adult female. This female initiated the posture mainly with her adult female kin. In subsequent years, these relatives became frequent participants in the posture with each other as well as with nonrelatives. Over the years the posture increased in frequency and duration and spread to the majority of adults and also to a few adolescents and older juveniles. The pattern persisted after removal of the apparent originator. Am. J. Primatol. 43:339–346, 1997. © 1997 Wiley-Liss, Inc.     

A case report of a novel type of stick use by wild chimpanzees

We have found evidence that wild chimpanzees used stout sticks to dig into one end of a decayed fallen trunk from the side and a long stick with a frayed end to dig into or brush its stump, in the Moukalaba Reserve, Gabon. This type of stick use by wild chimpanzees has not been recorded in any habitat. This finding should contribute to future studies and discussions of variations in tool use and cultural processes among wild chimpanzees. Electronic Publication     

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.     

Third-party postconflict affiliation of aggressors in chimpanzees

Postconflict management strategies have been defined as any postconflict interaction that mitigates the negative consequences of the preceding agonistic conflict. Although most studies have investigated postconflict interactions between former opponents or between victims and uninvolved bystanders, interactions between aggressors and bystanders have received much less attention. In this study, we examined a database of 1,102 agonistic interactions and their corresponding postconflict periods in two outdoor-housed groups of captive chimpanzees in order to test the occurrence of postconflict third-party affiliation of aggressors. Our results confirmed the occurrence of appeasement, i.e. postconflict affiliation by a bystander toward an aggressor, but failed to detect the occurrence of postconflict affiliation directed from aggressors toward bystanders. Appeasement rates did not differ according to the sex of the involved individuals. In addition, appeasement occurred more often in the absence of reconciliation than after its occurrence suggesting that appeasement may act as an alternative to reconciliation when the latter fails to occur. Both study groups showed behavioral specificity for appeasement, i.e. context-specific use of certain behaviors, supporting the view that chimpanzees exhibit highly visible explicit postconflict affiliation.     

Histologic examination of bone development in juvenile chimpanzees

The purpose of this study is to determine whether histologic skeletal development in chimpanzees (Pan troglodytes) differs from that in humans. Currently, minimal quantitative data are available on the bone histology of great apes. In addition to providing baseline data on juvenile chimpanzee bone histology, the data generated by this study have potential applications for studying the comparative development between chimpanzees and humans and other primates, as well as investigating the evolution of human bone development, differences in development among limb elements, and differences in histology related to locomotor function. The study sample includes thin sections from the femoral, tibial, and fibular midshafts of 13 chimpanzees originally prepared by Kerley ([1966] Tulane Stud. Zool. 13:71-82) as part of a study on skeletal age changes in the chimpanzee. Twelve juveniles, ranging in known age from 2-15.3 years, and one adult, with a known age of 35 years, are represented. For each specimen, numbers of osteons, osteon fragments, and non-Haversian canals were counted, and percent lamellar bone was estimated. Results were compared with data extracted from Kerley ([1965] Am. J. Phys. Anthropol. 23:149-164) on a juvenile human sample. Results indicate that juvenile chimpanzees and humans exhibit similar age-related changes in histologic variables. However, age is not as strong a predictor of variation in microstructural variables in chimpanzees as it is in humans.     

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.     

Use of gesture sequences in chimpanzees

Gestural communication in a group of 19 captive chimpanzees (Pan troglodytes) was observed, with particular attention paid to gesture sequences (combinations). A complete inventory of gesture sequences is reported. The majority of these sequences were repetitions of the same gestures, which were often tactile gestures and often occurred in play contexts. Other sequences combined gestures within a modality (visual, auditory, or tactile) or across modalities. The emergence of gesture sequences was ascribed to a recipient's lack of responsiveness rather than a premeditated combination of gestures to increase the efficiency of particular gestures. In terms of audience effects, the chimpanzees were sensitive to the attentional state of the recipient, and therefore used visually-based gestures mostly when others were already attending, as opposed to tactile gestures, which were used regardless of whether the recipient was attending or not. However, the chimpanzees did not use gesture sequences in which the first gesture served to attract the recipient's visual attention before they produced a second gesture that was visually-based. Instead, they used other strategies, such as locomoting in front of the recipient, before they produced a visually-based gesture.     

The diet of chimpanzees in the Budongo Forest Reserve, Uganda

Chimpanzee diets are highly variable, but in all cases dominated by ripe fruit. Previous work has suggested that in the Budongo Forest Reserve, Uganda, ripe fruit remains available throughout the year, but dietary data for chimpanzees at this site remain sparse. This paper details the diet of a recently habituated community of Budongo chimpanzees living in the Sonso region. Chimpanzees of this community spent 64.5% of their feeding time eating fruit, and 19.7% eating arboreal leaves. Terrestrial herbaceous vegetation formed only a minor component of the diet. In these general dietary characteristics, Budongo chimpanzees show greater similarity to those of the Gombe National Park than they do to those in the geographically closer and floristically more similar Kibale Forest National Park. The diet was dominated by the fruit of four species and leaves of two species, although the composition of the diet varied from month to month, remaining diverse. Figs were consumed throughout much of the year, and in consequence, should perhaps be regarded as a staple, rather than fallback, food. A period of food scarcity was not apparent in this study and future comparative nutritional investigation will be required to determine whether these chimpanzees face a time of dietary hardship.     

Tool use by wild chimpanzees (Pan troglodytes) to obtain termites (Macrotermes herus) in the Mahale Mountains,Tanzania

Wild chimpanzees (Pan troglodytes) used probes made of vegetation to fish for termites (Macrotermes herus) in the Mahale Mountains of western Tanzania. Data on both the artefacts and behavior associated with their use were recorded over a 5-month period. The chimpanzees of one unit group, B Group, were seen four times to use the tools to extract the insects from their mounds. A sample of 290 tools was collected and analyzed in terms of age, seasonality, length, width, class of raw materials, species, methods of making, extent of use, and damage incurred through use. There were differences across groups in tool use in feeding on termites; some could be related to biotic factors, but others appeared to be cultural differences.     

Resocialization of a group of ex-laboratory chimpanzees, Pan troglodytes.

In order to determine if socially deprived chimpanzees could establish an integrated social unit and reproduce, a group of wild-born individuals from a single-cage laboratory environment were released onto a small island in a South Florida tourist park in 1975. The present study was undertaken during June and July of 1988 to evaluate the long term results of the experiment and to document the reproductive history of the chimpanzees since their release on the island. The evidence presented in this paper suggests that it is possible for laboratory chimpanzees to be resocialized and to reproduce successfully.     

Familial incidence of multiple births in a colony of chimpanzees (Pan troglodytes)

This paper describes the incidence of multiple births in the Yerkes Chimpanzee colony for a period of about 63 years. Pedigrees are presented for all multiple births. They demonstrate the recurrence of twins in relatively few family lines which can be traced back to a small number of ancestors. The findings suggest that twinning is a family trait in chimpanzees and they support the hypothesis that the incidence of multiple births is genetically influenced in this colony. In addition, a relatively high level of inbreeding may have enhanced the incidence of multiple births in these family lines. Similar findings are known from human populations.     

Trauma, degenerative disease, and other pathologies among the Gombe chimpanzees

The well-known and extremely well-documented chimpanzees from Gombe National Park were analyzed for presence of skeletal pathologies. Of the 15 animals available for study, 11 were old and complete enough to permit systematic analysis. Of these, 10 showed some evidence of skeletal pathological involvement. The most common type of lesion seen resulted from trauma. Those chimps with the most fractures (Old Female, 3; Flo, 4; Hugo, 8) are consistently the oldest individuals in the sample. In addition to accidental falls, the most common cause of trauma was from interpersonal violence, resulting in bite wounds (see in two individuals) and fractures (see in three individuals). Conversely to trauma, degenerative disease was exceedingly rare in this population, found in no large intervertebral joints (N = 344) and only two major synovial joints (N = 186). In fact, the complete lack of osteophytosis, even in older individuals, stands in stark contrast to the situation seen in modern humans, perhaps in our species reflecting a biomechanical cost of bipedality.