Imaginary Play in chimpanzees (Pan troglodytes)

Imaginary Play was studied in a group of five signing chimpanzees and it was found that chimpanzees engage in imaginary play similar to that found in human children. Fifteen hours of remote videotapes were analyzed for instances of imaginary play. Behaviors were defined as imaginary play by meeting a predetermined criteria which allowed them to be classified into one of six different categories of imaginary play. Six instances of imaginary play were found and these were classified into the two categories of Animation and Substitution. Observations of imaginary play in other research with chimpanzees were discussed.     

Functional analysis of chimpanzee (Pan troglodytes) private signing

The chimpanzee's use of American Sign Language (ASL) to communicate with humans and with each other has been empirically demonstrated in several reports, but this is the first research to experimentally examine their use of sign language in a nonsocial fashion: private signing. This experiment examined the private signing behavior of five signing chimpanzees, using a remote videotaping technique with no human present. It was found that all five chimpanzees signed to themselves for a total of 368 instances. These instances of private signing were classified into nine different functional categories as has been done in the analysis of private speech and signing in hearing and deaf human children. Similar to humans, a few of the categories accounted for the majority of the instances of private signing. These findings empirically demonstrate a behavior similar to private speech and signing in humans.     

Leaf-grooming by a wild chimpanzee in Mahale

During the course of systematic observations of the leaf-grooming behavior by the chimpanzees (Pan troglodytes) of the Mahale Mountains National Park, Tanzania, I recovered a louse from a leaf “groomed” by an adult male chimpanzee after a typical leaf-grooming session. During the leaf-grooming session I observed a small object on his lower lip. He picked up a leaf, transferred the small object from his lip to the leaf, folded the leaf and crushed the folded side of the leaf with his thumb. I present this observation as further evidence of the “squashing ectoparasites” hypothesis for leaf-grooming.     

Potential hominin plant foods in northern Tanzania: semi-arid savannas versus savanna chimpanzee sites

Savanna chimpanzees are useful as referential models for early hominins, and here potential differences between chimpanzee and early hominin ecology is the focus. Whereas chimpanzees inhabit only a handful of modern African savannas, there is evidence that early hominins occupied relatively more open and arid savannas than those in which chimpanzees live. In order to help expand potential models of early hominin palaeoecology beyond savanna chimpanzee-like scenarios, and to provide a basis for future modeling and testing of actual hominin diets, this study compares the types of plant foods available in modern semi-arid savannas of northern Tanzania to plant foods at savanna chimpanzee sites. The semi-arid savannas are not occupied by modern chimpanzees, but are potentially similar to environments occupied by some early hominins. Compared to savanna chimpanzee habitats, the northern Tanzania semi-arid savanna has a lower density and fewer species of trees that produce fleshy fruits. Additionally, the most abundant potential hominin plant foods are seasonally available Acacia seeds/pods and flowers, grass seeds, and the underground parts of marsh plants, as evidenced by vegetation surveys and by studies of the diets of baboons that forage in similar areas. The information from this study should be useful for framing hypotheses about hominin diets for sites with palaeoenvironmental contexts similar to those of the northern Tanzania semi-arid savannas and for contextualising tests of actual hominin diets (e.g., those based on dental microwear or isotopes).     

Chimpanzee predation in the Mahale mountains from August 1979 to May 1982

Fifty-four episodes of predatory behavior of wild chimpanzees were recorded in Mahale, western Tanzania, from August 1979 to May 1982. The chimpanzees most frequently hunt in two seasons, during May, and from August to December. Longer-term fecal analysis indicates that predation frequency is significantly higher in the dry than in the rainy season. The seasonality of predation might be the result of the sum of various ecological factors, at least one of which is the birth season of the prey species. Most of the prey are juvenile blue duiker, bushbuck, bushpig, red colobus, and red-tailed monkeys. Sex difference is recognized in the prey selection and in the hunting method employed. Apparent local difference in the predatory behavior between Mahale and Combe chimpanzees (in Mahale,females hunt more frequently, and blue duiker is the most frequent prey) can be understood in terms of the difference either in the observation methods or in the faunal diversity and density. Other aspects of predatory behavior also are reported.     

Chimpanzees (Pan troglodytes) use markers to monitor the movement of a hidden item

Four chimpanzees (Pan troglodytes) monitored the movement of hidden items in arrays of opaque cups. A chocolate candy was hidden in an array of four cups and temporarily presented paper markers indicated the location of the candy (which otherwise was not visible). These markers were either non-symbolic or symbolic (lexigram) stimuli that in other contexts acted as a label for the hidden candy, and the array was either rotated 180° after the marker was removed or the array remained in the same location. For three of four chimpanzees, performance was better than chance in all conditions and there was no effect of the type of marker. These experiments indicate that chimpanzees can track the movement of a hidden item in an array of identical cups even when they never see the item itself, but only see a temporarily presented marker for the location of that item. However, there was no benefit to the use of symbolic as opposed to non-symbolic stimuli in this performance.     

Chimpanzee deaths at Mahale caused by a flu-like disease

A flu-like disease spread among chimpanzees (Pan troglodytes schweinfurthii) of the M group at Mahale Mountains National Park, Tanzania, from June to July 2006. This epizootic or epidemic killed up to 12 chimpanzees. The obvious evidence of their deaths came from finding the bodies of three infants who had previously shown some symptoms of the disease. At least one of these infants died of pneumonia. In addition, nine chimpanzees were missing after the outbreak. These individuals were assumed to have been killed by this epizootic because most of them had contact with the infected individuals on the last days they were observed. We also found two dead bodies during this period, which were thought to be those of two missing individuals. We confirmed 23 (35.4%) of 65 individuals of the M group showed some symptoms of the disease, although most of them (20/23) did not die. More than half of them (14/23) had kin showing symptoms. Since this epizootic may have been caused by contact with humans, it will be necessary to establish and follow appropriate protocols for researchers, tourists, and park staff to observe chimpanzees, and to explore the mechanism of disease transmission from humans to chimpanzees and among chimpanzees.     

An apparatus and procedure for studying the choice component of foraging in a captive group of chimpanzees (Pan troglodytes)

An apparatus is described which was used to investigate the choice component of foraging in a captive group of chimpanzees maintained in a large, outdoor compound at the Yerkes Regional Primate Research Center Field Station. The utilization of more than one apparatus would allow the investigation of other ecological and psychological concepts in nonhuman primates housed under semi-natural conditions.     

Responses to a stranger mother-son pair in the wild chimpanzee: A case report

A stranger mother-son pair of the chimpanzee was observed twice interacting with conspecifics of a neighbouring unit-group: first, when the mother and son accidentally encountered them within the core area of the former; second, when the mother and son temporarily immigrated for about one week. On both occasions, the mother and son were severely attacked by adult males of the neighbouring unit-group, and would have been killed had it not been for human intervention. The main target of the aggression was not the infant, but the mother. Some adult males intervened and prevented other males and females from attacking the mother-son pair. Moreover, most adult males displayed an ambivalent attitude since they showed aggression towards them on one occasion, but groomed, reassured and played on another. The reasons for the variable responses of adult males to a stranger female are discussed in terms of possible differences in their mating strategies.     

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

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

Chimpanzee microsatellite PCR primers applied to paternity testing in a captive colony

Previously designed primers for the polymerase chain reaction (PCR) amplifying microsatellite DNA segments containing GT/AC dinucleotide repeats in the chimpanzee (Pan troglodytes) genome were used for paternity testing in a breeding colony in captivity. Combinations of three PCR primers identified the fathers of all the tested 40 chimpanzees born in an eight-year period. The results suggested: (1) a positive (though not conclusive) correlation between male rank and number of offspring; (2) choice of mating partners by the female rather than by the male; and (3) absence of stable mating pairs over the years. For studies of chimpanzees in captivity and in the wild, these primers should be useful for paternity testing, for investigating genetic variations, and for improving genetic maintenance of breeding colonies.     

Group Size and Composition of Colobus guereza in Kyambura Gorge, Southwest Uganda, in Relation to Chimpanzee Activity

We documented and assessed the influence of chimpanzee activity on group size and composition of Colobus guereza in Kyambura Gorge, southwest Uganda, from July to September, 1994 and in February and March 1996. The population density of colobus is very high: 347 individuals per km ². Density differed outside activity centers of chimpanzees (525 individuals per km ² ) and within the centers (186 per km ² ). We identified a total of 24 colobus groups, ranging between 3 and 13 individuals. Of the 24 groups, 22 were one-male groups. Groups were smaller and the percentage of subadults and juveniles was lower in groups within chimpanzee activity centers. Estimates of home ranges are between 1.7 and 6.2 ha, but neighboring home ranges overlapped 80%. Only a territory of approximately 0.5 ha was defended by the alpha male.     

A note on the chimpanzee ecology of the Ugalla Area,Tanzania

Results of a nine-day survey of the chimpanzee habitat in Ugalla area of western Tanzania in 1975 is reported. The most dominant vegetation of the area wasJulbernardia globiflora woodland. Evidence of chimpanzees, both indirect (such as beds, faeces, and food remnants) and direct (calls and actual observation), suggests that chimpanzees are sparsely distributed throughout the area, but that they disproportionately useBrachystegia bussei woodland along escarpments andCynometra-Albizzia riverrine forests. The hilly country of Sisegwa/Mnyangwa was the only area where chimpanzees appeared to be comparatively abundant. Mammal hair found in faeces indicates mammal-predation by the chimpanzees in this area. Hard-shelled fruits ofStrychnos were apparently bitten open without the use of extra-somatic objects. The food repertoire included fruits of the generaAzanza, Canthium, Cordia, andTamarindus.     

Predation on mammals by the chimpanzee (Pan troglodytes)

With respect to prey selectivity and predation frequency, chimpanzees (Pan troglodytes) show local differences as well as diachronic variability within the same population. When data on predation from three long-term studies at Mahale, Gombe, and Tai are compared, some differences and similarities emerge; Mahale is more like Gombe than Tai in regard of prey selection but features of hunting at Tai with respect to predation frequency are not conspicuous. The most responsible factor for diversity in prey selectivity is a distinct “prey image” maintained by chimpanzees of different populations, although it is necessary to clarify in future studies why and how such tradition develops. Relative body size of chimpanzees to prey species and/or the degree of cooperation among members of a hunting party may explain the variability in prey size selected at each site, the latter influencing the frequency of successful hunts at the same time. Although various degrees of habituation and different sampling methods including artificial feeding might have obscured the real differences, recent data from the three populations do not seem to be biased greatly by such factors. Nevertheless, it is still difficult to make strict comparisons due to the lack of sufficient standardized data across the three populations on the frequency of hunting and predation. It is suggested that the size or demographic trend of a chimpanzee unit-group, especially the number of adult males included, necessarily influences its hunting frequency as well as its prey profile. It is also suggested that factors which bring these males together into a party (e.g. fruit abundance, swollen females, conflict between unit-groups etc.) strongly affect theactual hunting and kill rates. Other possible factors responsible for the local differences are forest structure (e.g. tree height), skilful “hero” chimpanzees, and competition with sympatric carnivorous animals. A total of at least 32 species have been recorded as prey mammals of chimpanzees from 12 study sites and the most common prey mammals are primates (18 species), of which 13 species are forest monkeys. Forest monkeys, colobine species in particular, are often the most common victims of the predation by chimpanzees at each site. We may point out a tendency toward selective hunting for the forest monkeys in terms of the selectivity of prey fauna among all three subspecies of chimpanzees, including populations living in drier environment. The mode of chimpanzee hunting seems to correspond to the highest available biomass of gregarious, arboreal monkeys in the forest, colobine species in particular. In contrast, bonobos (P. paniscus) are less carnivorous than chimpanzees, only rarely preying on a few species of small mammals. The sharp contrast of the two allied species in their predatory tendencies appears to have something to do with the differences in the structure of primary production between their habitats.     

Plant Species with Potential as Food,Nesting Material,or Tools at a Chimpanzee Refuge Site in Caddo Parish,Louisiana

Surplus chimpanzees live in research laboratories where they will likely remain for the rest of their lives. An alternative to laboratory housing is an outdoor enclosure in a warm climate. Before construction, researchers should conduct a vegetation survey because chimpanzees use vegetation daily. Chimp Haven, Inc. is developing a chimpanzee sanctuary in Caddo Parish, Louisiana, and we conducted a vegetation survey at the site to 1) characterize the abundance and structure of vegetation; 2) identify plants with utility as food, nesting material, or tools; 3) determine the abundance and distribution of useful vegetation; and 4) identify any possibly hazardous vegetation. We established 48 plots, quantified the woody vegetation, and identified potentially useful and hazardous plant species from the published literature. Vegetation at the site was secondary growth from logging of loblolly pine (Pinus taeda), the most abundant tree. Other abundant trees included oak (Quercus spp.), elm (Ulmus spp.), sweetgum (Liquidambar styraciflua), and maple (Acer spp.). Small plants (1–9.9 m tall) constituted 95% of all vegetation. Forty-one of 64 plant species have edible vegetative parts, while 35 species have edible reproductive parts. We identified 55 potential nesting trees by size (dbh ≥ 25 cm) and 4 species used as tools by captive great apes. Useful vegetation was concentrated in areas with topographic relief or in a floodplain, while flat areas with fields had less. We recommend that the floodplain be cropped for fruit and browse and enclosures encompass areas with relief and fields, creating a diverse habitat.     

Behavioral Ecology of Sympatric Chimpanzees and Gorillas in Bwindi Impenetrable National Park,Uganda: Diet

Via a field study of chimpanzees (Pan troglodytes schweinfurthii) and gorillas (Gorilla gorilla beringei) in Bwindi Impenetrable National Park, Uganda, we found that their diets are seasonally similar, but diverge during lean seasons. Bwindi chimpanzees fed heavily on fruits of Ficus sp., which were largely ignored by the gorillas. Bwindi gorilla diet was overall more folivorous than chimpanzee diet, but was markedly more frugivorous than that of gorillas in the nearby Virunga Volcanoes. During 4 mo of the year Bwindi gorilla diet included more food species than that of the chimpanzees. Three factors in particular—seasonal consumption of fibrous foods by gorillas, interspecific differences in preferred fruit species, and meat consumption by chimpanzees—contributed to dietary divergence between the two species. When feeding on fruits, gorillas ate Myrianthus holstii more frequently than chimpanzees did, while chimpanzees included more figs in their annual diet. Chimpanzee diet included meat of duikers and monkeys; gorilla frequently consumed decaying wood.     

Age differences in spatial positioning of males in a chimpanzee unit-group at the mahale mountains National Park,Tanzania

Proximity partner choice by male chimpanzees of various age classes was analyzed in relation to their spatial positioning. Field work was carried out twice at the Mahale Mountains National Park, Tanzania. Proximity data were recorded at 3 and 10m from the focal animal. The data for the proximity between the focal male and other individuals allowed the males to be classified into two categories according to both criteria: early adolescence to young adult, and prime to old age. Between the males, the 3m proximity data permitted a classification into two categories as above, but those for 10m did not. These two spatial distances thus probably have different meanings for the males. The numbers of male proximity partners and proximity with the alpha male also allowed the males to be classified into two categories: early and late adolescence, and young adult to old age. Together, the above results support the classification of males into three age-graded categories: (1) early and late adolescence, (2) young adult, and (3) prime to old age. This does not arise because the males of each category form an age group. Prime or older males are most frequently in proximity, while their juniors consistently attempt to approach them. However, even prime or older males are not equally in proximity with one another. Their proximity partners change as time passes. Probably recognizing such changes, they form coalitions or are in rivalry. The sexual interest of adolescent males is probably a factor stimulating them to separate from their mothers, and to approach older males. Young adult males, even though physically mature, do not have equal proximity relations with older males. They are not yet sufficiently qualified to join the coalitions formed by their seniors.     

Inversion effect in perception of human faces in a chimpanzee (Pan troglodytes)

Three experiments investigated the inversion effect in face perception by a chimpanzee (Pantroglodytes) under the matching-to-sample paradigm. The first two experiments addressed the inversion effect in the perception of human faces. In Experiment 1, the subject received identity matching using 104 photographs of faces and houses presented in four different orientations. The chimpanzee showed better accuracy when the faces were presented upright than when they were inverted. The inversion effect was not found for photographs of houses. In Experiment 2, the subject received rotational matching in which the sample and comparisons differed in orientation. The subject showed a clear inversion effect for faces but not for houses. Experiment 3 explored the hemispheric specialization of the face inversion effect with chimeric (artificially composed) faces. The subject showed no visual-field preference when the chimeric faces were presented as samples under nonreinforced probe testing, while the inversion effect was evident when the discrimination was based on the left part of the chimeric sample. The results suggested that the face-inversion was specific to the left visual field (i.e. right hemispheric processing). In general, these results were consistent with those found in humans in similar testing situations.     

Polymorphic microsatellite DNA amplification customized for chimpanzee paternity testing

DNA segments containing GT/AC dinucleotide repeats in the chimpanzee (Pan troglodytes) genome were screened. Thirteen transformedE. coli colonies were identified with the (GT)₁₀ probe to have chimpanzee DNA fragments containing (GT)_n repeats. These potentially polymorphic (variable n) DNA segments were sequenced. Primers for the polymerase chain reaction (PCR) amplifying these DNA segments were designed. Six pairs of primers yielded polymorphic PCR products. Three of them revealed considerable length polymorphisms and heterozygosities in a group of captive chimpanzees. For studies on chimpanzees in the wild and in captivity, these primers should be useful for paternity testing, for investigating genetic variations, and for improving the genetic maintenance of breeding colonies. The strategy adopted in the present study to obtain PCR primers amplifying polymorphic microsatellite DNA segments may well be applicable to almost all eukaryotic organisms.