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.     

Establishing the presence of a body temperature rhythm in chimpanzees (Pan troglodytes) using a tympanic membrane thermometer

Seven chimpanzees (Pan troglodytes) were trained to present their ears so that a tympanic nembrane thermometer could be inserted. Temperatures were collected from both ears of each subject every 3 hours for 72 consecutive hours. The presence of a body temperature rhythm, well documented in other mammals, was established. Each ear demonstrated its own rhythm, but the rhythms in both ears generally mirrored each other. Similarities in the temperature rhythms of cagemates were found. These data are the first evidence of a body temperature rhythm in chimpanzees, and they represent a non-invasive method of measuring the 24-hr rhythms in both human and non-human primates.     

Chimpanzees' (Pan troglodytes) choice of prey among termites (macrotermitinae) in western Tanzania

This study examines factors affecting chimpanzees' preying on termites, especially their choice of prey species. Regular surveys of a large sample of termite-mounds in the Mahale Mountains, Tanzania, confirmed that chimpanzees of B Group obtainedMacrotermes, which were relatively uncommon, by the use of fishing-tools, but ignored the much more abundantOdontotermes. This preference appeared to reflectMacrotermes' more extended swarming period, greater accessibility, larger size, and less noxious taste than the soldiers ofOdontotermes. Similar factors probably underly the chimpanzees' choice ofMacrotermes at Gombe, butPseudacanthotermes spiniger are also common there, and their absence from the diet is less easily explained. In contrast, the chimpanzees of K Group at Mahale prey mainly onP. spiniger;Macrotermes are apparently absent, andP. spiniger appear to be more abundant, accessible, and palatable than the alternativeOdontotermes.     

What chimpanzees (Pan troglodytes) learn in a cooperative task

To examine the development of cooperation in a captive group of chimpanzees (Pan troglodytes), we designed an apparatus which required the simultaneous traction by two animals to get a reward. Two chimpanzees, an adult male and an infant female in a group of six, produced most of the successful responses (pulling on two handles simultaneously). Visual behavior was used to try to determine what chimpanzees learned about the cooperative task. Propositions were made to investigate what kind of learning could be attributed to chimpanzees and were confronted with results. Both subjects learned the link between the presence of fruits on the apparatus and the possibility of getting a fruit. They also learned the importance of the partner at the apparatus to make a successful response. Only the adult male learned to take into account the behavior of the partner at the apparatus before pulling a handle. From a methodological point of view, the glances made by the animals can constitute a useful behavioral indicator of what the subjects learned in a given social situation.     

Comparing infant and juvenile behavior in bonobos (Pan paniscus) and chimpanzees (Pan troglodytes): a preliminary study

The dichotomy between the two Pan species, the bonobo (Pan paniscus) and chimpanzee (Pan troglodytes) has been strongly emphasized until very recently. Given that most studies were primarily based on adult individuals, we shifted the “continuity versus discontinuity” discussion to the infant and juvenile stage. Our aim was to test quantitatively, some conflicting statements made in literature considering species differences between immature bonobos and chimpanzees. On one hand it is suggested that infant bonobos show retardation in motor and social development when compared with chimpanzees. Additionally it is expected that the weaning process is more traumatic to chimpanzee than bonobo infants. But on the other hand the development of behaviors is expected to be very similar in both species. We observed eight mother–infant pairs of each species in several European zoos. Our preliminary research partially confirms that immature chimpanzees seem spatially more independent, spending more time at a larger distance from their mother than immature bonobos. However, the other data do not seem to support the hypothesis that bonobo infants show retardation of motor or social development. The development of solitary play, environmental exploration, social play, non-copulatory mounts and aggressive interactions do not differ between the species. Bonobo infants in general even groom other group members more than chimpanzee infants. We also found that older bonobo infants have more nipple contact than same aged chimpanzees and that the weaning process seems to end later for bonobos than for immature chimpanzee. Additionally, although immature bonobos show in general more signs of distress, our data suggest that the weaning period itself is more traumatic for chimpanzees.     

Heterochrony and sexual dimorphism in the skull of the Liberian chimpanzee (Pan troglodytes verus)

Allometric methods and theory derived from principles of relative growth provide new and powerful approaches to an understanding of the nature and development of sexual dimorphism among living primates. The Frankfurt collection of Liberian chimpanzee skulls and mandibles provides a large skeletal sample from a single natural population of wild shot animals, including individuals of all ages and both sexes, and allows investigation of allometric and heterochronic patterns of sexual dimorphism. Univariate, bivariate, and multivariate analyses are utilized in this study in order to ascertain the ontogenetic nature of male-female differences in the skull of the Liberian chimpanzee. The results of univariate and multivariate analyses indicate that, while overall levels of sexual dimorphism in the chimpanzee skull are small, the greatest differences are in dimensions of the viscerocranium, while neurocranial dimensions and orbital size tend to be less dimorphic. Bivariate regressions of 21 cranial variables against basicranial length document positive allometry in many facial and mandibular dimensions, and isometry or negative allometry for most neurocranial dimensions. The data confirm previous work in chimpanzees and other anthropoid primates suggesting that males and females are “ontogenetically scaled” in most cranial traits. That is, males and females share the same cranial growth trajectories, although ending up at different points. Both rate and time hypermorphosis are suggested as underlying causes of ontogenetic scaling in the Liberian chimpanzee.     

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.     

Severe Aggression Among Female Pan troglodytes schweinfurthii at Gombe National Park, Tanzania

Aggression is generally more severe between males than between females because males gain greater payoffs from escalated aggression. Males that successfully defeat rivals may greatly increase their access to fertile females. Because female reproductive success depends on long-term access to resources, competition between females is often sustained but low key because no single interaction leads to a high payoff. Nonetheless, escalated aggression can sometimes immediately improve a female’s reproductive success. Resisting new immigrants can reduce feeding competition, and infanticide of other females’ young can increase a female’s access to resources. East African chimpanzees live in fission-fusion communities in which females occupy overlapping core areas. Growing evidence indicates that reproductive success correlates with core area quality, and that females compete for long-term access to core areas. Here we document 5 new cases of severe female aggression in the context of such competition: 2 attacks by resident females on an immigrant female, a probable intracommunity infanticide, and 2 attacks on a female and her successive newborn infants by females whose core areas overlapped hers. The cases provide further evidence that females are occasionally as aggressive as males. Factors influencing the likelihood and severity of such attacks include rank and size differences and the presence of dependable allies. Counterstrategies to the threat of female aggression include withdrawing from others around the time of parturition and seeking male protection. We also discuss an unusual case of a female taking the newborn infant of another, possibly to protect it from a potentially infanticidal female.     

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.     

Spatial aspects of spontaneous object grouping by young chimpanzees(Pan troglodytes)

I report spontaneous spatial object grouping in five chimpanzees (Pan troglodytes)ranging from 1 to 4 years of age. I recorded subjects' spontaneous interactions with groups of objects, noting the spatial relations in the groupings and the constructive processes that the subjects adopted. Though one subject developed vertical stacks, none of them realized horizontal alignments or spatial correspondences between groups. All subjects showed consistent trends in their constructive processes toward manipulating objects in relation to the body: they increasingly manipulated objects globally, that is to say, they moved or held objects together with the same part of the body. They also increasingly placed objects on the body or in correspondence to their symmetrical body parts. The increasing importance assigned by chimpanzees to body- object relations over object- object relations contrasts with human developmental trends in the domain of manipulative space.     

Social parameters and urinary testosterone level in male chimpanzees (Pan troglodytes)

Studies investigating relationships between social parameters (such as dominance rank, rates of aggressive and sexual behaviors) and androgen (particularly, testosterone) levels in male primates have yielded inconsistent results. In the present study, we address the relationship between androgens, male dominance rank and rank-associated behaviors in two groups of captive chimpanzees, a species characterized by a pronounced dominance hierarchy between adult males. By combining behavioral observations with urinary testosterone (T) measurements, we found that the differences in T concentrations between males were small and not obviously related to their dominance rank. T levels were not related to the rates of initiated aggression and copulatory behavior, but a significant negative relationship between male T level and the rates of strong aggression received was apparent. Our findings, combined with those of others, suggest that any relationship between dominance rank and T depends upon the extent to which individual rank-associated behaviors (e.g. aggressive/sexual) are themselves related to T.     

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.     

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.     

Preliminary report on predatory behavior and meat sharing in tschego chimpanzees (Pan troglodytes troglodytes) in the Ndoki forest,northern Congo

Predatory behavior ofPan t. troglodytes in the Ndoki Forest was confirmed by both direct observation and fecal evidence. Eight out of 214 fecal samples (3.7%), collected during 16 months, contained vertebrate tissue. The prey species were a terrestrial bird, two monkey species including crowned guenon, a squirrel, and probably a pangolin. This rate suggested that predation in the Ndoki population can occur as frequently as in other populations. Chimpanzees were also directly observed to eat an infant crowned guenon, a hornbill, and a duiker. An adult female used a branch apparently in an attempt to drive out a hornbill from its nest hole, though no bird was observed to come out. Chimpanzees were attracted to meat, and were observed begging and sharing over the meat. Predatory behavior is common toPan andHomo, but not toGorilla, implying that the common ancestor of the former two genera acquired this behavior after separating from gorillas.     

Captive breeding, paternity determination, and genetic variation in chimpanzees (Pan troglodytes) in the Australasian region

DNA “fingerprinting” using polymorphic (CA)-repeat microsatellite markers was used to quantify the level of genetic variation present in chimpanzees (Pan troglodytes) in the Australasian region. These markers were also used to determine the paternity of chimpanzees born at Taronga Zoo over a 20-year period. The results suggested that the dominant male in the colony was responsible for siring most, but not all, of the offspring. Where the dominant male was excluded from paternity, the sire was identifiable if all candidate males were available for typing. This enabled us to prove the captive origin of offspring born in the colony during this period. Thus, microsatellite analysis was a useful tool for assignment of familial relationships and improving genetic management of breeding colonies.     

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.     

Play behaviour and its effects on social development of common chimpanzees (Pan troglodytes)

The aim of the study was to monitor the social development of infant and juvenile common chimpanzees (Pan troglodytes) through their play behaviour at Taronga Zoo in Sydney in order to examine the possible effects of captivity (such as limited opportunities to play) on social development. Play behaviour was observed by focal animal sampling to determine individual differences, and their relationship to age, sex, and relatedness of the subjects. Analysis revealed marked individual variations in social, solitary, and object play behaviours indicative of a relatively well-balanced social and physical environment. Subjects showed a marked preference for play-partners of a different age compared to their own, and initiated interactions with similar frequency with members of both sexes. Many social-play dyads consisted of related individuals, and familiarity with prospective play-mates was the most decisive factor in social interactions.     

An advantage for concavities in shape perception by chimpanzees (Pan troglodytes)

The significance of concavity in object shape perception by chimpanzees (Pan troglodytes) was investigated in a matching-to-sample procedure. For the task, chimpanzees were required to choose a polygon stimulus that was identical in shape to a sample. The incorrect alternative was defined by the addition or subtraction of a concave or convex apex. Chimpanzees were more sensitive to the concave deformation than to the convex deformation. This tendency conforms to the theories of human visual perception that have treated concave features as important factors in reconstructing three-dimensional structures from two-dimensional images. Our results suggest that shape representation in chimpanzees is similar to that in humans and that chimpanzees visually process two-dimensional images in the same manner as humans.     

Is human conversation more efficient than chimpanzee grooming?

Clique sizes for chimpanzee (Pan troglodytes) grooming and for human conversation are compared in order to test Robin Dunbar’s hypothesis that human language is almost three times as efficient a bonding mechanism as primate grooming. Recalculation of the data provided by Dunbar et al. (1995) reveals that the average clique size for human conversation is 2.72 whereas that of chimpanzee grooming is shown to be 2.18. The efficiency of human conversation and actual chimpanzee grooming over Dunbar’s primate grooming model (always one-to-one and a one-way interaction) is 1.27 and 1.25, respectively, when we take role alternation into account. Chimpanzees can obtain about the same efficiency as humans in terms of quantity of social interactions because their grooming is often mutual and polyadic. The fieldwork was supported by a grant from the International Scientific Research Program (07041138 to T. Nishida) of the Monbusho (Japanese Ministry of Education, Science, Sports, and Culture). Michio Nakamura is a research fellow at Japan Monkey Centre. He received his Master of Science degree from Kyoto University in 1996. He is carrying out research on the grooming behavior of chimpanzees at Mahale, Tanzania, for his doctorate.     

Multidimensional auditory stimulus control in a chimpanzee (Pan troglodytes)

An adolescent female chimpanzee (Pan troglodytes) was trained to discriminate auditory compound stimuli differing in tonal frequency and/or tone on-off rate. Following acquisition training and overtraining, she was shifted to multidimensional stimulus control testing using redundant relevant auditory stimulus sets with discriminability of elements in each dimension varied systematically. Although the control by both dimensions changed significantly as a function of discriminability, the degree of dimensional control was stronger in the tone on-off rate than in the tonal frequency. These results clearly demonstrated “attentional” control of the chimpanzee's auditory discrimination behavior and the interaction between two dimensions of auditory stimuli. The author is now at the Department of Psychology, Primate Research Institute, Kyoto University as a transfer student of the Doctor course.