Development of the hand and wrist bones in chimpanzees

Skeletal developmental of chimpanzees was studied cross-sectionally. By application of the TW2 method, we described the skeletal development of chimpanzees and compared their skeletal development with humans'. A development pattern of chimpanzees repeated accelerations and decelerations displaying “early-juvenile trough,” “pre-adolescent peak,” “mid-adolescent trough,” and “post-adolescent peak” in incremental curves. Sex differences in skeletal development are slower development in males during infant and early juvenile phases, and greater increment around the adolescent phase in males. Females are fully mature at younger ages than males, e.g. about one and a half years. In comparison with chimpanzees, humans have such characteristics as a longer slower period of juvenile development and a shorter spurt-like adolescent fast period which ends with full maturity.     

The growth pattern of chimpanzees: Somatic growth and reproductive maturation inPan troglodytes

Growth of chimpanzees reared at the Kumamoto Primates Park of Sanwa Kagaku Kenkyusho Co. Ltd. was studied cross-sectionally from the viewpoints of somatic growth and reproductive maturation. Distance and velocity curves were expressed using spline function method. Males showed adolescent growth acceleration in body weight, with a peak at 7.86 yrs of age, but not in trunk length. Females showed continuous rapid growth from mid-juvenile to adolescent phase in both body weight and trunk length, but no isolated adolescent spurt. The Sanwa chimpanzees matured at about 12.5 yrs of age for females and 15.0 yrs for males. The mean adult weights and trunk lengths were 53.2 kg and 507.8 mm for males and 42.7 kg and 481.6 mm for females. The Sanwa chimpanzees had similar growth patterns to those of the Yerkes chimpanzees, although they showed a slight delay in infancy, and a higher growth rate from the early juvenile phase onwards. Growth patterns in these two laboratories may be regarded as “normative” for laboratory-reared chimpanzees. They matured earlier than wild chimpanzees by more than two years. The major reason for the retarded maturation in wild chimpanzees is the delay of growth from infant to the early juvenile phases (0–4 yrs of age), probably owing to a limited nutritional supply from the mother. Development of the testes comprised three phases: slow growth from infant to juvenile (until 6.4 yrs); rapid growth around adolescence (until 9.2 yrs); and adult (mean testicular volume, 187 cm³). Setting the nutritional standard at 2,000–2,600 Cal/day (= Kcal/day) per adult, calories were considered for captive chimpanzees in each age class.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

Piagetian stage 5 in two infant chimpanzees (Pan troglodytes): The development of permanence of objects and the spatialization of causality

We investigated the level of cognitive development of two chimpanzee infants, both tested at 14 and 19 months of age, within the Piagetian framework of cognitive development. We administered tasks related to the understanding of object-concept—visible displacement tasks-and the operation of physical causality—the support problem-and observed responses similar to those of human infants. Both subjects reached stage 5 object-concept when they were 19 months of age: only at this time, in fact, were chimpanzees able to find the object wherever it was hidden. Stage 4 errors still characterized infants' performance when they were 14 months old. However, only one of the 19-month-old subjects was able to solve the support problem: she ignored the support when the goal object did not rest on it, showing that the understood the necessity of spatial contact between the target and the intermediary object. On the contrary, the other subject was not proficient in such a task because he drew the support even when the reward was placed beside it. At 19 months of age its level of causality still remained characteristic of the fourth stage.     

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.     

Body size and proportions in chimpanzees,with special reference toPan troglodytes schweinfurthii from Gombe National Park,Tanzania

Body weight, cranial capacity, linear and joint area data from ten free-ranging adult chimpanzees from Gombe National Park, Tanzania with known life histories allow study of variation in a local population and comparison to other populations ofPan troglodytes and toPan paniscus. Because individuals in the Gombe population are small compared to other common chimpanzees, they provide a useful comparison toPan paniscus. Body weight and some linear dimensions overlap withPan paniscus. However, cranial capacity, tooth size, and body proportions of Gombe individuals lie within the range of otherPan troglodytes and are distinct fromPan paniscus.     

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.     

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.     

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.     

Hand preferences in chimpanzees (Pan troglodytes), bonobos (Pan paniscus), and orangutans (Pongo pygmaeus) in food-reaching and other daily activities

We observed 36 captive great apes [31 chimpanzees (Pan troglodytes),2 bonobos (Pan paniscus), and3 orangutans (Pongo pygmaeus)]reaching for items of food and engaging in other spontaneous behaviors. We consider circumstantial factors that could influence the preferred choice of one hand or the other. Most of the subjects (81%) showed a significant hand preference in food reaching that is consistent in directionality with the hand preferences that they showed during other spontaneous behaviors. The results show that the postural adjustment required when carrying out an action seems to influence directly the expression of manual laterality in individuals. Moreover, the results indicate the possible existence of a relationship between maturational factors and persistence in directionality of hand preferences.     

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.     

Success and Understanding in Cognitive Tasks: A Comparison Between Cebus apella and Pan troglodytes

The recent boom in cognitive studies on chimpanzees and capuchins allows an analysis of the cognitive processes and behavioral tendencies underlying their performances when faced with a variety of problems. In the laboratory, but less so in nature, Cebus and Pan show remarkable convergence in their overall success in solving problems involving the use of tools and cooperation. Behavioral ingredients such as explorative tendencies, manipulative skills, social tolerance, and cognitive capacities contribute to their success. However, in experiments in which carefully controlled conditions were implemented, e.g., cooperation and tool-using tasks, differences between the two taxa emerged in the role played by such ingredients in fostering success. Although it is difficult to establish the nature of these differences, a profitable way to look at them is from outside: from the point of view of what children do when tested in similar tasks. If we consider the ways in which children experience or achieve initial success and then become fully proficient in solving similar tasks, we can appreciate the different recipes for success that Pan and Cebus present.     

Food Supply and Chimpanzee (Pan troglodytes schweinfurthii) Party Size in the Budongo Forest Reserve,Uganda

A central issue in socioecology is the nature of the relationship between an organism's environment and its social structure. In chimpanzees, the fission-fusion social system is thought to minimize feeding competition for primary dietary components: ephemeral, dispersed patches of ripe fruit. Intragroup feeding competition is thought to force individuals into small parties. Informal observations in the Sonso region of the Budongo forest had suggested that in this habitat, food supply was such that feeding competition was less important in determining grouping patterns than elsewhere. We used data collected on food supply and party sizes over a 4-year period to investigate this suggestion. In accord with theoretical expectation, sizes of foraging parties fluctuated with the size of food patches. However, party sizes showed either negative or no relationship with habitat-wide measures of food abundance. Likewise party sizes showed little relationship to overall measures of food dispersion. For important dietary items, both fruit and leaves had patchy distributions, though the degree of clumping was not strong, and fruit was not more clumped than leaves. Generally, abundant food appeared to be less patchy, and chimpanzees appeared to use more patches as food became more abundant rather than forming larger parties. We suggest that both dispersal and abundance need to be considered when investigating the impact of food supply on grouping patterns, and that the importance of food as a factor in determining chimpanzee grouping patterns declines with increasing levels of abundance.