An adult female chimpanzee, named Ai, who had experience in a cardinal-labeling task with Arabic numerals, was trained on a sequential-responding task with these numerals. Initially, she was given a free sequential-responding test (test for ordinality of numerals), which showed no transfer of performance from the cardinal training; she responded almost randomly. Then, Ai was shifted to differential-reinforcement training of 2-item sequences. After learning the 36 possible 2-item sequences, Ai successfully transferred her performance to 3-, 4-, and 5-item sequences. Reaction-time analyses further revealed a serial position effect and a symbolic distance effect during her sequential-responding performance; these effects are commonly observed in comparative judgement by humans.

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In three experiments, five chimpanzees were given an object-sorting task to assess their categorizing ability. In preliminary training, chimpanzees were presented a set of two identical objects (AA) and one odd object (B). They were trained to sort the objects in two categories, AA and B; four kinds of objects were used in this training. All the chimpanzees were able to learn this type of sorting easily. In Exp. 1, 2, and 3, test stimulus sets were inserted in random positions among the sets of training. In test trials, the test sets differed for each trial, and the chimpanzees always received food regardless of how they sorted. In Exp. 1, test sets were novel objects for the subjects. In Exp. 2, the objects in each test set were identical either in color or in shape, and could be sorted on the basis of the other dimension. In Exp. 3, the objects in each test set were different one another, and could be sorted on the basis of either color or shape. In test trials of the experiments, chimpanzees sorted categorically and their performance were highly significant. The implications of these results and the utility of the object-sorting task are discussed.

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Effects of the arrival of a younger sibling on the first-born was examined to investigate the attachment of a captive infant chimpanzee (Pan troglodytes). The subject was a first-born female infant chimpanzee that had been reared artificially from two months. Each response of the subject was observed and video-recorded in conditions where the mother cared for the sibling, the mother cared for a pig toy, or a stranger cared for the sibling. The results showed that the subject was especially likely to protest the mother-sibling interaction. It seems that the subject was to recover mother's attention by taking part in the mother-sibling interaction. These results clearly showed that the attachment of an infant chimpanzee was similar to that of human infants.

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During the study period of the bonobo at Wamba, Zaire, 1991, two femal bonobos, which I called Judy (3 years old) and Kema (2 years old), were brought to the base camp. Their mothers had been killed by poachers. They had already been taken care of more than eight months at a Protestant mission. I began to try to rehabilitate them, with the aim of returning them to the wild. I took them to the forest every day and gradually introduced them to the members of our study groups, E1 and P. Two months after, I made contact with the P group and we left Kema alone to feed in the center of the group. I left the area because Kema would have returned to me if I had stayed in sight. I went back and looked for her after a while, but neither Kema nor any members of the P group could be found. When I went to the nesting site of the P group early the next morning, Kema was observed in an adolescent male's bed. He kept hold of Kema and she clung to his abdomen. Thus, Kema became a member of the P group. On the other hand, though we continued the rehabilitation to Judy, she could not be returned to the forest because of her extreme dependence on people.

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Social relations of 2 male (6 and 9 years old) and one female (9 years old) chimpanzee orphans were compared with those of non-orphans of similar age and sex. Each orphan lost its mother at the age of 5, 7, and 7 respectively. Two orphans, a 5-year-old male, and a 9-year-old female, spent more time alone, and were groomed less, than their non-orphan counterparts. The 9-year-old male orphan, however, did not differ from his counterparts in terms of both time spent alone and frequency of being groomed. The age-sex class of the orphans' closest associates depended on their age-sex class and on the availability of siblings. All the orphans “met” with a larger number of group members than their respective counterparts. Although the sample size is small, the loss of mothers appeared to facilitate, rather than retard, the sociability of young orphan chimpanzees in this study. A special case of the behavior of a 4-year-old female infant, who lost her mother at the early age of 3 was also described.

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An ecological survey on chimpanzees was carried out in the Kalinzu Forest, Republic of Uganda, between October 1992 and March 1993. The research consisted of direct observation of chimpanzees and a population census based on nest counts from line transects. The population census provided the estimate density of 2.5 chimpanzees/km². The Kalinzu Forest consists of two types of vegetation: Parinari dominant primary forest and Musanga dominant secondary forest. The estimate density of chimpanzees was higher in Musanga dominant forest than in Parinari dominant forest. The presence of two types of vegetation in the habitat was thought to allow the high density of chimpanzees in the Kalinzu Forest.

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Preliminary results of an extensive survey on the diurnal primate fauna in south-western Congo are reported. The survey was carried out in Region de Niari and Lékoumou from November, 1992 to December, 1992. I confirmed the presence of Pan troglodytes troglodytes and Cercopithecus pogonias by direct observations and the presence of Gorilla gorilla gorilla, Mandrillus sphinx, Cercopithecus cephus and C. nictitans by indirect evidences. Local people informed the presence of Colobus satanus, Cercocebus torquatus, C. albigena and Miopithecus talapoin, but I could not confirm them myself. Population densities of Pan t. troglodytes in the area were caluculated from nest counts. The population densities were higher in the areas near the border of Gabon and in the eastern part of Region de Lékoumou than the other areas. The differences in the population densities in each area seemed to be related with differences in hunting pressure. Average population density in the study areas was far lower than that in Ndoki Forest in the northern part of Congo, but allmost equal to throughout Gabon or in the part of Equatorial Guinea.

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Recent development in biotechnology [DNA-related techniques] enables us to applyin wide range of biology; systematics, evolution, intraspecific variation and individual identification. Non-invasivecollection of biological samples is now available in combination with in vitroamplification of DNA segments by PCR. Applicability of DNA-related techniqueswas summarized and the methods obtaining DNA from biological materials were reviewed. In particular, the potential use of polymorphic microsatellite DNA (GT dinucleotide repeat) amplified by PCR was emphasezed with some examples of successful application in captivity and in the wild.

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Analysis of DNA polymorphisms was viewed as a new means of individual discrimination in studies of wild chimpanzees. DNA typing methodology was summarized for field primatologists, who often lack required knowledge of molecular biology, and expected impact of DNA typing on studies of wild chimpanzees was discussed. In particular, behavioral and social aspects were dealt with. A guide to noninvasive collection of samples in the field was appended.

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Chimpanzees have been widely used in the field of experimental medicine because of their phylogenic affinity to human beings. Natural populations of the ape continue to decrease and an inconsistency between “Protection” and “Use” is coming to the front. For instance, about 150 chimpanzees have been used for research on hepatitis B in Japan recently, and most of these were obtained in the wild. The breeding of chimpanzees in captivity is going well around the world, and some facilities are beginning the control of chimpanzee breeding now. It is necessary to establish a responsible raising system for chimpanzees throughout their entire life span, considering both the characteristics of this species as an experimental animal, and the rise in social consciousness concerning animal welfare.

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Studies of primate locomotions have clarified the characteristics of human orthograde bipedal walking and have presented models of pre-habitual bipedal locomotion. Among nonhuman primates, chimpanzees have many characteristics of bipedal walking similar to those of humans. In order to investigate these similarities, development of chimpanzee bipedal locomotion was kinesiologically studied. The data were obtained semi-longitudinally from six chimpanzees of the age of two months through nineteen years. Voluntary bipedal walking of the infant chimpanzee until one year of age showed some patterns different from those of human walking. From two years of age, chimpanzees started to adopt a type of walking which economizes energy expenditure as in humans. From four years of age, their walking presented many similarities to those of humans, though there were many varieties of patterns in the chimpanzee bipedal locomotion among individuals and from step to step in an individual. The living chimpanzee after four years of age is useful for making models of the evolution of human bipedalism.

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Important themes of future experimental studies of chimpanzee behavior are discussed from the standpoint of comparative cognition. Intelligence of chimpanzees is clearly the most important aspect in understanding this species. In particular, the interactions of separate cognitive aspects such as language, memory, and reasoning ought to be analyzed. The study of fundamental perception is also important because it constrains intelligence. Expression and perception of emotion have not been investigated systematicaly so far and studies of these aspects are needed. Description and communication of emotion are important, as they are related to recognition of mental states of others. Individuality is one of the characteristics of primates and should be approached not only from field observation but also experimentally. Development and aging are important aspects to study as well. In particular, aging related to social environment should be analyzed. All of these aspects ought to be compared not only with humans but also with phyletically lower species, because otherwise the uniqueness of chimpanzees is never uncovered. Finally, caution on thoughtless use of anthropomorphism in understanding this species is raised.

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Experiments on the auditory and vocal functions of the chimpanzee were reported. The first main focus was on the basic auditory functions such as auditory sensitivity and difference thresholds, on the auditory cognition such as auditory-visual intermodal integration, and on the speech perception such as the prototype and context effects. A chimpanzee showed difficulties in the auditory-visual inter-modal integration. The second focus was on the close auditory-vocal interrelationship. It was reported that the chimpanzee had a W-shaped auditory sensitivity. The perception experiments showed that the second formant was not important for the perception of human vowels and vowel-like vocal sounds of the chimpanzee. The acoustic analyses showed that the second formant was constant between these vowel-like vocal sounds. These results indicated that the auditory and vocal functions were closely inter-related each other. The third focus was on the early vocal development of an infant chimpanzee. A comparison in vocal development between chimpanzee and human infant suggested that the chimpanzee infant did not reach to the Oller's Expansion Stage of the human vocal development. The high larynx and the small pharinx were suggested to be partially responsible for the limitation of the vocal development and the repertoire of vowel-like vocal sounds in the chimpanzee.

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It has been proposed that chimpanzees use a number of toxic plant species for their medicinal value. Based on behavior, plant pharmacology, and ethnomedical information, hypotheses concerning the medicinal use of some of these plants by chimpanzees include the following: control of parasites, treatment of gastrointestinal disorders, regulation of fertility, and possible anti-bacterial or anti-hepatotoxic activity. With regards to bitter pith chewing and whole leaf swallowing behaviors, 20 medicinal plant species have been observed to be used not only by chimpanzees, but also by bonobos and lowland gorillas at 7 sites (Mahale, Gombe, Kibale, Kahuzi-Biega, Wamba, Tai, Bossou) across Africa. A detailed description is given of the research program currently being carried out by the author and colleagues of the international research team, The C. H. I. M. P. P. Group, and in particular, of the ongoing multi-disciplinary research into the chimpanzee use of Vernonia amygdalina (Del.) in the Mahale Mountains National Park Tanzania. The hypothesis that this species has medicinal value for chimpanzees comes from detailed observations by the author of ailing individuals' use of the plant. Quantitative analysis and assays of the biological activity of V. amygdalina have revealed the presence of two major classes of bioactive compounds. The most abundant of these constituents, the sesquiterpene lactone vernodalin, and the steroid glucoside vernoioside B1 (and its aglycones) have been demonstrated to possess antibiotic, anti-tumor, anti-amoebic, anti-malarial, anti-leishmanial, and anti-schistosomal properties. At Mahale, the particular parts of an additional 12 plant species ingested by chimpanzees are recognized for their traditional use against parasite or gastrointestinal related diseases in humans. Their physiological activities are now being investigated in the laboratory.

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The behavior of chimpanzees of Bossou has been studied since 1975. The core-area of the Bossou chimpanzees was then separated about 6km from that of adjacent chimpanzee groups by savanna, though lone chimpanzees may sometimes have passed through. From the middle 1980s expansion of cultivated fields began to destroy the forests of the chimpanzees and the adjacent chimpanzees gradually disappeared. The rebellion in Liberia, which occurred by the end of 1989, produced many refugees, who came to Bossou and other villages near the frontier. The number of Bossou chimpanzees has decreased since 1990. The Government of Guinea decided to estab-lish a forest reserve enclosing the core-area of Bossou chimpanzees. The Japanese Government also decided to help establishment of the Bossou Institute of Environmental Research to promote research and conservation efforts.

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The distribution of gorillas and chimpanzees overlaps extensively in eastern Zaire. A similar density is estimated for the 2 kinds of ape in lowland tropical forests, while the density is higher for gorillas than for chimpanzees in montane forests. These differences are reflected in their food selection and range utilization in both habitats. Like chimpanzees, gorillas tend to eat many kinds of fruit and to consume insects regularly in lowland forests. Gorillas and chimpanzees tend to select different food items and to range in different vegetation types in montane forests. The low availability of fruits in montane forests may be responsible for the low density of chimpanzees. When availability of fruits declines, the 2 kinds of ape adopt different strategies. Gorillas exhibit folivorous characteristics and decrease day journey length. Chimpanzees are always extensive frugivores and may possibly increase their ranging area. These findings of their ecological characteristics must be considered in conservation planning. Kahuzi-Biega National Park (6, 000km²) includes both montane and lowland forests and provides a variety of habitats for gorillas and chimpanzees. The recent census conducted in montane forests indicates a slight increase of gorilla population in this decade. However, gorillas and chimpanzees tend to concentrate their ranging in the small areas which are well protected by the Park. The increasing human population around the Park has gradually destroyed the ape's habitats everywhere. Recent developments in tourism and organization of NGO contribute financial supports for the country and knowledge to the local people to realize the value of their natural resources. More international attention is needed to increase conservation activities and to protect fauna and flora from the hazards of human disturbances in this area.

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Recent advances in conservation biology are discussed for the future of the wild African apes. Forest destruction in the continent and fragmentation of the ape populations give rise to the serious possibility of continuous local extinction of apes. The spatial design of protected areas (single large or several small), the effective population size, the MVP, the Allee's effect, and synecological factors are considered. The participants who are concerned about conservation of the apes can contribute to their survival with these scientific understandings. Some personal opinions are proposed for the survival of apes.

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