More than 30 years have passed since chimpanzee research camp was set up at the Mahale Mountains in Tanzania. Besides the continuous long-term research on chimpanzees, various research and descriptions on climate, plants, vegetation and animals have been made. In this paper, we made general descriptions about not only chimpanzees but also about other various aspects of Mahale which were obtained during the long term research and also some information for people who plan to visit Mahale. For details of chimpanzee research in Mahale, please refer to literature list in our web page (http://gorilla.zool.kyoto-u.ac.jp/ChimpHome/reference.html).

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This review summarizes the findings from 40 years of research on a chimpanzee group at Bossou, Guinea, conducted mainly by two research teams, one from the University of Amsterdam, Netherlands, and the other from Kyoto University, Japan, and reports the current conservation status of the chimpanzee group.
Research in the 1960's by the Dutch team consisted of short-term, ‘testing-a-hypothesis’ type projects, which focused on the chimpanzees' agonistic behavior towards predators. They used a unique field-experiment method, with an artificial leopard, to see how the chimpanzees responded to the stimulus. The experiments revealed a variety of agonistic reactions by chimpanzees, including tool-using behavior such as throwing a branch and using a stick as a club.
In 1976, the Japanese team launched a long-term project, based on recognizing each chimpanzee individually. Although diverse topics have been covered to date, a focus has been tool use. Starting with the first substantial direct observation of nut cracking by wild chimpanzees, many other types of tool use have since been described, including ant dipping, pestle pounding, and algae scooping. A series of field experiments followed that revealed many details about nut cracking by chimpanzees: hand preference, metatool, developmental process, etc. Feeding ecology is a more recent topic, and the utilization of oil palm as a ‘keystone resource' when fruit is scarce, using two types of tool, proved to have significant ecological importance. Unique social characteristics like male immigration, close between-female relationships, and females’ high reproductive performances have been brought to light and require more ecological and genetic study to understand their uniqueness comprehensively.
As for the conservation status of Bossou chimpanzees, the population size has fluctuated, but has been essentially stable during the study period. The reproductive parameters appear good, but juveniles of both sexes tend to disappear for unknown reasons. The people of Bossou have a strong religious motivation for conserving small patches of forest and the chimpanzees living there, and there is good collaboration among the Bossou people, government institutions and researchers when dealing with conservation problems. Current concerns seem to be the genetic isolation from a neighboring chimpanzee population on Mt. Nimba, and crop damage caused by the chimpanzees.

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Studies of bonobos at Wamba started in 1973 when Takayoshi Kano found the village as a promising field site during his extensive survey in Congo Basin. One of the study groups was artificially provisioned with sugarcane in 1976. Luo Scientific Reserve was established in 1987 under the cooperation between CRSN and Kyoto University for the conservation of bonobos and other primates. Demographic data has been accumulated from two study groups for 20 years. Compared to chimpanzees, these populations showed lower infant mortality and shorter interbirth intervals. Luo Reserve, covering 481km² and containing 200 bonobos, consists of two areas that are divided by the Luo River. The north area contains home ranges of the study groups, and larger human populations inhabit it. The population density of bonobos is higher in the north area, owing probably to the mixture of various vegetation types, including dry primary forest, secondary forest, and swamp forest. Intensive studies on behaviors and social structures can be carried out both at provisioning sites and in the natural forest. The south area is much greater and less disturbed by humans. It is a suitable site for ecological surveys in a larger scale.

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Six primate species including chimpanzees (Pan troglodytes schweinfurthii) inhabit the Kalinzu Forest Reserve located in southwestern Uganda. Following an extensive survey of Uganda by Kano in 1992, Hashimoto carried out a population estimate for chimpanzees in the Kalinzu Forest in 1992-1993, and found that the density of chimpanzees was considerably high. Since 1997, we have conducted several studies to reveal relationships between habitat use by primates and forest types; including population census of chimpanzees by nest counts, biomass census for diurnal mammals, vegetation census, census for assessment of fruit abundance, and direct observations of chimpanzees and monkeys. We distinguished 4 forest types in the study area: mixed mature forest, Parinari dominant mature forest, Parinari dominant secondary forest, and Musanga dominant secondary forest. We found high population densities of primates including chimpanzees in Musanga dominant secondary forest where fruit of Musanga leo-errerae is available throughout the year. There was also a high density of chimpanzees in mixed mature forest, probably sustained by diverse fruits available for different season. A mixture of various vegetation types including both primary and secondary vegetations may support high density of primates in the Kalinzu Forest. However, too much human activities such as intensive logging and hunting may cause an unrecoverable damage for primates and other animals. Further studies will help to find out a manner of sustainable land management to maintain fauna and flora in the Kalinzu Forest.

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Ecological study of wild chimpanzees (Pan troglodytes schweinfurthii) has been conducted in Ugalla area, western Tanzania. Ugalla is one of the driest habitats of chimpanzees. Also, Ugalla River is the eastern boundary of chimpanzee distribution. This area covers 2, 800km² with elevation from 1, 100m to 1, 600m. The majority of Ugalla area is deciduous woodland dominated by Brachystegia sp. and Julbernardia sp. (‘Miombo’ in local name). Woodland dominated by B. bussei is formed in mountainous areas. Two types of evergreen forests were also formed in mountainous areas. One is a small patchy forest dominated by Monopetalanthus richadsiae (Kabamba-jike) on a hill or beside a cliff, and the other is a kind of riverine forest dominated by Julbernardia unijugata (Kabamba-dume) along a steep valley. During the dry season, chimpanzees frequently used these forests as sleeping sites, and B. bussei woodland as feeding sites. Nest census showed that the population density of chimpanzees in Ugalla was 0.05 individual/km², although the density of mountainous areas was higher than that of flat areas. Four or five communities (unit groups) each of which has approximately 30 individuals may inhabit the Ugalla. The both estimations indicate that the total number of 120-150 chimpanzees inhabit this area. If several communities divide the whole Ugalla area, each community should have a huge home range. For a certain period, however, chimpanzees might be ranging in a small part of their annual home range, and seasonally shift such areas. In the daytime, chimpanzees formed a small feeding party to exploit poor and sparse food resources. On the other hand, they formed a larger sleeping party at night, because of high predation pressure of large carnivores. Understanding such chimpanzee adaptation to dry and open habitat in the savanna woodland can shed light onto behavioral ecology of early hominid. Besides seven species of primates including chimpanzees inhabit the Ugalla area. Other large and middle-sized mammals and rodents in Ugalla are also listed in tables of this report.

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Extensive surveys of wild chimpanzees (Pan troglodytes) were conducted in the southwestern Rukwa Region, Tanzania. The chimpanzees in Loasi River Forest Reserve and Lwafi Game Reserve are currently the southernmost population among all known wild chimpanzees. Nests of chimpanzees and information obtained from local people show that these chimpanzees inhabit an area of, at least, about 70km belt in length with 25km width along the eastern shore of Lake Tanganyika and Lukalo Escarpment between the Tembwa River Basin and the Kafukoka River Basin (1, 250km²). Further surveys are needed for understanding historical change of chimpanzee distribution and adaptation of chimpanzees to arid surroundings of savanna woodland. In addition, proper conservational planning is indispensable to protecting chimpanzees and other wild animals in this area.

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We conducted nest-census surveys of wild chimpanzees in the Lilanshimba and its surrounding hills on the north (right) bank of the Malagarasi river, Tanzania, in three different periods between February, 1995 and March, 1996 and obtained the following results.
1. The chimpanzees have an isolated distribution area of about 316km² between S 05: 05-S 05: 14, and E 29:58-E 30:20, separated from the southern population by the Malagarasi, and from the northeastern population of the Gombe National Park with a gap of 80km. This gap is intersected by a road and a railway that is densely populated by humans.
2. Population density of chimpanzees was estimated at 0.101-0.142hd/km² for the whole area. However, nests were densely found only in the central section of 175km² where the density was estimated at 0.151-0.227hd/km². Nest distribution suggested only the central section had permanent resident chimpanzees. The total population of chimpanzees over 3-4 years of age was estimated to be only between 32 and 45.
3. Their range has been shrunken with increasing habitat-destruction by woodcutters and immigrant farmers. The current most serious menace to their survival is the mass influx of refugees from Democratic Republic of Congo. The settlement established for them in the eastern section of the chimpanzee range has always contained twenty to forty thousand refugees since 1997. Their cultivation and hunting (differently from Tanzanians, they have no food taboo against meat of chimpanzees) may be destructive to chimpanzees of Lilanshimba.

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The impact of chimpanzee hunting on populations of several mammalian species was examined by analyzing the data of population census on these mammals and the previous reports of chimpanzee hunting at the Mahale Mountains National Park, Tanzania. The annual kill rates (1.3-9.0%) of red colobus monkeys by the chimpanzees were estimated to be almost the same as the population growth rate of this species. These kill rates were equal or slightly higher than those reported from the Tai National Park, Ivory Coast, but extremely lower than those reported from the Gombe National Park, Tanzania. The impact of chimpanzee hunting on other prey mammals (redtailed monkey, blue monkey, blue duiker, bushbuck and warthog) seems to be small, because the annual kill rates of these species by the chimpanzees were estimated to be smaller than their population growth rates or the hunting frequencies on them by the chimpanzees were very low.

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Activity budgets of wild female chimpanzees (Pan troglodytes schweinfurthii) in three reproductive states (estrous, anestrous, lactating) were compared with each other. Three lactating females, five anestrous females and seven estrous females in Mahale Mountains National Park, Tanzania were the subject of focal sampling and time spent for feeding, resting and moving was examined. For each of three categories of activity, there was no significant difference of time spent between each reproductive state. Those females spent about 40% of their daytime for feeding, about 30% for resting and about 40% for moving. One of the reasons of indifference might be the type of parties which females attended when they were observed. In most cases the females were seen in bisexual parties. Lactating females are expected to need more nutrition than cycling females and it might affect their activity budget. But the party type they attended might also affect the budget.

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Fecal samples of chimpanzees were analyzed to reveal the feeding ecology of chimpanzees in the Kalinzu Forest. Proportion by volume of fruit seeds was 83% and all samples contained such seeds. Thus chimpanzees of the Kalinzu Forest were found to be highly frugivorous as reported for chimpanzees elsewhere in Africa. Ant fragments were found in feces almost every month, and from 9% of total fecal samples analyzed. Evidence of meat eating was found. Bones and fur appeared in 2% of the samples. The location and vegetation type where fecal samples were collected was recorded. This was done to help access habitat utilization patterns among the four vegetation zones (Musanga dominant secondary, Parinari dominant secondary, Parinari dominant mature, mixed mature). Fig seeds were found in 57% of the samples, indicating that fig fruits are an important resource for these chimpanzees. Samples containing fig seeds were found in all vegetation types suggesting that figs are widely dispersed throughout their habitat. It is expected that Musanga leo-errerae plays an important role in maintaining a high density of chimpanzees in the Kalinzu Forest. Chimpanzees fed on large amounts of a fewer number of fruit species in the secondary forest and fed on smaller amounts of more fruit species in the primary forest. In the primary forest, it is likely that utilization of these many fruit species is dependent on their availability. Fecal analysis can provide quantitative data on the feeding ecology of chimpanzees at the early stages of a study when direct observations are difficult. We found a tendency for the seeds of fruit species found in the feces to match the vegetation types where they were deposited by chimpanzees, suggesting that perhaps over the short term Kalinzu chimpanzees utilized the same vegetation types over consecutive days. Analysis of feces content and vegetation type where they are found is a promising methodology to collect preliminary data about habitat use by chimpanzees.

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I have observed many chimpanzees with injuries on their hands or feet in the Kalinzu Forest, Uganda. Of 16 male chimpanzees identified, 2 had a snare wire embedded in their hand. Another 7 male chimpanzees also had injuries on their limbs, which were likely caused by snares including a loss of an entire hand/foot, a clawed hand or wrist, and a loss of some digits. Such injuries caused by encounters with snares have frequently been reported from other chimpanzee study sites in Uganda: such as the Kibale Forest and the Budongo Forest. Although it is uncertain whether such injuries influence survival or reproduction of chimpanzees, it is important to continue investigation on the actual conditions of chimpanzee injuries and the human hunting practices in their habitats.

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Sand manipulations in four captive female chimpanzees (Pan troglodytes) were experimentally analysed. Every experimental session was done at the individual situation. Each individual was observed in the experimental booth under four 30min. conditions; with an experimenter and no object, with an experimenter and 16 objects, with an experimenter and 7 objects, and with no experimenter and 7 objects. In every conditions, 10kg. sand was mounted at the centre of floor in the booth. Comparing the amount of time of sand manipulations under each conditions, the conditions with an experimenter and objects facilitated chimpanzees to manipulate sand, although the small number of objects was more efficient. For the ultimate purpose of abstracting the intelligence of chimpanzee, we made the ethogram of sand manipulation. Each bout of sand manipulation observed was categorized into four contexts; relating with their own body and object, relating with only their own body, relating with only object, and specific manipulation. The cases of sand manipulation initiated with “scoop”, “drop”, “grasp”, “scrape”, and “touch” were the most popular for all contexts. Chimpanzees could spontaneously construct the triad relationship of sand (with objects), experimenter, and themselves. Apparent “pretend play” could not be observed in the present study, but some of nearly “pretend play” were observed. These observational evidences allowed us to speculate that chimpanzees can symbolically manipulate sand.

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One female chimpanzee was tested on perception of orientation of faces using a visual search task. In Experiment 1, the subject showed better performance in the tasks in which the upright human faces were presented as a target or distractors than the task in which only the horizontal and inverted faces were presented. Furthermore, the subject responded faster when the upright face was the target than when the upright faces were distractors. This asymmetry was not evident when the horizontal and inverted faces were combined. Superiority in detecting the upright stimulus was also observed when the upright and horizontal chimpanzee faces were combined, but not when the stimuli were photographs of houses (Experiment 2). When each stimulus was different in identity from each other but the target could be identified on the basis of its orientation, the performance was not so severely impaired when the subject searched the upright faces of humans and chimpanzees. The subject showed difficulty in detecting the house target in this condition. It was suggested that the subject searched the upright faces after she had identified the stimuli as “faces”.

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This article discussed “Theory of Mind”, especially those aspects that concern an deception, understanding of the seeing-knowing relationship, joint visual attention, and pointing in primates, with reference to several experimental studies. These investigations suggest that chimpanzees are capable of understanding other conspecifics' knowledge, but not that of human, while monkeys have an ability for joint visual attention with conspecifics, but less evidence with humans, except one paper. However, we need to develop more sophisticated test and collect data from many species of primates to identify what species possess which aspects of mental state attribution and at what point during development.

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The Kumamoto Primates Park, Sanwa Kagaku Kenkyusho CO., Ltd. had successfully bred chimpanzee from 1982 to 1999. The breeding statistics of 100 pregnancies, observed for the 17 years, were reviewed. The breeding females were 24 wild born and 3 captive born. Neonatal diagnoses were performed on the next day of the birth. Of 100 pregnancies, diagnosed by urinary CG test and/or ultrasonography, 11 resulted in abortions, 5 in stillbirths, and 85 in live births (containing a monozygotic twins). The mean birth weight and gestational period of 84 live born infants was 1793g (n=74, 930-2400) and 229.4 days (n=84, 181-250). Seven of 11 abortions occurred in early stage of pregnancies (45-65 days). Infant mortality in the first year of life was 10.7%: 6 died from 7 to 16 days of age, 3 died after 50 days of age. Three of dead 6 neonates were low birth weight (under 1500g). There was no infant died under 7 days of age or over 1 year of age. Perinatal mortality was calculated at 0.12. 73.2% of deliveries occurred in the nighttime (n=82). Placentaphagia were observed in 65.7% cases of 73 parturitions. The seasonal difference was significant on frequency of conceptions (χ²=10.16, p<0.02), but not significant on frequency of births (χ²=7.62, p>0.05). Twenty-nine infants were nursery-reared primarily due to inadequate maternal care (48%) or low birthweight (28%). Only one infant died under nursery-reared condition. These data provide useful information to sustain captive chimpanzee populations.

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The present study attempted to detect ovulation to facilitate ovulation detection for artificial insemination in a chimpanzee using hemagglutination inhibition test for urinary luteinizing hormone/chronic gonadtropin (LH/CG test) and hemagglutination test for urinary estrogen (E test). We detected an estrogen peak during the follicular phase and an LH surge by this method. These tests allowed for an estimation of ovulation time and were more reliable than the method of evaluating by the sex skin swelling pattern. After the artificial insemination, we carried out pregnancy diagnosis by LH/CG test and E test. LH/CG and E levels increased 13 days and 7 days after the LH surge, respectively. We confirmed that the combination of both tests could be useful for indirect diagnosis of pregnancy as early as the second week after the LH surge. We used ultrasonography for definitive diagnosis of pregnancy. The fetal biparietal diameter was 27mm at 86 days gestation (from the LH surge). We measured the heart rate of mother and fetus from 99 days gestation to delivery without anesthesia. The present study suggests that ultrasonography is a safe and noninvasive technique for real-time monitoring of pregnancy.

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This report describes new medical apparatuses as they have been applied to morphological studies on primates, especially on the four species of extant great apes (Pan troglodytes, Pan paniscus, Gorilla gorilla, Pongo pygmaeus). We report here on the results of studies using the following apparatuses; pQCT (peripheral Quantitative Computed Tomography), MRI (Magnetic Resonance Imaging), and DEXA (Dual Energy X-ray Absorptometry). The high-resolution tomograms offered by pQCT and MRI are fine enough to study, without invasion or destruction, the detailed morphology (including internal structure, density, and other physical parameters) of living animals, precious specimens, and fossils. The use of serial tomograms, AVS (Application Visualization System), offers three-dimensional images, while pQCT and DEXA offer various parameters vital to studies of biomechanics, nutrition, and ecology; for example, bone mineral density either in the cortical or trabecular parts of bone or the percentage of fat. These new methods will certainly contribute much to morphological, ecological, and physiological studies on primates.

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Tall climbing frames were introduced into an outdoor compound for captive chimpanzees as a way of environmental enrichment. Behavioral changes were assessed in terms of the utilization of three dimensional space. Prior to the present study, a group of eleven chimpanzees had been kept in an approximately 700m² semi-natural compound enriched with an 8m tall climbing structure, planted trees, and a stream. Chimpanzees in the wild spend more than half of the day in trees, preferring to stay high above the ground. In July 1998, we introduced a new enrichment device into the compound: tall climbing frames 15m in height. The climbing frames consisted of three high towers equipped with platforms and ropes to climb up and down and to traverse between the towers, as well as being connected to the existing set of frames. We videorecorded the chimpanzees' behavior in the new environment during the daytime from 9:30am to 4:30pm continuously. Chimpanzees spent 81% of the observation time on the climbing structure, during 39% of which they occupied locations more than 8m above ground, in the space newly made available. All chimpanzees used the climbing structure throughout the day with little individual difference. The change in activity budget clearly showed that the 15m high climbing frames proved instrumental in facilitating three dimensional space utilization promoting the psychological well-being of captive chimpanzees.

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