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Human beings of all cultures build some form of shelter, and the global distribution of Homo sapiens depends on this basic trait. All great apes (chimpanzee, bonobo, gorilla, and orangutan) build analogous structures (called nests or beds) at least once a day throughout their adult lives, which suggests that this elementary technology was present before the hominid lines separated. This thesis investigates the variability and function of specifically wild chimpanzee shelters. I compared characteristics of chimpanzee nests, nesting trees, nest shape, and architecture in two savanna-dwelling populations on opposite sides of Africa: Fongoli, Senegal, and Issa, Tanzania. Savanna habitats are the most extreme habitats in which chimpanzees survive today, and may represent a similar environment to that in which early hominins evolved in the Plio-Pleistocene (Chapter 2). Investigating variation in nest-building within and between these two extreme habitats made it possible to tackle hypotheses of the shelter function of nests (Chapter 3).The influence of environment, specifically the role of protection from disease vectors and fluctuating temperatures, was assessed through a novel experiment in which I slept overnight in arboreal chimpanzee nests and on the bare earth (Chapter 4). To assess whether or not nests serve as an anti-predation function, I compared nesting in Issa, where predators are abundant, to Fongoli, where they are absent (Chapter 5). I provided further support for the thermoregulatory function of nests by showing that chimpanzees build more insulating nests in adverse weather conditions (Chapter 6).Nest-building is a learned behaviour, but its ontogeny is little known. I investigated social sources of variation in nest building in Fongoli to examine whether sex and age differences exist in nest building duration, nest position, shape and architecture (Chapter 7). Finally, ecosystem engineering is a consequence of animal construction, from ants to humans. I investigated use-wear traces around nests to assess niche construction of nest- building. I showed that chimpanzees repeatedly re-used these specific nest-spots within trees, which are pre-fabricated for future building through repeated pruning and shaping of these structures (Chapter 8).Nest building in great apes may be the foundation of constructivity in hominids. This thesis describes proximate functions and influences on nest-building variation in wild chimpanzees that help to model the evolution of shelter in hominids.

This study examined three aspects: estimation of chimpanzee (Pan troglodytes) population size using nest density as a proxy, description of the plant community and assessment of human impacts to chimpanzee habitat in Kwitanga forest, western Tanzania. The overall estimated mean chimpanzee population density was 0.69(0.31–1.54) individuals per km2 and a mean population size of 15(7-34) weaned individual chimpanzees in the forest. The natural vegetation in Kwitanga consists mainly of miombo woodland, dominated by Brachystegia-Julbernadia tree species, poorly developed riverine forest, cultivated land and oil palm plantation. Assessment of the abundance of nesting trees in the landscape revealed that tree species composition along transects were significantly different to nesting sites (trees surrounding the actual tree that contains a nest) (Kolmogorov-Smirnov test: KSa = 2.0148; D = 0.3934: P < 0.05). Thirteen tree species were used for nests; the most used species were B. bussei, B. utilis, B. mirophylla, J. globiflora and P. tinctorius. The assessment on scarcity of nesting tree species in the landscape revealed that such species were abundant by proportion (KSa = 0.5883; D = 0.2308; P > 0.05), and species-specific density (Wilcoxon Z-test: Z = - 1.0265; U1= U2 = 13; p > 0.05). Trees in size classes between 10 cm and 40 cm diameter dominated the forest. The study on size suitability showed that there were significant differences (using ANOVA with Tukey’s HSD post hoc test) in tree diameter size among the three groups: transects, nesting sites, and nesting trees. Nesting trees were unique in size to the other two groups. The mean size of nesting trees was larger compared to both nesting sites and transects (27 ± 1.1 cm; 23 ± 0.7 cm and 18 ± 0.5 cm) respectively. Similar differences existed in tree densities between nesting sites and transects (Wilcoxon test: Z = 1.8104; U1 = 46, U2 = 61: P< 0.05), with nesting sites presenting higher tree density. These results indicated scarcity in trees of a size suitable for nesting, and nesting materials.. Nesting tree species occur in the landscape, though their sizes and higher tree species density at nesting sites determined nesting location choice and specific nesting tree selection. Tree felling indicated by stumps was the major threat to the availability of suitable nesting trees, with a higher encounter rate of seven (7) stumps per km and contributed 48 % of total human disturbance, followed by established fields in the forest. The analysis on the direction of the major threat to the habitat revealed that, the main road cutting through the forest is a key to tree felling. Encountered stumps declined with increased distance from the main road towards the forest edge, with more stumps in between 0 -100 m (P< 0.05; log (Y) = 1.7017 - 0.0007(X); R2 = 0.6705). Such findings implied that the prison inside the forest is a iii major cause of habitat decline. At least 30 tree species constituted the group of stumps. Julbernadia globiflora and Uapaca kirkiana were the most felled tree species. High human disturbances implied by higher human activities encounter rates, and overlapping tree size classes between felled and standing trees were the major threats to chimpanzee habitat in Kwitanga forest. High chimpanzee density and population size estimates in Kwitanga forest renders this area a potential for conservation in the Greater Gombe Ecosystem Program. Kwitanga being the largest remaining natural forest near Gombe National Park, it will increase habitat size to allow chimpanzee dispersal and feeding area. Such movements across heterogeneous landscapes would allow long-term survival through reduced competition, increased genetic diversity and ability to absorb minimal environmental shocks

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付記する学位プログラム名: 霊長類学・ワイルドライフサイエンス・リーディング大学院 / 京都大学 / 新制・課程博士 / 博士(理学) / 甲第24466号 / 理博第4965号 / 新制||理||1709(附属図書館) / 京都大学大学院理学研究科生物科学専攻 / (主査)教授 古市 剛史, 准教授 Huffman Michael Alan, 教授 今井 啓雄 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

An important element in understanding the evolutionary origin of human language is to explore homologous traits in cognition and communication between primates and humans (Burling, 1993, Hewes, 1973). One proposed modality of language evolution is that of gestural communication, defined as communicative movements of hands without using or touching objects (de Waal, 2003). While homologies between primate calls and language have been relatively well explored, we still have a limited understanding of how cognitive abilities may have shaped the characteristics of primate gestures (Corballis, 2003). Chimpanzees (Pan troglodytes) are our closest living relatives and display some complex cognitive skills in various aspects of their gestural behaviour in captivity (de Waal, 2003, Pollick and de Waal, 2007). However, it is not yet currently clear to what extent these abilities seen in captive apes are typical of chimpanzees in general and to what extent cognitive capacities observed in captive chimpanzees have been enhanced by the socio-cultural environment of captivity such as language training. In this Ph.D. research, I investigated the cognitive skills underlying gestural communication in both wild and language trained chimpanzees, with a special focus on the repertoire and the intentionality of production and comprehension. The study of cognitive skills underlying the production of the repertoire and the role of intentionality is important because these skills are cognitively demanding and are a prerequisite in human infants for their ability to acquire language (Baldwin, 1995, Olson, 1993). My research suggests that chimpanzee gestural communication is cognitively complex and may be homologous with the cognitive skills evident in pre-verbal infants on the cusp of language acquisition. Chimpanzees display a multifaceted and complex signal repertoire of manual gestures. These gestures are the prototypes, within which there is variation, and between which the boundaries are not clear-cut, but there is gradation apparent along several morphological components. Both wild and language trained chimpanzees communicate intentionally about their perceived desires and the actions that they want the recipients to undertake. They do not just express their emotions, but they communicate flexibly by adjusting their communicative tactics in response to the comprehension states of the recipient. Whilst chimpanzees communicate their intentions flexibly, the messages conveyed are specific. However, recipients comprehend gestures flexibly in light of the signaller’s overall intentions. Whilst wild and language trained chimpanzee gestural communication revealed similar cognitive characteristics, language trained chimpanzees outperformed wild apes in that they had ability to use signals which made distinctions that human deictic words can make. Whilst these differences between wild and language trained chimpanzees may be due to the different methodological approaches used, it is conceivable that language training may have influenced captive ape cognitive skills in the representational domain. These results from wild and language trained chimpanzees indicate that chimpanzees possess some form of cognitive skills necessary for language development and that cognitive skills underlying repertoire and use in chimpanzees are a shared capacity between humans, other apes and a common ancestor. These findings render theories of the gestural origins of language more plausible. Related publications: 1. Roberts, A. I., Vick, S.-J., Roberts, S. G. B., Buchanan-Smith, H. M. & Zuberbühler, K. 2012. A structure-based repertoire of manual gestures in wild chimpanzees: Statistical analyses of a graded communication system. Evolution and Human Behavior, Published online: http://dx.doi.org/ 10.1016/j.evolhumbehav.2012.05.006 2. Roberts, A. I., Vick, S.-J. & Buchanan-Smith, H. 2012. Usage and comprehension of manual gestures in wild chimpanzees. Animal Behaviour, Published online: http://dx.doi.org/10.1016/j.anbehav.2012.05.022

There has been much discussion regarding whether the capability to perceive speech is uniquely human. The “Speech is Special” (SiS) view proposes that humans possess a specialized cognitive module for speech perception (Mann & Liberman, 1983). In contrast, the “Auditory Hypothesis” (Kuhl, 1988) suggests spoken-language evolution took advantage of existing auditory-system capabilities. In support of the Auditory Hypothesis, there is evidence that Panzee, a language-trained chimpanzee (Pan troglodytes), perceives speech in synthetic “sine-wave” and “noise-vocoded” forms (Heimbauer, Beran, & Owren, 2011). Human comprehension of these altered forms of speech has been cited as evidence for specialized cognitive capabilities (Davis, Johnsrude, Hervais-Adelman, Taylor, & McGettigan, 2005). In light of Panzee’s demonstrated abilities, three experiments extended these investigations of the cognitive processes underlying her speech perception. The first experiment investigated the acoustic cues that Panzee and humans use when identifying sine-wave and noise-vocoded speech. The second experiment examined Panzee’s ability to perceive “time-reversed” speech, in which individual segments of the waveform are reversed in time. Humans are able to perceive such speech if these segments do not much exceed average phoneme length. Finally, the third experiment tested Panzee’s ability to generalize across both familiar and novel talkers, a perceptually challenging task that humans seem to perform effortlessly. Panzee’s performance was similar to that of humans in all experiments. In Experiment 1, results demonstrated that Panzee likely attends to the same “spectro-temporal” cues in sine-wave and noise-vocoded speech that humans are sensitive to. In Experiment 2, Panzee showed a similar intelligibility pattern as a function of reversal-window length as found in human listeners. In Experiment 3, Panzee readily recognized words not only from a variety of familiar adult males and females, but also from unfamiliar adults and children of both sexes. Overall, results suggest that a combination of general auditory processing and sufficient exposure to meaningful spoken language is sufficient to account for speech-perception evidence previously proposed to require specialized, uniquely human mechanisms. These findings in turn suggest that speech-perception capabilities were already present in latent form in the common evolutionary ancestors of modern chimpanzees and humans.

Humans have a tendency to engage in economically irrational behaviors such as gambling, which typically leads to long-term financial losses. While there has been much research on human gambling behavior, relatively little work has been done to explore the evolutionary origins of this behavior. To examine the adaptive pressures that may have led to this seemingly irrational behavior in humans, nonhuman primates were tested to explore their reactions to gambling type scenarios. Several experiments based on traditional human economic experiments were adapted for use with a wider variety of primate species including chimpanzees and capuchin monkeys. This allowed for testing multiple species using similar methodologies in order to make more accurate comparisons of species abilities. This series of tasks helps to elucidate risky decision-making behavior in three primate species.

Primates have traditionally been considered having a poor sense of smell compared to other orders of mammals, like carnivores, due to reduced olfactory structures of the primate brain. This thought, however, is slowly changing. There are now a range of studies showing that primates do use their sense of smell, for example in chemical communication. However, few studies have been carried out on olfactory-related behaviors in Great Apes. The aim of this study was to assess the occurrence of olfactory-related behaviors in captive chimpanzees (Pan troglodytes). The results do not only show that chimpanzees use their sense of smell, but also a behavioral difference between male and female chimpanzees. There was a significant difference between male to female smelling of the anogenitals and male to male smelling of the anogenitals (p = 0.0001) and also a difference between the occurrences of males and females touching an object with the hand and then smelling at the hand (p = 0. 0007). There was a significant difference between male and female frequency of smelling at an object (p = 0.001) and a significant difference between the occurrences of male and female smelling at foods and liquids (p = 0.003). There were no observations of chimpanzees performing a scent-marking behavior. These results suggest that chimpanzees use their sense of smell, from investigating new objects to the inspection of food and other chimpanzees. It would be interesting in future studies to study the difference between male and female frequency of olfactory-related behaviors.

Studies of nesting behaviours of free-ranging apes typically focus on ecological variables such as preferred tree species and areas within the home range, heights of nests, and nest group sizes. However, nesting in captive apes is rarely studied, despite the ubiquity of this sleep-related behaviour. The paucity of field data is often attributed to the inherent difficulty in observing what is essentially a nighttime behaviour. Captive settings can provide researchers with an ideal opportunity to record nesting and sleep-related behaviours, yet such research on captive apes is also scant. Topics addressed include current practices in zoos regarding conditions for sleep in great apes, the potential effects of social and environmental factors on sleep site selection, the motor patterns involved in nest construction, preferred nesting structures and substrates, and nocturnal behaviours. This thesis documented and empirically tested hypotheses concerning nest-related activities in captive chimpanzees, with an aim to generate practical recommendations for enclosure design, sleeping areas, sleeping structures, and nesting substrates that have implications for the welfare of captive apes. As with the few reports that already exist, most chimpanzees in this research frequently constructed night nests. When building a nest, some techniques appeared to be universal across individuals and groups, where others were group-specific or occasionally characteristic of only certain individuals. An experiment showed that specific materials are preferred over others for nest building. Many chimpanzees appeared to express persistent preferences for particular sleeping sites, and for some this was to maintain proximity to kin or other closely bonded individuals. In one group, individual sleeping site preferences changed across seasons, although again this was subject to individual differences. Video analyses of nighttime behaviours demonstrated that, although nests/sleep sites are primarily used for rest subsequent to retirement, a number of social and non-social activities were performed throughout the night. In conjunction with analysis of postural and orientation shifts, these data are unique in describing the nocturnal behaviours of chimpanzees out with a laboratory setting. Several aspects of nest-related behaviours showed a high degree of inter-and intra-group variation. Although this cautions against generalising findings across captive populations, research of this type has applied implications for the management of captive ape species, and can add to our as-yet meagre understanding of their nest and sleep-related behaviours.