[in Japanese]

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Meat-eating and hunting behavior by blue monkeys (Cercopithecus mitis) was observed on several occasions in the Kalinzu Forest, Uganda. The monkeys ate three squirrels and a frog. Multiple members of a group comprising more than 10 individuals engaged in repeated simultaneous hunts on the ground for about 2 weeks following the first meat-eating episode. Blue monkeys in the Kalinzu Forest do not often eat meat; however, such behavior may occur intensively for short periods. It is possible that the initial predation provoked subsequent hunting attempts in the rest of the group. This "hunting craze" ceased after 2 weeks. The predatory tendency appeared to be motivated by some social factor, such as other members' success, because there was no evidence for the influence of an environmental factor.

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[in Japanese]

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[in Japanese]

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I studied huddling groups of Japanese macaques (Macaca fuscata) in the Arashiyama E troop at the “Arashiyama Monkey Park Iwatayama” in Kyoto, central Japan. Japanese macaques made physical contact with other individuals and formed huddling groups when air temperatures were low. The 99-101 adult females and 26-36 adult males in the study troop formed 345 huddling groups during 42 scan samplings in the winter of 2001, and 376 huddling groups during 52 scan samplings in the winter of 2002. The average size of huddling groups was 2.34 (range: 2-7) individuals in 2001, and 2.31 (range: 2-6) individuals in 2002. There was no huddling group of two males. Females more frequently huddled with females than with males. Two maternal kin related females huddled more frequently than unrelated females did. Mother-daughter pairs huddled most frequently. Two individuals usually huddled ventrally-ventrally, ventrally-laterally, and ventrally-dorsally. The distribution of huddling group sizes shows that the approaching individuals did not choose a particular size of huddling. However, the approaching individuals chose locations where they simultaneously contacted with two individuals 1.5 times more frequently than locations where they contacted with only one individual. This choice made the shape of huddling groups triangular and diamond-shaped more frequently than expected. By decision making of each individual, specific patterns emerged in the shape, composition, and position of each individual in huddling groups. As well as huddling behaviors, two and more primate individuals were involved in various social interactions. During the interactions, primates make their decision based on complex cognitive mechanisms and non-linear functions, compete and cooperate with the same opponents in their troop, and predict and manipulate the opponent’s behavior. These traits in social interactions among primates might make their society more complex and interesting.

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Chimpanzees form a multi-male/multi-female unit-group and the members of the group usually split into temporary parties. They sometimes exchange long-distance calls, pant-hoots (PH) between parties and utter PH in chorus within a party. Although most studies on PH have focused on the sociobiological functions for vocalizers or the referential functions, such studies based on individualistic or anthropocentric viewpoint do not tell us how chimpanzees interact with others by using PH. This study aims to analyze how the chimpanzees of Mahale connect their actions through PH and how they organize their social fields beyond visual contact with involvement of others in sight, by applying ethnomethodology and focusing on hearers’ actions. Case analyses based on the result of their usual interval for exchanging PH (10 sec.) revealed that both vocalizers and hearers practiced the same “call-answer” form. Utilizing this form, not only vocalizers could construct an auditory social field between parties but also non-answering hearers could observe the field. Even if PH hearers headed to the place from which they heard the PH, they sometimes restrained themselves from answering to hear whether or not the answer was uttered by other parties, and anew uttered PH to elicit the voluntary answer from the party with whom they tried to interact. Meanwhile, PH hearers sometimes answered immediately regardless of the contexts in which the PH was uttered. Employing these two hands, they would organize their auditory social fields. Once two parties constructed their auditory social field by exchanging PH, one could wait for next call from another or they could get to meet visually with repeating PH exchanges. On the other hand, PH hearers sometimes terminated or deferred those interactions, which hearers’ attitudes were supposed to generate the society in which the members could stay apart from each other even beyond PH distance. In conclusion, these hearers’ various actions show the sociality related to their dynamic fission-fusion society and engaging in non-referential interactions. When we say that chimpanzees’ society is complex, we may be often thinking of the process of interactions resulted from such their unique sociality.

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