Kosei Izawa

Palm-fruit cracking behavior of wild black-capped capuchin (Cebus apella)

While some reports that capuchins crack nuts or hard-shelled fruit to eat have already been presented, it has been unknown whether such behavior is only one of the varied feeding habits of capuchins or if it is also a behavior adaptive to their habitats, a behavior which requires the use of hands and mastering of skill related to tool-using behavior. On a border of La Macarena National Park in Colombia, the authors minutely observed the feeding behavior of the black-capped capuchin, in which the monkey skillfully fed on the albumen of the fruit of cumare, a kind of cocoid palm-fruit, using two different methods, according to the degree of ripeness of the fruit. The characteristic behavior developed by the black-capped capuchin while eating the fruit of cumare could be fixed as one of the higher level adaptive behaviors of the animal to his habitat.

Foods and feeding behavior of wild black-capped capuchin (Cebus apella)

Having various kinds of food in its food repertoire, the capuchin (Cebus apella) fed mainly on fruit and insects. Feeding behavior varied according to the kind of food and such behaviors were effective ones performed by the capuchin, which seems to know well both the nature of the plants and habits of the animals it eats. It can also be said that they are highly intellectual ones. In addition, because of the strong relationship between the capuchins feeding behavior and its habitat, it can be concluded that its behavioral activities were adaptive ones formed by its own positive action.

Social behavior of the wild black-capped Capuchin (Cebus apella)

The author undertook a field survey of the capuchin (Cebus apella) lasting 60 days from December 1976 to January 1977, and determined the basic daily activity of its groups and spacing of group members in the day time. Furthermore, based on studies of various types of interactions between individuals of the groups, he was able to show that (1) decisive rank orders exist both among adults and among sub-adults of both sexes; (2) grooming at the resting time is peculiar to adult males; (3) with quite mild agonistic interactions being maintained, a high tolerance exists between the group members; (4) alpha males represent individuals which can be called leaders of groups; and (5) a strong psychological or spiritual bond exists among the adult males, which can be termed a “male-bond.” Furthermore, according to comparative studies on some adjoining groups, it was found that the group structure is strongly influenced by the individuality or character of the adult males of each group. The present findings are generally in agreement with those forC. apella studied by the author and other researchers in other localities. It can be safely said therefore that these findings are probably common to this species of monkey. Based on a comparison with findings for three other species ofCebus, the author attempts to clarify the points of difference betweenC. apella and these three other species ofCebus from the viewpoint of behavioral science and sociology.

Foods and feeding behavior of monkeys in the upper Amazon basin

Eleven species of the New World monkeys inhabit the basin of the River Caquetá in the upper Amazon. Twice for a total of 16 months the author studied the foods and feeding behaviors of 10 species of monkeys in the basin of the River Caquetá, particularly in the two study areas established in the basin of the River Peneya, a tributary of the River Caquetá. Sixty-seven adult monkeys of 10 species were collected, mainly in the basin of the River Peneya, for morphological study, so that the author had a chance to analyze their stomach contents. Some characteristics of the food habits of 10 species of the New World monkeys inhabiting the same area were made clear by means of direct observations in the wild and the analysis of the stomach contents.

Reproduction of Wild Japanese Macaque Females of Yakushima and Kinkazan Islands: A Preliminary Report

Wild Japanese macaque females of the Yakushima and Kinkazan populations exhibited similar reproductive features. (1) Births/female/year (BR: 0.27–0.35) was lower than those of provisioned troops, but (2) infant mortality (IM: 0.23–0.25) was higher than those of provisioned troops. (3) The interbirth interval (IBI) following the death of infants was 1.5–1.6 years, shorter than that following surviving infants (2.2–2.4 yrs). (4) Birth sex ratio (BSR) did not differ from 1∶1. There was no consistent correlation between (5) female age and IM, (6) maternal rank and offspring BSR, or (7) maternal rank and reproductive success. On the other hand, (8) BR of Yakushima females was significantly lower than that of Kinkazan females. In particular, (9) Yakushima females stopped reproduction earlier than Kinkazan females, although (10) the first birth of Yakushima females was about one year earlier than Kinkazan females. (11) BR exhibited a humped curve against female age in Yakushima, but it was uncertain whether old-aged females of Kinkazan exhibited a post-reproductive life span (PRLS). (12) The survivorship for female juveniles was lower than that for male juveniles in Yakushima, whereas the survivorship for male juveniles was lower than that for female juveniles in Kinkazan. These data may indicate that Yakushima females more severely compete for resources than Kinkazan females, because of high population density, whereas the population density of Kinkazan might be limited by climate (e.g. heavy snow) rather than density dependent ecological effects.

Group Sizes and Compositions of Monkeys in the Upper Amazon Basin

Eleven species of New World monkeys inhabit the basin of the upper Amazon. Twice, for a total 16 months, the author studied the group sizes and compositions of these species in the basin of the Rivers Caquetá and Putumayo, particularly in the two study areas established in the basin of the River Peneya, a tributary of the River Caquetá.Data obtained by the author were compared with those on the same and close relative species living in other places. And the author could conclude that each species, showing a considerable range of variation in group size and composition, has a common specificity for the social structure of the unit group.

Unit groups of chimpanzees and their nomadism in the savanna woodland

I chose an area in the savanna woodland of Western Tanzania covering about 45 km2 and made an intensive sociological study of the chimpanzees visiting this area. Three components constituting a chimpanzee population were recognized: large-sized groups, smallsized groups, and lone individuals.I took notice of the groupings of large-sized groups, and classified them into the following three statuses: the state of congregation, the state of partition, and the state of dispersion.Provided that the productivity of food was stable, large-sized groups carried on their nomadism regularly, no matter what their main food might be. During the period in which the food supply was scarce, however, large-sized groups presented two types of nomadism: rapid movement in the state of congregation, and extreme dispersion.Two large-sized groups were found and each had its own nomadic range of about 120 km2 respectively, 20% of which overlapped. Small-sized groups and lone individuals did not have their own ranges, and it is possible that they moved over wider ranges than the large-sized groups.

Inter-annual variation of reproductive parameters and fruit availability in two populations of Japanese macaques

Among wild Japanese macaques, which have clear reproductive seasonality, correspondence between fruit-food production in the mating season and birth rate in the following year was confirmed in two different habitats. One of the study areas was evergreen broad leaved forest on Yakushima Island, for which demographic and fruiting data for seven years were used. The other was a deciduous-coniferous mixed forest on Kinkazan Island in the cool temperate zone, for which 11 years of data were used. From the fruit-crop data, each year was classified as a good or bad fruiting year for each population. At both habitats, female macaques had fewer babies after bad fruiting years than after good fruiting years. In Yakushima, small troops had a lower birth rate than large troops and this tendency was clear after bad fruiting but not after good fruiting. On the other hand, in Kinkazan such differences due to troop size were not found. These findings were consistent with the observation that intertroop encounters occur more often and are more agonistic in Yakushima than in Kinkazan and large troops tend to be dominant to small troops in the Yakushima population. Thus annual fluctuations in fruit production appear to increase the difference in birth rates between troops of different sizes through intertroop competition in Yakushima, but not in Kinkazan.

Soil-eating byAlouatta andAteles

Among 12 species of New World monkeys studied in La Macarena Region and the River Caquetá basin of Colombia, onlyAlouatta seniculus andAteles belzebuth were frequently observed to eat soil. They do this at particular sites on the ground called “salados” by local people. They also eat termite nests found on tree trunks. OnlyAteles drink the water of salado sites. The chemical properties of 17 soil samples and 5 water samples were analyzed. The results are discussed in relation to the question of whyAlouatta andAteles eat soil.

Does Troop Size of Wild Japanese Macaques Influence Birth Rate and Infant Mortality in the Absence of Predators

For the wild Japanese macaques of Yakushima and Kinkazan Islands, we analyzed the relationship between the troop size or the number of adult females of each troop, infant/adult female ratio (IFR; crude birth rate), and infant mortality (IM) in habitats with no predators. In Yakushima, IFR was positively correlated to troop size and the number of adult females. In Kinkazan, however, IFR tended to decrease with the number of adult females. This difference may be due to the difference in troop size; i.e. in Yakushima, where troop size was small, IFR may increase with that of troop size, because a relatively larger troop is likely to the advantage in intertroop competition. In Kinkazan, where troop size was large, however, IFR is likely to decrease with troop size, because intratroop competition may increase. Thus, the present data roughly supportWranghams model of the social structure of female-bonded primates, and suggests that there is an optimal troop size for birth rate (BR). On the other hand, there was no clear correlation between IM and the troop size or number of adult females of each troop.