Yukimaru Sugiyama

Cultures in chimpanzees

As an increasing number of field studies of chimpanzees (Pan troglodytes) have achieved long-term status across Africa, differences in the behavioural repertoires described have become apparent that suggest there is significant cultural variation. Here we present a systematic synthesis of this information from the seven most long-term studies, which together have accumulated 151 years of chimpanzee observation. This comprehensive analysis reveals patterns of variation that are far more extensive than have previously been documented for any animal species except humans. We find that 39 different behaviour patterns, including tool usage, grooming and courtship behaviours, are customary or habitual in some communities but are absent in others where ecological explanations have been discounted. Among mammalian and avian species, cultural variation has previously been identified only for single behaviour patterns, such as the local dialects of song-birds,. The extensive, multiple variations now documented for chimpanzees are thus without parallel. Moreover, the combined repertoire of these behaviour patterns in each chimpanzee community is itself highly distinctive, a phenomenon characteristic of human cultures but previously unrecognised in non-human species.

CHARTING CULTURAL VARIATION IN CHIMPANZEES

Cultural variation among chimpanzee communities or unit-groups at nine long-term study sites was charted through a systematic, collaborative procedure in which the directors of the sites first agreed a candidate list of 65 behaviour patterns (here fully defined), then classified each pattern in relation to its local frequency of occurrence. Thirty-nine of the candidate behaviour patterns were discriminated as cultural variants, sufficiently frequent at one or more sites to be consistent with social transmission, yet absent at one or more others where environmental explanations were rejected. Each community exhibited a unique and substantial profile of such variants, far exceeding cultural variation reported before for any other non-human species. Evaluation of these pan-African distributions against three models for the diffusion of traditions identified multiple cases consistent with cultural evolution involving differentiation in form, function and targets of behaviour patterns.

Tool-using and -making behavior in wild chimpanzees at Bossou, Guinea

The behavior of wild chimpanzees at Bossou, Guinea, was studied from November 1976 to May 1977 recognizing each chimpanzee without artificial feeding. During the study period some tool-using and tool-making behavior was observed, as follows: (1) Although water drinking using a “leaf-sponge” was not seen, that using a “leaf-spoon” was observed for taking water from the hollow of a tree. (2) “Termite fishing” was not seen in this group although there were many termite hills in the moving range of the chimpanzees. They dug termites from the hollow of a tree by pounding with a small stick. Similar use of a stick was made for digging up the resin from a tree. (3) “Aimed throwing” was frequently observed in adult males for attacking an observer, and in adolescents and juveniles as mischief against an observer or for their own play. (4) “Nut cracking” with a pair of stones was seen for removing the ovule from palm-seeds. Particular stones were repeatedly used by many chimpanzees for a long period. (5) “Branch hauling” represented difficult work. Patient and inventive manufacture of proper sticks was necessary for capturing branches which they were unable to reach normally.Local variations in the tool-using patterns and manufacturing ability of chimpanzees are discussed.

On the social change of hanuman langurs (Presbytis entellus) in their natural condition

I have already reported some of the socio-ecological studies of hanuman langurs (Presbytis entellus) conducted by the Japan-India Joint Project in Primates Investigation over a period of two years from April, 1961. Its main research area was a tropical dry deciduous forest lying to the west of Dharwar in Mysore State, India (SuGIYAMA 1964). The first step of the project was the study of general ecology of langur troops living on and by the road running westwards from Dharwar to Haliyal (SuGIYAMA 1964). It was made clear that there are two types of groups: the bisexual troop that comprises 16 animals on the average usually including only one adult male and the male group that consists of male langurs only. Moreover, another close investigation was made into seven troops and one male group inhabiting around the spot of 21 km from Dharwar.3) It became clear by that investigation that each of these troops settles down in a home range of about 17 hectares, while the male group is always moving by choice where any troop does not exist, and that there is strong antagonism between the troop-males and the male group (SuGIYAMA et al. 1965). The infant langur has many chances to be held by the females of the troop other than the mother (infant transferring) and grows up to be a member of the troop that has little social differentiation. Moreover, the infant langur is allowed to behave freely in the troop by every member. I f it is a male infant, no antagonism arises between the infant and the leader even when he grows up into a mature male (SuGIYAMA 1965).

Population Dynamics of Japanese Monkeys with Special Reference to the Effect of Artificial Feeding

Population dynamics of Japanese monkeys (Macaca fuscata) have been studied at Mt. Ryozen, central Japan, between 1969 and 1980. The troop had been artificially fed until August 1973 and, since then, has been living in its natural habitat without artificial feeding. Increase in body weight, primiparous age, age-specific natality, survivorship and mortality, population and biomass growth rate, and age of disappearance of young males were compared between the two study periods, with and without artificial feeding. Comparison of population parameters in each study period was also done between social classes, central and peripheral. As shown, in table VII, it was revealed that artificial feeding was an important factor in population growth and, furthermore, that this effect was mainly on the kin-groups of the central class of the troop. In the natural habitat without artificial feeding most of the population parameters showed almost the same figure for kin-groups of central and peripheral classes.

Aging and fertility patterns in wild chimpanzees provide insights into the evolution of menopause

Human menopause is remarkable in that reproductive senescence is markedly accelerated relative to somatic aging, leaving an extended postreproductive period for a large proportion of women. Functional explanations for this are debated, in part because comparative data from closely related species are inadequate. Existing studies of chimpanzees are based on very small samples and have not provided clear conclusions about the reproductive function of aging females. These studies have not examined whether reproductive senescence in chimpanzees exceeds the pace of general aging, as in humans, or occurs in parallel with declines in overall health, as in many other animals. In order to remedy these problems, we examined fertility and mortality patterns in six free-living chimpanzee populations. Chimpanzee and human birth rates show similar patterns of decline beginning in the fourth decade, suggesting that the physiology of reproductive senescence was relatively conserved in human evolution. However, in contrast to humans, chimpanzee fertility declines are consistent with declines in survivorship, and healthy females maintain high birth rates late into life. Thus, in contrast to recent claims, we find no evidence that menopause is a typical characteristic of chimpanzee life histories.

Life history of male Japanese monkeys

Publisher Summary This chapter discusses the social structure of Japanese monkeys, renunciation of the natal troop, approach to and joining of the troop by Hanarezam, and longevity and mortality of male Japanese monkeys. The multimale and multifemale troop of Japanese monkeys at Takasakiyama is controlled by a group of leader males, while females and infants occupy the central part of the troop under the protection of leader males. Most male Japanese monkeys desert their natal troops and spend much of their long life as wanderers. Although, some male Japanese monkeys, which disappear, must die, comparisons with the survival curves of females and some individually known cases indicate that many others, which leave the troop survive. It is uncertain, whether many males died in or out of the troop, and the critical reason for the difference between the mortalities of the sexes is not known, it is likely that the hanarezaru are less able to find food and encounter many more dangers. The study presents that observing the life history of Japanese monkeys from the long-range viewpoint, the rank order, the social role, and social hierarchy regulate social friction among spontaneously coexisting animals.

Social structure and dynamics of wild chimpanzees at Bossou, Guinea

A small population of wild chimpanzees was studied at Bossou, Guinea, for six months from November 1976 to May 1977. All the chimpanzees except dependent infants were identified without artificial feeding and were observed from within 20 m almost every day. The population size of 21 chimpanzees was little changed from 1967. Although the sex ratio (male/female) of immatures (infants, juveniles, and adolescents) was 0.833 in January 1977, the adult sex ratio was 0.429. More than half of the males must therefore have disappeared. No desertion of males from the Bossou group was confirmed during the study period but two emigrated males from other groups did come to join the Bossou group for a short period.Four out of six mothers had two or three children. From the age discrepancy of brothers/sisters, the mean birth interval from a mother was estimated to be about four years. An elder sister of two infants who had an age-gap of only three years, or perhaps less, disappeared without receiving sufficient care from her mother.Mothers who had infants aged about 1 year or more showed swelling of their sexual skin and were confirmed to mate with males.

Social organization of chimpanzees in the Budongo Forest, Uganda

A population of wild chimpanzees in the Budongo Forest, Uganda, was studied between September, 1966, and March, 1967, by means of habituation and identification of each individual. This article deals with the grouping patterns, social units, and social organization of the chimpanzees in their natural habitat. Although parties of chimpanzees form groups of many patterns according to each particular situation and have no permanent membership, many chimpanzees live within a certain restricted area and gather to form parties consisting, in the main, of chimpanzees acquainted with each other. More than 50 individuals combined by social bonds in a loose regional population which is separated from other populations without recourse to geographical or physical barriers, though it maintains friendly contact with neighboring chimpanzee residents and with strangers. No particular individual group leader can be found, but any adult, especially a male, may act as a nucleus of each party.

Hand preference and tool use in wild chimpanzees

The hand preference of chimpanzees in their natural habitat was studied at Bossou, Republic of Guinea, West Africa. The quantitative difference in left/right hand use was small in food picking and carrying. In contrast, the chimpanzees employed either the right or left hand in nutcracking behavior using a pair of stones. All adults and many adolescents and juveniles utilized one hand exclusively for holding a hammer stone. Left hand preference was more prevalent among adults. However, when adolescents and juveniles were included, there was no significant bias in the ratio of left/right handers. Nut-cracking behavior requires long-term learning of the fine manipulation of stones and nuts by both hands. Each hand has a separate role, and the hands work together in nut cracking. The differential and complementary use of both hands may be a prime factor promoting exclusive hand preference in chimpanzees comparable to that of humans.