The reproductive biology of a free-ranging troop of Japanese monkeys

Quantitative data on the reproductive biology of Japanese monkeys (Macaca fuscata), especially of females, are reported here. Arashiyama B troop shows stable annual breeding periodicity, and has mating seasons between October and March. In mating seasons, females show estrus with rather consistent cyclicity, and are in estrus for a total of 35 days on an average. The mean length of estrous cycle is 34 days. Although most females show estrus inter-menstrually, some show peri-menstrually; i.e., estrus does not always synchronize strictly with ovulation. Pubescent females between 3.5 and 6.5 years show estrus, but with low sexual activity. Middle-aged females between 7.5 and 16.5 years show high sexual activity with high conception rate. Old-aged females over 17.5 years show low sexual activity. Females with surviving infants have lower sexual activity than those without infants. There is found no significant correlation between female's ranking and sexual activity. This study was financed partly by the Cooperative Research Fund of the Primate Research Institute, Kyoto University.     

Alliance formation in a free-ranging troop of Japanese macaques

Alliance formations in a troop of free-ranging Japanese macaques, which had been provisioned 16 months before the present study was begun, were observed at the feeding ground for about 300 hr from April 1973 to March 1974. The patterns of alliance formations and their roles were described. The leader male had a quite unique role in his alliance formations; he allied much frequently with the aggressees and attacked the aggressors. Besides, the leader male allied more frequently with babies, yearlings, 2-year-old animals, and adult females, while he frequently attacked the 3- and 4-year-old animals and adult males. The animals who belonged to the same matrilineal group always allied with one another. Except the leader male, the troop members rather preferred to ally, except in those cases where the former diads involved their matrilineal group members, with the first aggressors. Networks of such alliance formations in relation with the social organization of Japanese macaques are discussed.     

Male leadership change in a free-ranging troop of Indian rhesus monkeys (Macaca mulatta)

The male leadership of a troop of rhesus living at the foot of the Kumaon foothills of India was studied from January to December of 1965. The troop, inhabiting a region of fields and forests, varied in size from a maximum of 20 after the birth season to a minimum of 14 in December during the breeding season. The troop initially contained two adult males with the occasional presence of a third, more peripheral male. This third male disappeared in March and was perhaps identical with the male who began to appear in August and succeeded in displacing the dominant male from the troop. The second initial male succeeded to the dominant position in September. During the breeding season various extra-troop males followed and occasionally penetrated the troop. The second male had difficulty in maintaining his position against one of these, who had perhaps been the peripheral male at the beginning of 1965.     

Behavioral characteristics of old female Japanese monkeys in a free-ranging group

Fourteen female Japanese monkeys of the Arashiyama-B group ranging in age from 11 to 29 years were observed to elucidate the behavioral characteristics of aging monkeys. A positive significant correlation was found between the occurrences of rest and age, and a negative significant correlation between the occurrences of auto-grooming and age. Younger female monkeys tended to be in contact with or in proximity to group members, while older female monkeys tended to spend much more time alone. As for the grooming interactions, younger female monkeys more often groomed others than did older female monkeys. Also, the former engaged in grooming more frequently than in being groomed, while the latter spent more time in being groomed than in grooming. The old female monkeys showed no marked decline in rank, but some of them were surpassed by their adult daughters.     

Behavioral development of a malformed infant in a free-ranging group of Japanese monkeys

The behavioral development of a malformed male infant in a free-ranging Japanese monkey group, whose hands were completely missing and whose hind feet were distorted, was investigated during the first one year of life, by comparison with normal infants. In the first few weeks of life, the malformed infant was not able to move by himself and was almost completely dependent on his mother's help. He gradually became able to creep with his forelimb elbows and distorted hind feet at about the first month of life, and was able to walk bipedally on his hind feet, though unstably, after the sixth month of life. His locomotor ability, however, was essentially inferior to that of normal infants throughout the first one year of life. His social interactions with the group members were different from those of normal infants. Normal infants increased their interactions with sameaged infants or older juveniles through active behavior-like play, whereas the malformed infant developed relations particularly with adults through behavior such as passive body contact. The conditions for survival of the observed malformed infant are discussed.     

Playmate relationships of immature free-ranging Japanese monkeys at Katsuyama

The playmate relationships of immature Japanese monkeys were analyzed with respect to age, sex, and dominance rank class of the matrilines in a larger-sized free-ranging group. One-year-old immature males showed the largest number of play partners and the highest frequency of social play. Older immature females tended to play with younger animals of both sexes, whereas immature males of all ages played with same-sexed and like-aged peers. While high-ranking immature males continued their play partnerships with other animals until 4 years of age, middle/low-ranking males did not. The large number of peers and possible play partners may intensify their selectivity of play partners in relation to dominance. The forming of playmate networks by high-ranking immature males may explain the delay in group shifting of high-ranking animals.     

Presbytis entellus: Birth in a free-ranging primate troop

During a 20-month study of two troops ofP. entellus in a village habitat in West Bengal one of seven births was observed. The female came down to the ground 21 minutes prior to parturition and returned to the trees 19 minutes later. She was accompanied by two adult females; there was no adult male present in the troop. The amount of time spent on the ground was significantly greater than expected for that time of year.     

Development of infant twin Japanese monkeys (Macaca fuscata) in a free-ranging group

The behavioral development of infant twin Japanese monkeys in a free-ranging group during the first 12 months of life was reported and compared with that of single born infants. There were no clear differences in mother-infant interactions toward either twin or single infants, but the twins showed a clear nipple preference. The twins spent much time in contact with and proximity to each other and as their interactions were peaceful no dominance relations between them were assumed. Each twin interacted with other infants and juveniles less frequently than did the single infants.     

Intra-troop spacing mechanism of the wild Japanese monkeys of the Koshima troop

The average frequencies of communicative behavior, social behavior, and social encounters (inter-individual proximity within three meters) per hour for a monkey were obtained in their natural habitat by tracing several adult males and females of a Japanese monkey troop living in the Koshima islet. The spatial distribution patterns and the density of troop members within the expanse of the troop at any moment were investigated by tracing several adult femals. Frequency distributions of the monkeys found within five and 10 meters were compared with a Poisson distribution. The frequencies of social encounters and of social interactions of Japanese monkeys were distinctly low, except between mothers and their offspring. The density of monkeys within the expanse of the troop at any moment was very low. Both aggressive behavior and inter-individual proximity (within three meters) were distinctly low when monkeys were foraging for natural food. An avoiding mechanism among troop members plays an important role in maintaining the social structure of these Japanese monkeys. This mechanism works in two ways: each individual does not approach others too closely; the density of monkeys within the expanse of the troop is low at all times.     

Tests to determine the responsiveness of free-ranging Japanese monkeys in food-getting situations

Experiments were performed on a free-ranging Japanese monkey troop (Arashiyama-B troop) in order to study the various levels of response caused by excitement and the characteristics of each monkey's action as observed under a series of stimulating situations carried out step by step through the giving of peanuts to the monkeys in various ways. The following results were obtained: (1) Three types of responses, that is, Threat response, Fear response, and Negative response were observed. (2) In response types, fairly evident individual differences exist along side sexual and age differences. (3) Similarity of response tendencies were not readily recognizable between a mother and her children. (4) Between two sisters with a slight disparity of age, the younger showed a stronger threat response. (5) Among females more than 4 years old, the lower the rank, the stronger the fear response.     

A description of genealogical rank changes in a troop of Japanese monkeys (Macaca fuscata)

Rank changes among females of a troop of 154 Japanese monkeys (Macaca fuscata) are described. A medium ranking female, with support from the alpha male, successfully challenged the alpha female. Following this dominance shift, almost all members of the two genealogical groups underwent rank changes. The observations provide some evidence that the role of alpha female may be competed for, just as the alpha male position is, in macaque social groups.     

Signals found in the grooming interactions of wild Japanese monkeys of the koshima troop

Signaling behaviors appearing in grooming interactions of wild Japanese monkeys were analysed. Vocal signals found in the grooming interactions had the content of asking the objective animal “if the vocal signaler may groom the recipient animal.” They could be divided into two categories of vocal sounds, VG-1 and VG-2. The former was uttered in common by all the troop members. The latter was uttered just before grooming by the groomer and is considered to have deeper connection with grooming. Each individual uttered mainly one kind of vocal sound out of VG-2, and the preferred vocal sounds for each individual differed. Furthermore, VG-2 differed in different troops. Behavioral signals had the content of showing “the acceptance of grooming” or showing “the request to be groomed.” The appearance of these signaling behaviors was closely related to the inter-individual relationships of grooming partners, especially as to whether or not they had blood relationships. Basically the monkeys have a system in which they must avoid each other, except in the case of mothers and their offspring, and if they had to approach too closely against this basic system, as in grooming interactions, there appeared signaling behaviors as mentioned above.     

Object manipulation in a captive troop of Japanese monkeys (Macaca fuscata): A developmental analysis

A captive troop of Japanese monkeys (Macaca fuscata) was presented with a nylon rope, a wooden cube, and an iron tube, and their subsequent manipulations were observed in detail. In total, 202 manipulation patterns were distinguished on the basis of three components: the actions performed, body-parts used, and relations to other objects. The developmental changes in these modes of manipulation were analyzed cross-sectionally, revealing four characteristics: (1) the most manipulative members of the troop were those aged 2–3 and 4–6 years old; (2) most of the manipulatory repertoire appeared by 4–6 years old; (3) actions such as Roll, Rub, and Slide and the use of bodyparts continued to increase in variety until 4–6 years old, while the variety of other actions showed plateaus after 2–3 years old or an earlier age; and (4) secondary manipulations appeared at 1 year old and continued to increase in variety even after 4–6 years old.     

Interactions among adult males and females before and after the death of the alpha male in a free-ranging troop of Japanese macaques

This report documents the social interactions among adult Japanese macaques in a free-ranging troop before and after the death of the alpha male, who died at 28 years of age after occupying his rank position for 17 years. The alpha male’s physical condition had deteriorated due to his extreme age for several months before his death. However, he maintained his alpha position. When he was attacked by the second-ranking adult male, he was rescued by the alpha female. Thereafter, whenever the second-ranking male approached him, the alpha male screamed for the alpha female’s support. The number of adult females to whom the alpha male maintained proximity during his last four months was similar to that during the same period of the previous year. Prior to his death, the alpha male was observed in close proximity to the alpha female much more frequently than was the second-ranking male. These results indicate that the alpha male maintained his position by depending on female support and particularly that of the alpha female.