Comparative study of grooming relationships among wild Japanese macaques in Kinkazan A troop and Yakushima M troop

The influences of socionomic sex ratio (SSR; adult males/adult female) and troop size upon male-male, female-female, and male-female grooming relationships were examined and compared between two wild Japanese macaque troops (Kinkazan A and Yakushima M troops) in Japan. The Yakushima M troop was smaller and had a higher-SSR than the Kinkazan A troop. Between the troops, (1) the male-male grooming frequency and number of partners were greater in the Yakushima M troop than in the Kinkazan A troop; (2) the female-female grooming frequency and number of partners were not different; and (3) the male-female grooming frequency and number of partners were not different. Based on these features, the patterns of female-female and male-female grooming relationships appear to be independent of SSR and troop size variations. In contrast, male-male grooming relationships are influenced by both factors, especially SSR. Frequent grooming interactions among males may be useful for the continued coexistence of relatively many males especially in a higher-SSR troop.     

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.     

Initiation and solicitation in male-female grooming in a wild Japanese macaque troop on yakushima island

Grooming initiation among adult males and females of a Japanese macaque troop was analyzed during the non-mating season. Some gestures (“solicitation”) elicited grooming from partners at a high rate. Grooming initiation patterns were divided into two main types: (1) a male often solicited a female to groom him immediately after approaching her and was groomed by her; and (2) a female approached an alpha male selectively, and immediately groomed him. After a female groomed a male, she rarely solicited him to groom her and instead often moved away from him. These results indicated that males were motivated to be groomed, while females were more highly motivated to groom. Sex differences in grooming motivation can be explained by sex differences in the benefit to be groomed.     

Familial interactions of male rhesus monkeys in a semi-free-ranging troop

Although the central and stable position of female rhesus monkeys in semi-free-ranging bands has been observed and described, the position of the developing male in the social group is not as well delineated. The present study is an attempt to describe interactions of 18 males with members of their families. Quantitative observations were made on one band (E) of rhesus monkeys on Cayo Santiago. Incidences of behavior recorded were joining, grooming, and threatening. The resulting data were analyzed by comparing the behavior of the males studied toward members of their genealogy as well as unrelated members of the social group. Behavior of family and non-relatives toward the males was also revealed. Statistical analysis revealed that the male subjects engaged in more positive social interactions within the matrifocal family than with other members of the genealogy, and in turn, more such behavior was observed within the genealogy than with unrelated monkeys. Threatening behavior within the genealogies was infrequent. Age effects were noted in that family members directed more interactions toward younger males and as males matured, they groomed more but joined family members less frequently. These data suggest mechanisms of socialization within the genealogy that may be different from those employed within the unrelated social group.     

Socio-sexual factors of troop fission in wild Japanese monkeys (Macaca fuscata yakui) on Yakushima Island,Japan

The troop fissions which occurred in a wild population of Japanese monkeys (Macaca fuscata yakui) were observed from 1977 to 1979 on Yakushima Island. The fissions were initiated in the breeding season by non-troop males who established a consort relation with estrous females. In order to analyze the socio-sexual factors which accelerated the fissions, the male emigrations and immigrations before and after two successive fissions, and the copulation frequencies, competition among males and preferences of mating partners in both sexes in the 1977–78 breeding season after the first fission were examined. The results indicated that three factors (a large number of non-troop males, a shortage of troop males and the females' choice of mating partners) effectively influenced on the establishment of consort relationships between non-troop males and estrous females. It is suggested that these factors may exert different effects on the troop disorganization in relation to troop size. In small-sized troops, a large number of non-troop males and a shortage of troop males may lead to stronger competition between them, and the females' choice affected by prolonged intimate relations with the dominant TMs may reduce their priority of access to estrous females. This situation possibly stimulates fission or male emigration in small-sized troops under the natural conditions on Yakushima Island. In contrast, in large-sized troops under isolated conditions, a surplus rather than a shortage of troop males may contribute to troop disorganization, as most former studies have suggested. A higher socionomic sex ratio may decrease the mating activities of subordinate troop males and increase the competition among them. This situation possibly accelerates the fission of large-sized troops through prolonged interactions between females and subordinate or peripheral troop males. A lower ratio and the females' choice, however, raise the mating chances of subordinate troop males and may not promote the fission of large-sized troops under isolated conditions. This study was financed in part by a Grant-in-Aid for Special Project Research on Biological Aspects of Optimal Strategy and Social Structure from the Japan Ministry of Education, Science and Culture, and by the Cooperative Research Fund of the Primate Research Institute, Kyoto University.     

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.     

Maternal and alloparental care in a troop of free-ranging Japanese monkeys

In four years of observation of a free-ranging Japanese monkeys, reproductive rate, physical development of infants, maternal care and alloparental care were studied. Primiparous mothers, orphanned mothers and old mothers showed different types of maternal care from typical multiparous mothers, and the reproductive success of each of these categories of mother also differed. Among nulliparae, 2-year-old females showed the most interest in infants. Adult females were generally indifferent to other females' infants and came to act aggressively toward them with increasing age and maternal experience.     

The daily activity rhythm in a troop of wild Japanese monkey

An assessment of the daily activity rhythm of wild Japanese monkeys was tried both from the calculation of the proportion that each activity occupied in the total activities and the “nomadograph,” representing temporary change in the pace of the daily movement. Seasonal and day-to-day changes are recognized in the daily activity rhythm of the troop of wild Japanese monkeys. It seems that seasonal change in the daily activity rhythm corresponds to the seasonal fluctuation of food supply and atmospheric temperature. From autumn to early winter, when much food is available, a clear-cut pattern of activity emerges; namely, three intensive feeding periods are recognized in a day. Moreover, day-to-day variation in the activity rhythm is fairly small and the activity pattern thus becomes standardized. In winter, when least food is available, activity of monkeys drops to the lowest level of the year. Day-to-day variation in the activity rhythm is great. Two to four intensive feeding periods in a day are recognized. In early spring and summer, when food supply is rather scarce, there exist two to three intensive feeding periods in a day. During the heat of the day in summer, activity of monkeys is conspicuously low.     

A new approach to evaluating troop deployment in wild Japanese Monkeys

In winter when the mountain slopes are covered with deep snow, it is easy to obtain quantitative data on the two-dimensional deployment of members of a troop of wild Japanese monkeys. We observed the deployment of a troop on a slope from the opposite side of a river. The deployment patterns, evaluated on the basis of the relative distance from the central point (centroid) of the troop, were different for each sex and age category. Adult females, infants, and 1-year-olds tended to be grouped together and were concentrated near the center of the troop. On the other hand, adult males were randomly spaced. These tendencies suggest that the deployment reflects the social structure of the duplicate concentric-circle model originally proposed by J. Itani (1954).     

Population genetics of Japanese monkeys: I. Estimation of the effective troop size

In order to estimate the genetically effective troop size of Japanese monkeys, we have to know the pattern of distribution of the numbers of gametes contributed by the individual members of the parental population to the next generation. The author inspected the observation records of macaque troops made by a number of socio-ecologists and found that the relationship between sexual rank and sexual activity of adult males could be approximately expressed by the law of geometrical series. Assuming that the genetic contribution of male parents to the next generation was proportional to their sexual activity and that the numbers of gametes contributed by the female parents formed thePoisson distribution, the author derived a formula for estimating effective troop size (N), namely, whereN_c was the census number andN_m andN_f the numbers of male and female parents, respectively, of the troop. Moreover, assumingN_m=0.2N_c andN_f=0.3N_c as an average, the effective size could be estimated as 36% or less of the census number.     

Changes in dominance rank and division of a wild Japanese monkey troop in Arashiyama

This article forms the second report on the Arashiyama troop of Japanese monkeys and concerns a troop division which took place in June, 1966, and various problems of rank and consanguinity which accelerated the division. (1) The hypothesis advanced in the first report has been verified; (2) at the time of troop division, several consanguineal groups formed one unit; (3) among 16 consanguineal groups, those from 1st to 7th in rank joined the A troop, while those from 8th to 16th joined the B troop; (4) dominance relation between the two division troops was B troop>A troop, reflecting the former ranking between the leader males of the two troops; (5) shifting of monkeys from one troop to the other after division occurred frequently, but males began to make their own movements when they attained 4 or 5 years of age and rarely moved together with their mothers or other consanguineous-relatives; (6) monkeys which were continuously in the same troop after division almost always obtained higher ranks than did monkeys who frequently shifted from one troop to the other; (7) after division, some males joined neither of the two division troops but formed a group, a so-called all-male group or male party, and moved about independently.     

Inter-male associations in a wild Japanese macaque troop on Yakushima Island,Japan

Adult male association and its annual change were studied in a wild population of Japanese macaques (Macaca fuscata yakui) on Yakushima Island, Japan. Unlike many other Japanese macaque troops, adult troop males frequently maintained proximity and exchanged grooming with one another in both the mating and non-mating seasons, and the dominance relationship rarely appeared in such inter-male associations. The few cases of agonistic interactions occurred mostly when estrous females or food resources were immediately concerned. Although troop males were very intolerant to newly appeared solitary males (new males) during the mating season, close associations were formed between troop males and new males as soon as the mating season terminated. The consort of new males and lower-ranking troop males with estrous females was frequently disturbed, but these males could copulate no less frequently than higher-ranking males. A comparison among macaque species suggests the existence of two forms of inter-male association: (1) the frequent association based on the symmetrical exchange of social behaviors; and (2) the infrequent and asymmetrical association related to the dominance relationship. The form of inter-male association seems to be influenced by whether or not males can keep close associations with females throughout the year.