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.     

Changes of dominance rank,age, and tenure of wild Japanese macaque males in the Kinkazan a troop during seven years

Male age-rank and tenure-rank relationships were studied for seven years in unprovisioned Japanese macaque (Macaca fuscata fuscata) troop on Kinkazan Island, Japan. Males whose estimated ages were between 15 and 19 yr old monopolized the highest ranks, while older males whose estimated ages were ≥ 20 yr old tended to decline in rank, resulting in a humped age-rank curve. The ranks of males tended to rise as their tenure in the troop increased. The departure of higher-ranking males was the social mechanism for changes in rank, suggesting that the disappearance of higher-ranking males plays an important role in determining rank dominance.     

Intertroop Transfer and Dominance Rank Structure of Nonnatal Male Japanese Macaques in Yakushima, Japan

We examined the interaction between intertroop transfer and male dominance ranks in a wild population of Japanese macaques (Macaca fuscata yakui) in Yakushima using data collected over 15 years. Intertroop transfer tended to maintain a linear, stable, and age-graded dominance rank order among nonnatal males irrespective of variation in troop size or composition. All males that joined a troop at the top of the rank order were prime adults. Among males joining at lower ranks, entry at the most subordinate position in the hierarchy was common. Males joining at lower ranks tended to join troops in which all other resident males were the same age or older. Adult males tended to join troops with few or no males. Young males tended to join troops with many resident males, and in which a relatively large proportion of males was other young ones. Intertroop transfer was responsible for most rank changes of resident males. The most common cause of males rising in rank was the emigration or death of a higher-ranking male. Males fell in rank most frequently as a result of a new male joining the troop at the top of the hierarchy. Rank reversals among resident males were rare. The cumulative effects of male transfers produce sociodemographic variation within a troop over time and sociodemographic diversity among troops in a local population. A key feature of intertroop diversity is that larger troops have a significantly greater proportion of young males than smaller troops. This diversity also creates the potential for intertroop variation in the severity of male competition and provides a range of options for transferring males.     

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.     

Variation in Intergroup Encounters in Two Populations of Japanese Macaques

The nature of intergroup encounters differed between two populations of wild Japanese macaques (Macaca fuscata): the Yakushima and Kinkazan populations. In the Yakushima population, intergroup encounters were more likely to result in the displacement of one group, intergroup agonistic interaction was common, and intergroup dominance was usually distinct. When displacement occurred at Yakushima, larger groups tended to dominate smaller ones. Conversely, in the Kinkazan population, intergroup encounters rarely resulted in displacement, intergroup agonistic interaction was rare, and intergroup dominance was usually unclear. Thus, monkeys in Yakushima appear to defend resources actively during encounters, while those in Kinkazan usually did not defend resources. The frequency of encounters was significantly higher in Yakushima than in Kinkazan. The two populations had very different group densities and traveling speeds, both of which directly influence the chance of encounters. Taking these differences into account, we compared the observed frequency with those predicted by the ideal gas model. The observed frequencies in both populations were about one-third of the number expected with the model, which suggests that the differences in encounter frequency were caused by differences in group density and traveling speed. We discuss this intraspecific variation in light of economic defendability in connection to habitat differences and the evolutionary significance of resource defense behavior.     

Home range structure and inter-group competition for land of Japanese macaques in evergreen and deciduous forests

The per capita home range area of Japanese macaques,Macaca fuscata, is significantly smaller in evergreen forest than in deciduous forest, though a corresponding difference in food resource utilization patterns has never been described. The present study compared the home range utilization pattern of Japanese macaques living in two habitats: the Yakushima population inhabits an evergreen forest, while the Kinkazan population inhabits a deciduous forest. We found that in the Yakushima population, (1) food density was higher; (2) inter-feeding bout sites distance was shorter; (3) daily travel distance was shorter; (4) home range size was smaller; and (5) the unit value of the main home range was higher, than in the Kinkazan population. Yakushima groups utilized a small home range area intensively, compared to Kinkazan groups. We also found that a Yakushima group shared 24% of its main home range with neighboring groups, though a Kinkazan group shared only 10% with other groups. It is supposed that food distribution affects daily ranging pattern, and ultimately the social relationships between groups in Japanese macaques.     

Aggressive intergroup encounters in two populations of Japanese macaques (Macaca fuscata)

It is predicted that variation in intergroup relationships in group living primates reflects the cost and benefit of resource defense. We tested the applicability of the model by examining population difference, group difference, and seasonal difference in behaviors during intergroup encounters in two populations of Japanese macaques (Macaca fuscata), one of six groups from Yakushima Island, and the other of three groups from Kinkazan Island. We found that the nature of intergroup encounter varied with group identity, reproductive seasonality, and population. Yakushima groups showed aggressive behaviors more frequently than did Kinkazan groups and the difference was consistent with the food competition model, both because of the involvement of females, and because home ranges were smaller on Yakushima than on Kinkazan, and thus more defensive. Both sexes of animals participated in aggressive interactions, but males were more aggressive than females. Furthermore, Yakushima population showed more agonistic intergroup behaviors during the mating season than the non-mating season. Also during the encounters, intergroup mating was observed, but only in Yakushima. It is concluded that intergroup relationships reflect the mate guarding behavior by group males. However, the agonistic relationship during non-mating season, especially that of among females, is also consistent with the food competition model. It is also noted that males' behavior toward other groups can also be interpreted as a form of investigative behavior before possible transfer into a new group.     

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 supportWrangham's 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.     

History and Present Scope of Field Studies on <Emphasis Type="Italic">Macaca fuscata yakui</Emphasis> at Yakushima Island,Japan

Field studies on Japanese macaques on Yakushima Island started in the mid-1970s, >25 yr after the emergence of Japanese primatology, in response to criticism of methods using provisioning and the desire to find the socioecological factors influencing the social life of macaques in natural habitats. We habituated macaques without provisioning mainly in the coastal warm-temperate forest and found that they lived in small troops with a high socionomic sex ratio. Observations of several troop fissions and troop takeovers by nontroop males suggest that Yakushima macaques have a different social organization from that of Japanese macaques in other habitats. For example, youngest ascendancy as the dominance relationhip among sisters, which usually occurs in provisioned troops, was absent in Yakushima macaques. We compared their ecological and social features with those of Japanese macaques at Kinkazan (cool-temperate forests) and found that abundance of high-quality foods may cause stronger intra- and intertroop competition at Yakushima. Female Yakushima macaques may more positively solicit nontroop males to associate with them during the mating season. Such a tendency may promote frequent male movement between troops and frequent troop fissions. Though ecological factors form social features of Japanese macaques, some features such as male association and movements between troops are not accounted for via socioecology. Recent field studies have focused on macaques living at higher altitudes in Yakushima and on individual survival strategies by taking diverse viewpoints and using new technologies. DNA analysis of fecal samples shows low genetic diversity and suggests the macaques’ recent expansion from lowland to highland forests in Yakushima. The population censuses conducted annually indicate that the higher-altitude macaques have a larger home range but a similar group size versus their counterparts at low elevations. The unsolved issues in socioecology will pose a challenge to the younger generation of primatologists. Conservation of macaques and their habitat is one of our major activities at Yakushima. The level of protection has gradually increased in the National Park at Yakushima and, via our various conservation efforts, its most important area was designated a World Heritage Site by UNESCO in 1993. However, large-scale logging in the 1960s and 1970s caused the loss of macaque habitats and led to increased crop damage by them in the 1980s. We have proposed effective methods to protect cultivated fields from macaques as well as several plans for sustainable use of forests, such as ecotourism and a fieldwork course for university students. Local residents and researchers have created several nongovernment organizations (NGOs) to promote conservation and nature study at Yakushima. The role of local NGOs is particularly important to mitigate conflicts between people and wildlife. Though hundreds of macaques are still captured as pests annually in Yakushima, we continue the conservation measures and spread awareness of conservation in cooperation with the local NGOs.     

Birth-season variation in Japanese macaques,<Emphasis Type="Italic"> Macaca fuscata</Emphasis>

Japanese macaques, Macaca fuscata, exhibit an annual reproductive cycle that apparently is maintained intrinsically. Translocation of nine troops to new latitudes within the northern hemisphere has had minimal effect on the timing of birth seasonality in these troops; translocation of one troop to the southern hemisphere has resulted in a 6-month forward displacement of birth seasonality in this troop. Limited available evidence indicates that, in the latitudinal zone between Toimisaki (31°22′N) and Kinkazan (38°17′N), mean birth date in in-situ troops becomes earlier as latitude of troop localities increases; the same relationship between mean birth date and latitude apparently does not apply to in-situ troops south and north of the Toimisaki–Kinkazan latitudinal zone. Within the Toimisaki–Kinkazan latitudinal zone, earlier mean birth dates at higher latitudes may permit infants to achieve an adequate level of development before the earlier onset of poor winter food conditions. South of the Toimisaki–Kinkazan latitudinal zone, winters are relatively mild and may be less of a factor in infant survival; north of this zone, poor winter food conditions persist so long that earlier infant births may be maladaptive. Electronic Publication     

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.     

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.     

Effects of habitat differences on feeding behaviors of Japanese monkeys: Comparison between Yakushima and Kinkazan

Feeding behaviors of Japanese monkeys (Macaca fuscata) were compared between a warm temperate habitat (Yakushima Island: 30°N, 131°E) and a cool temperate habitat (Kinkazan Island: 38°N, 141°E). The composition of diet and the activity budget in the two habitats were very different. Time spent feeding on Kinkazan Island was 1.7 times that on Yakushima Island. Two factors seem to be responsible for these: (1) the energy required for thermoregulation of monkeys on Kinkazan Island is greater than that on Yakushima Island; and (2) the food quality, which affects the intake speed of available energy, is lower on Kinkazan Island. However, monkeys in both habitats increased their moving time and decreased their feeding time when they fed on foods of relatively high quality. Such foraging strategies are predicted by optimal foraging models. Time spent social grooming on Yakushima Island was 1.9 times that on Kinkazan Island, although there were slight seasonal changes in both areas. The difference in time spent social grooming might be explained by the overall difference in feeding time and day length between the two habitats.     

Mass mortality of Japanese macaques in a western coastal forest of Yakushima

The mass mortality of wild Japanese macaques (Macaca fuscata Blyth) was observed in a warm temperate forest of Yakushima, southern Japan. Demographic changes of eight troops between August 1998 and August 1999 were studied and 56% of macaques disappeared from the five intensively studied troops. Mortality varied among troops: two troops became extinct, while another troop did not decrease in size. The rate of mortality of the other troops was between 33 and 80%. The variation in mortality among the troops was either the outcome of local concentrations of mortality or of intertroop competition. The rate of mortality decreased with increasing distance from the two extinct troops and with increasing troop size; these two factors could not be separated statistically. The direct cause of death was diagnosed as pneumonia for four out of five fresh carcasses. The fleshy fruit production in autumn 1998 was the lowest in 14years, and macaques had relied on leaves earlier than in usual years. It was exceptionally hot and dry in the summer of 1998. The exceptionally poor fruit production and hot summer of this year, with the resulting shortage of high-quality foods, was consistent with the scenario that mass mortality was due to the poor nutritional conditions. However, the possibility that epidemics caused the mass mortality cannot be ruled out. Our findings proved that primates in a seemingly stable habitat experience fluctuations in demographic parameters under natural conditions.     

Population genetical study of Japanese macaques,Macaca fuscata,in the shimokita A1 troop,with special reference to genetic variability and relationships to Japanese macaques in other troops

The genetic variations of 35 individuals of the Shimokita A1 troop of mainland Japanese macaques,Macaca fuscata fuscata, which live at the northern end of the habitat of the species, were investigated using 33 electrophoretically detectable blood protein loci. Among the loci examined, six were polymorphic. The average heterozygosity per individual was calculated as 0.0442. This was the highest value among all troops of Japanese macaques so far investigated. The mainland macaques of the Shimokita A1 troop were more differentiated genetically from other mainland macaque troops than were Yaku macaques, the subspeciesM. f. yakui.     

Vertical distribution of wild Yakushima macaques (Macaca fuscata yakui) in the western area of Yakushima Island, Japan: Preliminary report

A census of wild Yakushima macaques (Macaca fuscata yakui) was carried out in a 23-km² area of the western coast of Yakushima Island, Japan. We analyzed the census data to investigate changes in monkey distribution associated with the vertical distribution of vegetation. In the lowland coastal zone of 0–300 m above sea level (a.s.l.), 4.8 troops and 62.4–99.8 monkeys are estimated to have existed per km². In the mountainside zones of 300–900 m a.s.l., the troop density decreased to 1.3–1.6 troops/km². Since there was no difference in size between the coastal and mountainside troops, population density should decrease with altitude to about 30–36 monkeys per km². On the other hand, 2.4 troops and about 36 monkeys were estimated to have inhabited per km² in the mountain summit zone of 900–1,323 m a.s.l. Nature Conservation College     

Somatometrical features of Japanese monkeys in the Koshima islet: In viewpoint of somatometry,growth, and sexual maturation

The Japanese monkeys inhabiting Koshima islet were investigated morphologically, and compared with those living in other areas of Japan. The morphological features of the Koshima monkeys are thought to reflect many interrelated factors. Their body size is the smallest inMacaca fuscata fuscata. The lower latitude and the warmer winter of the islet represent the major factors in this small body size. Another physical characteristic is their longer limbs, which may be related to the same environmental factors. The adult males of the Koshima troop show the widest variation, while the variation in the adult females is the narrowest, among the troops ofMacaca fuscata examined. This may be explained either by sexually differentiated growth, that is, males continue to grow considerably after 8 years of age, whereas females do not; or by isolation, that is, males sometimes immigrate into or emigrate from the islet, whereas almost of all the females remain there. It was found that the influence of food limitations on body weight depends on sex and age; babies and juveniles, and adult males did not lose their body weight, but monkeys aged from 3 to 7 years and adult females had lost much weight compared to those of the same ages and sexes measured in 1963 (feeding was not limited). This fact may support the idea of “sex-age-class selection” proposed byMori (1979), but the weight loss pattern could be explained by changes of body composition with growth. The growth of the anterior trunk length, too, was restrained. Sexual maturation in males was delayed by at least one year.     

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.     

Regional differences in the infection of wild Japanese macaques by gastrointestinal helminth parasites

A coprological survey of gastrointestinal parasites in wild Japanese macaques (Macaca fuscata), from 14 natural habitats was done. Ova of five nematode species (Trichuris trichiura, Strongyloides fuelleborni, Streptopharagus pigmentatus, Oesophagostomum aculeatum, andGongylonema species) and a worm of the cestode species,Bertiella studieri, were detected. Some differences found in rates of infection by sex were observed in the 14 areas. Differences based on age were found in only troops in which the infection rates ofStrongyloides fuelleborni, Streptopharagus pigmentatus, andTrichuris trichiura were higher in the juvenile monkeys. The number of parasite species was related to the geographical and climatic conditions of the habitat of the troop: troops living in areas cold in winter were infected by fewer parasite species than those in southern warmer areas.     

Social interactions among adult male langurs (Presbytis entellus) at Rajaji Wildlife Sanctuary

A population of langurs (Presbytis entellus)at the Rajaji Wildlife Sanctuary in northern India was investigated for 1820 hr throughout a 10-month period in 1978. Data were collected from four bisexual troops and the adult males that ranged outside of bisexual troops. Most (60%) of the observation hours occurred with a main study troop from which social and ecological data were collected. The langur population at Rajaji shows pronounced birth and mating seasons. The population density is high (ca. 80/km ²), with about 75% of the adult males living outside of bisexual troops, which typically are large and multimale. Males outside of bisexual troops occur in small all-male bands or as isolates. Relations between bisexual troops and all-male bands are characterized by relatively low levels of aggression, and members of all-male bands are able to associate with bisexual troops for prolonged periods during the mating season. As a result of these associations, nontroop males are about as successful as troop males in achieving reproductive access to troop females. These associations between bisexual troops and all-male bands occurred with a minimal amount of agonistic behavior and without mortality or injury to troop females or immatures.