Affiliative relations among male Japanese macaques (Macaca fuscata yakui) within and outside a troop on Yakushima Island

Male Japanese macaques (Macaca fuscata yakui) in a troop on Yakushima Island frequently groom other males. However, previous studies have not compared the social relations of troop males to those of non-troop males. I followed all troop males and non-troop males in and near a troop during a mating season and during the following non-mating season and recorded their neighbors, grooming, and agonistic interactions. Comparisons of the social relations of troop males and non-troop males with other troop members revealed that grooming and agonistic interactions with females during the mating season were similar between troop and non-troop males. However, troop males groomed each other more often and had fewer agonistic interactions among themselves than did non-troop males. Compared to what occurred in the mating season, troop males groomed females less often and exchanged grooming bouts more often with other troop males during the non-mating season. One non-troop male groomed females more frequently than did any troop male in both seasons, and this male groomed troop males more frequently than did any troop male in the non-mating season. This male immigrated into the troop during the following mating season. Regardless of their competition with respect to reproduction, male Japanese macaques on Yakushima Island maintain affiliative relations, probably to cooperatively defend fertile females from non-troop males.     

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.     

Influence of fluctuation in the operational sex ratio to mating of troop and non-troop male Japanese macaques for four years on Kinkazan Island, Japan

Taking advantage of a marked yearly fluctuation in the number of estrous females, I studied the differences in mating success between troop males and non-troop males in an unprovisioned group of Japanese macaques. Fluctuation in the defendability of estrous females by troop males, as predicted by the operational sex ratio (the number of estrous females per troop male), strongly affected the mating with ejaculation (successful mating) per observation day of both troop and non-troop males. When operational sex ratio was low, troop males monopolized successful mating inside the troop. No successful mating of non-troop males was observed inside the troop. In contrast, both troop and non-troop males were able to mate often inside the troop when operational sex ratio was high. These findings suggest that troop males obtained the benefit of secured successful mating in the troop because troop males could mate successfully even in mating seasons with a low operational sex ratio, and the chance of successful mating for non-troop males will increase as the ability of troop males to monopolize estrous females decreases.     

Dominance status of adult male Japanese macaques: Relationship to female dominance status,male mating behaviour,seasonal changes,and developmental changes

Aggressive dominance orders of all adults in a confined troop of Japanese macaques (Macaca fuscata) were determined each mating and birth season during a 4-year interval. Males outranked more females in the mating than in the birth season, and some males shifted back and forth from ranks lower than female ranks in the birth season to ranks higher than female ranks in the mating season. Mating behaviour (number of female partners in mount and ejaculation series and ejaculation frequency) did not differ among males with ranks higher than, as high as, or lower than those of most females, nor did individual males mate more in years, when they were high-ranking than in years when they were not. There was a correlation, however, between ejaculation frequency and the number of females defeated by males. A pattern of increasing male rank with age was found.     

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.     

Measuring male-female relationships during the mating season in wild Japanese macaques (Macaca fuscata yakui)

Heterosexual relationships during one mating season were examined in a wild troop of Japanese macaques (Macaca fuscata yakui) on Yakushima Island, Japan. Validation tests of putative mate choice behaviors demonstrated that female initiation and maintenance of proximity, female lookback at the male, and sexual presents to the male, were associated with increased mating. Male grooming the female was also associated with increased mating. Ten dyadic social behaviors were subject to principal components analysis to empirically define behavioral dimensions of male-female relationships. The analysis yielded four relationship dimensions: ‘Mutual Choice and Male Coercion,’ ‘Female Choice’ (two types), and ‘Mutual Choice’ Dyads tended to be characterized by more than one dimension. The results suggested that females sought matings with multiple males of various dominance ranks. Female relationships with high ranking males contained elements of male coercion and mate guarding, however, because these males attempted to inhibit females from mating with lower ranking males. The correlation between each relationship dimension and mating success depended, in part, on the dominance rank of males. Relationships involving high ranking males, which were most likely to contain elements of male coercion and mate guarding, were associated with mating success. Relationships involving low ranking males, which usually lacked such coercive elements. were less strongly correlated with mating success. These results, obtained from a wild troop, are compared to those previously obtained in captive and provisioned groups of Japanese macaques.     

Do males have a better chance of mating when the number of estrous females is equal to or greater than the males' ordinal rank? Testing the hypothesis in Japanese macaques

This study was designed to test the hypothesis that male primates in multi-male/multi-female social groups with a clear male dominance hierarchy have a better chance of mating when the number of estrous females is equal to or greater than, as opposed to less than, the males' ordinal rank. I studied a Japanese macaque (Macaca fuscata fuscata) troop during mating seasons from 1992 to 1995. The mean daily operational sex ratio (OSR; the number of estrous females per troop male), which was calculated on observation days, was 0.21, 1.9, 0.48, and 3.1 in 1992-1995, respectively. Overall, focal animal sampling of males yielded 118 male-day records. The male-day records for each male were divided into the two estrous female number conditions: 1) the male-day records when the number of estrous females was equal to or greater than the male's ordinal rank, and 2) the male-day records when the number of estrous females was less than the male's ordinal rank. In the 1993 and 1995 mating seasons, when the number of estrous females was equal to or greater than the ordinal rank of each male, all of the males were observed mating. Conversely, when the number of estrous females was less than the ordinal rank of some male, they were not observed mating in the 1992 and 1994 mating seasons. The percentage for each male across each male's total mating opportunity was <20% when the number of estrous females was less than the male's ordinal rank. By contrast, the percentage for each male across each male's total mating opportunity exceeded 45% when the number of estrous females was equal to or greater than the male's ordinal rank, except for one male. Of all the male-day records for males observed mating with ejaculation, 41 were obtained when the number of estrous females was equal to or greater than the male's rank; conversely, only three records were obtained when the number of estrous females was less than the male's ordinal rank. Therefore, it appears that males have a better chance of mating when the number of estrous females is equal to or greater than the males' ordinal rank, as opposed to when the number is less than their ordinal rank.     

On the fission of troops of Japanese monkeys

The troop fission of Japanese monkeys has been observed in 11 troops, and the total number of fissions observed numbered 22. Examined cases of fission relative to season, amount of food, troop size and socionomic sex ratio of the main troop and to individuals that acted as nucleus in forming a branch troop and females, exhibited variance, not being uniform. But inquiry into troop fission as seen from the standpoint of the mechanism maintained by Japanese monkeys' society indicated (1) troop fission checks the growth of troop size and increases the socionomic sex ratio of the main troop, (2) troop fission is an effective mechanism for the maintenance of class structure among adult males, and (3) the possibility that troop fission functions to check inbreeding.Thus, it must be said in general that troop fission, along with single desertions of males, plays a very important role as one mechanism for the maintenance of the society of Japanese monkey. However, the branch troop is often composed of a large number of males and a small number of females; in short, it is under very difficult conditions that a branch troop starts on its way to becoming a fully established Japanese monkey troop.The troop fission is an effective mechanism for the maintenance of the main troop, but not too effective for that of the branch troop.It cannot be said that there are abundant data on troop fission of primates other than Japanese monkey. But, from limited data, we can find various forms of troop fission according to each species, and it may be ultimately related to the maintenance mechanism of the primate society.     

Male aggression and the sexual behavior of Japanese monkeys

The factors that regulate male aggressive behavior towards females during the mating season and their relationship to the sexual behavior of Japanese monkeys were investigated. Observations were made on the Shiga A troop in Nagano Prefecture for 132 days during both the non-mating and mating seasons in three successive years. As a result, chasing towards females was observed in males older than 4 years. The frequencies of this type of behavior increased in the mating season. The chasing rank of the individual males did not correlate with the male dominance rank but with the tree-shaking rank. Chasing was directed not only at estrous females but also at non-estrous females. Pairs of both sexes in which chasing was observed, tended to have sexual interactions. Both hormonal and social factors should be considered in the regulation of chasing. The role of aggression in the formation of new male-female bonds in discussed.     

Display behavior of three troops of Japanese monkeys (Macaca fuscata)

In this paper the display (i.e., “branch-shaking”) behavior of three troops of Japanese monkeys—the confined Oregon troop as reported byModahl andEaton (1977), the semi-free-ranging Arashiyama West troop and the free-ranging Arashiyama B troop—are compared. The comparison reveals several similarities and dissimilarities between the Oregon troop and the two genetically related Arashiyama troops. The similarities include three display postures (shaking, kicking and leaping) and an increased frequency of male but not female displaying during the breeding season. The dissimilarities include the absence of two Oregon display postures (tossing and swinging) and collective displaying among Arashiyama monkeys. The hypothesis ofModahl andEaton (1977) that male displaying influences the females' choice of male mating partners is discussed. The evidence suggests the Oregon monkeys have incorporated male displaying into their socio-sexual behavior to a greater extent than Arashiyama monkeys. However, field observations indicate that males who migrate to the Arashiyama B site during the breeding season can influence female choice by “advertizing” their location with displays.     

Group fission in a semifree-ranging population of Barbary macaques (Macaca sylvanus)

During a 16-month study of semifree-ranging Barbary macaques (Macaca sylvanus) the group under observation divided into two groups. Observations were carried out in 1987–1988, at «La Montagne des Singes,” Kintzheim, France. A subgroup of monkeys, which was already cohesive at the beginning of the study, became progressively autonomous in relation to the rest of the main group, during the mating season. Overt aggression between the males of the two groups during this period brought about the fission. Only low-ranking genealogies left their group of origin. Dominance relations between females remained identical in both groups except for one lineage. The alpha male and the alpha female of the subgroup had a close relationship before the fission occurred. The sequence of agonistic intergroup relations is described and analyzed in relation to male sexual competition and female alliance power. The results suggest that: (1) the males of the subgroup instigated the fission because it was the best strategy for them to counter sexual competition; and (2) the females followed the males in order to maintain their alliance network, necessary to insure their dominance status over subordinate females.     

Female mating strategy in an enclosed group of Japanese macaques

Female Japanese macaques (Macaca fuscata) are noted for mating with multiple males and for their ability to exert mate choice. In a captive group of Japanese macaques housed at the Primate Research Institute of Kyoto University, Japan, behavioral and endocrine data were combined to examine female mating strategies. During one breeding season, daily behavioral observations were conducted on females who exhibited copulatory behavior. Blood was collected from females twice weekly and their ovulatory periods estimated by analyzing hormone profiles. Females began mating shortly before ovulation, peaked at ovulation, and continued receiving ejaculations for up to ten weeks after conception. Females were more responsible than males for inbreeding avoidance with matrilineal kin. Males sometimes approached females from their own matriline, but females avoided such males and expressed mate choice behavior preferentially toward non-matrilineal males. Over the entire mating season, females did not choose non-matrilineal males on the basis of displays, dominance rank, age, weight, or weight change during the mating season. When females were likely to conceive, however, they expressed mate choice behavior toward males who displayed most frequently. Female mating strategy may include both mate choice at ovulation and other, non-procreative functions.     

Homosexual incest avoidance among females in captive Japanese macaques

This paper reports a systematic pattern of homosexual incest avoidance among females in a captive group of Japanese macaques (Macaca fuscata) culled from the Arashiyama-West troop known for its high rates of female homosexuality. The study group included three matrilines and two generations. Between eight and 11 females were sexually active over four consecutive mating seasons, and all engaged in both heterosexual and homosexual activity. While all females performed homosexual acts with almost all possible non-kin partners, they systematically avoided homosexual interactions with their mother, daughters, and sisters. This pattern could not be explained either in terms of kin not being simultaneously in estrus, kin avoiding affiliative interactions in general, or non-kin utilizing the tension-reducing effect of estrus to affiliate exclusively with each other. In contrast to homosexual females, heterosexual pairs of relatives (brother-sister, mother-son) were sometimes incestuous. Assuming that female homosexuality expresses the reproductive strategy of females unconstrained by male influence, the present results point to the strong tendency of females to avoid incest and suggest that males are primarily responsible for the reported exceptions to incest avoidance.     

Female Defensibility in a Small Troops of Japanese Macaques vis-à-vis Nontroop Males and Copulation on the Periphery of the Troop

I provide data compiled over 4 yr on the mating behavior in small troops of wild Japanese macaques on Yakushima Island. The key parameters are the number of sexually receptive females, the number of nontroop males (NTMs), and copulation on the periphery of the troop. I analyzed the following aspects: 1) changes in the proportion of copulation with high-ranking males (HRMs) and NTMs, 2) variations in factors such as fluctuation in the number of sexually receptive females and troop males and their effects on the number of visiting NTMs, 3) the effect of attempted interruption of mounting series by other males, and 4) some aspects of copulation on the periphery of the troop. Throughout the study, 56% of the total number of females mated most frequently with the α-male in a single mating season. However, the relative mating success of HRMs varied over the years and between individuals. The number of visiting NTMs varied depending on the number of receptive females and troop males. Females tended to mate with the NTMs when they appeared around their troops. The direct effect of interruption of the mounting series by other males is equivocal. The females mated with the low-ranking males (LRMs) and NTMs on the periphery of the troop, which increased the possibility of mounting series ending with ejaculation. Females actively sought opportunities for copulation on the periphery of the troop by moving there or initiating close proximity with LRMs and NTMs there. On Yakushima Island, the mating success of HRMs was not always as high as that predicted by the priority of access model. The injury status of the HRM, the number of visiting NTMs, and female choice are all considered to influence a male’s mating success.     

The behavior of peripheral males during the mating season inMacaca fuscata

The mating season behavior of peripheral male Japanese macaques (Macaca fuscata) at Arashiyama West were studied during the 1994/1995 mating season. Although all peripheral males increased their proximity to the main troop, there was great variation in this behavior, from those who became virtually indistinguishable from the main troop males to those who moved in and out of the main troop in a clandestine fashion, to those who had only visual contact, from a distance of 25 m, with the main troop. The subsequent behavior of males displaying these patterns was compared, as was the behavior of peripheral to main troop males. Specifically, they were investigated for variation in three behavioral strategies which may function to increase access to mates: aggressive intimidation; affiliation with unrelated main troop females; and courtship display. The results show that peripheral males are a more diverse group than previously described, and that one group of peripheral males was able to successfully join the main troop, becoming indistinguishable from main troop males with regard to these behaviors which enhance access to mates.     

Seasonal rank changes for adolescent and subadult natal males in a free-ranging group of rhesus monkeys

Changes in dominance rank for adolescent and subadult natal males in a semi-free-ranging rhesus macaque group were seasonal. Three 4-year-old natal males of the highest-ranking matriline occupied high ranks in the adult male dominance hierarchy during the premating period. In the mating season they dropped in rank, and this decrement was related to a concomitant drop in their alliances. After the mating season, these males rose in rank along with their two 3-year-old kin to occupy ranks 2–5 and 7–8 in the adult male dominance hierarchy. Three-year-old natal males of matrilines lower ranking than first did not become integrated into the hierarchy at this time.     

Sexual strategies of female Japanese macaques (Macaca fuscata)

Evidence is reviewed that female Japanese macaques have multiple male mating partners when they are available and show a preference for mating with sexually unfamiliar males. Several lines of evidence suggest that this aspect of female sexual behavior results in the offspring of an individual female being sired by more than one male thereby maintaining the genetic diversity of the troop. Evidence is presented in this paper that a decrease in the number of adult troop males and a lack of extra-troop migrant males in the Arashiyama West troop of Japanese macaques following transplantation to a ranch in south Texas had consequences for the sexual behavior of the females.     

Who is Responsible for Fission in a Free-ranging Troop of Baboons?

The study troop of chacma baboons (Papio cynocephalus ursinus) at Mkuzi Game Reserve, Zululand, South-Africa, comprised of about 76 members that split into two new troops. The events leading to this troop fission will be described and its possible causes will be discussed. Troop fission among baboons is generally attributed to the withdrawal of low-ranking females from the main group, as a result of the cost of food competition and its effect on their reproductive success. At Mkuzi, no evidence for food competition among females was recorded in terms of rank-related time spent feeding or other time—budget components, feeding-bout length, diet composition or context of female aggression. Moreover, no evidence for rank-related differential reproductive success was found in terms of inter-birth intervals or infant survival. Female mortality was, however, related to dominance rank, with circumstantial evidence suggesting that cause of mortality was predation by leopards. Rate of female disappearances, aggression levels among females, and the percentage of time they spent in proximity to other adult troop members increased after fission. Relatively short inter-birth intervals and extremely low infant mortality rate at Mkuzi resulted in a small number of receptive females at any one time, and therefore in high costs of male sexual competition as expressed in the high levels of male aggression and woundings, both reduced after fission. It is suggested that this troop fission may have been initiated by the resident males, triggered by the high cost of sexual competition, and forced on the females, who were, consequently, subjected to higher risk of predation. The troop fission was preceded by a long process of increasing tendency for sub-trooping. It was initiated by the four resident males who kept a large distance apart from each other, herded oestrous female associates away from others and were followed by other females. The females generally tended to stay close to associates, males and females. These parties were followed by the peripheral and immigrant males who had no female associates, and eventually two distinct daughter troops were formed.     

Demography, range use, and behavior in black lemurs (Eulemur macaco macaco) at Ampasikely, northwest Madagascar

We studied a black lemur population over a 2-year period (1992-1993) and 8 years later (2000) in a 50-ha secondary forest in northwest Madagascar. All of the animals were marked to investigate population dynamics and seasonal variation in ranging and behavior, and new data on black lemurs were obtained. Our data on demographic characteristics were expanded to include other forest sites and contrasted with those collected in other Eulemur macaco macaco field studies, in relation to human activity and the presence of introduced and cultivated plant species. Density is affected by deforestation and hunting. Group size and home range depend on the composition of the forest and probably food patches. Sex ratio at birth varies according to the number of females per group, a result that fits the local resource competition model. Groups are multimale-multifemale, and adult females form the core of the groups. Reproductive parameters indicate sharply defined seasonal breeding, a high female reproductive rate, and birth synchrony. Changes in group composition reveal male and female juvenile dispersal, male transfer between groups at the time of mating, and adult female transfer and group fission when groups exceed a critical size. At mating and birth, intergroup agonistic encounters occurred at home-range boundaries, and larger groups were dominant over smaller groups. Patterns of intragroup interactions suggest that males compete for access to groups of females during the mating season, and that females may compete for food resources during the birth season. Our study also reports female social dominance and lack of sexual weight dimorphism in this species.     

Secondary sex ratio variation in the Cayo Santiago macaque population

Secondary sex ratios (SSR) were calculated from 1,385 offspring delivered by 372 females in the Cayo Santiago population of free-ranging rhesus monkeys (Macaca mulatta) from 1976 through 1984. The SSR for the entire colony ranged from 0.86 to 1.46 males per female (combined total: 1.08), but no significant difference was observed (P > .05). SSR values were compared among the troops for each year. The SSR differed significantly among the six social groups (P < .05) only in 1978. The annual SSR of each troop was compared over 9 years. Significant variation was found only in group O. The annual SSR was significantly skewed (P < .05, males > females) for three troops in 3 separate years. The SSR did not vary according to troop rank. No significant difference was found among the 17 matrilines of the population, but comparison of matrilines within each social group revealed a significant difference in the SSR (P < .02) for the three matrilines in group I. This was due to the significantly skewed SSR (P = .0080, females > males) of the DM genealogy in that troop. SSR values were not related to matrilineal rank. Individual dominance rank did not bias the SSR. Complete reproductive histories for 266 females showed no evidence of significantly skewed SSR values. Age-related effects on the SSR were examined by using cross-sectional and cohort-based analyses. The SSR did not vary significantly (P > .05) with maternal age, but it was significantly skewed (P < .05) toward males at the ages of 5 and 9 years. Parity had no significant effect (P > .05) on SSR values. Wide variation occurred in the SSR of the Cayo Santiago population. Rank-related adjustment of the SSR at the level of the troop, matriline, or individual, as reported in short-term studies of other primate social groups, may reflect normal annual variation in the SSR evident only from longitudinal observations of large multigroup primate populations.