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.     

Palmar dermatoglyphics as a means of identifying individuals in a baboon population

Dermatoglyphic patterns provide a reliable, permanent means of identifying individual primates in wild populations. Unlike the conventional marking techniques applied in wildlife biology, they are not prone to fading, loss, or distortion. Nonetheless, they have not been previously used for identification in primate field studies. We report here two simple techniques for recording dermatoglyphs in the field and describe an application of the method to a long-term study of population dynamics among baboons (Papio hamadryas, sensu lato)in central Ethiopia. Members of a baboon population were live-trapped, and replicas made of their palmar dermatoglyphics, in 1973, 1982, 1983, and 1984. By comparing the 1973 set with the later samples, we were able to identify four animals, two of each sex. All had been subadult or newly adult in 1973, as determined by dental eruption. Eleven years after their first capture, both females were still members of the same troop, although this had apparently amalgamated with a neighboring group. Both males had migrated. One had moved from one olive baboon group to another; the other (a hybrid) had moved from the hybrid zone described by Nagel (1973) into an olive troop. Ten animals were identified in both the 1983 and the 1984 samples, and one of these had previously been recorded in both 1982 and 1973. Establishing identity by means of dermatoglyphics promises to be a useful tool in studies where sampling episodes are widely separate in time.     

Troop size and human-modified habitat affect the ranging patterns of a chacma baboon population in the cape peninsula, South Africa

Differences in group size and habitat use are frequently used to explain the extensive variability in ranging patterns found across the primate order. However, with few exceptions, our understanding of primate ranging patterns stems from studies of single groups and both intra- and inter-specific meta-analyses. Studies with many groups and those that incorporate whole populations are rare but important for testing socioecological theory in primates. We quantify the ranging patterns of nine chacma baboon troops in a single population and use Spearman rank correlations and generalized linear mixed models to analyze the effects of troop size and human-modified habitat (a proxy for good quality habitat) on home range size, density (individuals/km(2) ), and daily path length. Intrapopulation variation in home range sizes (1.5-37.7 km(2) ), densities (1.3-12.1 baboons/km(2) ), and daily path lengths (1.80-6.61 km) was so vast that values were comparable to those of baboons inhabiting the climatic extremes of their current distribution. Both troop size and human-modified habitat had an effect on ranging patterns. Larger troops had larger home ranges and longer daily path lengths, while troops that spent more time in human-modified habitat had shorter daily path lengths. We found no effect of human-modified habitat on home range size or density. These results held when we controlled for the effects of both a single large outlier troop living exclusively in human-modified habitat and baboon monitors on our spatial variables. Our findings confirm the ability of baboons, as behaviorally adaptable dietary generalists, to not only survive but also to thrive in human-modified habitats with adjustments to their ranging patterns in accordance with current theory. Our findings also caution that studies focused on only a small sample of groups within a population of adaptable and generalist primate species may underestimate the variability in their respective localities.     

Troop Extinction and Female Fusion in Wild Japanese Macaques in Yakushima

We observed three cases of troop extinction and two cases of female fusion in the wild population of Japanese macaques on Yakushima Island, Japan. Troops P and T decreased in size relatively slowly over a few years until each troop consisted of only three monkeys. Several months later, the remaining adult female of P merged with the adjacent troop S, followed by the remaining female of T. S subsequently also decreased in size and disappeared about 2 years later. In the early stage of troop decline, the mortality rate of adult females was as low as in a growing troop, but the birthrate was quite low. In the late stage of troop decline, the mortality rate increased and the birthrate remained low. An important factor leading to troop extinction may be an increase in population density and the resulting increase in intergroup competition. During the period when P and T declined and ceased to exist, the range of the adopted troop shifted to cover their previous ranges. In the fused troop, there was no severe aggression directed towards the immigrant females or harassment from residents of the adopted troop and there was affiliative social interaction between the immigrant females and resident members. These results agree with previous reports on female fusion: it occurs when the shrinking group consists of one or no adult member, and the immigrant females are not at a severe disadvantage in their adoptive group. A possible benefit for immigrant females is to avoid disadvantage of one-adult group in conflict with conspecifics. A possible cost for immigrant females is transfer to the other troop or to unfamiliar area or both. The cost to transfer to another group may not be high because the members of the adoptive troop are relatively tolerant to immigrants. The cost to transfer to unfamiliar range may be minimized by immigration to the troop whose range shifted to the immigrants' former range.     

非人灵长类种群数量调查方法综述

监测估算野生动物的种群数量是保护的核心工作。由于气候变化和人类活动的影响,野生动物种群常处于不稳定的状态。非人灵长类是动物界的高等类群,具有复杂的社会行为、丰富的物种多样性,全球有701种 (含亚种),生活在多种类型的栖息地中,包括热带雨林、沼泽森林、红树林、次生林、落叶林、季雨林、山地森林,和包含孤存林、长廊森林、热带旱生林、山地草甸、地中海灌木林的稀树草原和干草原,以及荒漠、干旱的山地,甚至是雪地。绝大多数非人灵长类处于濒危的状态,长期有效的监测对于灵长类的保护十分重要。物种多样性和栖息地类型的多样性使得灵长类种群数量的调查方法多种多样。本文归纳总结了目前常用的非人灵长类种群数量调查方法的类型、基本原理、适用场景和局限性,并以研究实例加以分析;介绍了无人机、热成像、计算机学习系统等新技术应用在调查方法中的进展,希望为今后的非人灵长类野外数量调查、种群监测提供参考和启发。     

Social dynamics of the golden snub‐nosed monkey (Rhinopithecus roxellana): female transfer and one‐male unit succession

Among primates that form multilevel societies, understanding factors and mechanisms associated with the movement of individuals between groups, clans, and one‐male social units offers important insight into primate reproductive and social strategies. In this research we present data based on an 8‐year field study of a multilevel troop of Sichuan snub‐nosed monkeys (Rhinopithecus roxellana) in the Qinling Mountains of China. Our study troop contained 78–126 individuals, and was usually organized into 6–8 one‐male units (OMU). The majority of OMUs were composed of networks of unrelated females and their offspring. We found that 59.7% (43/72) of subadult and adult females in our study troop transferred between OMUs (n=66) or disappeared (n=7) from the troop. In the majority of cases, two or more females transferred together into new OMUs or troops. In R. roxellana, new OMUs formed in several ways. During 2001–2008, 16 adult males appeared in the study troop. Over this period, we observed 13 different males who became harem leaders either by taking over an existing harem or by attracting females from other OMUs into their harem. We also observed four OMUs from a neighboring troop to successfully immigrate into the study troop. The number of individuals in these newly immigrated OMUs was significantly smaller than that number of individuals in resident OMUs. During harem formation, fighting between adult males was rarely observed, and female mate choice appeared to play a crucial role in harem male recruitment and replacement. These results suggest that golden snub‐nosed monkeys are organized in a nonmatrilineal social system. Female mate choice and possibly incest avoidance appear to play important roles in female transfer, male tenure, and OMU stability. Am. J. Primatol. 71:670–679, 2009. © 2009 Wiley‐Liss, Inc.     

Life history and the competitive environment: trajectories of growth,maturation, and reproductive output among chacma baboons

The social environment is a key feature influencing primate life histories. Chacma baboons (Papio hamadryas ursinus) are a female-bonded species with a strict linear dominance hierarchy. In this species, the allocation of energy to competing demands of growth and reproduction is hypothesized to vary as a function of competitive ability, which in turn increases with social rank. Since growth rate is a major component of life history models, measures of age-specific growth were used to analyze variation in life history traits across social ranks. Weights of 42 immature baboons were obtained without sedation or baiting from a troop of well-habituated chacma baboons in the Okavango Delta, Botswana. Using demographic and weight data from this wild population, five main findings emerged: 1) Weight for age and growth rate of infant and juvenile females are positively associated with maternal rank. 2) Male growth is not influenced by maternal rank. 3) Female growth shows smaller variation across feeding conditions than male growth. 4) Low-ranking adult females continue investment in offspring through prolonged lactation until they reach a weight comparable to that of high-ranking infants. 5) The benefit of rank to reproductive success shown in this study is 0.83 additional offspring. Reproductive span determined predominantly by age at maturation contributes 27-38% to the difference in expected number of offspring by rank, vs. 62-73% due to reproductive rate. These findings have major implications for understanding the role of social environment in phenotypic plasticity of life history traits, and in the evolution of primate life histories.     

Intertroop relationships among Japanese monkeys

Intertroop relationships among Japanese monkeys, which have been paid only scant attention for the past 20 years, are examined from several points of view. Japanese monkey troops are generally distributed in such a way as to concentrate locally, that is, to form a local concentration of troops (LCT). About 20% of the nomadic ranges of the troops within LCT's overlap; but in their natural state, they seldom approach but rather to avoid one another. From observations of intertroop encounters at Takasakiyama, where three troops are provisionized and use the same feeding place, it has been found that there exists a dominant-subordinate relationship among troops, that monkeys of each troop have a clear consciousness of belonging to their troop, and that monkeys of different troops rate one another on the basis of their capability. The frequency of male transfer between troops within LCT's is by far higher than between LCT's. In Japanese monkey society, a troop only is a social unit and a social order higher than a troop is not seen; however, it is not impossible to consider an LCT a consanguineally connected group by reason of the transfer of males among the troops within it.     

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.     

Intermale relations and troop male membership changes in langurs (Presbytis entellus) in Nepal

Data on intermale social relations and troop membership changes in one Nepalese high-altitude population of free-ranging langurs (Presbytis entellus)are reported here. Data were collected from six troops by three observers and cover 32 months of observations. The predominantly multi-male troops indicate an alternating pattern of exclusions and introductions with gradual adult male replacement. Takeovers and infant killing were not observed. Analysis of adult social behavior records show qualitative and quantitative differences in intrasexual relations, with primarily agonistic social contacts occurring between males. Agonistic encounters between females and between males differ in frequency of occurrence, types of be-haviors used, cause, and consistency in direction of threats between individuals. Individual adult male frequency of interaction with females and immatures varied significantly, with the majority of these interactions occurring between the dominant troop male and other troop members. Data indicate that intermale dominance is a major factor in determining male access to fertile females: This appears to be achieved by either directly excluding males from the troop or effectively “controlling” their inter-actions with troop females. Data from these studies are compared with data from other Presbytis entellusinvestigations. Review of these data suggests that intraspecific variability in intermale social dynamics and type of troop male membership change are correlated with the percentage of nontroop males. It is suggested that environmental pressures resulting in social crowding can be critical in determing the occurrence of takeovers in some populations of Presbytis entellus.     

Primate population dynamics over 32.9 years at Ngogo, Kibale National Park, Uganda

We present census data for eight primate species spanning 32.9 years along the same transect at Ngogo, Kibale National Park, Uganda, demonstrating major changes in the composition of the primate community. Correlated with an estimated decline of ～89% in the red colobus population was an increase in encounter rates with chimpanzee parties. Our data, along with the unusually high rates of predation by chimpanzees on red colobus at Ngogo and the fact that the chimpanzee community at Ngogo is the largest ever recorded, support the conclusion that the red colobus decline was caused primarily by chimpanzee predation. This seems to be the first documented case of predation by one nonhuman primate causing the population decline in another. We evaluated disease and interspecific competition as other possible causes of the red colobus decline, but judged them to be relatively insignificant compared with predation by chimpanzees. Notable changes in encounter rates with other primate species may have resulted from forest expansion. Those for mangabeys, redtails, and black and white colobus increased significantly. Encounter rates increased for l'Hoest's monkeys too, but the increased sightings may have been an artifact of increased habituation. Sightings of blue monkey and baboon groups declined. There was no significant change in encounter rates for all species combined. The Ngogo primate community seemed to be in a nonequilibrium state, changing from one dominated by two species, a folivore (red colobus) and a frugivorous omnivore (redtails), to one dominated by three species of frugivorous omnivores (redtails, mangabeys, and chimpanzees). This study demonstrates the importance of long-term monitoring in understanding population dynamics and the role of intrinsic variables in shaping the species composition of a community.     

Serotonergic influences on life-history outcomes in free-ranging male rhesus macaques

Several studies have demonstrated that nonhuman primate males with low cerebrospinal fluid (CSF) levels of the serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA) exhibit antisocial behavior patterns. Included in these deleterious patterns are impulse control deficits associated with violence and premature death. No studies to date have longitudinally studied the long-term outcome of young subjects with low CSF 5-HIAA concentrations as they mature into adults. In this study we examined longitudinal relations among serotonergic and dopaminergic functioning, as reflected in CSF metabolite concentrations, aggression, age at emigration, dominance rank, and mortality in free-ranging rhesus macaque (Macaca mulatta) males. Our results indicate long-term consistency of individual differences in levels of 5-HIAA in CSF in the subject population from the juvenile period of development through adulthood. We found a significant negative correlation between 5-HIAA concentrations measured in juveniles and rates of high-intensity aggression in the same animals as adults. Further, CSF 5-HIAA concentrations were lower in juveniles that died than in animals that survived. For the young animals that migrated there was a positive correlation between CSF 5-HIAA concentration and age at emigration, whereas for the animals that remained in their troop until later in sexual maturity there was a negative correlation between CSF 5-HIAA concentration and age of emigration. After animals emigrated to a new troop, social dominance rank in the new troop was positively correlated with early family social dominance rank, but inversely correlated with juvenile CSF 5-HIAA concentrations. Taken together, our findings suggest that males with low central serotonin levels early in life delay migration and show high levels of violence and premature death, but the males that survive achieve high rank. These findings indicate that longitudinal measures of serotonergic and dopaminergic functioning are predictive of major life-history outcomes in nonhuman primate males. Low concentrations of CSF 5-HIAA are associated with negative life-history patterns characterized by social instability and excessive aggression, and positive life-history patterns characterized by higher dominance rank.     

Analysis of population changes by measurement of body weight in the Koshima troop of Japanese monkeys

Measurements of the body weight of monkeys in the Japanese monkey troop on Koshima islet in southern Japan have been made since 1970. Population changes in the troop have been recorded since 1952. The population changes were further analyzed on the basis of the body weight changes of the troop members. The recent history of the Koshima troop can be divided into three periods differing according to conditions of artificial feeding: (1) a semi-wild period (SW Period, 1952–63); (2) an artificial feeding period (AF Period, 1964–71); (3) and a restricted artificial feeding period (Non-AF Period, 1972–77). The AF Period represented a period of population growth, whereas the Non-AF Period was a declining one when the population density of the troop was roughly ten times that of most wild troops. These population changes, i.e., changes in population parameters especially in the population declining phase, could be fairly well understood from the general features of the body weight changes of the troop members, the slow body weight growth, elevation of age at first birth, and small size of adult females. Reproduction and survival were affected by seasonal and yearly changes in body weight. The pattern of changes in body weight displayed seasonal peaks in the autumn and spring. Of these, the former suggests that fruit eating in the autumn is an important factor in the reproduction and growth of the monkeys.     

Habitual fission-fusion and social organization of the Hakone troop T of Japanese macaques in Kanagawa prefecture,Japan

To analyze the socioecological factors of habitual fission-fusion of troop members, which is an underreported phenomenon in Japanese macaques, the seasonal pattern of fission-fusion within the Hakone troop T in Kanagawa Prefecture, Japan, was examined. Although almost all the study troop members were included in a large-sized group in winter, a portion of its members of ten formed small subgroups from spring to autumn. The frequencies and age-sex composition of these subgroups changed seasonally. All troop members participated, more or less, in subgroup formation. Subgroups tended to be composed of animals of the same age-sex class. Troop members did not fission along matrilineal lines. Although the study troop members repeatedly joined with and parted from subgroups, the characteristic social structure of Japanese macaque troops was maintained. Habitual fission-fusion among troop members may be one of a number of foraging strategies that facilitate efficient food gathering when the population density exceeds and /or reaches the carrying capacity of the area. The seasonal variation of pattern and composition type of each subgroup could be attributed to alternation of attractive food plant species, as well as age, rank, and sexual activity of both sexes.     

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.     

Primate Communication: By Nature Honest, or by Experience Wise?

We review evolutionary views on honesty and deception and their application to studies of nonhuman primate communication. There is evidence that some primate signals are likely to be accurate on the basis of costliness. They appear most often in contexts that include overtly competitive interactions in which unrelated individuals have limited access to information about one another. However, both game theoretic models and most empirical work suggest that costly signals are not often likely to be the basis for honest communication in nonhuman primates. Inexpensive signaling can exist in contexts wherein communication occurs among related animals, something common among many nonhuman primate societies. Another condition in which inexpensive signaling is possible and that is also typical of nonhuman primates, is when sender and receiver both benefit from coordinated interactions. Additionally, when individuals interact repeatedly and can use past interactions to assess the honesty of signals and to modify future response to signals, low-cost signals can evolve. Nonhuman primates appear to deal with the problem of deception via skeptical responding, which can be largely accounted for by learning rules and the fact that they live in stable social groups and can recognize one another and recall past interactions.     

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.     

Evidence of allomaternal nursing across one-male units in the Yunnan snub-nosed monkey (Rhinopithecus Bieti)

Background

Allomaternal nursing, common in several species of social mammals, also has been reported in nonhuman primates. However, the function of this behavior in enhancing infant survivorship remains poorly understood.

Methodology and Principal Findings

The study was conducted on a free-ranging group of the Yunnan snub-nosed monkey (Rhinopithecus bieti) in the Baimaxueshan Natural Reserve. Direct observation and ad libitum sampling were used to record allocare behavior during a 20 month field study. R. bieti exhibits a multilevel social organization in which a large single troop, consisting of over 100 individuals, is divided into many one-male units (OMUs: 6∼41). These OMUs coordinate their daily activities, and feed, forage, travel, and rest together. Here we report on one case of infant temporary adoption in which an adult female from one OMU engaged in allomaternal nursing and cared for an infant from a different OMU of the same troop. This event began when the mother and her five-month-old infant were found to became separated accidentally. The victim infant was observed staying in another OMU. Over the next several days we observed a lactating female in the new OMU to care for and nurse both her infant and the immigrant infant, who also was tolerated by and cared for by the harem male.

Conclusions and Significance

Our findings suggest that lactating primate females are primed to care for young infants and, that the misdirected parental care hypothesis may offer the strongest explanation for allomaternal nursing in R. bieti.     

Kinship in colonial tuco-tucos: evidence from group composition and population structure

Kinship plays a significant role in shaping the social and geneticstructures of many vertebrate populations. Evidence of kinship,however, may be substantially influenced by the spatial andtemporal scales over which co-ancestry is monitored. For example,while data on social group composition may yield little indicationof relatedness among reproductive partners, data on the demographicstructure of a population may reveal considerable shared ancestryamong mates. We explored relationships among social group composition,individual movements, and population-level patterns of kinshipusing data from a 7-year field study of the colonial tuco-tuco(Ctenomys sociabilis), a group-living subterranean rodent thatis endemic to southwestern Argentina. Our analyses indicatethat social groups are composed of 1–4 generations ofclosely related females and a single, immigrant male, suggestingthat reproductive partners are not related to one another. Monitoringindividual movements, however, revealed that (1) most male dispersaloccurs within the local population and (2) most new social groupsare founded by females born in the study population, indicatingthat individuals reared in different burrow systems may shareconsiderable co-ancestry. Simulation analyses revealed thatup to 67% of reproductive partnerships consist of animals thatshare co-ancestry within the last 5–7 generations. Thus,while analyses of social group composition provide little evidenceof kinship among reproductive partners, population-level analysesof dispersal and group formation suggest that co-ancestry amongmates is common. These findings have important implicationsfor interpreting social interactions and genetic structure inthis species.     

Influence of artificial food supply on population parameters and dispersal in the Hakone T troop of Japanese macaques

A free-ranging troop of Japanese monkeys was observed for seven years from April 1971 to March 1978 in the Hakone area, Kanagawa Prefecture, Japan. This troop was fed artificially between 1956 and 1977. The artificial food supply was reduced by about half after 1974. The troop-size fluctuated around 100 between 1971 and 1974, but fell drastically from 91 in 1975 to 58 in 1978. Population parameters were compared between the two periods of 1971–1974 and 1975–1977. Clear differences between the two periods were found in primiparous age, ratio of non-natal resident males to all resident males, ratio of newcomers to non-natal resident males, age-specific disappearance rate, and proportion of deserters observed in the study area. A correlation existed between the number of males and females of 5 or more years of age in the troop. The numbers in the three age-sex groups (natal males, non-natal males, and females of 5 or more years of age in the troop) were closely connected with one another. The scarcity of food supply may have caused not only males but also females to disperse. The drastic decrease in troop-size after 1974 could be based on the disappearance of adult females. The cause of the dispersal of young males and adult females could have been mutual competition among the troop members for food, and that in adult males could have been competition for females.