On the dynamics of the hanuman langur populations of jodhpur (Rajasthan,India)

The city of Jodhpur (26°18′N, 73°8′E) supports a population of about 900 hanuman langurs (Presbytis entellus) divided into 24 bisexual troops and 12 all-male bands in an area of 60 km². This population has been censused from 1968 to 1978. Over this period the population of bisexual troops has remained stable around 700, while the population of all-male bands has increased from 160 to 230 individuals. The bisexual troops show a tendency towards a reduction in population growth rate with increasing troop size, with troops over 50–60 tending to split. Very small troops may grow by large scale immigration. Although a number of male changes and mortality through infanticide have been recorded, there is no evidence of a regular periodicity in the occurrence of initial, growth and mature phases in the life history of a bisexual troop. Unlike the bisexual troops, the all-male bands show no tendency towards a reduction in growth rate with the increase in band size, but show a continuous growth of band size over the study period. Langurs of Jodhpur rely heavily on cultivated fields for their sustenance. This cultivation has been on increase over the study period, and since the males invade cultivation more readily, they may have been able to take fuller advantage of these increasing resources and affect a population increase that has not been possible for the bisexual troops.     

Ecology and behavior ofPresbytis thomasi in Northern Sumatra

A field study of 23 bisexual troops, ranging in size from 3 to 21 members ( =8), and two all-male groups of the Thomas's leaf monkey (Presbytis thomasi) was conducted in North Sumatra from November 1981 to April 1984. Most troops (N=19 or 82.6%) contained only one adult male. Two troops and one group were most intensively studied. The home range was 12.3–15.7 ha for the two bisexual troops, and only 1.7 ha for the one, all-male, ten-member group. Fruits composed more than 50% of their diets. Vocalizations were classified into 13 types. Births occurred at any time of the year. Among three males of a bisexual troop, serious fights were observed: two males died of wounds and the former beta male became the new alpha male. After this social change, the home range area of this troop gradually shifted eastward. But, 3.5 months after the social change, a 9-month-old infant male stayed alone in the western part of its former range. Thereafter, he became a solitary male and sometimes went into the riverine area of the Bohorok river. The occurrence of male replacement suggests instability of multi-male organization in bisexual troops. Moreover, the different mortality rate between males and females and the unequal sex ratios forced by the formation of one-male troops, maintained high tension levels among males competing on females.     

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.     

Social stability and change among forest hanuman langurs (Presbytis entellus)

The social organization of hanuman langurs (Presbytis entellus, Colobinae) was studied in Kanha Tiger Reserve, Central Indian Highlands between 1980 and 1983, followed by six brief return visits over ten years. Censuses of the 7 km² Kanha meadows demonstrated little change in population density and structure between 1982 and 1990; the population was consistently composed of one-male troops and all-male bands. During the return visits the focal C troop extended its known 74.5 ha range by only 5.6%. By 1993 two identified, habituated, adult females remained within the troop. The adult male was resident in C troop for ≥nine years and eight months.     

Fate of ousted male residents of one-male bisexual troops of Hanuman langurs (Presbytis entellus) at Jodhpur,Rajasthan, India

Little is known about the fate of adult male residents after they are ousted from bisexual one-male troops of Hanuman langurs (Presbytis entellus) in the course of adult male replacements. In a long term study at Jodhpur, Rajasthan, it was possible to reconstruct partial life histories of several ousted residents. One resident was killed during the male change. Ousted residents did not regain residency despite their continued invasions into bisexual troops. It is assumed that the males' chances to take over and to defend a troop are restricted to an age of 9–14 years, when the males are in prime physical condition. One male became solitary for some months while trying to regain residency of his old troop, before joining some “alien” males. As a rule, males are likely to rejoin their own male bands if they are ousted after short periods of residency. If the residency exceeds 3 months then the ongoing structural change in the former band may prevent their reintegration. However, in such cases, ousted residents which belonged to the same band may reunite and mingle with another male band which lacks prime males. Weaned sons may follow their fathers after ousting. In the case of numerous weaned offspring, fathers and sons may together form at least temporary new male bands.     

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

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

The variable social organization of hanuman langurs(Presbytis entellus), infanticide,and the monopolization of females

Data from 24 wild populations of hanuman langurs (Presbytis entellus)in south Asia are used to test hypotheses seeking to explain variation in troop structure and the incidence of infanticide. The occurrence of infanticide is associated with a one-male troop structure and not with a high density. The density, predation, and economic-advantage hypotheses, as explanations for the occurrence of one-male and multimale troops, are not supported by the review. However, the monopolization hypothesis is not contradicted; the number of adult males per troop is significantly correlated with troop size and with the number of adult females per troop. Therefore it is suggested that a one-male troop structure will arise if a male is able to monopolize a group of females, a multimale troop if he cannot. One-male troops may predispose to infanticide because of high variance in male mating success and high intermale competition between groups rather than within troops. If female dispersion determines troop structure, it is speculated that females could manipulate males to form a multimale society if the advantages in terms of infant survival and intertroop conflict exceeded the costs in terms of not producing infanticidal “sexy sons.”     

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.     

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.     

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.     

Status of Trachypithecus geei in a Rubber Plantation in Western Assam, India

Golden langurs (Trachypithecus geei) are an endangered species in a limited area of Northeast India and Bhutan. They are confined to a forest belt in western Assam between the Manas River in the east, Sankosh in the west and Brahmaputra in the south along the Indo-Bhutan border. Due to habitat destruction, their populations are restricted to fragmented forest pockets, especially in India. We compared data on an isolated population of golden langurs in the rubber plantation of Nayakgaon in the Kokrajhar district of Assam, May 2002 with an earlier census in 1997. We counted a total of 52 individuals in 3 troops in 2002. The average troop size is 17.3 (r = 7–26). The ratio of adult male to adult females is 1:3.16. Of the total population 9.6% were adult males, 21.1% were adult females, 17.3% subadult males, 7.7% subadult females, 19.2% juveniles and 25% infants. In 1997 Srivastava et. al., recorded 38 individuals in 5 troops with an average troop size of only 7.6 . Apparently troop fusion has occurred. The increased population is encouraging.     

Adult male replacement and social change in two troops of hanuman langurs (Presbytis entellus) at Jodhpur,India

I studied the process of adult male replacement and social change in two one- male troops (B20 and B21) of hanuman langurs (Presbytis entellus)at Jodhpur, India. Male-male competition lasted for about 6 months before the successful takeover of one troop (B20). During that period, five adult males from three neighboring bands (AMB7, AMB9, and AMB10) and a resident male of a neighboring troop (B21) were involved in taking over the troop. The latter male also copulated with six females during his interim residency, which suggests that he may have opportunistically maximized his mating chances with females of a neighboring group. During an intertroop interaction, a 14-month-old female infant of the other troop (B21) was fatally attacked by an adult female of the first troop and the infant eventually died. The attacker may have taken advantage of the disorganization created by male-male competition, perhaps to eliminate a future food competitor. In addition, the first troop gained an additional feeding area from the other troop’s range; it included a sleeping site and a waterhole, indicating that territorial fights during social instability may have led to the expansion of the winner’s resource area.     

Long distance mobility of male Japanese macaques evidenced by mitochondrial DNA

A 487-nucleotide sequence in the polymorphic D-loop region of matrilineally inherited mitochondrial DNA was compared in samples from 14 (9 adult males and 5 females or young) Japanese macaques (Macaca fuscata fuscata) of two troops at Gagyusan in Takahashi City, Okayama Prefecture, Japan. The majority (7 out of the sampled 9) of the adult males associated with the troops had nucleotide sequences of six distinct types, all of which were different from that of the Gagyusan troop females, whereas two young solitary males shared the same sequence. The present study exemplified a case in which the majority of adult males immigrated from outside the local population. Notably, two of the males were revealed to share the same sequence determined for a matriline 45 km away. Electronic Publication     

Male life history in natural populations of Japanese macaques: Migration, dominance rank, and troop participation of males in two habitats

This paper compares male life history parameters of two populations of Japanese macaques (Macaca fuscata Blyth, 1875), studied without provisioning: Yakushima (M. f. yakui), a subtropical forest habitat in southwestern Japan, and Kinkazan (M. f. fuscata), a temperate, deciduous forest habitat in northeastern Japan. The males of the two sites experienced similar life histories with respect to several traits. Age at natal dispersal was at about 5 years. Average troop residence was about three years. Most males joined troops at the bottom of the rank order, although a few males joined troops at the top rank. Dominance ranks of males tended to rise with the death or departure of higher ranking males. Visiting males accounted for about 41% of observed mating at both sites. However, the two sites differed in the sex ratio of troops, partly because a larger proportion of males apparently lived outside of troops in the Kinkazan site compared to Yakushima. In particular, non-natal young males were absent from the main study troop at Kinkazan. Large within-species variation may exist in the degree to which males associate with troops.     

Social Relationships Among Ring-Tailed Lemurs (Lemur catta) in Two Free-Ranging Troops at Berenty Reserve, Madagascar

We observed two free-ranging troops of ring-tailed lemurs at the Berenty Reserve, Madagascar. Kinship affinities in these troops are known only for mothers and their offspring 4 years of age. We attempted to quantify social relationships. Almost all agonistic interactions were dyadic, and triadic agonistic interactions, such as alliances, were very rare. Dominance hierarchies in both sexes in the two troops were not linear. As in cercopithecine monkeys, mothers were dominant over their adult daughters. However, the daughters were not ranked immediately below their mothers. Close proximity and social grooming occurred more frequently between closely related females, such as mother–daughter and sister–sister dyads, than between unrelated females. Frequent-proximity relations also occurred between adult males that had emigrated from another troop and entered the present troop together, even though they did not rank closely to one another. Subordinates were likely to groom and to greet dominants more frequently than vice versa. During group encounters, particular females were involved in agonistic interactions with animals of other troops, regardless of dominance rank. Adult males, regardless of their dominance rank, but not adult females, constantly tried to drive solitary males away.     

Life-history characteristics of a wild population of vervets (Cercopithecus aethiops sabaeus) in Barbados,West Indies

Life history data are presented for a population of vervets, Cercopithecusaethiops sabaeus, in Barbados, West Indies. The data were obtained from two habituated troops and from vervets captured during a large-scale trapping program. Individuals of known age from one troop were weighed periodically, and separate growth curves generated for males and females. The mean weight of captured adult females was 3.3 kg; that of adult males, 5.3 kg. The average age at sexual maturity is estimated at 34 months for females and 60 months for males. Vervets give birth throughout the year, but most infants are born between April and July. The average interbirth interval following a surviving infant is 11.8 months. The mortality of juveniles is heaviest between birth and 2 years of age and decreases thereafter. Males emigrate from their natal troops at sexual maturity and one incident of a juvenile female emigrating is reported.     

Consortship and Mating Success in Chacma Baboons (Papio cynocephalus ursinus)

Chacma baboons (Papio cynocephalus ursinus) show a lower consortship take‐over rate and longer consortship duration than the other savannah baboons ( Bulger 1993 ). It has been argued that researchers have focused on atypically small troops with few adult males, resulting in low competition for access to oestrous females. Consortship data from two mountain baboon troops containing seven and four males, respectively, were analysed to determine whether the troop with the greater number of males showed a weaker correlation between mating success and rank due to an expected higher consortship take‐over rate. No consort take‐overs were observed in either study troop and mating success in both troops was correlated strongly with male rank. The distribution of days spent in consortship amongst the males could be explained by the priority‐of‐access‐model. The degree of cycle overlap determined the number of males observed consorting oestrous females, whereas the number of males did not influence the relationship between rank and consorting activity.     

Some aspects of infanticide and intermale competition among langurs,Presbytis entellus,at Dharwar,India

Conspecific infanticides by male langurs depresses population growth in their densely populated habitats. An infanticidal model developed from demographic parameters obtained in the Dharwar study area predicts an almost stable population. On the other hand, a non-infanticidal model predicts a population growth by 2.6% per year. The effect of frequent troop usurpation and infanticide on the control of population growth must be strong if the natality rate is high. For subadult and juvenile surplus males, it must be difficult to survive and to mature in the all-male party in its poor habitat. However, from calculations for living adult males and the number of troops at Dharwar, most adult males are thought to be able to obtain a troop within five years of first challenge of usurpation. Dominant males do not always take over a troop containing more females than do subordinate males. These simple assessments require further intensive field studies to determine the precise differences between infanticidal and non-infanticidal populations and whether or not dominant males make a greater genetic contribution than subordinate males to subsequent generations.     

Life history variables of wild troops of formosan macaques (Macaca cyclopis) in Kenting,Taiwan

A study on population dynamics of wild Formosan macaques (Macaca cyclopis) in Kenting, southern Taiwan, was conducted from March 1985 to August 1990. At first, only one monkey troop was studied. It fissioned in 1987 and both of the daughter troops have been observed since then. Total number of animals increased from 10 to 29 over the years, but the sizes of individual troops have never been more than 20. Seasonality in breeding has been detected: copulations were concentrated in the period from November to January and 75% of all the 28 births occurred between April and June. Time of birth by parous females without offspring from the preceding year was earlier than that of lactating females. Young females gave their first births at 4 or 5 years of age. Total birth rate over the study period was 0.8 infant per female per year. Hunting was the main cause of death while natural mortality rate was low for the animals. There was only one adult male in each troop for most of the time. Troop males in the two daughter troops have been replaced two or three times in the three years by some solitary males that moved around in the area. The reproductive parameters of Formosan macaques in Kenting were found to be more similar to that of rhesus monkeys than to Japanese macaques. And a case of higher reproductive success in a high-ranking matriline was reported.     

Sociological study on the troop fission of wild

During the period from June to July 1983, the Hanyama-A troop of wild non-provisioned Japanese monkeys on Yakushima Island began to show signs of troop fission. Adult females together with their infants and juveniles subdivided into two groups, the Hanyama-K group and Hanyama-M group. After the subdivision, all of the troop males were observed vacillating between these two female groups. During the mating season, non-troop males were also observed moving around the two female groups. After this mating season, one of these non-troop males was found to have entered and become the alpha male in one of the groups, while higher-ranking adult males of the original troop settled into the other group. Each fissioned group was strongly considered to be composed of either high-ranking matrilines or low-ranking matrilines as observed previously in provisioned troops. The dominance relation between the two fissioned groups indicated that dominance rank reversal between these two female kin groups must have occurred during the course of subdivision of the troop. However, different from most previous cases of troop fission, there was no indication that males ever participated in the subdivision of the original female group. This was disrupted not as a result of males' involvement, but only as a result of antagonism among females, which initiated the troop fission. The main factor which appeared to determine when and in which fission group males eventually settled was the competition between the troop males' coalition and non-troop males and their ability to monopolize females. The present process of troop fission suggests a dual strategy between males and females (Wrangham, 1979, 1980) even in the society of Japanese macaques.