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.     

云南无量山印支灰叶猴社会结构初步研究

乌叶猴属物种主要以一雄多雌的小群活动,其群体大小一般不超过20只。泰国东北部的印支灰叶猴生活在一雄多雌或多雄多雌群的小群中,而云南无量山的印支灰叶猴却生活在多雄多雌的大群中,有些群大小超过100只,但是对无量山印支灰叶猴的社会结构缺乏研究。2012年9月至2015年7月,在云南无量山国家级自然保护区大寨子片区开展一群习惯化印支灰叶猴的社会结构研究。采用10min间隔的焦点动物瞬时记录法,记录焦点成年雄性5 m范围内不同性别年龄个体的数量。观察期间共有594次准确识别焦点雄性5 m范围内其它个体年龄性别的有效数据 (至少有1只其他个体)。其中,焦点雄性周围出现其它成年雄性的几率为44.2%,数量为(0.62 ± 0.85)只;同时出现成年雄性和成年雌性的几率是32.5%。取食时焦点雄性周围出现其它雄性的比例 (60.0%) 和数量 (平均0.93只) 都大于休息和移动时,数量最多为5只成年雄性。结果表明该群灰叶猴的社会结构不是由多个OMU和AMU组成的重层社会,而是多雄多雌的社会结构。无量山印支灰叶猴群内成年雄性间相互容忍度较高,个体的空间分布在取食时尤其密集,说明无量山印支灰叶猴的食物丰富 (至少在某些季节),这也部分解释了为什么无量山印支灰叶猴能够生活在大群中。本文为进一步研究亚洲疣猴社会结构的多样性和进化提供了重要的基础资料。     

My primate studies

In this paper, I describe my 62 years in primatology focusing on some of the key findings from fieldwork conducted in Japan, India, and Africa. My first study on nonhuman primates described in detail the division of a troop of Japanese macaques at Takasakiyama. After that, I had an opportunity to work on Hanuman langurs at Dharwar, India. These langurs lived in one-male, multi-female groups. This type of group structure was maintained through takeovers by all-male parties. The adult male and all juvenile males were chased out of the group. By this process, the one-male, multi-female group system was maintained. The incoming adult male bit and killed all infants in the group. Mothers who lost their infants went into estrus and mated with the newly arrived male. For many years, scientists ignored these events or ruled them out as abnormal behavior. My work on Japanese macaques suggested that concentrated resources created by artificial feeding exaggerated dominance rank hierarchies among individuals, whereas it is comparatively relaxed in the natural environment. I also investigated the population dynamics of a troop and the life histories of individuals. From these studies, I documented the frequency of twin births, the carrying of dead infants by mothers, and the occurrence of physical malformations. These observations were made possible through artificial feeding, revealing the merits and demerits of this approach. I pointed out that authors and journal editors must be careful to acknowledge important elements of the environment where studies are conducted, and these should be described when reporting results in scientific articles. My studies of chimpanzees were conducted at Bossou, Guinea. I suggested that there are males who lived outside of bisexual groups. Chimpanzees in this population made and used many kinds of tools. Some of them were observed only at Bossou, and a few were only discovered 20 years after the establishment of Bossou as a research site. After decades of research on tool use in this species, I also suggested that there are cultural zones throughout the geographic distribution of chimpanzees.

     

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.”     

Male competition and coalitions in langurs (Presbytis entellus) at Jodhpur,Rajasthan, India

During a 15 month study on free ranging langurs (Presbytis entellus) at Jodhpur, Rajasthan, India, 5 adult male replacements were observed as a result of nontroop male invasions into the home ranges of 3 neighbouring one-male troops comprising 16–28 members each. Jodhpur langurs have no breeding season. Periods of instability during resident male changes lasted 11–119 days. Linear dominance hierarchies could be detected within the 3 main rival male bands of 2, 5, and 28–35 members. The respective alphas drove their allies away after their bands succeeded cooperatively at occupying a troop. During gradual replacements interim residencies alternated with multi-male stages. A large band's alpha may have had better chances to win the competition, since adult and nonadult allies functioned as “buffers” in agonistic encounters. The role of kin selection in structuring the composition of male bands and male coalitional behaviour cannot yet be quantified. Tactical “deceit” of powerful males to cause unrealistic expectations and in this way agonistic engagement of less strong males can be ruled out. “Sneaking copulations” is a proximate advantage for subordinate supporters, since they participated in 61.9% of all sexual interactions. Female promiscuity might reflect a strategy to induce male-male competition and thus select for a strong resident.     

Female sexual swellings in the Asian colobine Simias concolor

During a preliminary study of pig-tailed langurs (Simias concolor) in the Pagai Islands, Indonesia, it was discovered that females exhibited conspicuous swelling of the urogenital triangle. The pig-tailed langur is the first Asiatic colobine found to have prominent sexual swellings and the only colobine with sexual swellings that lives in one-male groups. Because all anthropoids with conspicuous sex skin typically live in groups having female-biased adult sex ratios, it is possible that females might compete amongst themselves for the male in one-male groups, or the best males in multimale groups. Sexual swellings may therefore have resulted from sexual selection for signals attractive to males in female-female competition, as suggested earlier by Bercovitch (California Anthropologist 8:9–12, 1978). Prolonged observation of recognizable individuals will be required to test this hypothesis in the pig-tailed langur and other species.     

Solitary male chacma baboons in a desert canyon

Solitary and paired adult (nine) and subadult (one) male chacma baboons, Papio ursinus, were observed over a period of years living in part of a wooded desert canyon not used by adjacent troops. These extratroop males were silent when alone and gave only one alarm vocalization, the “wa-hoo” call, when paired. The space occupied by them is unsuitable for use by troops according to criteria for adequate sleeping sites and access to water. But the foods available to them, especially figs, but also other fruits and fresh acacia seeds, were abundant. These foods are more highly preferred by baboons than those foods available to troop members. Troop members deplete these resources and shift to less preferred foods with lower water content and longer processing times. All of the adult members of the troop adjacent to these isolated males were infected with a skin disease. Isolated males were not so afflicted and so cannot have originated from, or ever been a part of, this troop. They probably moved to the space where they were observed from other inland troops, traveling to their current home range along the narrow canyon river course.     

Male reproductive success in harem troops of hanuman langurs (Presbytis entellus)

Based on cross-sectional and longitudinal data collected in 1967–1988 by various observers, male reproductive success was studied in the Hanuman langurs of Jodhpur, India. The harem-structured social organization ensures a high degree of paternity certainty. Births occur throughout the year, with significant peaks and minima in March and November, respectively (n =398).The interbirth interval averages 16.7 months (n = 114).The duration of harem residencies varies between 3 days and ≥ 74.0 months, with a mean of 26.5 (n = 64). Harem holder replacements occur during all months of the year. No male achieves residency in more than one troop, suggesting that residency is associated with a distinct peak in the resource holding potential of a given male. Reproductive success among males varies considerably. Male mortality is high due to migration and intrasexual competition, leading to an adult sex ratio of 1:4.9. It is estimated that one-quarter of all adult males will never gain harem residency. Conceptions achieved outside harem residencies are so rare (4.7%) that a viable low-risk strategy, opting for longevity instead of harem residency, is unlikely. Tenure length has a stronger influence on male reproductive success than harem size because interbirth intervals are significantly shorter in small harems than in larger ones. It is assumed that females in one-male breeding structures compete for sperm and that such competition is more intense in larger harems.     

The social organization of forest hanuman langurs(Presbytis entellus)

The social organization of hanuman langurs (Presbytis entellus;Colobinae) was studied in Kanha Tiger Reserve, Central Indian Highlands, for 2300 hr (1980–1985), in a mosaic of moist deciduous forest and anthropogenic meadow. The langur population density was 46.15/km ² and the mean troop and band sizes were 21.7 and 14.0, respectively. Of 14 troops, 13 were one-male and 1 was trimale. The population adult sex ratio was 1:2.5. The majority of female sexual solicitations was directed toward the harem male. The birth season was December to May, with an estimated gestation of 171–224 days. A review of langur reproductive seasonality suggests that breeding throughout the year is confined to those populations able to exploit human food sources. Mortality during the first year of life was 40%, including infanticide. A significant positive correlation was found between the age of an infant at death or disappearance and the mother’s subsequent interbirth interval. Five cases of social change are described, including female transfer, one-male to multimale change, troop formation, and gradual and rapid replacement of troop males. Takeover-associated infant killing by band males, in an undisturbed moderate-density population, supported the sexual-selection/infanticide hypothesis but not the social-pathology hypothesis. However, it could not be directly confirmed that an invading infanticidal male gains a reproductive advantage. The male tenure of harems was estimated to be 45 months.     

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.     

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.     

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.     

Attacks on a wild infant ring-tailed lemur (Lemur catta) by immigrant males at Berenty, Madagascar: interpreting infanticide by males

An orphaned infant ring-tailed lemur (Lemur catta) was attacked persistently by immigrant males and disappeared with severe wounds at Berenty Reserve, Madagascar. Prior to the attacks, two troop members disappeared. On 20 November 1998, the only resident male in Troop C2B disappeared suddenly. After the disappearance, nine males from three neighboring troops approached, but only six males continued to shadow the troop. Of the females, the one lactating female attacked the males the most frequently. On 21 January 1999, the lactating female disappeared and her infant was orphaned. Subsequently, five attacks on the infant by immigrant males were observed for five consecutive days from January 23 to 27. The aggression was persistent and specifically targeted the infant, suggesting that the attacks were purposeful aggression, rather than redirected or accidental aggression. The primary attacker was the most dominant of the immigrant males, and mated with females in the next mating season.     

Troop history,female reproductive strategies and timing of male change in Hanuman langurs,Presbytis entellus

Female reproductive data are presented from 9 years of longitudinal observations on two troops of Hanuman langurs (Presbytis entellus) living around Jodhpur, India. On the basis of 89 live births interbirth intervals were calculated to examine the effect of demographic factors on reproductive behaviour and troop composition. Sex of an infant seems to influence the length of intervals which are longer after the birth of female infants at an average of 1.7 months. It is suggested that this may be an outcome of differential maternal investment by allocating more time and energy towards female infants who run a higher mortality risk than male infants, at least up to an age of 27 months. Troopspecific interbirth intervals are influenced by social events. If the last infant is still alive when the next one is conceived, the intervals are significantly longer than after the premature loss of an infant (Bijolai troop: 15.6 vs. 12.1 months; Kailana-1 troop: 16.7 vs. 11.4 months). During undisturbed male tenureship intervals are shorter than after a male change (Bijolai troop: 14.3 vs. 16.0 months; Kailana-I troop: 15.6 vs. 17.5 months). Thus the frequency of male changes can influence the demography of a troop. Furthermore, the data suggest that take-overs are optimally timed by males. New males tend to take over a troop when most of the females are cycling.     

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

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

Social relationships between adult central males and kinship groups of Japanese monkeys at Arashiyama with some aspects of troop organization

Using focal-animal and instantaneous sampling techniques, seven adult central males of the Arashiyama-B troop of Japanese monkeys were observed during nonmating seasons from 1976 to 1978. The partners of these males in social activities (allogrooming and agonistic) and nonspecific body-contact, and those found in 1-m proximity were identified. The results indicated that: (1) a lack of observable associations as well as agonism was noticed among the adult central males; (2) a tendency was observed for each adult central male to associate with more than one kinship group and for most of the kinship groups to associate with more than one adult central male each. Many of the adult central males and kinship groups changed associations with each other from year to year; (3) the observed frequency of associations, which finally became zero, between any such male as had kins inside the study troop and his kins was statistically lower than the expected one; (4) some of the female youngsters had strong associations with particular adult central males; and (5) since one kinship group that had lost associations with all the adult central males left the troop, it is suggested that associations with at least one adult central male must be important for binding each kinship group in the troop.     

Postconflict behaviour of wild Indian langur monkeys: avoidance of opponents but rarely affinity

Friendly postconflict (PC) interactions between former opponents have been described for a large number of primate species held in captivity. We investigated conflict management behaviour for wild Hanuman langurs, Semnopithecus (Presbytis) entellus entellus, in India, using a large sample of over 6000 agonistic and affinitive interactions recorded in one one-male/multifemale troop and three all-male bands. We compared dyadic PC affinity with the dyadic baseline affinity during the overall observation time to minimize biases of traditional matched-control samples. PC affinity was recorded during only 15% of all dyads (immature male-immature male 0%, adult male-adult male 0%, adult male-immature male 5%, adult male-adult female 0%, adult female-adult female 42%). PC affinity is probably absent amongst males because their dominance relationships are strongly asymmetrical, leaving little room for emotional insecurity. Dyads among females, on the other hand, reflect frequent rank changes and close kinship which probably corresponds to higher levels of emotional uncertainty and greater need for PC affinity. Overall, PC affinity reached only 26% of the randomly expected value. Thus, the vast majority of langur monkey opponents avoided each other after conflicts. Avoidance as a low-cost option for group-living animals to cope with conflicts is often not possible in captivity. This suggests that reports of high rates of reconciliation may be at least partly artefacts of captivity. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

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.