Take-over and infanticide in South Indian Hanuman langurs (Presbytis entellus)

A take-over and infanticide were observed in a South Indian population of Hanuman langurs (Presbytis entellus). A one-male, bisexual troop of langurs (Troop B1) was attacked by a band of two adult males and one subadult male. During the take-over, the resident male and one elderly female were driven from the troop. The youngest infant, about two months old, was fatally wounded by an attack from the dominant incoming male (S1). However, other young infants in Troop B1 were left unharmed. All three incoming males remained in Troop B1 but the troop appeared to remain functionally one-male, as S1 did not allow the other adult male to copulate. There was no sign that S1 attempted to eject the other two males from troop B1. © 1993 Wiley-Liss, Inc.     

Infanticide and juvenilicide in Hanuman langurs (Presbytis entellus) around Jodhpur,India

Ten cases of infant killings and 2 cases of juvenile killings were observed in two troops of Hanuman langurs, (Presbytis entellus) around Jodhpur, India. Fatal attacks on infants and juveniles are classified into four categories. The process of infanticide was observed from start to end and is described in detail for 3 cases. The age of the victims ranged from 0.2 to 48 months. The interbirth interval among females whose infants were killed is significantly shorter compared to females whose infants survived. In ourt study, 7 cases support the reproductive advantage hypothesis, that infanticide is an adaptive behaviour to increase male reproductive success. The remaining 5 cases do not fit into the reproductive advantage hypothesis. In these cases, victims are over 8 months old, and as such their deaths could not shorten the interbirth interval. It appears that by killing older infants and juveniles the males obtain an advantage in resource competition for their offspring. An alternative is that new males chase or peripheralise the older infants and juveniles, which leads to 97% predominant uni-male troop structure in Jodhpur.     

Twins in free-ranging Hanuman langurs (Presbytis entellus)

Two pairs of twins were observed in free-ranging Hanuman langurs (Presbytis entellus) at Jodhpur, India. Each twin had a preferred nipple for suckling, the preference of which developed during the first 5 weeks of life. The behaviour of the twins was mostly synchronized. In more than 60% of all activity bouts both showed the same behaviour, with “nipple contact” and “playing” prevailing. Differences in physical strength and development were apparent within each pair. While the total amount of allomothering was almost the same, individual weekly scores differed considerably.     

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.     

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.     

Patterns of grandmaternal behaviour in free-ranging Hanuman langurs (Presbytis entellus)

The behaviour of two Hanuman langur grandmothers towards their grandchildren is examined with emphasis on the spatial relationship, the contact behaviour, and vigilance. Interaction patterns with infants and juveniles are analysed separately to disclose the influence of a social partner's reproductive value and the variance of this value on grandmaternal behaviour. The shape of grandmaternal behaviour seems to differ for male and female grandchildren, and it seems to depend on the reproductive value of both, the grandmother and the grandchild. These results are in accordance with sociobiological hypotheses. Evaluation of costs and benefits suggests that grandmaternal behaviour in langurs can be called investment.     

Weaving a tight social net: Allogrooming in free-ranging female langurs (Presbytis entellus)

We studied grooming among adults of a one-male multifemale troop of free-ranging Hanuman langurs (Presbytis entellus)living near Jodhpur, India, for 9 years. The 11–13 females devoted about 6% of their day to allogrooming. Adult males, whose tenures averaged 2.2 years, were transient figures in the troop's history, as reflected by their rather peripheral role in the grooming network. Females groomed males 4–40 times more frequently (1006 episodes) than vice versa- (176 episodes). Adult females received 97% of all grooming from other adult females (6655 episodes). Although females exhibited an age- inversed dominance hierarchy, they did not compete for grooming access to particular troop mates. Dyads of all possible rank differences occurred as frequently as expected: 51% of grooming was directed up the hierarchy and 49% down it. Young, high- ranking individuals gave and received significantly more grooming than the oldest, low- ranking females did. The pattern seemed to be influenced by kin selection because of the presumably high degree of female relatedness. They invested most in troopmates with the highest reproductive value, i.e., the youngest individuals. This trend was coupled with a preference of closest kin (mothers and daughters). Reciprocity was the outstanding feature since all adult females groomed and were groomed by all others. Such a tight social net might establish the necessary cohesion during frequent territorial disputes with neighboring troops.     

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.     

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.     

Father-son recognition in hanuman langurs (Presbytis entellus): A field experiment in India

A juvenile male langur, about 15 months old, was removed from his natal one-male-multi-female troop and reintroduced after 3.3 weeks. In attempts to protect the juvenile, his presumed father, the troop's resident male, charged the primatologist who removed and released the individual. After the second removal, the juvenile was introduced into a neighboring male band. The resident male attacked the band members to keep them away from his females. However, after 3.4 weeks of separation, the father and the son recognized each other, because the resident male showed no aggression towards his son and the latter did not run away from him. Kin-recognition is considered to be a mechanism in structuring coalitions within langur male bands.     

Biosocial functions of grooming behavior among the common Indian langur monkey (Presbytis entellus).

An intensive study of the Indian langur monkey (Presbytis entellus) reveals an interplay between biological and social processes. This study which involved captive animals and over 1,500 observation hours suggests that grooming behavior alone cannot be used to measure status differences between the sexes, nor as a means to understand how pathogens carried by ecto-parasites are controlled. It is shown that the type of grooming exhibited in an interactional setting and the region of the body presented by one animal to another for grooming is often determined by the immediate social events and by the nature of the relationship existing between the participants. For these Colobine langur monkeys grooming behavior not only facilitates integration but it also enables an animal to manipulate a tense situation into a peaceful one. Without reference to many of the other patterns of behavior which only relatively, not absolutely differentiate age and sex classes, grooming behavior cannot be entirely understood.     

Assessment of female reproductive status in captive-housed Hanuman langurs (Presbytis entellus) by measurement of urinary and fecal steroid excretion patterns

The study reports on the use of urinary and fecal hormone measurements for monitoring female reproductive status in captive-housed Hanuman langurs (Presbytis entellus). Matched urine and fecal samples collected throughout 7 complete menstrual cycles of two females, and during part of one pregnancy in a third female were analyzed. Estrone conjugates (E1C) and immunoreactive pregnanediol glucuronide (PdG) in urine and immunoreactive estradiol (E2), progesterone (P4), pregnanediol (Pd) and 20α-hydroxyprogesterone (20αOHP) in feces were measured by enzymeimmunoassay. E1C and PdG in urine were excreted in a cyclic pattern with E1C levels increasing 3- to 4-fold during the follicular phase to reach preovulatory peak values 2 days before a defined rise in PdG concentrations. Cycle lengths ranged between 20 and 34 days comprising a variable follicular phase of 7–21 days and a more consistent luteal phase of 12–14 days. High pressure liquid chromatography (HPLC) analysis of fecal extracts confirmed the presence of all fecal hormones measured, but indicated large amounts of additional immunoreactivity in the three progestin assays. The patterns of excretion of fecal E2 and all three fecal progestins corresponded well with those of steroid metabolites in urine in showing a clear and well defined follicular phase E2 rise followed by a luteal phase progestin increase. Measurement of 20αOHP immunoreactivity revealed the most stable baseline and the highest follicular/luteal phase differential. Levels of all hormones were clearly elevated during pregnancy although urinary E1C and PdG showed a more pronounced increase compared to fecal metabolites. The results indicate that urinary and fecal hormone analysis can be applied to noninvasive monitoring of reproductive status in the Hanuman langur. © 1995 Wiley-Liss, Inc.     

Grooming site preferences in female langurs (Presbytis entellus)

Factors influencing grooming site preferences in adult female Hanuman langurs (Presbytis entellus) were investigated. The females belonged to a free-ranging harem troop (Jodhpur, India) and were observed for 569 hr by focal-female sampling. Decisive factors for grooming site preferences were the following: autogrooming was determined mostly by site accessiblity. Allogrooming was significantly concentrated on parts that are inaccessible to the groomee. Close female kin groomed significantly longer, more frequently, and more precisely at inaccessible body parts. Lower-ranking females were groomed significantly less often and more briefly but also more precisely at inaccessible parts. However, the latter might be due to a lower-ranking subjects desire to face away from the higher-ranking groomer in order to avoid eye contact. The data suggest that the groomee determines the sites being groomed.     

Birth dynamics in Hanuman langurs,Presbytis entellus of Jodhpur,India

Ten years data on birth peak, birth rate and interbiith interval inPresbytis entellus of Jodhpur have been presented. Although Hangman langur females breed round the year, there is some concentration of births during January–March while fewer births occur during October–December. It seems that provisioning and crop raiding together may provide better feeding opportunities to breed year round. However, it remains unclear whether environmental factors allow langur females to deliver more infants during January–March. During 1984–86 the birth rate was uniform for the whole population (0.63). While there was a variation within the troops from year to year, data suggest that resident male replacements do alter birth rate. It goes down when resident males are replaced frequently. The interbirth interval ranges between 7.0 and 76.5 months (average, 16.88 months;n = 112). Abortions and still-births reduced the interbirlh interval to 7.1 months (range 7.1-21.1; average, 11.4 months;n= 8) compared to the normal inlerbirth interval following infant survive its first 4.1 months of life (range 10.7-76.5 months; average, 17.28 months;n = 86). However, infant loss under the age of 4.1 months did not reduce the interbirth interval except in two cases (range 7.0-51.8 months; average, 17.27 months;n = 18). Maternal rejection or weaning begins at about 8 months of age and lasts until infants are 12 months old. In this population, the probability of twin births was worked out to be 0.79 per 100 births.     

Acoustical communication among free-ranging common indian langurs (Presbytis entellus) in two different habitats of North India

Acoustical signals of free-ranging Presbytis entellus were analyzed with the aid of sonagrams. Tape-recordings were from two ecologically-different habitats in North India, the Kumaon Hills on the southern slope of the Himalayas and the plains habitat of Rajasthan. The acoustical quality and the spectrographic structure of the signals are described and their communicative functions within the social context discussed. We found significant differences in the acoustical repertoire of the langurs of the two habitats both in the tone quality and the spectrographical structure of single signals serving the same functions in both regions and in functional deviations of identically or similarly structured vocalizations. Some of these differences appear to be phylogenetic adaptations to the different environmental conditions of the habitats or to be related to special types of social organization in the two separate langur populations.     

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.     

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.     

Feeding and ranging patterns of forest hanuman langurs (Presbytis entellus)

The feeding and ranging patterns of a troop of hanuman langurs (Presbytis entellus, Colobinae) were studied in Kanha Tiger Reserve, central Indian Highlands for 1850 hr (1981–1982), in a mosaic of moist deciduous forest and anthropogenic meadow. The location, size, and species of each tree within the 74.5-ha troop annual range was known and the phenology of all tree species was sampled. According to scan sampling, the troop spent 25.7% of the daytime feeding, with range use concentrated on an island of dry deciduous forest. Whereas adjacent troops occupied only the periphery of the focal troop's range, all-male bands occupied its center, especially during takeover and infanticidal attacks. The troop consumed items from 60 of the 67 species of trees and woody climbers available; mature leaves (34.9% of feeding time), fruits (24.4%), leaf buds (10.6%), flowers and flower buds (9.5%), young leaves (3.6%), insects (3.0%), and gum (1%). The monthly utilization of fruit, open leaf buds, and flower buds is correlated significantly with their abundance, and the troop spent significantly more time feeding and less time moving when consuming mature leaves. Comparison of tree dispersion and langur ranging patterns suggests that the distribution of the most important food trees is a major influence on their range use.     

Patterns of reproduction and mortality in two captive colonies of hanuman langur monkeys (Presbytis entellus)

Longitudinal reproductive and mortality data collected from two colonies of Hanuman langur monkeys (Presbytis entellus) in California (University of California, Berkeley; San Diego Zoo) are presented. Approximately 10 years of data from each facility reveal that langur monkey females reach reproductive maturity between 3 and 5 years and have median birth intervals, following the birth of a live infant that survives beyond 9 months, of approximately 15.5 months. Births are not seasonal at either facility and pregnancy failure rates at UCB are approximately 30%. Mortality of subadults was highest during the neonatal period (<30 days), and probability of Sarvivorship at 5 years is between .41 and .50. Observed differences and similarities in patterns of reproduction and mortality between the two colonies and field populations are discussed.