Dominance,age, and reproductive success in free-ranging female hanuman langurs (Presbytis entellus)

Correlations among female age, dominance, and reproduction were investigated for a 12-year period in free-ranging, provisioned Hanuman langurs (Presbytis entellus), living in one-male groups near Jodhpur in Rajasthan, India. Of 2940 displacement episodes, 27% occurred over natural food, 26% over provisioned food, 8% over grooming, 23% over position and shade, and 16% for other reasons. It was possible to reconstruct a displacement hierarchy that was linear and stable over short periods but fluctuated according to the age composition of the troop, resulting in an age inversed dominance structure. Females occupied top ranks as soon as they experienced menarche (around 2.4 years of age) and gradually declined thereafter, with postmenopausal females (≥30 years) being the lowest ranking individuals. Old females tended to be peripheral, while young females were highly social and active. Fertility peaked at about 7 years and gradually decreased thereafter, but infant mortality was much higher in young females than in old ones. During years when females gave birth, their ranks, especially those of old females, were higher than the average expectation for their age class, which suggests that females compete more vigorously if they have an infant. Reproductive success (i.e., infant survival to ≥2 years) declined significantly from high-over middle-to low-ranking females but did not differ for the three age classes investigated, because the higher fecundity of young females was balanced by better rearing success of older females. These results are discussed in light of the controversy over whether the langur social system is strongly influenced by kin selection (Hrdy and Hrdy, 1976; Dolhinow et al., 1979).     

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.     

Rotavirus antibodies in hanuman langurs (Presbytis entellus)

Serum samples from wild Hanuman langurs (Presbytis entellus) from Mysore State, India, were compared to samples from a laboratory colony from Davis, Calif., for antibodies to rotavirus, which is an important cause of gastroenteritis in mammals. Animals from the laboratory colony had a higher frequency and higher levels of antibody than wild animals. It is likely that wild populations of langurs have a much lower incidence of rotaviral infection than laboratory populations, which are exposed to both crowded conditions and rotaviruses from other species.     

Hormonal correlates of reproductive seasonality in wild female hanuman langurs (Presbytis entellus)

To date, it is not known whether the seasonal occurrence of sexual behavior and mating in free-ranging Hanuman langurs at Ramnagar, Nepal, is correlated with seasonal changes in female ovarian function, and, if so, which factor(s) triggers the onset of the reproductive period. Using noninvasive fecal hormone analysis in combination with behavioral observations, this study was carried out to: 1) investigate and characterize seasonal patterns of ovarian cyclicity and timing of conception in wild langur females living in a highly seasonal habitat; and 2) examine the relationship between seasonal patterns of ovarian cyclicity, behavioral estrus, and female physical condition. Behavioral data and fecal samples were collected during a total period of 14 months from nine females living in a multi-male group. Physical condition of the females was assessed monthly by visual inspection, using a seven-fold scale. Ovulatory cycles and timing of conceptions were identified by the measurement of immunoreactive pregnanediol glucuronide (iPdG) in extracted feces. Hormone profiles in individual females revealed a clearly seasonal distribution in the occurrence of ovulatory cycles, which were restricted to the period from July to October. The distribution of female estrus behavior showed a similar seasonal pattern, and in total 88.2% of all estrus periods observed in the focal females were accompanied by ovulation. Onset of ovarian cycles as well as mating activities were strongly correlated with the onset of the rainy season. Females conceived, on average, in their second ovulatory cycle (pregnancy length: 211.6 +/- 3.4 days), with timing of conception being confined to the months when animals showed an improved physical condition. Collectively the present data clearly suggest that in seasonally-breeding langurs at Ramnagar, ecological conditions (rainfall, food availability, and quality) influence the onset of ovulations and timing of conceptions.     

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.     

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.     

Predator mobbing by an all-male band of hanuman langurs (Presbytis entellus)

An all-male band of 15 Hanuman langurs alarm barked and mobbed a leopard in Sariska Tiger Reserve, a forest in Rajasthan, India. After initially alarm calling and barking in response to the leopard's presence five animals persistently followed and watched the leopard for about an hour. During this time they were barking and tooth grinding. Both the initial alarm calling and the following mobbing can be interpreted as altruistic behaviour. However, unlike the situation in bisexual troops, Hanuman langur males may not be related to other members of the group and the evolution of such behaviour cannot necessarily be explained by kin selection.     

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.     

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.     

Infanticide in an undisturbed forest population of hanuman langurs,Presbytis entellus

Observations of infanticide in a troop of undisturbed, forest hanuman langurs by members of an invading all-male band are reported. The data, whilst consistent with the sexual selection hypothesis, did not support the social pathology hypothesis. Data from different langur populations supported the prediction, derived from the sexual selection hypothesis, that troop take-overs should occur between the birth and mating seasons. The occurrence of take-overs in different langur populations was associated with a predominantly one-male troop structure and not with high density.     

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.     

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.”     

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.     

Male tactics and reproductive success in the harem polygynous bat Saccopteryx bilineata

Alternative tactics in reproductive behavior enable individualsto maximize their fitness in relation to competitors in thesame population. In many taxa, territoriality is a common tacticof males to increase their reproductive success. In the batSaccopteryx bilineata, territorial males defend roosting areasfor females against other males and court females throughout the year. Peripheral males in the same colonies do not defendterritories but compete with territorial males for reproductionwith females. In this study, we monitored the behavior of themales in a natural colony over three reproductive seasons.We compared morphological and age data and measured the reproductiveoutput of males adopting the territorial or peripheral tactic.No differences in body size or weight were detected betweenmale types, but the probability of adopting a tactic seemedto be age dependent. Peripherals were often young males andreplaced territorials in several cases, whereas the oppositecase was not observed. Peripherals were not excluded from reproduction,but territorials were more likely to reproduce. Variation in reproductive success was high within both male tactics, andthe reproductive success of some peripherals was comparableto territorials, but, on average, the reproductive successof territorials was more than twice as high. Therefore, behavioraltactics do not seem to be equally profitable in general butmay represent different phases in the reproductive life of manyS. bilineata males.     

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.     

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.     

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.