Social relationships between adult male and immature rhesus macaques

Social relationships of adult male rhesus macaques (Macaca mulatta) were studied over a period of 14 months. Sixteen focal males were chosen from a single group in the Cayo Santiago colony, Puerto Rico. Immatures were defined as infants, yearlings and 2-year-olds. There was a tendency for males to spend more time in proximity to immatures in the birth seasons than in the mating season. Time spent in proximity to immatures was correlated with male dominance rank. Several male-immature dyads had persistent relationships and nine were apparent throughout the study period. Most of the latter involved the top-ranking males. There were no consistent effects of sex or rank of the immature on the distribution of persistent relationships. In almost all male-immature dyads the immature was primarily responsible for maintaining proximity. Two ways were found in which immatures could benefit from these relationships. Protection and agonistic aiding of immatures by adult males were rare, but occurred exclusively in dyads with persistent relationships. In addition, immatures apparently gained greater access to food resources as a result of their relationships with adult males. There was no clear evidence of adult males benefiting from these relationships.     

Social dominance and reproductive behavior in male rhesus monkeys

Altmann's model describing the relationship of social dominance to breeding behavior in some non-human primate species has been tested using data from the Cayo Santiago rhesus colony. Although some of the model's assumptions are clearly not met by field observations, a good fit is often found for groups containing relatively few sexually mature, non-pregnant females. It is suggested that genetic change could be rapid under conditions described by this model. It is estimated that a “beneficial mutation” could spread through all the breeding males in as little as six generations regardless of group size. The speed at which an allele can spread through the group is discussed in terms of the mean length of female receptivity.     

Familial interactions of male rhesus monkeys in a semi-free-ranging troop

Although the central and stable position of female rhesus monkeys in semi-free-ranging bands has been observed and described, the position of the developing male in the social group is not as well delineated. The present study is an attempt to describe interactions of 18 males with members of their families. Quantitative observations were made on one band (E) of rhesus monkeys on Cayo Santiago. Incidences of behavior recorded were joining, grooming, and threatening. The resulting data were analyzed by comparing the behavior of the males studied toward members of their genealogy as well as unrelated members of the social group. Behavior of family and non-relatives toward the males was also revealed. Statistical analysis revealed that the male subjects engaged in more positive social interactions within the matrifocal family than with other members of the genealogy, and in turn, more such behavior was observed within the genealogy than with unrelated monkeys. Threatening behavior within the genealogies was infrequent. Age effects were noted in that family members directed more interactions toward younger males and as males matured, they groomed more but joined family members less frequently. These data suggest mechanisms of socialization within the genealogy that may be different from those employed within the unrelated social group.     

Social and hormonal influences on behavior of adult male, female, and pseudohermaphroditic rhesus monkeys

We previously demonstrated that in a simple pair test situation the expression of adult male sexual behavior by rhesus monkeys depends on both prenatal (organizational) and adult (activational) androgen exposure. In the present study we used a more complex social situation (trio tests) to evaluate the behavior of males, females, and female pseudohermaphrodites. In these trio tests, the experimental subjects were tested with two estrogenized stimulus females simultaneously. Sex differences in behavior were made apparent by this complex testing situation that could not have emerged in the pair test. Gonadectomized males and female pseudohermaphrodites, but not ovariectomized females that were concurrently receiving TP, exhibited increased male sexual behavior in trio tests compared to pair tests. In trio tests, the males and pseudohermaphrodites showed evidence of partner preference by interacting almost exclusively with one of the two stimulus females. These "preferred females" in turn were responsible for the majority of the proceptive behavior exhibited in these tests. Ovariectomized females rarely displayed male sexual behavior in either test situation. These results further support the hypothesis that prenatal androgen exposure predisposes monkeys to exhibit masculine behavior traits when they reach adulthood and are exposed to the activational influences of androgens.     

Social interactions between captive adult male and infant lowland gorillas: Implications regarding kin selection and zoo management

Interactions between unrelated and related silverback‐infant dyads are compared in an attempt to assess the influence that kinship may have on male parental behavior. Observational data were collected on each member of two silverback‐infant dyads, in two separate enclosures at the Lincoln Park Zoo in Chicago, IL. The silverback was the father of the infant in one dyad, and unrelated to the infant in the other. Each infant was responsible for initiating most of the encounters with its respective group silverback. However, based on the frequency and duration of interactions, there is a significantly higher degree of affiliation and tolerance within the silverback‐offspring dyad. Furthermore, the unrelated infant was the recipient of more than 40% of the agonistic behaviors exhibited by the silverback, whereas no such encounters were recorded within the related dyad. Although alternative explanations must be considered, these findings are consistent with kin selection theory, are similar to observations documented for wild mountain gorillas, and provide uncommon comparative data on adult male interactions with related and unrelated infants. In addition, this study offers behavioral information relevant to the management of captive gorillas, which often requires the introduction of immatures into non‐natal groups. Zoo Biol 18:53–62, 1999. © 1999 Wiley‐Liss, Inc.     

Social relationships between adult females and the alpha male in wild tufted capuchin monkeys

Primates are notable for the widespread presence of long-term female-male associations which go beyond the mating context. However, little attention has been given to the factors that affect within-species variation in female-male relationships, especially among New World primates. Although detailed accounts of heterosexual relationships in Cebus species are scarce, a few studies have suggested the occurrence of strong associations between adult females and high-ranking males. This study explores affiliative relationships between females and the alpha male during the nonbreeding season in wild tufted capuchin monkeys (Cebus apella nigritus). Affiliative relationships were explored through female-male patterns of spatial proximity and grooming. By adopting a social network approach, we analyzed: (1) whether the alpha male is the preferred male partner for females and, (2) whether variation (if any) in female-alpha male affiliation can be explained through both female individual characteristics and social network metrics. Our results showed that alpha males were the favorite male partner for adult females in the proximity networks, but this did not hold true in the grooming networks. In addition, female-alpha male interaction patterns showed considerable variation, with only some females being strongly associated with the alpha male. Our results suggest that such a variation can be explained by female dominance rank, level of centrality (the quantity and intensity of spatial connection with other females) and prestige (the quantity of grooming received by other females) in female-female social networks. Taken together, these findings highlight two aspects of female-alpha male relationships in tufted capuchin monkeys: the alpha male represents the most socially integrated male in the group, and females with high dominance ranks and high centrality in both proximity and grooming networks show stronger relationships with the alpha male.     

Social relationships between adult male and female rhesus macaques: 1. Sexual consortships

The sexual relationships of 15 adult male rhesus macaques (Macaca mulatta), of one social group in the Cayo Santiago colony, Puerto Rico, were studied during the 1981 mating season. Two criteria were used to determine whether or not a focal male was in consort in a given 20-min observational sample. One hundred and thirty-two consortships were recorded. The distribution and duration of all consortships, and the distribution of those consortships that coincided with the estimated time of conception, were positively correlated with male dominance rank and length of tenure. Correlations with dominance were stronger than those with tenure. Older females had more consortships with focal males than younger females. There was no relationship between female rank and the distribution of consortships. Consortships did not give exclusive access to receptive females although they may do in feral situations. Males were primarily responsible for maintaining proximity in about two thirds of consortships. The four top-ranking males were primarily responsible in all but one of their consortships. Almost all of those in which the female was primarily responsible involved younger, slightly lower-ranking males. This pattern may have resulted from the females being attracted to the latter males although other interpretations are possible. The partner who was primarily responsible for maintaining proximity also tended to be the predominant groomer, supporting the view that grooming plays a role in the maintenance of sexual consortships. Almost a third of consortships were with females who had conceived, suggesting that males could not accurately assess female reproductive state. Consortships maintained by the male were longer than those maintained by the female. Males may try to increase their chances of fertilising a female by prolonging the consortship. High-ranking males may have been more successful at this, resulting in the positive correlation between male dominance rank and consortship duration.     

The distribution pattern of rhesus and Assamese monkeys in Nepal

Surveys of the distribution and some ecological characteristics of rhesus monkeys (Macaca mulatta) and Assamese monkeys (M. assamensis) in Nepal were conducted during 234 days in 1976, 1978, and 1984. Rhesus monkeys dominated in the tropical, subtropical, and temperate forests below 3,000 m a.s.l. all over Nepal. Assamese monkeys were patchily distributed along rivers in the tropical and subtropical areas. Both species principally utilized forests parapatrically. The mean troop size of rhesus monkeys (29.5) was significantly larger than that of Assamese monkeys (19.1). Discontinuous distribution of Assamese monkeys probably appeared as a result of the expansion of rhesus monkey distribution in the mid- and late-Pleistocene. Because of small distribution areas and small numbers of monkeys, urgent conservation policy must be pursued.     

Social relationships between adult male and female rhesus macaques: II. non-sexual affiliative behaviour

The social relationships of adult male rhesus macaques (Macaca mulatta) in Group I of the Cayo Santiago colony were studied over a period of 14 months. Relationships were found in which adult males and sexually mature females were persistently close to one another in nonsexual contexts, both within and across seasons. Males of long tenure and high dominance rank tended to have more female partners, and more persistent relationships, than more recent immigrants of lower rank. Correlations with length of tenure were stronger than those with dominance rank. Closely-related females tended to have persistent relationships with the same male. In most cases the female was primarily responsible for maintaining proximity in non-sexual contexts. Dyads which were persistently within 5 m of each other in the birth season were more likely to form a consortship in the subsequent mating season than those which had a brief relationship. A similar tendency was apparent in the 1 m data but it was not statistically significant. There was no association between persistent proximity during the birth season and the occurrence of long, or multiple consortships, nor with the maintenance of proximity or direction of grooming between consort partners. The pattern of consortships was not closely related to the formation of persistent relationships in the subsequent birth season. Females occasionally received protection from their male partners and, in some cases, spent more time in the feeding corral with them than did other females. Affiliative relationships can be very enduring and may have long-term benefits that were not apparent during the study period.     

The association between rank and reproductive success of male rhesus monkeys

The paternity of 202 of 220 offspring of rhesus monkeys housed in six separate half-acre field cages at the California Primate Research Center was determined by genetic marker techniques. Reproductive success of the adult males was statistically significantly correlated (r = 0.76, P <0.0005) with rank. Marked systematic changes in reproductive success were, however, observed for two adult males during the three years covered by this study. Based upon these results and those of another study, it is argued that changes in rank position typically follow, rather than precede, changes in reproductive success.     

Group changing in free-ranging male rhesus monkeys

Group changing behavior of maleMacaca mulatta was studied over a six-year period at the rhesus monkey colony on two coastal islands at La Parguera, Puerto Rico. Males first left their natal group at a mean age of 47 months and became solitary for the first time at a mean age of 64 months; all had left their natal groups by seven years of age. Age, mating season, sex ratios of adult males and females in the social bands, and geographical barriers all had significant effects on the group shifting. Population size, rank of mother or being an orphan did not significantly affect the changing process. Two factors, age (size) and seniority in the group, were important in determining a male's rank in his new group.     

Separation of preadolescents from infant rhesus monkeys

Each of eight infant rhesus monkeys was paired with a preadolescent conspecific for two months and then separated. Four of the infants were mother-reared and four were isolate-reared. Separation responses were compared with data from preseparation and reunion phases of the study for all pairs. The results indicate that (1) although males interact with infants in a parental fashion, preadolescent females show a greater capacity for parental behavior, (2) both preadolescents and normal (mother-reared) infants contribute to the development of a social bond, (3) isolate infants contributed little to the development of a social bond and were relatively less-valued as social partners by their preadolescent cagemates.     

Sociability and responses to video playbacks in adult male rhesus monkeys (Macaca mulatta)

Studies of several primate species have suggested the existence of a personality dimension typically labeled ‘Sociability,’ which reflects an animal’s tendency to interact with others. The hypothesis that Sociability is related to social skill was tested in the present study by exposing six high- and six low-Sociable adult male rhesus macaques to videotaped presentations of unfamiliar males displaying aggressive or affiliative behaviors. Low-Sociable animals displayed higher frequencies of yawn, lower activity and tended to have higher durations of watching during the presentations that displayed social signals, and significantly fewer lipsmacks to presentations that depicted no social behavior. In response to viewing threats, tooth-grinds, yawns, and lipsmacks, both low- and high-Sociable animals’ most frequent response was to gaze avert; low-Sociable animals, however, had nearly twice the latency to gaze avert than did high-Sociable animals. The low-Sociable animals’ greater tendency to ‘sit and stare’ during the videotaped playbacks suggests that low-Sociable animals have poorer social skills. The possible developmental origins of variation in Sociability, and the functional consequences of such variation for survival and reproduction are discussed.     

Confirmatory factor analysis of personality structure in adult male rhesus monkeys (Macaca mulatta)

Reports from different laboratories have suggested that nonhuman primates have somewhat similar dimensions of personality. To date, however, no attempts have been made to statistically replicate a specific factor structure. In the present report, two independent observers recorded the behavior of 58 adult male rhesus monkeys, and then rated the animals with the use of a 50-item personality instrument. A confirmatory factor analysis (CFA) of the ratings resulted in the replication of a previously described four-factor personality structure [Maninger et al., American Journal of Primatology 61:73-83, 2003]. The first two dimensions-Sociability and Confidence-showed strong loadings and are similar to Affiliation and Agency dimensions in humans. The remaining dimensions-Equability and Irritability-were less clear, and it is possible that additional traits will have to be identified before a more robust structure can be established for these dimensions.     

Social enrichment of the environment with infants for singly caged adult rhesus monkeys

The practicability of social enrichment for singly caged adult rhesus monkeys was examined. Twenty-nine weaned rhesus monkey infants were removed from breeding troops to avoid overcrowding and were placed with unfamiliar singly caged adults. An adult-infant pair was considered compatible when (1) the two animals started huddling with each other within the first 5 days after pair formation and (2) the infant showed no signs of depression and took its share from a limited amount of favored food. Adult-infant pairs were compatible in 90% (26/29) of cases. Compatibility depended neither on the sex, age, and origin of the adult nor on the sex of the infant. There was no evidence that partners lost interest in each other during 7–11 months of follow-up observations. Three adults exhibiting stereotypical behavior abandoned their peculiar habits after they had lived with their young companions for 4 months. It was concluded that the often-heard notion that rhesus monkeys are highly aggressive should not prevent simple attempts to provide singly caged animals with a companion.     

Social responses to abnormal infant monkeys

Experimental modification of an individual's behavior can be used to evaluate the range of group social reactions to him. This principle is used in evaluating the degree to which macaque groups compensate for an infant's clumsiness, consequent on reduced visual acuity from an experimental cataract. Evidence is presented to support the following propositions: Defective infants are not killed by the group even in crowded conditions; compensatory care is given during the first year, primarily by the mother and to a certain extent by other animals in the group; isolation of the infant begins in the second year; social responses to the defective infant reflect normal social responses. Compensatory care of chronically defective individuals is a consequence of evolution of social behaviors adapted to nurture young individuals over a long period of dependence and to protect other group members during temporary periods of weakness.