Male-male Interactions in Heterosexual and All-male Wild Mountain Gorilla Groups

Variation in male dispersal and behavior patterns are components of intraspecific differences in social systems. A comparison of male behavior in different social settings can be useful for determining which behavioral mechanisms contribute to variability in social systems. Two heterosexual multimale groups and one all-male group of mountain gorillas (Gorilla gorilla beringei) were observed for over 1100 h at the Karisoke Research Centre, Rwanda. Data on proximity patterns, dominance relationships, aggression, agonistic interventions, affiliation, and homosexual behavior were compared among the males in these groups to examine the influence of female presence, sex ratio, group size, and kinship on male—male interactions. Males in the all-male group stayed closer together, affiliated more, exhibited more homosexual behavior, and were more aggressive toward each other than males in heterosexual groups. However, the males in heterosexual groups showed more wounding and more consistent dominance relationships. Kinship did not influence male-male relationships in the all-male group. The males in the heterosexual groups rarely interacted with one another; they may actively avoid close proximity to reduce aggression. Results suggest that the variable social system of mountain gorillas may be more strongly influenced by demographic factors, male-female social relationships, and male-male competition for mates than by any benefits of male-male relationships.     

Mating and Residence Patterns of Male Patas Monkeys

A longterm study of a population of patas monkeys (Erythrocebus patas) in Kenya indicated fluid male residence patterns. While a single adult male was present in each of the two main study groups for most of each year, several males were present and mating in groups during some conception periods. Tenures of males in heterosexual groups were generally short; some males were resident in both groups and some had more than one tenure in the same group. When not in heterosexual groups, males lived as solitaries or in all-male associations.     

Reciprocity and partner preference in grooming of female blue monkeys

Grooming among adult and older juvenile females in a wild group of blue monkeys (Cercopithecus mitis stuhlmanni) is analyzed and related to agonistic behavior. Both grooming and agonistic behavior were less frequent than would be expected in baboon and macaque groups. Fair shares of grooming were given and taken, both within and between interactions, in amost dyads, and all females were seen to groom with at least half the others. The reciprovity of grooming was its most outstanding feature. There was no evidence that grooming was preferentially directed at kin. Frequent grooming partnerships fell into two clusters, one of which ranked higher than the other. We suggest that grooming throughout the group helps to establish a coherent team of females which effectively, defends its territory in daily encounters at the boundaries with neighboring groups.     

Differential effects of kinship,dominance, and the mating season on female allogrooming in a captive group ofMacaca fuscata

An analysis of allogrooming (total times spent grooming individual partners) of 8 sexually mature females (3–12 years of age) in a captive group of 17 Japanese macaques, shows that during the nonmating season, grooming distributions were characterized by high proportions of grooming given to family members and/or higher ranking nonkin. During the mating season, all eight females showed significant shifts in their grooming distributions, and four females showed significant shifts in grooming between their nonestrous and estrous periods (defined behaviorally). Fox six of eight females, mating season grooming was characterized by either high proportions of grooming given to family members and/or heterosexual and homosexual partners. It was found that within dyadic sexual relationships, dominants gave more grooming to subordinates than the former received, in contrast to a reversal of this pattern in the majority of these same dyads during the nonmating season. This is interpreted as one short-term function of grooming: a dominant asymmetrically grooms a subordinate sexual partner to maintain proximity with (or reduce tension in) the latter. The two remaining focal females (middle ranking, nulliparous) differed from the other females in that they shifted their mating season grooming to subordinate nonkin, despite the lack of evidence that this was a result of sexual interactions, patterns of partner availability, competition, patterns of grooming reciprocity, or agonistic alliance support. From these results, it is suggested that in some contexts, grooming of subordinate nonkin may function to reduce tension in thegroomer. In the Japanese macaque, this latter possibility and the asymmetric grooming of subordinate homosexual partners may prove to be exceptions to the general rule that female cercopithecine grooming of nonkin flows up the dominance hierarchy.     

Grooming relationships of adolescent orphans in a free-ranging group of Japanese macaques (Macaca fuscata) at Katsuyama: a comparison among orphans with sisters, orphans without sisters, and females with a surviving mother

The present study examined grooming relationships of adolescent females in a free-ranging group of Japanese macaques (Macaca fuscata) at Katsuyama. To assess whether the loss of the mother influenced the grooming relationships of adolescent females (5–7 years old), we compared the time spent in grooming interactions and the number of grooming partners among the following three groups: 6 adolescent orphans with sisters, 9 adolescent orphans without sisters, and 11 adolescent non-orphans with surviving mothers. In Japanese macaques, grooming most frequently occurs between mothers and their daughters. Therefore, it is expected that if the mother is lost, orphans will devote less time to grooming interactions than non-orphans. However, the time spent in overall grooming interactions did not differ among the three groups. While non-orphans maintained grooming relationships with their mothers, orphans acquired alternative grooming relationships with other group members. Orphans adopted two kinds of tactics to compensate for the loss of the mother. First, adolescent orphans with sisters developed more affiliative grooming relationships with their sisters than non-orphans with sisters. Secondly, adolescent orphans without sisters spent more time in grooming interactions with same-aged females and non-related adult females. Moreover, regarding grooming interactions with same-aged females and non-related adult females, orphans without sisters had a larger number of grooming partners than non-orphans. These results indicate that adolescent females have enough flexibility to develop their grooming network after the loss of their mothers, and that the lack of mother and sisters might accelerate socialization of adolescent females and enable them to be integrated in reciprocal adult grooming relationships.     

Grooming, social bonding, and agonistic aiding in rhesus monkeys

An analysis of simultaneous grooming bouts in a captive group of rhesus monkeys (Macaca mulatta) failed to provide evidence of competition to groom high ranking partners. Not only were grooming supplantations rare, but the highest ranking individuals performing grooming did not groom the highest ranking animals receiving grooming. Lower ranking partners, however, did more grooming in nonkin dyads. Grooming partners aided one another in agonistic episodes, but the individual receiving the aid did not groom the individual providing the aid more than vice versa. Kin dyads did aid and groom one another at greater than expected rates, but the aider did not receive the greater proportion of grooming in the dyad. Males participated in more grooming than expected, but their grooming was not related to aiding either with regard to one another or female partners. Animals that were targeted in joint aggression, or aided against, received significantly less grooming from their opponents. A general social relationship expressed in partner preferences, social grooming, and agonistic aiding better explained the observed pattern than any model based on the exchange of services for favors in different currencies.     

Observations on the behaviour and ecology of the Patas monkey (Erythrocebus patas) in the Waza Reserve, Cameroon

Observations on the behaviour and ecology of Patas monkeys in Cameroon complement those made in Uganda by Hall (1965) and contribute to an understanding of the proximate factors involved in the maintenance of Patas social structure and to seasonal changes in their behaviour and ecology. The heterosexual groups had a mean size of 21. Five all-male groups were seen. High proportions of similarly sized infants indicate that there is a birth season at Waza from November to January inclusive. At the peak of the dry season intergroup contacts were very common at the water holes. The frequency of agonistic encounters increased remarkably at this time, especially between monkeys of different groups. The nature of these encounters indicated that the harem males are effective in driving off extragroup males and that females and juveniles are instrumental in maintaining space and social exclusiveness between heterosexual groups. The frequency of interspecific encounters also increased at the peak of the dry season.     

Long-term study of the social dynamics of patas monkeys (<Emphasis Type="Italic">Erythrocebus patas</Emphasis>): group male supplanting and changes to the multi-male situation

Data on social changes in patas monkey (Erythrocebus patas) groups were collected to clarify the general characteristics of male supplantation and to evaluate the overall role of supplanting in patas society. Seven patas groups were observed in Kala Maloue National Park, Northern Cameroon for 11 years. Analysis of this data revealed that social change, such as male supplanting, was restricted to the mating season. Male supplanting occurred in the course of outsider males seeking to gain access to estrous females within the heterosexual group and supplanting was inevitably followed by a multi-male situation arising in the group. Many cases of multi-male invasion were preceded by the supplanting of resident males and the multi-male situation arose due to a temporary absence of serious aggression towards invader males by the new resident males. Notably, an all-male group was found only once and it did not contribute to the supplanting of resident males in the one-male group. Electronic Publication     

The influence of behavioral context and social characteristics on the physical aspects of social grooming in rhesus monkeys

The extent to which dominance status and sex can influence the physical act of grooming was examined in two groups of rhesus monkeys. Both the sex and the dominance status of the groomee, but not of the groomer, were found to affect the body sites groomed and the positions assumed by the animals during the grooming bout. Females were groomed more on the back and head and less on the tail, rump, upper leg, and lower arm than males. Females with infants tended to face away from the groomer. Higher-ranking groomees were groomed more on the tail and rump and less on the upper leg and back than lower-ranking groomees. Higher-ranking groomees spent more time lying down during grooming than lower-ranking groomees, while lower-ranking groomees faced away from the groomer more then higher-ranking groomees. The behavioral interactions just prior to and immediately after grooming were also recorded. Although the onset of grooming was preceded by social interactions between the partners, the end of grooming was followed by a complete break in interactions. Particular types of social signals displayed by the groomee just prior to grooming were highly correlated with the grooming of specific body sites. These results suggest that the groomee controls the behavior of the groomer by the social signals it displays and the positions it maintains during the grooming bout. Thus, the grooming act itself may play an important role in the social relationships between group members.     

Grooming,kinship, and co‐feeding in captive spider monkeys (Ateles geoffroyi)

Allo‐grooming is perhaps the most powerful affiliative behavior observed in non‐human primates. However, the functional significance of grooming in New World monkeys has not yet been fully understood, perhaps because grooming is less frequently observed in platyrrhines. To differentiate the potential role of affiliative investment and/or kinship on sharing access to food (co‐feeding) in spider monkeys, behavioral data on grooming, embracing, and feeding were collected from two different groups of captive study subjects: a familiar/kin group and a non‐familiar/non‐kin group. The results of this study suggest that family‐related spider monkeys that engage in grooming tend to share access to food resources more than unfamiliar conspecifics that do not groom. One explanation for this difference is that the unfamiliar study subjects had not yet invested in the affiliative social network, were not reciprocating their affiliative investments and hence, had a higher tendency toward single animal monopolizing resources. Degree of relatedness alone was not found to be a determinant for sharing the access to food, suggesting that familiarity in spider monkeys is based on the extent to which animals invest in affiliative relationships. In this study, only animals that had engaged in long‐term grooming and recognized each other as familiar shared the access to food. Therefore, it might be likely that in spider monkeys, long‐term grooming of high intensity has to be developed for co‐feeding to occur. Zoo Biol 20:293–303, 2001. © 2001 Wiley‐Liss, Inc.     

Social behaviors of all-male proboscis monkeys when joined by females

In a riverine forest along the Menanggul River, which is a tributary of the Kinabatangan River, Sabah, Malaysia, I observed an all-male group of proboscis monkey (Nasalis larvatus) consisting of 27–30 (mean: 28.8) individuals. This large size of the all-male group seems to be attributed to habitat fragmentation because of the expansion of oil palm plantations. A few females joined this all-male group. Sub-adult females copulated with subadult or large juvenile males. Since the mean male tenure period of this monkey was estimated to be longer than female maturity, and prematured females might leave their natal one-male groups to avoid inbreeding and temporarily participate in the all-male group where males were permissive to them. Even when females joined this group, no conflicts occurred among males.     

Mating patterns,mate choice,and birth season heterosexual relationships in free-ranging rhesus macaques

Birth season adult heterosexual nonkin relationships of 50 free-ranging female rhesus macaques (Macaca mulatta) in two social groups at Cayo Santiago, Puerto Rico were examined using focal follow (289 hr) and ad lib data. Eighty-eight percent of subjects had at least one relationship characterized by particularly high frequencies of spatial proximity, grooming, or both. These were designated “friendships.” Males intervened in aggressive interactions more frequently on behalf of Friends than non-Friends. Female aggressive support of males was extremely rare. Higher-ranking males experienced more friendships than lower-ranking males. High-ranking females had higher-ranking Friends than low-ranking females. Older females had higher-ranking Friends than younger females. Females groomed high-ranking Friends more than they were groomed by them, whereas they groomed low-ranking Friends less than they were groomed by them. In one social group, high-ranking females were more likely than low-ranking females to groom their Friends more than they were groomed by them. Males were more responsible than females for spatial proximity maintenance in 9 of 14 Friend dyads for which sufficient data were available. Neither male nor female dominance rank affected responsibility for proximity maintenance in Friend dyads. Eight of 24 females had friendships with males with whom they had completed copulations during their conception peri-ovulatory period of the preceding mating season. Two of 19 females completed peri-ovulatory copulations with Friends during the following mating season. Friendship was not correlated with either of two demonstrated female mate choice indicators: (1) proximity maintenance during estrus; or (2) cooperation with male “hip-grasp” courtship attempts. Males directed “muzzle-up” courtship signals at lower rates toward Friends than toward non-Friends. These and other investigators' results indicate that (1) protection from aggression is the primary benefit to female rhesus macaques of birth season heterosexual relationships; (2) the most effective protectors are in greatest demand as Friends; and (3) friendship has no effect or an inhibitory effect on mate choice in this species. Benefits to males of friendships were not apparent from this study but may include coalitional support against lower-ranking males.     

Intergroup social dynamics of the Cayo Santiago rhesus (Macaca mulatta) with special reference to changes in group membership by males

Observations were made on the rhesus monkeys,Macaca mulatta living on the island of Cayo Santiago over a two-year period. Agonistic behaviors between members of different groups were the most common type of inter-group interaction, typically occurring in the vicinity of the feeders. Instances of social grooming and copulation between members of different groups were observed very infrequently.Changes in groups membership were made almost exclusively by males, particularly three-and four-year-old animals, and the changes occurred predominantly during the autumn breeding season. Peripheral all-male subgroups were preferred by males changing groups, perhaps because siblings or peer-group associates were to be found in those subgroups. The process of joining a new group by forming an affectional relationship with another male is described briefly. It is suggested that the phenomenon of group membership change by adult males is not an artifact of the island colony but its high frequency may be a consequence of the tremendously overcrowded conditions on the island.     

Group size, grooming and fission in primates: a modeling approach based on group structure

In social animals, fission is a common mode of group proliferation and dispersion and may be affected by genetic or other social factors. Sociality implies preserving relationships between group members. An increase in group size and/or in competition for food within the group can result in decrease certain social interactions between members, and the group may split irreversibly as a consequence. One individual may try to maintain bonds with a maximum of group members in order to keep group cohesion, i.e. proximity and stable relationships. However, this strategy needs time and time is often limited. In addition, previous studies have shown that whatever the group size, an individual interacts only with certain grooming partners. There, we develop a computational model to assess how dynamics of group cohesion are related to group size and to the structure of grooming relationships. Groups’ sizes after simulated fission are compared to observed sizes of 40 groups of primates. Results showed that the relationship between grooming time and group size is dependent on how each individual attributes grooming time to its social partners, i.e. grooming a few number of preferred partners or grooming equally or not all partners. The number of partners seemed to be more important for the group cohesion than the grooming time itself. This structural constraint has important consequences on group sociality, as it gives the possibility of competition for grooming partners, attraction for high-ranking individuals as found in primates’ groups. It could, however, also have implications when considering the cognitive capacities of primates.     

Urinary androgen and corticoid levels in captive, male Western lowland gorillas (Gorilla g. gorilla): age- and social group-related differences.

Urinary androgen and corticoid levels were measured for 52 captive male Western lowland gorillas to examine age-related variance and potential differences resulting from various social situations. Significant diurnal variation was present in both hormones. Age-related differences in androgens revealed that males experienced two stages of androgen increase and one stage of decrease: increases occurred from juvenile (less than 10 yr of age) to subadult (between 10-13 yr) and subadult to young adult (14-20 yr), whereas decreases occurred from young adult to adult (> 20 yr). Age-related differences in corticoid levels varied depending on the time of day, but morning corticoids were greatest in juvenile males, followed by young adult males. The type of social grouping was associated with differences in corticoid levels, as animals housed socially (in either a heterosexual or all-male group) had similar corticoid levels, whereas solitary males showed greater corticoid levels than their socially-housed counterparts. The increased levels of corticoids in solitary-housed males suggest this management strategy might not be optimal, although more data are needed. Additionally, the significantly greater levels of androgens and corticoids in young adult male gorillas may present management challenges, and thus zoos may need to consider increasing the flexibility of their current management practices with respect to males.     

Reciprocation and interchange in wild Japanese macaques: grooming, cofeeding, and agonistic support

Social primates spend a significant proportion of their time exchanging grooming with their group companions. Although grooming is mainly exchanged in kind, given its hygienic and tension-reducing functions, it is still debated whether grooming also provides some social benefits, such as preferential access to resources (e.g., food or mating partners). In this study we analyzed grooming distribution among wild female Japanese macaques living in two groups on Yakushima. We tested the tendency of monkeys to reciprocate the amount of grooming received, and to direct their grooming up the hierarchy. Then we analyzed the relation of grooming to three of its possible benefits: reduced aggression, increased tolerance over food, and agonistic support against a male aggressor. The data were analyzed by means of row-wise matrix correlations. Grooming was highly reciprocated (i.e., exchanged in kind) and directed up the hierarchy in both the study groups. No significant relationship was found between grooming and aggression. Conversely, grooming favored tolerance over food, since it was positively correlated with presence on the same food patch, close proximity, and close approaches (both within 1 m) during feeding. Grooming was also positively related to agonistic support against adult males, although this relationship became nonsignificant when we controlled for kinship. Although these results are not definitive, they suggest that monkeys may derive various social benefits from grooming. This conclusion is supported by the fact that in various primate species animals tend to prefer high-ranking individuals as grooming partners.     

Social relationship and hair cortisol level in captive male chimpanzees (<Emphasis Type="Italic">Pan troglodytes</Emphasis>)

Understanding how social relationships affect long-term stress is important because stress has a profound impact on the welfare of animals and social relationships often exert a strong influence on their stress responses. The purpose of this study was to investigate the relationship between social behaviors and long-term stress levels as assessed by hair cortisol (HC) concentration. The subjects were 11 chimpanzees living in an all-male group (divided into two sub-groups) in Kumamoto Sanctuary, Kyoto University, Japan. Behavioral data were collected between December 2014 and March 2015. The total observation time was 129 h. Hair samples were collected in late March and early April 2015, and cortisol was extracted from the hair and measured with enzyme immunoassay. The hair growth rate was estimated to be 1.33 ± 0.06 cm/month. The results revealed that there was a positive correlation between the rate of receiving aggression and HC levels. We also found a significant negative correlation between the balance between giving and receiving grooming (grooming balance index: GBI), which was calculated by subtracting the rate with which grooming is given from that with which it is received, and the rate of receiving aggression and between the GBI and HC levels. Thus, individuals receiving higher levels of aggression also tended to give grooming for relatively long periods compared to the time they were being groomed. In contrast, the rate of initiating aggression did not have a relationship with either HC levels or any measure of social grooming. We did not find social buffering effects, as there was no correlation between mutual social grooming and HC levels. These results show that not only aggressive interactions but also overall social situations in which animals do not have balanced relationships with others might result in the long-term elevation of cortisol levels in captive male chimpanzees.     

The ecology of the introduced patas monkey (Erythrocebus patas) population of Southwestern Puerto Rico

This paper presents the results of a study on the introduced, free-ranging patas monkey population of Southwestern Puerto Rico (SWPR). It describes information on the population size, social group composition, diet, daily ranging patterns, and patas home range during a 3 year period. The patas monkey population in the study area consisted of approximately 120 individuals in four heterosexual groups and several all-male bands. Within their home ranges (26.8 km²), the population density was 4.47 individuals/km². Home range size among the population's four heterosexual groups varied from 3.72 km² to 15.39 km², and minimum daily distance traveled ranged from 0.8–2.0 km. In general, the social structure and mating system of this population parallels what has been described for African populations. However, habitat use, ranging behavior, and the quality of intergroup interactions suggests that patas of this population exhibit territorial behavior. Am. J. Primatol. 45:351–365, 1998. © 1998 Wiley-Liss, Inc.     

Grooming interactions among adult chimpanzees at Bossou,Guinea, with special reference to social structure

Grooming and proximity interactions among chimpanzees at Bossou, Republic of Guinea, were analyzed as an index of friendly and affinitive relationships among adult males, among adult females, and between the sexes. Data from the first (1976–1977) and the third (1982–1983) study period were used. The expected value of their interactions was calculated from the number of adult males and females in the group and also from the observed frequency of combinations of adult males and females in the parties (temporary foraging groups). In the pooled data from the two periods, there was little difference between grooming and proximity (without grooming). The frequency of male-female grooming and proximity interactions was lower than expected, and that of female-female interactions was higher than expected. The frequencies of male-male grooming and proximity were intermediate but fluctuated. Male-male grooming frequency was lower than that recorded in chimpanzees of East Africa. Characteristics of same-sex affinitive interactions, especially between Bossou chimpanzee females, clearly differ from those of East African chimpanzees and are more like those recorded for female-related groups of Japanese macaques (Macaca fuscata).These differences indicate the variability and flexibility of chimpanzee social structure.     

The social component of dominance relationships in rhesus monkeys (Macaca mulatta)

An all-male rhesus group was added to a second group, one animal at a time, at weekly intervals, in reverse order of their dominance ranks. Significant positive correlations prevailed for the host group dominance ranks throughout the study, but the dominance ranks of the introduced males were random with respect to their original ranks. A second experiment repeatedly introduced the alpha and beta males of a multi-male heterosexual group into a second group where they were the lowest-ranking animals. On each return they reclaimed alpha and beta positions. When the alpha and beta males of the second group were introduced to the first group, they became the lowest-ranking animals in the group. Reversal of the direction of introduction again demonstrated that relative ranks were dependent on the social context.