Lethal intergroup aggression by chimpanzees in Kibale National Park, Uganda

Chimpanzees (Pan troglodytes) have hostile intergroup relations throughout most or all of their geographic range. Hostilities include aggressive encounters between members of neighboring communities during foraging and during patrols in which members of one community search for neighbors near territory boundaries. Attacks on neighbors involve coalitions of adult males, and are sometimes fatal. Targets include members of all age/sex classes, but the risk of lethal intergroup coalitionary aggression is highest for adult males and infants, and lowest for sexually swollen females. The best-supported adaptive explanation for such behavior is that fission-fusion sociality allows opportunities for low-cost attacks that, when successful, enhance the food supply for members of the attackers' community, improve survivorship, and increase female fertility. We add to the database on intergroup coalitionary aggression in chimpanzees by describing three fatal attacks on adult males, plus a fourth attack on an adult male and an attack on a juvenile that were almost certainly fatal. Observers saw four of these attacks and inferred the fifth from forensic and behavioral evidence. The attackers were males in two habituated, unprovisioned communities (Ngogo and Kanyawara) in Kibale National Park, Uganda. We also summarize data on other intercommunity attacks at Ngogo. Our observations are consistent with the "imbalance of power" hypothesis [Manson & Wrangham, Current Anthropology 32:369-390, 1991] and support the argument that lethal coalitionary intergroup aggression by male chimpanzees is part of an evolved behavioral strategy.     

Grooming Between Male Chimpanzees at Ngogo,Kibale National Park. I. Partner Number and Diversity and Grooming Reciprocity

Allogrooming serves many social functions in primates. Grooming can help individuals to service social relationships generally, sometimes reciprocally, and may be particularly important in the development and maintenance of alliances. However, time constraints limit the number of partners with whom one individual can groom enough to maintain cooperative relationships. As a result, the size of its grooming network may reach an asymptote as the size of its group increases, and it may distribute its grooming less equally among potential partners. Chimpanzees live in multimale, fission-fusion communities; males are philopatric, and commonly associate and groom with each other. Males form within-community alliances that influence dominance rank and access to mates, and allies groom with each other regularly; males also cooperate in aggression between communities. The chimpanzee community at Ngogo, in Kibale National Park, Uganda, is unusually large and has more males than any other known community. Field data show that adult Ngogo males groomed far more with other adult males than with females or with adolescent males, in contrast to a previous report (Ghiglieri, 1984). Adolescent males groomed adults much more than the reverse; males groomed and were groomed by females about equally. Individual males groomed mostly with a small number of other males. On average, males at Ngogo had only slightly more male grooming partners overall and had the same number of important partners as those of males in a much smaller community in the Mahale National Park, Tanzania, and they distributed their grooming less equitably. These results fit those expected if limits on available grooming time cause males to have a loyalty problem as the number of potential grooming and alliance partners increases. Despite differences in the extent and equitability of their grooming networks, males at both Ngogo and Mahale showed reciprocity in grooming. Grooming reciprocity has been demonstrated for captive chimpanzee males, but the Ngogo findings are the first demonstrations of reciprocity in wild communities.     

Grooming Between Male Chimpanzees at Ngogo,Kibale National Park. II. Influence of Male Rank and Possible Competition for Partners

Allogrooming contributes to the development and maintenance of social relationships, including those that involve alliances, in many primate species. Variation in relatedness, dominance rank, and other factors can produce variation in the value of others as grooming partners. Several models have been developed to account for variation in the distribution of grooming in relation to dominance ranks. These start from the premise that individuals are attracted to high-ranking partners, but time limits, direct competition, and prior grooming engagement between high-ranking individuals can constrain access to them. Sambrook et al. (1995) formalized some of these models and showed the importance of taking group size variation into account when assessing them. Chimpanzees form multimale communities in which males are the philopatric sex. Males commonly associate and groom with each other; they also form dominance hierarchies and form alliances that influence dominance ranks and mating success. Both male rank and the rank distance between partners are significantly correlated with the distribution of grooming between males in an extremely large chimpanzee community at Ngogo, Kibale National Park, Uganda, that has more males than any other known community. High-ranking males had more grooming partners than mid- or low-ranking males. Grooming predominantly went up the dominance hierarchy, but was also concentrated among males that were close in rank. Rank and rank distance apparently both affected grooming independently of reciprocity in grooming and independently of the frequency with which males associated in temporary parties. However, the data do not clearly indicate how constraints on access to partners might have operated. Published data from a smaller chimpanzee community at Mahale show no rank or rank distance effect on male grooming. These results and earlier, conflicting findings on the association between dominance rank and grooming in male chimpanzees indicate that variation in group size, i.e., the number of males per community, probably influences the strength of any such effects, as happens for grooming between females in several cercopithecine species. Data on coalitions at Ngogo support the argument that high-ranking males are valuable social partners, and similarity in strategies of alliance formation may influence the distribution of grooming.     

New Cases of Intergroup Violence Among Chimpanzees in Gombe National Park,Tanzania

Despite considerable attention to chimpanzee intergroup violence, the number of observed cases remains small. We report 4 cases of intergroup violence that occurred in Gombe National Park, Tanzania, between 1993 and 2002. We observed (3 cases) or inferred (1 case) males from the Kasekela community to attack members of their 2 neighboring communities: Mitumba and Kalande. In 1993, Kasekela males killed and ate a female infant from Mitumba. In 1998, Kasekela males captured 2 infants (sex unknown) from Kalande, one of which escaped and the other was killed and eaten. Also in 1998, Kasekela males attacked an adolescent male from Kalande. The victim was alive but severely injured by the end of the attack. The intensity and duration of the attack are comparable to other attacks that resulted in fatal injuries. In 2002, observers found the body of an adolescent male from Mitumba following an incursion by Kasekela males into the area. The injuries inflicted on the Mitumba male together with circumstantial evidence suggest that Kasekela males killed him. The attacks support the view that intergroup violence is a persistent feature of chimpanzee societies and that the primary benefit attackers gain from them is reduced competition for resources.     

New Intercommunity Infanticides by the Chimpanzees of Ngogo,Kibale National Park,Uganda

Hostile intercommunity relations, including attacking and killing extra-community infants of both sexes have occurred at most wild chimpanzee sites. We describe three recent cases of intercommunity attacks on infants committed by members of the Ngogo chimpanzee community in Kibale National Park, Uganda. Two of the attacks resulted in confirmed infanticides while a third attack probably resulted in the infant's death. In common with previous accounts of chimpanzee infanticides, the attacks described here occurred during boundary patrols outside the Ngogo community's usual range, adult and adolescent males were the main participants, one infant was cannibalized after being killed, and the victims’ mothers did not accompany the attacking party back to the Ngogo range. However, the patrol parties during each infanticide were larger than before and included females from the Ngogo community. Our observations indirectly support both the range expansion and imbalance of power hypotheses, which address why and under which conditions chimpanzee intercommunity encounters lead to aggression. These cases of intercommunity infanticide add to the growing database of the phenomenon in wild chimpanzees.     

Violent coalitionary attacks and intraspecific killing in wild white-faced capuchin monkeys (<Emphasis Type="Italic">Cebus capucinus</Emphasis>)

During 12 years of observation, we have observed three confirmed and two inferred lethal coalitionary attacks on adult male white-faced capuchins (Cebus capucinus) by members of two habituated social groups at Lomas Barbudal Biological Reserve, Costa Rica. In one case, an alpha male was badly wounded and evicted from his group, and when later found by his former groupmates he was attacked by several of them and died less than 24 h later. In two other cases, lone extra-group males were mobbed by adult and immature males of a bisexual group. One victim's abdomen was torn open and he died less than 24 h later. A second victim was quite badly bitten but may have escaped. The fourth and fifth cases resulted from intergroup encounters. One victim lost the use of both arms but may have survived, whereas the other died of unknown causes within an hour of the attack. The observed death rate from coalitionary aggression at our site is approximately the same as that reported for eastern chimpanzees. Because at least three of the five observed incidents involved large coalitions attacking lone victims, they support the general hypothesis that imbalances of power contribute to intraspecific killing in primates. However, the occurrence of lethal coalitional attacks in a species lacking fission–fusion social organization poses a challenge to the more specific version of the imbalance-of-power hypothesis proposed by Manson and Wrangham in 1991 to explain chimpanzee and human intergroup aggression.     

New cases of inter-community infanticide by male chimpanzees at Ngogo,Kibale National Park,Uganda

Infanticide by males has been recorded in four chimpanzee populations, including that in Kibale National Park, Uganda. Some infanticidal attacks occur during inter-community aggression. The sexual selection hypothesis does not easily explain these attacks because they may not directly increase male mating opportunities. However, females in the attackers’ community may benefit by expanding their foraging ranges and thereby improving their reproductive success; thus infanticide may increase male reproductive success indirectly. We report two new cases of infanticide by male chimpanzees at Ngogo, Kibale National Park. Like two previous cases, these occurred during a boundary patrol and were almost certainly between-community infanticides. The patrolling males attacked despite the proximity of males from the victims’ presumed community. This probably explains why, unlike the earlier cases, they did not completely cannibalize their victims. Such attacks seem to be relatively common at Ngogo and infanticide may be an important source of infant mortality in neighboring communities. Our observations cannot resolve questions about the sexual selection hypothesis. However, they are consistent with the range expansion hypothesis: the infanticides occurred during a period of frequent encounters between communities associated with a mast fruiting event, and Ngogo community members greatly increased their use of areas near the attack site during another mast fruiting event one year later. Our observations contribute to growing evidence that lethal intergroup aggression is a common characteristic of wild chimpanzee populations.     

Adolescent male chimpanzees do not form a dominance hierarchy with their peers

Dominance hierarchies are a prominent feature of the lives of many primate species. These hierarchies have important fitness consequences, as high rank is often positively correlated with reproduction. Although adult male chimpanzees strive for status to gain fitness benefits, the development of dominance relationships is not well understood. While two prior studies found that adolescent males do not display dominance relationships with peers, additional research at Ngogo in Kibale National Park, Uganda, indicates that adolescents there form a linear dominance hierarchy. These conflicting findings could reflect different patterns of rank acquisition across sites. An alternate possibility arises from a recent re-evaluation of age estimates at Ngogo and suggests that the report describing decided dominance relationships between adolescent males may have been due to the accidental inclusion of young adult males in the sample. To investigate these issues, we conducted a study of 23 adolescent male chimpanzees of known age during 12 months at Ngogo. Adolescent male chimpanzees exchanged pant grunts, a formal signal of submission, only 21 times. Recipients of pant grunts were late adolescent males, ranging between 14 and 16 years old. In contrast, younger adolescent males never received pant grunts from other males. Aggression between adolescent males was also rare. Analysis of pant grunts and aggressive interactions did not produce a linear dominance hierarchy among adolescent males. These data indicate that adolescent male chimpanzees do not form decided dominance relationships with their peers and are consistent with the hypothesis that the hierarchy described previously at Ngogo resulted from inaccurate age estimates of male chimpanzees. Because dominance relationships develop before adulthood in other primates, our finding that adolescent male chimpanzees do not do so is surprising. We offer possible explanations for why this is the case and suggest future studies that may help clarify the matter.     

Hormonal Mechanisms for Regulation of Aggression in Human Coalitions

Coalitions and alliances are core aspects of human behavior. All societies recognize alliances among communities, usually based in part on kinship and marriage. Aggression between groups is ubiquitous, often deadly, fueled by revenge, and can have devastating effects on general human welfare. Given its significance, it is surprising how little we know about the neurobiological and hormonal mechanisms that underpin human coalitionary behavior. Here we first briefly review a model of human coalitionary behavior based on a process of runaway social selection. We then present several exploratory analyses of neuroendocrine responses to coalitionary social events in a rural Dominican community, with the objective of understanding differences between in-group and out-group competition in adult and adolescent males. Our analyses indicate: (1) adult and adolescent males do not elevate testosterone when they defeat their friends, but they do elevate testosterone when they defeat outsiders; (2) pre-competition testosterone and cortisol levels are negatively associated with strength of coalitionary ties; and (3) adult males usually elevate testosterone when interacting with adult women who are potential mates, but in a striking reversal, they have lower testosterone if the woman is a conjugal partner of a close friend. These naturalistic studies hint that reciprocity, dampening of aggression, and competition among friends and allies may be biologically embedded in unique ways among humans.     

Intragroup lethal aggression in wild spider monkeys

We report the first evidence of intragroup coalitionary aggression leading to the death of a wild young adult male spider monkey. During a long-term study of a well-habituated community at the Otoch Ma'ax Yetel Kooh reserve in Yucatan, Mexico, a young adult male sustained severe injuries repeatedly between January and March 2002. On 1 April 2002 the same male was the victim of an intragroup attack by at least one adult male that resulted in his death. We highlight several causes of intragroup aggression that may account for the killing.     

A within-group gang attack on a young adult male chimpanzee: Ostracism of an ill-mannered member?

During a long-term study of wild chimpanzees in Tanzania, an unusual gang attack on a young adult male by the alpha male and seven other members of the same unit group (community) was observed and videotaped. Before the gang attack, the victim had not pant-grunted to the alpha male or to other adult males except for the second-ranked male, but had often bullied adult females without apparent reason. The alpha male's violent behavior, therefore, might have been punishment of or revenge against the ill-mannered young chimpanzee. This is the first record of an adult male other than an ex-alpha male becoming the object of ostracism by wild chimpanzees, although the victimized male did manage to return to the group after more than three months, when an ex-alpha male succeeded in reestablishing his former position.     

Alpha male chimpanzee grooming patterns: implications for dominance “style”

In social primates, individuals use various tactics to compete for dominance rank. Grooming, displays and contact aggression are common components of a male chimpanzee's dominance repertoire. The optimal combination of these behaviors is likely to differ among males with individuals exhibiting a dominance “style” that reflects their tendency to use cooperative and/or agonistic dominance tactics. Here, we examine the grooming behavior of three alpha male chimpanzees at Gombe National Park, Tanzania. We found that (1) these males differed significantly in their tendency to groom with other males; (2) each male's grooming patterns remained consistent before, during and after his tenure as alpha, and (3) the three males tended to groom with high‐ middle‐ and low‐ranking partners equally. We suggest that body mass may be one possible determinant of differences in grooming behavior. The largest male exhibited the lowest overall grooming rates, whereas the smallest male spent the most time grooming others. This is probably because large males are more effective at physically intimidating subordinates. To achieve alpha status, a small male may need to compensate for reduced size by investing more time and energy in grooming, thereby ensuring coalitionary support from others. Rates of contact aggression and charging displays conformed to this prediction, suggesting that each male exhibited a different dominance “style.” Am. J. Primatol. 71:136–144, 2009. © 2008 Wiley‐Liss, Inc.     

Intra‐community coalitionary lethal attack of an adult male southern muriqui (Brachyteles arachnoides)

We report on the first evidence of intra‐community coalitionary lethal aggression in muriquis (Brachyteles). The event occurred in southern muriquis (Brachyteles arachnoides) during a long‐term study (>15 years) of two social groups inhabiting mostly pristine Atlantic forest habitat in the Parque Estadual Carlos Botelho, southern São Paulo State, Brazil. The attack took place deep in the core area of the Group Caetê home range. Tense agonistic behaviors and vocalizations preceded the lethal coalitionary attack, and the tension increased over a 36–48 hr period. One adult female and two unidentified individuals also took part in a coalition led by six adult males. The members of the coalition collectively approached, embraced, immobilized and repeatedly bit the entire body of an adult male, resulting in severe bleeding injuries and the victim's death in less than 1 hr after the attack commenced. Combined ecological, behavioral and spatial data related to the event indicate that this was an intra‐community attack and suggest social tensions related to mating competition as the proximate trigger of the coalitionary killing. The attack resembled those reported for chimpanzees, with clear numeric superiority and a low risk of injury to aggressors, resulting in the death of a lone conspecific victim. This observation (n=1) is suggestive of a capacity for escalated aggression in muriquis and reinforces arguments for the potential adaptive significance of intra‐community aggression in male philopatric societies, as reported for spider monkeys and chimpanzees. These characteristics challenge the view of the muriquis as a peaceful primate and support the general hypothesis that imbalances of power contribute to intra‐specific killing in primates, such as chimpanzees and humans. Am. J. Primatol. 71:860–867, 2009. © 2009 Wiley‐Liss, Inc.     

Violent coalitionary attack by female mandrills against an injured alpha male

Female contact aggression against males is relatively rare in species in which the adult males are larger than the females, but it has the potential to influence group structure, male group membership, tenure, and dominance rank. We report an incident in which female mandrills living in a semi-free-ranging group in Franceville, Gabon, attacked a male that was apparently incapacitated after a fight with another male and was unable to escape. The attack involved the alpha male and did not occur in a sexual or infanticidal context. Other adult and adolescent males observed the attack, but when one adult male attempted to participate he was chased away by the females. This observation adds to reports of female coalitions excluding unwanted males from primate groups, or even killing them. The fact that this can also occur in mandrills suggests that females have a degree of control over male group membership, despite the large degree of sexual dimorphism in this species, and highlights the importance of coalitions in primate social organization.     

Adolescent male chimpanzees (Pan troglodytes) form social bonds with their brothers and others during the transition to adulthood

Social relationships play an important role in animal behavior. Bonds with kin provide indirect fitness benefits, and those with nonkin may furnish direct benefits. Adult male chimpanzees (Pan troglodytes) exhibit social bonds with maternal brothers as well as unrelated adult males, facilitating cooperative behavior, but it is unclear when these bonds develop. Prior studies suggest that social bonds emerge during adolescence. Alternatively, bonds may develop during adulthood when male chimpanzees can gain fitness benefits through alliances used to compete for dominance status. To investigate these possibilities and to determine who formed bonds, we studied the social relationships of adolescent and young adult male chimpanzees (N = 18) at Ngogo in Kibale National Park, Uganda. Adolescent male chimpanzees displayed social bonds with other males, and they did so as often as did young adult males. Adolescent and young adult males frequently joined subgroups with old males. They spent time in proximity to and grooming with old males, although they also did so with their age peers. Controlling for age and age difference, males formed strong association and proximity relationships with their maternal brothers and grooming relationships with their fathers. Grooming bonds between chimpanzee fathers and their adolescent and young adult sons have not been documented before and are unexpected because female chimpanzees mate with multiple males. How fathers recognize their sons and vice versa remains unclear but may be due to familiarity created by relationships earlier in development.     

Affiliative relationships and reciprocity among adult male bonnet macaques (Macaca radiata) at Arunachala Hill, India

In captivity, male bonnet macaques (Macaca radiata) frequently express "friendship" toward one another, including affiliative behavior such as huddling, grooming, coalitionary support, and sitting in close proximity. The purpose of this study was to determine whether wild adult male bonnet macaques also express "friendship" by investigating whether or not (1) adult male bonnet macaques have affiliative social relationships with other males, (2) the strength of social relationships varies among dyads, (3) there is time-matched reciprocity in allogrooming among dyads, and if so, whether the level of reciprocity occurs within a bout of grooming, a day, or over 2 months (the limit of this study), and (4) a correlation exists between the strength of social relationships and dominance ranks among adult males. Focal samples totaling 150 hr on all seven adult males in one study group were conducted to record both agonistic and affiliative interactions. Agonistic interactions were used to construct a dominance hierarchy, whereas affiliative interactions (sitting in proximity to within 1 m with and without grooming) were used to quantify the existence and strength of social bonds within dyads. Results show that adult male bonnet macaques had differentiated affiliative relationships with other males in their group. There was little reciprocity of grooming within a bout of grooming or within a day, but greater reciprocity over the study period of 2 months. There was no correlation between dominance ranking distance and the strength of affiliative relationship within dyads; however, within dyads lower-ranking males groomed higher-ranking males more than vice versa. This study suggests that friendships in male bonnet macaques are characterized not by immediate tit-for-tat reciprocal altruism, but by reciprocity over a longer time span, and that affiliative social relationships may be less constrained by agonistic relationships than is the case in more despotic species of macaques.     

The development of affiliative and coercive reproductive tactics in male chimpanzees

Like many animals, adult male chimpanzees often compete for a limited number of mates. They fight other males as they strive for status that confers reproductive benefits and use aggression to coerce females to mate with them. Nevertheless, small-bodied, socially immature adolescent male chimpanzees, who cannot compete with older males for status nor intimidate females, father offspring. We investigated how they do so through a study of adolescent and young adult males at Ngogo in Kibale National Park, Uganda. Adolescent males mated with nulliparous females and reproduced primarily with these first-time mothers, who are not preferred as mating partners by older males. Two other factors, affiliation and aggression, also influenced mating success. Specifically, the strength of affiliative bonds that males formed with females and the amount of aggression males directed toward females predicted male mating success. The effect of male aggression toward females on mating success increased as males aged, especially when they directed it toward females with whom they shared affiliative bonds. These results mirror sexual coercion in humans, which occurs most often between males and females involved in close, affiliative relationships.     

Sexual behavior of adult male chimpanzees of the Mahale Mountains national park,Tanzania

This study, based on 687 hr of focal observations, aims to describe overall patterns of the sexual behavior of the adult male chimpanzees of the Mahale Mountains, to compare the results with previous reports, and to explain the variations between studies. Genital inspection of cycling females by adult males was eight times as frequent as that of lactating females, and twice as frequent as that of pregnant females. Inspection of the genitals of cycling females increased dramatically 7–10 days before the onset of maximal swelling and gradually decreased as the day of ovulation approached. Adult males likely obtained information on the attractivity of females by inspecting their genitals. Mating was usually initiated by male courtship and followed by pelvic thrusts in a dorsoventral posture, performed on, rather than above, the ground, which continued for 7 s. on average, and was typically followed by female squeaking and darting from the male, or by the male grooming the female. Higher-ranking males mated with females in the peri-ovulatory period more frequently than did lower-ranking males. In particular, two alpha males mated with such females more often than did any other adult males. A male who interfered with a mating pair was dominant over the mating male in other agonistic contexts. The duration of intromission was correlated with neither dominance rank nor age. However, when an adult male declined in rank from alpha in 1991 to third in 1992, he showed a significantly shorter duration of intromission. This indicates that for a particular male, the alpha rank guaranteed longer duration of intromission. Allies of alpha males tended to mate with peri-ovulatory females more frequently than expected from their low dominance ranks. The number of mating partners was not correlated with male dominance rank, but was sometimes negatively correlated with male age. Females were significantly more likely to emit a copulatory squeak when mating with younger, rather than older, adult males. Male dominance rank and the rate of female copulatory squeaking were not correlated. Weaning infants regularly interfered with their mothers' mating. Occasionally, unrelated adolescent males and rarely females pushed themselves in between copulating adults. Female choice was indicated when they performed a “penis erection check” or took the initiative in courtship, or on the other hand showed strong reluctance to mate with particular males. Young adult males more often received erection checks than did prime males, while none of the three old adult males did. Courtship initiated by estrous females was not directed to two of the oldest males, the exception of which was the alpha male. The oldest males, except for the alpha, were consistently avoided by many estrous females, both young and old. In response to female reluctance, males behaved violently, however, this was not effective, because other more dominant males came to rescue the female. Neither courtship nor mating was seen between mature sons and their mothers, nor between brothers and sisters.     

Age differences in social interactions of young males in a chimpanzee unit-group at the Mahale Mountains National Park,Tanzania

The behavior and social interactions of young male chimpanzees were studied in relation to their age change. The data were obtained at the Mahale Mountains National Park, during a four-month period in 1986. Early adolescent males, becoming independent of their mothers, spend a long time near adults of both sexes. Late adolescent males are not tolerated by the senior males. Although such animals do not stop traveling together with their seniors, they are separated from the other members including the males of their own age class, and each of them lives a relatively lonely life. Where seniors are not nearby, they perform charging displays in front of estrous females. Young adult males tend to remain in the proximity of the alpha male, and can associate with their seniors without pant-grunting. Although some young adult males dominate over some senior males, increasingly performing charging displays, they do not appear to be permitted to associate intimately with their seniors; they are not yet considered to have attained social maturity. Prime and senior males are strongly bonded with one another, being able to associate intimately with those of their own or senior age classes including the alpha male. A young adult male's rise in rank is not connected with joining the “adult male-cluster,” nor does a senior male's decline necessarily means his dropping out from the cluster: the social position of male chimpanzees cannot be understood solely from their agonistic dominance rank. The alpha male plays a leading part in integrating the males of the unit-group. Young adult males and their seniors tend to associate most frequently with him, and all the males of the early adolescent or senior age classes pay attention to his movements.     

A case report of a male rank reversal in a group of wild white-faced capuchins (Cebus capucinus)

During the course of a study of social relationships in wild, white-faced capuchins at Lomas Barbudal, Costa Rice (May 1990–May 1993), the alpha male was deposed by a subordinate male. The rank reversal was preceded by a decline in proximity maintenance by females to the alpha male, and an increase, in the amount of aggression directed toward the alpha male by the beta female and her female coalition partners. At the time of the rank reversal, females switched from giving thegargle vocalization exclusively to the old alpha male to gargling to the new alpha male; however, juveniles were less consistent with regard to which male they gargled to. At the time of the rank reversal, most adult females reduced the time spent in proximity and grooming with the old alpha male, and increased the time spent in proximity and grooming with the new alpha male. In contrast, juveniles' patterns of affiliation with males did not change in a predictable way following the reversal. The social strategies employed by capuchin monkeys during this rank reversal are compared with those of chimpanzees.