Effects of age, sex, and reproductive status on scent marking frequencies in the golden lion tamarin, Leontopithecus rosalia

This study reports on the longitudinal changes in scent marking frequencies of male and female lion tamarins in relation to age, reproductive status, and group composition. Juvenile males and females in family groups and subordinate males in trios (2 males, 1 female) scent marked infrequently. Juvenile females scent marked less than juvenile males and began scent marking later. Adult pair-bonded males and females scent marked with similar frequencies. Females showed scent marking increases during mid-pregnancy, but their scent marking decreased both before and again after parturition. Both males and females exhibited decreases in scent marking while transporting dependent infants.     

Effects of age and sex on intra-group spacing behaviour in juvenile savannah baboons,Papio cynocephalus cynocephalus

Twenty juvenile members of known genealogies in two baboon groups were studied over a 16-month period to evaluate a number of predictions about juvenile spacing behaviour based on the natural history of savannah baboons. Young juveniles (1–2·5 years old) approached more frequently and spent more time in proximity to other group members than did old juveniles (3–5·5 years old). In particular, young juveniles associated more closely with their mothers, particular adult males (possible fathers) and age-peers than did old juveniles. Approaches of young juveniles towards unrelated, high-ranking adults were more likely to occur during feeding than were those of old juveniles. Also, following such an approach, young juveniles were more likely than old juveniles to begin feeding immediately. The overall rates of feeding of old juveniles were depressed when they were in proximity to unrelated, high-ranking adults, whereas the feeding rates of young juveniles were not. Juvenile males approached adult males more often than did juvenile females. Juvenile females approached unrelated adult females more often than did juvenile males. Sex differences also existed in juveniles' choices of unrelated adult female neighbours. Juvenile females associated most often with lactating females, whereas juvenile males associated primarily with cycling females. During group resting, juvenile females approached adult females from higher-ranking matrilines more often than they approached adult females from lower-ranking matrilines. Juvenile males did not exhibit this attraction. Also, among old juveniles, females associated closely with their mothers, whereas males did not. Taken together, the results support the hypotheses that juvenile baboons associate with group members in ways that (1) enhance the probability of surviving an early period of high mortality, (2) create opportunities for social learning of sex-typical behaviours/skills, and, for females, (3) facilitate acquisition of familial dominance status.     

Agonistic Interactions of Juvenile Savanna Baboons

19 juvenile members of known genealogies in two wild baboon groups were studied over a 16-month period to compare the ontogeny of agonistic experience and dominance relations for males and females. Juveniles of all age-sex classes were disproportionately likely to receive aggression from and submit to adult males per unit of time spent in proximity. This pattern intensified with increasing juvenile age. With age, juvenile females more often submitted to unrelated adult females from higher-ranking families, whereas this was not true for juvenile males. All juveniles received aggression from older group members more often during feeding than was expected by chance. High rates of agonistic interaction with unrelated adult females accounted for old juvenile females (3–5.5 years-old) interacting agonistically more frequently than male age peers and young juveniles of either sex (1–2.5 years-old). Adult females were also more aggressive toward females among young juveniles, suggesting that adult females target females among juveniles for aggression and resistance to rank reversal. Within juvenile age groups, males dominated all females and all younger males, irrespective of maternal dominance status. Dominance relations among female age-peers were generally isomorphic with relations among their mothers. No juvenile targeted any older male for rank reversal. Males targeted all older females, whereas females typically targeted only older females from families lower-ranking than their own. The strong sexual dimorphism in adult body size in baboons may explain why juvenile males' dominance relations with peers and adult females are not structured along lines of family membership as is true for the less dimorphic macaques. Acquisition of higher agonistic status probably allows juveniles of both sexes to increase their success in within-group feeding competition during late stages of juvenility, which, in turn, could affect important life-history traits such as age at menarche and adult body size.     

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.     

Social behaviour and infant carrying in a group of moustached tamarins,Saguinus mystax (primates: Platyrrhini: Callitrichidae), on Padre Isla,Peruvian Amazonia

The social behaviour of a group of eight moustached tamarins,Saguinus mystax, (five males, three females) was studied on Padre Isla in northeastern Peru. About 60% of all allogrooming was done by the two adult males in the group, and about 11% by a young adult female. All other group members groomed very little. The adult breeding female received more grooming than any other group member. After the death of the adult female (preyed upon by an anaconda) the amount of active allogrooming remained constant for all group members except for the young adult female, who increased her contribution to about 30%. Her preferred grooming partner was the subadult female, which generally screamed when being groomed by the young adult female and terminated grooming by going away. This kind of grooming relation is termed “forced grooming” and is interpreted as a possible social control mechanism. The young adult female groomed the adult males more often after the death of the adult female than before. This might have had the function of strengthening the social bond with the adult males and in obtaining the breeding position in the group. After the death of the adult female, the vulva of the young adult female grew to full adult size. Agonistic behaviour was less frequent than allogrooming. Most aggressive interactions (50%) originated from the subadult male of the group. The young adult female was the target of most of these aggressions. Extremely little aggression occurred between the three females. The young adult female was the only individual who tried to emigrate from the group during the study period. Her attempt to join a neighbour group failed due to rejection by all four members of this group. All group members participated in carrying an infant, but the adult males and the young adult female carried most frequently. Contribution to infant carrying varied with the infant's age.     

Demographic and reproductive patterns in moustached tamarin monkeys (Saguinus mystax): Implications for reconstructing platyrrhine mating systems

In this paper we address a series of questions concerning reproductive opportunities, kinship, dispersal, and mating patterns in free-ranging moustached tamarin monkeys (Saguinus mystax). Between 1980 and 1990 information on group size, composition, and migration patterns was collected on marked groups of moustached tamarins inhabiting Padre Isla, an island in the Amazon Basin of northeastern Peru. In 1990, 86% of 114 animals residing in 16 social groups were trapped, examined, and released. Mean group size was 7.0, including 2.2 adult males and 2.0 adult females. None of these groups was characterized by a single adult male-female pair. In groups with more than one adult female, only the oldest female produced offspring. An examination of dispersal patterns indicates that transfers between groups were common and fell into several categories, including immigration of individual males and females, simultaneous transfer of pairs of subadult and/or adult males (sometimes relatives) into the same social groups, and group fissioning in which males and females of the splinter group join another small social group. We have no unambiguous cases of 2 adult/subadult females migrating together into the same social group. All 6 groups for which reproductive data were available were characterized by either a polyandrous or polygynous (polygyandrous) mating pattern. The results of this study indicate that moustached tamarins reside in small multimale multifemale groups that are likely to contain both related and unrelated adult group members. Kinship and social ties among males appear to be stronger and more longlasting than kinship and social ties among females. We contend that the modal mating system of moustached and many other tamarins is not monogamous, and offer the possibility that cooperative infant care and mating system flexibility in callitrichines evolved from a polygynous mating pattern. © 1993 Wiley-Liss, Inc.     

Aggressive behavior in female golden hamsters: development and the effect of repeated social stress

In male golden hamsters, agonistic behavior matures during puberty, changing from play fighting to adult-like aggression. In addition, this transition is accelerated by repeated social subjugation early in puberty. However, little is known about the development of agonistic behavior in females. In the present study, we compared the development of agonistic behavior in male and female golden hamsters. Furthermore, we also tested the effects of repeated social subjugation on the development of agonistic behavior during puberty. Hamsters were tested for agonistic behavior in the presence of a smaller intruder at different intervals during puberty. Several observations were made. First, the frequency of attacks remained stable in females, while varying in males. Second, the transition from play fighting to adult-like aggression occurred at earlier time periods in females than in males. Finally, a clear transitional period marked by attacks focused on the flanks was observable in males around mid-puberty. However, this transitional period was not apparent in females. In addition, juvenile females were exposed to aggressive adult males or females. In both cases, repeated exposure to stress had no statistically significant effect on the development of agonistic behavior. After 2 weeks of subjugation, exposure to aggressive adults had no effect on serum cortisol levels, indicating that juvenile females habituate to repeated social stress. These data show significant sex differences in the development of agonistic behavior and adaptation to repeated stress in juvenile golden hamsters.     

The reproductive status of nonbreeding group members in captive golden lion tamarin social groups

Reproductive activity is limited to only one female in many species of callitrichid primates (marmosets and tamarins): daughters and subordinate females do not produce offspring. A suppression of ovulatory cyclicity is responsible for the lack of reproductive activity in three species of callitrichids studied to date. This study evaluated the endocrine status of golden lion tamarins (Leontopithecus rosalia) housed as daughters or sons in family groups and of individuals housed in isosexual peer groups. Daughters 17 months of age and older and a subordinate female had high levels of estrogen excretion. Mean levels of estrogen excretion in these females were similar to those of nonpregnant, breeding adult females (17.14 ± 6.82 versus 11.93 ± 6.33 μg/mg creatinine, respectively). Estrogen profiles were similar to those of breeding adult females, with sinusoidal cycles in estrogen excretion. Younger daughters in family groups (10 and 12 months old) showed markedly lower levels of estrogen excretion (0.84 ± 0.58 μg/mg creatinine). Estrogen profiles lacked the sinusoidal nature of cycles in older daughters and breeding females, and elevations in estrogen excretion occurred frequently and remained elevated for 1 or 2 days. Plasma testosterone levels in males varied widely, but mean concentrations did not differ among males housed in different social conditions. These results suggest that older daughters and subordinate females may be capable of expressing normal ovarian function in the presence of a breeding adult female. This finding may account for two unusual observations in the lion tamarin: the high level of female-female aggression and the presence of groups in the wild with more than one actively breeding female.     

Patterns of affiliation among immature rhesus monkeys (Macaca mulatta)

The affiliative interaction patterns of the immature members of a group of rhesus monkeys at the Yerkes Regional Primate Research Center reflected a strong bias toward matrilineal kin, although this effect was modified by age and sex variables. Association with kin decreased with age, particularly for males. Juvenile males showed less of a kin bias in their behavior than did juvenile females, especially for grooming. Juvenile males also exhibited a preference for interaction with other males. The diminished association with kin and the same-sex bias may be reinforced in adolescence as adult males begin to aggressively target adolescent males involved in agonistic encounters with females or immatures. Adolescent males did not decrease their levels of social interaction relative to those of adolescent females; however, these males preferentially associated with other males (predominantly their own age-sex class) and specifically avoided females and younger animals, both kin and nonkin. Avoidance may diminish conflicts with females or immatures which could result from association, thereby decreasing the potential for selective aggressive interference by adult males. Juvenile and adolescent females maintained strong ties with their kin and preferentially associated with other females and immatures. The breadth of interaction of females with other females may facilitate the establishment of dominance relationships as females mature. Familiarity and predictability may also decrease the necessity of more severe agonistic interaction.     

Immigration in wild groups of golden lion tamarins (Leontopithecus rosalia)

Seventeen territorial groups of wild golden lion tamarins were monitored for periods of 10–76 months. Immigration into established groups was rare (0.48 immigrating individuals per group per year) and occurred mostly in the context of replacement of breeding individuals. Nonreplacement immigration events usually occurred in conjunction with some other change in group composition (e.g., an emigration or another immigration). Aggression by resident tamarins toward potential immigrants appeared to be the proximate factor limiting movement into groups. Most such aggression was intrasexual, but potential female immigrants were sometimes chased by male as well as female residents. Immigration was highly male biased (85% of individuals). Factors possibly contributing to this bias were inheritance of breeding positions by adult daughters (reducing female and increasing male immigration opportunities), ability of males but not females to join groups already containing a same-sex breeding individual, and the fact that potential female immigrants appeared to face some intersexual as well as intrasexual aggression. Male and female roles in the maintenance of a monogynous mating system are considered in light of these results. Contrasts with data from intruder studies on captive golden lion tamarins [French & Inglett, Animal Behaviour 37:487–497, 1989] are discussed. © 1996 Wiley-Liss, Inc.     

The ontogeny of sex differences in the behavior of patas monkeys

Many studies of sex differences in primates have been based on small experimental groups of peers in which only a limited range of social behavior could be expressed. In addition, the first few months of life are often the focus of such studies, with relatively little attention paid to older juveniles. In this study, 11 male and 9 female juvenile patas monkeys, living in a captive social group with all age-sex classes available, were observed between 1 and 4 years of age. A subset of seven patas monkeys was also observed between birth and 1 year of age. Here, we report the development of sex differences in independence, play, grooming, positioning behavior, and aggression over the juvenile period. Juvenile male patas monkeys played more and in longer bouts than females, but wrestling (rough-and-tumble play) was not more common among males. There were few differences in behaviors directed to male and female juveniles by other group members. Distinct differences emerged only in the behaviors of the juveniles themselves, with females being more active participants in social and aggressive interactions than males. In general, sex differences in patas monkeys show a mixture of patterns, some of which are predictive of adult sex differences and some of which appear to be specific to the particular demands of the juvenile period in this species     

High rates of pregnancy loss by subordinates leads to high reproductive skew in wild golden lion tamarins (Leontopithecus rosalia)

Across taxa, cooperative breeding has been associated with high reproductive skew. Cooperatively breeding golden lion tamarins (Leontopithecus rosalia) were long thought to have a monogynous mating system in which reproduction was limited to a single dominant female. Subordinates with few reproductive opportunities delayed dispersal and remained in the natal group to provide alloparental care to siblings, thus allowing dominant reproductive females to meet the energetic needs associated with high rates of reproduction and successful infant rearing. The goal of this study was to re-assess monogyny in wild golden lion tamarin groups based upon pregnancy diagnoses that used non-invasive enzyme immunoassay for progesterone and cortisol, combined with weekly data on individual weight gain, bi-annual physical examinations noting pregnancy and lactation status and daily behavioral observations. We established quantitative and qualitative criteria to detect and determine the timing of pregnancies that did not result in the birth of infants. Pregnancy polygyny occurred in 83% of golden lion tamarin groups studied. The loss of 64% of subordinate pregnancies compared to only 15% by dominant females limited reproductive success mainly to dominant females, thus maintaining high reproductive skew in female golden lion tamarins. Pregnancy loss by subordinate adults did not appear to result from dominant interference in subordinate hormonal mechanisms, but more likely resulted from subordinate abandonment of newborn infants to mitigate dominant aggression.     

Sex-Specific Aggression and Antipredator Behaviour in Young Brown Trout

Sex differences in adult behaviour are often interpreted as consequences of sexual selection and/or different reproductive roles in males and females. Sex-specific juvenile behaviour, however, has received less attention. Adult brown trout males are more aggressive than females during spawning and juvenile aggression may be genetically correlated with adult aggression in fish. We therefore tested the prediction that immature brown trout males are more aggressive and bolder than immature females. Because previous work has suggested that precocious maturation increases dominance in salmonids, we included precocious males in the study to test the prediction that early sexual maturation increase male aggression and boldness. Aggression and dominance relations were estimated in dyadic contests, whereas boldness was measured as a response to simulated predation risk using a model heron. Independent of maturity state, males initiated more than twice as many agonistic interactions as females in intersexual contests. However, males were not significantly more likely to win these contests than females. The response to a first predator attack did not differ between sex categories, but males reacted less to a second predator attack than females. Sexual maturity did not affect the antipredator response in males. Since there is no evidence from field studies that stream-living immature male and female salmonids differ in growth rate, it appears unlikely that the sex differences demonstrated are behavioural consequences of sex-specific investment in growth. It seems more likely that sex-specific behaviour arises as a correlated response to sexually selected gene actions promoting differential behaviour in adult males and females during reproduction. Alternatively, sex differences may develop gradually during juvenile life, because a gradual developmental program should be less costly than a sudden behavioural change at the onset of sexual maturity.     

Unraveling the dispersal patterns and the social drivers of natal emigration of a cooperative breeding mammal,the golden lion tamarin

The study of the social drivers of animal dispersal is key to understanding the evolution of social systems. Among the social drivers of natal emigration, the conspecific attraction, aggressive eviction, and reduced social integration hypotheses predict that sexually mature individuals who receive more aggressive behavior and are engaged in less affiliative interactions are more likely to disperse. Few reports have explored these proximate factors affecting emigration in cooperatively breeding species, particularly of Neotropical primates. In this study, we investigated the dispersal patterns and tested the social drivers of natal emigration in the golden lion tamarin (Leontopithecus rosalia) — an endangered species inhabiting Atlantic rainforests fragments in Brazil. We used behavioral and demographic data collected during 7 years from 68 groups of tamarins inhabiting 20 forest fragments. Our analyses from the 160 dispersing individuals showed that dispersal success is higher for males and for those engaged in parallel dispersal, but that males and females use different strategies to enhance their dispersal success, males immigrate into established groups while females form new groups. We did not find high levels of agonistic behavior among group members before natal emigration. Instead we found that conspecific attraction drives natal emigration in both sexes, while additionally the low level of affiliative interactions within the natal group triggers male emigration. We discuss natal emigration in the broader perspective of the cooperative breeding system and the implications of these findings for the conservation of the species.     

The role of scent marking in the social communication of wild golden lion tamarins, Leontopithecus rosalia

The role of scent marking in the social communication of mammals is widely variable. One reason for this variation is that the function of scent marking may vary with different ecological and social conditions. The purpose of this study was to test four nonexclusive hypotheses explaining the role of scent-marking frequency in different ecological and social contexts for wild golden lion tamarins. Relative to ecological contexts, we compared scent-marking frequency during seasons of abundant and scarce food resources. Relative to social contexts, we compared scent-marking frequency when groups were isolated and when groups were in the presence of neighbouring groups. We found that the tamarins used scent marking to mark the location of food resources. Additionally, males used scent marking to communicate intrasexual dominance within their groups, while females did not. Our results also indicate that alpha females increased their scent-marking frequency to communicate to members of other groups, while the presence of members of other groups did not elicit a similar response by alpha males. We did not find evidence for a territorial function of scent marking in golden lion tamarins. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour      

Variation in Helper Type Affects Group Stability and Reproductive Decisions in a Cooperative Breeder

Recent studies have shown that differences in life history may lead to consistent inter‐individual variation in behavioural traits, so‐called behavioural syndromes, animal personalities or temperaments. Consistencies of behaviours and behavioural syndromes have mainly been studied in non‐cooperative species. Insights on the evolution of cooperation could be gained from studying individual differences in life histories and behavioural traits. Kin selection theory predicts that if an individual’s reproductive ability is low, it had to aim at gaining inclusive fitness benefits by helping others. We tested this prediction in the cooperatively breeding cichlid Neolamprologus pulcher, by assessing reproductive parameters of adults that had been tested earlier for aggressiveness and for their propensity to assist breeders when they had been young (‘juveniles’). We found that juvenile aggression levels predicted the acceptance of a subordinate in the group when adult. Males which were aggressive as juveniles were significantly more likely to tolerate a subordinate in the group when compared with males which were peaceful as juveniles, whereas females which were more aggressive as juveniles tended to expel subordinates more often. Females produced significantly smaller clutches when paired to males which had helped more as a juvenile, despite the fact that adult males hardly provided direct brood care. There was no evidence that females with a high propensity to help when young, produced smaller clutches or eggs when adult, but they took longer to lay their first clutch when compared with females with a low propensity to help when young. These results suggest that variation in behavioural types might explain variation in cooperation, the extent of group‐living and reproductive decisions.     

One for all and breeding for one: Cooperation and competition as a tamarin reproductive strategy

In this paper I examine behavioral strategies used by male and female tamarins to increase individual reproductive opportunities while continuing to maintain a high level of group cohesion and social cooperation. Tamarins of the genus Saguinus are characterized by social groups generally composed of more than one adult of each sex, but a breeding system in which only a single female in each group gives birth. The breeding sovereignty of a single dominant female limits the reproductive opportunities of subordinate females as well as the reproductive opportunities of resident adult males.^1-3 Despite extreme variability in year-to-year reproductive success among members of the same social group, field studies indicate that within-group intrasexual aggression and fighting are rare, and that both breeding and nonbreeding individuals expend time and energy cooperatively caring for young, defending productive feeding sites, and assisting in food harvesting activities.^4-11 In fact, Caine¹² has argued that “co-operation, tolerance, and flexibility” are the primary themes of tamarin social interactions (p. 218). A major question that remains unanswered, however, is how such high levels of cooperation could have evolved in a social system characterized by emigration of both adult males and females from the natal group, polyandrous mating, and intense reproductive competition.     

Aggression with mixed age-sex groups of bolivian squirrel monkeys following single animal introductions and new group formations

The social organization of the Bolivian squirrel monkey (Saimiri boliviensis boliviensis) is thought to be sexually segregated, with males and females forming separate social groups during the nonbreeding season. To investigate the influence of this social order on patterns of aggression, controlled single animal introductions within established groups and establishment of new groups were studied in a systematic manner. Behavioral observations were made using an all-occurrences technique to sample all agonistic interactions. In study I, 4 animals of each age-sex class (adult males and females, juvenile males and females) were introduced one at a time into 4 different social groups composed of 1 adult male and 8 to 10 adult females. Behavioral observations were made prior to and after the introductions. Newly introduced adult males received significantly more contact aggression than other age classes. Only the adult females increased aggression after the introduction of new animals. In study II, new social groups were formed and behavioral observations were made following formation. One group was formed from 7 pairs of familiar females and an unfamiliar adult male. This group had a high frequency of aggression during the first half hour, with contact aggression rising to peaks at 3 and 5 h. The second group consisted of 10 familiar females, 2 pairs of familiar females and an unfamiliar male. There was a significant peak in contact aggression 3 h into the observation.     

Testing Functional Hypotheses for the Behavior of Resident Pine Voles, Microtus pinetorum, Toward Non-Residents

Members of a social group should attempt to maximize their fitness by maintaining an optimal group composition. Allowing an immigrant into the group may be beneficial or costly depending on the characteristics of the immigrant as well as the composition of the group. Therefore, we examined behavioral interactions between pine voles to test three functional hypotheses proposed to explain behavior of residents toward non‐residents: the resource defense, mate defense, and benefit of extra‐pair copulation hypotheses. To test these, we examined the effects of age, sexual experience and sex of non‐residents as well as the effects of sex of residents on the behavior of residents. Neither male nor female residents showed affiliative behavior toward non‐residents. Residents were more aggressive toward non‐residents than vice versa. The frequency of same‐sex aggression was greater than opposite‐sex aggression for male residents and this aggression was directed at adult male non‐residents to a greater degree than at subadult males. Resident males were least aggressive toward adult females. We found no differences in the behavior of females toward subadults, sexually naive adult non‐residents or sexually experienced adult non‐residents. Females also displayed similar amounts of aggression toward male and female non‐residents. Therefore, for males, aggression may function in defense of a mate while for females, aggression functions in resource defense. For both sexes, aggression is likely to play a role in the regulation of group composition.     

Patterns of injury in zoo-housed spider monkeys: A problem with males?

Aggression among wild spider monkeys is most frequently reported to occur between the sexes, with adult males directing aggression towards adult females and the aggression is normally non-injurious. After two severe instances of aggression in the group of spider monkeys housed at Chester Zoo, we developed a questionnaire to investigate the frequency, direction and possible reasons for aggression in zoo-housed spider monkeys. We sent our questionnaire to 55 zoos worldwide and obtained records from 26 groups, which yielded detailed accounts of 143 aggressive incidents: 56 events for the actors and 127 events for the targets of aggression. We found that zoo-housed spider monkeys are predominantly maintained in small social groups, with a single adult male, two adult females and their offspring. Of the aggression reported, 23.1% of incidents resulted in severe or lethal injuries. Adult males were the most frequent actors of aggression and accounted for 66.7% of incidents. Six cases of male–male aggression were lethal. The most striking pattern was that adult males directed aggression towards non-adult males more than any other age/sex category. The most frequently reported context of aggression was tension between adult and non-adult males. These findings contradict previous reports from wild spider monkeys where female-directed male aggression is most frequently reported. In light of our findings, we recommend that males form the core of the group and that females be relocated among groups to reflect the wild condition of male philopatry and female dispersal. In addition, enclosure design should allow opportunities for the monkeys to segregate themselves from other group members, simulating fission, which is a conflict management strategy for avoiding aggression in wild spider monkeys.