Reactions of adult and immature squirrel monkeys to intergroup exposure

Initial encounters between unfamiliar animals raise the practical problem of controlling aggression and provide the opportunity to examine changes in social structure that may occur as groups merge. Social interactions and spatial grouping patterns were examined in newly formed squirrel monkey groups, in which a subgroup of familiar adults was introduced to a subgroup of familiar immature squirrel monkeys. Yearlings (10–11 months) and subadults (20–50 months) generally remained spatially distinct from adults, and intergroup interactions often consisted of adult-initiated antagonism. Adults exhibited sexual segregation in their spatial grouping patterns and interactions, whereas yearlings and subadults generally showed sexual integration. These data suggest that there is considerable adult resistance to integration of unfamiliar immatures into established adult social groups. Zoo Biol 17:519–524, 1998. © 1998 Wiley-Liss, Inc.     

Psychosocial and hormonal aspects of hierarchy formation in groups of male squirrel monkeys

Accounts of primate social dominance hierarchies often imply that the achievement of superior status is a “goal”, akin to a valued resource or commodity, and that hierarchies emerge in multimale groups from prolonged competitive conflicts over social status. This possibility is not consistent with our observations of five newly formed triads of adult male squirrel monkeys (Saimiri sciureus). Stable linear hierarchies based on clear asymmetries in the direction of intermale agonism and genital displays were established quickly, with virtually no reciprocal fighting, and in the absence of rank-related differences in plasma cortisol or testosterone. Although affiliative social overtures were initiated more often by high-ranking and middle-ranking males, affiliative overtures were directed equally often toward all members of each group. From the outset of the study all males, regardless of rank, spent an average of 33% of their time huddling in affiliative contact with male cagemates. These results suggest that in newly formed groups of adult male squirrel monkeys, social hierarchies reflect an expedient convention that reduces conflict and facilitates the formation of small cohesive groups. © 1994 Wiley-Liss, Inc.     

Social organization and social behavior in two subspecies of squirrel monkeys (Saimiri sciureus).

Social organization and social behavior were examined in two subspecies of squirrel monkeys which differ markedly in the degree of sexual dimorphism. The Bolivian squirrel monkeys, the subspecies with greater sexual dimorphism, manifested a sexually segregated form of social organization, while the social organization of the Guyanese monkeys was sexually integrated. Dominance relationships were found to reflect these patterns of sexual segregation or integration; in the Bolivian social groups separate linear dominance hierarchies were established within each sex while the Guyanese monkeys established a single linear hierarchy which included both males and females. Relationships between males and females in the two subspecies appear to be regulated by two distinct mechanisms, dominance in the Guyanese monkeys and sexual segregation in the Bolivians.     

Age differences and developmental trends in alarm peep responses by squirrel monkeys (Saimiri sciureus)

Alarm calls can code for different classes of predators or different types of predatory threat. Acoustic information can also encode the urgency of threat through variations in acoustic features within specific alarm call types. Squirrel monkeys (Saimiri sciureus) produce an alarm call, known as the alarm peep, in highly threatening situations. Infant squirrel monkeys appear to have an innate predisposition to respond to alarm peeps but require experience to associate alarm peeps with the appropriate type of predatory threat [Herzog & Hopf, American Journal of Primatology 7:99-106, 1984]. Little is known about age-related differences in the type or frequency of response to alarm peeps, or the development of alarm peep response in infants. The purpose of this study was to test experimentally the response strategies of different age classes of squirrel monkey to the playback of alarm peeps that were produced by infants, juveniles, or adults. Results suggest that infants, juveniles, and female subadults respond more frequently to alarm peeps than do adult females. Infant squirrel monkeys showed different behavioral strategies in response to alarm peeps as a function of age. Adult females differentiate between infant and adult alarm peeps by responding more frequently to the alarm peeps of adult females. These data demonstrate that squirrel monkeys use acoustic information to discern when to respond to the alarm peeps from conspecifics, and that infants gradually develop an adult-like response to alarm peeps over the first year of development.     

Social influences on plasma testosterone levels in male talapoin monkeys

Three social groups of laboratory-housed talapoin monkeys (Miopithecus talapoin) consisting of four adult males and four or five adult females, were observed over a 4-year period. All females were ovariectomized and given estradiol implants at intervals to render them sexually attractive; except for two castrated males with testosterone implants, all males were intact. Sexual and aggressive interactions were recorded, and testosterone levels were measured in plasma taken from males twice weekly. In each group males formed a linear dominance order, defined in terms of the direction of aggression between animals. The hormonal responses of intact males were monitored with respect to the presence of attractive females, access to these females, and transfer from the social group to isolation. In all groups the behavioral and endocrine responses of males to these treatments were rank related. In some instances, rising in rank was associated with elevated testosterone and falling in rank with decreased testosterone; these hormonal changes were associated with changes in sexual and aggressive interactions. The effects of sexual and aggressive behavior on plasma testosterone titers are discussed.     

Sociophysiology of squirrel monkeys

Primate sociophysiology is an emerging discipline concerned with understanding the proximate mechanisms that contribute to the generation and maintenance of species-typical social systems. Studies of squirrel monkeys illustrate that sociophysiological processes are more varied than is commonly assumed with respect to both the effective social dimensions that influence physiological function and the nature of concomitant physiological effects. For adult squirrel monkeys, a major consequence of social stimulation is altered regulation of pituitary-adrenal, pituitary-gonadal, and autonomic function. In females, socially-induced physiological changes appear to be independent of specific interindividual relationships with other adults, whereas in males, many sociophysiological effects can be understood only when specific relational attributes are considered. In all instances, adult relationships are associated with distinctly different sociophysiological profiles than have been found for the mother-infant relationship and do not conform to the stress/buffering model within which they are often interpreted.     

Higher relatedness within groups due to variable subadult dispersal in a rainforest skink,Gnypetoscincus queenslandiae

Abstract Field observations of groups of the prickly forest skink, Gnypetoscincus queenslandiae (Reptilia: Scincidae), from north‐eastern Australia, that consist of different sized individuals under the same log have generated speculation about the social structure and dispersal patterns of this species. A total of 411 skinks were sampled from 12 rainforest sites on the Atherton Tableland in the Wet Tropics of north‐eastern Australia. Relatedness statistics calculated using nine microsatellite DNA loci showed that prickly forest skinks are significantly more related to animals within their own group than to those in other groups, and there is a significantly greater relatedness between subadults less than 2 years old and adults within the same group. This relationship was no longer apparent between individuals estimated to be 2 to 3 years old and adults in the same group. Thirty per cent of individuals estimated to be less than 2 years old were likely to be the offspring of an adult under the same log, whereas only 7% of individuals between 2 and 3 years old were. Using mark‐recapture techniques, movement distances between 0 and 94 m were recorded, with an average movement distance of 12.8 m, or 1.5 m per month between captures. Movements of 0–5 m were the most frequent for all ages and sexes. Subadults tended to move further per month on average than adults, but there was no difference in average movement between adult males and females. Thus I found little evidence to support a hypothesis of complex social structuring in prickly forest skinks. Rather, groups of lizards under logs appear to be a result of high, but variable, dispersal of subadults in their first 2 years.     

Cage design and configuration for an arboreal species of primate

The squirrel monkey (genus Saimiri) is an arboreal primate from equatorial South America. This species forms large social groups that consist of multiple females and males of varying ages, from infant to adult. As the use of squirrel monkeys in research continues to grow, an understanding of optimal cage design and environment is essential. The University of South Alabama Primate Research Laboratory houses a breeding colony of 350 squirrel monkeys. Each group cage, measuring 4.5 X 2.5 X 1.5 meters, can contain up to 20 animals. A breeding group consists of one adult male, eight to ten adult females, and varying numbers of infant and juvenile animals. In order to determine the most suitable cage environment for the squirrel monkey, a series of studies were carried out to compare various perch materials and cage configurations. Squirrel monkeys preferred a poly-vinyl-chloride pipe perch (rigid) over rope perches (non-rigid). When provided with multiple levels of perches, all levels were used. Males tended to distribute their activities randomly at different levels. In a two tiered perch arrangement, females concentrated 67% of their social activity on the top tier. In a triple tier configuration, females concentrated 66% of their travel on the top tier. These results indicate that by creating a cage environment with multiple tiers of horizontal perches the effective cage space can be doubled or tripled. This provides an effective means of reducing population density without enlarging the dimensions of the cage or reducing social group size.     

Group composition effects on social behaviour of captive squirrel monkeys (Saimiri sciureus)

Feral and semi-feral squirrel monkeys form sexually segregated subgroups. Observation of social interaction among laboratory animals revealed significant differences in social behaviour as a function of group composition. Females were more active in Unisexual groups. They engaged in more affiliative behaviour and were less often the target of agonistic attack. Adult females with young avoided adult males. ‘Aunts’ and Nulliparous females initially avoided these same males, but later spent over 50% of their time in close proximity to them. Results are discussed in terms of squirrel monkey social ecology, and successful child-rearing.     

The role of play in social organization: Comparative observations on squirrel monkeys (Saimiri)

Various functional theories of play stress that social play is essential for the practice and learning of sex roles, dominance relationships, troop culture, integration of individuals into the troop structure, the control of aggression, etc. Data on squirrel monkeys (Saimiri) in natural environments indicate that social interaction and troop integration can develop in various manners in the absence of social play.Comparative observations were made on squirrel monkeys in a seminatural environment in Florida and 43 natural environments in Panama, Colombia, Peru, and Brazil. There was a broad range of variance in the data on ecology, troop size, troop cohesiveness, average individual distances, frequency of play, etc. In some environments, individuals in the infant and juvenile age classes engaged in social play for approximately 1.5 to 3 hours a day. However, in one environment, not a single incidence of social play occurred during 261 hours of close range observation. The troops in which no play occurred were very cohesive (i.e., they seldom fragmented), and the animals traveled at close individual distances. Agonistic interactions were not uncontrolled. Copulations were observed; and 85 percent of the adult females were accompanied by infants, which indicates a normal rate of reproductive success for the species.Data are presented on friendly, aggressive, sexual, and spacing behavior in squirrel monkeys. These data indicate that (1) social play is not necessary for the development and/or learning of an adaptive modicum of social interaction patterns and troop cohesion, but (2) the opportunity to play provides learning experiences in which young animals can develop more complex, varied social interaction patterns and stronger habits for engaging in frequent social exchanges.     

Male and female range use in a group of white‐bellied spider monkeys (Ateles belzebuth) in Yasuní National Park,Ecuador

Spider monkeys (Ateles sp.) live in a flexible fission–fusion social system in which members of a social group are not in constant association, but instead form smaller subgroups of varying size and composition. Patterns of range use in spider monkeys have been described as sex‐segregated, with males and females often ranging separately, females utilizing core areas that encompass only a fraction of the entire community range, and males using much larger portions of the community range that overlap considerably with the core areas of females and other males. Males are also reported to use the boundary areas of community home ranges more often than females. Spider monkeys thus seem to parallel the “male‐bonded” patterns of ranging and association found among some groups of chimpanzees. Over several years of research on one group of spider monkeys (Ateles belzebuth) in Yasuní National Park, Ecuador, we characterized the ranging patterns of adult males and females and evaluated the extent to which they conform to previously reported patterns. In contrast to ranging patterns seen at several other spider monkey sites, the ranges of our study females overlapped considerably, with little evidence of exclusive use of particular areas by individual monkeys. Average male and female home range size was comparable, and males and females were similar in their use of boundary areas. These ranging patterns are similar to those of “bisexually bonded” groups of chimpanzees in West Africa. We suggest that the less sex‐segregated ranging patterns seen in this particular group of spider monkeys may be owing to a history of human disturbance in the area and to lower genetic relatedness between males, highlighting the potential for flexibility some aspects of the spider monkeys' fission–fusion social system. Am. J. Primatol. 72:129–141, 2010. © 2009 Wiley‐Liss, Inc.     

Subspecies differences in hormonal and behavioral responses after group formation in squirrel monkeys

The behavioral and hormonal responses of squirrel monkeys of the Bolivian and Guyanese subspecies were compared after a group formation procedure. Two groups of each subspecies, consisting of five females and three males (later reduced to two) were observed daily during the week of group formation and for nine weeks following removal of a single male from each group. Measures of plasma cortisol were examined in the females after the initial group formation and after the groups were reduced by one male. The levels of plasma testosterone were assessed in all the males during the initial week of group formation. Linear dominance hierarchies were determined both within and across the sexes in both subspecies. The frequency and directionality of low-level aggressive interactions indicated that females of the Bolivian subspecies were dominant to the males, while the males of the Guyanese subspecies ranked over all the females. Additionally, the Bolivian squirrel monkey females showed an elevation of plasma cortisol on the day of group formation, which declined 48 hr later, then reelevated after the groups were reduced by one male and declined gradually over a nine-week period. Guyanese females showed little change in cortisol levels during both periods. This suggests fundamental hormonal, as well as behavioral, differences between the two subspecies. The change in plasma testosterone levels in the males during the initial week of group formation was positively correlated with social status. Furthermore, differences in the dynamics within individual groups for each subspecies were reflected by the levels of plasma cortisol of the female members.     

Microsatellite analysis of kinkajou social organization

Kinkajou social groups generally consist of one adult female, two males, one subadult and one juvenile. Based on analysis of variation in 11 microsatellite loci, we assess the degree of kinship within and between four social groups totaling 25 kinkajous. We use exclusion and likelihood analyses to assign parents for seven of the eight offspring sampled, five with >/= 95% certainty, and two with >/= 80% certainty. Five of six identified sires of group offspring came from the same social group as the mother and pup. Adult males and females within a group were unrelated and subadults and juveniles were offspring of the group adults, suggesting a family structure. All five identified paternities within a social group were by the dominant male of the group. However, this copulation asymmetry does not necessarily reflect cooperation due to kinship ties between the two adult males within a group as one of two adult male pairs sampled was unrelated. Neighbouring male kinkajous were more closely related to each other than neighbouring female kinkajous, suggesting that females disperse more often or farther than males.     

Social organization of captive monandrous squirrel monkey groups (Saimiri sciureus).

1 adult male and 4 adult female squirrel monkeys were observed together as a group, isolated from all other monkeys. 3 of the 4 females were deafened for a previous experiment. Deafening, however, had no apparent, permanent effect on social behavior. Social dominance hierarchy was evaluated in a variety of situations. The results were compared with those of a similar set of observations on the females prior to the introduction of the male. Before the male was introduced, the dyadic interactions involving food stealing, body grasping, and sexual behaviors were indicative of a female linear rank order. After the male was introduced, the rank order among the females generally remained intact, with the male becoming the highest ranking member in the group. The noteworthy exception to the stability involved the highest ranking female, whose position in the hierarchy was threatened. Heterosexual interactions predominated. Homosexual behavior was also observed, although appreciably reduced in frequency as compared to the all-female group situation. A similar rank order hierarchy was observed in a second group of squirrel monkeys comprised of 1 adult male and 4 adult females. None of these monkeys was deaf.     

Group size,composition, and reproductive success in wild common marmosets (Callithrix jacchus)

Data from published sources about size and composition of wild common marmoset groups (Callithrix jacchus) were analyzed to see if the number of juveniles in a group is closely related to the number of other group members. Mean group size was 8.7 members including 4.4 adults (1.8 females, 2.5 males), 2.9 subadults, and 1.4 juveniles. The number of juveniles was significantly positively correlated to the number of adult males. Groups with one or two adult males had significantly fewer juveniles (mean: 1:1 juveniles) than groups containing more than two adult males (mean: 2.0 juveniles). Apart from a different number of subadults, results showed obvious similarities between common marmosets and tamarins of the genus Saguinus in size and composition of subgroups of adults as well as the key role of adult males in mediating the reproductive success of a breeding female. Common marmoset females seem to gain direct fitness benefits in increased reproductive success from the presence of a larger number of adult males. Whether or not other group members get fitness benefits depends on the reproductive strategy of adult males (monogamy vs. polyandry), their kinship, and on the genetic relationship of nonbreeders to the offspring of the breeding female. © 1995 Wiley-Liss, Inc.     

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.     

A comparative analysis of subgroup structure and spatial relationships in captive baboons and squirrel monkeys

Subgroup structure, spacing patterns, and the relationship between spatial and behavioral interations were compared for captive baboons and squirrel monkeys. Analysis of the structure, intensity, and permanence of subgroups revealed that the baboons formed low intensity, overlapping subgroups which were relatively flexible while the squirrel monkeys segregated into permanent, high intensity, mutually exclusive cliques. Clique associations and social proximity relationships were found to be better predictors than dominance rank of the nature and frequency of behavioral interactions in the two colonies.     

Population Genetics,Dispersal, and Kinship Among Wild Squirrel Monkeys (Saimiri sciureus macrodon): Preferential Association Between Closely Related Females and Its Implications for Insect Prey Capture Success

Little genetic information is available to evaluate hypotheses concerning the parameters that affect population genetic structure in primate taxa that exhibit interspecific variation in social systems, such as squirrel monkeys (Saimiri). Here, we used genetic data to assess dispersal patterns, kin structure, and preferential association with same-sex kin in a wild population of Saimiri sciureus macrodon. We also analyzed behavioral data to assess whether individuals that maintain shorter interindividual distances show increased insect foraging success. If there was greater male than female dispersal, then we expected mean pairwise relatedness, F _ST values, and intragroup mean corrected assignment indices to be greater among adult females than among adult males. We also expected matrices of pairwise affinity indices (PAIs) for “association” (time spent ≤5 m) and “proximity” (time spent ≤10 m) among female dyads to positively correlate with a matrix of female pairwise relatedness. Not only did we find support for female philopatry, but we also found significant positive relationships between the relatedness matrix and each of the PAI matrices: females were more likely to be associated with (and proximal to) close female relatives than more distant relatives or unrelated individuals. Foraging analyses revealed that females had higher insect capture rates than males, and this sex difference may be related to a smaller mean interindividual distance among closely related female group members. Our result shows how estimates of genetic relatedness are useful for testing predictions regarding the evolution of sex-biased dispersal patterns, as well as potential relationships between kin-biased social behaviors and foraging success.     

Social grooming between squirrel monkeys and uakaris in a seminatural environment

Young squirrel monkeys (Saimiri sciureus) were reported grooming an adult female uakari (Cacajao calvus rubicundus) on four different occasions. Furthermore, the uakari was noted grooming two squirrel monkeys in separate instances. These observations took place in a seminatural rainforest (The Monkey Jungle; Goulds, Florida, U.S.A.) where provisions are provided. Some possible hypostheses tendered to account for this unusual behavior included (a) the unaverted interaction of food-seeking and fur-cleaning behavior, and (b) the compatibility of play-curiosity activities by squirrel monkeys with the uakaris' need for social contact.     

Male behavior through the breeding season in Saimiri boliviensis boliviensis

The Bolivian squirrel monkey (Saimiri boliviensis boliviensis) is a seasonal breeder. Male squirrel monkeys show distinct morphological and behavioral changes prior to and during the breeding season. A “fatting syndrome” includes increased body weight, increased levels of androgens, and in the Bolivian subspecies, an increasingly active role in the social organization of the group. In this study, the behavior of ten adult male Bolivian squirrel monkeys was analyzed over a 6-month period prior to, during, and after the breeding season. Each was housed as the only adult male in a breeding unit with six to ten adult females and one juvenile male. Employing a principle components method, 11 behavioral clusters were generated from 27 responses. Their activity clusters were identified as follows: sexual activity that showed a peak around the time of peak conceptions; excitatory activity that was initially high but decreased throughout the breeding season; and maintenance activity that did not change across the breeding season. The changing social behavior of the male squirrel monkey parallels physiological changes and is correlated with changing androgen levels.