Vocalizations and social behaviour of captive groups of feral-reared squirrel monkeys (Saimiri sciureus)

The social behaviour and vocalizations of two well-established groups of squirrel monkeys were recorded during 80 1/2-hr periods. Sonographs portray the physical characteristics of 24 vocalizations discriminable to the human ear. Twelve of these calls occurred sufficiently often to correlate them with each other and with social behaviours. The occurrence of any one of the 12 frequently emitted vocalizations was associated with the occurrence of several other vocalizations. Vocalizing was significantly and positively correlated with approach, withdrawal, touch, grasp or hold, and wrestle. These behaviours were significantly and positively correlated with one another. The notion that vocalizing is associated with motivational and emotional states was discussed. This study was done in partial fulfillment of the B. Sc. Honours degree.     

Social hierarchy under different criteria in groups of squirrel monkeys,Saimiri sciureus

Under different criteria the individual members of groups of squirrel monkeys show different social capacities. The ranking of the subjects was much the same for Restraining and Genital display. The hierarchies for Approaching and Following fitted well with each other, showing few similarities with the above two. Location of individual ranks for Withdrawing tended to be the opposite to that of Approaching and Following. Restraining and Genital display showed quasi-linear hierarchies, with males on top and females at the bottom of them. For Approaching, Following, Withdrawing, and Genital inspection the results varied from quasi-linear structure to circular or even unisexual arrangement. As a rule the animals behaved towards partners close in rank to themselves. Several individual roles could be isolated: An alpha male role, directing Restraining and Genital display to all other partners more frequently than any of them towards him, basing his ability more in adequate distribution of total performance among social partners than in high total frequency; an omega male role under the same criteria, whose function would be to connect with the hierarchy of females and a scapegoat role, a very passive female receiving all kinds of attention from most subjects.     

Captive breeding of squirrel monkeys,Saimiri sciureus and Saimiri boliviensis: The problem of hybrid groups

The electrophoretic variability of blood proteins coding for up to 32 genetic loci was analyzed in 108 squirrel monkeys (Saimiri sciureus, Saimiri boliviensis, hybrids) from two captive colonies. Twelve polymorphic loci with 31 alleles are reported. The biallelic Ada* locus, G-statistics and Hardy-Weinberg genotype equilibria are useful for recognizing hybrids between S. sciureus and S. boliviensis. Backcrosses in hybrid stocks and gene flow in a natural hybrid belt, however, complicate the taxonomic diagnosis of captive specimens: S. sciureus phenotypes imported from Peru possessed the allele Ada*132, which generally characterizes S. boliviensis (or species hybrids). The complex taxonomy of Saimiri spp. Requires careful planning of captive breeding. We suggest a genetic analysis of the founder individuals before their inclusion in the European studbook population and to breed S. sciureus from Guyana separately from Peruvian imports, because the latter bear a greater risk of being taxonomically heterogeneous. Zoo Biol 17:95–109, 1998. © 1998 Wiley-Liss, Inc.     

Mycobacterium kansasii infection in squirrel monkeys (Saimiri sciureus sciureus)

Abstract: This report documents asymptomatic infections of Mycobacterium kansasii in four of five tuberculin positive squirrel monkeys (Saimiri sciureus sciureus). The mycobacterial DNA amplified by polymerase chain reaction (PCR) from a bronchial lymph node had no affinity for the species specific probes of M. tuberculosis, M. avium, and M. intracellular, thus allowing the presumptive diagnosis of an atypical mycobacterial infection. Infection by Mycobacterium kansasii was confirmed by culture of bronchial lymph nodes from three monkeys. The source of the infection was never identified.     

Experimental analysis of the nature of social context in captive groups of squirrel monkeys (Saimiri sciureus)

The nature of social context as a factor affecting grouping behavior is experimentally examined in captive groups of squirrel monkeys by recording the effects of systematic removal and return of individuals on the distributions of non-agonistic interactions and prolonged (huddle) contacts among the remaining group members. Observed changes in the distributions of these interactions among the remaining individuals are analyzed in terms of the age-sex class of the individual(s) removed, age-sex distributions of the individuals remaining, and the classes of dyadic relationships severed by the removals. Results indicate that, at least so far as these spacing-related behaviors are concerned, (1) the social environment does not act as a configurational whole on the grouping behavior of individuals, (2) the effect of social context on grouping behavior may be analyzed as the effects of specific dyadic relationships upon others, and (3) not all dyadic relationships significantly affect all others in a social group, i.e., not all of the social environment is relevant to the interactions between all pairs of individuals.     

Biochemical and hormonal correlates of dominance and social behavior in all-male groups of squirrel monkeys (Saimiri sciureus)

This study examined the relationship between dominance rank and several physiological and behavioral measures in stable, captive, all-male squirrel monkey groups. Four groups, each containing three males, were observed for 12 weeks during the breeding season. Relative dominance ranking among males in each group was based on the direction of agonistic behaviors displayed. For each subject, whole blood serotonin (WBS), plasma testosterone (T), and cortisol (C) were sampled 4 to 6 times over the course of the study. Samples were separated by 1- to 2-week intervals. Each group had a stable linear dominance hierarchy. WBS had small intraanimal variance and was positively related to dominance rank. In contrast, T and C were highly variable within subjects and were unrelated to dominance rank. Among alpha males, concentrations of T and C were positively correlated, and WBS and C were negatively correlated. The effect of dominance rank on the relationship between within-animal fluctuations in WBS, T, and C and behavior was also assessed. In dominant, but not subordinate subjects, intraanimal fluctuations in WBS correlated with agonistic behavior initiated, and fluctuations in C and T correlated with huddling. In beta and gamma males, C was related to agonism received, and in gamma males to food stealing received. Dominance status also affected endocrine response to the stress of capture but not the rate of sneezing. Sneezing was positively correlated with T concentrations irrespective of dominance rank. These results extend the association between WBS and dominance rank previously reported in Old World monkeys to a New World monkey species, support previous suggestions that mean T and C titers are not reflective of dominance rank in well-established groups, and indicate that dominance rank affects adrenocortical response to the stress associated with capture and anesthesia.     

Play vocalizations of squirrel monkeys (Saimiri sciureus)

Vocalizations occurring during play bouts were studied in 2 pairs of young male squirrel monkeys. Two main call types, one having four variants, are described. Vocalization rate varied with the type of ongoing behavior and with play bout duration, an association considered to be indicative of motivation to play. Structural differences also varied with bout duration and longer bouts had longer and more complex calls. In addition to providing direct information about motivation, vocalizations may have a metacommunicative function in alerting adult group members (not play partners) to the presence of playful activity.     

Chemotherapy of haemobartonellosis in squirrel monkeys (Saimiri sciureus)

Splenectomised Saimiri sciureus squirrel monkeys are being used increasingly as an experimental host for human malarial studies, notably for the assessment of candidate vaccines against Plasmodium falciparum blood-stage infection. Recently, we have reported that colony-reared S. sciureus monkeys are asymptomatic carriers of Haemobartonella sp. and that patent Haemobartonella infection, activated following splenectomy, may interfere with the course of P. falciparum parasitaemia in these animals. For several years, splenectomised S. sciureus monkeys were routinely submitted to oxytetracycline therapy before their use in malarial studies in order to prevent a possible spontaneous Heamobartonella infection. However, we report here that such antibiotic therapy is often ineffective and that neoarsphenamine chemotherapy may be considered as an alternative to cure both latent and patent haemobartonellosis in S. sciureus monkeys.     

Studies with timed-pregnant squirrel monkeys (Saimiri sciureus).

Timed-pregnant monkeys were produced in a large nonhabituated colony of Saimiri sciureus of Bolivian origin. In a colony of 373 females and 40 males, 277 females (74%) were considered to be inseminated, based on microscopic observation of sperm and/or detection of a coagulum (plug) in the vagina. Forty-six full-term progeny were delivered. The mean gestational period was 152.5 days (SD = 3.9 days). For continuous cohabitation, the median time to insemination was five days, with 75% of inseminations occurring within eight days. Pregnancy evaluation (mouse bioassay) indicated a high level of resorptions within the first 50 days of gestation. This may help explain the low birth rates reported for other nonhaibuated colonies.     

Effect of separation distance on isolation call structure in squirrel monkeys (Saimiri sciureus)

Isolation calls of captive squirrel monkeys were recorded by separating infants from their natal group members and then permitting vocal contact between the “lost” baby and the group at systematically varied distances. Separated infants gave longer calls at greater separation distances from their natal group members, and responding adults and juveniles similarly extended the length of their vocalizations. In the longer variants, a highfrequency element was prolonged, which is considered to be an example of the net advantage of a “frequency window” in the ambient noise of environments.     

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.     

Food-storing behavior in captive squirrel monkeys (Saimiri sciureus)

Observations of food-storing in caged squirrel monkeys are described. Frequencies of storage and attempted retrievals increased with the introduction of novel objects. The type of storage site, its location and defense, all indicate hiding of food or favored objects to avoid stealing attempts rather than food or object play behavior.     

Reconciliation in captive Guyanese squirrel monkeys (Saimiri sciureus)

The tendency for agonistic interaction to increase the probability of friendly interaction between social partners has been demonstrated across a range of Old World primates. While research on such post-conflict behavior proceeds into an hypothesis-testing phase, new comparative information must accumulate to provide full phylogenetic perspective on primate social behavior. Data from New World and prosimian primates are yet extremely limited. We studied captive squirrel monkeys (Saimiri sciureus) via post-conflict (PC) and matched control (MC) observations and analyzed results using both the PC-MC and time-rule methods. Former opponents maintaining affiliative relationships soon engaged in friendly interaction following large proportions of agonistic interactions, whereas non-affiliated individuals, including virtually all male-female pairs, reconciled conflicts rarely. Close-proximity approaching and huddling contact constituted the principal modes of post-conflict amicability. Agonistic interactions of relatively high intensity were most likely to be reconciled and most likely to be reconciled via physical contact. High vulnerability of Saimiri to predation may have favored this species' strong inclination to reconcile soon after agonistic interaction. Research on free-living populations of this and other primate species is needed to illuminate similarities and differences across taxa.     

Abnormal behaviors in nursery-reared squirrel monkeys (Saimiri sciureus)

Seventeen squirrel monkeys (Saimiri sciureus), 11 nursery-reared and six mother-reared, were monitored to clarify the type and degree of deviant behaviors that result from rearing this species in the nursery. Two observation periods were used: the first when the subjects averaged 6.7 months of age, the second when they averaged 15.5 months. Thirteen activities involving variations of nonnutritive orality, stereotypic posturing, and agitated behaviors were seen in the nursery-reared subjects, but never in the mother-reared subjects. No consistent gender, subspecies, or age differences were evident. Squirrel monkeys, like chimpanzees and some Old World monkeys, do develop atypical self-directed behaviors when deprived of normal stimulation during early development.     

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.