Rearing condition and plasma cortisol in rhesus monkey infants

Previous studies comparing plasma cortisol levels in mother-reared and nursery-reared rhesus monkey infants under baseline and stress conditions have reported conflicting findings. Differences in subject age, procedures, and specific rearing history may account for many of the discrepant findings. In the present study, mother-reared infants from large social groups, peer-only reared animals, and infants reared with surrogates and limited peer contact were studied in different test conditions across the first 6 months of life. Infants were sampled under three conditions: following a neonatal assessment at Days 14 and 30, immediately upon capture on Day 60, and after 30-min isolation periods on Days 90, 120, and 150. Mother-reared infants exhibited higher cortisol levels on Days 14 and 30 than did both types of nursery-reared infants. In addition, Day 60 basal values of mother-reared infants were higher than those of both peer-reared and surrogate/peer-reared infants. However, on Days 90, 120, and 150, both mother-reared and peer-reared infants exhibited higher cortisol levels in response to separation and 30-min isolation than did the surrogate/peer-reared infants. These differences may reflect group-specific variations in physical environment, capture time, feeding regimen, or diurnal HPA axis rhythms. Am. J. Primatol. 46:311–321, 1998. © 1998 Wiley-Liss, Inc.     

Early social experience affects behavioral and physiological responsiveness to stressful conditions in infant rhesus macaques (Macaca mulatta)

Studies on early development have demonstrated the profound effects of early social experience on the behavioral development and physiology of young rhesus macaques. Given these relationships, we hypothesized that rhesus macaques exposed to different nursery-rearing conditions may develop unique biobehavioral profiles. If this is true, the assessment of temperament may allow us to pinpoint successful rearing environments, thus improving the overall health of nonhuman primates that are raised in captive environments. We conducted biobehavioral assessments in order to examine differences in the development of infants raised under four different peer-rearing conditions (continuous pairing (CP), intermittent pairing, CP with partner rotation, and intermittent rotational pairing) and compared these animals with data from a mother-reared control group. Overall, continuous rotationally paired animals were most similar to mother-reared controls on most behavioral and temperament measures, suggesting that more socially complex rearing environments (greater number of social partners) favor a more active behavioral style. Cortisol profiles of mother-reared controls were similar to both CP groups, and these three groups had higher cortisol concentrations than the intermittent rotational-pairing group. In addition, intermittently paired infants displayed a significantly higher frequency of self-stroke behavior during a human intruder challenge, an abnormal behavior also known as floating limb which has been shown to be a precursor of self-biting. Overall, the data are consistent with the idea that social complexity in the nursery, as operationalized in our continuous rotational pairing, leads to a biobehavioral profile that is most similar to that of infants raised by their mothers in large, socially complex, cages.     

Behavioral abnormalities in captive nonhuman primates

In this study, we dealt with 11 species of nonhuman primates across 10 zoos in India. We recorded behavior as instantaneous scans between 9 a.m. and 5 p.m. In the study, we segregated behaviors for analyses into abnormal, undesirable, active, and resting. The 4 types of abnormal behavior exhibited included floating limb, self-biting, self-clasping, and stereotypic pacing. In the study, we recorded 2 types of undesirable behavior: autoerotic stimulation and begging. Langurs and group-housed macaques did not exhibit undesirable behaviors. A male lion-tailed macaque and a male gibbon exhibited begging behavior. autoerotic stimulation and self-biting occurred rarely. Males exhibited higher levels of undesirable behavior than did females. Animals confiscated from touring zoos, circuses, and animal traders exhibited higher levels of abnormal behaviors than did animals reared in larger, recognized zoos. The stump-tailed macaque was the only species to exhibit floating limb, autoerotic stimulation, self-biting, and self-clasping. Our results show that rearing experience and group composition influence the proportions of abnormal behavior exhibited by nonhuman primates in captivity. The history of early social and environmental deprivation in these species of captive nonhuman primates probably is critical in the development of behavioral pathologies. Establishing this will require further research.     

Persistent Effects of Peer Rearing on Abnormal and Species-Appropriate Activities but Not Social Behavior in Group-Housed Rhesus Macaques (Macaca mulatta)

Nursery rearing of rhesus macaques (Macaca mulatta) alters behaviors but may be necessitated by maternal rejection or death, for research protocols, or for derivation of SPF colonies. The Tulane National Primate Research Center maintains a nursery-reared colony that is free from 9 pathogens as well as a mother-reared colony free from 4 pathogens, thus affording an opportunity to assess the outcomes of differential rearing. Nursery-reared macaques had continuous contact with 2 peers and an artificial surrogate (peer rearing). Focal sampling (432 h) was collected on the behavior of 32 peer-reared and 40 mother-reared subjects (age, 1 to 10 y; immature group, younger than 4 y; adult group 4 y or older). All animals were housed outdoors in like-reared social groups of 3 to 8 macaques. Contrary to expectation, no rearing effects on affiliative or agonistic social behaviors were detected. Compared with mother-reared subjects, peer-reared macaques in both age classes had elevated levels of abnormal appetitive, abnormal self-directed, and eating behaviors and lower levels of locomoting and vigilance (highly alert to activities in surrounding environment); a trend toward reduced foraging was detected. Immature but not adult peer-reared monkeys demonstrated more enrichment-directed behavior and drinking and a trend toward more anxiety-related behavior and inactivity. No new rearing effects were detected in adults that had not been detected in immature subjects. Results suggest that modern peer-rearing practices may not result in inevitable perturbations in aggressive, rank-related, sexual, and emotional behavior. However, abnormal behaviors may be lifelong issues once they appear.Abbreviations: MR, mother reared; PR, peer rearedRearing history is an important consideration when addressing the needs of macaques in captivity. In breeding colonies, nursery rearing may be a necessary management intervention due to maternal incompetence or death and when a foster dam cannot be identified. In addition, nursery rearing may be required for specific types of research. Decades of research broadly indicate that a combination of an artificial surrogate, human interaction, and social contact with peers is the best way to rear macaques in the nursery, a strategy that will avoid the devastating effects of total-isolation rearing^12,19,20 and allow the animals to successfully integrate into and breed in larger social groups.³⁴ However, even with modern nursery-rearing practices, the behavioral and physiologic profiles of nursery-reared macaques differ from those of macaques that have been raised with their mothers in a social group. Behaviorally, nursery rearing is associated with an increased risk for developing repetitive stereotypies, self-biting, self-wounding, and noninjurious self-directed abnormal behavior.^{3,10,16,30,31,35,41} In addition, some evidence suggests that nursery rearing results in heightened anxiety^13,21,42 and lower levels of environmental exploration.⁶ With regard to social behavior, nursery-reared macaques show decreased levels of grooming, play, and social reciprocity, and the presence of companions does not appear to buffer them from stress.^26,42 In addition, nursery rearing is associated with increased fear and aggression.^27,44 Sexual and maternal deficits may occur as well.^15,17,18,38In addition to effects on behavior, physiologic changes have been identified in macaques reared in the nursery setting. Differential rearing affects brain architecture involved in cognition,³⁷ emotional processing²⁵ and vulnerability to adverse effects of stress.⁴⁰ Although evidence concerning rearing effects on the hypothalamic–pituitary–adrenal axis is equivocal, differences including reduced levels of oxytocin, norepinephrine, and homovanillic acid in the cerebrospinal fluid have been reported.^22,27,28,44 Studies have identified several indicators of immune system alterations in nursery-reared macaques, such as decreased proportions of cytotoxic and suppressor T cells, reduced natural killer cell activity, and increased lymphocyte proliferation.^9,29With regard to social management in the nursery, strategies fall into 2 main categories: peer rearing, involves continuous cohousing, whereas surrogate–peer rearing involves brief periods of cohousing of otherwise singly housed infants. Although infants in both rearing conditions may be provided an inanimate surrogate, surrogate–peer-reared infants are housed for the majority of the time with the inanimate surrogate only, with the intention that infants’ need for clinging to an attachment figure will be directed toward the surrogate, even when peers are present. However, this distinction is generalized, and both nursery-rearing categories may involve variations across facilities. Moreover, a subset of the literature differentiates between these housing conditions and compares them. In comparison with surrogate–peer rearing, peer rearing is associated with lower levels of stereotypic and self-injurious behavior, ^31,35,36 whereas surrogate-peer rearing appears to mitigate the increased anxiety observed in peer-reared subjects.^12,20,40 In addition, surrogate–peer-reared macaques show less social clinging, fear, and aggression and more exploration and play than do their peer-reared counterparts.^5,7,35,36Although the literature on the nursery rearing of macaques is extensive, many of the studies concerning the behavioral effects of rearing involve both infants and older subadults or evaluations of behavior indoors and under test conditions. Therefore these populations need to be characterized more thoroughly under the conditions in which they are housed. The relative costs and benefits of the 2 forms of nursery rearing may vary with time and housing condition, especially when the ultimate goal is to maintain the animals long-term and for breeding purposes. For example, nursery-reared macaques may be eventually housed in small outdoor groups, particularly as part of the process of deriving SPF colonies,³⁸ and the literature in the context of their behavior in a more naturalistic group setting is sparse.The question of which nursery rearing practice optimally equips macaques with species-normative behaviors to live in an outdoor group-housed situation is best assessed by comparing mother-reared, peer-reared, and surrogate–peer-reared subjects in similar physical and social conditions. However, even when all 3 categories of animals are unavailable, comparing mother-reared with peer-reared macaques is valuable for assessing the downstream consequences of nursery-management decisions. The objective of the current study was to characterize the behavior of peer-reared, outdoor group-housed rhesus macaques compared with that of mother-reared, outdoor group-housed subjects. Although we expect broad social and reproductive competence in these animals, we test the prediction that peer rearing results in significant perturbations in social behavior as well as heightened anxiety. Characterizing this population is necessary for determining its behavioral needs. If the long-term effects of rearing mimic signs of current reduced wellbeing, it is difficult to assess the need for intervention and the expected response to that intervention. This assessment will allow us to measure the cost of management decisions designed to mitigate rearing-related abnormal behaviors, to predict or interpret the behavior of breeding groups consisting of peer-reared macaques, and ultimately, to contribute to the literature that may guide our ability to make evidence-based decisions regarding different nursery-rearing strategies. Furthermore, this study uses subjects of widely varied ages in both rearing categories to gain information on the long-term stability of rearing differences with increasing age.     

Le comportement du Chevrotain africain,Hyemoschus aquaticus Ogilby (Artiodactyla,Ruminantia)

The purpose of this study was to test the influence of social isolation during infancy on learning behavior in rats. Rats, reared isolated (n = 55) or paired (n = 60) for a period of 50 days following weaning, were tested on different learning tasks in an operant conditioning chamber. Isolation rearing produced significantly better learning when the training period directly followed the different housing conditions. After a 28 day period of social isolation for the subjects raised paired during infancy no differences in learning between isolated and paired reared animals could be observed. The differences are discussed in relation to the effects of stimulus deprivation.     

Nature Needs Nurture: The Interaction of Hormonal and Social Influences on the Development of Behavioral Sex Differences in Rhesus Monkeys

Thirty years of research on early social and hormonal environments and their relationship to the expression of behavioral sex differences in rhesus monkeys are reviewed. These studies demonstrate that whether aggressive and submissive behaviors are sexually dimorphic depends primarily on the social and not the hormonal environment. Early rearing environments without mothers or allowing brief periods of peer interaction produced higher levels of male aggression and female submission. Presenting behavior was expressed more by females than males in environments with high male aggressivity and female submissiveness. No sex differences in presenting occurred in low aggressivity environments, unless monkeys were reared isosexually, when males presented more than females. Rough and tumble play and foot-clasp mounting were consistently exhibited more by males than females across all rearing environments studied, but rearing environment affected the degree of the sex difference. When reared isosexually males displayed less, and females more, foot-clasp mounting than when heterosexually reared. No social environment increased the low frequency of female rough and tumble play. Suppressing neonatal androgen in males did not effect any sexually dimorphic behavior. Prenatal androgen administration to genetic females masculinized many aspects of their juvenile behavior, consistently increasing rough and tumble play and foot-clasp mounting across different social environments. Thus the sexually dimorphic behaviors which showed the smallest variability across social contexts were the most profoundly affected by the prenatal hormonal environment. These studies demonstrate that the expression of consistent juvenile behavioral sex differences results from hormonally induced predispositions to engage in specific patterns of juvenile behavior whose expression is shaped by the specific social environment experienced by the developing monkey.     

Hormonal effects of early rearing conditions in the infant rhesus monkey

Mother-reared and nursery-reared rhesus monkeys were evaluated during the first month of life to assess the effects of early rearing on endocrine status in infancy. Plasma cortisol and growth hormone (GH) levels were measured in two conditions: (1) basal and (2) 30 min following removal from either the mother or the nursery. Nursery-reared infants had lower basal GH levels and higher cortisol levels than did mother-reared infants. Both GH and cortisol levels rose significantly following separation and reached similar levels in the mother-reared and nursery-reared infants. Mother-reared animals exhibited higher GH levels in response to a pharmacological GH-stimulation test. Thus nursery rearing of primate infants significantly affected the baseline secretion of two important endocrine systems, but did not appear to alter markedly the acute endocrine response to a psychological stressor.     

Lipogenic potential in liver of the preweanling rat: influence of dietary cholesterol

We examined the effect of a lower dietary cholesterol load on hepatic lipogenic capacity and plasma cholesterol concentrations during the normal suckling period in artificially reared preweanling rats. The artificially reared rats were fed a milk formula that contained low or normal concentrations of cholesterol during the period from the 5th to 17th day after birth. The activities of HMG-CoA synthase and HMG-CoA reductase in livers of 17-day-old rat pups reared on the low-cholesterol diet were enhanced three- to five-fold over those observed in the age-matched rats in the normal cholesterol and mother-reared control groups. The concentration of cholesterol in plasma of rats reared on the low-cholesterol milk was about 20% lower than that for mother-reared controls. In contrast, rats reared on milk with normal cholesterol content exhibited plasma cholesterol levels about 25 and 50% higher than the mother-reared and low cholesterol groups, respectively. The long-term metabolic consequences of rearing rats on milk formulations without adequate cholesterol remains to be determined.     

Weight gain in captive chimpanzee infants: Comparisons by sex,rearing, and colony

Weight gain has been monitored for 13 years in a mixed longitudinal study of captive chimpanzee growth and development. This report presents results of a comparative analysis of weight relative to age in 175 animals during the first 24 months in four sex/rearing groups (hand-reared females, hand-reared males, mother-reared females, and mother-reared males) from three colonies with different physical, nutritional, and social environments (Primate Foundation of Arizona, University of Texas M.D. Anderson Cancer Center Department of Veterinary Resources, Bastrop, TX, and White Sands Research Center, Alamagordo, NM). The Lowess method is used to generate fits of weight vs. age for each group and colony, with which individual animals at these and other colonies may be compared for assessment of developmental status. Comparisons of the curves, using the jackknife approach, show that there are significant differences between the curves, indicating that rearing and environmental parameters may be factors in weight gain rate and must be considered in such an assessment. Rearing effects may be the dominant of these factors in weight gain. © 1996 Wiley-Liss, Inc.     

Variables influencing the origins of diverse abnormal behaviors in a large sample of captive chimpanzees (Pan troglodytes)

The developmental origin of abnormal behaviors is generally associated with early rearing environments that lack sufficient physical and sensory stimulation. However, other factors should also be considered. A large sample of captive chimpanzees (128 males and 140 females) was surveyed for the presence or absence of 18 abnormal behaviors. Origin variables included the subject's source (zoo, pet, performer, or laboratory), rearing (mother‐ or hand‐reared), and sex. Animals were assessed while held at the Primate Foundation of Arizona, University of Texas M. D. Anderson Cancer Center, or White Sands Research Center. There was a confound among origin variables; more hand‐reared animals than expected were from laboratories. Logistic regression tested the relationship of rearing and source, with sex as a secondary predictor variable, to each of the abnormal behaviors. There was no clear association between any abnormal behavior and source. However, for coprophagy, relative to animals from the laboratory, zoo animals tended to show a higher prevalence, while performers tended to show a lower prevalence (when rearing and sex were controlled). Rocking and self‐sucking were significantly more likely in hand‐reared animals. Coprophagy and depilation of self were significantly more likely in mother‐reared animals. When rearing and source were statistically controlled, the only significant sex difference was a higher prevalence of coprophagy in females and a higher prevalence of rocking in males. In a second, smaller sample of 25 males and 33 females from Southwest Foundation for Biomedical Research, no significant sex association was found for coprophagy, urophagy, rocking, or self‐depilation. In this second sample, coprophagy was also significantly more likely in mother‐reared than hand‐reared subjects. The association of some abnormal behaviors with mother‐rearing suggests that some form of social learning may be involved in the origin of some of these behavior patterns. This indicates that some abnormal behaviors may not be always be indicative of reduced psychological well‐being in captive chimpanzees. Am. J. Primatol. 48:15–29, 1999. © 1999 Wiley‐Liss, Inc.     

Behavior of nursery/peer-reared and mother-reared rhesus monkeys from birth through 2 years of age

The behavior of 8 nursery/peer-reared and 16 mother-only reared rhesus macaques was observed between birth and 5 months of age, with follow-up studies conducted when the animals were 10–21 months old and living in large social groups. Nursery-reared neonates were more awake, active, and irritable than mother-only reared monkeys. From 1 to 5 months of age the nursery/peer-reared animals exhibited a greater variety of behaviors than the mother-only reared infants, which spent the majority of the time in ventral contact with mothers. As juveniles the groups were indistinguishable with the exception of more self-directed behaviors observed in the nursery/peer-reared monkeys. Both rearing conditions, by virtue of their atypicality, imposed restrictions on social development. The behavioral similarity of the juveniles while in the large social group may be a function of maturation or due to the rehabilitative effect of the large social group.     

Pair-rearing infant monkeys (Macaca nemestrina) using a “rotating-peer” strategy

Appropriate rearing conditions for captive primates are important for both research and breeding purposes. In an earlier study, pigtailed macaque infants that were pair-reared with a single continuous partner exhibited excessive social clinging and could not adapt to living in large social groups at 8–10 months of age. In the present study, eight macaques were pair-reared until they were 6 months old. Each member of an animal's four-monkey social group served as a home-cage partner. In an attempt to reduce excessive mutual clinging, the pairs were rotated every 2–3 days to increase the variability of social stimulation in the home cage. However, these infants developed abnormal social behaviors that were in some cases even more extreme than those exhibited by infants pair-reared with a single continuous partner. A second goal of this experiment was to study interlaboratory reliability for the development of social behavior. The animals were divided into two groups, one housed in a nursery and the other in a biological safety level 3 virus laboratory. Some differences were detected between the two groups, demonstrating the necessity of controls in biobehavioral developmental research. Am. J. Primatol. 41:141–149, 1997. © 1997 Wiley-Liss, Inc.     

Postweaning environmental and social factors influencing the onset and expression of agonistic behavior in Norway rats

Two studies were conducted to determine the importance of the postweaning environment and social milieu in regulating the expression of intraspecific aggression in Norway rats. In Experiment 1, male rats were housed either individually or in pairs at 21 days of age. In addition, one-half of the singly housed and paired animals were given experiences with intruders during maturation. At 85 days of age, all animals were given a brief intruder test and then removed from their postweaning environment and provided individually with homecages for a two week period until tested for aggression toward intruders. Results of intruder tests given during maturation indicated agonistic exchanges appeared earlier and more frequently in cages housing a single resident than cages with cohabiting males. However, agonistic exchanges between singly reared residents and intruders had detrimental consequences in adulthood especially under long-term combat situations. That is, although individually reared animals, with early fighting experiences, were capable of initiating intraspecific aggression, such individuals were unable to defend their homecage over a long period of time as evidenced by the high number of wounds and tendency to lose body weight during adult fighting.In Experiment 2, male Norway rats were reared in pairs from 21 days of age and identified as dominant or subordinate on the basis of intracolony social interactions shown during maturation. At 80 days of age, animals were paired with individually reared males in an unfamiliar cage for a 20 day period and examined for agonistic behavior toward intruders at 100 days of age. Group-reared subordinate males exhibited defensive behavior during confrontations with individually reared animals and incurred more wounds and lost more body weight than their cohabiting partner. In addition, subordinate males showed significantly fewer offensive postures toward intruders than individually reared cohabitants. In contrast, group-reared dominant animals did not differ from individually reared males in display of agonistic patterns, in number of wounds, and body weight changes during the period of cohabitation. These findings demonstrate that early rearing factors have pronounced effects on agonistic behavior. Animals experiencing defeat during development are more likely to lose agonistic confrontations in unfamiliar territory than either animals dominant in their early social interactions or animals without the experience of winning or losing agonistic encounters. These results have implications for the understanding of agonistic behavior and predicting outcomes of animal contests, and reveal important differences in agonistic experiences among animals reared in groups.     

Is it the Song or the Singers? Acoustic and Social Experiences Shape Adult Reproductive Tactics and Condition

When sexual signals are perceived during growth and development they can provide information regarding the social conditions likely to be encountered as an adult. Perception of cues related to the presence and density of future mates and potential competitors can result in altered adult phenotypes. Previous studies have shown that adult male Teleogryllus oceanicus field crickets from a Kauai, Hawaii population reared alone and without hearing conspecific song are more phonotactic than those reared with song. These naïve males also reduce investment in body size and immunity. Here we examined whether another source of population density information, the presence of other males, affects behavior, size, and immunity. Specifically, we examined satellite behavior as evidenced by strength of phonotaxis, body condition, and immune response in males reared singly and in groups in the presence and absence of conspecific song. Body condition did not vary with rearing density, and immune response did not vary with either acoustic environment or rearing density. Interestingly, group-housed males were more phonotactic than singly-housed males. This pattern was largely driven by the low levels of phonotaxis exhibited by males that were singly-housed in the presence of conspecific song. These findings suggest that males respond to social cues in addition to conspecific song, but that these cues do not necessarily provide concordant information.     

Mobility of surrogate mothers and persistent neophobia in cynomolgus monkeys (Macaca fascicularis)

In search of the relevant difference between mother rearing and surrogate rearing with respect to the emergence of neophobic behavior in macaques, we tested the hypothesis that mobility of surrogate mothers prevents the development of neophobic behavior in cynomolgus macaques. The experimental group consisted of ten surrogate-reared subjects which during their first year got rides on surrogate mothers moving through the cage. The control group consisted of nine subjects reared with immobile surrogate mothers. Between the age of 7 and 27 months the reactions to two different novel objects were tested. First exposure to one object occurred at 6 months of age and to the other object at 20 months. The kind of object and the age of first exposure made no difference. Contrary to our expectations mobility of surrogates did not affect the incidence of neophobia: most subjects in both groups persistently avoided the objects. This finding seems to support Hofer's hypothesis that the mother acts as a regulator of the infant's behavior and physiology.     

The effects of rearing method on social behaviors of mentored,captive‐reared juvenile California condors

Puppet‐reared and parent‐reared captive‐bred California condor (Gymnogyps californianus) juveniles were studied before their release into the wild. Behavioral data were collected during social interactions within two cohorts of juveniles (N = 11) and their adult mentors (N = 5). The purposes of this study were to (1) document the social behaviors of mentored juvenile California condors, and (2) compare social behaviors for two different rearing methods (puppet‐reared versus parent‐reared) during two phases of the mentoring process (San Diego Wild Animal Park versus release sites). Of the 17 behaviors examined by 2 × 2 analyses of variance (ANOVAs), two significant interactions between the rearing method and mentoring phase were found: pulls feathers and feeds alone. For both behaviors, parent‐reared condors engaged in these activities more often at the zoo and less often at the release pens than did the puppet‐reared condors. The main effect of rearing was also significant for two behaviors: near others, and receives contact aggression from other. Parent‐reared birds were more likely to be near another bird and receive contact aggression, regardless of mentoring phase, than puppet‐reared birds. The effect size for 16 of the 17 behaviors was greater for the rearing method than for mentoring phase. Rearing method differences may persist long‐term, as parent‐reared adult mentors were significantly more aggressive than puppet‐reared adult mentors. Dominance relations were examined for both cohorts, with the first cohort exhibiting a strong linear relationship (h′ = 0.86, P = 0.018), whereas the second cohort exhibited a moderate but non‐significant linear hierarchy (h′ = 0.63, P = 0.21). The rearing method had no effect on dominance among the juveniles, but adults were probably dominant to juveniles (P = 0.052; the difference was nearly significant). Although social behaviors between the two rearing groups were similar in most respects, this study is the first to document measurable differences between puppet‐ and parent‐reared captive‐bred California condor juveniles. Zoo Biol 27:1–18, 2008. © 2007 Wiley‐Liss, Inc.     

Factors predicting increased incidence of abnormal behavior in male pigtailed macaques

To identify factors predicting abnormal behavior in laboratory monkeys, we observed all available singly housed 4- to 11-year-old male pigtailed macaques (Macaca nemestrina), the species/age/sex group most likely to be referred to the Washington National Primate Research Center's Psychological Well-Being Program for behavioral assessment. Of the 87 subjects, 29 had been referred to the program whereas 58 had not. Abnormal behavior was unrelated to the subject's housing location (biocontainment vs. other facility) or invasiveness of research. Nursery-reared subjects displayed more abnormal behavior than mother-reared subjects. Across and within rearing categories, the proportion of the first 48 months of life spent singly housed was positively related to the amount of abnormal behavior at maturity. This effect was stronger for subjects separated from the mother for clinical rather than experimental reasons, and least for mother-reared subjects. Locomotor stereotypy, by far the most frequent form of abnormal behavior, was positively related to time in single housing but was unrelated to rearing. These results reinforce the importance of tactile social contact during juvenility for the prevention of abnormal behavior in social primates. They also suggest that self-directed abnormal behaviors and locomotor stereotypies have different etiologies.     

Nonsocial behavior of captive infant gorillas

Frequencies of eight nonsocial behaviors (object contact, environmental exploration, mouthing, self-directed behavior, display behavior, solitary behavior, rest, and locomotion) were obtained for 20 infant lowland gorillas (Gorilla gorilla gorilla) between 14 and 36 months of age. They lived in 13 groups in 10 zoological collections. Approximately 12 hours of one-zero data were collected on each animal. Behavioral data were analyzed with regard to the following independent variables: rearing history of the focal animal (mother-reared vs. human-reared), time of day (a.m. vs. p.m.), sex of the focal animal, age of the focal animal, and complexity of the physical and social environment. Results indicated significant differences in the frequency of behaviors within each independent variable, including selfdirected behavior, rest, environmental exploration, and display behavior with rearing history. Additional significant differences in the frequencies of behavior were also found, including mouthing behavior and locomotion with infant age.     

Injury risks among chimpanzees in three housing conditions

Meeting the psychological needs of chimpanzees (Pan troglodytes) can be a challenge given their aggressiveness on the one hand and the complexity of their social lives on the other. It is unclear how to balance the need to provide opportunities for species-appropriate behavior against potential risks of injury chimpanzees may inflict on each other. This study evaluates the suggestion that simpler social environments protect chimpanzees from wounding. Over a two-year period all visible injuries to 46 adult males, 64 adult females, and 25 immature chimpanzees were recorded at the Yerkes Regional Primate Research Center. Approximately half of the subjects were mother-reared, and the rest were nursery-reared. Housing included compounds containing about 20 chimpanzees, interconnected indoor-outdoor runs for groups of up to 12 individuals, and smaller indoor-outdoor runs for pairs and trios. Annual wounding rates were calculated for serious wounds (extensive injuries and all those requiring veterinary intervention) as well as for minor wounds. Compound-housed chimpanzees incurred the highest level of minor wounding, but serious wounding levels were not affected by housing condition. Even with a period of dominance instability and elevated levels of wounding in one compound, compound chimpanzees were not injured more than those in smaller social groups over the long term. Nursery-reared females in moderate-sized groups were wounded more than mother-reared females. Also, nursery-reared males and females were wounded less often when paired with mother-reared companions. Overall, this study indicates that maintaining chimpanzees in pairs and trios would not be an effective means for reducing injuries. The management of wounding in chimpanzee colonies is influenced more by the sex and rearing composition of a colony.