American Journal of Primatology 3215S170 (1994) RESEARCH ARTICLES Behavioral Effects of Enrichment on Pair-Housed Juvenile Rhesus Monkeys STEVEN J. SCHAPIRO AND MOLLIE A. BLOOMSMITH University of Texas M . D. Anderson Cancer Center, Science Park, Department of Veterinary Resources, Bastrop, Texas Among captive primates, inanimate environmental enrichment can lead to measurable changes in behavior indicative of an improvement in psychological well-being. Although this has been demonstrated repeatedly for singly caged primates, the relationship is not as well studied for pairhoused animals. Study of the pair-housed setting has become increasingly relevant because of the social housing mandate of the Animal Welfare Act regulations. We therefore observed 68 juvenile rhesus monkeys born in 1988 and 1989 and living in mixed-sex pairs from the ages of 2 to 3 years. All pairs were compatible. Half of the pairs received two types of enrichment, while the remaining pairs served as controls. Enriched and control juvenile subjects differed in the amount of time that they spent being inactive, playing, and drinking, but did not differ in the amount of time they spent interacting with their partner. Grooming and play were the two most common socially directed activities in both groups, a species-appropriate pattern. Males played more and vocalized less than did females. Overall, enriched and control subjects spent equivalent amounts of time located within a social distance of one another, but there was some difference between groups in allocation of behaviors while near the pairmate. Environmental enhancers were frequently utilized, and led t o relatively small changes in behavior between control and enriched subjects, suggesting that the presence of a partner for juvenile rhesus monkeys acts as a form of enrichment that may dilute the effects of inanimate environmental enhancements. o 1994 Wiley-Liss, Inc. Key words: environmental enrichment, pair-housing, rhesus monkeys, psychological well-being INTRODUCTION Recent legislation mandating the enhancement of captive primates’ environments raises an important question: Which enhancements are most effective, not only in terms of the primates’ psychological well-being but also in terms of cost? Cost-effectivenessis not the primary concern, but ineffective measures are a waste of scarce resources and should be replaced with measures that more effectively enhance the social, physical, and occupational needs of captive primates. It is Received for publication October 30, 1992; revision accepted July 27, 1993. Address reprint requests to Steven J. Sehapiro, Ph.D., University of Texas M.D. Anderson Cancer Center, Science Park, Department of Veterinary Resources, Route 2, Box 151-B1, Bastrop, TX 78602. 0 1994 Wiley-Liss,Inc. 160 / Schapiro and Bloomsmith therefore imperative that the effects of various environmental enhancements be studied in detail. Although many such studies have already been conducted [e.g., Bayne et al., 1991; Bloomsmith et al., 1988; Line & Morgan, 19911 and reviewed [Fajzi et al., 19891, one area that has yet to receive adequate attention is that of pair-housed primates. Few studies have reported on environmentally enriched pairs nor have many discussed comparisons of social and nonsocial enrichment for the same animals [except see Reinhardt, 19901. Our study therefore focused on two factors: nonsocial enrichment and pair housing. Nonsocial, or “inanimate,” enrichment often takes the form of providing primates with inanimate objects that encourage species-typical behavior. Many studies of inanimate enrichment have shown behavioral changes indicative of improved psychological well-being as defined by increases in species-typical behavior [e.g., Bayne et al., 1991; Bloomsmith et al., 1990; Bryant et al., 1988; Novak & Drewsen, 1989; ONeill et al., 19911. It has been argued that increases in species-typical behaviors and decreases in atypical behaviors are indicators of improved psychological well-being [Line, 1987; Novak & Suomi, 19881.Therefore, if the behavior of captive primates can be affected to more closely approximate the behavioral patterns of their free-ranging counterparts, these changes will be judged as evidence of improved psychological health. Particularly in situations of social restriction, physical, feeding, and occupational enhancement procedures have been shown to increase the amount of species-typical behavior andlor decrease the amount of abnormal behavior displayed by primates [e.g., Bayne et al., 1991; Bloomsmith et al., 1990; Bryant et al., 1988; Fajzi et al., 19893. Even among primates housed in social groups, inanimate enrichment has produced similar beneficial changes [Bloomsmith et al., 1988; Byrne & Suomi, 1991; Chamove et al., 19821. Housing primates in pairs is not new [Brandt & Mitchell, 1973;Chamove, 1973; Harlow, 19631, but the current climate emphasizes pair housing as a potential improvement over single housing, since pair housing provides opportunities for social interaction. Although many attempts to pair monkeys have worked out quite well [Crockett et al., 1991; Eaton et al., 1991, 1992; Line et al., 1990; Reinhardt et al., 1988;Reinhardt, 19891,others have not been as successful [Chamoveet al., 1973; Ruppenthal et al., 19911. The clear message is that a universal enrichment procedure of pairing primates will not be appropriate across all ages, all species, or in all settings. In general, pairs of animals in which both members are not infants [Brandt & Mitchell, 1973; Crockett et al., 1991; Eaton et al., 1991; Line et al., 1990; Reinhardt, 19891are likely to be more successfulthan pairs formed with two infants [Chamove et al., 1973; Ruppenthal et al., 19911. From a management point of view, then, there will be situations in which it is appropriate to house animals in pairs because it improves psychological well-being, and there will be situations in which pairing will actually diminish psychological well-being. This caution does not necessarily preclude a pairing that is an atypical social grouping for a particular species (e.g., adult male-infant pairs, adult female-adult female pairs, etc.). In the present investigation, we sought to determine whether physical and feeding enrichment of pair-housed juvenile rhesus monkeys was effective, and whether it was necessary to provide subjects with both social and inanimate enrichment, using enriched and control pairs of subjects. MATERIALS AND METHODS Specific Pathogen-Free (SPF) Breeding Program This study was conducted on juvenile rhesus monkeys that were part of the SPF breeding program at The University of Texas M. D. Anderson Cancer Center, Science Park. Using a progressive program of social and housing manipulations, Enrichment and Pair-Housed Juveniles / 161 the traditional breeding colony is being converted into a colony that is free of Herpesvirus simiae, SIV, SRV, and STLV [Voss et al., 19911. Infants were left in their natal groups for 1 year, were then housed in single cages for a year, which was followed by a year of housing in mixed-sex pairs. The final step in the derivation strategy was to form unimale breeding groups at 3 years of age from the formerly paired animals. The process of socialization (first year), followed by restriction (second year), followed by gradual resocialization (third year), prior t o full social integration (fourth year) was specifically designed to minimize both viral transmission and long-term behavioral disturbance. The goal was to build an SPF colony with good reproductive abilities. Subjects and Housing Two groups of rhesus monkeys (Macaca mulattu) served as subjects. Group 1 consisted of 34 juveniles (18 males, 16 females) born in 1988 and Group 2 comprised another 34 juveniles (17 males, 17 females) born in 1989. All lived in ageand sex-matched pairs for the entire year of the study and all pairs formed were compatible. For each group, half of the animals received an environmental enrichment program, and half served as controls, receiving no environmental enrichment. Although control subjects could see the enrichment devices when they were brought to the experimental subjects, most had only limited sensory access to subjects actually using enrichment. All subjects were provided with monkey biscuits twice daily, were given half of an orange three times per week, and had water available ad libitum. Subjects were housed in rack-mounted Harford stainless steel cages (88%had 8.2 square feet of floor space; the remainder had 6.2 square feet) with sensory access to similarly housed subjects. They lived in an outdoor building with sensory access to group-housed as well as pair-housed conspecifics and were exposed to natural variation in environmental conditions. Enrichment Enriched subjects simultaneously received physical and feeding enrichers. Physical enrichment consisted of the continuous availability of two chain perches, one with an attached plastic rattle, a hard toy and a chewable toy, and a piece of fleece. The goal of these enhancements was to provide the subjects with objects that might stimulate species-typical behavior related to manipulating, climbing, and playing. Feeding enrichment consisted of five different enhancements presented throughout each workday, with the order of presentation of enhancements rotated daily. Three enrichment devices used were an astroturf foraging mat [similar to Bayne et al., 19921,a polyvinyl chloride (PVC) foraging tree [Schapiro et al., 19911, and an acrylic food puzzle [Schapiro et al., 19911, each filled with 20 g of popcorn, peanuts, sunflower seeds, or corn. The two other feeding enhancements were a 100-ml cup of frozen juice and 125 g of fresh produce (50 g of vegetable and 75 g of fruit). The flavor of the juice and the specific produce items were changed weekly. Two devices or two portions of each feeding enhancer were presented a t a time to every pair, except in the case of the PVC foraging tree. On weekends and holidays, an abbreviated enrichment routine was followed in which pairs received only one set of enrichment devices (either the PVC trees, acrylic puzzles, or most frequently, the astroturf mats) and the regular orange supplement. The goal of giving these enhancements was to provide situations that required the animals to work to obtain food and to supply novel foods that required time to process and consume. 162 / Schapiro and Bloomsmith Data Collection Fifteen-minute focal animal observations [Altmann, 19741were conducted on all subjects from ages 2 to 3 years. Four hundred and sixty hours of observations were conducted on Group 1 between May 1990 and May 1991, and 465 hours of observations were conducted on Group 2 between May 1991 and May 1992. Data were collected using a Tandyo 102 portable computer and The Observer@[Noldus, 19911, an observational software package. Data were collected between 0830 and 1730 h throughout the year, were balanced for time of day, and included periods during which feeding enrichments were “full,” “partially full,” and “empty.” Abnormal and social behaviors were emphasized on the ethogram of mutually exclusive behaviors (see Table I). Interobserver reliability for cumulative durations of behaviors within observation sessions was measured monthly for a total of four observers and the Kappa coefficient [Martin & Bateson, 1986; Hollenbeck, 19781 averaged 230. In addition to recording the behavior of the subjects, the following measures were recorded simultaneously: location in relation to the pairmate (social location), whether the behavior was directed a t the cagemate (social direction), and whether enrichment was being used (enrichment use). Operational definitions of these conditions appear in Table I. Interobserver reliability as measured by the Kappa coefficient averaged 234, .83, and 3 0 for social location, social direction, and enrichment use, respectively. The Observer program allows for analyses of combinations of behaviors and conditions (e.g., socially located, socially directed grooming; or nonsocially located, self-directed play, etc.) and thus social location, social direction of behaviors, and enrichment use included occurrences of more than one of the previously mentioned, mutually exclusive behavior categories. Data were analyzed using multivariate analysis of variance (MANOVA)techniques within the Systat@statistical package. Individual behaviors from the ethogram were grouped into the categories of activity outlined in Table I. The dependent measures used in the analysis were the cumulative durations of each activity category for each subject during the entire year of pair housing, resulting in a total of 68 data points per activity (35 enriched subjects, 33 controls). The two extra enriched animals resulted from the replacement of an enriched pair with a new pair midway through the study. A 2 x 2 x 2 MANOVA examining group (1 or 2), treatment (enriched or control), and sex (male or female) effects on the mutually exclusive categories of activity was performed. In addition, separate 2 x 2 x 2 ANOVAs were conducted for the same effects on social location and on social direction of behavior. Separate ANOVAs were necessary to prevent skewing of the main analysis since these conditions represented combinations of the mutually exclusive behavior categories. RESULTS The overall multivariate test was significant [Pillais = .47; P 5 .0011, and comparison of enriched subjects to controls showed a significant difference based on the experimental treatment [F(9,52) = 5.0, P 5 .0011. Subsequent univariate tests indicated that enriched subjects spent significantly more time being inactive [F(1,60) = 9.5, P 5 .011, more time playing [F(1,60) = 7.6, P 5 .011, and less time drinking [F(1,60) = 8.0, P 5 .01] than did controls (see Table 11). Control and enriched subjects did not differ in durations spent in any other activities, nor did they differ in time spent located near or interacting with their partner. Abnormal behavior was infrequent in all groups. Group 1and Group 2 animals did not differ Enrichment and Pair-Housed Juveniles I 163 in any activities. Male subjects played significantly more than did females [F(1,60) = 5.2, P 5 .05] and vocalized significantly less [F(1,60) = 20.8, P 5 .001]. There were no significant two-way or three-way interaction effects. The specific activities that comprised the categories of socially directed behavior and socially located activity were identified. Table I11 contains the mean amount of time spent in each category and the distribution of some behaviors within these categories. Enrichment items were used frequently (mean use was 24.0 min per h), whereas slightly less time was spent near a partner (mean of 22.8 min per h for all subjects) or interacting with the partner (mean of 12.5 min per h for all subjects). For both control and enriched subjects, feeding was rarely, but inactivity was frequently, engaged in within a social distance of the cagemate. All subjects spent less than one-fifth of their feeding time within 8 cm of their partner, and enriched subjects spent about 1min less per h feeding near the partner than did controls. DISCUSSION The combination of feeding and physical enhancements provided to enriched subjects affected their behavior when compared to the control subjects, but the effects were neither as widespread nor as large as enrichment effects have been for singly caged rhesus [Bayne et al., 1991; Bryant et al., 19881.Although these effects were statistically significant, whether they are of practical significance is a question. It may be possible t o address the issue of practical significance by examining how subjects choose to alter their behavior in response to enrichment. Age-related influences on the effects of enrichment [O’Neill et al., 19901 have been documented, thus these findings apply most specifically to rhesus monkeys between the ages of 2 and 3 years. Enriched subjects played for durations approaching those typical of rhesus juveniles in the wild [Lindburg, 19711. Enrichment successfully promoted play among these juvenile subjects, and this change was of a desirable behavior in a species-typical direction, and therefore indicated an improvement in psychological well-being [Line, 1987;Novak & Suomi, 19881. Control and enriched subjects spent similar amounts of time feeding, a finding inconsistent with previous feeding enrichment studies for singly or group-housed subjects [Bayne et al., 1991; Bloomsmith et al., 1988; Byrne & Suomi, 1991; Chamove et al., 19821. Many of these studies used subjects as their own controls, increasing the likelihood of post-test behavioral changes in response to the removal of enrichment (the rebound effect discussed by Bayne & Dexter [ 19921). Additionally, many were considerably shorter in duration than the present investigation, providing less opportunity for the attractiveness of feeding enhancement to diminish. Enriched subjects in the present investigation were presented with five feeding enhancements every workday for a year, and each contained only a limited quantity of food. The long duration and the cumulative frequency with which the enhancements were encountered may account in part for not achieving the major goal of increasing time spent feeding. The discrepancy between control and enriched groups in the amount of time they spent feeding within a social distance of their partner is evidence for competition between pairmates for enrichment foods. Dominant control monkeys attempted to get as many orange pieces as possible, and when the subordinate was able to get some orange, it would often move away to eat alone. This pattern of competitive, solitary eating of a desirable food, supplied in limited quantity, was more frequent among enriched subjects, who were provided with numerous treats each day. Despite this pattern of feeding alone, enriched subjects spent as much 164 I Schapiro and Bloomsmith TABLE I. Categories of Behaviors Analyzed, Behaviors Recorded, and Operational Definitions Mutually exclusive categories of behavior Inactivity Sitting with no discernible focus of attention Sit Sitting or lying down with eyes closed Sleep Sexual Abnormal sexual behavior Sexual behavior that is improperly conducted Oral or manual manipulation of the genitals Masturbate A male mounting a partner with a properly oriented Normal sexual behavior double-foot-clasp mount; the female equivalent of normal (given) sexual behavior given would be “present” A female being properly mounted by a male Normal sexual behavior (received) Drinking Ingestion of water Drink Grooming Normal care behaviors of the animal’s body surface Groom (self) Normal care of another animal’s body surface by the focal Groom (given) animal Receipt by the focal animal of normal care of the body surface Groom (received) by the pairmate Feeding Ingestion of food items, including chewing Eat Manual manipulation of food items or food sources not directly Forage related to putting food in the mouth Playing Includes some or all of the following: swinging by all or a few Play limbs, rolling around, shaking, jumping, and/or gymnastics; when enrichment devices are involved (toys, etc.), play includes behaviors other than manipulating or directed locomotion with the device; when a social partner is involved, play includes chasing, wrestling, play fighting, etc. Abnormal behaviors The ingestion of urine from hands, cage structures, or directly Urophagy Focal animal performs extremely directed pulling out of own or Pick (given) partner’s hair or skin Self-explanatory Suck digit Raising and pressing hand to the eye on the same side of the Salute head Undirected, repetitive locomotor activity Pace Exaggerated throwing of the head when encountering a Head toss barrier, such as a cage wall Ingestion of feces or materials picked from feces Coprophagy Self-directed “ h a r d biting or hitting Aggression (self) A catch-all category to record all other types of abnormal Abnormal (other) behavior, including bowing, crouching locomotion, bizarre postures, etc. Explore Snifling a n object or pairmate Olfactory explore Visual exploration of the inside of the cage and/or its contents, Investigate including the pairmate Visual exploration of the environment outside of the cage Look Vocalization Self-explanatory, analyzed by frequency Vocalize (Continued) Enrichment and Pair-Housed Juveniles I 165 TABLE I. Categories of Behaviors Analyzed, Behaviors Recorded, and Operational Definitions (Continued) Simultaneously recorded information Enrichment use includes whenever the focal subject is in Enrichment use contact with or has its attention focused on a n enrichment item Socially directed behavior All behaviors that are directed at a pairmate or directed a t Socially directed the focal subject by a pairmate All behaviors that are not directed at the pairmate (Nonsocially directed) Socially located When the focal subject is less than 8 cm from the pairmate Social location TABLE 11. Mean Durations Spent in Selected Activities, Comparing Enriched to Control Subjects Across G r o u p s (in minutes/observation hour)+ Group 1 Activity Inactivity Sexual behavior Drinking Grooming Feeding Playing Abnormal behavior Exploration Vocalization Enrichment use Socially directed behavior Socially located Group 2 Average Control Enriched Control Enriched Control Enriched 2.67 0.31 2.56 10.00 19.71 2.83 2.26 9.87 20.42 0.00 11.85 22.01 3.70 0.72 2.20 9.95 16.77 3.28 1.89 8.66 17.52 26.78 12.55 21.63 2.70 0.46 2.95 12.93 16.52 2.37 2.06 9.63 21.22 0.00 13.23 23.90 4.82 0.38 1.85 10.14 16.35 3.51 1.87 9.16 19.79 21.31 12.46 23.55 2.67* 0.38 2.75* 11.42 18.17 2.61* 2.16 9.75 20.80 0.00 12.52 22.90 4.27 0.55 2.02 10.04 16.56 3.40 1.88 8.92 18.69 23.97 12.50 22.62 +Activity will not sum to 60 min. *Frequency of occurrence. *P 5 0.01 for comparison of enriched to control time as controls within a social distance of, and interacting with, their partner, thus they seemed to compensate for eating alone by spending more time near each other during nonfeeding activities. Feeding enrichment programs have been shown to decrease levels of some positive social interactions [Bloomsmith et al., 19881 (social play and social grooming specifically [Byrne & Suomi, 19911).Therefore, feeding enrichment may not be effective for achieving goals of increased levels of social interactions, which are sometimes used as indicators of improved psychological well-being. The enrichment program did not affect the amount of time that subjects spent near their pairmate, but it did influence the allocation of socially located activities across treatment conditions. Enriched subjects actively altered their patterns of social location as their own behavior changed. Enriched subjects spent significantly more time being inactive (sitting and sleeping) than did controls, yet the implications for psychological well-being of increased inactivity are not clear. Rhesus monkeys in natural conditions spend time being inactive [Lindburg, 19711, and many enrichment programs strive to emulate natural behavior patterns, yet few enrichment programs aim to increase inactivity (nor do they aim to increase 166 / Schapiro and Bloomsmith TABLE 111. Partial Breakdown of Socially Directed Behavior and Behaviors Performed While Socially Located (in minutes/observationhour) Socially directed behavior Total Social grooming Social play Other Socially located behavior Total Feeding Inactivity Other Control Enriched 12.52 6.70 2.38 3.44 12.50 7.08 2.72 2.70 22.90 3.16 2.52 17.22 22.62 2.24 4.06 16.32 aggression or other natural, but undesirable, activities in the captive setting). Since most of the inactive time was also spent near the partner (over 94% for all pairs), enriched subjects spent an additional 1.5 min per h being inactive but near their partner to compensate for the extra 1min per h they spent eating alone. Even though the number of minutes of behavioral change was not large, this evidence for behavioral compensation suggests that these changes were functionally significant to the subjects. Enriched subjects spent significantly less time drinking than did control subjects. Again the implications for such a behavioral change in relation to psychological well-being are unclear. It is possible that the extra produce and frozen juice that enriched subjects were given decreased their requirement for water. The enrichment program did not influence the amount of time that subjects spent interacting with one another. This is contrary to several other studies that have reported changes in social interactions for socially housed primates as a function of feeding enrichment in designs where subjects served as their own controls [Bloomsmith et al., 1988; Byrne & Suomi, 19911. Studies using separate control groups eliminate the possibility of behavioral changes in response to the discontinuation of enrichment (rebound effects [Bayne & Dexter, 19921).The constant availability of both the same partner and inanimate enhancements over a 1-year period may account for the lack of an observed effect on social interactions. Social grooming and social play accounted for over 80% of all socially directed behaviors for all groups, a pattern that is typical of juvenile rhesus monkeys living in other settings [Caine & Mitchell, 1979; Lindburg, 1971; Sade, 19721. The findings of more play behavior and less frequent vocalizations for male subjects than for females were compatible with previous examinations of sex differences in young rhesus. These studies examined subjects with rearing histories that varied from social isolation to natural conditions [Baysinger et al., 1972; Hinde & Spencer-Booth, 1967; Lindburg, 1971; Mitchell, 19791, a range that would cover the present subjects who were reared socially, later socially restricted, and then gradually resocialized. The SPF derivation program does not appear to prevent the development of normal sex differences in behavior. There were several factors that contributed to the success of the pairing phase of this derivation program. All pairs were compatible, there was little abnormal behavior, and there were fewer injuries or health problems among pairs than among singly or group-housed subjects [Schapiro & Bushong, in press]. The social restriction for 1 year that preceded pair housing may have increased the subjects’ probability of interacting amicably with a peer. Two other possible influences were Enrichment and Pair-Housed Juveniles / 167 the age of the subjects (about 2 years at initial pairing) and their early social experience during the first year in the natal group. Studies have documented that social groups of rhesus monkeys are easier to form with young animals and those that are already socially experienced [Bernstein, 1991; Bernstein & Draper, 1964; Bernstein et al., 19741. Infants, although young, may not have the requisite social experience to be successfully paired with one another [Chamove et al., 1973; Ruppenthal et al., 19911. Our findings suggest that 2- to 3-year-old rhesus with some social experience could be easily pair housed in many laboratory settings. Several other laboratories have demonstrated that rhesus monkeys in various age-sex combinations can be successfully pair housed [Brandt & Mitchell, 1973; Eaton et al., 1991, 1992; Reinhardt, 1989; Reinhardt et al., 19881. Although inanimate environmental enrichment had some beneficial effects for pair-housed juveniles, the magnitude of behavioral changes observed was less than usually seen in studies of enrichment involving singly-housed animals [Bayne et al., 1991; Bryant et al., 19881, and more specifically, abnormal behavior was not affected by enrichment. Even though subjects had been socially restricted during the preceding year, abnormal behavior was still infrequent. Most behavior categorized as abnormal was pacing, although some animals maintained infrequent and idiosyncratic stereotyped behavior that developed while singly caged. The presence of the pairmate may have diluted the effects on behavior of the perches, food puzzles, etc. Social enrichment is generally considered to be the most beneficial [but see Coe, 1991 and Ruppenthal et al., 19911 enrichment option [Bayne, 1991; Bramblett, 19891, because species-typical behaviors are expressed to the greatest extent when conspecifics are available. Socially directed activities were expressed by paired monkeys at levels typical for rhesus juveniles [Lindburg, 19711, even among control subjects in unenhanced cages. Except for an increase in play as a function of the inanimate enrichment program, there were few behavioral changes measured that could easily be interpreted as influencing psychological well-being. Line and Morgan  suggest that measuring the effect of enrichment on psychological well-being is better served by analyses of behavioral change than by simple analyses of enrichment use. While this is reasonable, the current study provides an interesting counterpoint; enrichment was used during 40% of observation time yet did not lead to large-scale behavioral changes. Pair-housed subjects actually spent more time near their enrichment than they did near or interacting with their partners, emphasizing the attractiveness of the enhancements employed. Inanimate enrichment may not alter behavioral durations for paired primates as it does for those that are singly-housed, but it still can provide important behavioral options for laboratory monkeys, and cost-effective enhancements should be implemented. CONCLUSIONS 1. A combination of physical and feeding enrichment increased the time spent playing and being inactive, decreased the amount of time spent drinking, but did not affect durations spent feeding in juvenile pair-housed rhesus monkeys. 2. Male subjects housed in pairs spent more time playing and vocalized less frequently than did female subjects. 3. Time spent interacting with or near the partner did not differ across treatment conditions, but enriched subjects compensated for time spent eating enrichment foods alone by spending more time inactive near the partner than did controls. 168 / Schapiro and Bloomsmith 4. Inanimate enrichment was well-used and potentially beneficial in the paired captive setting, but was not as effective at improving psychological wellbeing as inanimate enrichment has been for socially restricted subjects. ACKNOWLEDGMENTS We thank A. Kessel, D. Bushong, and D. Oubari for their dedicated collection of data, K. Vela and D. Glasgow for their data management efforts, and J. McMahan and M. Smith for providing the enrichment. This work would not have been possible without the support of M.E. Keeling, D.V.M., and the primate section staff. Thanks also to K. Flynn a t Scientific Publications, M. D. Anderson Cancer Center, for editing advice. 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