The Provision of Cage Furnishings As Environmental Enrichment at the Primate Foundation of Arizona

S. Howell, E. Mittra, J. Fritz, J. Baron
Primate Foundation of Arizona
P.O. Box 20027
Mesa, Arizona 85277-0027

The purpose of environmental enrichment is to provide a complex social and physical environment sufficient to allow individuals to express species-typical behavior patterns [Benn, 1995]. An enriched environment has been correlated with an increase in social and sexual behaviors for nonhuman primates, in general [Bayne, 1989], and more specifically, for monkeys [Line and Morgan, 1991 Macaca mulatta]. The importance of this has long been stressed [Murphy, 1976] in promoting the psychological well-being of captive nonhuman primates and countering the effects of boredom that may result in maladaptive and species atypical behavior patterns [Brent et al, 1991; Fritz and Howell, 1993; Paquette and Prescott, 1988; Pereira et al, 1989; Rumbaugh et al, 1989].

For chimpanzees, environmental enrichment has included: (1) the provision of space sufficient for play and exercise [Brent et al, 1989, 1991; Traylor-Holzer and Fritz, 1985] ; (2) feeding enrichment to encourage foraging behavior [Bettinger et al, 1992; Bloomstrand, 1987; Brent and Eichberg, 1991; Grief et al, 1992; Lambeth and Bloomsmith, 1994; Martin et al, 1991; Maki et al, 1989], (3) manipulable objects or 'toys' to encourage exploration and play [Pruetz and Bloomsmith, 1992; Shefferly, 1988; Shefferly et al, 1993], (4) bedding to foster nesting behavior [Brent, 1992; Poenisch, 1992]; and (5) novel items to enhance the environment, including uprooted trees [Maki and Bloomsmith, 1989], a sandbox [Purdy p.c., 1996] , novel toys [Paquette and Prescott, 1988] , and ice cube treats [Fritz and Howell, 1993].

Traylor-Holzer and Fritz [1985] were among the first to publish the potential of cage furnishings as enrichment for captive chimpanzees (Pan troglodytes). They reported that upper level benches and horizontal and vertical poles were preferred by captive chimpanzees and should be considered an important source of enrichment. Since that time, others have considered chimpanzee preferences for varied furnishings including, ropes, runways, connecting chutes, concrete slabs, grass, floor substrates and benches [Brent et al, 1991; Chamove, 1989; Schwandt, 1996]. RecentlyI multi-level deck platforms [Suarez and Forter 1995] and large hammocks [Wolper, 1995] have been suggested as additional cage furnishings to promote species-typical behavior patterns.

The Primate Foundation of Arizona (PFA), a chimpanzee breeding colony and behavioral research center, houses chimpanzees in large, enriched outdoor enclosures that provide a variety of cage furnishings to the chimpanzees. The goal of the present study is to investigate the use of various furnishings and their association with particular behavior patterns. While Traylor-Holzer and Fritz (1985) considered indoor furnishings at the Primate Foundation of Arizona, we consider here the use of outdoor furnishings at the same institution. We then examine the relationship between the use of various cage furnishings and time spent in species typical behavior patterns. Age and sex differences in use of particular furnishings were also tested.

Subjects and Apparatus. Subjects included 34 captive chimpanzees housed in seven social groups of varied age/sex composition, including 14 males and 20 females, 20 adults (10 years or older) and 14 subadults (2 to 9.9 years of age). Each group was provided bi-weekly access to the large outdoor enclosures for exercise and play [see Fritz and Howell, 1993 for further detail]. Observations were collected on alternating weeks when subjects had access to the outdoor enclosures. Cage furnishings were similar in each outdoor enclosure and included a variety of horizontal, climbing and nesting furnishings (Table 1 ).

Table 1. Cage Furnishings
 Horizontal Furnishings  Benches (metal), Logs (recycled plastic or wood
 Climbing Furnishings  Ropes (fire hose or braided rope), Poles (metal)
 Nesting Furnishings  Suspended Barrel "Igloos" (plastic), Tubes (Rubber), Weelbarrows (metal)


Procedures. A focal animal scan sampling method was used to record behavior and cage furnishing use [Martin and Bateson, 1993] .The data set included slightly more AM than PM observations due to high afternoon outdoor temperatures during Arizona's peak summer months (July and August). During these months, the chimpanzees often prefer to be inside, rather than in their large outdoor enclosures, and outdoor activity is less than other times of the year. A total of 499 scans were collected by two observers with 85% inter-observer reliability. Behavioral variables were combined into six general behavioral activity categories: (1) SOCIAL ACTIVITY (play, groom, aggression, fear, embrace, tandem walk, present; (2) SOLITARY ACTIVITY (solitary play, allogroom, nest, forage, drink, and object manipulation); 3) TRAVEL/LOCOMOTOR ACTIVITY (hang, climb, swing, stand, knucklewalk, cantor, run; (4) ABNORMAL ACTIVITY (rocking, coprophagy, urophagy, regurgitate, depilate, spit); (5) INACTIVITY (sit, rest, sleep); and (6) OTHER (includes all behaviors that did not fit into any defined behavioral category).

Analysis. For each individual, we calculated the proportion of total scans where an individual used a particular cage furnishing or engaged in particular behavioral activities. We used a Friedman test statistic to consider variation in cage furnishing use (1) across general types of furnishings (HORIZONTAL, CLIMBING, NESTING) and (2) across specific types of furnishings (BENCH, LOG, POLE, ROPE, IGLOO, TUB, WHEELBARROW). A Chi-Square Goodness-of-Fit test was used to compare expected versus observed frequencies of general behavior patterns (LOCOMOTOR, SOCIAL SOLITARY, SIT, REST/SLEEP, AND OTHER) on particular types of cage furnishings (HORIZONTAL, CLIMBING, NESTING). A Chi-Square test was also used to compare age and sex differences in behavioral activity patterns. For Chi-Square tests, we could not include ABNORMAL activity because its cell frequencies were too low. Significance level was set at p < .05.


Cage Furnishing Preferences. We found that individuals used HORIZONTAL furnishings (benches and logs), more than CLIMBING (poles and ropes) or NESTING ("igloo" suspended barrels, tubs, and wheelbarrows) furnishings. This result was significant (F=23.4, p = 0.000).

Among HORIZONTAL furnishings, we compared use of BENCHES versus LOGS and found no significant difference. Among CLIMBING furnishings, we compared use of POLES and ROPES, and --again -- found no significant use difference. Among NESTING furnishings, we also found no significant difference when we conducted paired comparisons of IGLOOS, TUBS, and WHEELBARROW use. However, our result for TUBS versus WHEELBARROWS approaches significance (Z=1.960, p = 0.05); individuals have a tendency to use TUBS more than WHEELBARROWS.

Activity and Furnishing Use. We expected various furnishings to be associated with particular activities. In particular, we expected HORIZONTAL furnishings would be associated with SOCIAL ACTIVITIES, CLIMBING furnishings would be associated with TRAVEL LOCOMOTOR ACTIVITIES, and NESTING furnishings would be associated with REST/SLEEP. However, our Chi-Square Goodness-of-Fit tests revealed no significant difference in frequency of activities performed on HORIZONTAL, CLIMBING, and NESTING furnishings. Chimpanzees did not partition out their activities to use of particular furnishings. While they showed a tendency to engage in social activities on HORIZONTAL furnishings, a tendency for TRAVEL LOCOMOTOR ACTIVITY on CLIMBING furnishings, and a tendency to REST/SLEEP on NESTING furnishings, these frequencies were not significantly different than expected.

Age and Sex Differences in Furnishing Use. Chi-Square Goodness-of-Fit tests revealed no significant difference in the frequencies of activities performed by males and females on HORIZONTAL, CLIMBING, and NESTING furnishings. However, Chi-Square tests did reveal significant difference in the frequencies of activities performed by adults and sub-adults on HORIZONTAL, CLIMBING, and NESTING furnishings (Chi Square = 39.85, df = 11, p < 0.05). Subadults used CLIMBING and NESTING furnishings more
frequently than did adults.


Results suggest a preference for horizontal furnishings above the enclosure floor. This corresponds to previous studies [Suarez and Forter, 1995; Traylor-Holzer and Fritz, 1985]. Large mesh, or wood and plastic "log" furnishings were used more frequently than climbing poles and ropes or nesting devices ("igloos," hanging tubs, and wheelbarrows). Thus, in planning appropriate enclosures for captive chimpanzees, it may be important to consider chimpanzee preferences for benches that allow one or more individuals to sit as high as possible above the floor or ground surface. Our results also suggest further
attention to age-specific environmental enrichment needs are warranted. Adults infrequently used "moving" furnishings (e.g., swinging ropes, hanging tubs, etc...) and seemed to prefer "stable" horizontal furnishings (i.e., benches, logs) above the enclosure floor.


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The animal data collection portion of this study was reviewed and approved by the Primate Foundation of Arizona Institutional Animal Care and Use Committee. This project was supported by NIH, NCRR Grant No. 2U42 RRO 3602-11. We wish to thank Dr. Leanne Nash for help in design of the analysis.

Reprinted with permission of the Editor of The Newsletter.

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