Comfortable Quarters for Nonhuman Primates in Research Institutions

Viktor Reinhardt

Animal Welfare Institute, PO Box 3650, Washington, DC 20007, USA

In the United States there are approximately 57,000 nonhuman primates kept in laboratories (United States Department of Agriculture, 2000). To safeguard their well-being and their suitability for valid scientific research the following primate-specific characteristics must be taken into consideration in the care and use of these animals.

Figure 1. "There is no such thing as a boring animal, rhesus or otherwise; only the conditions under which we keep them can be boring" (Mahoney, 1992, p. 36). Primates have intensive social needs; solitary confinement in a barren cage is a severe punishment for them (Sokol, 1993).

There are simple ways to provide captive primates with housing and handling conditions that address these five characteristics, thereby promoting both the well-being of the animals and the quality of research conducted with them.

Housing primates in groups is the ideal way to account for their social disposition. Conditions for long-term harmonious group-housing, however, are usually not met in research institutions. Aggression-related injury and social distress can often not be avoided when new groups are formed from previously single-housed individuals. The risk remains inherent even in established groups because of the spatial constraints set by confinement and the artificial instability of social relationships resulting from research and managerial stipulations and from health care considerations. It should be emphasized that these risks can be overcome in research facilities committed to exceptionally high animal husbandry standards (Hartner et al., 2001). Housing the animals in pairs offers a practicable alternative to group-housing. Protocols for the safe formation of compatible pairs of previously single-caged adults of the same sex have been documented for numerous species, including chimpanzees (Fritz and Fritz, 1979), baboons (Jerome and Szostak, 1987), squirrel monkeys (Gwinn, 1996), owl monkeys (Weed and Watson, 1998), marmosets (Jackson, 2001; Majolo et al., 2001) rhesus macaques (Reinhardt, 1989a), stump-tailed macaques (Reinhardt, 1994a), long-tailed macaques (Lynch, 1996), and pig-tailed macaques (Byrum and St. Claire, 1998). While adult animals need to be carefully familiarized before being introduced with each other in the same cage, there is little or no danger involved when new pairs are formed by introducing juvenile individuals with strange single-housed adults or by introducing unfamiliar juveniles with each other (Reinhardt, 1994b).

Figure 2. Being housed with a compatible companion –– here two male long-tailed macaques engrossed in social grooming –– is a good compromise for addressing the social needs of primates kept in research facilities. Photo by Richard Lynch, AstraZeneca, Wilmington.

Choice studies conducted with capuchin monkeys have demonstrated that the animals "value social companionship as they value food: It is a necessity, not a luxury" (Dettmer and Fragaszy, 2000, p. 303). The social companion is the one environmental enrichment option of which the caged primate never gets bored (cf., de Waal, 1992). Partners of compatible pairs spend about the same amount of time interacting with each other as wild animals do (Line et al., 1990; Reinhardt, 1990a; Brent, 1992a) `even' when they have lived together for several years (Ranheim and Reinhardt, 1989). This suggests that pair-housing is a reasonable option for addressing their social needs (Figure 2). The behavioral disorder of self-injurious biting is resistant to occupational therapy attempts (Preilowski et al., 1988; Kinsey et al., 1997; Novak et al., 1998) but can be cured by transferring the afflicted single-caged individuals to a compatible pair-housing setup (Line et al., 1990; Bushong et al., 1992; Reinhardt, 1999). Transferring single-caged individuals to compatible pair-housing not only improves their behavioral health, but it also decreases their susceptibility to physical health problems (Schapiro and Bushong, 1994), particularly to stress-related diseases (Schapiro et al., 2000). The two partners of a compatible pair do not differ from each other in terms of stress-sensitive parameters (Gonzalez et al., 1982; Reinhardt et al., 1991; Eaton et al., 1994). Rather than being a source of distress, the companion serves as a stress buffer in fear-provoking situations such as experiments requiring chair-restraint or tether-restraint (Mason, 1960; Coe et al., 1982; Coelho et al., 1991; Figure 3).


Figure 3. During potentially distressing experimental situations there should always be a compatible companion close by, serving as a psychological support.

The horizontally arranged double cage can provide a suitable primary enclosure for paired primates. It must be furnished with two feeders and two elevated resting sites, one in each half of the cage. A dividing panel with a passage hole close to the back wall of the cage minimizes the risk of squabbles over access to these essential resources and makes it possible for the two animals to sometimes get out of each other's sight. This avoids antagonism while fostering affiliation (Reinhardt and Reinhardt, 1991). The vertically arranged double cage does not offer suitable housing conditions because the dominant partner may monopolize the well-illuminated environment of the upper half thereby forcing the subordinate partner to spend most of the time in the dim environment of the bottom half (own unpublished observation; cf., Williams et al., 1988).

Housing primates in pairs does not interfere with husbandry procedures and common management and research protocols (Reinhardt et al., 1989; Schapiro and Bushong, 1994; Shively, 2001; Figure 4). If an animal has to be kept temporarily alone –– e.g., during intensive postoperative care or during a metabolic study –– the caging arrangement must allow the individual animal to maintain visual contact with at least one compatible conspecific (cf., Mahoney, 1992; Lindburg and Coe, 1995) to minimize the stress resulting from social deprivation (cf., Coelho et al., 1991). "We all realize that one is better off with the ups and downs of a social life than without a social life at all. Would it be any different with nonhuman primates?" (de Waal, 1992, p. 86).


Figure 4. Pair-housing does not jeopardize in any way the health status of animals with headcap implants.

While social contact and social interaction with another compatible conspecific is a prerequisite for the psychological and behavioral health of a primate, a trustful relationship with the attending personnel is essential for his/her well-being. Giving the animals names, rather than referring to them as numbered research objects helps to develop such a relationship (cf., Reese EP 1991; Sokol, 1992; de Waal, 1992). The compassionate and respectful attitude "conveys to the animal a quiet sense of assurance on which coping strategies can be developed for dealing with other stressful aspects of the laboratory" (Wolfle, 1987, p. 1221). The macho-type person is out of place in the animal room because s/he triggers distress reactions which will skew scientific findings even before the actual experiment has started. Typically, the animals will panic when such a person comes into their room (own unpublished observation; cf., Arluke and Sanders, 1996).

In order to provide not only a physically but also a psychologically comfortable environment, staff time must be set aside for interacting and communicating with the animals in a positive manner every day (cf., Home Office, 1989). "There should be no sharp demarcation between 'good guys' and 'bad guys.' Nonhuman primates are quick to forget, or perhaps forgive, the momentary fear or resentment they feel towards a human being who has just subjected them to an unpleasant experience if a strong bond of trust already exists with that person" (Mahoney, 1992, p. 35). The investigator, veterinarian or technician who pretends to be too busy to deal with the animals other than during experimental or clinical procedures lacks basic professional qualification.

Indoor enclosures of primates should take maximum advantage of the height of the room, allowing the installation of climbing structures and resting surfaces at different levels. Elevated structures not only increase the usable cage volume but also provide environmental enrichment by stimulating the animals to spend a major portion of their time engaged in species-typical arboreal activities. A perch can readily be installed in any cages, `even' in those that are equipped with a movable back-wall (Reinhardt and Pape, 1991; Watson, 1991). The monkey perch should be made of non-metallic, i.e., 'warm' material, and have a sufficiently large diameter so that the animal(s) can sit on it comfortably (Abee, 1985) or, as in the case of squirrel monkeys and lemurs lie flat on it with limbs dangling on either side for balance (own unpublished observation; McGivern, 1993).

The perch must be placed at a height that the animal(s) are able to sit on and under it in an unrestricted, i.e, not crouched position (Reinhardt and Reinhardt, 1999). Monkeys prefer to look out of their enclosure rather than hide in the back of it (van Wagenen, 1950; Reinhardt, 1989b). Elevated fixtures, therefore, have to be placed in such a way that the animal(s) can sit on them in a look-out position in the front of the cage (Figure 5). An adequate number of elevated sites must be provided for socially housed animals to avoid competition over access (Williams et al., 1988). When this condition is met, access to perches helps the animals to avoid social conflicts and foster affiliative relationships (Neveu and Deputte, 1996.)

Figure 5. The elevated resting surface should be placed in such a way that the animal can sit on it in a look-out position.

Nonhuman primates can get extremely frightened when a person dressed in protective garb approaches them. To minimize the stress, there should be sufficiently high structures which allow the animals to show a vertical flight response and retreat to a quasi safe location above human eye level (cf., International Primatological Society, 1993; Kaumanns and Schönmann, 1997; Wakenshaw, 1999). Mobile structures such as swings and ropes are generally less preferred than fixed structures (Williams et al., 1988; Howell et al., 1997), particularly in cages that provide only the bare minimum space for postural adjustment (Kopecky and Reinhardt, 1991).



Figure 6. Placing the food on the mesh ceiling of the cage is an inexpensive but very effective way of allowing primates to engage in foraging activities.

Figure 7. The primary feeder can be transferred into a foraging device by remounting it away from the access hole. Dexterity is now required to maneuver the biscuits through the mesh covering the face of the box.

Since primates are biologically programmed to spend the major portion of their time gathering and processing food, feeding enrichment provides optimal environmental stimulation for them. The urge to forage is so strong that they will work for food even when identical food is placed right next to them (Markowitz, 1979; Evans et al., 1989; Reinhardt, 1994c). Distributing the food on the chain-link or mesh ceiling of the enclosure rather than in food boxes, troughs or on the floor is perhaps the simplest way to trigger foraging behavior for standard food and supplemental food, such as fruits, vegetables and bread (Figure 6). Depending on the size of the individual food pieces, macaques increase their foraging time more than 100-fold when their daily standard biscuit ration is placed on the mesh ceiling of their cage rather than in ordinary, freely accessible food boxes (Reinhardt, 1993a). The same effect can be achieved when the food box is remounted a few centimeters away from its access hole (Reinhardt, 1993b). Dexterity is now required to maneuver the biscuits through the mesh covering the face of the box (Figure 7). These two feeding enrichment options use structural elements of the cage, redesigned in such a way that they serve as primary feeders for the daily standard food ration. Therefore, no extra time is needed to clean them and bait them with special treats. The animals only work for food that they actually eat (Murchison, 1994; Reinhardt and Garza-Schmidt, 2000). This avoids the accumulation of spoiled foodstuff, a problem which commonly occurs with ordinary feeders, when the animals hoard food and waste part of it by dropping it on fecal material.

Figure 8. In their natural environment marmosets show 'tree-gouging' and 'exudate-feeding'. A simple gum- feeder can support this behavior under laboratory conditions. Photo by Katie Eckert, University of California, San Francisco. 

Marmosets and tamarins are adapted to probe for embedded food in order to extract it. Simulating a natural food-source with an artificial device stocked with gum (McGrew et al., 1986; König et al., 1987; Kelly, 1993) or baited with raisins mixed with corn cob (Molzen and French, 1989) is cheap and easy but allows the animals to engage in extensive foraging activities (Figure 8). Chimpanzees are proficient in using twigs to extract termites from logs and mounds. Simple probefeeder devices filled with sticky foods –– such as applesauce, mashed bananas, jam –– can encourage this mode of foraging in captivity (Murphy, 1976; Goodall, 1979; Nash, 1982; Maki et al., 1989; Gilloux et al., 1992; Perret et al., 1998; Figure 9).

Figure 9. In the wild, chimpanzees are proficient in extracting termites from logs and mounds. Probefeeders can promote this behavior in the research laboratory. Photo by Kai Perret, Allwetterzoo Münster, Germany.

Straw, woodchips, woodwool, and argilla espansa are ideal foraging substrates in the form of deep-litter on the solid floor of pens (Chamove and Anderson, 1979; Fragaszy and Adams-Curtis, 1991; Brent, 1992b; Beck, 1995; Brown et al., 1995; Riviello and Misiti, 1995; Baker, 1997) or distributed on trays mounted under the mesh floor of cages (Bryant et al., 1988; Mahoney, 1992). When mixed with seeds, grain, or other small edible items such materials promote intensive foraging behavior (Burt and Plat, 1990; Byrne and Suomi, 1991; Combette and Anderson, 1991; Grief et al., 1992; Poenisch, 1992; Figure 10). The distracting effect of this feeding enrichment technique is so strong that it reduces social antagonism in group-housed animals (Chamove et al., 1982; Boccia, 1989).


Figure 10. Woodchips provide an ideal foraging substrate for group-housed primates; here a group of stump-tailed macaques foraging for seeds. Photo by James R. Anderson, University of Sterling.

All captive primates should be fed daily at least one whole, medium-size fruit or vegetable (Figure 11a,b,c). The time required by animal care personnel to cut produce into small pieces can be spent in much more meaningful ways (cf., Smith et al., 1989; Kerridge, 1997). For example, portioning the daily standard food ration in several rather than a single feeding, probably does not take more time than chopping the supplemental produce for the animals, but it increases substantially the amount of time they can engage in foraging activities (cf., Taylor et al., 1997).



Figure 11a,b,c. Primates deserve fresh fruit or vegetables on a daily basis. It would be a waste of time to chop the produce for the animals; they have the time and they enjoy doing it themselves.

Branch segments of dead deciduous trees –– red oak disintegrates into flakes that are so small that large quantities pass sewage drains without clogging them (Reinhardt, 1992a) –– are perfect toys for primates, stimulating not only processing but also manipulative and play activities (Figure 12). They constantly change their form and texture due to wear and dehydration and, therefore, retain their stimulatory value (Reinhardt, 1989b; Eckert et al., 2000). Commercial toys lack the natural, ever-changing texture of wood; this is probably the reason why the animals quickly lose interest in them (Crockett et al., 1989; Line et al., 1989; Hamilton, 1991; Pruetz and Bloomsmith, 1992; Kessel and Brent, 1998), unless several different toys are offered and substituted regularly with new ones (cf., Paquette and Prescott, 1988; Weick et al., 1991). Access to a variety of manipulable objects seems to be particularly beneficial for capuchins and baboons, who exhibit sustained interest in them and respond with a significant reduction in abnormal behaviors (Brent and Belik, 1997; Boinski et al., 1999).


Figure 12. Branch segments are perfect toys for primates. Constantly changing their texture and configuration due to wear, these wooden toys do not lose their stimulatory value over time.

A major contention is the need for proper illumination in the caging arrangement of medium- and small-sized primates. In order to minimize housing expenses, these animals are traditionally kept in two-tier cages, with one row stacked on top of another. This doubles the number of primates that can be accommodated in one room, but involves serious implications for the individual animals. Those relegated to the lower rows are restricted to a terrestrial lifestyle, unable to withdraw in alarming situations and retreat to a safe place above the human predators who periodically capture them and subject them to distressing, or even deadly procedures. Moreover, the sanitation tray, which runs the length of the room beneath the upper tier of cages, reduces significantly the amount of light that can penetrate to the lower-cage tier (Schapiro et al., 2000); "animals in the lower tier are thus relegated to a permanent state of semi-gloom" (Mahoney, 1992; p. 32). The cave-like living quarters of bottom-row caged animals is often so dim that caretakers routinely have to use flashlights to identify and inspect them (Figure 13). It has been noticed in marmosets that the housing environment of lower-row caged animals can be so poor that it results in markedly reduced fertility (Heger et al., 1986). Routinely rotating animals between bottom and top tiers (National Research Council, 1998) offers no solution to this problem. It merely "rotates" the problem by alleviating the situation for lower-row subjects, while aggravating it for the same number of upper-row subjects. At the same time it introduces the additional stress-variable associated with cage transfer (Mitchell and Gomber, 1976; Phoenix and Chambers, 1984; Crockett et al., 1993; Schapiro et al., 1997). Even if techniques can be developed to assure uniform illumination, the bottom tier cage will remain a potential source of distress whenever personnel enters the room (cf., Kaumanns and Schönmann, 1997).

Figure 13. Even though it is the prevailing housing arrangement, the double-tier caging system is unacceptable both for ethical and scientific reasons.

In order to provide ethically and scientifically acceptable caging conditions, nonhuman primates must be housed in single-row cages to assure that (a) all animals receive the same quantity and quality of light, (b) all cages are of sufficient height so that occupants are in a position to retreat above animal care personnel, and (c) all animals in the room can be adequately inspected.

Training nonhuman primates to cooperate during procedures is one of the most significant options of making life a little bit more bearable for laboratory primates. It not only challenges the animals' high degree of intelligence, offers them –– and the caregivers –– some relevant distraction and eliminates data-confounding distress responses, but it also increases personnel safety by no longer giving the animals reason to defend themselves by means of biting or scratching during compulsory immobilization. To be forcefully removed from the familiar cage and subdued during painful husbandry and research procedures must, indeed, be a terribly frightening experience for a monkey or an ape. Research data collected from such an animal are tainted by the subject's stress reactions (review: Reinhardt et al., 1995) and, therefore, have questionable scientific value (Figure 14).

Figure 14. Scientific data collected from a subdued animal are skewed by the subject's fear response.

With gentle firmness, patience and positive reinforcement many primate species can be conditioned to work with –– rather than against –– personnel during common procedures such as transfer to a holding area (Goodwin, 1997; Bloomsmith et al., 1998), capture from the home cage (Reinhardt, 1992b), capture from the group (Reinhardt, 1990b,c; Kessel-Davenport and Gutierrez, 1994; Mendoza, 1999; White et al., 2000), blood collection (McGinnis and Kraemer, 1979; Reinhardt, 1991; Laule et al., 1996; Moore and Suedmeyer, 1997), blood pressure measurement (Smith and Ansevin, 1957; Mitchell et al., 1980; Turkkan, 1990), systemic injection (Spragg, 1940; Levison et al., 1964; Byrd, 1977; Priest, 1991; Reinhardt, 1992c; Figure 15a,b), urine collection (Kelly and Bramblett, 1981; Ziegler et al., 1987; Bond, 1991; Anzenberger and Gossweiler, 1993; Shideler et al., 1994), saliva collection (Bettinger, 1998; Bettinger et al., 1998), topical drug application (Reinhardt and Cowley, 1990; Segerson and Laule, 1995), oral drug application (Turrkan et al., 1989), semen collection (Brown and Loskutoff, 1998), insemination (Desmond et al., 1987), vaginal swabbing (Bunyak et al., 1992; Hernándes-López et al., 1998) and veterinary examination (Brown, 1998). The initial time investment in the training quickly pays off in: (a) a reduction of time required to obtain a sample, administer a drug or capture an animal, (b) a reduction of risks associated with defense aggression, (c) a reduction in the use of pharmacological restraint agents, (d) more reliable research data (Elvidge et al., 1976; Reinhardt, 1992c; Schnell and Gerber, 1997; National Research Council, 1998) and a more satisfactory relationship between handling personnel and research subject (Figure 16a,b,c,d).



Figure 15a,b. There is no need to forcefully restrain an animal for Ketamin injection, thereby introducing stress as an uncontrolled variable even before the actual experiment has started. Primates are intelligent and can be readily trained to cooperate during such a simple procedure.

Providing primates in research institutions with primate-adequate housing and humane handling conditions is no sentimentalism. On the contrary, it is essential to employ such refined methodology in order to adhere to the very basic principles of good science. A primate who behaves like a primate and who is free of distress, certainly has a greater potential of being a useful research model than one who is a behavioral cripple as a result of understimulation and one who experiences distress during research-related procedures.




Figure 16a,b,c,d. It takes less than a cumulative total of one hour to train adult male rhesus macaques to cooperate – rather than resist – during blood collection in the familiar home cage (Reinhardt, 1991).



Abee CR 1985 Medical care and management of the squirrel monkey. In Handbook of Squirrel Monkey Research Rosenblum LA, Coe CL (ed), 447-488. Plenum Press, New York, NY

Anderson JR, Chamove AS 1984 Allowing captive primates to forage. In Standards in Laboratory Animal Management. Proceedings of a Symposium 253-256. The Universities Federation For Animal Welfare, Potters Bar, UK
Full Text:

Anzenberger G, Gossweiler H 1993. How to obtain individual urine samples from undisturbed marmoset families. American Journal of Primatology 31, 223-230

Arluke A,Sanders C. R. 1996 Regarding Animals. Temple University Press, Philadelphia, PA

Baker KC 1997. Straw and forage material ameliorate abnormal behaviors in adult chimpanzees. Zoo Biology 16, 225-236

Baskerville M 1999 Old World Monkeys. In The UFAW Handbook on the Care and Management of Laboratory Animals Seventh Edition (edited by Poole, T. and English, P.), 611-635. Blackwell Science, Oxford, UK

Beck RPA 1995. A study of environmental enrichment in groups of captive lion tamarins (Leontopithecus rosalia & Leontopithecus chrysmelas). RATEL (Journal of the Association of British Wild Animal Keepers) 22(4), 112-126

Bettinger T 1998 Saliva Collection of Trained Adult Male Gorillas (Videotape with commentary). In Workshop –– Advances in Primate Training. Twenty-first Annual Meeting of the American Society of Primatologists. O'Neill-Wagner P, Stone A (eds). Cleveland Metroparks Zoo, Cleveland, OH

Bettinger T, Kuhar C, Sironen A, Laudenslager M 1998. Behavior and salivary cortisol in gorillas housed in an all male group. American Zoo and Aquarium Association (AZA) Annual Conference Proceedings, 242-246

Bloomsmith MA, Stone AM, Laule GE 1998. Positive reinforcement training to enhance the voluntary movement of group-housed chimpanzees within their enclosure. Zoo Biology 17, 333-341

Boccia ML 1989. Long-term effects of a natural foraging task on aggression and stereotypies in socially housed pigtail macaques. Laboratory Primate Newsletter 28(2), 18-19
Full Text:

Bond M 1991. How to collect urine from a gorilla. Gorilla Gazette 5(3), 12-13

Boinski S, Swing SP, Gross TS, Davis JK 1999. Environmental enrichment of brown capuchins (Cebus apella): Behavioral and plasma and fecal cortisol measures of effectiveness. American Journal of Primatology 48, 49-68

Brent L 1992a. The effects of cage size and pair housing on the behavior of captive chimpanzees. American Journal of Primatology 27, 20

Brent L 1992b. Woodchip bedding as enrichment for captive chimpanzees in an outdoor enclosure. Animal Welfare 1, 161-170
Full Text:

Brent L, Belik M 1997. The response of group-housed baboons to three enrichment toys. Laboratory Animals 31, 81-85
Full Text:

Brockway BP, Hassler CR, Hicks N 1993 Minimizing stress during physiological monitoring. In Refinement and Reduction in Animal Testing Niemi SM, Willson JE (eds), 56-69. Scientists Center for Animal Welfare, Bethesda, MD

Brown CS 1998 A Training Program for Semen Collection in Gorillas (Videotape with commentary). Ohama: Omaha's Henry Doorly Zoo.

Brown CS, Loskutoff NM 1998. A training program for noninvasive semen collection in captive western lowland gorillas (Gorilla gorilla gorilla). Zoo Biology 17, 143-151

Brown DL, Calcagno J, Gold KC, Thompson S 1995. Effects of environmental enrichment on nonsocial and abnormal behavior of captive lowland gorillas (Gorilla gorilla gorilla). American Zoo and Aquarium Association (AZA) Regional Conference Proceedings , 29-35

Bryant CE, Rupniak NMJ, Iversen SD 1988. Effects of different environmental enrichment devices on cage stereotypies and autoaggression in captive cynomolgus monkeys. Journal of Medical Primatology 17, 257-269
Full Text:

Bunyak SC, Harvey NC, Rhine RJ, Wilson MI 1982. Venipuncture and vaginal swabbing in an enclosure occupied by a mixed-sex group of stumptailed macaques (Macaca arctoides). American Journal of Primatology 2, 201-204

Burt DA, Plant M 1990. Observations on a caging system for housing stump-tailed macaques. Animal Technology 41, 175-179
Full Text:

Bushong D, Schapiro SJ, Bloomsmith MA 1992. Self-aggression in nonhuman primates: A review of its development/possible causes, methods of therapeutic treatment, and its relevance to the zoo situation. American Zoo and Aquarium Association (AZA) Regional Conference Proceedings , 723-728

Byrd LD 1977 Introduction: Chimpanzees as biomedical models. In Progress in Ape Research Bourne GH (ed), 161-165. Academic Press, New York, NY

Byrne GD, Suomi SJ 1991. Effects of woodchips and buried food on behavior patterns and psychological well-being of captive rhesus monkeys. American Journal of Primatology 23, 141-151

Byrum R, St. Claire M 1998. Pairing female Macaca nemestrina. Laboratory Primate Newsletter 37(4), 1
Full Text:

Chamove AS, Anderson JR 1979. Woodchip litter in macaque group. Animal Technology 30, 69-74
Full Text:

Chamove AS, Anderson JR, Morgan-Jones SC, Jones SP 1982. Deep woodchip litter: Hygiene, feeding, and behavioral enhancement in eight primate species. International Journal for the Study of Animal Problems 3, 308-318
Full Text:

Coe CL, Franklin D, Smith ER, Levine S 1982. Hormonal responses accompanying fear and agitation in the squirrel monkey. Physiology and Behavior 29, 1051-1057

Coelho AM, Carey KD, Shade RE 1991. Assessing the effects of social environment on blood pressure and heart rates of baboon. American Journal of Primatology 23, 257-267

Combette C, Anderson JR 1991. Réponses à deux techniques d'enrichissement environmental chez deux espèces de primates en laboratoire (Cebus apella, Lemur macaco). Cahiers d'Ethologie 11, 1-16

Crockett CM, Bielitzki JT, Carey A, Velez A 1989. Kong toys as enrichment devices for singly-caged macaques. Laboratory Primate Newsletter 28(2), 21-22
Full Text:

Crockett CM, Bowers CL, Sackett GP, Bowden DM 1993. Urinary cortisol responses of longtailed macaques to five cage sizes, tethering, sedation, and room change. American Journal of Primatology 30, 55-74

Desmond T, Laule GM, McNary J 1987. Training to enhance socialization and reproduction in drills. American Zoo and Aquarium Association (AZA) Regional Conference Proceedings , 352-358

Eaton GG, Kelley ST, Axthelm MK, Iliff-Sizemore SA, Shiigi SM 1994. Psychological well-being in paired adult female rhesus (Macaca mulatta). American Journal of Primatology 33, 89-99

Eckert K, Niemeyer C, Anonymous , Rogers RW, Seier J, Ingersoll B, Barklay L, Brinkman C, Oliver S, Buckmaster C, Knowles L, Pyle S 2000. Wooden objects for enrichment: A discussion. Laboratory Primate Newsletter 39(3), 1-4
Full Text:

Elvidge H, Challis JRG, Robinson JS, Roper C, Thorburn GD 1976. Influence of handling and sedation on plasma cortisol in rhesus monkeys (Macaca mulatta). Journal of Endocrinology 70, 325-326

Evans HL, Taylor JD, Ernst J, Graefe JF 1989. Methods to evaluate the well-being of laboratory primates. Comparison of macaques and tamarins. Laboratory Animal Science 39, 318-323

Fragaszy DM, Adams-Curtis LE 1991 Environmental challenges in groups of capuchins. In Primate Responses to Environmental Change Box HO (ed), 247-264. Chapman and Hall, New York, NY

Fritz P, Fritz J 1979. Resocialization of chimpanzees. Journal of Medical Primatology 8, 202-221

Gilloux I, Gurnell J, Shepherdson D 1992. An enrichment device for great apes. Animal Welfare 1, 279-289
Full Text:

Gonzalez CA, Coe CL, Levine S 1982. Cortisol responses under different housing conditions in female squirrel monkeys. Psychoneuroendocrinology 7, 209-216

Goodall J 1979 Anti-boredom devices for primates. In Comfortable Quarters for Laboratory Animals, Seventh Edition , 16. Animal Welfare Institute, Washington, DC

Goodwin J 1997. The application, use, and effects of training and enrichment variables with Japanese snow macaques (Macaca fuscata) at the Central Park Wildlife Center. American Zoo and Aquarium Association (AZA) Regional Conference Proceedings, 510-515

Grief L, Fritz J, Maki S 1992. Alternative forage types for captive chimpanzees. Laboratory Primate Newsletter 31(2), 11-13
Full Text:

Gwinn LA 1996. A method for using a pole housing apparatus to establish compatible pairs among squirrel monkeys. Contemporary Topics in Laboratory Animal Science 35(4), 61

Hamilton P 1991. Enrichment toys and tools in recent trials. Humane Innovations and Alternatives in Animal Experimentation 5, 272-277

Hartner M, Hall J, Penderghest J, Clark L P 2001. Group-housing subadult male cynomolgus macaques in a pharmaceutical environment. Lab Animal 30(8), 53-57

Heger W, Merker H-J, Neubert D 1986. Low light intensity decreases the fertility of Callithrix jacchus. Primate Report 14, 260
Full Text:

Hernándes-López L, Mayagoitia L, Esquivel-Lacroix C, Rojas-Maya S, Mondragón-Ceballos R 1998. The menstrual cycle of the spider monkey (Ateles geoffroyi). American Journal of Primatology 44, 183-195

Home Office 1989 Animals (Scientific Procedures) Act 1986. Code of Practice for the Housing and Care of Animals Used in Scientific Procedures. Her Majesty's Stationery Office, London, UK
Full Text:

Howell SM, Mittra E, Fritz J, Baron J 1997. The provision of cage furnishings as environmental enrichment at the Primate Foundation of Arizona. The Newsletter 9(2), 1-5
Full Text:

International Primatological Society 1993. IPS International guidelines for the acquisition, care and breeding of nonhuman primates, Codes of Practice 1-3. Primate Report 35, 3-29
Full Text:

Jackson MJ 2001. Environmental enrichment and husbandry of the MPTP-treated common marmoset. Animal Technology 52, 21-28

Jerome CP, Szostak L 1987. Environmental enrichment for adult, female baboons (Papio anubis). Laboratory Animal Science 37, 508-509

Jorgensen MJ, Kinsey JH, Novak MA 1998. Risk factors for self-injurious behavior in captive rhesus monkeys (Macaca mulatta). American Journal of Primatology 45, 187

König A, Rothe H, Radespiel U, Darms K, Bodemeyer J 1987. Nagehölzer für Krallenaffen. Zeitschrift des Kölner Zoo 30(3), 107-108

Kaumanns W, Schönmann U 1997. Requirements for cebids. Primate Report 49, 71-91

Kelley TM, Bramblett CA 1981. Urine collection from vervet monkeys by instrumental conditioning. American Journal of Primatology 1, 95-97

Kelly K 1993. Environmental enrichment for captive wildlife through the simulation of gum feeding. Animal Welfare Information Center Newsletter 4(3), 1-2 & 5-10
Full Text:

Kerridge FJ 1997. Behavioural enrichment of ruffed lemurs (Varecia variegata) based upon a wild-captive comparison of their behaviour. Primate Eye 63, 36-37

Kessel AL, Brent L 1998. Cage toys reduce abnormal.behavior in individually housed pigtail macaques. Journal of Applied Animal Welfare Science 1, 227-234

Kessel-Davenport AL, Gutierrez T 1994. Training captive chimpanzees for movement in a transport box. The Newsletter 6(2), 1-2
Full Text:

Kopecky J, Reinhardt V 1991. Comparing the effectiveness of PVC swings versus PVC perches as environmental enrichment objects for caged female rhesus macaques. Laboratory Primate Newsletter 30(2), 5-6
Full Text:

Laule GE, Thurston RH, Alford PL, Bloomsmith MA 1996. Training to reliably obtain blood and urine samples from a diabetic chimpanzee (Pan troglodytes). Zoo Biology 15, 587-591

Levison PK, Fester CB, Nieman WH, Findley JD 1964. A method for training unrestrained primates to receive drug injection. Journal of the Experimental Analysis of Behavior 7, 253-254

Lindburg DG, Coe J 1995 Ark design update: Primate needs and requirements. In Conservation of Endangered Species in Captivity Gibbons EF, Durrant BS, Demarest AJ (eds), 553-570. SUNY Press, Albany, NY

Line SW, Markowitz H, Morgan KN, Strong S 1989 Evaluation of attempts to enrich the environment of single-caged non-human primates. In Animal Care and Use in Behavioral Research: Regulation, Issues, and Applications Driscoll JW (ed), 103-117. Animal Welfare Information Center National Agricultural Library, Beltsville, MD

Line SW, Morgan KN, Markowitz H, Roberts J, Riddell M 1990. Behavioral responses of female long-tailed macaques (Macaca fascicularis) to pair formation. Laboratory Primate Newsletter 29(4), 1-5
Full Text:

Lynch R 1998. Successful pair-housing of male macaques (Macaca fascicularis). Laboratory Primate Newsletter 37(1), 4-5
Full Text:

Macy JD, Beattie TA, Morgenstern SE, Arnstern AFT 1999. The use of guanfacine to control self-injurious behavior in nonhuman primates. Abstracts of the AALAS [American Association for Laboratory Animal Science] Meeting, 9

Mahoney CJ 1992. Some thoughts on psychological enrichment. Lab Animal 21(5), 27,29,32-37

Majolo B, Buchanan-Smith HM, Morris K 2001. Factors affecting the successful pairing of unfamiliar common marmoset (Callithrix jacchus) females. Primate Eye 73, 12-13
Full Text:

Maki S, Alford PL, Bloomsmith MA, Franklin J 1989. Food puzzle device simulating termite fishing for captive chimpanzees (Pan troglodytes). American Journal of Primatology 19 (Supplement 1), 71-78

Markowitz H 1979 Environmental enrichment and behavioral engineering for captive primates. In Captivity and Behavior Erwin J, Maple T, Mitchell G (eds), 217-238. Van Nostrand Reinhold, New York, NY

Mason WA 1960. Socially mediated reduction in emotional responses of young rhesus monkeys. Journal of Abnormal and Social Psychology 60, 100-110

McGinnis PR, Kraemer HC 1979 The Stanford outdoor primate facility. In Comfortable Quarters for Laboratory Animals, Seventh Edition, 20-27. Animal Welfare Institute, Washington, DC

McGrew WC, Brennan JARJ 1986. An artificial 'Gum-tree' for marmosets (Callithrix j. jacchus). Zoo Biology 5, 45-50

Mendoza SP 1999 Squirrel Monkeys. In The UFAW Handbook on the Care and Management of Laboratory Animals Seventh Edition UFAW [Universities Federation for Animal Welfare] (edited by Poole, T. and English, P.), 591-600. Blackwell Science, Oxford, UK

Mitchell DS, Wigodsky HS, Peel HH, McCaffrey TA 1980. Operant conditioning permits voluntary, noninvasive measurement of blood pressure in conscious, unrestrained baboons (Papio cynocephalus). Behavior Research Methods and Instrumentation 12, 492-498

Mitchell G, Gomber J 1976. Moving laboratory rhesus monkeys (Macaca mulatta) to unfamiliar home cages. Primates 17, 543-547

Molzen EM, French JA 1989 The problem of foraging in captive callitrichid primates: Behavioral time budgets and foraging skills. In Housing, Care and Psychological Wellbeing of Captive and Laboratory Primates Segal EF (ed), 89-101. Noyes Publications, Park Ridge, NJ

Moore BA, Suedmeyer K 1997. Blood sampling in 0.2 Bornean orangutans at the Kansas City Zoological Gardens. Animal Keepers' Forum 24, 537-540

Murchison MA 1994. Primary forage feeder for singly-caged macaques. Laboratory Primate Newsletter 33(1), 7-8
Full Text:

Murphy DE 1976. Enrichment and occupational devices for orang utans and chimpanzees. International Zoo News 137(23.5), 24-26
Full Text:

Nash VJ 1982. Tool use by captive chimpanzees at an artificial termite mound. Zoo Biology 1, 211-221

National Research Council 1998 The Psychological Well-Being of Nonhuman Primates. National Academy Press, Washington, DC
Full Text:

Neveu H, Deputte BL 1996. Influence of availability of perches on the behavioral well-being of captive, group-living mangabeys. American Journal of Primatology 38, 175-185

Novak MA, Kinsey JH, Jorgensen MJ, Hazen TJ 1998. Effects of puzzle feeders on pathological behavior in individually housed rhesus monkeys. American Journal of Primatology 46, 213-227

Paquette D, Prescott J 1988. Use of novel objects to enhance environments of captive chimpanzees. Zoo Biology 7, 15-23

Perret K, Büchner S, Adler HJ 1998. Beschäftigungsprogramme für Schimpansen (Pan troglodytes) im Zoo. (Environmental enrichment program for chimpanzees in zoos) [German text with English summary]. Der Zoologische Garten 68, 95-111

Phoenix CH, Chambers KC 1984. Sexual behavior and serum hormone levels in aging rhesus males: Effects of environmental change. Hormones and Behavior 18, 206-215

Poenisch T 1992. Bedding for enrichment. The Newsletter 4(1), 1
Full Text:

Preilowski B, Reger M, Engele H 1988. Combining scientific experimentation with conventional housing: A pilot study with rhesus monkeys. American Journal of Primatology 14, 223-234

Priest GM 1991. Training a diabetic drill (Mandrillus leucophaeus) to accept insulin injections and venipuncture. Laboratory Primate Newsletter 30(1), 1-4
Full Text:

Pruetz JD, Bloomsmith MA 1992. Comparing two manipulable objects as enrichment for captive chimpanzees. Animal Welfare 1, 127-137
Full Text:

Ranheim S, Reinhardt V 1989. Compatible rhesus monkeys provide long-term stimulation for each other. Laboratory Primate Newsletter 28(3), 1-2
Full Text:

Reese EP 1991 The role of husbandry in promoting the welfare of laboratory animals. In Animals in Biomedical Research Hendriksen CFM, Koeter HBWM (eds), 155-192. Elsevier, Amsterdam, Netherlands

Reinhardt V 1989a. Behavioral responses of unrelated adult male rhesus monkeys familiarized and paired for the purpose of environmental enrichment. American Journal of Primatology 17, 243-248
Full Text:

Reinhardt V 1989b. Evaluation of the long-term effectiveness of two environmental enrichment objects for singly caged rhesus macaques. Lab Animal 18(6), 31-33
Full Text:

Reinhardt V, Houser WD, Eisele S 1989. Pairing previously singly caged rhesus monkeys does not interfere with common research protocols. Laboratory Animal Science 39, 73-74

Reinhardt V 1990a. Time budget of caged rhesus monkeys exposed to a companion, a PVC perch and a piece of wood for an extended time. American Journal of Primatology 20, 51-56

Reinhardt V 1990b. Avoiding undue stress: Catching individual animals in groups of rhesus monkeys. Lab Animal 19(6), 52-53
Full Text:

Reinhardt V 1990c Catching Individual Rhesus Monkeys Living in Captive Groups (Videotape with commentary). Wisconsin Regional Primate Research Center, Madison, WI
(Available on loan from Animal Care Audio-Visual Materials, WRPRC, 1220 Capitol Court, Madison, WI 53715, USA)

Reinhardt V, Cowley D 1990. Training stumptailed monkeys to cooperate during in-homecage treatment. Laboratory Primate Newsletter 29(4), 9-10
Full Text:

Reinhardt V 1991. Training adult male rhesus monkeys to actively cooperate during in-homecage venipuncture. Animal Technology 42, 11-17
Full Text:

Reinhardt V, Pape R 1991. An alternative method for primate perch installation. Lab Animal 20(8), 47-48
Full Text:

Reinhardt V, Reinhardt A 1991. Impact of a privacy panel on the behavior of caged female rhesus monkeys living in pairs. Journal of Experimental Animal Science 34, 55-58
Full Text:

Reinhardt V, Cowley D, Eisele S 1991. Serum cortisol concentrations of single-housed and isosexually pair-housed adult rhesus macaques. Journal of Experimental Animal Science 34, 73-76
Full Text:

Reinhardt V 1992a. Environmental enrichment branches that do not clog drains. Laboratory Primate Newsletter 31(2), 8
Full Text:

Reinhardt V 1992b. Transport-cage training of caged rhesus macaques. Animal Technology 43, 57-61
Full Text:

Reinhardt V 1992c Improved handling of experimental rhesus monkeys. In The Inevitable Bond. Examining Scientist-Animal Interactions Davis H, Balfour AD (eds), 171-177. Cambridge University Press, Cambridge, UK
Full Text:

Reinhardt V 1993a. Using the mesh ceiling as a food puzzle to encourage foraging behaviour in caged rhesus macaques (Macaca mulatta). Animal Welfare 2, 165-172
Full Text:

Reinhardt V 1993b. Enticing nonhuman primates to forage for their standard biscuit ration. Zoo Biology 12, 307-312
Full Text:

Reinhardt V 1994a. Social enrichment for previously single-caged stumptail macaques. Animal Technology 5, 37-41
Full Text:

Reinhardt V 1994b. Pair-housing rather than single-housing for laboratory rhesus macaques. Journal of Medical Primatology 23, 426-431
Full Text:

Reinhardt V 1994c. Caged rhesus macaques voluntarily work for ordinary food. Primates 35, 95-98
Full Text:

Reinhardt V, Liss C, Stevens C 1995. Restraint methods of laboratory nonhuman primates: A critical review. Animal Welfare 4, 221-238
Full Text:

Reinhardt V 1997. The Wisconsin Gnawing Stick. Animal Welfare Information Center (AWIC) Newsletter 7(3-4), 11-12
Full Text:

Reinhardt V 1999. Pair-housing overcomes self-biting behavior in macaques. Laboratory Primate Newsletter 38(1), 4
Full Text:

Reinhardt V, Reinhardt A 1999. Are legal cage space requirements sound? Laboratory Primate Newsletter 38(2), 5-6
Full Text:

Reinhardt V, Garza-Schmidt M 2000. Daily feeding enrichment for laboratory macaques: Inexpensive options. Laboratory Primate Newsletter 39(2), 8-10
Full Text:

Riviello MC, Misiti A 1995. An alternative to woodchip as a foraging substrate for tufted capuchin monkeys (Cebus apella). Primate Report 42, 24
Full Text:

Schapiro SJ, Bushong D 1994. Effects of enrichment on veterinary treatment of laboratory rhesus macaques (Macaca mulatta). Animal Welfare 3, 25-36
Full Text:

Schapiro SJ, Nehete PN, Perlman JE, Sastry KJ 1997. A change in housing condition leads to relatively long-term changes in cell-mediated immune responses in adult rhesus macaques. American Journal of Primatology 42, 146

Schapiro SJ, Nehete PN, Perlman JE, Sastry KJ 2000. A comparison of cell-mediated immune responses in rhesus macaques housed singly, in pairs, or in groups . Applied Animal Behaviour Science 68, 67-84

Schapiro SJ, Stavisky R, Hook M 2000. The lower-row cage may be dark, but behaviour does not appear to be affected. Laboratory Primate Newsletter 39(1), 4-6
Full Text:

Schnell CR, Gerber P 1997. Training and remote monitoring of cardiovascular parameters in non-human primates. Primate Report 49, 61-70
Full Text:

Segerson L, Laule GE 1995. Initiating a training program with gorillas at the North Carolina Zoological Park. American Zoo and Aquarium Association (AZA) Annual Conference Proceedings, 488-489

Shideler SE, Savage A, Ortuño AM, Moorman EA, Lasley BL 1994. Monitoring female reproductive function by measurement of fecal estrogen and progesterone metabolites in the white-faced saki (Pithecia pithecia). American Journal of Primatology 32, 95-108

Shively CA 2001 Psychological Well-Being of Laboratory Primates at Oregon Regional Primate Research Center. Willamette Week, Portland, OR, March 21, 2001
Full Text:

Smith A, Lindburg DG, Vehrencamp S 1989. Effect of food preparation on feeding behavior of lion-tailed macaques. Zoo Biology 8, 57-65

Smith CC, Ansevin A 1957. Blood pressure of the normal rhesus monkey. Proceedings of the Society for Experimental Biology and Medicine 96, 428-432

Spragg SDS 1940. Morphine addiction in chimpanzees. Comparative Psychology Monographs 15, 1-132

Sokol KA 1993. Commentary: Thinking like a monkey –– "primatomorphizing" an environmental enrichment program. Lab Animal 22(5), 40-45

Taylor WJ, Brown DA, Lucas-Awad J, Laudenslager ML 1997. Response to temporally distributed feeding schedules in a group of bonnet macaques (Macaca radiata). Laboratory Primate Newsletter 36(3), 1-3
Full Text:

Turkkan JS 1990. New methodology for measuring blood pressure in awake baboons with use of behavioral training techniques. Journal of Medical Primatology 19, 455-466
Full Text:

Turkkan JS, Ator NA, Brady JV, Craven KA 1989 Beyond chronic catheterization in laboratory primates. In Housing, Care and Psychological Wellbeing of Captive and Laboratory Primates Segal EF (ed), 305-322. Noyes Publications, Park Ridge, NJ

United States Department of Agriculture 2000 Animal Welfare Report –– Fiscal Year 2000. U.S. Department of Agriculture –– Animal Care, Riverdale, MD
Full Text:

United States Department of Agriculture 1991. Title 9, CFR (Code of Federal Register), Part 3. Animal Welfare; Standards; Final Rule. Federal Register 56(No. 32), 6426-6505
Full Text:

de Waal FBM 1992 A social life for chimpanzees in captivity. In Chimpanzee Conservation and Public Health: Environments for the Future Erwin J, Landon JC (eds), 83-87. Diagnon/Bioqual, Rockville, MD

van Wagenen G 1950 The monkeys. In The Care and Breeding of Laboratory Animals Farris EJ (ed), 1-42. John Wiley, New York, NY

Wakenshaw V 1999. The management and husbandry of Geoffroy's marmoset. International Zoo News 46(1), 3-15
Full Text:

Watson DSB 1991. A built-in perch for primate squeeze cages. Laboratory Animal Science 41, 378-379

Weick BG, Perkins SE, Burnett DE, Rice TR, Staley EC 1991. Environmental enrichment objects and singly housed rhesus monkeys: Individual preferences and the restoration of novelty. Contemporary Topics in Laboratory Animal Science 30(5), 18

White G, Hill W, Speigel G, Valentine B, Weigant J, Wallis J 2000. Conversion of canine runs to group social housing for juvenile baboons. AALAS [American Association for Laboratory Animal Science] 51st National Meeting Official Program, 126

Williams LE, Abee CR, Barnes SR, Ricker RB 1988. Cage design and configuration for an arboreal species of primate. Laboratory Animal Science 38, 289-291

Wolfle TL 1987. Control of stress using non-drug approaches. Journal of the American Veterinary Medical Association 191, 1219-1221

Ziegler TE, Bridson WE, Snowdon CT, Eman S 1987. Urinary gonadotropin and estrogen excretion during the postpartum estrus, conception, and pregnancy in the cotton-top tamarin (Saguinus oedipus oedipus). American Journal of Primatology 12, 127-140

Viktor Reinhardt is Laboratory Animal Advisor to the Animal Welfare Institute in Washington, DC. He is a clinical veterinarian and ethologist and did extensive research in reproductive physiology, animal husbandry and ethology in cattle, muskox and bison.

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