foraging under natural conditions accounts for a substantial portion of the diurnal activity budget (Herbers 1981; Malik and Southwick 1988; Marriott 1988; Milton 1980; Strier 1987). Several foraging devices are available commercially, and many are individually designed and constructed ''in house"; these products offer a substantial range of price, ease of integration into husbandry procedures, sanitizability, and durability. Food can also be dropped into a substrate that partially obscures it from view. Feeding can present an opportunity for positive interaction between animals and caregivers (Bayne and others 1993a); however, hand feeding poses a potential hazard to personnel and therefore should be used selectively.
Earlier it was stated that routine practices minimize distress because they are predictable. But novel foods and feeding routines can be used for enrichment. They should be carefully monitored to ensure that animals are not so disturbed that they fail to consume their normal dietary intake. Novel foods, such as treats, can immediately be recognized as pleasant and need not be considered a potential source of stress.
Restraint of animals for examination and treatment might be unavoidable, but most primates resist handling. Restraint should be as brief as possible and carefully tailored to the species, training, and experience of the animals. Insufficient restraint can result in injury to handlers, and undue force can result in injury to an animal. Injuries due to excessive force are of particular concern in the handling of small animals such as squirrel monkeys and marmosets.
To reduce the stress of physical or chemical restraint, many primates can be trained for routine procedures (Reinhardt 1997d). Rhesus monkeys have been trained to enter transport cages to present a limb for injection or venipuncture (Bunyak and others 1982; Heath 1989; Reinhardt 1991b, 1997a) to cooperate in the use of vascular access ports (McCully and Godwin 1992), and to present their perineum for examination and swabbing (Bunyak and others 1982). Even singly housed savanna baboons (Turkkan and others 1989), chimpanzees (Bloomsmith and others 1994; Byrd 1977; Laule and others 1992, 1996), and group-housed monkeys (Goodwin 1997; Knowles and others 1995; Phillippi-Falkenstein and Clarke 1992; Reinhardt 1990a; Williams and Bernstein 1995) have been trained to assist with clinical procedures, such as blood collection and injections, and to move into holding pens. Such training eliminates the need to anesthetize an animal for a procedure that lasts only a few seconds, reduces the time required to obtain a sample, reduces the use of pharmacological restraint agents, and, more important, gives the animal a degree of control in the situation.
Several basic principles are common to all training procedures. First, the appropriate response needs to be apparent to the subject. For example, if an animal is required to enter a compartment from the home cage, it should have