1993a; Rumbaugh and others 1989), including ice cubes with or without flavoring (Fritz and Howell 1993b).
When social grouping is not possible, attention must be given to the needs of the singly housed animal. These needs change with age, health, and experience. Immature chimpanzees respond positively to the opportunities to play or be groomed by a familiar human (Fritz and Fritz 1985; Reisen 1971; Shefferly and others 1993), and can prefer social interaction to food (Mason and others 1962, 1963). Older animals, too, benefit greatly by interactions with known caregivers (Baker 1997; Fritz and Howell 1993a; Laule and others 1992, 1996). Dogs also provide infant chimps with a playmate (Black 1992; Thompson and others 1991). Even when single housing is required, such as for biocontainment, much can be done to enrich the environment (Brent and others 1989; Fritz and others 1997; Lambeth and Bloomsmith 1992; Nadler and others 1992). These and many other enrichment options discussed throughout this report demonstrate relatively simple strategies to enrich the lives of these animals. Not the least of these approaches is positive human interaction (Fritz and Howell 1993a; Mason 1965). See also NRC (1997b) and the chapter in the Universities Federation for Animal Welfare handbook (Fritz and others in press) for additional discussion of chimpanzee biology, behavior, housing, and enrichments.
Apes in the wild have a diverse diet that is based on fruits and selected leaves and stems but can also include roots, bark, nuts, insects, bird eggs, and small mammals (Goodall 1963, 1986; Napier and Napier 1985). The natural diet of gorillas includes a greater percentage of fibrous plants than commonly eaten by other apes. In captivity, if necessary, apes can be maintained on a commercial diet specifically prepared for primates; however, they seem to relish a more varied diet that includes fruits, vegetables, and treats. If apes are fed only natural foods, a wide variety of items to ensure adequate protein intake, as well as vitamin and mineral supplements, should be provided. The nutritional management of nursery-reared infant chimpanzees have been reviewed by Fritz and others (1985).
Foods may be presented in clean feeders, cut into small pieces and widely scattered, or left whole and unpeeled to extend feeding time (Bloomsmith 1989). Also, spreading selected treats, such as nuts and grains, in bedding or grass will give apes an opportunity to forage. If apes are housed in social groups, it is necessary to provide enough food so that the most timid animal in the group can get its full allotment, or positive reinforcement training can be used to overcome severe competition at mealtime (Bloomsmith and others 1994). For enrichment, such food items as honey, mustard, peanut butter, raisins, and nuts can be placed in puzzle or foraging devices (Maki and others 1988, 1989). Some moderation should be practiced in the use of high-calorie treats.