macaques submerge potatoes and grains in water to remove dirt (Itani and Nishimura, 1973), and several macaque species dive and swim to retrieve food (Malik and Southwick, 1988; Suzuki, 1965).
Leafy vegetables, browse, and higher-fiber commercial extrusions have been used to provide environmental enhancement and may be important for physiologic reasons in highly folivorous species, such as howlers and the Colobinae. Lemurs and great apes also can benefit from appropriate sources and amounts of high-fiber foods (Gould and Bres, 1986; Edwards, 1995; Popovich et al., 1997). These foods tend to increase the time spent in feeding, can reduce aberrant behavior, favor the production of formed rather than liquid stools, and are useful in the control of obesity. The National Zoological Park in Washington, DC, has a list of East Coast browse species that were judged to be safe for primate feeding. They include alder, amaranths, arborvitae, aspen, bamboo, beech, birch, blackberry, bush honeysuckle, butterfly bush, cattails, chicory, clover, comfrey, cottoneaster, cottonwood, daylily, dogwood, elaeagnus, elm, fig, forsythia, grasses, greenbriers, hackberry, hawthorn, hazelnut, hibiscus, Japanese silver grass, kerria, kudzu, linden, maple (except red maple), mock orange, mulberry, nasturtium, Oregon grape holly, pear, pickerel-weed, poplar (except tulip poplar), purslane, raspberry, redbud, rose, snowberry, violets, water hyacinth, and willow (Gross, 1990; Shumaker, 1995; McClung, 1999). Browse species that have been listed in peer-reviewed publications may be found in Chapter 10.
Studies at the Duke University Primate Center demonstrated that several local plants could be substituted for mango leaves in captive sifaka diets. Plant-species preferences were exhibited by both lemurs and sifakas, and there were seasonal preferences for particular plant parts (Pereira et al., 1989). Because some browses contain toxic chemicals or have a tendency to form indigestible phytobezoars, they must be selected and used with care (Ensley et al., 1982; Fowler, 1986; Knapka et al., 1995).
Nothing is more basic to the health and well-being of captive nonhuman primates than proper nutrition and dietary husbandry. Deficiencies or excesses of specific nutrients have been shown to produce specific signs of illness that reflect their metabolic roles (National Research Council, 1978; Machlin, 1990; Knapka et al., 1995; O’Dell and Sunde, 1997). Furthermore, there is a well-established relationship between nutritional status and susceptibility to infectious disease (Ullrey, 1993). Thus, the provision of a nutritionally balanced diet in amounts sufficient to meet daily energy and nutrient needs must not be subverted by well-intentioned but ill-advised uses of food in systems of environmental enhancement. A rational balance of the science of nutrition with knowledge of feeding behavior and of feeds appropriate to meet physiologic and psychological requirements is fundamental to the development of a successful feeding program. In turn, a successful feeding program is a vital part of animal well-being. The subject is very complex, and human perceptions of nonhuman-primate behaviors in response to changes in their environment might not be reliable guides to the perceptions of the nonhuman primates in question (Robinson, 1998). Attempts to resolve this complexity by using food in environmental enhancement must always consider physiologic, as well as psychological needs.
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