Caged Birds Scenic Birdfood

Abstract- Psittacines are often classified as seed eaters despite studies that have established great diversity in food habits in the wild. While seeds are consumed, so are flowers, buds, leaves, fruits and cambium. Some psittacines consume parts of >80 species of grasses, forbs, shrubs and trees. In addition, insects may be important. Although there are few controlled studies of the requirements of psittacines, it is probable that most nutrient needs are comparable to those of domesticated precocial birds that have been thoroughly studied. Commercial seed mixes for psittacines commonly contain corn, sunflower, safflower, pumpkin and squash seeds, wheat, peanuts, millet, oat groats and buckwheat, although other seeds may be present. Because hulls/shells comprise 18-69% of these seeds and they are removed before swallowing, a significant proportion of typical seed mixtures is waste. Some of the seeds also are very high in fat and promote obesity. Common nutrient deficiencies of decorticated seeds include lysine, calcium, available phosphorus, sodium, manganese, zinc, iron, iodine, selenium, vitamins A, D, E and K, riboflavin, pantothenic acid, available niacin, vitamin B-12 and choline. Attempts to correct these deficiencies by incorporating pellets into seed mixes are usually thwarted by rejection of the pellets and disproportionate consumption of items that are more highly favored. An extruded diet formulated to meet the projected nutrient needs of psittacines was fed with fruits and vegetables to eight species of psittacines was fed with fruits and vegetables to eight species of psittacines for the 66% observed during the previous 2 y when these psittacines were fed seeds, fruits and vegetables. Although this extruded diet was well accepted in a mixture of fruits and vegetables and met nutrient needs, analyses have shown that not all commercial formulated diets are of equal merit. J. Nutr. 121: S193-S205, 1991.

Indexing Key Words:

· symposium · birds · psittacines · seed · composition · nutrient · requirements · formulated diet · gout

Aviculturists often classify caged birds on the basis of their apparent food preferences in captivity (1). The Psittacidae comprise a family of birds with stout, hooked bills commonly called seed eaters despite field studies (2-5) establishing great diversity in food habits in the wild. Psittacines are widespread in tropical and south temperate areas of the world, with major populations in the neotropics and Australia. These regions vary widely in rainfall and temperature and in the food plants that the environment will support (6). Since indigenous psittacines coevolved with their food supply, their food choices in an undegraded habitat represent a nutritional wisdom built on generations of experience. However, studies of caged psittacines suggest that the nutritional wisdom of wild birds does not transfer to captive birds offered cultivated seeds as their principal food. In fact, specific instances of failed dietary husbandry based on seed mixtures have led to this review of natural dietary habits of certain psittacines, the nutritional limitations of seeds and the development of diets formulated to be nutritionally complete.

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FOOD SELECTION BY CERTAIN WILD PSITTACINES

Biologists with significant field experience will testify how difficult it is to gather quantitative food intake data on free-living birds. Even qualitative information is difficult to gather. Nevertheless, the following reports illustrate the diversity of food choices in the wild and the opportunity such diversity provides for meeting nutrient needs.
Cannon (4), in a study of the diets of Eastern (Platycercus eximius) and Pale-headed (P. adscitus) Rosellas in Queensland, Australia, spent over 200 h in each of two study areas observing food consumption by these two species throughout the year. Both study areas had been modified from their primitive state by agricultural practices, including cultivation of alfalfa (Medicago sativa), milo or grain sorghum (Sorghum bicolor) and oats (Avena sativa). Some regions were pastured, and seeds in dung were consumed. Food plants used by Eastern and Pale-headed Rosellas included grasses, forbs, shrubs and trees, and these psittacines fed on 82 and 47 plant species, respectively. Both rosellas fed mainly on fruits and seeds and to a lesser extent on flowers. In addition, significant intakes of insects were noted, particularly during July when coccids and psyllids attached to Eucalyptus leaves constituted nearly 50% of the diet of the Eastern Rosella.
Saunders (2) studied the food habits of the short-billed form of the White-tailed Black Cockatoo (Calyptorhynchus funereus) in two areas of Western Australia. The clearing of woodlands had degraded the habitat to some extent, and in one study area, parent birds were forced to forage over long distances to find adequate food for their nestlings. Because this effort was only partly successful, growth rates of the young, fledging weights and breeding success were lower than in the area where large amounts of native vegetation were available close to nest sites. A total of 30 plant species was exploited in the two nesting areas, with flowers and seeds being the main parts eaten. Some plant species were parasitized by insects whose larvae developed in the flowers or stems. Larvae from the families Cerambycidae and Pyralidae were identified in the crops of nestlings in sufficient numbers to suggest deliberate collection. The nonbreeding season was characterized by some change in food plants, partly as a consequence of seasonal environmental change and partly due to migration to areas of improved food availability. The two populations o cockatoos fed on a total of over 30 species of plants during the nonbreeding season. The seeds of pine species were particularly important to one population. Insect larvae were also consumed.
Wyndham (3) studied the food habits of the budgerigar (Melopsittacus undulatus) in inland mideastem Australia. This region is characterized by open or lightly timbered plains and a few remnant mountain ranges. It is semiarid to arid, east to west, and rain falls primarily in the summer in the north and in the winter in the south. Seeds from 21 to 39 species of ground plants were eaten depending upon area. No plant food from upper vegetational strata and no insects were identified in crop con- tents. The seeds eaten had a mean length from 0.5 (Eragrostis spp.) to 2.5 mm (Astrebla squarrosa). Most seeds were intermediate in this range and weighed (with husk) from 0.36 to 1.33 mg. The seeds were normally husked before being swallowed. Diet choices appeared to be governed largely by availability.
Snyder et al. (5), in a broad study of the biology of the Bahama Parrot (Amazona leucocephala bahamensis), presented some observations on its food habits. This species was first cited as endangered in 1966 (7). A small population lives on the low limestone island of Abaco, the second largest of the Bahamian Islands. A second population lives on the island of Great Inagua. Abaco's climate is subtropical with an average rainfall of 154 cm. Monthly temperature means range from 21 to 27 degrees celsius. The geology of Great Inagna is similar to that of Abaco, but it is much drier, with a mean annual rainfall of 70 cm. Monthly mean temperatures range from 24 to 29 degrees celsius. Bahama Parrots were observed feeding on 16 plant species. They were catholic in their tastes and ate the inner portions of green, unopened Pinus caribaea cones, stems of woe vine (Cassytha filiformis), fruits of wild dilly (Manilkara bahamensis), cinnecord (Acacia choriophylla), poisonwood (Metopium toxiferum) and naked wood (Myrcianthes fragrans), and the fruit and inner bark (cambium) of Caribbean pine. They also fed on the fruit or seeds of wild tamarind (Lysiloma latisiliquum), jumbay (Leucaena leucocephala), sea grape (Coccoloba uvifera), buttonwood (Conocarpus erectus), buffalo top palm (Thrinax morrisii), silver top palm (Coccothrinax argentata), Tabebuia bahamensis, Bursera simaruba, Swietenia mahagoni and Sabal palmetto.
It is apparent that, except for millet (Panicum milioides), which may be eaten by wild budgerigars in agricultural areas, most seeds found in mixtures sold for caged psittacines are foreign to the experience of their free-living relatives. Since this is true, it is appropriate to compare the nutrient composition of these cultured seeds with the nutrient requirements of the birds to which they are fed. By this means one can identify potential deficiency problems and develop a strategy to correct them.

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NUTRIENT COMPOSITION OF SEEDS

Commercial seed mixtures for psittacines commonly contain corn, sunflower, safflower, pumpkin and squash seeds, wheat, peanuts, millet, oat groats and buckwheat. Other seeds that may be present include milo, rice, niger, hemp, canary grass, rape, flax, sesame, anise, fennel, lettuce, false flax, poppy, pea, caraway and teazle. Some psittacines are also fed Brazilnuts, English walnuts, cashew nuts, hazelnuts, almonds, macadamia nuts, pistachio nuts, beechnuts, pinyon nuts and pecans. The common and scientific names of these seeds are presented in Table 3 . The proportions of seeds in five commercial products sold in the United States are shown in Table 4 .
Those seeds that have a separable hull/shell are decorticated (husked) by many psittacines before swallowing. Proportions of hull/shell and kernel that have been determined gravimetrically are presented in Table 5 . Because hulls/shells comprise 18 to 69% of these seeds, a very significant proportion of typical seed mixtures offered to psittacines is waste. In addition, as can be seen in Table 6 , nutrient analyses of whole seeds can present a distorted view of the nutrients provided by the seed after the hull/shell has been removed. The impact of decortication by psittacines upon nutrients actually entering the digestive compartments of the gastrointestinal system has been determined for products P and T in Table 4. Analyses of product P for protein (dry basis) as sold and after decortication give concentrations of 14 and 18%, respectively. Like analyses of product T give respective protein concentrations of 17 and 23%. These comparisons assume that the ingredients will be consumed in the proportions in which they are presented. This is unlikely, however, since most birds favor certain items and partly or totally reject others. Thus, nutrient intakes from self-selected diets based on mixtures of seeds are highiy unpredictable.
The nutritional weaknesses of seeds are apparent when the nutrient concentrations in Table 7 are compared with the nutrient requirements of precocial birds in Tables 1 and 2.
Only three seeds (peanuts, pumpkin/squash and sunflower) appear to provide enough protein to meet the needs for growth. Of these, peanuts are deficient in sulfur amino acids (methionine plus cystine) and marginal in threonine when amino acid concentrations are expressed as a percent of protein concentration and are compared with like expressions of need. Peanuts, pumpkin/squash and sunflower seeds also are very high in fat and metabolizable energy (ME) (24.27-25.52 kJ/g of dry matter). Thus, protein and amino acid concentrations of these seeds, expressed per unit of ME, are lower than protein and amino acid requirements that are given by the NRC (8) for diets that typically supply 12.97-15.06 kJ ME/g of dry matter. In addition, the high fat level in these seeds leads to obesity, which is a significant problem in some psittacines (17).
Other nutrient deficiencies for growth in most of the seeds in Table 7 include calcium, available phosphorus, sodium, manganese, zinc, iron, vitamins A, D and K, riboflavin, pantothenic acid, available niacin (18), vitamin B-12 and choline. With respect to seeds in which alpha-tocopherol concentrations have been determined, vitamin E activity may be marginal to deficient because other evidence (19) suggests that requirements for support of normal vitamin E stores in birds and prevention of hepatic microsomal peroxidation are greater than the requirements given by the NRC (8). In addition, the high concentrations of unsaturated fatty acids in peanuts, pumpkin/squash, safflower and sunflower seeds lead to increased vitamin E requirements (20). Iodine and selenium concentrations vary with the region in which the seeds are grown. Three samples of safflower seed (including hull) that were analyzed in the Michigan State University Comparative Nutrition Laboratory had selenium concentrations ranging from 0.11 to 1.76 mg/kg dry matter. Selenium concentrations in corn have been shown to range from 0.01 to 2.03 mg/kg (21).
The inadequacies of these seeds for growth apply generally for reproduction and, to a lesser extent, for maintenance of adults. While most nutrient requirements decline as a percentage of dietary dry matter for reproduction as compared with early growth, certain seeds are still deficient in essential amino acids, and most or all are marginal to deficient in calcium, available phosphorus, sodium, manganese, zinc, iron, iodine, selenium, vitamins A, D, E and K, riboflavin, pantothenic acid, available niacin, vitamin B-12 and choline. Calcium requirements for egg production by psittacines are not likely to be nearly as high as they are for domestic poultry. The latter species have been selected for high egg production, and Leghorn-type chickens regularly produce >=260 eggs per year. While psittacines may produce several clutches of eggs per year in captivity, and the mineral in egg shells is principally calcium carbonate; the extra demands of intermittent egg production appear to be met by calcium withdrawn from skeletal reserves as long as dietary calcium concentrations are sufficient to fill those reserves during nonlaying periods. The calcium concentrations of the seeds in Table 7 are not adequate for this purpose, but field experience with formulated diets suggests that ~1% calcium in dietary dry matter is sufficient for reproduction in psittacines.
Assuming that a cultivated seed mixture could be assembled that would meet nutrient needs if completely consumed, it is difficult to prevent preferential self-selection of favored but nutritionally unbalanced foods. The radiograph shown in Figure 1 was taken of a rachitic, 8-wk-old Timneh African Gray Parrot (Psittacus erithacus timneh) that was fed principally corn from a seed mix by its parents.

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FORMULATED DIETS

The use of seed mixtures as food for captive psittacines has a long-abandoned historical precedent in the poultry industry. When the nutrient requirements of domestic birds were identified, it was soon established that growth, reproduction and long-term health were much improved by feeding complete formulated diets. Thus, seed mixtures were replaced by mash, pellets or crumbles that met specific needs for energy, amino acids, essential fatty acids, minerals and vitamins. Hatchability, chick viability, normal feathering and resistance to disease increased dramatically.
Attempts have been made to correct the limitations of seeds by coating them with vitamin and mineral suspensions or solutions, or by including a pelleted supplement in the mix, as has been done in products Q, R, S and T in Table 4. Supplement coatings are largely lost when the hulls are removed as the seeds are eaten. Powdered supplements commonly separate from the food that is eaten and are not consumed. In addition, commercially available supplements are not generally interchangeable because they vary greatly in composition. Thus, if they were to be consumed, nutrient deficiencies might still be evident, or nutrient excesses or imbalances may result. Supplement pellets frequently are not eaten, and their effectiveness suffers from disproportionate consumption of items in the seed mix that are more favored but are poorer sources of nutrients.
The sensory systems used by birds in the selection of food have been studied only to a limited extent. Some birds respond to visual or olfactory cues. Some apparently can taste sugars in food or water. Many birds, including psittacines, also have a tactile bill-tip organ (Figure 2) that assists them in the identification, selection and manipulation of food (22). It is probable that size, shape and texture are important in the food choices that psittacines make.
Although many birds can be trained to accept pellets as the sole diet, a properly designed extrusion more nearly mimics the physical characteristics of preferred food items. Even so, when an extruded diet was offered with seeds, fruits and vegetables to three adult Timneh Arican Gray Parrots, seed consumption predominated, as shown in Table 8 . The parrots were individually housed and were offered weighed amounts of each food item each day for 9 wk. Sufficient quantities were provided so that small amounts of each item were left uneaten. One day per week, the uneaten food was sorted, dried and reweighed. After conversion of the amount of food offered to a dry basis, consumption of each item was calculated from the difference between dry matter offered and dry matter remaining. While consumption of the extrusion varied appreciably, even the highest intakes (22% of dietary dry matter) did not correct the nutrient deficiencies of the seeds that were so highly favored. When nutrient concentrations were estimated for the average intakes shown in Table 8, the diet was marginal or deficient in methionine, calcium, available phosphorus, sodium, manganese, zinc, riboflavin, vitamin B- 12, available niacin, pantothenic acid, vitamin A and vitamin D.
Because it was apparent that offering an extrusion in a mixture with seeds was not an effective way of meeting nutrient needs, the seeds were gradually withdrawn (over 2-3 d) from food offered to the following five species of psittacines: Green-winged Macaws (Ara chloroptera), Yellow-headed Amazons (Amazona ochrocephala oratrix), Citron-crested Cockatoos (Cacatua sulphurea citrinocristata), Amboina King Parrots (Alisterus amboinensis) and Northern Rosellas (Platycercus adscitus). One pair (male and female) of each species was housed together and,after a week of feeding a seed-free diet, daily consumption of each food item was determined for 7 d (Table 9) .
Consumption of the extrusion was much less variable than when it was offered with seeds, and average intake was slightly >80% of dietary dry matter. When this system of dietary husbandry was used, consumption of the other items in the diet did not produce a nutritional imbalance. This was true even though fruit and vegetables comprised nearly 60% of the total dietary fresh weight. The explanation, of course, relates to their high water content and to the fact that they, as well as the extrusion, were good sources of many nutrients. As a consequence, nutrient requirements were met in every instance and dietary fat concentrations were not excessive.
In a broader test of the suitability of this dietary strategy, a comparison was made of the fledging percentage of parent-raised chicks of eight psittacine species whose parents had been fed seeds, fruits and vegetables for 2 y and then were fed an extrusion, fruit and vegetables, but no seeds, for 1 y (Table 10) The numbers of chicks hatched per year were not significantly different (P> 0.05), but fledging percentage was greatly improved (P <0.01) by the substitution of an extrusion for seeds (90 vs. 66%).
The nutrient specifications for this extrusion are presented in Table 11 . It may be fed as the sole diet or mixed with fruits and vegetables, as long as it constitutes >=40% of the weight of the diet as fed (wet basis). When calculated on a dry basis, the extrusion should constitute >=80% of the diet.
The process of extrusion induces certain physical and chemical changes in the diet that are advantageous (23). The high temperatures destroy microorganisms with pathogenic potential and depolymerize starches that may otherwise be difficult for young birds to digest. By adjustment of the conditions of manufacture, extruded particles of various shape, size and physical texture can be produced.
Questions have been raised in the lay literature concerning the appropriate amount of dietary protein for psittacines, and some have suggested that a protein percentage in the low to mid 20s may be harmful. The implication is that these levels of protein overwork the liver and kidneys and may cause gout. It is apparent from the earlier discussion that psittacines can be expected to have a typical dietary requirement for protein, and this protein must be well balanced, i.e., it must contain the correct proportions of 10 or more essential amino acids if the birds eating the diet are to be healthy and productive. The data already presented suggest that protein requirements for growth of domestic precocial birds and cockatiels are >=20% of dietary dry matter. This number assumes high protein digestibility and a near-perfect mix of essential amino acids. Earle and Clarke (24) found that the apparent digestibility of protein in white and red millet and in canary grass seed by budgerigars ranged from 72 to 91%. These and other cultivated seeds are generally limiting in lysine and/or methionine. Protein and amino acid requirements of adult precocial birds tend to be lower than the requirements for growth, but of course, adult precocial birds do not feed their young as do adult psittacines. Whether handfed or parent-fed, the nutrient needs of young altricial birds are presumably the same. Thus, breeding adult psittacines that are raising their young require diets that are adequate to support growth.
Undoubtedly, adult psittacines that are not in a breeding colony or from whom young birds have been removed for hand rearing have lower dietary protein and amino acid requirements. However, the minirnum requirements for maintenance of adult psittacines have not been determined. Unfortunately, the adult pet nonbreeding bird is most likely to be fed items that are not nutritionally complete. If appropriately compounded formulated diets are diluted with treats, the nutritional strengths of the formulated diet will help compensate for the nutritional weaknesses of the treats. On the other hand, if formulated diets contain only the minimum maintenance requirements, nutritionally imbalanced treats cannot be regularly fed without endangering health.
What if an adult nonbreeding psittacine is fed only a nutritionally balanced diet, such as the extrusion in Table 11, without dilution with other foods? Will its liver and kidneys be overworked and will it get gout? Birds are uricotelic, and uric acid is the principal end product of nitrogen metabolism (25). It is produced in the liver and kidney and is excreted via renal tubular secretion and to some extent via glomerular filtration.The nitrogen in uric acid may come from the diet or from the catabolism of body tissues. Dietary protein in excess of need, poor quality dietary protein (even at low dietary protein concentrations) or low food intake (resulting in tissue catabolism for energy) will increase uric acid excretion in the urine. However, no one has been able to induce primary liver or kidney damage in normal birds by feeding a nutritionally complete diet containing high levels of well-balanced protein. Hasholt and Petrak (26) have described gout in cage birds and note that this is a metabolic disease of obscure etiology. Uric acid and urates are deposited in various tissues instead of being excreted by the kidneys. Studies in some strains of chickens suggest that hyperuricemia and gout may result from genetic impairment of the renal tubular secretory mechanism for uric acid and the site of the defect is the peritubular membrane (27).
Peterson et al. (28) found that susceptibility to articular gout in a selected line of chickens was transmitted as a recessive genetic trait. However, gout was apparent only in susceptible chickens fed an 80% protein diet and was not seen when these chickens were fed 20% protein. In normal chickens, gout was not seen when they were fed either a 20 or 80% protein diet.
Featherston and Scholz (29) and Austic and Cole (30) found that the normal chicken could excrete dietary nitrogen in excess of need, even when dietary protein concentrations were three times the requirement. Plasma uric acid levels did rise, although nowhere near as drastically as they did after >=72 h of fasting (31). The feeding of dietary protein concentrations of 20, 40 and 60% resulted in plasma uric acid concentrations of 480,1130 and 1070 µmol/L (8, 19 and 18 mg/dL), respectively (30). When a 20% protein diet was withheld for 72 h, plasma uric acid rose to µ4160 ~mol/L (70 mg/dL), or ~10 times the initial levels (31). Further fasting (10 d) ultimately produced plasma uric acid concentrations of ~14,870 µmol/L (250 mg/dL). One hour after refeeding the diet, plasma uric acid fell to 830 µmol/L (14 mg/dL) and by 6 h had returned to the base level. Presumably, factors that would limit food intake, such as water deprivation, subordinate social position, infections or specific nutrient deficiencies might produce a similar effect. Even the time of blood sampling in relation to the time of feeding has been shown to alter plasma uric acid concentrations 2- to 3-fold (31).
With respect to nutrient deficiencies, Miles and Featherston (32) found that plasma uric acid concentrations were elevated to 1490 µmol/L (25 mg/dL) when growing chickens were fed 0.6% dietary lysine but fell to ~710 µmol/L (12 mg/dL) as dietary lysine concentrations were raised to the requirement. This increase in plasma uric acid associated with lysine deficiency was a result of catabolism of the other amino acids that could not be used for synthesis of tissue proteins. Such a response is typical of that seen when lysine-deficient seeds comprise most of the diet. If the diet is also deficient in vitamin A, as a seed diet is likely to be, there may be sufficient renal damage to interfere with uric acid elimination, causing an elevation in blood uric acid concentration and resulting in urate deposits in the kidneys and ureters (33). A number of drugs also have been shown to influence uric acid excretion (34, 35). It is apparent, then, that gout in birds is a multifactorial disease. A diet that is deficient in protein, specific amino acids or vitamin A is potentially much more damaging than a properly formulated diet that may provide somewhat more protein than needed for maintenance. Despite the advantages of a well-formulated diet for psittacines, there are large deviations between the nutrient concentrations of a number of commercial products, advertised as nutritionally complete, and the probable nutrient requirements of birds to which they may be fed. When 11 diets from eight manufacturers were analyzed,both nutrient deficiencies and excesses were revealed (36). Of 18 analytical values for each product, the following nutrients and their indicated concentration ranges (dry basis) were particularly disturbing: (in g/kg) crude protein, 150-310; calcium, 1.8-15.4; phosphorus, 2.9-10.6; calcium/phosphorus ratio,0.62-1.97; sodium, 0.3-4.1; (in mg/kg) iron, 80-4200; copper, 8-132; zinc, 31-939; manganese, 15-1055. These ranges include values that are low enough to produce clinical signs of ill health. Notable are the low values for calcium, phosphorus, sodium, zinc and manganese. High values that may lead to clinical signs of toxicity include those for iron, copper, zinc and manganese. An inverse calcium/phosphorus ratio would impact adversely on the metabolism of these two elements. Some of the other extreme values may not produce specific clinical signs but may impair growth and reproduction. Since analyses for amino acids and vitamins were not performed, it is possible that a number of additional nutrients may have been present in deficient or excessive (37) amounts. Thus, it is important that the nutrient specifications of commercial formulated diets be carefully reviewed (and confirmed) before they are used.

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¹ Presented as part of the Waitham International Symposium on Nutrition of Small Companion Animals, at University of California, Davis, CA 95616, on September 4-8,1990. Guest editors for the symposium were James G. Morris, D'Ann C. Finley and Quinton R. Rogers. ² Journal paper from the Michigan Agricultural Experimental Station, East Lansing, MI 48824. ³ To whom correspondence should be addressed: Department of Animal Science, Michigan State University, 205 Anthony Hall, East Lansing, MI 48824. ⁴Present address: Allen and Baer Associates, 5320 Olney-Laytonsville Road, Olney, MD 20832. ⁵ Present address: Energy and Protein Laboratory, Beltsville Human Nutrition Research Center, United States Department of Agriculture, Beltsville, MD 20705.

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ACKNOWLEDGMENTS

Technical assistance was provided by P. K. Ku and S. R. DeBar of Michigan State University and by W. Schulenburg of the Zoological Society of San Diego.

LITERATURE CITED
1. VRIENDS, M. M. (1984) Simon and Schuster's Guide to Pet Birds. Simon and Schuster, New York, NY.
2. SAUNDERS, D. A. (1980) Food and movements of the short-billed form of the White-tailed Black Cockatoo. Aust. Wildl. Res. 7: 257-269.
3. WYNDHAM, E. (1980) Environment and food of the budgerigar Me1opsittacus udulatus. Aust. J. Ecol. 5: 47-61.
4. CANNON, C. E. (1981) The diet of Eastern and Pale-headed Rosellas. Emu 81:101-110.
5. SNYDER, N. F. R., KING, W. B. & KEPLER, C. B. (1982) Biology and conservation of the Bahama Parrot. Living Bird 19: 91-114.

6. ESPENSHADE, E. B.,JR. ed. (1990) Goode's World Atlas, 18th ed., Rand McNally, Chicago, IL.
7. VINCENT, J. (1966) Red Data Book, vol. 2, Aves. Int. Union Conserv. Nat. Resources, Morges, Switzerland.
8. NATIONAL RESEARCH COUNCIL (1984) Nutrient Requirements of Poultry, 8th rev. ed., National Academy Press, Washington, DC.
9. ROUDYBUSH, T. E. & GRAU, C. R. (1986) Food and water interrelations and the protein requirement for growth of an altricial bird, the cockateil (Nymphicus hollandicus). J. Nutr. 116: 552- 559.
10. GRAU, C. R. & ROUDYBUSH, T. E. (1986) Lysine requirement of cockatiel chicks. Am. Fed. Avicult. Res. Report Dec.-Jan., pp. 12-14.
11. HANSON, J. T. (1990) Weight gains and food intakes in hand-raised large parrot chicks, 1984-1986. Proc. Ann. Conf. Assoc. Avian Vet., Phoenix, Az, pp. 75-82.
12. MCCARTHY, M. A. & MATTHEWS, R. H. (1984) Composition of Foods: Nut and Seed Products, Agric. Handbook No. 8-12. Human Nutr. Info. Serv., U.S. Dept. of Agric., Washington, DC.
13. MCDANIEL, L. (1990) Proximate Analysis of Common Cage Bird Seeds and Applications to the Diet. M.S. Thesis. University of California, Davis, CA.
14. JONES, D. B. (1941) Factors for Converting Percentages of Nitrogen in Foods and Feeds into Percentages of Proteins, U.S. Dept. Agric. Circ. No.183, U.S. Dept. Agric., Washington, DC.
15. NATIONAL RESEARCH COUNCIL (1988) Nutrient Requirements of Swine, 9th rev. ed., National Academy Press, Washington, DC.
16. YOUNG, L. G., LUN, A., P0S, J., FORSHAW, R. P. & EDMEADES, D. E. (1975) Vitamin E stability in corn and mixed feeds. J. Anim. Sci. 40: 495-499.
17. MCDONALD, S. E. (1990) Anatomical and physiological characteristics of birds and how they differ from mammals. Proc. Ann. Conf. Assoc. Avian. Vet., Phoenix, AZ, pp. 372-389.
18. GHOSH, H.P., SARKAR, P. K. & GUHA, B. C. (1963) Distribution of bound form of nicotinic acid in natural materials. J. Nutr. 79: 451-453.
19. COMBS, G. F., JR. & SCOTT, M. L. (1974) Dietary requirements for vitamin E and selenium measured at the cellular level in the chick. J. Nutr. 104:1292-1296.
20. GRIFFITHS, T. W. (1961) Studies on the requirement of the young chick for vitamin E. 2. The effects of different sources and levels of dietary lipids on live-weight gain and body vitamin E storage. Br. J. Nutr. 15: 271-279
21. ULLREY, D. E. (1974) The selenium-deficiency problem in animal agriculture. In: Trace Element Metabolism in Animals-2 (Hoekstra, W. G., Suttie, J. W., Ganther, H. E. & Mertz, W., eds.), pp. 275-293, University Park Press, Baltimore, MD.
22. GOTTSCHALDT, K.-M. (1985) Structure and function of avian somatosensory receptors. In: Form and Function in Birds (King, A. S. & McLelland, J., eds.), vol. 3, pp. 375-496, Academic Press, New York, NY.
23. CAMIRE, M. E., CAMIRE, A. & KRUMHAR, K. (1990) Chemical and nutritional changes in foods during extrusion. Crit. Rev. Food Sci. Nutr. 29: 35-57.
24. EARLE, K. E. & CLARK, N. R. (1991) The nutrition of the budgerigar (Melopsittacus undulatus). J. Nutr. (in press).
25. O'DELL, B. L., WOODS, W. D., LAERDAL, O. A., JEFFAY, A. M. & SAVAGE, J. E. (1960) Distribution of the major nitrogenous compounds and amino acids in chicken urine. Poult. Sci. 39: 426-432.
26. HASHOLT, J. & PETRAK, M. L. (1982) Gout. In: Diseases of Cage and Aviary Birds (Petrak, M. L., ed.), pp. 639-645, Lea and Febiger, Philadelphia, PA.
27. ZMUDA, M.-J. & QUEBBEMANN, A. J. (1975) Localization of renal tubular uric acid transport defect in gouty chickens. Am. J. Physiol. 229: 820-825.
28. PETERSON, D. W., HAMILTON, W. H. & LILYBLADE, A. L. (1971) Hereditary susceptibility to dietary induction of gout in selected lines of chickens. J. Nutr. 101: 347-354.
29. FEATHERSTON, W. R. & SCHOLZ, R. W. (1968) Changes in liver xanthine dehydrogenase and uric acid excretion in chicks during adaptation to a high protein diet. J. Nutr. 95: 393-398.
30. AUSTIC, R. E. & COLE, R. K. (1972) Impaired renal clearance of uric acid in chickens having hyperuricemia and articular gout. Am. J. Physiol. 223: 525-530.
31. OKUMURA, J.-I. & TASAKI, I. (1969) Effect of fasting, refeeding and dietary protein level on uric acid and ammonia content of blood, liver and kidney in chickens. J. Nutr. 97: 316-320.
32. MILES, R. D. & FEATHERSTON, W. R. (1974) Uric acid excretion as an indicator of the amino acid requirement of chicks. Proc. Soc. Exp. Biol. Med. 145: 686-689.
33. ELVEHJEM, C. A. & NEU, V. F. (1932) Studies in vitamin A avltaminosis in the chick. J. Biol. Chem. 97: 71-82.
34. BERGER, L., Yu, T. F. & GUTMAN, A. B. (1960) Effect of drugs that alter uric acid excretion in man on uric acid clearance in the chicken. Am. J. Physiol. 198: 575-580.
35. SHIDEMAN, J. R., ZMUDA, M. J. & QUEBBEMANN, A. J. (1981) The acute effects of furosemide, ethacrynic acid and chiorothiazide on the renal tubular handling of uric acid in chickens. J. Pharmacol. Exp. Ther. 216: 441-446.
36. NATIONAL RESEARCH COUNCIL (1980) Mineral Tolerance of Domestic Animals. National Academy Press, Washington, DC.
37. NATIONAL RESEARCH COUNCIL (1986) Vitamin Tolerance of Animals. National Academy Press, Washington, DC.

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