The pet bird population consists largely of psittacine species, passerines, and other avian families, such Ramphastidae, which includes toucans.
Psittacine birds eat mainly a plant-based diet and can be classified overall as florivorous (flower-eating). The content of the diet—fruit, nectar, seeds, or a combination—varies by species. Some species also ingest insects and carrion as a small part of their diet. Although requirements and dietary sensitivities vary among psittacine species, pelleted and extruded diets that have been produced for parrots have tremendously improved their nutritional intake and subsequent health and quality of life. However, pelleted diets differ in content and quality and must be evaluated individually. Extruded pellets in different shapes and sizes are available for maintenance and breeding purposes. Many pellets contain omega-3 fatty acids as well as probiotics. Some species (eg, lories and lorikeets) need specific diets containing a high water content, easily digestible carbohydrates, a mixture of proteins, and a balanced vitamin and mineral supplement.
Psittacine nutrition has been a focus of research for the past several decades. Several myths of psittacine nutrition have been debunked during this period. For example, grit, needed by some passerines and Columbiformes (pigeons and doves) to aid in mechanical digestion of seeds ingested whole, is not needed by psittacines that remove seed hulls before ingestion. Monkey chow biscuits, traditionally fed to psittacines as part of a nutritionally complete diet are actually nutritionally incomplete, and some brands tend to harbor bacteria or promote excessive gram-negative bacterial growth when included in bird diets. Strictly seed diets, regardless of supplementation, are suboptimal for psittacine species because seeds are deficient in vitamin A, protein (the amino acids lysine and methionine, in particular), calcium, and other nutrients. Conversely, excessive vitamins, such as vitamin A, which are often offered to birds consuming pelleted diets, can have equally detrimental effects. Oversupplementation of iron should also be prevented in birds that were originally seed feeders, such as grey parrots (commonly known as Congo African grey parrots) given a carnivore diet with a high amount of iron.
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Feeding a carnivorous diet should be prevented because it has been shown to cause iron storage disease in grey parrots, which are predominantly herbivorous. Regularly, "special food items," such as fruits and vegetables, are fed not only to psittacines but also to passerines. Care should be taken in what is fed, and extra items should not disturb the ingredient and nutritional balance in the diet. However, some special food items in limited quantities have shown health benefits. For example, blueberries are often provided. They are generally accepted by most birds and contain (in addition to a substantial amount of sugar) beneficial fiber, vitamin C, vitamin K, and flavonoids. Flavonoids are antioxidants that have several health benefits. Feeding fresh, not thawed, blueberries is recommended, because the active amount of flavonoids (anthocyanin) declines when berries are frozen.
Protein for Psittacines
Protein (amino acid) requirements of psittacines have not been well established. The amino acid deficiencies most consistently noted in psittacine birds on seed- and table food–based diets are lysine and methionine. Fiber content must always be considered when determining dietary protein requirements, because increased fiber can influence protein digestibility and nitrogen excretion. Birds (eg, nectar-feeding lories and lorikeets) eating low-fiber, more readily digestible diets may do well on diets with easily digestible protein at levels as low as 3–5%. Adult maintenance levels of protein recommended for budgerigars and cockatiels (7–12%) are lower than those recommended for grey and Timneh parrots (10–15%). Protein requirements for growing birds and egg-laying hens are higher than those for maintenance in all birds. Periods of heavy molt also greatly increase protein requirements, particularly the need for the sulfur-containing amino acid cysteine, because feathers are made up predominantly of protein and average 25% of the total body protein content of birds.
Excessively high dietary protein has the potential to cause renal insufficiency and gout in birds with preexisting renal impairment or a genetic predisposition to gout. Cockatiels with no preexisting renal disease have been shown to tolerate extremely high dietary protein levels (up to 70%) with no renal impairment (1). A genetic predisposition to renal disease/gout has been documented in some strains of poultry and may occur in other avian species.
Sudden, dramatic increases in dietary protein may overload the kidneys, producing hyperuricemia and visceral gout. When increased dietary protein is indicated, it should be increased gradually to avoid renal damage.
Fat for Psittacines
Dietary fat provides essential fatty acids, energy, and hormone precursors. It also contributes to egg yolk formation and aids in absorption of fat-soluble vitamins.Diets should contain 5–12% fat, depending on the species, general body condition, and physiological stage and brood condition (reproductive state). At least 1% of the dry diet should consist of polyunsaturated fat (eg, linoleic acid). Hyacinth macaws need a higher amount of dietary fat, which they can easily digest, than other psittacine birds, because hyacinth macaws' natural diet consists primarily of high-fat palm nuts. Fat can be increased by including nuts as 15% of their total daily diet. However, excessive dietary fat in all psittacine species (especially in sedentary pet birds) leads to obesity, metabolic diseases, cardiac disease, and atherosclerosis (see also Pet Birds). The fat requirements of psittacines for reproduction are generally lower than those of poultry, because psittacines’ altricial young do not require the same quantity of dietary fatty acids as do chickens' precocial young. However, diets that are borderline fat-deficient often manifest as problems in either psittacine hens during reproduction or chicks at birth.
Vitamins for Psittacines
Vitamin A is necessary for vision, reproduction, immunological integrity, and growth, and for the maintenance of epithelial cells in respiratory, GI, and renal tissues. Vitamin A deficiency has historically been noted in psittacines on all-seed diets, so supplementation is commonly recommended. However, indiscriminate supplementation can lead to vitamin A toxicosis, as well as to decreased absorption of other fat-soluble vitamins and carotenoids. In nature, psittacines do not consume vitamin A but obtain vitamin A precursors such as carotenoids from various plants. Some carotenoids in birds are precursors for the body’s formation of vitamin A. Carotenoids also act as antioxidants and are necessary in some species (eg, canaries and flamingos) for feather pigmentation. Pelleted diets should contain vitamin A at levels of 5,000–8,000 IU/kg of feed. Higher amounts should be avoided. Sources of vitamin A added to bird feed are not regulated, and quality control issues have been documented. Ideally, a quality pelleted diet for psittacines will contain multiple carotenoids and other vitamin A precursors, with a minimum level of preformed vitamin A.
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Vitamin D forms include D1, D2, and D3. D3 is the most active form and should be used. The primary function of vitamin D is to increase absorption of dietary calcium and phosphorus. Vitamin D can be obtained either directly from the diet or from UVB (285–315 nm) light exposure that transforms 7-dehydrocholesterol in skin to vitamin D3 (cholecalciferol) which is then converted to active vitamin D3 (1,25-dihydroxyvitamin D) in the liver and kidneys. How much vitamin D parrots get in nature from foraging or through UVB rays from sunlight is unknown.
Vitamin D deficiency is probably rare in nature. Birds living in polar conditions get their vitamin D during the winter by consuming diets high in vitamin D (eg, fish, plankton). In the absence of natural sunlight, the minimum oral vitamin D requirement for grey parrots is likely to be 500–1,000 IU/kg.
Vitamin D deficiency may be caused by dietary deficiency or lack of exposure to UVB radiation. Dietary deficiency occurs when an unsupplemented, unbalanced, seed-based diet is fed and when "cafeteria-style" feeding is allowed, which results in unbalanced dietary consumption. It is possible that species variation exists among psittacine species in their requirements for UVB light; however, more studies are needed. Unfortunately, many birds are housed totally indoors, and owners often mistakenly assume either that the birds do not need direct sunlight or that the sunlight the birds receive through glass will supply UVB radiation.
To ensure their pets receive adequate UVB exposure to help prevent vitamin D deficiency, pet bird owners should be encouraged to expose their birds to direct sunlight (with appropriate cautions regarding excessive heat) or to purchase and properly use UVB bulbs. However, pet bird owners must consider that the farther away from the equator, the less UVB is generated, especially in late autumn, winter, and early spring. In some bird species, UVA and/or UVB exposure may affect vitamin D synthesis, the finding of food, overall well-being, and feather colors, but again, more research is needed.
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Vitamin D toxicosis is caused by excessive dietary supplementation. Some psittacine species, notably macaws, are sensitive to excessive dietary vitamin D and may develop soft tissue calcification and renal failure. Toxic dietary vitamin D levels for psittacines have not been established, but levels of vitamin D3 that may be toxic for poultry begin at 5,000 IU/kg of feed, although some studies suggest levels up to 40,000 IU/kg may be safe (2).
For discussion of vitamin E, see Nutrition in Piscivorous (Fish-Eating) Birds.
For More Information
Klasing KC. Comparative Avian Nutrition. CAB International; 1998.
Robbins CT. Wildlife Feeding and Nutrition. Cunha TJ, ed. Academic Press; 2013.
Nutrient Requirements of Poultry. NRC; 1994.
References
Koutsos EA, Klasing KC, Smith J, Woods LW. Adult cockatiels (Nymphicus hollandicus) metabolically adapt to high protein diets. J Nutr. 2001;1(7):2014-2020. doi:10.1093/jn/131.7.2014
Kumar R, Banga HS, Brar RS. Effects of dietary vitamin D3 over-supplementation on broiler chickens' health; clinicopathological and immunohistochemical characteristics. J Vet Physiol Pathol. 2023;2(2):20-31. doi:10.58803/jvpp.v2i2.21
