The pet bird population consists largely of psittacine species, primarily passerines and other genera such as those that include toucans. Psittacines eat mainly a plant-based diet and can be classified overall as florivores. The content of the diet—fruit, nectar, seeds, or a combination—varies by species. Some species ingest a percentage of insects or carrion. Although requirements and dietary sensitivities vary among psittacine species, the pelleted and extruded diets that have been produced for parrots have tremendously improved the nutritional intake and subsequent health and quality of life of these birds. However, pelleted diets differ in content and quality and must be evaluated individually.
Psittacine nutrition has been the focus of research over the past 3 decades. Several myths of psittacine nutrition have been debunked during this period. Grit, while probably necessary for some passerines and Columbiformes to aid in mechanical digestion, is not needed by psittacines. If seeds are consumed by psittacines, they are hulled before ingestion. Monkey chow biscuits are 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. Deficiencies of vitamin A, protein (the amino acids lysine and methionine in particular), calcium, and other nutrients occur in most psittacine species on seed-based diets. Conversely, excessive vitamins, such as vitamin A, are added to some pelleted diets, which can have equally detrimental effects.
Protein (amino acid) requirements of psittacines have not been well established. The amino acid deficiencies most consistently noted in psittacine birds on seed-based and table-food diets are lysine and methionine. Fiber content must always be considered when determining dietary protein requirements, because increased fiber causes increased fecal protein “loss.” Birds with low-fiber, more readily digestible diets (such as nectar-feeding lories and lorikeets) may do well on diets with easily digestible protein levels as low as 3–5%. Adult maintenance levels of protein for budgerigars and cockatiels (7–12%) are lower than those for African Grey parrots (10–15%). Protein requirements for growth and for egg-laying hens are higher than maintenance levels in all birds. Periods of heavy molt also greatly increase protein requirements, particularly the need for the sulfur-containing amino acid cysteine, because feathers 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 pre-existing renal impairment or a genetic predisposition to gout. Cockatiels with no pre-existing renal disease have been shown to tolerate extremely high dietary protein levels (up to 70%) with no renal impairment. A genetic predisposition to renal disease/gout has been documented in some strains of poultry and many 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.
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. Excessive dietary fat leads to obesity, metabolic diseases, cardiac disease, and atherosclerosis (also see Pet Birds). The requirements of psittacines for reproduction are generally lower than those of poultry, because the psittacines' altricial young do not require the same quantity of fatty acids as do the precocial young of chickens. However, diets that are borderline deficient often manifest as problems in either the psittacine hen or the chicks during reproduction.
Vitamin A and Carotenoids
Vitamin A is necessary for vision, reproduction, immunologic 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. Indiscriminate supplementation, however, leads 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 pelleted diets contain levels of vitamin A in excess of 10,000 U/kg of feed (which has been shown to be toxic in cockatiels). The source of vitamin A that is added to bird feed is not regulated, and significant quality control issues have been documented. High levels of vitamin A found in some lory and lorikeet commercial diets have been linked to vitamin E deficiency, decreased fertility, and an increased incidence of iron storage disease. Ideally, a quality pelleted diet for psittacines will contain multiple carotenoids and other vitamin A precursors, and a minimum level of vitamin A.
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 (such as canaries and flamingos) for feather pigmentation.
The primary function of vitamin D is to increase absorption of calcium and phosphorus. Vitamin D can be obtained either directly from the diet or from UV light exposure. Vitamin D is not a naturally occurring dietary element for birds—their natural source of vitamin D is sunlight. In the absence of natural sunlight, the minimum oral vitamin D requirement for African Greys is likely comparable to that of commercially raised poultry (200 IU/kg), but some UV light is also critical in this species for optimal activation of vitamin D3.
Vitamin D deficiency may be caused by dietary deficiency or lack of exposure to UV radiation. Limited studies have shown that species variation in psittacines for UV light requirements exist; notably, African Greys require consistent UV exposure to maintain adequate vitamin D3 and, therefore, calcium levels. Unfortunately, many birds are housed totally indoors, and owners often mistakenly assume either that they do not need direct sunlight, or that the sunlight they receive through glass will supply UV radiation. Owners of pet birds should be encouraged to exposed their bird to direct sunlight (with appropriate cautions regarding excessive heat) or to purchase and properly use UV bulbs.
Vitamin D toxicity is caused by excessive supplementation. Some psittacine species, notably macaws, are sensitive to excessive dietary vitamin D, and may develop soft-tissue calcification and renal failure. Toxic levels for psittacines have not been established, but levels that may be toxic for poultry begin at 2,800 IU/kg of feed.
For discussion of vitamin E, see Nutrition: Exotic and Zoo Animals: Nutrition in Piscivorous Birds.
Last full review/revision July 2011 by Joeke Nijboer, PhD; Teresa L. Lightfoot, DVM, DABVP (Avian)