Care must be taken with vitamin supplements not to provide too much calcium. Cockatiels, budgerigars, some grass parakeets and finches live in arid climates and eat mainly lower nutrient, seed diets. They have evolved to conserve nutrients and water and thus they may be more sensitive to high levels of calcium and D3 in their diets. Birds of the neotropics, with access to abundant, varied foods, have not needed to conserve nutrients in their body and may have higher daily dietary needs. Calcium absorption occurs mainly in the upper intestine and is regulated by Vitamin D3.
Some absorption also occurs in the lower intestine.
High protein diets and more acid in the intestines appear to aid in calcium absorption. High fat diets may produce fatty acids in the intestines which can reduce available calcium by forming insoluble calcium soaps. Phosphorus Phosphorus may affect more biological sytems than any other element. It is an important element in many body functions including bone formation, acid-base balance, metabolism of fat and carbohydrates, egg formation and in the proteins, carbohydrates and lipids used throughout the body. Plant sources often contain phosphorus combined with phytin, and animals such as birds lack the enzyme phytase necessary to make the phosphorus available.