[huntress]

The normal uropygial gland produces vitamin D3 precursors that are preened onto the feathers. Upon exposure to ultraviolet light (particularly UVB), the precursors will be converted to active D3, which will then be ingested when the bird preens again.
For activation of the uropygial gland secretion, a bird needs exposure to natural, unfiltered sunlight (not through glass or plastic) or exposure to a full-spectrum fluorescent light (changed regularly as recommended by the manufacturer and placed within 18 inches of the cage). While formulated diets should contain adequate amounts of vitamin D3, any birds, especially greys, with calcium problems should always have the uropygial gland evaluated, and it should be recommended that they receive some sunlight or full-spectrum artificial lighting. Some species of psittacines do not possess an uropygial gland (including Amazon parrots, hyacinth macaws) and emus, ostriches, cassowaries, bustards, frogmouths, many pigeons and woodpeckers do not possess one, either.
t has been observed that African Greys living outdoors (and exposed to natural sunlight) rarely suffer from seizures, so it seems clear that the interrelation between the uropygial gland, ultraviolet light and vitamin D3 are responsible for normal calcium homeostasis in the African Grey parrots, and most likely in other African species.

I had this stuff for you to look at. Its the most natural and effective way for birds to assimilate the calcium levels they need. Feed -thru supplimentation helps but you have no way of knowing if your bird is actually getting all they need. If there digestive sytem can even handle that means of intake. They were designed to create this absoption thru the preen gland AND natural sunlight so that would tell me its the BEST for them. Its no myth that the preen oils contain the necc. precursors for turning the Vitamins into the system. It is proven. Our bodies do not digest everything we put into our mouths, matter of fact unless your taking a liquid vitamin you are in fact Passing most of the vitamins pill you may take. Same can happen with our fids and unatural supplimentation.