But the birds appear to have mechanisms which allow them to adjust to conditions. Much has been learned from captive breeding efforts and from pet bird owners as more and more birds are being housed and fed under different circumstances. We in aviculture have made great strides in just the last 30 years. And we learn more and more each day about the needs of our birds. Other examples of different species needs can be seen in conures and macaws, which for the most part require a higher fat, low protein diet.
Amazons also are sensitive to too much protein.
Also worthy of mention is the choice of cooked vs raw foods. Most of the information I have read has had to do with the orange veggies such as carrots, sweet potatoes, yams and the like. Remember, this was discussed in regards to the human body, so we do not know if it affects our birds' chemistry make up as well. It is entirely possible that birds store certain vitamins in their bodies and when that supply runs low then they eat the very same vegetables and fruits which they ignored only yesterday. This can go on for long lengths of time and it most certainly could explain the sudden turn around that some of our birds make.