Back to the original question...you could feed your birds bread crumbs for a day and it would not do any permanent damage. Keep in mind that the average life span of a dual purpose chicken is a couple of years. If your birds are also your pets, that you plan to keep for their normal natural life, then you should consider long term effects of over feeding calcium. As for protein, it is water soluble and although it is processed through the kidneys, there is no real proof that it damages the kidneys to the extent that it shortens life. All the studies I have looked at say more protein MAY cause this or that.
A birds metabolism is so high that any short term excess will quickly run it's course. Check out the labels on your feed. Most commercial feeds are identical except for calcium and protein...and also keep in mind that those numbers are not exact. They are numbers for the "Batch" and are at best an average number.