None of these creatures has asked to be brought into captivity. I believe with all my heart that it is incumbent upon the permit holder to give their birds the best quality life possible, which can be MANY years. Don't launch yourself into this lifestyle unless you are prepared to sacrifice many things. Never look back. Live your soul's desire.
Castings are very cool.
The regurgitation of the casting sets in motion yet another chain of events in the food chain. What has now become useless to the raptor now provides sustenance for lower organisms, like beetles and various unsundry bugs. The fur and feathers of the prey is like fiber for us, a crucial part of their digestive system. I LOVE mashed potatoes, but I would die if I tried to live on them. In the beginning, raptors had to be sacrificed in order to determine what they had eaten, but now all the biologists have to do is find the mandibles in the castings and compare the indentions as they are slightly different between the rodent species.