Lots of fish. Catching them, then preparing them for the bird. The first week, I pulled off small pieces with hemostats or tweezers and fed Orville until his crop was full, about a pecan size bulge in his chest. After that, I could cut the fish in pieces and feed him bones and all. He would reject any piece too big or too bony with a very vigorous head shaking, slinging the offensive piece to the side.
He ate vigorously and gained weight daily. He also visibly grew daily. Soon I was using a paper cutter to initial cut the fish, then game scissors to cut the pieces o fail size. He ate the entire fish, entrails and all. I thought there may be some hidden vitamin or biome ingredient hidden somewhere in the fish. I occasionally gave him vitamins for the rare (2 so far) frozen fish I gave him.
He eats a little over one full size bream a day now, 150-200 grams.He has gained from 41 grams to 720 grams in 26 days. When he fills his crop, it gives him about a 10% temporary weight gain.
I am doing a little falconry training already. Hooding him occasionally and briefly and under supervision. I am constantly touching him, especially his talons (although I have not had one that was footy yet) and his beak (they all have pecked badly). I am carrying him around exposing him to everything, all our cats and dogs, cars, outside flying birds, etc.
I am keeping him well fed at all times as I have read this can help with screaming. We shall see.