They have to have very little human contact. They are best raised in a "Johnny house" where they can see out when they perch up high, but when they are down at ground level in the house they see nothing but each other. (once they are release and see something at groundlevel they, ah, flush(?not sure if that is the word) up and away from it )Some people even set it up so that their feeders are on the outside so that they don't have to enter the Johnny house except to catch birds for release or dog training purposes.
Those that have human contact daily, are handled, are exposed to family pets, and the daily comings and going of people are nothing better than a food source for the neighborhood cats!