It is even worse to the frightened Grey because it cannot escape by flying. The result is a phobic African Grey. This isn't the only cause of phobias in African Greys, but it is one of the more common reasons. If the bird has not reached a social level where it can naturally distinguish between friends and predators it will fall back on its genetically patterned wild animal instincts, which say that something that chases from above is a predator. We can make this assumption because we know that Congo Greys are in part ground feeders in their natural environment and that their most feared predators are hawks which attack from above.
Greys feeding on the ground can only escape a hawk by flying.
Imagine the instinctive terror of not being able to fly to escape a predator coming after you from above, as we humans must appear when chasing a Grey who is on the floor. An interesting fact about Rosies is that they are the only Cockatoo species that is raised after weaning in nursery trees, supervised by adult nanny birds. Wild Rosies don't have the behavior problems that we see in domestically bred Galahs. Sam's theory is that our domestically bred Galahs need and are not getting those extra months of nursery care before they are ready to be individuals in the flock. Perhaps, and this is still in the theory stage, Congo African Greys also live as young juveniles in a nursery situation, being cared for and nurtured by an older Grey until they are around one year old, and then go with the flock as individuals.