Hand raised parrots think they are people and become extremely dependent.
When you spend hours on end with one every day for ten years, and then stop (as happened to Alex) they wither away. First they start pulling out their feathers, some of them self mutilate. Then they just waste away.
They never revert to recognizing birds as their flock, they are permanently imprinted on humans. But they are flock animals and without companionship and entertainment they just pine away slowly.
Alex’ story is actually pretty sad. So is that of many, many hand raised parrots. Which is why I stopped breeding them, at one point I had a large exotic bird farm.