Cage Height: There is a definite correlation between altitude and attitude with captive parrots. Consequently, if a bird has an aggressive or dominant personality, this can be exacerbated if the cage allows it to sit above the human eye level in its environment. This is especially problematic with the so-called "cage-top playgyms" marketed with various types of cages. People often don't wish to give up their own living space, so tall but narrow cages and cage-top play areas are popular. Ironically, they also contribute to home-threatening behaviors. Aggressive or dominant psittacids can be lowered a couple of wayseither by lowering the cage, or by lowering the perches within the cage. Denying access to cage tops and removing the highest perches from tall climbing 'trees' can also help a great deal. If cage and playgym designs don't allow alteration, then (using Chris Davis' trick) one can raise the people. By placing a footstool or small ladder next to the cage, the owner thereby raises smaller humans to a position of higher rank.
If too high is potentially problematic with parrot behavior, so also is the opposite. A nervous, high-strung and/or phobic bird's condition can be worsened if its cage placement is too low. I also do not approve of the old technique of placing an aggressive parrot's cage on the floor. Being trapped on the ground must be terrifying to prey animals like psittacids, and the act of terrifying an animal has no place in behavior modification.
Height and Shouldering: As an addendum to the issue of height dominance, a common practice that can be especially dangerous is the ancient fashion of allowing parrots on shoulders. A popular custom over centuries of parrot custodianship, this practice probably didn't become especially dangerous until the advent of domestic-bred parrots. Wild caught parrots have a fundamental respect for humans as predators, whereas domestics have no such regard. As a result, domestics are capable of much greater violence towards people. Hence, allowing parrotsespecially adolescentsto shoulder is particularly dangerous, not just because of the superior altitude and therefore dominance of the bird. Shouldering parrots places the birds within easy access of extremely vulnerable (and valuable) parts of the owner's anatomy (eyes, ears, noses, lips, etc.), which are then subject to severe damage from the parrot's beak. This type of injury can permanently harm not only the human anatomy, but also the parrot-human bond. Damage can occur even if the bird didn't intend to bite but was startled into grabbing onto something to keep from falling. Knowing the parrot meant no malice does not decrease healing time. This is probably the only issue on which all experienced lay parrot behaviorists totally agree.
reference:
1 Blanchard, S. "Problems With Parrots On Shoulders." The Pet Bird Report, Issue #25, 1995.
2 Athan, M.S. "The Importance Of Being Tall." Guide to a Well-behaved Parrot. Barrons, 1993, 64-66.
3 Davis, C. "New Techniques in Pet Avian Behavior Modification." Proceedings of Annual Conference, Association of Avian Veterinarians. 1989, pp. 183-189.
4 Wilson, L. "Behavior Problems in Adolescent Parrots: Guide to a Well-Adjusted Pet." Proceedings of Annual Conference, Association of Avian Veterinarians, 1995, pp. 415-418.