I have 4 cockatiels in a small outside aviary. The aviary is big enough for the 4 of them but 2 of them have been plucked on the top of their heads. The two that havenít been are bonded, the ones being plucked arenít bonded. They were getting along but theyíve suddenly been plucked. I am unable to see which ones are doing the plucking but it is slowly getting worse. Just wandering why this could be happening and if itís the other cockatiels doing the plucking. Thanks