I didn't watch the video, because I didn't want to hear any heartbreaking sounds, but I'm sure I've seen something like that before. I've seen a lot of pluckers/mutilators in action.
I agree with
@JLcribber There is so much that birds need that is really hard/impossible for us to provide. I think that's why it's important to get as close as you possibly can, especially if you have a bird who's unhappy. It isn't your fault if it is behavioral, it's just that birds usually don't get what they need to be well balanced when they're captive. I myself don't think my Duckie gets what she needs, and though I'm always trying, it will probably never be possible.
How many hours a day do you spend with her one on one? Could you possibly look into getting someone to come visit her/spend time with her when you're not around? Do you take her outside on a harness into the sunshine? Could you start if not?
I don't know how long you've had her, but would it be feasible to start looking at rescues for another Hahns? Or at least planning to someday?
I think if a bird is stressed, there are a lot of avenues to look into or at least start considering...
Edit: I wanted to add this link that is a good primer for what a bird does during a typical day, and the importance of foraging. I think
@saroj12 first added it to the foraging section.
Maybe it will help you with some ideas to hopefully get her happier, and less interested in plucking.
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