Chase them around with a broom until they are too tired to pull feathers??
Please don't do that it was meant as humor!!
I don't know other than separating them, but that could backfire and would increase both birds stress levels, you would have to find some way to distract their attention from each other and keep them interested in something else.
This would be one of those circumstances that trick training might come in handy to keep them occupied with something other than preening each other. Flight recall training would also probably be useful for this pair. It seems to me that they do not have enough mental and physical stimulation so they spend the time preening. Perhaps you could get them interested in shredding toys, or foraging toys. I have also read that preening toys such as untreated feather dusters may be helpful in diverting their attention from preening themselves and each other. I hope this will be more helpful than my last reply.
Give them a nest and lots of stuff to chew - different materials from rolled up magazines to wood passing through cardboard, dried yucca, etc. But, some of them will just keep on doing it. Mami plucks Naida all the time. She has just finished growing the feathers that Mami had pulled out from her head, neck and chest but they will soon be gone because Naida actually asks Mami to preen her and Mami doesn't know any other type of preening but overdoing it. Sometimes, you just have to accept what it is and not worry about looks, you know...
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