What I did with my extremely beaky GCC was time out. If he started playing too rough and nipping I would put him ON his cage, ignore him and then go pick him up in 5 minutes or so. I kept repeating this and eventually he stopped nipping because he realized...ok nip means no fun! Good luck!

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No matter skin, feathers, scales or fur. We are all living creatures and should be treated rightfully so.
R.I.P Hiroshi. You were so loved and will be missed.