Hi intron, I am sorry to hear about your bird. I to have an Amazon and had the same problem. She is doing so much better now and she is almost back to normal and no longer biting her feet. I give her feet bath three times a day with 1 tablespoon of sea salt, warm water, two drop of Sultadmethoxine drop, and a little bit of Nolvasan antiseptic ointment in the water. First, I put her in the water for a good five minutes or so. Then I put the Nolvasan ointment on her and continue this three times a day. Her feet look wonderful and she can hold her food now with no problem. I am so glad she is back to normal. I wish you the best and I hope she gets better. I was told 20cm for an amazon bird collar. I will ask again to make sure. But is better to buy one all ready made for the bird. You can go to vetamerica.com and see how the bird collars looks like.