Quill mites you will need Ivermec which is obtained from your vet ...
Birds can loose their feathers like that from stress related illnesses
Ie: Mites , Quill mites, FM and moulting ....
I am looking at the feather that fell out and like i have said to others I am not a "VET"
but the quill end on a FM bird "usually" has a broken end - When i had issues
that was the first sign the vets told me it a dead give away ....
again contact local avian vet for a test - It looks like a premature feather that as fallen out due to the blood which is still in the shaft of the feather which