Late last Aug a drunk lady brought a gull into a shop ( In a box) saying she thought it had a broken wing .....its wings are OK but all its tail feathers were broken, snapped down at a 45 degree angle He has since pulled them all out and is a non flyer......how long before they grow back....? ...he has no tail feathers at all ..
I don't have the answer you need, but my first instinct would have been to seek veterinary help at the very start. It might be something straightforward, or it might be something more serious. However, having a wild bird in captivity for so long is not a good idea.
Any wild bird, or animal, that is rescued by the RSPCA or other organisations, including veterinary practices, are looked after in a way so they have little human contact, except for medical and feeding purposes, and that is kept to an absolute minimum, so when they are released back in to their habitat, they can continue to look after themselves.
Even the rehabilitation process is a controlled one to ensure the bird, or animal, relinquishes any human dependency and is able to survive as nature intends.
Mike
Flickr: Peak Rambler