Igor the blackbird is looking scraggy?

When we first met Igor the very tame blackbird he was completely bald and we asked on here about it and someone suggested soaking a few of the currents we fed him in TCP. This worked a treat and Igor grew new feathers on his head and looked as good as new. Now 9 months later he is looking grey on his head and the feathers around his neck are gone. I can see the quills on the feathers next to the baldness and it certainly looks like some kind of parasite is eating them away. We have tried the TCP treatment again but its not working anymore so I'm looking for suggestions.