@nomrbddgs:
I cannot even get a lice pesticide for my chickens because pesticides are banned.
Really? I've got that dust on stuff for my horses (Dry Kill) that kills lice. Mind you, I haven't bought any recently. Not sure if it works for bird lice, although I believe bird lice can affect horses. I think I had my bout with them when I had pigeons roosting in my run in shed. (yeah, lice are supposed to be host specific, but so are fleas, and cat flees certainly love me!)
Prednisone has some annoying side effects (thirsty, hungry, peeing more) and some potentially dangerous ones. Dumps the immune system so they are more prone to infections. And it can be difficult to properly taper them off if they have been on it long term. Been there, done that, years ago with my girl with the suspected brain tumour. Best to find out what the problem is ASAP, although it may well be seasonal. Did you try something less potent, like Benadryl (antihistamine), first?