No, I have a large flock (70 birds) on a deep litter flooring; I cannot pin down random feathers to the bird. I wouldn't be surprised if they dropped something like that, though.
Will do.
Oh that's interesting! This would explain why it doesn't seem to get better with the various treatments. Did you notice if your birds who had this issue had pieces of "chewed" up quill under them in the morning? When I clean off their droppings board in the morning I see that there is what looks like ground up or chewed up quill and feather follicle on it where Floki was sleeping...