it is NOT black head. It IS fowl pox. I have been raising birds for over 40yrs. and have seen it several times. Black head has no symptoms like the scabs your birds have. there is no treatment for fowl pox other than keeping them secure, well fed and watered and try to keep the flies and gnats away from them. Since they are already forming the scabs, you are pretty much through the worst part. Just keep an eye out for any infection setting in in any of the scabs.
The term blackhead comes from the infected birds sometimes developing an overall bluish tint or coloration of the head, not spots.
TV is absolutely right! I went back and did more looking and found the description/symptoms for the fowl pox. I am so sorry for giving you wrong information, that was never my intention.