Are they eating, pooping, bathing and looking healthy?
It can be moult, or parasites, malnutrition, bad type of feeders.
Please post a picture of your birds and feeders if you can.
Did you treat them with any medicines recently?
You might find your birds don't want to be handled while they are growing in their new feathers. The emerging quills (blood feathers) are tender until they mature and shed the sheath. Offering regular baths can be very soothing for birds growing in new feathers. The moisture helps them shed the dried sheaths covering the feathers.
Additional high oil seeds (safflower or hemp) can also be helpful to encourage lusterous plumage.
I love this site! I had to re-register --for some reason I was unable to contact the webmaster to figure out what was wrong with my first account (I was ny_lizzy). My Pearl who I adopted after she was downed by a hawk has been dropping feathers like crazy -- I swear she should be bald by now. Glad to find here this is pretty normal. Her face looks just like the pics posted in this thread.