Crimson wings with bald head

[Carmen]

I have a beautifull pair of Red-eyed Crimsonwings in my outdoor aviary.
But since a couple of months they are moulting. On the head. The male has already replaced his red spectacles
But now both their heads are bold, just like they have picked on them (that's a likely idea since they like to take care of eachothers feathers)
It looks really nasty...
What can I do about it?
Or is this probably going over in a matter of time?

[zookeeper]

I'm not familiar with crimsonwings, but I'd suspect a nutritional deficiency.