Baldness in Zebra finches

[Lauren]

I have a male called Joe who's been bred for show so is larger than average, and a normal male called Dobby. They are in the same cage with 2 other normals (fawn and grey both males)

None of them fight and we haven't noticed any over preening or plucking. However, Joe and Dobby have a lot of feathers missing. Mainly from around their necks, back of heads, above the tail and in Dobby's case on his stomach. The other 2 are absolutely fine. If it was mites surely they would all be like it? The normals are about 12 months old and Joe we don't know. We've had him for 3 years but were never told his age. When Joe started losing his feathers we assumed it was old age. Could Dobby be losing them in sympathy? They have palled up and are pretty much together 24/7 either on a perch, the floor or sleeping in a food bowl.

Any ideas what's going on please?

[CandoAviary]

Lack of vitamin A. Kelp green is a great source as well as Feather up by Bird Care Company or Feather Fast by Morning Bird.

[Chrismurdoch3]

Have you seen any form of aggression between any of the birds??

[Lauren]

Thanks I'll add some more vitamin A.

And no there hasn't been any aggression. They never fight just sit cuddled up. Or on top of each other, whatever takes their fancy lol.

[ac12]

'around their necks, back of heads, above the tail and in Dobby's case on his stomach.'

This sounds like plucking to me.
You will rarely see the plucker plucking the pluckee. But missing feathers in the locations you state indicate a plucking situation. Separate the plucked birds into their own cage and feed them lots of egg food, to regrow the plucked feathers. If the feathers regrow, and stay, the other 2 are probably the pluckers.

What I don't understand is how the plucked bird still cozys up to the bird that plucks him. Sort of a dominant/submissive pairing.