Zebra finch ageing process

[Lauren]

Hi, I have had 3 normal coloured zebra finches who were bred for show but only have 1 left now. They were Alfie, Joe and Cyril.
We had to pass on Cyril because he was vicious towards the other 2.

We don't know what age they were when we got them but as Alfie got older he started to lose his feathers from the back of his head and on the top of his tail. He ended up looking really bedraggled then finally died.

Now Joe is doing the same. He is bald along the back of his neck and a bit up his head and along the top of his tail. Is this normal ageing in finches?
Also, I have a totally normal sized, normal coloured zebra called Dobby, who was hatched last year and he is doing the exact same thing. Along his head,tail and stomach he's losing feathers. They don't have mites as our other 2 zebra's are ok. They are different colour mutations, fawn and grey, and I was wondering if its a colour mutation thing?
Any advice would be lovely please Thanks

[finchbreeder]

Could they be plucking each other? If so this could be because they are lacking something in their diet. Do they get sunshine exposure? If not I would suggest liquid vitamin D, not a problem here in Australia, but I understand it can be in Europe.
LML

[Niki_K]

It is likely to be due to plucking, or moulting. I have a zebbie who is about 11 years old, and he's still tight-feathered, as well as several other age ranges with no problems in this regard. It could also be stress-related, or if they are poorly. Are they exposed to a full light spectrum?
Colour mutation isn't likely to be playing a role in this.

[Lauren]

They sit in the window which is a bay and so quite large with the window open, and their cage is on wheels so they are taken outside quite often in the summer, pretty much everyday. If it was lack of vitamin D wouldn't all 4 be like it? We haven't seen any plucking, and they never fight amongst themselves. No obvious signs of stress, as Joe is the tamest and most chilled and will let us stand by the cage on face level with him while he inspects us. The others not so much but they are getting better. There's no cats or anything near us.
Is it worth giving them extra vitamin D anyway and seeing if it helps? if so what should I give them?

[finchbreeder]

As you say, does not sound like a vitamin D shortage. How about calcium? Trying to eliminate possibilities till we get the right one.
LML