Bald birds?

After starting to moult in October my 2 Black Rocks are still bald all round their rear end and legs. A couple of times you can see feathers starting to appear but then they are gone again.

I dont think they are being pecked by the Amber or the Bluebell and we have tried anti pecking spray.  (The amber has lost feathers as well but not as many as the Rocks)

They are bright and seem healthy and are just as silly as ever, they eat well and we have had 4 eggs most days ever since they all started laying.

The coop is clean and we spray with poultry shield there is no sign of mites so I am at a loss.

We use Aubiose in the coop has any one had any problems with this?

Any suggestion would be welcome?

HI, if you can see the first signs of feathers coming through, then they disapear, im afraid it sounds to me like they are being pecked/pulled out . Of course i could be wrong, but one of my little ex-batts took an age to feather up on her wings, the same thing was happening. It was only after 3 months when she came out the coop in the morning with the tiniest spot of blo on her wings that i realised they were being plucked out. I covered her wings in purple spray, and she now has lovely feathers......she just needed a chance to let them grow!

Sorry....purple spray is a disinfectant. Also known as gelatine violet. Available in chickeny and horsey places. Its very useful for chickens as they are drawn to the colour red, so if they have an injury or a speck of blood others are drawn to it and when they start pecking it can get very nasty. The purple masks the red colour giving what ever is red time to heal
http://www.flytesofancy.co.uk/chickenhouses/Gentian_Violet_Spray.html#a4018
Ive given a link to an on-line store, but it is available in lots of places

Thanks for the advice I now have 2 Purple Rocks Purple hands and a Purple tee shirt.

Does it come in any other colours as paint your chickens may be a winner, Dragons Den here I come?

Lets hope the silly beggars stop it now.