I suggest you take your budgie to an Avian Vet for a check-up and professional diagnosis. From the picture, I cannot tell if your budgie is going through a particularly bad molt or if he is over-preening.
How old is he and what kind of diet is he on?
Are the other two budgies male or female?
How large is your cage?
Have you seen either of the other two birds preening the one with the bald patch?
Have you been giving your budgie high protein foods to help him through his molt?
To familiarize yourself with the forums, please take the time to read through all of the How To Guides, the FAQs and the stickies located at the top of each section of the forum.
You'll find most of your basic questions are answered after you've read through all of them.
I'm looking forward to hearing all about your budgie and hopefully seeing some pictures soon!!
Paulie (my boy) is 4
Summer (my girl) is 3
Lola (the girl I rescued) I have no idea how old she is, but she is very very old. Her friend died so I introduced her to my birds and now she lives with them, I got her used to coming out and flying with them two but now she wont come out, she cant fly properly anymore, shes not well really, but she is very old.
Paulie and Summer have a thing going on, they tried to breed, she was laying eggs and they were preening eachother, he was feeding her but the eggs were infertile, that was at christmas time.
They are on seeds, fruits and vegetables, ive actually only just managed to get paulie to eat them, summer loves fruits and veg she runs straight over and starts eating but paulie wouldn't, however he has started copying her and now they are always eating fruit and veg.
As I write this paulie is stretching his wings on the perch and I think it is the same under his right wing. Hes preening himself now, I think its something bothering him under his wing, I don't know.
Summer and Paulie havent preened eachother since they were trying to breed.
Summer is the bully, she is in charge, Paulie is lovely, very sweet and never tries to peck other budgies out the way or anything, he really likes summer and sometimes she is nice back and other times she wants nothing to do with him. Lola is very old, shes actually smaller than the other two, I don't know if it is the whole 'american budgie' 'english budgie' thing. But she hasn't been looked after properly all her life.
All three get loads of time out of the cage, they have full flight of a room most of the day, they also have a large cage, I sometimes bring Paulie around the house with me if hes feeling brave, they have lots of toys and mirrors and like playing with stuff around the room. Paulie loves anything that crinkles, like crisp packets and sweet/candy wrappers. (im from the UK)
Sorry for writing so much, I hope ive explained clearly
They are very happy birds, Paulie is very vocal and is always chirping away and bobbing is head up and down, he even chirps quietly to himself when he goes to sleep.
Summer and Paulie are too old to breed and you need to ensure you have nothing in the cage that could be used as a nest and do everything possible to discourage breeding. Make sure there is a cuttlebone and mineral block in the cage as laying eggs depletes the calcium in the hen's body.
Given that the area under Paulie's wings seems to be getting progressively worse and you indicate something there seems to be bothering him I recommend you take him in for an appointment with a good Avian Vet to get a proper diagnosis.