That doesn't sound too good does it.
Looks like some feather picking on the back, the others may be picking at him.
Left leg, take a look at the scales - is there a break in the scales - can you tell if that's just superficial tissue damage or a little deeper - any green bruising?
He's got some thick legs on him, what breed is this supposed to be?
I would observe to see if he's getting trampled or picked on a lot - if so, then placing him by a barrier would be good. You want him to still see and hear the others. I would get some human B-Complex and give him 1/4 tablet once a day for a week.
The damage on the back is minimal and he should feather out o.k. I would check his vent just to make sure it's not been picked too.
Get a good look at his poop, photos of that would be good too. A puppy pad under him overnight is a good way to capture poop.