hi Dsk, that to me looks like the chicken hasn't yet grown feathers on its backside they dont look like pimples to me but the pic inst too good (hard to take i know). they look like skin spores that the feathers with soon be coming out of when they grow. anyway post another photo when you can ? is it UNDER the tail?
So hard to get a picture! They’re all over and yes, under the tail. I was scared it was an infection but I’m now fairly certain it as something to do with skin/feather/follicle stuff. The bumps appear attached TO feathers. Almost like a human louse nit. When the chick was wet, these bumps were everywhere. They’re covered up now by fluff and seem to be positively falling off as they’ve dried out. Weird.