I don't really know anything about stress bars, but for what it's worth there's a pretty good picture (Image 15) at http://www.spcollege.edu/hec/vt/VTDE/avian/7b.html The bird isn't a cockatiel, but the lines are very visible. BTW this site displayed properly in Internet Explorer but not in Firefox or Opera, so it's obviously not compatible with some browsers. So here's the pic - maybe you'll be able to see it here if the link won't work for you:
It's easy to find more pictures if you google for feather stress bars and then click Images.
I founds some pix's. The lutino wing is what is called 'hunger bars' because while in the nest the parents stopped feeding for a full day. All the others show some form of stress marks/bars. With all the pix's shown the cause was an interuption in their diet/eating.
I moved this thread to the Health section because it is not Mutation related. By the next molt, if diet is fine as you said, and he seems adjusted and happy in his environment the feathers should molt back in normally.
But when stress marks/bars are noted it is a red flag that something is wrong or was stressful to the bird. If they molt back in then a vet visit and bloodwork may be needed to find the cause of the problem. Since they are lower on his back, covering the location of the kidneys it could be protein related.
oops i did not see the reply!
Thanks for the help everyone, and the pictures Susanne,
I don't remember if i told you guys that we just moved. singerboy has been in a car three times in his LIFE more or less..
we moved them with a blanket over the cage securely in the back seat (to cause as little stress as possible) who knows.
He just finished his molt so it might be a while before we find out. but i am going to blame it on the move