Chick with bald back?

[SarahInAlaska]

I have 19 chicks and my older ones have feathered out quite nicely. One of my younger ones though has gone completely bald on his back. I haven't noticed anybody pecking at him and the much older chicks (almost 4 weeks) are in a separate brooder so my little guys (almost two weeks) aren't getting trampled to bits. Here's a picture of his back. Is it just normal feathering out or is something else wrong?

 

[SarahInAlaska]

It's been like this for a week.

 

[SarahInAlaska]

Any ideas? He's Gotten larger and feathered in elsewhere more since last week but these two spots are still bald. I haven't seen anyone pecking at him either and he seems fine otherwise.