Sores on baby chicks backs!!!

[boogiedown]

I have four chicks and four adult hens. The chicks are about eight weeks old we put them out with the adults about two weeks ago. The hens are figuring out pecking order but the chicks no their place and avoid confrontation. Everything seemed reasonably okay with the chicks sticking together and staying out of the way. I pick the chicks up one by one almost every day to check on them and today I found two with feathers missing and some sores on their backs. The skin seemed firm where the feathers were missing. The seem to have no behavioral changes and no other indications of poor health. Please let me know what you think this might be and what I could possibly due to help them, thank you in advance!!

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