Roo w/RED bottom

[Drive1968]

This looks really bad and it will not go away.
I have read that it is due to weather conditions, rain and humidity etc. Is there a cure or atleast some help. Yes RooRoo is doing find protecting his flock, running around, and eating well.
Thank you for any help,
James

 

[nuthatched]

Is he being picked by the others? Have you checked for mites,