Growth on side of rooster's head!
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Welcome to BYC. That looks like an ear infection, but not seeing the bird in person to make sure, it could also be a tumor. How long has it been there? Get some hydrogen peroxide, QTips, and plain neosporin or bacitracin ointment, and try to get some of the gunk out. Here are some good links to read about how to deal with an ear infection: