My nanday has a lump under his wing on his side

by Mike
(Georgia)

My mom and I really don't know what it is. We have a book but its from the 80's-90's, so we don't know if everything is up to date. Anyway, he lifts his wing and there was maybe a 1cm long lump on his side. He doesn't seem to be in pain so we don't know what to do.