Ok, I'm not 100% about all of it. Maybe they do just develop the characteristics of the other gender, but being fertile or nor does not mean they aren't male. Human men that are infertile are still men biologically.
I love your avatar btw.
As Kusanar said, a male that is infertile is a male biologically. However, a hen that develops male secondary sex characteristics is still biologically female. She still has an ovary, not testes, and it's just a hormone imbalance that causes her to develop some male traits.
Like a female human who develops a testosterone imbalance and starts growing facial hair. She's still female.