I had a Black Star hen that "turned into a rooster" once a few years ago. I had learned that this can happen back in Ag class in HS. In all my years it's only happened once. She was about 8 years old. I've read that they can have some hormonal changes when they get older and they start to transition. (Caitlin Jenner, you're not the first
) This one grew a larger comb, got longer spurs and crowed every day. She quit laying eggs though. I never saw her try to mount a hen though. I had 3 other roosters at the time. One night I forgot to lock the chickens up, and a raccoon came. Two of the roosters and she/he must have tried to defend the hens, and they were all dead the next morning. I think I wrote about this in some other thread a while back, sorry for the repeat.