Certain fish change sex for certain reasons. Sometimes it's because there are no fish of the opposite sex (clownfish and groupers). Sometimes (I believe, I'd have to look into it more), it's an age thing where they do develop to the opposite sex after a certain age
That's reptiles. There are theories that unstable incubation temps can kill off more of one sex, but the sex they are is what the egg was when it was first laid
I've seen it theorized on here that one ovary produces eggs and the other produces hormones.
These hens still have female coloring though. They're just more prepared for a zombie apocalypse than their lesser armed sisters
The only way to tell without using DNA testing would be to physically look inside the bird after putting it down. They're not going to be able to tell you anything by looking externally