i dont know if ducks can have that but ill look into it.
did some reserch on it yes your right ducks can have cayenne pepper, some people say its fine and other say its not good for your duck, saying it oled to a discharage from the anus that smelled terrible and the duck was not gaining much...
its a mule , from what i can see , amiga is right, it will lay eggs but they wont be fertile.
Amiga is very good at this kind of stuff you should trust her opinion.