My Mule duck has absolutely no caruncles at all but is a Mule for sure. She is absolutely huge and the only male with my Rouen was my huge Muscovy Drake. She has a head that looks more like her Mother and a body like her big huge Drake father.A detailed look at her bill would reveal that very quickly: Mule ducks almost always have that typical Muscovy bill with that large bean and there should be at least a trace of caruncles around the bill.