I have hatched my first ever lot of ducklings last October and I know 2 of the 8 will be mules as their dad is a mallard breed (crested drake) and mum is a Muscovy. I was told it'd be obvious who the mules are but not to me Six of the ducklings now make a definite QUACK, but 2 are larger than the rest and make a funny noise which sounds more like a Muscovy than a drake to me. My questions are : 1. Do drakes take time to perfect their call like cockerels? 2. What sound and other features do mules have that may help me identify them? 3. If the mules don't quack, how do I sex them?