WHY ARE THEY CALLED DUCKS?

The word duck (from Anglo-Saxon dūce), meaning the bird, came from the verb "to duck" (from Anglo-Saxon supposed *dūcan) meaning "to bend down low as if to get under something" or "to dive", because of the way many species in the dabbling duck group feed by upending (compare Dutch duiken, German tauchen = "to dive").

That's my answer then. They are called ducks BECAUSE they duck.