Come Fly With Me

So I've been thinking about this (perhaps a bit too much), and the whole premise of Peter and the Wolf doesn't make sense. First the duck and the bird tease one another by saying "what kind of bird are you if you don't swim?" and conversely, "what kind of bird are you if you don't fly?" Then the duck gets eaten by the wolf precisely because she can't fly.
Who ever heard of a duck that can't fly?

song: Come Fly With Me • artist: Frank Sinatra