Mine are doing pretty well too. Unfortunately, though, I've lost more than I would have expected. One died very young--she was weak and just never thrived and eventually just passed on. Another died thanks to a bad batch of feed. And a third died recently of unknown cause--I noticed her sitting apart from the others one day, breathing hard and not wanting to move much. A few hours later, I found her dead in the corner of the pen.
That's three out of sixteen babies. Very strange. I know the one was totally my fault, but the others... I don't know.
The remaining ducks are doing fine. I can't sex them, though. They quack and rasp constantly, but I can't tell which is doing what, and when I pick them up they stubbornly shut their mouths and won't talk.