He's probably a boy; they can't quack like the females can, but they can make some noise. Can he quack at all???

yes, if it tries very hard. They are 10 weeks. They all look like females at this point. At what age can you tell male vs. female? We went to follow up tonight and it seems healthy, integrating fine with the other wild ducks, eating, active, etc. I am not sure what to think.