What Gender are my 2 Black Swedish Ducks?

[Galaxy Pickle]

This is my 1st year with ducks. I have a faun Indian runner, and a rouen that I’m 99.9% sure they’re female. But my 2 black Swedish have me stumped. 1 of them has an obvious green sheen at the tip of their wing by the white bit. And a green sheen to their head but you have to kind of look for it. The other my husband says they have it too, but I honestly haven’t been able to tell. I also haven’t seen the male curly tail feathers yet.

Can y’all tell what they are? Or help me better understand how to figure it out?

 

[JedJackson]

Voice sexing is the best way. Males and females have different types of quacks. Should work after 8 or 9 weeks of age.

 

[CoriM]

Did you figure out your black swedish? If they don't have the tail curl by now, they are probably females. My two black swedish females are extremely loud - that's the easy way to tell. Males will have very quiet voices. My females are beautiful blue and green in the light. I really love this breed!