It Is hard to voice sex at first because they will still sometimes make duckling noises and only sometimes make adult duck noises. At 5-6 weeks is when you first will hear the changes. I feel like my KCs (girls) sounded like someone honked one of those horns you put on the handle bars of your bike, my Swedish girls honk when they get upset too, but it is a bit deeper. The sound the drake makes reminds me of a frog.
I'm not sure at what age distinctively male nuptual plumage comes in, but I think when they are this young males and females have the same coloration so you really can't tell by looking at them.
@chickens really do you know when males first have distinctive color? My only drake is a Swedish and the males and females look the same as each other all year.
