Sexing Call Ducks

[Callduckies]

I have 4 snowy call ducklings that are 4 weeks old. I'm not sure whether they are drakes or hens. Any tips on figuring out what I have or ideas as to what they are? I have a feeling 3 out of 4 are drakes

 

[RossAcres]

I see at least two drakes. Call ducks can be sexed easier by their quack than by their coloring at this age. With females they will have a loud QUACK and the males will have a raspier sound. But with snowies, you can start to tell the males by looking closely at their head feathers. The head feathers will be very dark, almost black, and have a green shine to them. The females will have dark or light brown feathering with no shine.