is it unusual to have a female duck that doesn't quack? or do I secretly have a male?

[allgoaton]

Ducks were ordered sexed as female. Three quack their little duck hearts out and are obviously female, one is super quiet. She's a blue swedish. Although she doesn't have a drake curl or the super dark head coloring, they are only 18 weeks/4 months old.

I am 90% sure that she did the peep-peep-peep-QUACK as a baby when they were getting their voices in, but since then not much quacking.

Here's a video of me chasing them around some. She(?!) is the one making the deepest mumble noise and is actually making the most noise, but I don't get an angry vocal response even when I grab her and hold her. She'll try to wriggle free, but make no noise and definitely no quacking fit. I've never heard the drake sort of frog sounding quack from her, but I also NEVER hear any type of quack.

So. Female duck or male duck? Is it possible to tell just from the chattering?

 

[Amiga]

Her voice is similar to my Achtie's voice. Acht is a female.