Ducks are 4 months old and still can't figure out gender

[donaldanddaisy]

my ducks are about 4 months old now and they still aren't showing any indication of gender. One has a loud quack and the other really quiet. Also haven't found any eggs yet if I have a female.

 

[Amiga]

http://www.majesticwaterfowl.org/artquacks.htm