help sexing buff ducks

[chickenzooo]

Can someone help me with sexing my buffs? They're about 2-3 months old now. The only difference is in their bills. Two of them have a purplish brown colored bill and another one has an orange bill. The one with the orange bill is a little bigger than the other two.
The bigger one with an orange bill also quacks more than the other two. They mostly sort of make a whistle noise.

 

[Ravynscroft]

Until the drakes get their drake feathers, the best way to sex ducks is by their voice... females have a loud distinctive quack while males have a quieter, more raspy whaaap-whaaap-whaaap sound... sounds like your bigger one might be a female... check out this link to hear the differences between male and female voices...

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