By about 8-9wks i was able to tell ours.. the males are noticeable bigger overall, the legs thicker, feet larger.. plus the females 'honk' LOL the males just hiss...my females fly like you wouldn't believe, my males only over.. there HUGE i swear my biggest one is starting to rival the turkey at thanksgiving(no he isn't destined for that) the hens have a rather feminine look to them sounds dumb but seriously it's there.
Edited by Going Quackers - 8/15/11 at 9:20am
My white ones are.. 3.5mths... I know some who are real experienced can tell sooner.. storey's guide to ducks says a hen is like over 60% smaller at 3wks than the drakes.. the farmer i got our newest chocolate pair picked out the hens for us..
Here is a pic i have of my biggest drake and one of my hens side by side.. note differences...hen on left.. drake on right.. they were 9wks ..