By voice. I don't trust drake feathers . Raspy not as loud voice=drake. Loud obnoxious honking and quacking= definately duck. Note, one duck I have is quite and won't quack unless I pick her up and seperate her from the flock. That is Laura. THe loud ubnoxious firl is Greta. (I name My Ducks after news and newtainment host such as BIll(Irielly), Sean(hannitty, Laura(ingram), Greta,(Van Sustrain) THe Runners are NancyGrace. But Nancy may be ANderson IF it don't quack soon.
My naming system makes it hard to eat a duck named Sean.