Sexing ducks by bills and feet?

[marvun22]

I have 3 adult black ducks (they are a cross between a swedish/cayuga and a fawn and white runner). The females have black/gray beaks and feet. The male has a yellow/green beak and orange feet (and a green head). I just assumed since my baby duck had the black/gray feet and beaks, it was a female. I just quack sexed the female, and sure enough it is a female. Do I have a lead here, or is this just random?

 

[Nebraskagirl]

Not sure about sexing by appearances. Voice sex and vent sexing is probably your best bet. I personally have not vent sexed, but voice sexing is the best way. I have Welsh Harlequins and beak color upon hatch is 90 percent accurate so I should have two girls. WRONG. Got a male due to voice sexing (they are about 8 weeks old now.) I am sure someone more experienced can give you more info. Can you post pictures?

 

[Going Quackers]

Yeah vent and voice for mallard derived , feet is 'scovie.. that and size. The colours were messing me up with my calls but the voices finally came through, definitely one drake, one duck!

If they are mixes that would definitely make colouring more inaccurate. Pictures would be great, even voice videos.