I've got 11 two week old ducklings. I saw a video on Metzer's website about vent-sexing day-old ducklings, but they said you can't do it on older ducklings, and I wondered why. You would think the penis would become even easier to see on the older boys! Any advice on sexing the older ones? I'd like to keep four or five girls and move out the rest sooner rather than later. Runner and Runner cross babies though they are all pretty upright like Runners. I'm in Northern California if anyone is interested in ducklings!