I don't know if those are call ducks or not, but you asked in the video of your ducklings how to tell their genders. http://www.metzerfarms.com/SexingVideo.cfm?CustID=1025320 This link is for a really great video from Metzer farms (a hatchery) on how to tell the genders of day old ducklings and goslings. I've tried it with my ducklings, and the video was really helpful.