We adopted two unwanted ducklings, who are just starting to get their adult feathers now. They act like Siamese twins, totally bonded and mimicking each other in an adorable way. The smaller gray-and-white-spotted one started quacking three days ago, so I guess she's a she (she's busy, louder, more assertive and will eat big slugs). (We call her Shadow) The larger white one, I assume is a Pekin ... THAT duck whistles !! Loud and long and medium pitch ... a rather pretty sound, though. It's not like anything in the site that Wifezilla suggested for sexing by voice. Sunshine, as we call her/him/it, is mellow and lets Shadow eat first/ swim first/ adventure first. Do you think Sunshine will be a drake ???