Hi there, I'm a very new duck owner. I've read Storey's Guide to Raising Ducks... but I'm still confused. Burt & Ernie were born at the end of August. I was told they were Mallard x Call crosses. They're about 6 weeks old, now. I keep looking for that curly butt feather thing that males get. Both their butts look about the same right now. Based upon their coloring I'd say I have a boy (dark) and a girl (light), but when will those curly butt feathers come in?