The raspy voice is a big clue to drake, especially at that age. The curl usually is seen after they molt into their adult colors at four months. I've seen white strips on both males and females.
Check out the mallards on this page. You will have to scroll down:
http://www.hunter-ed.com/wildlife/waterfowl.htm
Check out the mallards on this page. You will have to scroll down:
http://www.hunter-ed.com/wildlife/waterfowl.htm