I have six mallards that I got as ducklings about 6-7 weeks ago. Theyre starting to really feather out now and I noticed today that four of them have the faintest green tint to their heads in the sunlight. If I had to wager a guess Id say I had four males and two females. But I want other opinions. Their voices havent changed enough yet that I can tell who's quacking and who isnt.