We have a pair of mallards we purchased at TSC the first of March. We think we may have gotten lucky and got a drake and a hen. From what I have read mallard drakes start out colored like the hen but as they age they go thru "eclipse plumage" when they get the green head and their drake plumage. Right now they are basically the same except for one has an olive drab bill the other has yellow and black bill. the one with the olive bill has a darker back and its feet are solid blackish brown the other has some yellowish trim on its feet. The one with the olive bill is slightly bigger than the other. We have tried the quack/ whistle test and it is questionable at best. There is no doubt when it comes to our pekins definate quack verses the whistle but we bought them thru cackle hatchery sexed. We also have a pair of cyuga's that were strait run and they are basically identical except one is slightly larger than the other. So if anyone has any opinions they would be greatly apriciated.