Mallard Drake molting into female feathers? Do mallard drakes change sex?

[Maddieiceee]

So I have a pond behind my house where I have many ducks, some raised by me and some wild. There has been a Mallard drake and Rouen female who have been mated since her mate was killed by a fox (It's been about a year now) now, about 3 months ago, I released 2 Rouen ducks, which I had raised, to live in the pond (One is a male, one is female) at first, the Mallard would attack them and chase them away from his mate... but as of a month ago he has become very dosile around them and started to molt his feathers... but they're all coming in brown and patterned like a female. He has stopped mating with his female, and now all 4 ducks are spending a lot of time together. I went on a vacation for a week, and when I came back, I thought he was a mottled duck because I didn't even recognize him!
So I guess, I want to know if it's possible for a male mallard to change sex?

 

[Pyxis]

Mallard drakes only have the male specific feathering part of the year. It's called nuptial plumage. The rest of the year, they are in eclipse plumage, which looks pretty much just like the female's coloring all year round.

 

[The Moonshiner]

They get the more camouflage pattern of the female to help protect them from predators while they moult their flight feathers and can't fly or fly well.

 

[sourland]

X 2 what Pyxis said. He will color up again, and next spring he may very well become aggressive towards the other pair.