White Headed Drake?

[azhenhouse]

I agree with learycow, I think he is molting. I have one drake that looks like yours and the other one doesn't. Here are their pictures.

 

[roocrazy]

he is entering a stage of molt called eclipse...he'll almost look like a hen.

 

[LLCoyote]

Wow... major embarassment... I got them about 8 months ago and they were around a month or two old. It's just about time for him to molt so that could totally be the problem. I'm not sure why I didn't think of that x.x