I truly think you have a male and female....If they were both males, both would have the green on the head. But I am probably the last person you would want trying to help you sex a duck. LOL. I have 3 rescues myself and one purchased drake. He was supposed to be a Mallard as well, but I have my doubts. But the others, well they started getting their adult feathers, it was pretty hard to not see which were male and which were female. The males all got the green heads, and the females all turned brown with no green in sight Other than the tops of the heads, they all look pretty much the same though. Their bodies are all brown right now. Except for the grown drake I have. He is graying out after moulting, but was colored out when I got him. I hope this helps and doesn't confuse you even more...