Duck breed

[Flying Cat Coop]

I'd bet you're right. The bill color and that bit of black around his bill.. looks like the remnants of nuptial plumage.

If this is the case, you'd do best to add quite a few more females before spring. That or rehome a male.

I would only want to add 1-2 more females so I think one of the males is going to have to go.