Mottled ducks are a southeastern/gulf specie year-round. They're typically down in Florida, Louisiana, Alabama, Miss, etc. Sounds to me it was a hybrid AMBD x MALL. If one WAS to be shot up this way, it'd definitely be a vagrant & unlikely IMO. It's tough to say though because most hunters wouldn't be able to tell the difference, considering most have issues ID'ing ducks as it is.