Using a mallard call in the area isn't all that crazy...those ducks spend all year together, and sometimes respond very well. I'm sure we've all had Redheads, Ringneck, Pintail, Gadwall, Widgeon, Teal, Wood Ducks etc come in feet down over mallard decoys while sending out a few quacks to draw attention to our spread.
Also...there is a location along the Texas coast, locals say it holds mallards when daytime temps remain cold. It's an area between two islands one big & one small. One is named after a type of horse, and the other famous for fishing in the fall. To simply tell you the exact location would be a sham...I would rather be struck by a rock than tell you where they can be found.