The birds are black-bellied whistling ducks. As you have said, they are traditionally a tropical weather species but in last 30 years have made massive range expansion north. Louisiana now has more than 30,000 breeding black-bellies. They have been steadily moving north with the first nest in KY a few years ago. They are classified as a duck per federal/state hunting regulations. They can be hunted in Kentucky during regular duck seasons (Thanksgiving and later). Unfortunately as warm weather species they seem (even in Louisiana) to be headed south before regular seasons.