Those March/April birds are returning birds most likely. Redheads and Pintails winter down past the Laguna Madre into central Mexico and are some of the last to return.

The reason you see all those birds right after the season has to do with hunting pressure. They magically appear just after the season is out. Been that way for years.

The best thing that could ever happen to this State would be to force Alabama Power to put in some de-watering units along all the river shoreline they have raped and pillaged from the citizens of the State of Alabama. They haven't done a single thing for waterfowl that I know of other than direct the Marine Police to write you a ticket if you get out of your boat. Nobody ever thinks about that. Not a single piece of habitat improvement that I am aware of that was significant in any way.