they look like Hen Mallards, only "just a litte smaller" and "just a little different", and would definately get you into trouble....no doubt about it.....
Mottled Ducks are part of the Mallard Complex and as such are highly susceptible to gene flooding by the more aggressive Mallard.....used to be the other ducks in the complex maintained their integrity by a disassociation with Mallards on the breeding grounds even though they did mix on the wintering grounds.....
Mexican Ducks and Black Ducks have been swarmed by "feral" -"non-migratory Mallards" which seem to be more attractive to the hen's of the more somber colored species than their own species....
Mexican Ducks had a very limited range and were ultimately decided to be merely a "sub-species" of the Mallard.....I've always thought this was done because the "pure" line of Mexican Duck, at least in the U.S., was lost forever and if they had remained a full species then they would have had to have been listed as "endangered"...and that would have meant the closure of Mallard season in places where the remnants of that once unique bird occurred...and you know that wasn't going to be allowed to happen....
Mottled Ducks used to actually be considered to be two destinct sub-species...the Florida Mallard of the Southern Florida Peninsula, (Orlando and South with the occassional wanderer to the North), and the Mottled Duck of the Louisana, Texas Coast......the sub-species classification was dropped, (even though there was a geographical seperation and some noticeable taxinomic differences), and the bird became commonly known as "Mottled Duck", (although you will still hear some old Florida Duck hunters refer to them as "Florida Mallards", or "Florida Ducks").....younger Florida hunters seem to have settled on Mottled Duck which while I dislike, (as if anyone cares or asked), although not nearly so thoroughly as the even more common "MOTTLES"....acccckkk phhhhffffbbbbbbttttt).....
These days the "gap" in the range between the Louisiana/Texas population and the Florida population has closed....as Carl says there is a resident population in Alabama where in the 70's they were unheard of...and in Florida they are now common nester throughout the penninsula and into Southerrn Ga.....
They are one of the species that is always expanding its range Northwards and are often seen far from normal range, (for instance there are at least two records of them in Washington)....
Sadly the Mottled Ducks days as a pure species is fading...just as the introduction, and natural expansion, of Mallards to the NE has created a serious dilution in the Black Duck gene pool so too has the introduction of Greenheads to Florida in the form of feral birds, (everything from abandoned Easter ducklings to the game farm released birds to the agonizingly stupid Mallard release programs in S.C. and Va.), so that now instead of being "mixed" on only the wintering grounds they are now "mixed" on the breeding grounds as well.....
Florida Mallards were, and still are, a very special duck for me...my first BIG duck and always a rare one and remain a bird that I look forward to seeing, and shooting, when I'm in Florida so it hurts me to see so few of them in their "pure" form.....Florida has a well intentioned program that allows the killing of Feral Mallards outside the regular season but even if it had 100 times the participation that it now has they'd never remove enough park Mallards to stop the hybridizing....
I'm not sure what the status is in the Texas/Louisiana populations but I do know there are no shortages of feral, non-migratory populations of popcorn eaters and greenheaded trash ducks, so if there isn't already a noticeable hybridization problem there will be one soon.....
If you ever shoot what you think is one....COUNT IT AS A HEN MALLARD...unless you are in Southern Florida, Louisana, or Texas....you'll be safer for the decision.....
Steve