I wanted to thank all of you who responded to this thread (both on and offlist). We may never know the exact lineage of my duck, but I've learned a few things. For one, when trying to identify this bird, I first looked at the plumage and tried to figure out what it looks like. This approach had me almost totally convinced that my bird was a Blue-winged X Green-winged Teal hybrid (thanks Matt!). However, the facial pattern doesn't quite match, the chest coloration appears different (could be lighting, though), not sure about the speculum, size wasn't quite right, and the sound I heard the bird making was not a teal sound (always was a vocalization freak). So, I followed Sebastian's advice and checked out "Brewer's Duck." Like Ann, I didn't get it. I could not see Mallard or Gadwall in my bird at all (well, maybe the chest color and rear-end pattern. So, Brewer's Duck wasn't working for me. I think we can rule out Eurasian Green-winged Teal (bummer!), as well. I found myself lost in a tough ID conundrum....
After reading through the emails from the ID-Frontiers folks and an enlightening discussion with my friend KM (thanks!), I am leaning strongly in favor of a "Brewer's Duck"-type of handle for my bird. Here's why: a number of resources on duck hybridization (cutting-edge ornithology) point out that when ducks hybridize, they will often show a recessive trait (like an odd facial pattern) from a long-forgotten ancestor, rather than plumage details of either parent species (Mendel and peas stuff, I guess...). So, we may have been heading the wrong way by trying to match plumage details of my bird to potential parent species! The other things that have me leaning "Brewer's Duck" are: 1) the size of my bird isn't right for a teal bird is to big, even with accounting for sexual dimorphism. 2)the vocalization isn't right for teal, but perfect for a Mallard/Gadwall type of bird. 3) here is the kicker...the underwing! A fuzzy photo that I was embarrassed to post shows a fuzzy, blurry all-whitish underwing and my field notes alluded to this, as well. I got 2 quick looks at the underwing in the field and all I saw was whitish underneath. I began to discount this observation because it was so brief, it didn't fit for a teal (I didn't want to look dumb), and frankly I spent almost all of my time in the field trying to get that knockout photo of the underwing (rather than taking detailed, thorough notes like KM expects me too : )  Anyway, I think that a teal hybrid would have shown a teal-like underwing (whitish armpits and secondary coverts and dark edges and wingtips), but the underwing of my bird would absolutely support a Mallard or Gadwall parent species (which leads me again toward "Brewer's Duck!).
In short, I think now that the head pattern of my bird may be some 100,000 year old genetic remnant of an ancestral forebearer of today's ducks known as "Mallard" and "Gadwall".  With that in mind, I believe that the other plumage details may indeed support a "Brewer's Duck" identification.
OK, I need a beer...
Doug Willis
Liberty, MO
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P.S. Please feel free to chime in (on or offlist) with corrections or contributions!

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