Neat photos of an interesting bird! 
I still lean towards Green-Winged X Blue-Winged hybrid.
Not sure if the link I sent worked last time, but here is
another try:  (you can scroll thru several shots).

This was a captive bred bird, so at least its parents are known... and in my
humble opinion it looks strikingly similar to Doug's bird.  Of course, not all hybrids
are pure either, as they can get cross-bred to infinite levels.  As I looked at various
other captive cross-bred bird photos, it seemed a little weird, maybe even unethical to
some... but I suppose if you consider them as 'pets' and how most dogs are
mixes of something or other, then maybe it is not as bad?...

Good Birding,
Matt Gearheart
Shawnee, KS
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On Sun, Apr 4, 2010 at 8:13 PM, Doug Willis <[log in to unmask]> wrote:
Here is a post that I sent to the ID-Frontiers listserve. There are more comparison, profile and preening shots (including one that almost looks like it has a white scapular line...arrrrgh!) added to my flickr page. Thanks Linda!!
Doug Willis
Liberty, MO
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----- Forwarded Message ----
From: Doug Willis <[log in to unmask]>
To: [log in to unmask]
Sent: Sun, April 4, 2010 8:08:41 PM
Subject: Interesting Teal found in NW Missouri, USA

Hello Everyone:
I found and photographed a teal at Squaw Creek National Wildlife Refuge, NW Missouri yesterday, 4-3-2010, that has me perplexed. At first, I tried to make it into a Eurasian Green-winged Teal, but the lack of a prominent white scapular bar and other plumage details gave me pause. Next, I tried to apply the "transitional 1st year Goldeneye" formula (we get a lot of those here in NW MO) and opened my brand new Pyle Guide for guidance, quickly realizing that I'm in way over my head. Now, the specter of hybridization has entered the equation, with knowledgeable birder's from my area hypothesizing Blue-winged X Green-Winged Teal hybrid and "Brewer's Duck (Mallard X Gadwall hybrid). In short, we need help with this one, folks.

I never got a good shot of the underwing (or a really good look) and the size impression in the field was slightly, but noticeably, larger than nearby Blue-winged Teal. The vocalization was a raspy, nasally "wheeeemp" (in a quacking sort of way); rather like a snipe, but quieter.
Many Thanks In Advance!
Doug Willis
Liberty, MO USA

The Audubon Society of Missouri's Wild Bird Discussion Forum
ASM Spring Meeting: April 30-May 2. Cape Girardeau, MO

The Audubon Society of Missouri's Wild Bird Discussion Forum
List archives: https://po.missouri.edu/archives/mobirds-l.html