Unknown duck

[Shortsighted]

At first I thought this might be a Blue-winged Teal in eclipse plumage but it does not
have the white around the eyes. It's not a Mallard, or a Gadwall.
Guidance would be appreciated.
There were Green-winged Teal around (much smaller bodied).

[Paul O'Toole]

I am thinking a Gadwall.

[Shortsighted]

Thanks for your opinion.
I thought the forehead slope was not abrupt enough for a Gadwall and the bill is so slim,
like that of a Pintail or BW Teal. Even the pattern on the flank confused me. Then again,
even a sunrise confuses me, so it doesn't take much.

[Canoncan]

I am thinking a female Blue-winged Teal, Gadwall usually has white secondaries patch visible and this does not, but a picture is a picture, lots of behaviour could show it or conceal it.

[Shortsighted]

I thought the female BW Teal has white around the eye, while the male
does not. That's why I figured an immature male, which like most water fowl
tends to resemble a female. I wish I could locate BW Teal often enough to
learn what they look like.

[Rotarran]

Could be Green-winged Teal.  

On Allaboutbirds we see this picture of a female BWT


And now an image of a female GWT


I think the GWT is closer to the bird you photographed.

[Shortsighted]

Thanks for your suggestion. I also thought GWT (female) except that the GWT that were on site
appeared smaller and fed in small groups employing that repetitious dabbing motion.
The duck I photographed (from a distance) was alone and somewhat larger in size, but not as large as a Mallard, or Black duck.
I hardly stopped to feed at all and kept its head above water.

[Rotarran]

Did you take more pictures?  Maybe beside other ducks?  That way we might be able to compare its size to the other ducks (of other species).  Maybe it is a hybrid or a particular large Teal.

[thouc]

The body pattern feels more like Blue-winged Teal than Green-winged Teal to me.

/Thomas