The posted photographs are certainly worth a close look - a very intriguing
question. I had not realized before how difficult it is to distinguish
between female and/or juvenile Blue-winged and Cinnamon Teal with the males
are not present.
I checked Sibley's field guide, Cornell's "all about birds" website, and a
few other internet references.
Female Blue-winged Teal have a dark eyeline that contrasts with the part of
the face above the eyeline (which appears like a light supercillium - but
none of the references call it that), and with the rest of the face that is
grayish brown. Female Cinnamon Teal have a mostly uniform, warm brown face.
The references also note that Cinnamon Teal has a longer, heavier bill than
Blue-winged - almost approaching the large bill of a shoveler.
The two birds in the photo have a dark eyeline and contrasting face, and
the bill is not so heavy - it appears the bird carries it's bill
gracefully, definitely not out of proportion with it's head.
The references note subtle differences between the boldness of the pattern
made by body feathers and the light colored spot near the base of the bill,
but those field marks didn't help me one way or the other.
So - based on the dark eyeline and relative heaviness of the bill, I think
they are Blue-winged Teal.
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