What Am I?

On my Sunday hike in Back Bay National Wildlife Refuge, I saw a pair of these, swimming together in the marsh.  Can you figure out what they are from my clues?

Your first clue, and you are in luck,
Is to tell you that I'm a duck

That narrows the animal field
But the answer's not yet revealed

For though a duck, what is its kind?
Continue on, if so inclined

Was it of marsh, or of the sea?
'Twas in a marsh when seen by me

A color makes part of its name:
Primary color, I proclaim

It's speculum is blue as sky;
A white half moon leads 'fore its eye

In its name is a body part
Come on, think hard, be very smart!

This body part's of birds, not man,
And often measured by its span

I think you have enough clues now
To get the answer, I avow

Review the clues and take your guess
And if you're wrong, no need to stress!

Scroll

D

O

W
N
to reveal
what kind
of duck
I saw:

The answer to you I reveal:
A male and female blue-winged teal

You cannot see the blue speculum with its wings folded, but on the drake, the white half moon in front of the eye, and the white patch near the rump are the identifying marks.