March 2 Update
Since viewing this bird on Feb 27, I have returned to the pond on two subsequent days to view the bird resulting in unsatisfactory great looks nor photos.
I have since read the works by Jack Bushong ("The Bird We Always-Never Knew", March 12, 2020; ABA Media; Columns; Field Ornithology; American Birding Association) and by Steven G. Mlodinow ( "Mexican Duck Photo Essay", March 12, 2020; ABA Media; Columns; Field Ornithology; American Birding Association).
Their comments on field marks I observed (one central tail feather very slightly curved) and the width of the white bordering the speculum; both are acceptable for Mexican Duck.
Jack speaks of this species as being detected in March-April in the Denver area primarily due to the abundance of birders there. Good luck and hope more can be found. Steven's wonderful photo essay can give one a solid base of what to look for. As well, Macauley Library have lots of photos for review.
And the female of the species is difficult to discern - maybe we can find more of them too.
Original notes
Mallard like duck with a very bright yellow bill, light brown neck demarcated just above a darker brown breast and body, dark eye line on a light brown head with a dark cap. Paired in vicinity of a female Mallard. There was a slight curl on the tail tho’ unable to get a photo of this field mark. In flight the speculum had wide white bars. These two field marks lend to a hybrid I think. Photos tba.
