Mystery Bird: Male Lesser Scaup, Aythya affinis

Well, clearly a scaup. I'm going with Greater Scaup, based on Sibley's face-on comparison illustration, which shows a fatter head and a wider bill on Greater, which to my eye more closely matches this bird. I'd mention the purple sheen on this bird's head, too, but Sibley claims that the "oft-discussed head color differences in scaup are essentially useless in the field."

Going to go with lesser scaup. That purple sheen is pretty pronounced and the shape of the head appears to peaked as it would be in a lesser scaup. Using a photographic guide -- Birds of Eastern North America -- to help me with this ID

At work I am never able to load the photos so I will have to confirm when I eventually get home, however without even seeing the photo, my first "hunch" is based upon the fact that if the photo is indeed a Scaup (and not the similar Ring-necked) then because the lake at the Tom Bass Regional Park in Houston is a fresh water lake, it probably excludes the Greater Scaup (although I believe Lesser Scaup do sometimes frequent salt water in migration)...

I think I'll have to agree with Lesser Scaup, but for a couple of reasons not yet mentioned. First, the vermiculations on the back and sides appear rather coarse. Second, the bill appears straight-sided -- a Greater should spread outwards at the tip. Third, the black on the end of the bill is confined to the 'nail', instead of spreading out to either side.

I can't speak for Texas -- Sibley's shows Greaters as vagrants to the coast, and Nat.Geo. shows them as winter residents throughout east Texas. Here in Illinois, we find large flocks of both species on Lake Michigan, although Lesser's are more common on smaller bodies of water.
When I'm looking at Scaup, I usually look at the head shape -- with a bit of practice it's not hard to distinguish the two. At this angle, though, I can't see enough to use it.

OK, home now- I definitely agree this is a Lesser Scaup (Aythya affinis) but am a little puzzled by the season as it appears to be still in breeding plumage (end of November?): head, neck, and breast black; head with purplish iridescence; bill bluish with conspicuous black nib; back white, covered with thin, black wavy lines; white flanks (in non-breeding plmage I would expect to see some white edging on the breast and more of a brownish mottling on the back and sides)

Immediately excluding the somewhat similar Ring-necked Duck (Aythya collaris) because of the lack of white ring in the bill and absence of white stripe up the shoulder)...

I agree with Paul re. the black markings on the bill- in Greater Scaups (Aythya marila) I've also noticed that there is some "bleeding' on the edges, but not always- a better differentiator, I think, is the relative broadness of the bill, with the Lesser having a greater curve to the upper bill creating the flattened look... with reference to the head shape, I think at this angle one can indeed see clearly that the "bulge" is not on the front but widens at the back of the head (Lesser) whereas if this had been a Greater we would have seen an obvious bulge on the forehead.

As with John, I have found reliance upon the greenish (Greater) or purplish (Lesser) sheen on the head has been said to be unreliable however not because the light might make the green look purple or vice-versa, but because identification in poor light or at a distnace may not show the sheen- therefore, if one can indeed observe the sheen, I would argue that it is a positive ID as in this bird- Lesser Scaups have a purplish sheen, not green.

David, Scaup follow a typical duck-style molt strategy. Eclipse plumage is seen from July into early fall -- made ageing and sexing them a mess in August. By November most species have molted back into their typical plumage. (Two exceptions are Long-tailed Duck with a full winter plumage and Northern Shovelers, where the males at least take most of the winter for their molt back to breeding plumage.) The breast on this bird shows pale edgings, indicating very new plumage. I can say from experience that birds here in November show no sign of non-breeding plumage.

Thanks Paul, I see the edging now...

Would it be fair to say then that as in this case, as some duck species will molt in the Summer and stay in eclipse for this 3-month period (during which they also renew flight feathers) and then not have their second molt until the Fall (but other species will delay their second molt until the early Spring?) it would appear that a greater advantage is had by looking good early over migrating?

I understand that when paired, the female Scaup makes the choice of mate, so is there an age-correlated behavior where an advantage can be gained with older ducks coming out of eclipse earlier than younger ones, or is it that younger males look better earlier because they are seen (proven) to be more virile?

David -- I'm not really sure what drives the variation in molt timing for ducks. I do know that spring migration is typically earlier for ducks than most of the passerines, just as fall migration is somewhat later. I also know that at least some ducks pair in late winter before migrating north, in which case there would be a definite advantage to having breeding plumage on the winter grounds.

Yeah, I spoke too soon on this one. I even had misremembered which way the greenish-sheen/purplish-sheen arrow pointed. Now I want to go see some scaups IRL. :-)