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Solution by Bryan Guarente and Tony Leukering
Bryan Guarente provided an interesting and enlightening tack to the correct answer, so this solution will start with his words.
"We have a duck. There are only four ABA-area duck species that have black breast and vent with a white mid-body: Canvasback, Tufted Duck, Greater Scaup, and Lesser Scaup. I think we will see that a hybrid is not indicated because of the purity of the features on this bird. There is little that would indicate any other genes in the pool. The vermiculated back rules out Tufted Duck and Canvasback, leaving us with the conundrum of the scaup/scaups (sp?).
"Let's start at the front of the bird and move to the middle to determine what this bird is. The nail of the bill is small and black with no apparent stretching of the black in the horizontal along the edge of the beak (score: Lesser 1 :: Greater 0). The head color is purplish not greenish. It is hard to score lots of points for that because lighting can be especially tricky with anything iridescent (score: Lesser 1.5 :: Greater 0). The eye sits relatively far from the top of the head (score: Lesser 2.5 :: Greater 0). The highest point on the top of the head is well behind the eye and even shows a bit of a crest. Occasionally, Lesser can show a rounded head like Greater, but that usually occurs in actively diving birds, and Greater never seems to show a crest; the change typically goes the other way, where Lesser seems to have more of a rounded crown (score: Lesser 3.5 :: Greater 0). Only when you have good to great close-up views of scaup can you see the difference in the vermiculation density and extent. I can't say that I am confident in writing about the vermiculation on the back, but supposedly, Lesser shows fewer bars that are heavier than on Greater Scaup. More important to me, Lesser has vermiculation that extends beyond just the back, as the sides have vermiculation on them near where they meet the back. This only occurs in Lesser and is usually only visible in great specimens without much wear and usually manifests as a slightly dirty-looking side for Lesser versus Greater (score: Lesser 4.5 :: Greater 0). [Beware of over-exposure of photos like in the back of the white sides of this bird where the sensor is saturated; dirtiness disappears very quickly.]
"I don't see anything that would point to hybrid. We are sitting in a close battle (HA!) with Lesser Scaup way ahead. There is nothing Greater here that I see. I'm going with Lesser Scaup."
Indeed, Bryan covered most of the points, but I will expand on a couple. Head shape in the two scaup species is different in many more ways than simply the shape of the crown. As Tyler Bell noted, I wrote one of my In The Scope articles for Colorado Birds a while back on this very topic. Greaters have blockier heads that tend to look longer (deeper; forehead to nape) than tall with the high point in front of the eye and with very noticeable jowls in a head-on view. Lesser Scaup has a smaller head that usually appears taller than long with the peak behind the eye and with minimal jowls (unfortunately, not visible, here).
The big difference between the two in crown shape is that Lesser either typically holds its crown feathers more erect or they are simply longer. Or both. Thus, there is more head above the eye in Lesser than in Greater, with the eye just about centered top to bottom on Lesser and placed noticeably closer to the crown than the chin in Greater. As Bryan noted, this feature goes out the window with actively foraging Lessers, as they depress their head feathers before diving and may not re-erect them upon surfacing if they are going to immediately head back under the surface. I cannot tell you how many times that I have thought myself looking at a distant Greater Scaup, only to have it cease diving and turn into a Lesser.
Bryan and others also noted that our quiz bird's flanks are overexposed, a feature that I hoped to take advantage of in this picture, because Greaters do tend toward whiter sides/flanks. However, this feature can be tricky, because immature male Greater Scaup can take quite a while to completely replace brownish side and flank feathers in their preformative molt, which can extend into March. Additionally, as obliquely referred to by Bryan, worn male Lesser Scaup may have no apparent vermiculations on the sides, presenting a bright white appearance. So, in late fall and early winter, a male scaup showing bright white sides/flanks is almost certainly a Greater, while such birds in March and beyond could be either.
Finally, while many Greater Scaup have the black of the bill nail extending onto the bill proper in a trapezoidal shape, many have the black restricted to the nail, as in Lesser Scaup. I took this picture of an adult male Lesser Scaup on 2 March 2009 in the Palo Alto Baylands, Santa Clara Co., CA.
Incorrect species provided as answers:
Greater Scaup - 2
Congratulations to the 20 of 22 getting the quiz correct:
Kirk Huffstater
Tyler Bell
Robert McNab
Pam Myers
Margaret Smith
George Cresswell
Patty McKelvey
Peter Wilkinson
Christian Nunes
Nick Komar
Josh Parks
Claire Mix
Margie Joy
Jennifer Courtemanche
Thomas Hall
Bryan Guarente
Joel Such
Marcel Such
Sean Walters
Devich Farbotnik
Answer: Lesser Scaup
