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ABA Online Bird Photo Quiz 109

Answer

[+] Click Image for Larger Version

Quick! Waterbirds overhead! What are those?

While loons and grebes might be considered, our quiz birds’ red bills rule out all of those options, leaving us with ducks. Of course, there aren’t that many duck species with red bills (or, even, red on the bill): Wood Duck, perhaps a couple eiders, and a couple mergansers. Since the two species of eider that sport reddish on the bill do so only as high-plumaged males – and our quiz birds are obviously not that, we can rule out King and Spectacled eiders. In Wood Duck, too, bills with red are restricted to males, but in this case, males in most plumages have red on the bill. They also sport an odd pattern of white on the head, as do our quiz birds. However, male Wood Ducks have considerably less white on the underparts than shown here and have entirely dark undersides to the wings, so we’re left with the two species of merganser that can cause birders a bit of bother: Common and Red-breasted. The complex pattern of white on the heads of these birds is typical of youngsters of both species, being a feature of juvenal plumage.

While typically not very visible in the field, the precise pattern of the undersides of the wings can allow for separation of these two species, particularly in static pictures such as this one. Adult male Common Mergansers have dark primaries from below and a small bit of dark along the leading edge at the wrist; all the rest is white. Female and immature male Common Mergansers have a similar pattern, but with addition of a dark spur projecting almost to the body along the base of the secondaries and an almost albatross-like thumbprint in the patagium (between the wrist and the body). The underwing patterns of the two sexes of Red-breasted Merganser do not appreciably differ, but they are subtly different from those of non-adult-male Commons, in that they lack the thumbprint and that the dark spur along the base of the secondaries is shorter, ending well before the body.

While the underwing pattern is best seen on the upper bird of our four quiz birds, it is also detectable, if barely, in the left two birds on the bottom row. There is a short, dark spur extending from the primaries along the base of the secondaries ending well before the body and all three of these birds seem to lack the dark patagial thumbprint. Sharp observers will also have noticed that our birds sport dark patches around the eyes, a feature of molting immature males in their first winter/spring as they begin growing in the dark green head feathering typical of male Common and Red-breasted mergansers. Finally, the sharpest will have noticed that the bottom right bird has a reddish eye, ruling out all ages and sexes of Common Merganser.

I took this picture of four immature male Red-breasted Mergansers at the Cape May ferry terminal, Cape May Co., NJ, on 12 March 2011.

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The following people (listed by submission date beginning with the earliest) submitted correct answers for the April Bird Photo Quiz—Red-breasted Merganser: