Living the Scientific Life (Scientist, Interrupted)

tags: Wood Duck, Aix sponsa, birds, mystery bird, bird ID quiz

Rick Wright, Managing Director of WINGS Birding Tours Worldwide, writes:

What a sweet bird, friendly-looking and gentle! From near-extinction less than a century ago, this species has rebounded in its North American range to be the most abundant breeding duck in the eastern US -- and it is increasing in the west, too. Thanks to the profile view, we can start at the rear, where we're impressed by the long tail and long wingtip. There aren't many long-tailed ducks (I mean ducks with long tails); wigeons and Northern Pintail come to mind, as do Hooded Merganser and Wood Duck, plus a few seaduck species including the capital "L" Long-tailed Duck.

The extensive blue and white on the wing-- unusually noticeable in this pose -- identify our mystery right away as a Wood Duck. The diffuse white blotches on the flanks, the extravagant crest, the long "teardrop" around the eye, and the gray face and bill confirm the identification.

The alert among you will be wondering how we can rule out another species of Aix, the lovely little Mandarin Duck, which is frequently seen as an escape from captivity all around the world and has established breeding populations in western Europe and the US. A female Mandarin would never have an eyepatch this broad, usually showing instead a narrow eyering and "bridle" extending back onto the side of the head; the sides are more distinctly and more regularly spotted on Mandarin, too. The feathering at the base of the bill is slightly more vertical on Mandarin than on Wood Duck, in which, as here, the feathering extends onto the base of the bill. The very tip of the bill is pale in Mandarin, dark in Wood Duck. A distinguishing feature I have just learned myself is that the secondary coverts in Wood Duck are blue with a black terminal bar, plain in Mandarin Duck; it's a rare view that lets us make that determination, but we have here a rare view.

Because both species are common in captivity, both can be seen anywhere in the world; and because both are common in captivity, those escapes can include birds with puzzlingly anomalous plumage features. The list of known hybrids involving one or the other of these two species covers two pages in McCarthy [Handbook of Avian Hybrids of the World, Eugene M. McCarthy, Oxford University Press, 2006], making it always possible that a wandering Aix is the product of some odd miscegenation. Just as confusingly, both captive Wood Ducks and Mandarin Ducks occur as blond "sports," pale beige birds that in the worst of cases can be distinguished only by the shape of the feathering at the base of the bill. So look closely at Wood Ducks -- if not for their uncontested beauty, then at least for some small sense of certainty that that's what are actually looking at.

Review all mystery birds to date.