DBQ answers

12 01 2016

I got quite a few responses to this one, and I am not surprised that our usual ringers were right in here with both the clear i.d.s and the one that is, at least somewhat, in question. All three birds are ducks which all respondents recognized. The first two are in one category–ducks with a bluish speculum on the wing. Bird C is in a category of ducks with blue on the wing, but with that blue located on the upper wing coverts rather than the secondaries as in Birds A and B. Let’s take the Bird A/B pairing first.

I like when I have an all duck quiz since I can use Samuel Carney’s Waterfowl Wing Key. When we follow through that key for a bird with blue or purple on the secondaries, we get to a junction point where we are asked what borders the blue or purple patch. If it is hemmed in with white both above and below (that is to say, with white on both the greater coverts and on the trailing edges of those blue/purple secondaries), then we have a mallard, like such:

800px-Mallard_pair_in_flight

Mallards in flight. (Photo by Ingrid Taylar)

In this photo, one can see not only the clearly bordered speculum, but another helpful feature for when you have the underside of the wing to look at as well–a mallard’s underwing is a clean, clear white. This is in contrast to our other candidate among the blue-speculumed ducks, the American black duck, which has a characteristic brown streaking on the underside of the wrist.

An American black duck (ABDU to friends) is generally described as having no white border, front or back, around the blue, though in many images and in some descriptions, one may see a faint pale trailing edge to the secondaries. It’s pretty faint though. Great, so that was easy, no? White borders: mallard. No white borders: ABDU. Not so fast (0f course). Because these two species heard we were having an easy time of their identification, they decided to hybridize freely. Given the slight chance of pale tips to the secondaries in an ABDU, we can look at the forward border of the speculum for a firmer sense of what is happening here. In an ABDU, there should be no white at all on the greater coverts at that leading edge of the blue speculum. So, where are we now with respect to Birds A and B? A shows substantial white both fore and aft. Bird A looks like a mallard decisively to me (my decisiveness here is augmented by back up from most of our respondents on this quiz). Bird B has what we might technically term a “meh” amount of white on that forward border of the speculum. It’s faint, but it’s definitely there. While some of our quiz players think ABDU on this one, others raised the possibility that this is one of those ABDU x MALL hybrids, and I am inclined to agree. Would that we had more of the bird to go on, but the features here do seem intermediate between the two species.

Now, to Bird C. This one is in the group of ducks with a large amount of blue on the upper wing coverts rather than the secondaries. It’s hard to know if the secondaries ever had much color–they may have, but as my next blog post will address, blues and greens in bird feathers are a trick of the eye, and in a disheveled specimen, those colors may be lost almost entirely. In addition, in some species, the secondaries are green and iridescent in males, but green and non-iridescent (dull) in females. I don’t see much that catches my eye in the secondaries of Bird C at all, but if there is any green there, I would say it looks decidedly non-iridescent to my eye. What we have to go on is the blue, and then some white on the greater coverts, though they do not appear entirely white–more dark spotted with white rims. In the group of birds with blue on the coverts and a white band on the greater secondary coverts, our best candidates are blue-winged teal and northern shoveler (both raised by our respondents). How to differentiate them? The number one feature all the field guides point to are the distinct white shafts of the primaries in northern shovelers. Take a moment to appreciate them in this image:

 

Screen Shot 2016-01-12 at 11.05.37 AM

USFWS photo

As you can see in these images, the white band on the greater coverts in northern shovelers is uninterrupted, unlike the broken band with dark spots we have in Bird C. In addition, I do not see these obvious white primary shafts in Bird C. Taken together, these two features lead me to call this a blue-winged teal, and again, I draw unnatural courage in this i.d. from the fact that it came to me pre-identified by Craig Watson who works for USFWS down south, and also, so many of our crack dead bird experts told me they thought it was a blue-winged teal as well. I hardly ever see these, so I confess, I would not have come up with that right off the bat.

Next time, I will share with you what I’ve been reading about feather pigment, honest signals, and the flamboyant tails of motmots in the Yucatan.

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