DBQ answers

9 12 2015

Let us address Bird A, who met a bad end (and a Cessna) at 3,200 feet. The head was torn off by the force of the impact, and, left with only the feet and legs, and a bright white belly, we must make this i.d. without the benefit of a look at its back or upper wing surface. Some folks who examined the photos thought perhaps it was an oystercatcher, but looking at the feet especially, we can rule that out.

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Plane Bird feet

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Oystercatcher feet

Comparing the feet side by side, we that Bird A (Plane Bird) has a grayish cast to the legs and feet, with black coloration on the outside aspect. Bird A’s legs are also extremely flattened side to side, with a very narrow front profile. (Compare the width of the side view of the right leg with the left leg which is rotated so we see it head on). This gives the leg a blade like appearance. The oystercatcher’s legs are more rounded, and the extreme lateral flattening of Bird A’s legs is a fair giveaway of what species group we have here, and rules out other black and white birds with more rounded legs (like the alcids). There’s really nothing but a loon that shows this lateral compression of the leg and even toes to such an extent. It’s hard to appreciate the webbing in loons in many cases since their toes tend to fold together in a dead specimen. Take a look at this reference picture of a known loon and compare the features of the feet with Bird A, noting the color, the length of the three forward toes, and the extremely reduced hind toe in both specimens:

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common loon carcass (Photo by Gil Grant)

So the feet say loon, but what kind of loon? Our most likely suspects are common and red-throated (COLO vs. RTLO). Unfortunately, the best ways to distinguish the two are via features of the head and neck (absent here), the measurements (no size reference here), and the pattern of the feathers over the back and upper wing (not visible here). Can we make this i.d. to species with what we can see? Much as I wish otherwise, I do not think so. I was hopeful that something like the black stripe across the vent in Bird A might help, but take a look at these reference photos of various vents from various loons:

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RTLO with very faint dark line across vent. (Photo by Sarah Porter)

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RTLO with basically no vent line. (Photo by Jerry Golub).

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COLO with a fairly prominent vent line. (Photo by Dennis Minsky)

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There are cases (like differentiating Arctic from Pacific loons, apparently) where presence versus absence of a vent line can be your make or break feature. But for us, deciding between RTLO and COLO, it’s not much help. Either species can have a faint or a prominent vent line, so the fact that Bird A has a visible one doesn’t really tell us much.

Live birds flying overhead are sometimes the closest (ironically) we can get to the situation of trying to identify a dead bird from features of its undercarriage, and I refer you to such a case posted at the American Birding Association’s website here. In their analysis of that bird’s i.d., they point to a sense of how big the feet are relative to the body. Common loons have absurdly large feet compared with RTLO, whose feet tend to look more normally proportioned. You can appreciate this a bit when you compare the images above of the feet on RTLO vs. COLO. Which is true of Bird A? Huge feet, or not so huge feet? That’s a bit hard to tell from the angle we have. They seem somewhat outsized to me, but I’m not feeling super confident on that. Bob, who collected the bird from his plane’s wing, submitted feather samples to the Smithsonian for i.d. to species, so hopefully, we will receive word from on high for this one. Bob did email this week to say he has yet to hear from the Smithsonian. Perhaps we should run a letter writing campaign and on site protest bearing signs that read, “Who is Plane Bird!?”

I still have Bird B to address, but right now, I must run to pick up the kids. Next installment will be before your eyeballs later this week, I assure you.

 

 

 

 

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