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IVORY-BILLS  LiVE???!  ...

=> THE blog devoted to news and commentary on the most iconic bird in American ornithology, the Ivory-billed Woodpecker (IBWO)... and... sometimes other schtuff.
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"....The truth is out there."

-- Dr. Jerome Jackson, 2002 (... & Agent Fox Mulder)

“There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy.”

-- Hamlet

"All truth passes through 3 stages: First it is ridiculed. Second, it is violently opposed. Third, it is accepted as self-evident."

-- Arthur Schopenhauer






Friday, June 12, 2009

 

-- Of PIWOs and IBWOs --

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Somewhat oddly, in the last two months 4 different people, from different locales, have sent me either pictures or verbal descriptions of 'abnormal' Pileated Woodpeckers (PIWOs) they've seen, with small patches of leucistic white feathering on the back or wings. These were all cases of small, virtually insignificant (and UNsymmetrical) white patches on birds that couldn't conceivably be mistaken for Ivory-bills; indeed several such Pileateds have been recorded by now. But it does all remind one of the more fully white specimen that Cornell noted flying around the Big Woods over 3 years ago.
As I wrote at that time, the concern should not be about that particular leucistic bird (which also couldn't realistically be mistaken for an Ivory-bill), but rather about the possibility of its having parents, siblings or offspring (or even offspring's offspring) that might exhibit some intermediate degree of leucism, which by sheer chance might mimic the pattern of an Ivory-bill. Such a bird was claimed in Florida in the 1970's. If there were in fact such specimens flitting around here-and-there
through the Southeast, mimicking Ivory-bills on rare occasions, it might explain a lot --- indeed, in an older post, I called it the only real leg IBWO skeptics had to lean on.

And still today I believe the two likeliest possibilities to account for the full panoply of Ivory-bill sightings on record are:

A
) Some Ivory-bills exist, or

B
) Bilateral, dorsally-symmetrical leucistic Pileateds, matching the pattern of IBWOs, exist scattered thinly around the southeast.
(...and then one must still account for all the potential IBWO sounds, signs, and possible other data recorded; do-able, but no easy slam-dunk)

The ad-hoc generalization that normal Pileateds (and other even less likely surrogates) can account for ALL IBWO reports of the last few decades, from different observers, in different locales, under different circumstances, is but slimly fathomable (except by examining a mere subset of those reports). So while skeptics await a clear photo of an IBWO to move them forward, I await a clear photo of a look-a-like leucistic Pileated to alter the debate. Without it, possibility "A" above remains the simpler, more plausible scenario.

Meantime, Cornell reports at their website that this search season is over and they will post a summary report sometime during the summer. ...Translation: an official summary might see the light of day by next January.
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Comments:
Even Noel Snyder's pileated did not have symmetric white secondaries. Of course I don't know, but it is possible that this anomaly was an extreme example of something that is apparently rather common in pileateds. The tips of the flight feathers are sometimes pale. Apparently the pigment does not always distribute well down the feather, for whatever reason. In exceptional cases pale color may be extensive, but from what I have seen it is generally pale brown, not snowy-white. In the few cases I have seen where light color is extensive, individual feathers show this to very different degrees. Nothing like a smooth, snow-white trailing edge is produced.
 
For the most part what your readers are describing is not leucism nor is it abnormal. It is a common feature of normal Pileateds especially during molt when there are a few missing black feathers revealing white feathers that are usually concealed when perched. It has always been out there, but people are noticing it more now. The one Pileated I have seen in captivity (at the zoo in Nashville) has extensive white blotching like this, presumably from feather damage from either its close confinement or the injuries that lead it to become a captive rescue bird in the first place. When birds like these fly they reveal a perfectly ordinary Pileated pattern, with black and white in the flight feathers right where it belongs.

The documented cases of Pileateds with pale flight feathers I have seen have involved the primaries, not the secondaries, and as Fang noted the color is usually brown, not black. There is some indication though that this "brown" can image as white on black-and-white Reconyx cameras, which shoot in the near infrared rather than visible. Still, on a perched bird it makes light patches on the back that are much lower placed and smaller than the Ivorybill "white shield" created by white secondaries.
 
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