Friday, July 06, 2007

Bevier speaks.

Well, ok, he writes. Louis Bevier has posted his overview of the Ivory-billed Woodpecker situation. For those who have lost track, he is one of the Als in Siblet et al. Disappointingly, his article consists of nothing but a rehash of old arguments. Some of these have been agressively rebutted, a point he seems to find unimportant. In specific reference to the Luneau video, he still claims that the video shows conclusive features that identify the bird as a Pileated. He repeats the same, pervasive error of interpreting video compression artifacts as plumage features. He dismisses the possibility casually without actually addressing it. His argument that the black wedge should be visible on the underwing does not hold up either. When you subtract out the edge artifacts, there is neither black wedge nor black trailing edge resolved. Since the bird must have one or the other, the absence of either means that no conclusion can be drawn about the underwing pattern from these frames. In the frames (350 and 467) he claims show black secondaries on the left wing, the bird's wings are in fact not yet fully extended, remaining partially folded (compare apparent wing size with the following frames). Only one of these two frames shows clear black to the left of the white field; the other shows the black to the right of the white field. Interpreting where the black comes from on a partially folded wing is very tricky. In both cases, on the following frame where the wing actually is extended, the "black secondaries" have vanished; indeed the left wing is hardly visible at all.

For flight dynamics, once again he focuses exclusively on wingbeat rate. He does not even mention the more detailed flight mechanics and wing postures, which in the Luneau bird are a poor match for a Pileated. I would actually love to see his Pileated videos to have more material for comparison. If he's got a vid of a Pileated launching that has flight mechanics similar to the Luneau bird, then that will change everything from my perspective. But his own description reads "Deinterlaced video fields match precisely launch sequence from Arkansas in terms of timing of wing movement and reduced or blurred out black trailing edge to underwing." This seems to specifically exclude the other aspects of flight mechanics, which is where the Luneau bird is most sharply different from the Pileateds in all videos I have yet seen.

In his defense, he only references papers published in peer-reviewed literature and the video artifact and flight dynamics analyses haven't made it to publication yet; however, as he participates in multiple online fora he can hardly be unaware of them.

Same arguments, same faults, same failure to address fundamental criticisms.

And now, as I revisit the pages, many of the images are missing. Curious...


At 7:57 PM, Blogger dnolin said...


I don't understand why almost no one but you seems to think that flight mechanics is a big deal. Everyone wants to compare blurry still frames and make interpretations as to what they mean. Perhaps once someone publishes a position, defending it is more important than objectivity or truth.

At 5:41 AM, Blogger Bill Pulliam said...

It's because it has not yet been published in the literature, only discussed online. Bevier only addresses what has been published (though he uses his own unpublished and unpresented wingbeat data in his own analysis).


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