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David Sibley has a new post up at his blog better fleshing out his explanation of "wing-twisting" in bird flight in general, and with specific reference of course to the Luneau video. I'm sure there was some discomfort for David even re-visiting this whole issue at this late date, so I'm very thankful that he chose to take the time to do so, as it will help some better understand his position. I also realize his post won't end the frame-by-frame debate over just what is being seen in the Luneau bird, and I'd prefer to not get into an extended discussion here of specific frames that folks feel don't fit with David's rendering of matters, since the two interpretations simply don't seem resolvable. Given USFW/Cornell's rather dismissive take on David's position, I simply think it good that he has re-stated it:
(...As a sidenote, I will say that I think some of the confusion over this matter stems from the use of the perhaps overly-vivid term "wing-twisting" for what seems to me to be a more subtle turning, tilting, or bending of the wings, along with the 'curvature' David describes.)
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4 comments:
Sibley is entirely correct in saying that a the leading edges of a bird's wings tilt downward during downstrokes. This is an unremarkable fact that has long been understood. The issue of the Luneau bird's wings is considerably more complex, however, and Sibley et al. never seem to have taken into account the orientation of the bird relative to the camera line of sight. Early views are somewhat ventral despite the fact the bird is rising relative to the camera line of sight. In these views it should come as no surprise that no "wing-twisting" is required to see an underwing, even on the far wing. Later views are quite definitely somewhat dorsal and here are where some real incongruities arise in comparisons with pileated videos.
The Nolin pileated videos provide ready evidence of, among other things, the degree of such wing twisting and its effect on wing presentations for flushed pileateds. However, de-interlaced frames are necessary to really study the Nolin videos properly. The USFWS has de-interlaced frames.
The Nolin videos (NOT de-interlaced) are available here:
http://www.birdviewing.com/?page=ivorybillcenter
(also, at least one is on YouTube:
http://www.youtube.com/user/Kestango1#p/u/3/QFPEAQe0qCk
Actually, the latter video was constructed from de-interlaced frames.
Ahhh, THANKS Fang!!
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