Sunday, September 04, 2005

A note to cyberthrush

I like Cyberthrush (but I disagree with his conclusions). He's an "Ivory-bill believer" who is willing to question pieces of Cornell's evidence.

He recently wrote this:
Moreover, on BOTH the up and down wing strokes the bird seems to reveal far TOO MUCH white for a Pileated -- indeed, I'm amazed at those who now argue the bird could actually be a NORMAL Pileated, and need not even be leucistic!!??

I don't see anything on the video that's inconsistent with a normal Pileated.

In the Luneau video, I believe we are looking at the bird's white wing linings on both the upstroke and the downstroke. Remember, the camera angle is low (from the canoe), and the bird is powering mostly straight away, rising slightly. In that view, I believe we are seeing the mostly-white wing linings as the bird raises its wings, and we are also seeing those wing linings on the downstroke, as the bird powers ahead and slightly up. In some frames, I see what looks like a trailing black edge on the underwing, but the picture is so unfocused that I can't be sure.

Regarding the size of the bird in the video--anyone interested should take the time to look closely at Figure 1 in Cornell's paper. I think it's likely that Cornell misinterpreted the position of the bird in that frame--rather than perched as sketched with folded wing, I think the bird may have already lifted its wing to fly. The extensive white seen may be simply the white lining of a Pileated's wing, and any wrist-to-tailtip measurement would not be meaningful, since the wing is already in motion, and they need a measurement on a perched bird. In addition, I think the picture is so blurry that an accurate measurement just isn't possible.

And about that distant, black-and-white blob that's supposed to be a perched Ivory-bill (about 20 seconds before the "Ivory-bill" flies)? I think it's more likely to be a bit of out-of-focus vegetation.

Regarding the sightings--I don't know anyone who is suggesting that the observers were fooled by an oversized, symmetrical leucistic Pileated. I think the observers may have been fooled by a normal-sized Pileated with an abnormal amount of white on one upperwing. Such a bird was reported in the search area.

If observers glimpsed an oddball Pileated, they might be correct in saying that it "didn't look like a Pileated", and I think their perception of the bird's size and flight style may also be affected. When I look at accounts of the sightings, I don't see that a lot of consideration was given to the possibility of an abnormal Pileated.

Could a Pileated with abnormal coloring on only one wing pass for an Ivory-bill? I think so, given that the glimpses were fleeting. Of the seven robust sightings, I think that some observers only saw the pattern on one wing. Others may have seen only one wing well, and assumed that the white pattern on the other wing matched. Remember that this was not a lazily soaring hawk--those wings are flashing awfully quickly.

Regarding identifying the bird by "gizz", please also note that James Tanner said that size and flight style were not reliable ways to distinguish Ivory-bill from Pileated (please see #1 here). The observers were unlikely to have much experience with abnormal Pileateds, and they had no confirmed experience with Ivory-bills. Given that lack of specific experience, and given a brief glimpse, I think it's asking too much to expect the observers to reliably distinguish an abnormal Pileated from an Ivory-bill.