Wednesday, August 17, 2005

Was "Elvis" just a partially leucistic Pileated Woodpecker?

Cornell's Science report provides some details about a bird I'll call Elvis.

According to Cornell, Elvis was an Ivory-billed Woodpecker that was repeatedly seen (7-18 times) in a small, 4-square-kilometer Cache River area, but amazingly, the looks were all "fleeting glimpses". Despite truly massive observer coverage, remote cameras, etc, no one ever got a good look at Elvis' identifying field marks, let alone a good picture. Of five key fieldmarks separating Pileated and Ivory-billed Woodpeckers, the observers saw only one--over and over, they saw white on the trailing edge of the wings. Amazingly, in all those sightings, no one saw the white dorsal stripes, the white neck stripe ending before the bill, the longitudinal black stripe on the white wing underside, or the pale bill itself. Unlike an Ivory-billed woodpecker, Elvis apparently never said "kent", and it never once responded to a taped imitation of its call.

Cornell chooses to call seven of the sightings "robust sightings" of an "ivory-billed woodpecker". To me, Cornell's report raises many more troubling questions than it answers. Among them:

1. How could you possibly glimpse the bird so many times, yet only see one key field mark, while never seeing the other four? If the bird was really an IBWO, and it let you see the white trailing wing edges repeatedly, why wouldn't the other fieldmarks show up as well?

2. As a specific example, on page 152 of "The Grail Bird", Tim Gallagher says that he and Bobby Harrison had a "superb view of the back" of a flying IBWO at less than 80 feet away. Given that both observers had a "superb view", why did neither note the prominent white dorsal stripes?

3. With so much observer coverage, in such a small area, how could you possibly avoid getting a good, close view of the bird, as well as some good photos? I'm not comfortable with "the bird was unbelievably wary" as an explanation. See my previous thoughts here. Wary enough to detect and avoid remote cameras? Wary enough to detect and avoid many camoflauged observers sitting quietly watching potential roost holes and foraging areas?

4. Why was there evidently only one bird, never a pair, with never any evidence of other breeding IBWOs nearby? Why would a single IBWO be present in this evidently marginal habitat, after over 60 years of searching with no breeding birds ever found?

Bottom line: I think Cornell gave way too much weight to one field mark (trailing white wing edges) that is not always reliable.

I think another hypothesis is a much better fit for the available facts: Consider an abnormal Pileated Woodpecker--a completely normal one, except that on one or both wings, it has some secondaries (and possibly primaries) that are white.

To an observer glimpsing a wing, this bird could indeed have trailing white edges. Of course, no matter what the view, no one would see the other four field marks mentioned above (white dorsal stripes, white line ending before eye, pale bill, and white underwing with the longitudinal black stripe). Depending on the view and the way the wings were held, the perched bird could look much like an ordinary Pileated. I think it's likely that Elvis was indeed relocated and seen well (perched) any number of times, but Cornell didn't realize it. Since it was clearly a Pileated when seen well, there was no excitement.

Of course I wasn't there, but I can picture people converging on the site of the latest Elvis glimpse, then heading off in the direction it last flew. After a frustrating search, only a Pileated Woodpecker is found. The searchers head home, convinced that the wary Elvis has given them the slip once again.

In "The Grail Bird" I see lots of this kind of thinking (from page 215):
She slowly lowered her binoculars and sat there repeating over and over, "The trailing edge was white, the trailing edge was white, the trailing edge was white...This can't be a pileated."

In all of "The Grail Bird", I don't see any accounts along these lines: "I glimpsed a large woodpecker that definitely had white trailing wing edges, but I couldn't see the other field marks. Maybe I saw an abnormal Pileated!" In fact, I used's "Search Inside the Book" feature, and I think it's telling that not a single occurrence of the words "leucistic", "albino" or "abnormal" were found in that book.

Of course, being a Pileated, it wouldn't give the "kent" vocalizations of the IBWO, and it probably wouldn't respond to an IBWO tape either. Being a Pileated, it probably wouldn't roam over a wide range, which could explain while the sightings were grouped so tightly.

Now how probable is the bird in the hypothesis--a otherwise normal Pileated that appears to have trailing white edges on the right wing?
Of course, birds with abnormal white patches are sometimes seen--check out this picture of a partially leucistic Tufted Titmouse, and this picture of a normal bird.

Abnormal Pileateds certainly do occur, and have been mistaken for IBWOs in Texas. Please see this link. Interestingly, last week, I saw that one of the Cornell searchers wrote this:
Leucisitic PIWO is absurd - we would have seen it regularly as I did one that had a strange pattern on her right wing.
In my opinion, in their paper, Cornell also hints that a partially leucistic Pileated may have been seen in the area:
We would expect any strikingly plumaged leucistic individual in the study area to have been observed regularly.
To me, the above wording could be consistent with "yes, we did see a Pileated with some abnormally white secondaries in the area."

Could a Pileated with abnormal coloring on only one wing pass for "Elvis"? 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.

Yes, I know that in a few cases, secondary field marks supposedly favored IBWO over Pileated. Things like apparent size, apparent bill/neck length, and perceived flight style are sometimes mentioned. I think it's a real reach to place much emphasis on these items, which, in my opinion, are notoriously unreliable. This is especially true given a fleeting glimpse of the bird, given that none of the searchers (obviously) have any previous authenticated IBWO experience, etc.

In conclusion, I like the "abnormal Pileated" hypothesis because to me, it seems to fit the evidence much more plausibly than anything else I've seen. I like it better than the "It's a lone, super-wary IBWO" theory because to be correct, it doesn't require an unprecedented ornithological miracle, coupled with a major change in IBWO behavior. I also like it because it doesn't require that any observers be hallucinating, dishonest, or incompetent--I don't believe that any of those things are true.

(8/27/05 update--I've edited this post to refer to an "abnormal" Pileated. I think the original "partially leucistic" wording was too restrictive.)

No comments: