Ivory-billed questions

There is a new paper out in Science magazine that purports to cast doubt on the last year's celebrated rediscovery of the Ivory-billed Woodpecker in the forests of Arkansas. The first author is David Sibley, renowned birding author and artist. Sibley's target—the brief, blurry video, shot by David Luneau in 2004, that is the only photographic evidence yet presented for the woodpecker's modern existence. Sibley and his co-authors argue that the bird seen in that video is, in fact, a common Pileated Woodpecker.

In response to this new paper, some of my favorite bird bloggers are giving up on the Ivory-billed. GrrlScientist at Living the Scientific Life wrote a post titled, "Goodbye Beautiful Dream", saying, "This bird's existence becomes less credible, more tenuous, with every passing day." Nuthatch at Boostrap Analysis wrote, "In the world of science, a situation of this nature would generally be considered to be at the 'back to the drawing board' stage. And I think that's where the IBWO is at. Still awaiting rediscovery."

After reading the Sibley paper, and the response to it written by the team that announced the original re-discovery last year, I am not so ready to give up. In fact, reading once again the evidence that the Cornell team led by John Fitzpatrick has put together, as well as their comprehensive analysis of the grainy video, I am impressed anew at the strength of their case. In comparison, the analysis by Sibley and his collaborators appears incomplete—their conclusions, therefore, unconvincing.

I have only yet briefly perused the evidence on both sides at this point, so my opinions may evolve. But right now, I am troubled by the tendency of Sibley and his collaborators to casually dismiss evidence contradicting the pileated hypothesis and supporting the ivory-billed hypothesis.

To take one example, Fitzpatrick's team has suggestive evidence that the fast wingbeats and direct flight-pattern of the bird in the video is far more consistent with the ivory-billed hypothesis than the pileated. Sibley dismisses this in one sentence at the end of his paper: "We agree that 'we lack sufficiently comparable data for objective comparison' of these features." He and his co-authors spend a little more space on this subject in the supplemental materials, stating that "identification based on the wingbeat rate of the bird in the Arkansas video requires clear evidence both that it can be matched by an ivory-billed woodpecker and that it cannot be matched by a pileated woodpecker."

The wingbeat rate of ivory-billeds is unknown, but the Cornell team has presented suggestive historical evidence that it is similar to the wingbeat rate of the bird in the video. The wingbeat rate of pileateds should be simple to measure, since they are so common. But Sibley's group has apparently made no effort to study this. The Cornell group, on the other hand, has looked into this issue and reports on their web site:

The wingbeat frequencies of Pileated Woodpeckers in our videos from Arkansas are 2-4 beats per second in level flight (many examples) and 4-7.5 beats for short periods during hasty departures (n = 5). Moreover, experts who have studied Pileated Woodpecker flight using video analysis timed the fastest departures at 7 beats per sec (Tobalske 1996, personal communication). Thus, wingbeat frequency of the woodpecker in the Luneau video [8.6 per second] is faster than any recorded Pileated Woodpecker.

Sibley's case would be more persuasive if he took this evidence contradicting his hypothesis more seriously. On this point, this is not a mere argument over the precise placement and color of a few pixels in a fuzzy image.

As another example, Sibley and his co-authors gloss over the substantial amount of non-video evidence that the Cornell team published a year ago.

The recent sight records (1, 4) were all very brief and most involved a single observer, matching the pattern of reported observations over the past few decades (5–8). Although such observations provide strong impetus for continued searching and habitat protection, they cannot be taken to confirm the species' presence because they do not provide independently verifiable evidence.

The Cornell team, naturally, does not take lightly this casual dismissal of the bulk of the evidence bolstering their case. They write, in a footnote in their response to Sibley's paper:

Sibley et al. (2) incorrectly claim that the sight records we reported (1, 10) ‘‘were all very brief and most involved a single observer, matching the pattern of reported observations over the past few decades.’’ In no case since the 1940s was a report of an ivory-billed woodpecker (such as the original one by Gene Sparling) promptly followed by multiple repeat sightings in the same area—sightings that included a close encounter shared by two individuals, each having extensive experience with pileated woodpeckers in southern forests. After studying the evidence at length, the Bird Records Committee of the Arkansas Audubon Society voted unanimously to accept the documentation of ivorybilled woodpecker (www.arbirds.org/ivory_billed_woodpecker.html). Comparable validation by critical and experienced local experts has not occurred following any previous report of this species.

No one would give a hoot about this video if there hadn't been so many other sightings by so many experienced individuals in the same area in a short span of time. By not acknowledging the significance of these sightings, Sibley shortchanges his own argument.

This whole controversy should be moot relatively soon. With the exhaustive nature of the search that has been going on in the Arkansas woods this winter, if the Ivory-billed Woodpecker inhabits those forests, there should be plenty more circumstantial evidence soon forthcoming. If no such evidence is presented over the next few months, then strong skepticism of the continued existence of the ivory-billed will be more than justified.

Comments

[Nuthatch]

I wouldn't say I've given up. My point is just that from a scientific point of view, the alternate possibility (the null hypothesis), that it is a Pileated Woodpecker, cannot be conclusively ruled out. Even if Sibley's argument was less persuasive than Fitzpatrick's, the burden of real, verifiable proof is on Fitzpatrick to disprove the null hypothesis.

[Peter]

Sorry to misinterpret your position, Nuthatch.

While Fitzpatrick do have that burden, of course, they already have put together a compelling case. By not engaging that case in full, arguing for or against its strengths and weaknesses, Sibley appears to be (to put it perhaps a bit harshly) cheating.

We'll all know soon enough, though.

[socialpyramid]

I can't believe how polarizing the debate has become over whether this bird still lives. Check out this intense, and entertaining, flame war! The Daily Green