The Imperial Film
Note: Those who did not come here via Cyberthrush's blog might be interested in the debate between me and David Sibley on these matters in the comment section of this post.
Also note: My subsequent post elaborates more on the wingbeat rate and flight dynamics issues.
As should be widely known by now, the legendary film of a female Imperial Woodpecker shot in Mexico in the 1950s has finally been published and is available for all to see. Contrary to the conspiracy theories advances by Scott Crocker and others, this film does not in fact undermine the claim that the infamous video shot by David Luneau in Arkansas in 2004 is an Ivory-billed Woodpecker. In fact, even on first viewing, it would appear to support the Luneau et al Ivorybill claim.
The Lammertink et al paper covers the film itself, its history, and the present-day circumstances at the spot where it was filmed; I will not delve in to that here. Please read the article and view the video at the site I linked above if you have not already done so. My focus here will be on the impact this film has on analysis of the Luneau video, as it fills a major data gap that seriously impeded that analysis until now: the lack of any films of Ivory-billed Woodpeckers in flight for comparison. Of course, the Imperial Woodpecker is not the same species as our North American Ivorybill, but it is very closely related. I don't have the reference at hand, but wasn't there a recent genetic study that found that the genetic distance between the Imperial and the North American Ivorybill was about the same size as the distance between the Cuban and North Amercian Ivorybill subspecies? I believe it is fair and justifiable to use the Imperial as a close analog to what our Ivorybill would have looked like on film.
For the record, I had no advance access to this film. I saw it for the first time on the day of publication last month, same as everyone else. So I have not had months or years to examine it, nor were any of my earlier conclusions about the Luneau video influenced by having viewed the Imperial film, having spoken to anyone who had viewed it, or even having heard any credible rumors as to what it contained.
All of my previous analyses of the Luneau video can be reached from this link which is the same as the one in the right-hand sidebar on this blog. I will take this work as read and will not repeat it in detail, simply refering to my important conclusions and findings. Anyone who read my work could tell that I had very strong leanings towards an Ivorybill identification for this bird, and found multiple major and fatal flaws in the Sibley et al analyses that concluded that this video was consistent with a poorly-imaged Pileated Woodpecker. However, the lack of any suitable Ivorybill comparison material left unresolved dangling issues in several areas that have stopped me from proclaiming that this bird was definitively an Ivorybill. These issues fell into two areas: the launch sequence, and the flight mechanics (structure and pattern of wingbeats).
First, to the launch sequence. This focuses on Infamous Frame 33 of the Luneau video, when a flash of white appears from behind a tree trunk just as the bird launches in to flight. The Cornell interpretation has been that this is the white shield on the back of the bird, and they used this to estimate the size of the bird. Sibley et al felt this flash showed the underside of a raised wing, and my own examinations of launch sequences of Pileated Woodpeckers led me to agree with this alternative interpretation. However, in contrast to Sibley et al, I found that the subsequent frame strongly suggested that the trailing edge of this underwing was white, not black, and that all the supposed black trailing edges they identified in the entire video were nothing but edge artifacts created by the digital imaging process. Hence even this alternative interpretation pointed to Ivorybill, not Pileated.
Now having seen the Imperial film, I have to say I may have been mistaken in disagreeing with Cornell's interpretation of this sequence. The behavior shown by the Imperial in the two launch sequences in the film is a very good match for the Cornell hypothesis and very different from that shown by typical Pileateds. Of course, as I mentioned before, both interpretations (when you stop misinterpreting imaging artifacts as plumage) come down on the Ivorybill side of the scale; but the Cornell interpretation is much stronger in both providing an unambiguous view of the "white shield" and in giving a size estimate that is outside of the Pileated range and right on for an Ivorybill. So this is a much heavier brick in the Ivorybill tray.
Flight mechanics: Flap rate
Discussions of the flap rate of the bird in the Luneau video generated a great deal of controversy. Its wingbeat frequency was higher than that shown in any of the Pileated Woodpecker comparison material available; in spite of claims of unpublished videos showing otherwise, there has still not been a video of a Pileated Woodpecker presented to the public in which the bird achieves and sustains such a rapid wingbeat rate. Of course, the real problem was that there was no film of an Ivorybill in flight to indicate whether or not this species actually possessed a rapid and sustained flap rate. Sibley and others argued that as a larger species, it should be expected to show a slower flap rate.
The Imperial isn't an Ivorybill, but it is very closely related and even larger. As discussed by Lammertink et al, it shows a very fast flap rate, considerably faster than what is typical for a Pileated. In the first 5 wingbeats of the second flight sequence, it achieves 8 flaps/second, nearly matching the Luneau bird.
I think we can safely conclude now that the Ivorybill had a fast, sustained flap rate, significantly faster than that of the Pileated, and likely extremely close to what the Luneau bird shows.
Flight mechanics: Wingbeat patterns
The flight of a Pileated Woodpecker after launch typically consists of a short series (3 to 7) of fairly rapid wingbeats, then a break into bounding flight where individual or paired wingbeats are separated by bounds (periods when the wings are folded in to the body and the bird functions as a ballistic missile). Sustained cruising flight of a Pileated generally continues this pattern of discrete flaps separated by bounds: flap....flap,flap....flap....flap....flap...
The flight of the Imperial contrasts sharply with this. In the first flight sequence the bird executes 7 wingbeats without a break before it moves out of sight. In the second it completes 15 steady wingbeats then executes a bound. After the bound, it resumes steady flight with 5 more uninterrupted flaps before it disappears from view. In the final sequence, the launch is not visible. When the bird appears in frame it is in steady flight, and completes at least 12 wingbeats before closing up into a bound and "cannon-balling" until the end of the film. One could describe the flight of this bird more as "flapapapapapapapapapapapapap.....flapflapflapflapflap"
The Luneau bird is in view for 4 seconds from launch to its final diappearance. It passes behind trees intermittently during this time. It is in continuous view shortly after launch for about 1.2 seconds, during which it completes 10 uninterrupted flaps without a hint of bounding flight. For the rest of the video, every time it reappears between the trees it appears to be engaged in steady wingbeats without bounds. There is no point at which the wingbeats appear to have stopped or even be separated by brief bounds. The bird completes 23 visible wingbeats during these 4 seconds; if you watch in slow motion and count along with the rhythm there seem to be no breaks, and interpolating behind the trees yields about 27 flaps in this time. This is a far better match for the Imperial than for a Pileated.
Flight mechanics: Wing movements
The film is shot at 24 frames per second (fps) which means that there are only a few frames (typically 3-4) representing each wingbeat. Hence, in any given wingbeat there are only a few wing postures shown. However, each flight sequence shows multiple wingbeats, and the adjacent flaps are often viewed from a similar angle and occur at about the same rate. However, as the flaps and camera shutter are never in perfect synch, each successive wingbeat is imaged at different point in the flap cycle. So, one can composite several adjacent wingbeats to create an approximate representation of what a single wingbeat would have looked like had it been shot at a higher frame rate. This is similar to the manner in which films of rotating objects (vehicle tires, fans, etc.) often will appear to show the object spinning in slow motion, or in reverse. I have constructed these composite wingbeats for two of the three flight sequences in the Imperial film, with interesting results. The second sequence yields the most attractive result, whith three successive flaps combined in to one: