Monday, November 14, 2011

Woodpecker Wingbeats Revisited

I didn't really want to dredge all this old stuff out again, but it has remained a point of contention and misaprehension, and of course there are some new datums to consider.

Years ago I posted a graph of some comparative wingbeat data between the bird in the Luneau video and some known Pileateds, without comment. Well, it seems time to repost this with additional data, and with comment. I have added the two launch sequences of the Imperial Woodpecker, and the data presented by Louis Bevier for his best (fastest, most Luneau-like) Pileated (click image for a larger view):



First some comments on the Bevier data (for those curious my original response to his articles is here). These have only been presented in very limited, summary form without the actual videos being made available. I realize that he is operating on the notion that he only needs to find one Black Swan (to refute the statement that All Swans Are White), and feels that there was no need to lay out extensive results. But the swan in question was described in a somewhat roundabout way, and on closer inspection it kinda begins to look sort of whitish, really. The main point of fogginess is the way he expressed the wingbeat frequency data, which initially suggested that the flap rate of this champion flapper Pileated only dropped from 8.8 Hz to 7.5 Hz over 12 wingbeat cycles. But the numbers he gave were cumulative through 12 cycles, not the individual value for the 12th cycle. Reworked from the data points given, you get what I have plotted, showing averaged of 8.8 Hz for cycles 1-5, 7.4 Hz for cycles 6-9, and 6 Hz for cycles 10-12, which is a much more substantial dropoff than suggested by the data as originally presented. One also has to wonder at the comparison between captive birds being released from human hands versus a free-flying bird launching from a tree; both the starting dynamics and the bird's likely mental state would seem to be very different between the two. Jumping (dropping? being tossed?) from human hands is a pretty strange way for a woodpecker to initiate flight; on the other hand, flushing from a tree trunk in response to the approach of a couple of guys in a jon boat propelled by an electric trolling motor is a rather ordinary experience for a woodpecker in the Big Woods, I'd expect, and not likely to trigger extreme behaviors.

Next, some general comments about the graph. Like the earlier graph, it shows the Luneau bird holding steady and flapping the fastest of them all, with very little upward curve to its line (upward= slower wingbeats). The Pileateds start out near it, but tail off after several wingbeats. Even the Bevier bird does not in fact keep up (in contrast to the assertions at the original site), falling increasingly behind just like all the others. The Imperial lines bracket the Pileated data for the most part, but the salient feature here is that it also does not tail off (slow down), remaining steady and straight.

I have maintained all along that wingbeat rate per se is not an especially strong or informative piece of evidence, as it is just one tidbit of data about flight dynamics and many things can affect it. What I find more informative are the mechanics underlying these changes (or lack of changes) in wingbeat rate. There is a qualitative feature of Pileated flight that causes this tailing off in wingbeat rate. After around 3-7 wingbeats, all the launching Pileateds I have seen videos of begin inserting brief closed-wing pauses in the upstroke between flaps. Initially these pauses are too brief to be obvious to the naked eye, but they are clearly evident on slow-motion video. As the flight proceeds the pauses grow into visible bounds (closed wing ballistic flight segments) separated by discrete flaps, which we all know as the classic Pileated cruising flight. It is the insertion of these discrete pauses that causes the apparent slowing of the wingbeat rate, not a dramatic reduction in the rate at which the wings are being moved during the flap. Again, all Pileated videos I have seen show this. I would expect the Bevier bird shows this too given its rapidly dropping flap frequency.

The Luneau bird does not display this flight behavior, which is why its flap rate holds steady. The Imperial does not display it either, with steady flaps until it either leaves the frame or closes up into one, discrete, readily visible bound. At the end of the one bounding segment that is shown until its end, the Imperial then resumes unbroken rapid flapping without pauses. It is worthy of note that in the Luneau video, as the bird reappears between trees in the later segments, it is always showing steady wingbeats, even at the very end. No closed wing bounds or pauses are discernible, though admittedly it gets hard to judge. This presence or absence of these brief upstroke pauses is a discrete qualitative difference between the flight styles of these birds, not a mere quantitative variation. It is a much "harder" distinction than the smallish differences in flap rates. I suspect that if this discussion were about virtually any other species of bird (even continental hyper-rarities), this type of feature would be readily promoted and accepted as a diagnostic character for resolving identification questions.

Summary: The flight of the Luneau bird is inconsistent with what appears to be the characteristic, even diagnostic, flight style shown by every Pileated video I have found. It is somewhat faster, but otherwise consistent, with the flight of the Imperial Woodpecker (in the one film that exists). Louis Bevier's "black swan" fast-flapping Pileated appears to be in front of a metaphorical and rhetorical bright light that makes it appear black; its actual color cannot be judged from the information available.

14 Comments:

At 7:06 AM, Blogger Mark said...

Thanks for posting this very cogent analysis. I'd be happy to cross-post my series on the same subject over here if you'd like. I didn't do so initially because the observations were for the most part in respsonse to David Sibley.

I also would be very interested in your take on the questions I raised about the Bevier sonogram, especially:
*******
Bevier's own sonogram may support what Bill Pulliam has said about wing tucking. The final beat in the cycle presented in the sonogram has a noticeably lower amplitude than the earlier ones, and the duration between the last two flaps appears to have increased. So I'm left to wonder whether this is the point at which the PIWO does its first wing tuck of the kind Bill has described.
*******
I'd also like to know if you have any more general observations with regard to that sonogram and the comparison with the Singer Tract bird.

 
At 7:31 AM, Blogger Bill Pulliam said...

Mark -- I have the same problem with the sonogram as with the rest of the Bevier stuff -- show me the pictures. I'd rather just see the video than try to hypothesize things from the abstracted data. There's a lot of inference and "deriving from first principles" here, when what is really needed is empirical evidence. This is what the Imperial film finally provided -- limited, of course, but actual data straight from the world, not from the mind of one person or another. My interest in digging back into all the old data again is limited, especially when I have already dug into it deeper and said more about it than most of the critics have.

 
At 7:39 AM, Blogger Mark said...

Understood.

 
At 8:46 AM, Blogger Mark said...

It's more than a little strange that Bevier had what seems to have been an easy time finding a "black swan" that no one else has been able to locate. Stranger still is his refusal to make whatever hard data he has available for independent review.

Apparently, some extraordinary claims don't require extraordinary evidence.

 
At 8:23 AM, Anonymous Anonymous said...

I doubt Louis Bevier or David Sibley will be losing much sleep over this 'very cogent analysis' / anti-scientific stupidity.

 
At 9:45 AM, Blogger Bill Pulliam said...

Anon 8:23 -- if you'd like to post a real rebuttal with some actual thoughts or ideas in it, please do. If all you have is insults, however, don't expect to see more of your contributions to the discussion put through.

Sibley and Bevier's sleep rhythms are of absolutely no concern to me.

 
At 12:59 PM, Anonymous Anonymous said...

There's no point debating with you. Sibley and Bevier and many others have made you look very foolish already. It would be like debating with a creationist.

Don't worry about posting my comments. There only for YOU to read. I'm not vain.

 
At 2:00 PM, Blogger Bill Pulliam said...

I gotta say I am even less concerned with my reputation among anonymous sniping trolls in the UK (why does so much of this stuff come from Manchester?) than with the sleeping patterns of the aforementioned birders.

 
At 2:20 PM, Blogger Bill Pulliam said...

Just for the record, maybe it is worth pointing out what I do care about; or at least what my goal is here. I am not set on proving any particular person right or wrong; I do not have a vested interest or professional reputation to defend, my birding reputation is fine (thank you very much). My purpose here is to point out places where I think there have been points misinterpreted or overlooked, and to provide independent analysis and discussion. I have pointed out what I have seen as errors and misjudgments by the Cornell team as well as by the various people who are critical of them. If you are curious to read through my own saga about the woodpecker craziness in Tennessee, you will find that in fact at many times in the past there has been quite a bit of tension between me and Cornell over some very sharp disagreements; but we have remained on professional terms about it.

My goal is to have my own alternative and particular interpretations and conclusions presented clearly and directly for the birding and ornithological communities to consider. What each reader takes from them and does with them is their own choice. I don't know that my writings have ever changed one single mind about the presence or absence of an Ivory-billed Woodpecker in Arkansas in 2004; that is beyond my control. I'm just for open exchange of ideas and an informed, dynamic discussion about any and all matters of concern in the world of birds. For all its faults (including but not limited to British trolls), the Internet remains one of the best fora on which to accomplish this dynamically, openly, and interactively.

 
At 3:06 PM, Blogger Mark said...

While I should probably leave this one alone, it's both hilarious and pathetic that this anonymous poster is accusing you of being "anti-scientific" and comparing you to a creationist when Bevier has flouted the norms of scientific discourse by failing to disclose his raw data (for years now) and Sibley won't even acknowledge that his own statements (on Cyberthrush's blog) reflect a significant change in his stance.

 
At 3:06 PM, Blogger Bill Pulliam said...

Continuing...

One of the things that has bugged me the most about this over the last six years has been the Hero Worship undertones to it -- the notion that Cornell must be right because they are Cornell, or that Sibley must be right because he is Sibley, etc. This is especially ironic in the latter case given the most recent article on David Sibley's own website about overconfidence and the idea that everyone makes mistakes, and these should be seen as learning opportunities. I seriously doubt that when he wrote that he was thinking to himself "everyone except for me, of course." And I have indeed tried to use the apparent mistakes I have found (mine and others) as learning opportunities. The notion that the birding world has been divided into two camps, each the unflappable devotees of one or the other of two sets of gurus, is really unhelpful and untrue. Never been much for infallible gurus myself.

These ideas are being put here just as comments on my own post rather than a new post of their own because had other plans for the next major series on my blog, and I don't especially want to hijack it much further.

 
At 7:52 AM, Anonymous Anonymous said...

Bill, regardless of whether you are ultimately right or wrong with your conclusions about the IBWO (I'm agnostic), I greatly appreciate and respect the time, thought, analysis, objectivity and writing that you have devoted to this subject and shared with the rest of us. Thanks! It amazes me how angry some become with those who have a different view. Don't let them discourage you from being you.

 
At 4:09 PM, Blogger Lori said...

Mr Pulliam,
When I was in college at NLU now UL M in Monroe, I was fortunate enough to live on land that backed upped to the D'arbonne national wildlife refuge. I was studing biology in particular bird behavior and psychology. I grew up hunting and fishing the area so I knew almost everything that lived in the area or migrated through. One overcast morning I began hearing the strangest noise and thought I was seeing a nest of Pileated Woodpecker but then when I got my binoculars I realized the bird was much larger,and with no red on its head! When she turned all I could see was a giant bill! I really did not know what I was seeing until I started talking to people at school who kept saying that there was no way. I just enjoyed watching she and her mate raising their young and gve up on the notion of what I was seeing. That was in 1992-1995. Now, I wished I would have been more persistent about the issue. I still believe what I saw was an ivory billed woodpecker because I saw the female of the species and that magnificent bill. Had I not been a poor college student at the time I could have had wonderful photos. I believe that they are still in isolated areas of wild swamps of Louisiana and Arkansas. If I could I would still be on the hunt for these beautiful birds. I did email Cornell as they were doing their study but I do know what the outcome of my report was.
Sincerely keep believing!
Lori

 
At 8:10 PM, Blogger Bill Pulliam said...

Lori -- If you check in here again, please post another comment that includes some contact information for you. I will not put it through moderation so your info will not be posted for spammers to snatch, but I will see it myself. Thanks.

 

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