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.