Tuesday, August 11, 2009


This is your brain on Ivorybills

On my return home on March 12, the first order of business was to flesh out my "official" account of the Bambam Incident before I read or listened to anything else. I had scribbled some quickies in the field at the time, and written up the incident in my field notebook at greater length later that same day, so it was mostly a matter of adding grammar, punctuation, context, locations, etc. I won't reproduce the writeup verbatim here, as it has been pretty thoroughly paraphrased and quoted in my previous post.

With that out of the way, I felt free to start listening to recordings and reading historical accounts. In terms of quality, rhythm, etc., recorded double knocks of Pale-billed Woodpeckers were awfully freekin' close to what I heard, if one were to put them through a massive mega amplifier. Contemporary descriptions by early 20th Century observers of Ivorybill double knocks were also sometimes uncannily accurate descriptions of the sounds from my 21st Century encounter. Loud, very loud, unexpectedly loud, everyone stressed this. I had a spine-chilling, we're-not-in-Kansas-anymore moment when I read this quote from Don Eckleberry, describing an encounter with a female Ivorybill in Louisiana:

With a few disordered feathers properly and vigorously rearranged, she gave her distinctive double rap, the second blow following so closely on the first that it was almost like an echo--an astonishingly loud, hollow, drumlike Bam-am!

In my own writeup I had describe the loudness of what I heard as "astounding" rather than "astonishing," and I had used a "b" where he used a hyphen in the onomatopoetic spelling of the sound. Other than that...

But what to make of this? Obviously some banging sounds in the woods do not an Ivory-billed Woodpecker make. We were not in any position to make any firm declaration about what the source of these noises was. But we could ponder, speculate, and infer. One thing seemed clear: the source of the noises was biological. They were heard in calm and near-calm winds, repeatedly within the same general area but not at the exact same spot, and they seemed to all be nearly identical. What else is going to do this but a mobile biological source? But.. WHAT biological source? The one critter that has been documented making a very similar sound is (at best) one of the rarest organisms on the continent, and this scraggly forest is hardly the right habitat for it.

Hold on, let's revisit that last statement. Do we really know what habitats a relict surviving Ivorybill would be using now in this century? This has of course been the subject of much debate. We have a modest amount of information about 19th and early 20th Century habitat usage; and that actually points to a moderate amount of plasticity: bottomlands, pines, virgin growth, cutover stands. But even if the species was restricted to old-growth bottomland hardwoods 70 years ago, are there strong reasons to conclude that any possible surviving birds would still be restricted to this habitat or its close approximations? Well, actually, no.

Many forest birds have modified their habitat usage in recent decades and centuries. Chimney Swifts are an obvious example; also quite telling is the Vaux's Swift which has only begun moving out of old growth and into chimneys in the last few decades. But of more direct relevance, consider the following quotes:

When found they are usually in regions of original forest growth, rarely being seen where the woods have been once cut over. [...] As this Woodpecker seems not to possess the faculty of adapting itself to the new conditions created by civilization, it is quite possible that it will not long survive the passing of our primeval forests. T. Gilbert Pearson, Birds of America, 1936.
Its presence in a region is more often revealed by the large cavities it excavates in dead stumps and trunks than by actual observation of the bird itself. [...] This species is common only in the wilder parts of its range. Frank M. Chapman, Handbook of Birds of Eastern North America, 1939.

Both of these early 20th Century characterizations are of the habitat requirements of the Pileated Woodpecker. In fact, as we all know, over the intervening decades Pileateds managed to adapt to forest fragmentation and second growth quite well, thank you, and are now widespread in habitats well beyond the range of what was described in the 1930s.

There's also another fundamental, perhaps somewhat tautological factor at work. If in fact Ivorybills were an obligate old-growth bird, then yes, they are now extinct. If they were never able to utilize second growth and fragmented forest, then there is absolutely no reason to be looking for them now anywhere. But even given the historical accounts of their habits they demonstrated a bit more flexibility than this; and given the actual history of Pileateds and various other forest birds since the industrial revolution, it seems brash and unjustified to presume that the habitat utilization of a 21st Century Ivorybill would be the same as that of one in the 19th Century.

All these intellectual ponderings are fascinating and intriguing, but more urgently we were in something of a campephilitic frenzy. On March 13th Bob heard another double knock near Forked Lake, another oxbow lake situated midway between Hushpucket and Rhodes Lakes. As an interesting linguistic side note, "Forked" in place names in this area is pronounced with two syllables, King James style. We all felt we had to strike while the zone was hot and before the leaves closed the canopy in and cut off sight lines. Rapid response took priority over full analysis of what we had; there'd be much more time for debate and discussion later. Scott was making arrangements for a mass invasion, an effort to get as many people as practical out in the WMA at the same time for a couple of days. Cornell was offering the loan of their Arkansas volunteer crew for a few days. TWRA, the Feds, and selected invited guests were set to rendezvous at Moss Island on March 20-21.

Other posts in this series:


At 11:26 AM, Blogger cyberthrush said...

Hey Bill, obviously I want to believe your intuitions are correct here, but am not clear how you can be so sure that the noise source must be "biological." Can gunshots or even mechanical equipment from different directions be 100% ruled out, or for that matter even independent IBWO searchers banging on tree trunks (not saying it's likely, just not fully dismissable)... sounds traveling through dense forest from a distance can be very difficult to interpret.
Anyway, looking forward to... the rest of the story.

At 1:14 PM, Blogger TN Forester Mike said...


Back in the late 80s I did a timber appraisal on the 18,000-acre block of Anderson Tully land just south of Moss Island that has become part of the Chickasaw National Wildlife Refuge. It contained a rather unusual, remote 200-acre section of cypress swamp that was so dense that it blocked out most of the midday sun. It was surrounded by stands of mature oak and sweetgum. It's a little hard to get to but might be worth the effort in an ongoing investigation.

At 3:02 PM, Blogger Unknown said...

"Jeeezus frikkin' Kryst is THAT the double knock everyone has been going on and on about for all these years? "

Bill, you obviously understand the difference between a Double Knock and a double knock. After hearing it live (Pale-billed in my case), the protestations that Pileateds occasionally make such a sound repeatedly and with such magnitude seemed to me unclear on the concept of a Double Knock.

To your knowledge, has anyone who has heard Campephilus Double Knock live ever reported hearing such a sound in the United States outside of potential Ivory-bill range? The answer to that question and the results of a "control" ARU analysis could be pivotal for reliably correlating the sound with the bird and managing a remnant population in the future.

At 9:25 AM, Blogger Bill Pulliam said...

Mike --

I'd be very interested to know more details about where this tract is situated in the current configuration of Chickasaw NWR. As I will get in to later, Chickasaw and Moss Island are connected by continuous forest corridors just a few miles long and it would seem likely that any semi-nomadic wanderer using Moss Island would also use Chickasaw. You have my e-mail address, don't you?

Cy --

I'd not claim certainty about the origins of any sound the source of which has never been directly and definitively observed by anyone anywhere. But, you have frequently discussed that you place special emphasis on sightings rather than blurry videos, ARU recordings, etc., because (paraphrasing here) you respect the skills, judgement, and expertise of experienced birders and value that higher than other more indirect evidence. I think the same thing applies to the double knocks. Live observers in the field with ample experience are in a position to make judgments about the quality and context of what they are hearing that you don't get from the so-called "objective" evidence. Ideal would be both of course; a live person hearing a sound and documenting it with a decent quality recording; but that is not the norm. Anyway, you know that in science nothing can be 100% ruled out, but the very strong judgement of these observers including me is that what we heard is exceedingly unlikely to have been human or mechanical in origin. As for other searchers, it would be REALLY hard to imagine freelancers working in those woods without our being aware of it. The area isn't that large, and the points of access are limited. I have found that I generally have a good sense of everyone else who is within about a mile of me. People are just not that quiet with cars and trailers and boat clunks and gunshots. And, of course, there are not very many of the Congaree double knock simulators out there, it's really unlikely that someone would be out in the woods using one that we were not aware of. Nor would it make sense for them to whack it so infrequently; standard protocol is 7 whacks 10 seconds apart every 30 or 60 minutes.

Joel --

I am not aware of that having happened. I suspect it would be pretty widely known if it had. I do know that many of the people who have heard DKs in the U.S. in recent years, including many of those who have heard them at Moss Island, have also heard Campephilus DKs in the tropics, and pretty universally describe them as identical.

At 2:55 PM, Blogger TN Forester Mike said...

I do not have your email address.


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