Black Woodpecker (Dryocopus martius) Foraging Behavior: More Support for an IBWO Diagnostic?

I’ll be returning to Louisiana in late February and hope to make a couple of more trips during peak search season. Frank has retrieved the cards from our game cams and is in the process of going through several weeks of images. In contrast to the last set, there have been no intriguing hits thus far.

Last month, I came across a very interesting post on the Woodpeckers of the World Facebook group. The link took me to a French website that features some videos of the Black Woodpecker (Dryocopus martius), a Eurasian species, and one of the largest woodpeckers in the world, surpassing the Magellanic in size. In another analogy to the Magellanic, the Black Woodpecker appears to have certain features that are more Campephilus-like than others in genus Dryocopus. This includes flight style; acording to Gerard Gorman’s monograph on the species, Black Woodpeckers don’t generally undulate in flight. More importantly, the size and appearance of the bill certainly evoke the IBWO – generally larger, thicker, and heavier than a Pileated’s. Bill length can reach over 70 mm (although the average is 53-56 mm). According to Tanner, the mean length for ivorybills ranged from 67.8 mm to 74.1 mm depending on sex and region.

For my purposes, this is the most interesting clip. It’s an outstanding sequence that shows a Black Woodpecker scaling bark from a medium-sized hardwood branch. I see the following aspects as being significant and supportive of the hypothesis on feeding sign I’ve discussed in several posts, including here, here, here, here, and here.

For the most part, the bird is removing bark with direct strikes, not the lateral blows of a Campephilus woodpecker. This is possible because the limb is relatively thin, and the bird is able to position herself so that direct strikes will have the same effect that a more lateral blow would have on the bole; she generally engages in lateral movements to flick away bark after it has been loosened. The clip also seems significant insofar as it reveals the amount of effort involved to remove large but very thin strips of bark. In addition, even though the bark is thin, it seems the bird is still removing it in layers, at least some of the time. I think the video tends to support my idea that the work we think is diagnostic – on boles with thick tight bark – is beyond what PIWOs can do physically. At the same time, the footage suggests that the high branch work that Tanner emphasized is likely within the capacity of a Pileated Woodpecker and is indeterminate as we suspect.

In looking at images of Black Woodpecker foraging sign online, it appears that – bill structure notwithstanding – they typically remove bark in layers, just as Pileated Woodpeckers do, and this is true on both hardwoods and softwoods. I have been unable to find any examples of Black Woodpecker work that closely resemble what we think is diagnostic for ivorybill, but examples of the layered scaling are easy to find, for example:

Here

Here

Here

Here

Here

And here.


The Two Faces of James T. Tanner – A Study in Selective Memory and Blindspots

In a 1936 letter to James Tanner before Tanner began his survey of possible ivorybill habitat in the southeast, Herbert Stoddard wrote, “The area where they (Ivory-billed Woodpeckers) may occur at present is simply tremendous, not restricted as many believe.” Stoddard continued, “. . . if I had the rest of my life for the purpose, I doubt I could cover adequately half the ground I now think worth investigating. When I say adequately I have in mind five days I spent looking especially for these birds with men such as Bob Allen and Alex Sprunt on an area of some ten thousand acres known to be frequented by several pairs of these birds without seeing one. Of course this was due to the element of luck, as others have gone in the same area for a few hours and seen one or two. But it indicates the time one would have to spend in these great river valleys to really be reasonably sure that the birds were absent or even extremely rare therein.” Tanner was one person, and he clearly didn’t have the time to devote to the thorough survey Stoddard suggested, but the later record suggests that he failed even more deeply to take Stoddard’s words to heart. Stoddard’s perspective leaves room for the possibility that Tanner grossly underestimated the ivorybill population in his monograph, something that might lead to very different projections about the likelihood of survival today. It also sheds additional light on the difficulties in searching for ivorybills and on what appear to be some significant blindspots in Tanner’s thinking about the species.

I recently wrote a Facebook post in which I stated Tanner had a “hard time” finding Ivory-billed Woodpeckers. A very prominent American birder and ivorybill skeptic promptly shot back asking for citations, which I provided; I wouldn’t play along with the snarky response, but the exchange gave me the impetus to write this post. To most birders, Tanner is a kind of heroic figure, a pioneer ornithologist, and the author of the only in-depth, definitive study of the Ivory-billed Woodpecker, a bird that, in Tanner’s telling (and even more so in the retelling), was a super specialist that depended on virgin forest for its survival. Tanner is also rightly seen as having played a central role in the development of modern environmentalism, fighting to save the Singer Tract itself and later helping to create Congaree National Park, one of the few remaining substantial old growth stands in the south.

Those who are more deeply steeped in ivorybill lore are likely to have a somewhat different perspective, even as they admire Tanner’s good qualities. In later years, Tanner became increasingly dogmatic about ivorybill habitat requirements and was usually harshly dismissive of  reports from others – including John Dennis in Texas and Agey and Heinzmann in Florida. (This dismissiveness began to take hold in the early 1950s.) By no later than 1985, and probably much earlier than that, Tanner had become convinced the ivorybill was extinct, a conviction that he usually leavened with the statement that he’d love to be proven wrong. Ivorybill aficionados may also raise questions about the 1930s surveys he conducted in the southeast, and the rapidity with which he dismissed almost every place he visited as being unsuitable, sometimes based on a visit lasting a day or two. Most of these visits were made outside of breeding season, at times when finding ivorybills was considerably more difficult.

Tanner may have been right to dismiss many of these areas, but the possibility that he might have missed several populations cannot be ruled out, especially in light of the letter from Stoddard, an established ornithologist with first-hand knowledge of the species. At minimum, Stoddard’s letter put Tanner on notice that ivorybills could be very difficult to find.

Were preconceived beliefs driving Tanner from 1937-1939; was he being cavalier in his dismissals; or was he simply doing his best to accomplish what Stoddard said would take a lifetime in a few weeks spread over three years? It was probably all of the above, but whatever the reason, his mindset became an even bigger problem as time went on, leading him to foment the false impression that ivorybills should be easy to find, a notion that informed the views of my interlocutor on Facebook and of many those who believe the species is extinct.

The fact is that when Tanner was in the Singer Tract, the only birds he could find on a regular basis were the “John’s Bayou Family”, the group first studied in 1935. Their nesting and roosting grounds were approximately 1 mile from Sharkey Road. From 1935-1939, the birds nested in the same general vicinity. Three of the four nests were in very close proximity to one another, and the greatest distance between any two nest sites was 3/4 of a mile. Despite this clustering, it took Tanner five days to find a nest in 1939, when he didn’t have J.J. Kuhn (who had been forced out of his job as Singer Tract Warden) to assist him.

While Tanner paid respect to and credited Kuhn, the passage of time has made it increasingly clear that he downplayed the degree to which he depended on Kuhn to find ivorybills. Kuhn had been observing the birds for several years before the 1935 expedition (which also took several days to find ivorybills), and it’s reasonable to infer that the John’s Bayou family was already somewhat habituated to human presence by 1935. Certainly after ’35, they were accustomed to human activity in the immediate vicinity of their nest sites.

The only other ivorybill Tanner saw was one he named Mack’s Bayou Pete, presumably a bird hatched in 1935 from a nest that Kuhn found. As with the John’s Bayou pair, this bird was found within a home range that had been roughly delineated in 1935; Tanner believed he could recognize Pete’s voice, but the bird was far more frequently heard than seen.

Edited to Add: I’ve been reminded that the 1935 Mack’s Bayou Nest failed, and that Pete more likely fledged in 1937. The fate of the adult Mack’s Bayou pair is unknown.

Tanner continued to correspond with informants in the Singer Tract until 1948 or ’49 and was advised that one or two birds remained until that time. As Tanner’s temporal distance from his experiences in the Singer Tract grew, so did the distortions in his memory. These distortions are perhaps most dramatically illustrated in an article he wrote entitled “A Forest Alive”, which was published posthumously in Birdwatch (2001), a British magazine. Prominent ivorybill skeptic Martin Collinson mentioned the article and quoted it at some length in a 2007 blog post:

http://proregulus.blogspot.com/2007/12/i-almost-certainly-ignored-this-article.html

Collinson concluded his post with this observation: “As others have pointed out… you can only rationalise the failure of the current searches if you don’t include the words ‘active and noisy’, ‘called frequently’ and ‘easier to see and follow’, in your dataset.”

Of course, Tanner’s observations applied only to the John’s Bayou birds studied in close proximity to a nest. More importantly, Tanner’s recollection was incomplete and inaccurate, and he corrected it in another, humbler, posthumous piece that appeared in Birdwatcher’s Digest (2000) under the title “A Postscript on Ivorybills”. Tanner began by observing that, “Like everyone else’s memory, mine forgets the annoying and unpleasant things and remembers the pleasing; the mosquitoes go but the birdsong remains. Mine is also likely to forget the important and regular events and retain the trivial and unusual.”

The article makes it clear that finding even the John’s Bayou birds (which had a known territory and roosting ground) could be difficult and was even harder outside of nesting season. Tanner concluded with this reminiscence: “Hunting in other areas of the Singer Tract for ivorybills was even more difficult and discouraging. My journal is full of such comments as ‘saw old sign, lots of impenetrable vines, and no ivorybills.’ The only other ivorybill we ever found outside of the one nesting pair and their offspring was a single male that we dubbed Mack’s Bayou Pete because of the area he usually inhabited. He was hard to find and once found was soon lost . . . ”  And to reiterate, Mack’s Bayou Pete’s home range was at least something of a known quantity.

By 1985, Tanner was advising the US Fish and Wildlife Service to classify the ivorybill as extinct. He gave the following reasons, to paraphrase:

1) The reports have been unconfirmed and they often describe behavior that is characteristic of Pileateds (flushing from stumps and logs).

Tanner described this as being rare in ivorybills, which may or may not be true, but it’s certainly not unheard of. Allen and Kellogg observed a female feeding on the ground. Moreover, not all reports involved this behavior.

2) There’s so much recreational use of areas where ivorybills used to be present that people should be hearing and seeing them, and there are no extensive areas of former IBWO habitat that are remote and unvisited.

What’s omitted from this analysis is the fact that the beginning of nesting season and the end of deer season are roughly congruent, at least in Louisiana. This means that there’s actually very little human traffic in many prime nesting areas during the times when birds are most active and vocal. And of course, the John’s Bayou area was not particularly remote, although other parts of the Singer Tract were considerably more difficult to reach.

3) Ivorybills are fairly conspicuous birds that, “if present . . . are not hard to find. Furthermore, the feeding sign they made (scaling bark from extensive areas of not long dead limbs and trees) could be easily recognized as a clue to their presence.”

With regard to the feeding sign, I have to wonder what Tanner would say about the sign we’ve found that appears to match this description perfectly. With regard to being easy to find, Tanner’s field notes and his reminiscence in “A Postscript . . .” make it clear that ivorybills were extremely difficult to find, except in extraordinary circumstances – in close proximity to a nest and perhaps with a good deal of habituation to human presence.

Tanner’s story is amazing. His monograph is seminal though not gospel. The in-depth examination of his work in Stephen Lyn Bales’s Ghost Birds is essential reading. Many of his later pronouncements, however, have done a disservice and continue to sow confusion more than two decades after his death.

I’m indebted to Fredrik Bryntesson for sharing Herbert Stoddard’s 1936 letter and reminding me of Tanner’s missive to USFWS. This piece is informed by years of discussion with Frank Wiley. He also made a number of constructive suggestions about the specific content. Direct descendants excepted, Frank was undoubtedly J.J. Kuhn’s greatest admirer.


Sweet Gums to Sweet Gums and More

In this post, I compared scaling on sweet gums in our search area with images of scaling on sweet gums taken by Martjan Lammertink in Congaree National Park; he has graciously granted me permission to post those images and some others here.

PIWOscaling_N_Banfield

Pileated Woodpecker Scaling on Pine – Photo by N. Banfield/Cornell Lab of Ornithology

Steinhagen_scaling_M_Lammertink

High Branch Scaling on Sweet Gum, Steinhagen, Texas – Photo by M. Lammertink/Cornell Lab of Ornithology

PIWOscaling_M_Lammertink

Pileated Woodpecker Scaling on Sweet Gum, Congaree National Park, Photo by M. Lammertink/Cornell Lab of Ornithology

The focus of the original post was on the direct comparison between known Pileated Woodpecker scaling on sweet gums and the work we are finding in our search area. The differences are quite dramatic. In this post, I will simply include a number of examples of suspected ivorybill work from both our old and new search areas without too much discussion. The differences should be self-evident, even without reference to bark chips. I have come to believe that much if not all of the high branch scaling that Tanner presented as being typical and (by implication at least) diagnostic is not necessarily inconsistent with PIWO work. Thus, in the absence of other indicators, the Steinhagen photos are potentially interesting but not highly suggestive. Note that in all three images of PIWO work on boles, there is clear evidence that the bark has been removed in layers. This is true even on the pine, where signs of this layered work are visible on the left, just above the bird. I now suspect the absence or near absence of layering on extensively scaled, tight barked hardwoods may be the single most important component in the gestalt and may even be diagnostic in itself.

Even when the scaling is quite extensive, the signs of layering are likely to be a giveaway, as in this example from public land near our old search area. The bark chips around the base of this tree were all small and gave further indication that the work had been done in layers.

Presumed Pileated Woodpecker Scaling on Snag, East-Central Louisiana, 2011

Heavily Scaled Snag, East Central Louisiana 2011, Presumed Pileated Work

DSC01431

Detail Showing Superficiality of Bark Removal – East-Central Louisiana, 2011

Pileated Scaling on Snag - East Central Louisiana 2011

Detail Showing Bark Removal in Layers – East-Central Louisiana 2011

Most of the images below have been discussed in other posts. The scaling is on oaks, hickories, and sweet gums and the differences in appearance should be self-evident.

Hickory4

Scaling on a Hickory Snag, Louisiana, October 2013

 

Hickory3Top

Hickory3

Scaling on a Hickory – Top to Bottom – Louisiana, June 2014

MMHIckory2

Scaling on a Dying Hickory, Louisiana, May 2013

 

Oak1

Oak Scaling, Louisiana, October 2013

 

 

SP5140 scaled hickory (2)

SP5143 scaled hickory (2)

Spscaled hickory (2)

Hickory Scaling, Louisiana 2013 – Photos by Steve Pagans

HairyWPwork

FWHickory1

Hickory Scaling with eyed click beetle and Hairy Woodpecker work. We suspect that there may be a correlation between IBWO and HAWO foraging strategies.


Photo by Steve Pagans

Sweet Gum Scaling, Louisiana, January 2014, photo by Steve Pagans

ScalingNewArea

Hickory Scaling, Louisiana, June 2013

Heavily scaled young oak with suspected IBWO work extending from the base to well up on the trunk. Large bark chips are visible around the base of the tree

Heavily scaled young oak or sweet gum with suspected IBWO work extending from the base to well up on the trunk. Large bark chips are visible around the base of the tree

Extensive Scaling High on a Living Oak, Louisiana, March 2012

Extensive Scaling High on a Living Oak, Louisiana 2012

Detail of extensive scaling on oak

Detail of Extensive Scaling on Oak

Extensive Scaling on Live Willow Oak, March 2012

Extensive Scaling on Live Willow Oak, Louisiana 2012

Scaling on freshly dead oak, East-Central Louisiana, January 2010

Scaling on freshly dead oak, East-Central Louisiana, January 2010. Tree was extensively scaled including lower on the bole. Some bark chips were the size of my forearm

Sweet Gum Scaling, East-Central Louisiana, 2009

Sweet Gum Scaling, East-Central Louisiana, 2009


Apples to Apples and Sweet Gums to Sweet Gums

I’ve been corresponding with Mississippi-based searcher Christopher Carlisle both privately and on Facebook, and our conversations have inspired some additional thoughts on bark scaling and led me to revisit Cornell’s 2006-2007 final report, which includes two interesting photos of Pileated Woodpecker work on sweet gums taken by Martjan Lammertink in Congaree National Park. I was familiar with the document, which is available here but had forgotten about the images. Scroll to page 30 (some additional images of interest from Texas appear on the following page.)

While it’s a tiny sample, there may be some value in comparing the Congaree photos with the work on two heavily scaled sweet gums in the Project Coyote search area.

Correction: the tree in the second image is a hickory.

Photo by Steve Pagans

Photo by Steve Pagans

ScalingNewArea

While it was not possible to examine this scaling up close, the bark appears to be tightly adhering on both trees, and the decay state is likely comparable to the Congaree sweet gum. The work in both cases is on the boles, and the size of the trees involved seems to be roughly comparable. Beyond that, the scaling is dramatically different in a number of ways. Most obviously, the suspected IBWO work from our search area is far more extensive than the PIWO work from Congaree (I suspect the small patches of scaling in the lower photo are the work of a Hairy Woodpecker). As I’ve discussed, PIWOs are not well-suited to scaling bark, anatomically, and it’s not a preferred or efficient feeding strategy – accounting for 23% of observed foraging behavior in Tanner and 7% in Patricia Newell’s more recent and PIWO-focused study.

The most significant difference though is in the appearance of the edges. When Pileated Woodpeckers scale tight-barked hardwoods, they typically remove the bark in layers, as in these images. This layered scaling is also very apparent in the photos from Congaree, and it’s absent from our sweet gums as well as from the extensively scaled oaks and hickories that we found in 2013-2014. Our trees show very extensive scaling with no indication that bark has been removed in stages; the edges are clean and incised and very large areas have been stripped, down to the sapwood. If Pileated Woodpeckers were the cause, it would be reasonable to expect that there would be some sign of layering, especially given the surface area involved, which far exceeds that shown in the Congaree photos or any others I know of (on hardwoods) from the Cornell searches.

The high branch work from Texas is intriguing, but the resolution of the images is insufficient to determine whether this clean scaling or whether there’s some excavation, especially on the lower portions. In addition the work is not nearly as extensive as some of the high branch work we’ve found.

 

Edited to add: I’m more intrigued by extensive work below the crown, as in these images. One tree (in the third photo is), definitely a sweet gum is from the old search area. The other tree, which I believe is an oak, is within a hundred yards of where I recorded kent-like calls in 2013, although the photos were taken a year before.

 

DSC03476DSC03478DSC03525

There are several other images of sweet gum scaling from Congaree in this report from the mobile search team, but this work does not involve the removal of bark from large contiguous sections of trunk, and the resolution is not sufficient to tell whether the bark has been removed in stages, although it appears to be in at least one of the four photographs. If I were to find it, I would assess this work as being mildly interesting but would not get excited about it in the absence of other indicators.

To return to my exchange with Chris, it gave me the opportunity to revisit this material, to give some more thought to my hypothesis about feeding sign, and to make some adjustments:

  • I think scaling on pines, even live ones, is physically possible for a pileated, although the bark will often show signs of having been removed in layers, meaning the edges will not appear as clean. Nonetheless, I do not think there’s a way of reliably determining what species has scaled a pine in the absence of a direct observation and suspect that even HAWOs and RBWOs can scale extensively even on recently dead pines.
  • For the work that I think is diagnostic, the species that I think are most reliable are oaks, sweet gums, and hickories. I think that the distinction is an easy one to make once you’ve seen the work firsthand.
  • In the old Project Coyote search area, we had persimmons, hackberrries, and honey locusts that had very suggestive scaling and lots of it. But the bark on honey locusts tends to loosen early in the decay process. Hackberry bark fractures, and while persimmon bark is thick and tight, it tends to loosen when the wood is still very hard. These qualities complicate the analysis, though I’m confident some of that work was done by IBWOs. There was a vast difference between the size of bark chips from known PIWO foraging on honey locusts and suspected IBWO foraging on the same species.
  • Extensiveness and quantity (concentrations) are important to look for too, especially when there are a lot of pines or an abundance of more easily scaled hardwoods. For this analysis, I include looking at high branch work but otherwise don’t ascribe a great deal of importance to “Tanneresque” sign, unless there’s a lot of it, and it’s associated with what I think is diagnostic.

I am not suggesting that this is the only way that Ivory-billed Woodpeckers forage. There may be seasonal and regional variations, but I suspect that some of this type of work will be present in any area where IBWOs are resident. It’s not necessarily easy to find. I agree with Fangsheath, from ibwo.net, that the failure to do so should not be treated as evidence of absence, but I’m convinced that finding this very specific type of work is compelling evidence that IBWOs are present.