Think of this as a prologue to some upcoming posts on evidence – including a more structured discussion of the evidence we’ve obtained over the years and my take on broader issues of evidence and the ivorybill controversy. Look for those at the end of this month and in July. There’s likely to be a trip report posted before then. I’m also planning a postscript to the Bits ‘n’ Pieces series that summarizes my thoughts in a more organized fashion. That will come sometime this summer. In addition, we will have trail cam imagery from seven deployments (plus unreviewed imagery from five cards) to examine over the summer. We’ll be adding an eighth camera later this month, targeting some scaling Tommy found last month. As discussed previously, we plan to leave these cameras in place for the foreseeable future.
In the meantime, I thought I’d share the details about and accompanying photographs related to two sightings Frank had in the old search area during the summer and fall of 2009, before my first visit. But first, I’d like to share a trail cam image from the location and deployment where we obtained a suggestive trail cam image a week after I had a possible sighting. With the passage of time, I had forgotten that the landowner’s grandsons (who are mentioned in one set of Frank’s notes) had reported seeing an ivorybill in the same immediate vicinity on the morning when Frank and I had an auditory encounter, and the day before my possible sighting.
This image below was captured in 2009, the day after the one mentioned above that we published years ago. The bird is in flight, just below the fork and to the left of the scaled trunk. I’ll leave it to readers to evaluate; I don’t know what it is, but I think the wing pattern is intriguing. You can click on this image (and the others) to view them in a larger format.
With regard to trail cam photos, this is a processed detail from another image from 2009 that Frank liked for ivorybill and that he may have posted on ibwo.net back in 2009 or 2010. I was initially intrigued by this image but was eventually convinced that it shows a Pileated Woodpecker with somewhat worn feathers and that the apparent long tail is due to the posture of the bird. It was a rare time when Frank and I agreed to disagree about an ivorybill related matter. I remain convinced the bird is a Pileated and won’t be including this in my planned discussion of our evidence, but I’m posting it here because Frank had such a strong opinion about it.
In summer and fall 2009, before my first visit to the property, Frank had two sightings in the course of which he obtained several photographs. These images are inconclusive at best, and the late Bill Pulliam had a critical take on the two Frank took during the first encounter. I’ll include the bulk of Bill’s analysis below; his commentary notwithstanding, I think these images are worthy of posting now. In retrospect, they are among the very few such images that have been obtained in conjunction with a sighting and with accompanying field notes. The context in which they were obtained, in a small area where there were multiple sightings and auditory encounters by multiple people over a period of six months, gives these notes and images added weight, in my view. I’m grateful to Amanda Wiley Legendre for giving me the go-ahead to post this material. All photos and field notes are by Frank Wiley
Here are screen caps of Frank’s handwritten notes (with a minor redaction to protect location information). The photographs follow.
Bill Pulliam compared the images with others showing the background without the bird present. This is what he had to say:
First Image: I’m actually having a very hard time making sense of this one. What I get as bird is the three large white areas, the small black spot between them, and a reddish or yellowish mass to the lower left. From the context of the two images thus would seem to be a side view of a bird flying to the left and somewhat away. At a glance it almost looks like a bird with a white body, white wings, dark on the breast, and rusty red head. In the absence of any other information, I would think it is some sort of duck except I’m not sure how to make the colors match up. The reddish blob to the left really does look like the head of a duck flying to the left.
I can’t reconcile this with a woodpecker of any kind, or with the description you provided. It might be a molting young little blue heron or white ibis, I suppose. It really kinda looks like a canvasback, except this is august, right? Even if I disregard the red head, I don’t see how to line it up sensibly.
Second Image: This one is even more problematic. There are the two white arcs that look like wings, but then there is a long narrow dark extension to their left. This time the foreground object comes out to be: I don’t know WHAT this might be. If I disregard the long thing to the left it might be something with white wings, but it’s hard to say more than that.
In summary — I can’t make sense of these objects to have any idea what to call them; the first one is not easy to reconcile with Ivorybill, the second is just hard to say anything about. Given that they are actually the same object, I’m still at a loss.
Sorry, not what you want to hear, but it’s what I come up with. Bill
In reading Bill’s comments for the first time in years, nearly a decade after he wrote them, I’m struck more by how perplexing he found the images to be than by his coming up with something I didn’t want to hear. I am also struck the level of detail in Frank’s description, which I also hadn’t looked at since he wrote it or shortly thereafter.
It’s worth bearing in mind that these photographs were taken with a mid-range, consumer 2008 DSLR with a very modest burst mode. It’s to Frank’s immense credit that he got any pictures at all under the circumstances; the same goes double for the next series.
This is Frank’s account of his November 8, 2009 sighting, which he wrote up in Word, again with a few redactions unrelated to the substance of the report. This was approximately a half mile from the camera trap location. Note that I don’t have copies of all the images Frank used in the figures below, so I’ve taken screen captures from the Word document. The images I do have are reproduced in full size at bottom.
Figure 1: Overview map of sighting area
On 11-08-09, Frank Wiley at approximately 7:30am CST was on speakerphone with Mark Michaels of New York. During the time we were on the phone I was approximately 1000 yards Southwest of the location shown in Figure 1 above. During that time while I had Mark on speakerphone, he heard several possible double raps (though over the phone he could not separate the individual raps), and at least one very loud single rap that he remarked upon as being very distinct and woody. These sound detections were quite loud to me, as the observer on the scene, and were obviously loud enough to be picked up at a considerable distance by the speakerphone microphone in my Blackberry. I had my Sony IC recorder running nearby at the time, but have not yet reviewed the recording to determine which (if any) of the putative sound detections it may have picked up.
During the time we were connected, Mark was able to make out calls of Pileated Woodpeckers, a Yellow Shafted Flicker, and Red Bellied Woodpeckers, as well as numerous other bird calls. Additionally, I identified by sight a number of other woodpeckers including 2 Downy Woodpeckers, a Yellow Shafted Flicker, numerous Red Bellied Woodpeckers, numerous Pileated Woodpeckers, 1 Hairy Woodpecker and a pair of Yellow Bellied Sapsuckers. Photos of all (time and date tagged) are available for review, except no photo of the Yellow Shafted Flicker.
Note: I do not have copies of the photos or the audio recording referenced above.
At one point, I stated to Mark that I was possibly being approached by an ivorybill. A black and white bird with the apparent giss of a large woodpecker was approaching my position. Before the bird reached me, it was mobbed by a small (3 or 4 birds) murder of crows, and fled to the North. The unknown woodpecker appeared slightly larger than a Pileated, but was slimmer in profile with seemingly longer wings. Its flight did not undulate as a Pileated normally would. I cannot ascribe any field marks to this bird that would definitively identify it as a Pileated or any other species of large woodpecker, so obviously, Pileated Woodpecker cannot be ruled out in this instance.
After the forest quieted down, I got off the phone with Mark, and staked out a small finger lake in the area for a couple of hours. Woodpecker activity remained higher than usual in the area, especially the Red Bellied and Pileated Woodpeckers. During this time, I heard some loud “hammering” that had a pop…POP-pop sequence coming from across the lake, at a distance I would estimate to be greater than 150 yds.
Slightly before noon I walked out of the forest to the home of a member of the family, that owns this tract of forest. I visited with him and his wife until their son M (14) and nephew B (14) returned from their morning squirrel hunt. As I planned to deploy a game camera, and having had one stolen a couple of weeks before, the boys had hooked a trailer to their ATV, and were hauling a caving ladder so I could strap the camera to a tree 10-12 feet off the ground to deter theft and meddling.
We were on the ATV (B riding on the trailer, M driving, and I was riding behind him) and headed to the spot where I planned to deploy the camera (in the forest approximately 100 yds West of the tree circled in Figure 1). Immediately after crossing the slough shown on the Southern portion of the map, B began pounding my back and shouting “There goes the bird!”
Though young, B and M have spent their lives in the woods. They have keen eyesight, and are becoming quite adept at identification of the larger birds common to the area by sight and sound. I have repeatedly tested them with Pileated visual and auditory contacts with “Is THAT the bird?” and they never claim that a Pileated is “the bird.” “The bird” we are discussing is the Ivory-billed Woodpecker.
M and I looked in the direction (North/Northeast). B was pointing and sighted the bird at approximately 275 yards, flying just above the canopy West to East. The bird did not “swoop” or “undulate” in the manner of most woodpeckers, and displayed distinct white plumage on both the dorsal and ventral secondary flight feathers. The bird’s giss was more slender, and longer, with a longer seeming tail than a normal Pileated. I quickly raised my camera and snapped off three quick shots. While the bird was definitely in the frame, I had bumped my focusing dial, and it was not focused at infinity for the zoom setting. Upon review, these three frames reveal nothing but blur, but have been retained for my records. This occurred at 1:38pm CST (2:38pm CDT on the camera). The bird then banked to its left (North) and disappeared from view.
M restarted the ATV and began moving North, when approximately 1 minute later, B shouted “There’s one on the side of that tree!” indicating a large pecan in the Northwest corner of the clearing. Both M and I looked up as three large black and white woodpeckers with trailing white secondary dorsal flight feathers flushed from the side of the tree. I am quite sure of our identification of these birds as Ivory-billed Woodpeckers.
Even though the range was extreme (later measured at approximately 225 yards), I raised my camera again (prefocused to infinity this time) and got off four shots of a bird fleeing to our left (West). These photos, Figures 2 thru 9, appear below. Figure 2, 3, 4, and 5 are the pictures as seen in the original file reduced for insertion into this document. Figure 6, 7, 8, and 9 are cropped and zoomed at the same pixel rate and resized for insertion into this document. In my opinion, except for the long tail, and odd wing shape, Figures 6 and 7 look somewhat like a crow. Figure 8 is apparently a large woodpecker with wings in a “tucked” position. Figure 9 is the same bird with the wings in an upward position. In both Figure 8 and 9, a long, substantial bill appears to be present. In Figure 9, the bird’s right wing shows possible white along the trailing edge in the location of the secondary flight feathers.
Again, the fact that he was able to get any photographs at all is a reflection of Frank’s skills, which he had honed as a hunter. And while these photographs are inconclusive, the description of what he observed lends them considerable weight in my view.
Here are the frames that I still have on my computer. A couple are processed and cropped somewhat differently. One includes an annotation that Frank omitted from the report, highlighting an American Robin to provide a sense of scale. It may be helpful to examine these higher resolution versions.
Matt spent several days in the search area after my departure. On the afternoon of March 19, he staked out a fresh cavity approximately .25 mile from a location where I recorded a double knock in apparent reaction to an ADK in 2014 and where we captured some intriguing trail cam images. This is about a mile from where Matt and Phil recorded numerous kent-like calls last year.
After more than two weeks of steady presence in the area, and no possible contacts, Matt heard and captured one distinct kent-like call a few minutes after sunset. On reviewing the audio, I found two additional calls about 16 minutes earlier on the recording. There’s also a very faint possible call that comes approximately 2 minutes and 35 seconds before the most distinct one; it’s so faint that I’ve opted not to extract and include it here. Before providing some commentary, Here’s Matt’s description of his experience and observations:
While on the stakeout described above, I began recording at 6:51 p.m., exactly thirty minutes prior to official sunset for that date and location of 7:21 p.m. For the four days prior to this one, I had been keeping notes on “last of the day” woodpecker sounds. Small sample size, but the woodpeckers had consistently gone silent at six to four minutes prior to official sunset on each preceding day. Falling into the trap of unwarranted speculation, I noted with some sadness that sunset had passed without any intriguing sounds.
The following clip runs approximately 1 minute and 45 seconds (to give a sense of the ambient sounds and conditions); the kent-like call comes at 1:36.
Here is a much shorter, amplified extract. The call should be easy to hear.
The sonogram suggests that the call has a fundamental frequency somewhere between 515 and 550 hz. There’s a strong second partial and a weaker third partial (the horizontal lines to the right of center). While the sonogram is not a perfect match for last year’s recordings (or the Singer Tract recordings for that matter), my ears and my common sense tell me that the source of the calls is the same. While the frequency is slightly lower than most of the calls recorded by Hill et al. on the Choctawhatchee, the structure is very similar. (See figures E and F.)
The two additional calls I found are very faint and presumably more distant. I was not able to tease out a sonogram with my software, even with a lot of amplification. The calls may be hard to hear without headphones, so listen carefully. The first clip is unamplified, and the second is pushed as far as was practical.
Bob Ford had the following to say about the first call (heard by Matt in the field):
“I spent a little more time on this one than I usually do . . . . I don’t do the sonogram analysis work myself but instead listen, compare to other known/recorded sounds, use my field experience etc.
I cannot think of a single thing that would make this sound other than ivory-bill. For me, it’s easy to dismiss the usual suspects like Blue Jay or tree squeaks etc. I fall back to turkey and wood duck. I’ve heard both species make sounds I never knew were possible from those animals. But in this case, even stretching, I can’t make it into turkey or wood duck. The sound is too robust, too “direct” (hard to explain, maybe I mean punctuated?), it’s a single sound (my experience turkey and wood duck continue even if its same sound). It’s not artificial, I believe it came from an animal. I agree, this is about as hot as it gets lead-wise.”
As I pointed out to Bob and the rest of the team, Matt’s call and the ones recorded last year have frequencies and structures that are closer to geese than some of the other confusion species, though I’m convinced that none of the calls we’ve recorded came from geese. These Canada Goose sonograms illustrate the similarity. Jackson, pp. 179-180, also notes the similarity between IBWO sounds and those made by geese.
Cornell’s criteria call for fundamental frequencies between 580 and 780 hz. (the frequency of the kents on the Singer Tract recordings). As already noted, Matt’s sound is somewhat lower pitched, but not outside the capacity of an Ivory-billed Woodpecker. The calls on the Singer Tract recordings that Frank and I described as the “wonka-wonkas”, examples starting at around 3:14, are both goose like and have lower fundamental frequencies.
It’s also worth reiterating that the Singer Tract birds were obviously agitated when those recordings were made, and as Tanner put it: ” . . . the kent note given in monotone and slowly or infrequently is the ordinary call note. When the bird is disturbed, the pitch of the kent rises, and it is repeated more rapidly frequently doubled, kent-kent, with the second note lower. (p. 62, emphasis added.)
Rob Tymstra, an accomplished Canadian birder and IBWO searcher, visited the search area a couple of weeks later, and on April 5, he reported the following from a location a few miles south of Matt’s capture:
“. . .at 11:55 am yesterday, I heard one clear kent-like note about 50-100 yards north of the bridge. I noted the pitch of the sound (using my ukulele) and compared it later to the soundclip Mark sent me a few days ago. The quality of the sound is similar but the pitch of my sound was about a whole note higher than yours. I didn’t hear or see anything unusual after that. I can’t say that it sounded like an ivorybill but it’s certainly a sound I’d never heard before (and I know most of the birdsongs).”
A whole note higher would likely place the fundamental frequency at the low end of Cornell’s range.
I’m personally convinced these calls and the calls recorded last year came from Ivory-billed Woodpeckers. It’s also my view that the recordings Matt and Phil have made are among the strongest evidence for the ivorybill’s persistence obtained to date.
I’m more puzzled by the difference between last year, when birds were calling very actively on at least one day, and it appeared that the sounds had at least two and possibly as many as four sources, and this year when calls have been so few and far between. I can’t help but wonder whether the difference might be due to nesting success last year and failure this year. Pure speculation on my part, but perhaps we’re getting close to resolving some of the mysteries.
If the sounds Matt captured last month were Ivory-billed Woodpecker calls, it seems likely that he was in the vicinity of a roost; however, Matt returned on the morning of March 21 and did not hear anything. (There was lots of avian and woodpecker activity.) No suggestive sounds were apparent on my review of that morning’s recording, so if there is a roost in the area, it seems unlikely that it was used on the night of the 20th. Whatever the case, the location is very short walk from the road, and I plan to devote several mornings and evenings to sitting in the area with recording device running and camera at the ready.
Edited to add: When Matt and I first discussed the call, I remembered that Don Eckelberry’s account and his description of the Singer Tract ivorybill calling around sunset. I’m grateful to Houston, of IBWO.net who was reminded of it too and sent me Eckelberry’s exact words:
. . . At 7:20, after I had finished all my notes and we were about to leave, she popped out and raced up the trunk to its broken top where, bathed in rich orange light of the setting sun, she alternately preened and jerked her head about in a peculiar angular way, quite unlike the motions of any other woodpecker I knew. I was tremendously impressed by the majestic and wild personality of this bird, its vigor, its almost frantic aliveness. She flew off after five minutes and in another five returned, calling once and going in to roost at 7:30 on the dot. By the time we regained the road it was quite dark.
Regular readers are no doubt familiar with some of the images shown below. The “neck bird”, which was photographed in our old search area in August 2009, has been discussed in a number of posts. I think it likely shows a female Ivory-billed Woodpecker, something that became clearer once I satisfied myself that what appeared to be red in the crest (in the wrong place for either Pileated or ivorybill) was likely an artifact and that the crest appears to be all black, as shown in the enhanced image below. The original captures (the first taken a minute before the neck bird appears and the second showing the neck bird) are immediately below that for those who haven’t seen them.
Years after the capture and probably after the first post about this image in 2014, I noticed that an object suggestive of a light colored bill was visible in both frames, apparently protruding from the lower cavity in the snag to the right of center. While I have shared this information privately with a number of people and did a vague Facebook post about it a couple of years ago, I’ve hesitated to blog about it or discuss it in detail. That changed after I showed it to Jay and Erik before we parted company on my last trip to Louisiana. When Erik suggested that the object might be a vine or some other intervening vegetation, I decided to go back through my files. I discovered that Frank had sent me several additional captures from the same deployment. I examined these frames and found that the apparent bill was absent from all of them.
Below are details from frames 1095 and 1096 showing the apparent bill, which changes position slightly from one frame to the next. The time lapse interval between images was 1 minute. Again, the cavity in question is the lower one (below the fork) in the snag to the right of and behind the one on which the neckbird is seen in 1096. These snags are black willows (Salix nigra), and the neck bird snag (with the large cavity apparently being used by a squirrel) fell between November 2009 and January 2010. I’m also posting the close-ups in tiled mosaic format so they can be viewed side-by-side.
For this round of image processing, I used Let’s Enhance, which enabled me to retain a large format for cropped and zoomed versions.
Next are two details from images captured a few days later. The possible bill is nowhere to be seen. The same is true for the other captures from this deployment. Thus intervening vegetation and artifact can be ruled out.
To summarize, the following two photos show what appears to be a bill in the cavity:
2009-08-11 7:48 am (image 1095.jpg)
2009-08-11 7:49 am (image 1096.jpg – the neck bird photo)
The following photos show a cavity with no apparent bill:
2009-08-14 6:19 am
2009-08-14 6:20 am
2009-08-14 6:21 am
2009-08-14 4:06 pm
2009-08-14 4:07 pm
2009-08-15 6:20 am
If this is a bill, it appears to be large and light colored, consistent with Ivory-billed Woodpecker. Both Erik and I noticed that, in frame 1095, a topmost part of the white dorsal stripe also may be visible. When Jay first saw the photos, he was reminded of the Neal Wright photos from Texas. Some images from the Singer Tract also come to mind.
Thus, this apparent bill resembles those of known ivorybills in cavities – in size, shape, orientation, and contrast. It is present only in frames 1095 and 1096 (the latter of which shows another possible ivorybill); it changes position over the course of a minute, from one frame to the next. There is no way to be sure images 1095 and 1096 show an Ivory-billed Woodpecker in a roost hole, but these facts, especially taken together, suggest that they may.
When I look back at what transpired in the old search area between August 2009 and November 2010, when the adjoining parcel was logged, it’s extraordinary. I may revisit those events in a future post or two.
For now, I’ll close by tying this into the Bits and Pieces series. The old search area is not one that would be deemed suitable under most habitat models. The images above were captured in a stand of black willows at the edge of a bean field. The other trail cam capture, where I had a sighting, was also within perhaps 30 yards of that field. When I look back at my assessment of the habitat from the time, I think I somewhat naively overstated its quality; however, there was a good deal of dead and dying timber, and it was in close proximity to several much larger habitat patches. If we did indeed capture ivorybills with our trail cams, their presence in this area may point to how the species has been able to adapt to more fragmented habitats.
Thanks to Erik Hendrickson for his input on this post and his help in making it clearer.
If you’ve been following this series (Part 1, Part 2, Part 3, Part 4, Part 5) you know it has focused primarily on preconceptions about ivorybill range and habitat types and how the actual record paints a very different picture from what many of us think we know about the Ivory-billed Woodpecker. As I noted in the most recent installment, if our knowledge of the Ivory-billed Woodpecker were based on the archaeological record alone, we’d think of it as an upland species. Further, we might very well assume that it ranged from the hills of Georgia, to the Alleghenies in Virginia, to central Ohio and west-central Illinois.*
While it may border on heretical to say so, I think there’s a plausible argument that the ivorybill’s range prior to around 1800 extended as far north as the mid-Atlantic states (New Jersey and Pennsylvania on the Eastern Seaboard) and as far north as central Ohio west of the Appalachians. I’m inclined to think this is likely based on a number of accounts including: Peter Kalm (a student of Linnaeus who reported the species was present in New Jersey and Pennsylvania in the 18th-century), Jefferson (1780s) and Nuttall (1840s) who included Virginia in the range, and Gerard Hopkins a Quaker from Maryland traveling to Indiana to meet with the Miami and Potowatami Nations. Hopkins described a female ivorybill at Piqua, Ohio (north of Dayton, elevation 873′) in 1804 (Leese, 2010.)
In addition, there’s the specimen that Wilson reportedly collected near Winchester, Virginia ca. 1810 (Jackson) and the central Kentucky specimen reportedly collected in the 1780s (Jackson, accepted by Tanner in 1989). As I see it, the tendency to treat these records as suspect is based, at least in part, on post-Civil War or post-Audubon “knowledge” about the ivorybill and its habitat, rather than anything intrinsically implausible about the claims themselves.
At minimum, one of the Ohio archaeological finds dates to the 15th or 16th century, so there’s strong reason to think that the ivorybill’s range extended that far north at the time of contact. North American Native populations began to decline after Columbus’s arrival, and De Soto’s expedition, 1539-1542, led to the collapse of the Mississippian culture. (De Soto also introduced the hogs that plague the southern forests to this day.) As a consequence, countless acres of formerly agricultural lands throughout the eastern United States were reforested and remained so into the 18th and 19th centuries. There’s little reason to think that the ivorybill’s range would have contracted at a time when the total acreage of potential habitat was increasing.
I’m reminded that tree girdling may have been an important factor. The only counterargument to the foregoing suggestion about the increase in total acreage after De Soto is that Native American agricultural activity declined drastically during that period, so that while habitat acreage increased, habitat quality may not have. Tree girdling and intentional burning likely played an important role in creating good conditions for ivorybills and could conceivably have led to range expansion during the Mississippian period and again temporarily during the first couple of hundred years of European settlement.
Ivory-billed Woodpecker use of girdled trees was noted by several early observers – notably Audubon, Gosse, and Scott (in Florida, later). While researching this aspect, I came across an interesting account from 1840s Central Louisiana, apparently just south of Alexandria (the citizens of that city are described as “chiefly gamblers or cunning speculators, a nest of incarnate devils, who live by cheating the latest comers, and, whenever possible, each other.”) I’m not aware of this account having found its way into ivorybill literature:
From Echoes from the Backwoods; or, Scenes of Transatlantic Life, Captain R.G.A. Levinge (1849).
With this as background, I’d like to propose an alternative explanation (or more accurately an alternative group of explanations) for the ivorybil’s decline. If you think, as I do, that the ivorybill has persisted, this may help explain how the species survived and may even provide some hope for its future, even in this era of mass, anthropogenic extinction.
When it comes to the decline and possible extinction, there has been a tendency to look for one or two causes. The IUCN Species Account gives the following reasons:
Logging and clearance for agriculture are responsible for the dramatic decline in numbers and range. These factors are likely to threaten any remaining population. Hunting has also been implicated in the rapid population decline, and it has been proposed that this was the primary cause of its decline, with habitat destruction playing a secondary role, but this theory is contentious (Snyder 2007, Hill 2008, M. Lammertink in litt. 2012).
Tanner emphasized the importance of logging during the post-Civil War era, although several of his data points seem to suggest that ivorybills were disappearing prior to the most active logging dates. He also stated that the ivorybill’s disappearance “coincided at least roughly with a time of active or rapidly increasing logging.” Elsewhere in the monograph, he focused on food supply, and I suspect that this, rather than logging per se was a more important factor in the ivorybill’s decline.
That’s not to say logging was unimportant; it clearly played a major role. To expand briefly on the point Bill Pulliam raised: by the late 19th century, the more adaptable Pileated Woodpecker, had been extirpated in many parts of its range, and many expected it to ‘go the way of the ivorybill’. That didn’t happen, and PIWOs returned to or became more common in many areas (my own included) as farming gave way to suburban development and forested acreage increased as a result. I’d suggest that for the ivorybill, habitat degradation, rather than habitat loss, was what initiated the decline, with extensive logging and then hunting accelerating an already existing trend.
That is to say, a number of additional anthropogenic factors likely played a role in the ivorybill’s decline and dwindling range, especially outside of Florida, where hunting and collecting likely had much greater impacts than elsewhere. Hasbrouck, writing in the 1890s, contrasted the lack of collecting in Louisiana, Arkansas, Missouri, and Tennessee with what was transpiring in Florida at the time. And it’s important to remember that Florida, which retained ‘frontier’ characteristics far longer than other parts of the eastern United States, was ground zero for the killing and collecting of birds – for commercial and ostensibly ornithological purposes. Ivorybills appear to have been more common in Florida than elsewhere by the second half of the 19th century, but it also seems probable that they were far more heavily persecuted there than anywhere else.
I’m hypothesizing that the shrinking distribution was correlated with settlement patterns in the northeastern part of that range and that by the middle of the 19th-century, east of the Mississippi, it had dwindled to the now familiar outlines, such as those shown on the IUCN range map.
The situation west of the Mississippi is somewhat more ambiguous. A specimen was collected at Forest Park, Missouri (near Saint Louis) in 1886, and there are records from west of the map in Texas dating to the early 20th century. Nevertheless, the general trend toward a shrinking range, which was frequently described in the 19th century literature, is clear.
European settlement brought about numerous changes in the land even before wholesale clearing of forests began.
As mentioned briefly in the discussion of tree girdling, Native Americans used fire for agricultural and wildlife management purposes, something that was likely beneficial for ivorybills. As Native Americans were exterminated, pushed out of their original homelands, or confined to small reservations, and as European settlers tried to control or eliminate fires, a significant factor contributing to tree mortality was likely reduced, dramatically.
Fulton’s invention of a commercially viable steamboat in 1807 revolutionized commerce, drastically accelerating the clearing of log jams from many watersheds in eastern North America. It’s fair to say that “widespread removal of instream wood for steamboat routes, timber rafts, and flood control was equally significant in decreasing floodplain sedimentation and river complexity, and in causing a fundamental, extensive, and intensive change in forested river corridors throughout the United States.” (Wohl, 2014.) As with changes in fire regimes, this clearing of log jams likely led to a decline in the number of stressed and dying trees along the riparian corridors that seem to have been so important for the ivorybill.
Perhaps equally if not more important in my view is the extirpation of the beaver. It is almost impossible to overstate the role of the beaver in shaping ecosystems throughout North America, a subject that’s addressed in engaging detail in Frances Backhouse’s Once They Were Hats. Beavers help create conditions that are good for woodpeckers by stressing and killing trees, through foraging and by changing hydrology. I’ve never tried to quantify it, but many, perhaps most, medium to large sized sweet gums in our search area show signs of beaver damage, and many others have been killed or severely weakened by beaver-caused flooding.
While beavers are not native to peninsular Florida, the ivorybill’s dwindling range elsewhere roughly tracks their decline; with extirpation starting in the northeast, moving West, and then South. (Southern beaver pelts were less valuable.) By 1900, beavers had disappeared from most of the southeastern US, and in Tanner’s day, a very small population persisted in the Florida Parishes of eastern Louisiana. Reintroductions began in the 1950s, and beavers are now considered a pest animal in Louisiana. It’s worth pointing out that the introduced beaver population in Tierra del Fuego appears to be benefitting the native Magellanic Woodpecker (Soto et al. 2012).
The resurgence of the beaver throughout the southeastern US is almost certainly producing substantially improved habitat conditions in many places. While the old growth forests may be virtually gone, it’s not inconceivable that ivorybill food sources are considerably more abundant now than they were in Tanner’s day, and if the species survived, conditions may actually be more favorable than they were in the 1930s and ’40s. It’s also worth pointing out that the southeastern United States is one of the few places in the world where forest cover has increased substantially in the 21st century.
It should be clear to readers of this series that the Ivory-billed Woodpecker inhabited a larger range and was able to exist in more varied habitats than most publications on the species suggest. This has implications for searchers and for what is deemed to be suitable habitat. For example, the trail cam images from the old Project Coyote search area were obtained near the edge of a bean field, and the putative ivorybill roost holes were in willows (more on that in my next post). Since ivorybills in the western part of their range seem to have lived in willow and cottonwood dominated riparian corridors, fast growing, short-lived willows might have played an important role in the species’ survival in other areas too, although willow-dominated habitat would be dismissed as unsuitable under conventional standards of habitat appropriateness.
It seems to me that even a slightly higher degree of adaptability would increase both the chances of survival and the likelihood that surviving populations might be overlooked due to preconceptions about habitat “suitability” ; this was doubtless one of the factors that led officials to dismiss the landowner in our old search area. Now that beavers are again abundant in the southeast, habitat that might otherwise have been deemed “unsuitable” may now be able to support ivorybills, even if the forest itself is not very old. While I don’t envision a recovery along the lines of what’s happened to the Pileated since my youth (when seeing my first one was a thrill as much for its scarcity as its beauty), I think it’s possible that ivorybill numbers have been increasing gradually and modestly over the past few decades. There was, of course, fairly intensive searching from around 2000-2010 (though it’s mostly over now), but it may be that the more numerous sightings from this period and afterwards are due to more than just the increased effort.
*The remains found in Native American middens were unlikely to have been trade goods; ivorybill parts seem to have been a valuable commodity for ceremonial use west of the Mississippi but not east of it, and in several cases, the remains found were tarsometatarsi, which would be consistent with use as food:
There is strong physical evidence of ritual value for woodpecker scalps and bills from the upper Midwest and Plains . . . Remains of the Ivory-billed Woodpecker can be found in sacred bundles, on pipe stems, on amulets, and with burials among the Native Americans of the region. The evidence comes from the western Great Lakes and the Plains; no
evidence of a particular use of Ivory-billed Woodpeckers has yet been un-
covered from the eastern area of the Great Lakes (Ohio, Indiana, and Michigan).
(Leese, 2006.) Leese also points out (in several of his publications) that there’s no evidence that ivorybill parts other than scalps and bills had any trade value.
A number of these midden records were accepted by Tanner in his unpublished 1989 update.
I had been planning to do a post with various ivorybill related tidbits in anticipation of the search season, which begins next month. That will be coming in a week or so, but I want to say a little more about Bill Pulliam first (beyond his Luneau video analyses, which I think should be dispositive). This decision was inspired in part by one of our advisors who pointed similarities between what Bill observed in Tennessee and what we’re seeing in Louisiana. While the physical characteristics of our old search area seem to have more in common with Moss Island, Tennessee than where we’re currently focused, Bill’s perspectives are relevant to both.
Edited to add: Moss Island is a small wildlife management area encompassing 3400 acres. I’m not sure what percentage is mature bottomland hardwood forest, but there are a variety of other habitat types. Compared to our search areas it is relatively isolated and distant from other large tracts of forest.
As an aside, Cyberthrush also has a post honoring Bill with a link to an eBird tribute.
With comments included, Bill’s series of posts on Moss Island runs to nearly 54,000 words. There’s no telling how long this series will remain readily accessible online, and indeed some of the images and sound files are no longer available. The entire series is worth reading and saving if you’re seriously interested in the ivorybill. It starts here.
On re-reading the posts for the first time in eight years, I’m struck by how much Bill influenced me without my recognizing it and/or how much the evolution of my understanding between 2009 and today is congruent with the ideas he expressed just as I was getting more deeply involved in searching.
Like Bill, I suspect that the near extirpation and revival of the beaver may be central to the ivorybill’s decline and survival (more about this in my next post). Like Bill, I think that Tanner’s model failed to account for environmental changes that had taken place in the preceding centuries. Like Bill, I think that if the ivorybill survived, it had to have adapted in ways that are inconsistent with Tanner’s a priori assumption that the species is old-growth dependent.
Bill was tough-minded and opinionated. There were times when I thought he considered me a somewhat annoying amateur. While we hadn’t communicated about it in recent years, he took a dim view of my efforts to make sense of feeding sign in the early days. Most of our correspondence took place in the 2000s, while he was still actively blogging about the ivorybill. After that, I sought his input sparingly.
My last exchange of emails with him pertained to the March recordings. Without quoting him directly, I think it’s fair to say he thought the calls were likely or more than likely Ivory-billed Woodpecker. He also thought it unlikely that birds were resident in our search area, based on the pattern of potential encounters, the paucity of strong sightings, and lack of conclusive evidence. I’m not sure I agree; I wish there had been a chance to explore this topic in more depth and that he’d been able to see our search area for himself. Nonetheless, his perspective has led me to consider that other nearby forested areas deserve more attention than we’ve given them to date.
I’ll conclude with three paragraphs from his final post in the Moss Island series. It’s as true today as it was in November 2009 (though I suspect nesting may take place in fragmented second growth, as in our old search area). I hope it inspires you to read the rest. More from me soon.
How does this relate to Moss Island? By Cornell standards, our habitat is unsuitable. Hence, our encounters are largely dismissed out of hand. By doing so, the Cornell approach has painted themselves into a rather nasty corner. The logic is simple. To all appearances, we have Campephilus-like double knocks that are at least as good as what has been heard in the “core habitat” such as Big Woods and Congaree. If one claims that in “core habitat” these represent evidence for the possible presence of Ivorybills, but in “marginal” or “unsuitable” habitat they provide no evidence for the possible presence of Ivorybills, one has committed a logical no-no of the first magnitude. If the same sounds come from places where you have concluded that Ivorybills are not going to be, then you should conclude that these sounds have no relevance to Ivorybills anywhere. Conversely, if you feel these sounds are evidence of the possible presence of Ivorybills in South Carolina or Arkansas, then you must also accept that they would be evidence of the same in Tennessee, Illinois, Mississippi, Florida, Louisiana, and Texas. You can’t have it both ways.
Anyone who seriously considers that Ivorybills might still persist, and that double knocks and other soft evidence have a relevance to indicating their possible presence, should accept that the evidence in total suggests their habitat requirements might be broader than has been assumed by Cornell et al. I’m not suggesting they will nest in fragmented second growth, or even use it as a full-time habitat; but there are ample indications that if these sort of encounters mean anything anywhere then the birds indeed are using fragmented “marginal” habitats for at least parts of their life history. These habitats are hugely more extensive than the “core” habitats, hence this possibility raises all sorts of further hypothetical possibilities for the natural history, survival, and conservation of the species, all of them positive. In the alternative philosophy to Cornell’s, you search where you have learned of rumors, whispers, or credible declarations that something of interest might have been seen or heard there. This of course requires a lot of judgement, and eventually everyone will draw the line somewhere; I’d not put much stock in reports from western Kansas, for example — although good double knocks in Nebraska or Vermont would settle a lot about what they might mean in Arkansas! But until and unless we actually find some reproducible birds and determine what their 21st Century habitat use patterns really are, minds should be kept open.
You will not get anyone involved in the Tennessee project to state that we have established the presence of an Ivory-billed Woodpecker anywhere in Tennessee as a statistical or scientific certainty. None of us has put an Ivorybill on his or her life list. However, if you asked us off the record for our own personal unscientific feelings, I think you would hear several confessions that indeed, some of us do strongly suspect that there has been at least one of these critters tormenting and taunting us in the delta woods for the last several years. Which means we also think that all that follows from this about habitat, behavior, distribution, etc. should be given serious consideration. Interconnected mosaics of fragmented second growth bottomland forest should be included within the spectrum of possible habitats for the species. You will not get anyone involved in the Tennessee project to state that we have established the presence of an Ivory-billed Woodpecker anywhere in Tennessee as a statistical or scientific certainty. None of us has put an Ivorybill on his or her life list. However, if you asked us off the record for our own personal unscientific feelings, I think you would hear several confessions that indeed, some of us do strongly suspect that there has been at least one of these critters tormenting and taunting us in the delta woods for the last several years. Which means we also think that all that follows from this about habitat, behavior, distribution, etc. should be given serious consideration. Interconnected mosaics of fragmented second growth bottomland forest should be included within the spectrum of possible habitats for the species.
On March 15, Phil Vanbergen and Matt Courtman recorded numerous kent-like calls at the same location where we heard several calls on March 11 and 12. Phil was able to record two of the March 11 calls. That capture is included in the post, along with Phil’s audio from the morning of the 15th. I heard two of the calls on the 11th; the second one in particular struck me as being consistent with the Singer Tract recordings; the first seemed a little low pitched to my ears, an observation that’s captured on the recording. Steve Pagans and I heard several calls on the 12th, but these were not recorded.
Matt obtained nearly three hours of audio, and to my ears the sounds are coming from 2-4 distinct sources; I had the same impression after listening to some of Phil’s clips. I have now listened all the way through Matt’s recordings several times and will share my analysis below. Matt and Phil are likely to weigh in later with their perspectives. I also have a couple of trip reports pending, so there should be a lot of activity on the blog in coming weeks.
To start with, I counted over 200 kent-like calls in all.
On the long clips posted here, I’ve edited out all of Matt’s ADK (anthropogenic double knock) series, which he did on the half hour. The knocks are very loud, as can be heard from the one trailing sound I’ve left in. I also snipped out several minutes of conversation between Phil and Matt. The ADKs seem to have led to more frequent calling and may have provoked some double knocks, something we may address in a future post.
Edited to add: On further review, there does not appear be a correlation between ADKs and more frequent calling. Clips like the one posted below can be deceptive. One kent-like call that overlaps with a knock has been deleted. There is also one possible knock in response. Caution, ADKs have not been completely spliced out, and they are loud. See bottom of page for brief clip and sonogram.*
Between 6:12 and 6:25 on the last long recording made that morning, there are five calls of differing durations and volumes, followed by what may be a double knock. Similarly, at the end of the full clip, starting at 14:14, 3 calls are bracketed by some potentially interesting knocks, 2 before and 1 or 2 after.
The first four clips below are shorter, amplified extracts on which the calls can be heard easily.
The first two of these are extracted from the final segment described above and include the interesting, tooting sounds and possible knocks.
The third clip includes multiple calls over 2 minutes and nine seconds, along with a wide variety of other sounds.
The fourth is four minutes long (pardon the airplane noise) and should provide additional context while also revealing some of the variations among the calls.
For those, like me, who don’t have professional sonogram software, I recommend using Sonic Visualizer – an easy to use, free program that enables you to watch the sonogram as you listen.
And for those who are unfamiliar with avian bioacoustics, this is a great place to start. I’m on a very steep learning curve myself and am prepared to stand corrected about any misstatements in this post.
Many of the sounds are audible on built-in computer speakers, but playback through headphones, earbuds, or external speakers is highly recommended.
I think these calls were likely made by Ivory-billed Woodpeckers. My perspective is based in part on the fact that I have spent all or part of nearly 40 days in close proximity to where the calls were recorded, starting in 2014. A considerable amount of this time was spent sitting quietly, and the total person hours spent in the area is well into the hundreds. We have had occasional kent-like calls, possible double knocks, and possible sightings over the years, but nothing approaching what transpired on the 15th.
Matt spent the morning of the 16th in the same location and did not hear any of the sounds, and Patricia and I spent 4 mornings and one afternoon there between the 23rd and 31st and heard no similar calls. I think this militates strongly against the idea that the source of the sounds is a common resident of the area.
Three alternative hypotheses have been suggested.
On the morning of the 15th, Phil proposed that the sounds might be tree squeaks. There appear to be multiple tree squeaks on the recording, some with similar pitches, but they bear little resemblance to the kent-like calls on the sonogram or to the ear. In addition, the calls sometimes come singly, sometimes in groups, and they vary in pitch, volume, and duration and seem to occur independent of wind velocity (on the 11th we noted that there was no wind.)
The first sound, at just after 4 seconds on the second clip, seems ambiguous. The sonogram is somewhat similar to the kent-like sounds, but the duration is very short, and it has a creaky quality. It’s also associated with the two creaky sounds that follow. These can be heard frequently over the course of the morning, and their appearance on the sonogram is nearly uniform.
One reviewer proposed Wild Turkey and Blue Jay as possible sources. I think turkey can be ruled out due to the absence of other turkey-like sounds associated with these very persistent calls.
Blue Jay strikes me as a more plausible alternative. Blue Jays can be heard at numerous times on Matt’s recordings. And Blue Jays are known to make kent-like calls, some of them very similar to known Ivory-billed Woodpecker sounds. This is likely not mimicry, since the most similar recorded calls I know of were obtained in upstate New York. The recordist noted the similarity. On the sonogram, the resemblance between these calls and either known Ivory-billed Woodpecker sounds or Matt’s recording is not as strong as it might seem to the ear. While they share a strong third partial, the Blue Jay fundamental is higher and some of the higher partials are considerably stronger.
It’s also important to note that on the Cornell Blue Jay recording, the kent-like calls are intermixed with typical Blue Jay vocalizations. Over the three hours of Matt’s recording, kent-like calls occur during periods when Blue Jays are vocalizing and during periods when Blue Jays are silent.
Some of the kent-like calls have harmonics consistent with Cornell’s recorded playbacks of Singer Tract calls at 145 meters. Many are lower in pitch. Most have a considerably longer duration, although to my untrained eye/ear, some seem close to the 80-100 ms duration on the Cornell recording. More on duration below.
On March 28, I did some playback of Singer Tract calls using an iPhone and a bluetooth speaker. Patricia recorded them on a Roland Edirol R09HR digital recorder. I’m including the recording and the sonogram for comparison. Like Matt’s recordings, the second partial is strong throughout, and the 1st, 3rd, and 4th appear to be weaker than for the Blue Jay shown above.
At various points, Phil also experimented with doing playback, using calls recorded in 2010 at the old Project Coyote site. (He also played back several other species – Red-bellied, Golden-fronted, and, possibly, Gila Woodpecker to gauge Red-bellied response, and Eastern Towhee out of personal interest.) Examples of putative ivorybill playbacks can be heard over the first 3 minutes of the fourth long clip posted above and also during the first part of the fifth. These sounds are longer but similar in tonal quality to the lower pitched calls. Their harmonic structure is different, however, with a fundamental at around 800 hz, a second partial at around 1600, and a fairly strong higher partial at approximately 5000 hz., and should be readily identifiable on the sonogram.
Phil’s playbacks do not seem to have provoked any kent-like replies. Blue Jays can be heard during the same time frame, but it’s not immediately apparent whether the recorded Blue Jay calls are responses or merely contemporaneous vocalizations. This segment includes some Blue Jay vocalizations.
With regard to Blue Jays and the numerous kent like calls heard from March 11, 12, and 15: to reiterate, many hours have been spent in this vicinity, with close attention being paid to kent-like sounds. These are heard infrequently and never before in such quantity or over such an extended period. If Blue Jays in the area were making these sounds, we almost certainly would have heard and recorded many of them over the years. In addition, both Steve Pagans and Matt Courtman are experienced and skilled ear birders and neither thinks these are Blue Jay calls.
It’s also worth pointing out that another potential confusion call can be heard on the recordings – White-breasted Nuthatch. The sound is similar but much weaker, as should be clear from the amplified March 15 excerpt. On the sonogram, just below the amplified recording, the calls show up very faintly, with dominant frequencies of around 2200-2400 hz and a relatively strong partial at 1700-1800.
I encourage people to listen through and draw their own conclusions. Input from those with expertise is welcome.
While I can’t say if any of these calls are a perfect match for the Allen and Kellogg recordings (some may be), many of them are close on the sonogram and similar to the ear. It’s important to bear in mind that the Singer Tract birds were likely agitated when those recordings were made, even though Tanner described some them as being good examples of kents. It’s also important to read Tanner’s descriptions carefully, though as is so often the case, his writing can be opaque. Perhaps his most important observation was that “all of the notes have the same nasal, trumpet-like quality.”
According to Tanner, “The notes of the nuthatches are the only bird calls I know that sound like the voice of an ivorybill; the Ivory-bill’s calls are much longer and pitched higher than the calls of a White-breasted Nuthatch, are more in the range of a Red-breasted Nuthatch.” (Emphasis added.) By contrast, Hasbrouck, writing in the 1890’s, described it as being “exactly like the note of the White-breasted Nuthatch” only much louder and stronger.
Tanner’s reference to Red-breasted Nuthatches has always confused me. I’m very much in Hasbrouck’s camp; I think the Singer Tract kents sound far more akin to White-breasted than Red-breasted Nuthatch. Either way, most of the Allen and Kellogg kents are lower pitched than typical White-breasted Nuthatch calls, as are the ones on Matt’s recording. In addition, the Allen and Kellogg kents seem to be of similar in duration to typical nuthatch calls, rather than longer or “much longer”. This too suggests that they are not typical but are more rapid and perhaps higher pitched due to agitation. Tanner wrote further, “[t]he kent note, given in monotone or infrequently, is the ordinary call note. When the bird is disturbed, the pitch of the kent rises, and it is repeated more rapidly, frequently doubled, kent-kent, with the second note lower. The prolonged and slurring, kient-kient-kient call I always heard when two or more birds were together.” This call was never recorded.
According to Allen and Kellogg, “kenting varied a great deal” and a male bird called “loudly and deliberately”, again suggesting that many calls were of longer duration than those on the recording. Tanner’s notes also point to this variability. At one point, he wrote of “1 and 2 syllable yaps”; he has the Mack’s Bayou bird (whose voice he claimed he could recognize) making a “kient-kient” and also transliterated calls with “keent keent” and “yeenh yeenh” (Bales). These renderings all suggest a more drawn out call than those on the Allen and Kellogg recordings. George Miksch Sutton described the Singer Tract birds’ calls as, “strange, bleat like, not quite sharp enough for a woodpecker’s cry. It was slightly nasal in quality and it sounded to me like ‘Gip!’, with a hard g“. Sutton’s description also suggests that many kents had a fairly long duration.
Edited to add: similarly, several observers (Audubon, Beyer, Hoyt) described ivorybill calls as “plaintive”; this too seems to imply calls of longer duration than what’s heard on the Singer Tract recordings.
Given the resemblance to the Singer Tract recordings and the lack of plausible alternatives, I posit that these calls are at worst highly suggestive of Ivory-billed Woodpecker.
*Possible knock and kent-like calls temporally associated with ADK series. Caution remnant ADKs are loud.
According to Tanner, scaling bark was the Ivory-billed Woodpecker’s primary foraging strategy during breeding season in Louisiana. Tanner wrote that the ivorybill is “capable of easily scaling away heavy bark that other woodpeckers could not loosen.” (Tanner 1942). All woodpeckers in genus Campephilus have specific anatomical characteristics that enable them to forage in this specialized way (Bock and Miller 1959). Following Tanner, most post-Singer Tract search efforts have looked for feeding sign as an indicator of presence. Because Tanner’s descriptions are somewhat vague and many of the photographs showing feeding sign are poor, these efforts have tended to focus on decay state and bark adhesion without taking bark characteristics and tree species sufficiently into account. I posit that tree species and bark and wood characteristics are key factors that should be considered. I further posit that extensive bark scaling on live and recently dead hickories (genus Carya) may be beyond the physical capacity of the Pileated Woodpecker.
As all regular readers know, I’ve been somewhat obsessively focused on bark and bark scaling since my earliest years of ivorybill searching. The reason for this interest is simple: it’s how Tanner found ivorybills or inferred their presence when he couldn’t find them (Tanner 1942). Unfortunately, as discussed in a number of posts, Tanner’s descriptions are somewhat opaque, and most of the published images of feeding sign, including those in the monograph, are not very illuminating. Indeed, some of them are consistent with pileated work that we’ve documented. Plate 8, shown below, is a prime example. The caption reads, “Ivory-bill feeding sign on a slender limb”.
Early on in my study of this subject, I hypothesized that certain kinds of bark scaling on hardwoods might be beyond the physical capacity of the Pileated Woodpecker. I still believe this to be true, a view that is supported by what we’ve documented for pileated and by numerous examples of pileated scaling from online sources. At the same time, the details of what types of work might belong in this category have shifted somewhat, especially as it has become clear that Pileated scaling can look like what’s shown in Plate 8 and that pileateds will scale bark from recently dead sweet gums.
This is not to suggest that ivorybills never scale small and medium-sized branches in a similar manner. According to Tanner they did so frequently; however, I have been focused on what may be diagnostic for ivorybill. It seems likely that there is considerable overlap between ivorybill and pileated work when smaller branches are involved (at least on sweet gums).
The sequences we obtained showing pileateds scaling a sweet gum limb have inspired me to look more deeply at the characteristics of hardwood bark and pursue some research avenues that I hadn’t considered previously. I’ve linked to some of the sources in recent posts, but I’ve had some additional insights that seem important enough to share. Every time I think I’ve run out of things to say on the subject, something new crops up.
Like virtually everyone else, I’ve followed Tanner and focused on two bark characteristics, “tightness” and thickness, but it recently struck me that other features might be important as well. And the literature, mostly from the lumber industry, supports this idea.
Tanner suspected that the Singer Tract ivorybills preferred sweet gums and Nuttall’s Oaks because the bark is thinner, and the thinner barked limbs had “more borers” than thick barked ones. While abundance of food was likely a factor, I suspect that, at least with respect to sweet gums and possibly Nuttall’s oaks, ease of scaling and access to food played a role.
It’s important to point out that in live trees, hardwood bark adhesion varies seasonally, with bark becoming tighter during dormant stages and looser (with considerably less variation from species to species) during the growing season. Bark is often if not always tighter on recently dead trees than on live ones (Stokland et al. 2012).
In addition, “The structural and chemical traits of dead wood, inherited from the traits of living trees, are also major drivers of wood decomposition and these traits vary greatly among tree species.” (Cornellisen et al. 2012). The authors of the linked paper point out that other factors, including size and site, can also contribute to the way that bark loosens post-mortem, but specific traits seem to be paramount, especially since the scaling we deem to be suggestive, whether on standing or downed wood, is on trees that are alive or are recently dead. Because the scaling has a very distinctive appearance, we also deem as suggestive hickory snags and stubs that appear to have been scaled some years ago, even if they are in a considerably later stage of decay overall. Bark attached to hard wood on these longer dead stubs and snags often remains tight for 3 or more years after death.
A 1978 report, entitled Bark and Wood Properties of Pulpwood Species as Related to Separation and Segregation of Chip/Bar Mixtures examined bark morphology and strength properties in 42 different pulpwood species and identified factors that impede the mechanical removal of bark from logs. These include: cellular structure, bark adhesion, bark strength, bark toughness, wood toughness, specific gravity/density, and moisture content. (Institute of Paper Chemistry 1978) One caveat about this report: a subsequent paper gives the sample size for each species, and in many cases (including sweet gums) it was only 2 (Einspahr et al. 1982)
It may be counterintuitive, but the authors found that shagbark hickory was far and away the most difficult bark to remove. (The tightly adhering layer is thin, beneath the dead bark that gives the species its shaggy appearance.) One key finding was that:
“Morphologically, the presence of fibers increases inner bark strength and, when sclereids (a type of cell) are present, bark strength is decreased. Inner bark strength, in turn, has a major influence on hardwood wood/bark adhesion. The multiple regression equation employing wood toughness and inner bark strength accounts for 72% of the wood/bark adhesion variation encountered.”
Sclereids are virtually absent in hickories (Nanko 1980) and a few other species that don’t approach the hickories in bark strength and bark and wood toughness (Eastern cottonwoods, yellow poplars, white ashes, and black willows). These tables are particularly illustrative:
Shagbark hickories are the extreme outlier in this study, in terms of adhesion, as well as in terms of inner and outer bark toughness and strength; there are very few shagbarks in our search area, and we have never found scaling on one. I have been unable to find specific information about bitternut hickory bark strength or toughness, but the industry’s debarking problem applies to all species in the genus Carya due to the near absence of sclereids in conjunction with the other factors. Moreover, the industry does not differentiate among hickory species (Timber Mart South 2016). This 1996 paper is worth quoting at length in this regard (full text is not readily accessible):
The amount of published literature dealing with hickory debarking is very limited. Often it is only mentioned as an example of one of the hardest tree species to debark. One study quantified this by measuring the strength of the bark-to-wood bond of 42 hardwood species, including hickory. According to Einspahr et al., the dormant season bark-to-wood adhesion for hickory is greater than 3000 kPa, which is a tenfold difference from the growing season and nearly three times as great as the dormant season wood/bark adhesion for quaking aspen (Populous tremuloides, L.), a species considered to be extremely difficult to debark in the northern United States.
Einspahr et al. also microscopically examined the failure zone in an attempt to correlate morphological differences with bark-to-wood adhesion. For hardwoods in general, they found that during the growing season, failure occurred in the cambium or in the xylem just inside the cambial zone. Conversely, dormant-season failure occurred in the inner bark. They also found that fibers in the bark increased the inner bark strength while sclereids decreased inner bark strength. Hickory bark can contain between 15 to 20 percent fiber and contains less than 0.05 percent sclereids.
While these studies have confirmed that hickory is difficult to debark, they have not addressed possible solutions to the problem. As a result, hickory is often left behind during harvesting, reducing the total usable fiber from a given stand and, over time, increasing the percentage of the species in the hardwood resource, compounding the problem of future harvests.
When a tree dies, the bark eventually loosens and detaches naturally as the cambium decays. After felling, the cambium remains alive until it has consumed all available food or dries out. Moisture loss, while causing cambial death, initially greatly increases the strength of bark attachment because additional bonding between fibers occurs as the secondary valence bonds with water are broken (Belli 1996).
Thus, even though hickory bark adheres less tightly than sweet gum bark during the growing season, it seems likely that it’s harder to scale year round, given its much greater wood and bark strength and toughness. It is also clear from my observations that sweet gum bark loosens far more rapidly than hickory bark post mortem. Note that we have found fresh scaling on both live and recently dead hickories.
Based on specific gravity of the bark – averaging 0.72 for shagbark and 0.60 for bitternut – and bark moisture content – averaging 34% of dry weight for shagbark, and 60% for bitternut – it seems likely that bitternuts are somewhat easier to debark than shagbarks but considerably harder to debark than virtually any other tree species in our search area.
Comparing bitternut hickories to other species, most oaks have a considerably higher average moisture content in their bark (Chestnut and Southern red, including Nuttall’s oaks, are exceptions) and similar specific gravities. Sweet gum bark has an average specific gravity of 0.37 and an average moisture content of 91% of oven dry weight. (Schlaegel and Willson 1983, Miles and Smith 2009). But oaks and sweet gums have sclereids, and sweet gums and all tested oak species score far lower on bark toughness and strength than shagbark and, by inference, bitternut hickories. Sweet gums and the tested oak species are fairly similar in these regards, but I suspect that the higher density and lower moisture content in oak bark makes it harder to scale and may mean that oak bark adheres more tightly than sweet gum bark for a longer period after death.
I posit that when it comes to woodpecker scaling, dormant season bark adhesion, inner and outer bark strength, and inner and outer bark toughness are all relevant factors. We know that Pileated Woodpeckers remove sweet gum bark with some difficulty and that even on medium-sized limbs, they are not consistently able to remove bark cleanly down to the sapwood. It’s also clear that bitternut hickory bark is very difficult to remove, second only to shagbark hickory in our search area. This further reinforces my view that the work on hickories is not the work of Pileated Woodpeckers.
Click here and here for examples of the hickories that are scaled in a manner we hypothesize is diagnostic for Ivory-billed Woodpecker. Also be sure to watch this YouTube video of a Crimson-crested Woodpecker (Campephilus melanoleucus) foraging. (Thanks to Phil Vanbergen for finding the clip and the scaled hickory at the second link.) I’m reposting the link to the video here because I think it very clearly illustrates many of the characteristics we associate with Ivory-billed Woodpecker work on hickories, although the species of tree being fed on is unknown. Note the striking similarity in appearance and also that the work of the substantially smaller billed Crimson-crested is not as clean around the edges as the work we’re ascribing to ivorybills.
There were no bitternut hickories in the Singer Tract, but there were congeners – pecans and water hickories. Tanner observed ivorybills scaling on these species twice and digging once. For pileateds, there were 4 instances of digging and none of scaling, as opposed to 5 scaling and 9 digging on sweet gums. The relative abundance of water hickory and pecan at Singer was 2.7%; approximately 10% of the trees in our search area are hickories, and hickories are second only to sweet gums in terms of the number of scaled trees we’ve found. While Tanner’s is obviously a minuscule data set, it may support the hypothesis that live and recently dead Carya bark is too tough for pileateds to scale extensively, if at all.
There are a number of hardwood species found in potential ivorybill habitat that are somewhere between sweet gums and hickories in terms of how easily scaled they may be and how soon after death bark decay and loosening set in – eastern cottonwoods, black willows, water tupelos, some oak species, red maples, green ashes, honey locusts, persimmons, and elms – in these species, it seems likely that close examination of the scaling and bark chips can provide some clues.
Previous Ivory-billed Woodpecker searches have focused on bark adhesion and state of decay when considering scaling as possible foraging sign. Bark morphology, dormant season adhesion, inner and bark outer strength, and inner and outer bark toughness, and wood toughness are all relevant to the ease with which bark can be scaled from live and recently dead hardwoods. Specific gravity and moisture content are also factors. Bark from trees in the genus Carya is difficult to remove industrially, and members of this genus are likely the most difficult trees to scale throughout the historic range of the ivorybill. Since Pileated Woodpeckers scale sweet gum branches with some difficulty and do not consistently remove bark down to the sapwood, it may be beyond the physical capacity of Pileated Woodpeckers to scale hickories extensively and cleanly, while leaving large pieces of bark behind. Extensive work on hickories that has a distinctive appearance may be diagnostic for ivorybills; this distinctive appearance of this scaling may also be the key to recognizing Ivory-billed Woodpecker foraging sign on other species.
This may be no more than an aside, but it may be a relevant data point. I recently observed a Pileated scaling briefly on a live 14″ DBH Norway maple in my yard near New York City. The photos show that the sap is flowing. The appearance of the scaling is exactly what I’d expect for Pileated, with strips about half an inch across. Norway maple may be a decent stand-in for sweet gum; while its bark has a higher specific gravity, 53 as opposed to 37, the moisture content of the bark is almost identical, 91% as opposed to 90%.
Bock, Walter J. and Waldron Dewitt Miller, The Scansorial Foot of the Woodpeckers, with Comments on the Evolution of Perching and Climbing Feet in Birds, American Museum Novitates, #1931, 1959
Belli, Monique L., Wet storage of hickory pulpwood in the southern United States and its impact on bark removal efficiency, Forest Products Journal. Madison 46.3 (Mar 1996): 75.
Cornelissen, Johannes H.C., Ute Sass-Klaassen, Lourens Poorter, Koert van Geffen, Richard S. P. van Logtestijn,Jurgen van Hal, Leo Goudzwaard, Frank J. Sterck, René K. W. M. Klaassen, Grégoire T. Freschet, Annemieke van der Wal, Henk Eshuis, Juan Zuo, Wietse de Boer, Teun Lamers, Monique Weemstra, Vincent Cretin, Rozan Martin, Jan den Ouden, Matty P. Berg, Rien Aerts, Godefridus M. J. Mohren, and Mariet M. Hefting, Controls on Coarse Wood Decay in Temperate Tree Species: Birth of the LOGLIFE Experiment, Ambio. 2012 Jul; 41(Suppl 3): 231–245.
Einspahr, D.W, R.H VanEperen, M.L. Harder et al. Morphological and bark strength characteristics important to wood/bark adhesion in hardwoods, The Institute of Paper Chemistry, 1982: 339-348.
Institute of Paper Chemistry, Project 3212, Bark and wood properties of pulpwood species as related to separation and segregation of chip/bark mixtures, Report 11, 1978.
Miles, Patrick D. and W. Brad Smith, Specific Gravity and Other Properties of Wood and Bark for 156 Tree Species Found in North America, United States Department of Agriculture, Forest Service. Northern Research Station, Research Note NRS-38, 2009.
Nanko, Hiroki, Bark Structure of Hardwoods Grown on Southern Pine Sites (Renewable Materials Institute series), Syracuse University Press, 1980.
Schlaegel, Bryce E. S and Regan B. Willson, Nuttall Oak Volume and Weight Tables, United States Department of Agriculture, Forest Service. Southern Research Station, Research Paper SO-l 86, 1983
Siry, Jacek, ed., Species Detail Report, Timber Mart-South, 2016
Stokland, Jogeir N., Juha Siitonen, and Bengt Gunnar Jonsson, Biodiversity in Dead Wood, Cambridge University Press, 2012
Tanner, J.T. The Ivory-billed Woodpecker,National Audubon Society, 1942.
Thanks to Fredrik Bryntesson, Steve Pagans, Chris Carlisle, and Bob Ford for their help with this post.