Strips, Flakes, Chips, Chunks, and Slabs: Squirrels, Pileated Woodpeckers, and Ivorybills, Part 4

Careful examination of bark chips found in conjunction with extensive scaling is one of the key elements in our diagnostic gestalt, but “chips”, a term I’ve been using for years, is both inaccurate and too vague for what we believe is being left behind by Ivory-billed Woodpeckers and for differentiating it from the leavings of other animals. Tanner used “pieces” of bark, ranging “from the size of a “silver dollar to the size of “a man’s hand.” A caption from the National Geographic article on the 1935 Allen and Kellogg expedition that refers to “large chunks of bark”.  The existing images of these pieces of bark suggest that chunks is the better term.

It’s important to reiterate that this discussion applies only to live and freshly dead hardwoods. Pines slough bark quickly after death. The process is slower in hardwoods, but as decay progresses, the bark loosens considerably, with the rate of loosening depending on species and environmental conditions. Once the bark has loosened sufficiently, PIWOs can and do scale bark extensively, sometimes leaving behind large chips. In the images that follow (from Allen and Kellogg and Tanner), the bark chips ascribed to ivorybills appear to come from considerably longer dead trees than some of the examples we’ve found, but the images are informative.

Ivorybill Scaling Courtesy of the Division of Rare and Manuscript Collections, Cornell University Library

Ivorybill Scaling Courtesy of the Division of Rare and Manuscript Collections, Cornell University Library

The small tree shown above, identified as a “dead gum” by the 1935 expedition, appears to be a hackberry or sugarberry not a gum, and a fairly long dead one; the pieces of bark at the base resemble ones we found beneath hackberries or sugarberries in our old search area, some of which were considerably larger (the one below is the largest).

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This colorized slide reveals more about the bark at the base of these pines than the black and white print in Tanner (Plate 9).

There’s also this example, (Plate 10 in Tanner), which appears to be in a considerably more advanced state of decay, and presumably looser, than much of the work we find most interesting. I suspect most of the grubs were placed on the chip for illustrative purposes; the caption “Beetle larvae from beneath bark of Nuttall’s oak” is ambiguous as to where the larvae, which appear to be small Cerambycidae, were actually found.

What I think is most salient in Tanner’s description of bark chips is shape not size. In this regard, it seems important to come up with a more specific set of terms to replace the commonly used “chips”. I’d suggest using chunks and slabs for suspected ivorybill work (although smaller pieces of bark may also be present). Pileated bark removal can involve chips, strips, or flakes, the last when they’re doing the layered scaling discussed here and here. I suspect that squirrels remove hardwood bark primarily or exclusively in strips, and of course, their bark removal on cypresses leaves shredded bark hanging from the trees.

Let’s take a closer look at the differences among pieces of bark we have reason to believe were left by squirrels, those we have reason to believe were left behind by Pileated Woodpeckers, and those we suspect were left behind by Ivory-billed Woodpeckers.

I collected a number of bark chips from the tree we know to have been scaled by a squirrel, and while these were removed before our camera trap revealed the source, there’s strong reason to think they too were left behind by squirrels.

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Note the uniformly elongated shape and the ragged appearance at the tops and bottoms of these strips of bark. This is not typical of bark that we infer or know to have been removed by woodpeckers, and it’s consistent with chewing, not scaling. The presumed squirrel strips I collected had the following dimensions:

9”x2.5”

7”x2.25”

5.75”x2″

7.5”x1.75”

4”x1.75”

The downed sweet gum from which they had been removed was a fairly young tree, and the bark is much thinner than on more mature ones. These strips were approximately 1/8″ thick. While this is a very small sample, we suspect (along with Houston from IBWO.net) that approximately 3″ is the upper limit for width when a squirrel is doing the bark removal.

Our research and observations suggest that Pileated Woodpeckers have two strategies for removing tight bark; one involves pecking around the edges until they can gradually pry off small pieces, and the other involves scaling away strips, sometimes in layers. Their physical structure precludes them from doing the extensive, clean scaling of tight bark that Tanner associated with ivorybills.

We suspect that this collection of chips, from a honey locust near a known Pileated nest, reflects the range of what the species is capable of doing on a tight-barked hardwood (and honey locust bark is relatively thin). The upper limit appears to be hand size, with many-quarter sized or smaller.

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The following are measurements of some fairly typical suspected Pileated strips from a sweet gum:

7”x1”

8”x.8”

7”x.8”

6”x.8”

The strips shown below, suspected Pileated Woodpecker leavings from a high branch, are on the large end of the spectrum for this category of work. The Peterson Guide is 9.5″ x 6.5″. I can’t rule squirrel out completely for these.

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Flakes resemble strips, but they are removed in layers, so that reaching the sapwood is a gradual process. Pileated scaling frequently has this appearance, something that seems frequently to be the case with congeners, including the larger-billed Black Woodpecker (Dryocopus martius).

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The chunks and slabs we suspect to be ivorybill work are significantly larger and thicker than strips, flakes and chips, although strips and chips may be present in the mix at the base of suspected feeding trees. Chunks are usually more irregular and varied in size and shape, and both chunks and slabs sometimes have what appear to be strike marks from a broad bill.

I kept one of the chunks scaled from the hickory tree on the homepage, a fairly typical example. It is 8.5″x3.5″ and .375″ thick. (It has undoubtedly lost some of its thickness after drying for over two years.)

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The sweet gum chunk with the apparent bill mark Frank is holding is 7.5″x3″ and .25″ thick. On mature, thicker barked trees most or all suspected ivorybill chunks, chips, and slabs will have been removed cleanly, all the way down to the sapwood.

Frank adds:

This particular bark “chunk” is intriguing on several levels. We have found that markings many describe as “bill marks” are really truncated galleries between the bark and sapwood. Marks made by woodpecker bills are distinctive, but somewhat subtle, and easily overlooked. This chunk actually has two interesting markings – markings that were left by the animal that removed the bark. The first is near the end of my left thumb – my right index finger is pointing toward it. It is about a quarter inch wide, a bit over a half inch long, and three sixteenths of an inch or so thick. The other is a “V” shaped “notch” at the end of the chunk, near the center of the photo. These places look as if they’ve been struck with a chisel – hard enough to rip the bark away from the sapwood/cambium. This suggests that, even though this bark was very tight, very few strikes were required to loosen and remove it. Granted that these marks are bill strikes, this suggests that the bird removing bark is indeed a powerful animal for its size. Back to Mark.

DSC00031The two preceding examples are on the smaller side for suspected ivorybill work; in the first, the density, tightness, and grain of hickory bark seem to be a limiting factor on size. Some of the larger examples are shown in the Bark Chip Gallery (as are several of the images shown above). A couple of additional examples of larger slabs are below. In the first, the oak was approximately 8 months dead (leaves attached), and the bark was still tight. (The fractured slab was damaged in transit.)

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Scaling and Squirrels, Part 3, A Closer Look at Surfaces and Edges

The first two installments in this series, which was inspired by the discovery that squirrels are doing some of the bark scaling in our search area, are here and here. This installment will consider the appearance of the scaling itself, and the next will focus on pieces of bark; “chips” no longer feels sufficient to describe the spectrum of what we’ve found, and using more specific terminology may shed more light on what we think is diagnostic and why.

I’ll begin with the work we are now presuming to have been done by squirrels. In retrospect, it’s easy for me to understand why I was fooled by this bark stripping. I was not seriously considering mammals as a source due in part to the extent of some of the work involved; I never saw incisor marks on the wood, something that’s often described as being an important indicator; similarly, I have been unable to find these marks in the photographs I’ve taken of stripping that we now presume to have been done by squirrels.

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Tanner’s Plate 8, “Ivory-bill feeding sign on slender limb. Courtesy of the Division of Rare and Manuscript Collections, Cornell University Library

In addition, I was somewhat misled by Plate 8 and the description of what Kuhn thought was diagnostic that his daughter shared with us. (Scroll down in this post to see where my thinking went astray.) It’s my current view that Plate 8 could conceivably be squirrel work. Tanner doesn’t state that he actually observed an ivorybill doing the scaling.

Between 1937 and 1939, Tanner observed actual scaling a total of 73 times, but it’s not clear how many instances he might have photographed. In hindsight, the scaling in Plate 8 is not particularly impressive; the scaled patch is relatively small; the bark is thin and the hanging pieces may be an indication of removal by gnawing rather than bill strikes. Adhering bits of shredded bark and cambium are evident in some of the work we believe to be squirrel, including on the tree where we captured a squirrel stripping bark (albeit much smaller ones in that case).

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Small bits of bark and cambium adhering to downed sweet gum limb after presumed scaling by squirrels.

In fact, I think one of the keys to recognizing that squirrels are likely responsible for removing bark is a ragged, shredded, or chewed up appearance to the bark and cambium, as in the examples below.

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The information we got from Mrs. Edith notwithstanding, I am going to examine the edges of scaled areas more carefully and be sure they are for the most part cleanly incised. This is one of the main criteria for ascribing the work to ivorybills (although by no means all Campephilus scaling falls into this category, and some can have ragged edges). As I’ll be discussing in the next post, I think that bark chip characteristics provide an even better diagnostic.

Now let’s turn to targeted digging and the similarities between what we’re finding and the work of other Campephilus woodpeckers. In some of my previous posts on bark scaling I’ve mentioned “little or no damage to the underlying wood”. “Little” is the operative word here. In most if not all of the examples of scaling associated with large Cerambycid exit tunnels that we’ve been able to examine up close, there are also indications of targeted digging, and we have seen similar targeted digging on some of the higher branch work we’ve found. Targeted digging involves the expansion of individual exit tunnels in varying degrees. This can range from what appears to be little more than probing with the bill to deeper and wider excavations, but this excavation is incidental to the scaling, whereas in Pileated Woodpeckers, scaling on tight barked-trees is typically incidental to excavation.

A magnificent series of photographs by Luiz Vassoler posted to the Flickr Campephilus group, showing a Crimson-crested Woodpecker scaling and doing targeted digging, is illustrative (scroll through to your right for the whole series). This is not to suggest that other woodpeckers can’t or don’t dig for larvae in a targeted way, only it’s more suggestive evidence for the presence of Ivory-billed Woodpecker in our search area, given the context and what’s known about the foraging behavior of  its congeners.

I’ll keep commentary to a minimum and post some examples from our area (the seven photos immediately below) and then links to work done by other Campephilus woodpeckers.

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Pale-billed (on palm):There’s no scaling here, but the exit tunnels have been expanded vertically, and the expansions resemble some of the rectangular ones above.

Pale-billed (at nest): Very targeted digging and slight expansion of some exit tunnels.

Pale-billed: On a scaled surface, some tunnels expanded.

Robust: I’m including this almost as much for how well it shows Campephilus foot structure and the rotation of the fourth toe and hallux.

Cream-backed: Somewhat more aggressive expansion of tunnels on longer dead wood.

Red-necked: Targeted digging to the right of the bird.

Crimson-crested: Elongated dig into exit tunnel.

Crimson-crested: another great shot of the Campephilus foot. Targeted dig at bottom of scaled area.

Crimson-crested: Video showing targeted digging on an unscaled area.

Magellanic: are the most Dryocopus-like in the genus in terms of foraging behavior. Note their smaller bills and relatively shorter necks. They seem to spend a lot more time feeding near the ground and excavating large foraging pits than the other species, but they too do a considerable amount of targeted digging.

Magellanic: The appearance of the scaling here is strikingly similar to what we think is diagnostic for ivorybill. The tunnel at bottom right has been expanded, likely with the tip of the bill. It looks as though there is more targeted digging above and to the left.

The two images below, showing targeted excavations on small limbs, associated with extensive scaling on young, freshly ambrosia beetle-killed sweet gums, bear a striking similarity to work by Crimson-crested  (the long furrows in particular) and Magellanic Woodpeckers.

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One final and more speculative observation that might be of interest to other searchers. I had dismissed this work on a live maple as likely pileated because it is generalized digging, not scaling. After going through so many images of Campephilus foraging sign, I’m a little more intrigued by it, as I see similarities to sign like this and this. Like some of the work on ambrosia beetle-killed sweet gums, this almost looks like a hatchet had been taken to the tree; the wood was not at all punky; and red maple at 950 on the Janka hardness scale, while not nearly as hard as bitternut hickory (1500), is harder than sweet gum (850). While I’m not proposing this as a diagnostic, it may be more interesting than I initially thought.

Maple 1

Unusual excavation on live maple

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Scaling and Squirrels: Part 2, Digging Deeper

Part 1 of this series is here, and the event that led to my writing it is discussed here.  I now expect to write 2-3 additional posts on this topic and may create a new page that summarizes the whole series. I’ve hidden the Bark Scaling Gallery page to be reworked later or incorporated into the summary.

This post will reiterate, revise, and expand upon earlier ones dealing with bark scaling and woodpecker anatomy. The next one will focus on certain characteristics of the scaling we think is being done by Ivory-billed Woodpeckers, on finer details that characterize it (based in part on comparison with work done by congeners), and on how to differentiate it from bark removal done by squirrels. The following entry will deal with bark chips in more depth, and from a slightly different angle than previous posts on that subject.

I had originally intended to address the next post’s planned content in this one, but as I started writing, I realized the long but necessary introduction would bury the lede. It soon became clear that I’d have to divide the post in two with this one for background.

The first important point is that woodpecker taxonomy is in a state of dramatic change, so much so that the American Ornithological Union is being advised to place Downy and Hairy Woodpeckers in separate genera and that their current genus, Picoides, should be divided into four. Notwithstanding the taxonomic upheaval, there’s no question that Campephilus woodpeckers and Dryocopus woodpeckers are only distantly related, that their similarities are the product of convergent evolution, and that these similarities are far more superficial – involving size and coloration – than structural or behavioral. Formerly, some incorrect taxonomic assumptions led to the lumping of Campephilus and Dryocopus into the “tribe” Camphelini, an idea that’s discussed and dismissed in the first paper linked to above. This has been one factor in perpetuating some fairly common and persistent misconceptions – that the two species are closely related, that they occupy or occupied the same ecological niche and might be competitors, and that hybridization might be possible (something I hear surprisingly often).

The following differences are relevant to this discussion:

  1. Bill size and shape. These are dramatically divergent as any comparison shot of specimens makes clear. It’s also worth noting that the three North American Campephili are closely related to each other. DNA analysis suggests the three are distinct species and the Cuban ivorybill may be more closely related to the Imperial Woodpecker than the mainland US species. This study suggested that divergence among the three took place between .08 and 1.6 million years ago. The southern members of the genus are more remote cousins, having diverged approximately 3.9 million years ago. At one time, the southern species were considered a distinct genus, and they have smaller bills, both objectively and relative to body size. Magellanic Woodpeckers have the smallest bills relative to body size in the genus, and their foraging behavior is more Dryocopus-like than their congeners’. DSC00866
  2. Neck length. The much longer neck of the ivorybill allows for a broader range of motion.
  3. Foot and leg structure. Campephilus woodpeckers have a unique variation on what have been called pamprodactylous feet. (Wikipedia and David Sibley both miss the vast difference between Campephilus foot structure and that of most other woodpeckers.) In this genus, the hallux (first) and fourth toe (the rear toes) are both on the outer edge of the foot; the toes can be rolled forward for climbing and backward for perching in a manner that looks more zygodactylous. (The preceding links to images of Sonny Boy, the juvenile ivorybill, and Kuhn are great illustrations.) The fourth toe is highly elongated, the longest toe on the foot, and the hallux, (in the ivorybill, the outermost toe) is relatively longer than in any climbing woodpecker species. The second and third (innermost toes) are angled inward. This is shown quite clearly in a number of the images from the Singer Tract, including Plate 13 in Tanner.

    Enlargement of image used for Tanner's Plate 13 showing foot structure. Courtesy of the Division of Rare and Manuscript Collections, Cornell University Library

    Detail of Tanner’s Plate 13 showing foot structure. Courtesy of the Division of Rare and Manuscript Collections, Cornell University Library

  4. Dryocopus woodpecker feet are closer to being truly zygodactylous – two in front, two behind, with limited mobility and the hallux as the inner rear toe, although the fourth toe can be rolled outward to some extent; this provides less stability when making lateral blows.
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    Pileated Woodpecker foot showing zygodactylous structure and slight outward rotation of fourth toe. Photo courtesy of Carrie Griffis, who posted it on the Woodpeckers of the World Facebook group and kindly granted permission to include it here.

    In addition, Campephilus woodpeckers typically climb and forage with their legs both farther apart and higher relative to their bodies than Dryocopus. This enables them to keep their lower bodies closer to the trunk and move their upper bodies more freely, providing more stability for making powerful, lateral blows.

    4. Tail structure: the ivorybill’s tail feathers are long, thin, barb-like, and stiffer than the pileated’s. The tail serves as an anchor and also helps allow for a broader range of motion.

    Tailfeathers

    Middle Tail Feathers: Flicker, Ivory-billed, and Hairy Woodpecker

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    Pileated Woodpecker Tail Feathers. Note how the longest one resembles that of a Flicker more than that of an ivorybill.

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    5. There other structural differences, including wing shape, but these are the main ones that point to how Ivory-billed Woodpeckers have evolved in a way that makes bark scaling their most efficient foraging modality, whereas Pileateds are far better suited to digging, using a perpendicular motion.

Much of the foregoing is based on Walter Bock’s  analysis of woodpecker adaptations for climbing, which was also discussed in depth here. I’ve tried to explain Bock’s key points in straightforward and less technical terms. A longer quote from Bock appears at the end of this post.*

In addition to these structural differences, Pileated Woodpeckers (and to the best of my knowledge all their congeners) regurgitate when feeding young. Campephilus woodpeckers carry food to the nest and appear to be highly dependent on beetle larvae when caring for their nestlings. This means that Pileated Woodpeckers have to ability to take advantage of multiple food sources during nesting season, while Ivory-bills have a more limited range of options. While I don’t think this supports Tanner’s theory of old-growth dependence, it does point to a higher degree of specialization that would impact numbers, range, and suitability of habitat.

At the same time, the anatomical differences and degree of specialization convince me that certain types of feeding sign are beyond the physical capacity of a Pileated Woodpecker and are likely diagnostic for Ivory-billed Woodpecker.

There is a dearth of clear images showing Ivory-billed Woodpecker feeding sign. There are a handful of photographs, most of them very poor. The majority were taken in the Singer Tract and some showing work on pines were taken in Florida by Allen and Kellogg.  Few of them depict the high branch work that Tanner described as being characteristic, and when they do, there’s virtually nothing that can be discerned from them. It is also not entirely clear that Tanner’s attribution of feeding sign to ivorybills was always based on direct observation, which makes us wonder whether some of the work might actually have been done by squirrels. Regardless, this makes it difficult to draw inferences from the existing body of imagery.

That said and with awareness of the perils in extrapolating, one lesser known image from the Singer Tract is worth comparing with the work on boles that’s been discussed in multiple posts.

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“The Blind at Elm Rock”, Ivory-billed Woodpecker nest tree and detail showing scaling and excavation on trunk. Courtesy of the Division of Rare and Manuscript Collections, Cornell University Library

This is a view of the 1935 nest tree, which was a red maple. It’s taken at a different angle than the more familiar shots, so it shows some large areas of scaling on the bole that the others do not. While I can do no more than infer that this was done by ivorybills, it’s clearly old, and there’s an abundance of excavation in the underlying wood; nevertheless, the edges and contours of the scaling are strikingly similar to the work we’ve found on boles, especially the area at the lower right, just above the intervening foliage.

This is the jagged appearance I described in the previous post; the similarities are most evident in the picture below and on the home page. ScalingNewArea

Because there are so few informative images of ivorybill feeding sign, the best available option is to look at the work of other Campephilus woodpeckers. Even though they are not as closely related as the Cuban ivorybill or the imperial, their morphology and foraging behaviors are similar; even the work of the smaller-billed but oft-photographed magellanic can provide some clues. I’ll examine this and some probable identifying features of squirrel scaling in the next post, which will take a close look at scaled patches on trees.

*”. . . in most woodpeckers, as, for example, the pileated woodpecker, the legs are held more or less beneath the body,the joints are doubled up,and the tarsus is held away from the tree trunk. This position of the legs is disadvantageous for the bird, because the body is held away from the tree trunk and the muscles of the leg are working at a mechanical disadvantage; the analogy is to the mountain climber who is standing on a narrow ledge with hand holds only beneath his chest. In the ivory-billed woodpecker, the legs are directed away from the center of the body, and the tarsus is pressed against the tree trunk. This method allows the body to be held close to the tree, with the joints of the leg extended. Hence the leg muscles have a mechanical advantage, because they are at the beginning of their contraction cycle and are acting along the length of the segments of the leg. When the body is held close to the trunk, it not only decreases the outward component of gravity but allows the tail feathers to be applied to the supporting surface for a greater distance from their tips. If the bird is climbing on smaller limbs, the feet can encircle the limb and thus obtain better support. However, no matter what size the limb is, the disposition of the legs and the spreading of the toes of the ivory-billed woodpecker furnish direct and powerful resistance to both the lateral and backward motions of the woodpecker when it is at work and, with the tail, furnish a tripodal base of great strength against the pull of gravity.”


Trip Report 12/26/15-1/2/16

I made the mistake of trying to save on flights (actually paid with miles this trip), flying out of LaGuardia and a change of planes in Dallas. I left New York with a bad cold, and the first leg of the trip was miserable. Little did I know that the second leg would be worse.

At 4:45 pm, fifteen minutes before boarding time in Dallas, my flight to Louisiana was still listed as “on time”, although there had already been a gate change. There were five or six more over the next couple of hours, and American Airlines personnel at the various gates were either willfully dishonest or utterly clueless. The flight finally boarded at around 7 pm. We left the gate and sat on the runway for an extended period. At one point, the pilot announced that some planes were turning back, but that our crew could remain on the runaway until 1:30 am.

The pilot turned out to be wrong, as regulations now forbid planes from sitting on the tarmac for more than 3 hours. Somewhere around 9:30, we headed back to the gate. It took a while to find cooperative personnel, but I was able to rebook my flight for noon the next day. Sick as I was, I opted for a hotel rather than a night on a cot in the airport. I had to eat a room I had booked in Louisiana but used points to get this one. I got there a little before midnight and was in bed around 1 am.

I had planned to spend the 27th in the field, but that wasn’t happening. To the extent possible, I will avoid American Airlines and connecting flights in the future. Fortunately, my cold improved rapidly, and my rental car was a 4-wheel drive, which might have been a serendipitous result of the delay.

On the morning of the 28th, Brian Wiley and I went to an area that’s readily accessible from the road because we had plans to meet Tom Foti a little later in the morning. I spotted the downed sweetgum that we later found was being worked on, at least in part, by squirrels from the road. I found some recent scaling trees in this area, one where we’ve had possible sightings, concentrations of possible feeding sign, and auditory encounters in the past. While I can’t rule out squirrel work as a possibility, both of these trees were standing and somewhat longer dead than the downed trees that we now suspect are mostly being stripped of bark by squirrels; however, there was no way to find bark chips.

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IMGP1227We met up with Tom at around 11 am, and we drove a few miles north to a location from which it’s easier to get into the mature bottomland areas. We spent the morning in this vicinity, where we’ve had a good deal of recent activity, but we did not see or hear anything of note.

I met Tom again the next morning, the 29th, and we covered a lot of ground, passing near a tree where we have a camera deployment (although we now suspect that much of the work was done by squirrels). We came upon another freshly stripped, downed sweet gum. Again, I now believe this to be squirrel work. (More on this in an upcoming post, but one indicator may be the presence of bark stripping on the underside of the limb at right.)

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Tom headed back to Arkansas, and I headed back to Frank’s house. On the way, I passed the downed sweet gum that’s visible from the road and noted that there was fresh work on it. I went to examine it and noted that there was also some recently deposited scat.

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I called Tom, and he turned around and met me. We collected the sample (which has a similar appearance to PIWO scat, although there was no urea, something that might point toward a mammal as the source). Despite the fact that we’ve documented squirrels stripping bark from this location, at over an inch long, this dropping was larger than and doesn’t resemble the images of squirrel scat found online. We are exploring the possibility of doing DNA testing on it . . . a very long shot indeed, but it may be worth a try.

Update, January 18: The consensus is that it’s not worth testing the scat.

Frank joined me on the 30th, along with Wylie Barrow and Tommy Michot, both great field people with a deep knowledge of bottomland forests and birds. They’re featured in Steinberg’s Stalking the Ghost Bird as leaders of “Team Elvis” south. It’s really amazing for laypeople like Frank and me to spend time with such experienced field biologists. Wylie probably knows more about the Singer Tract than anyone, and I’m looking forward to studying his materials on that subject. We didn’t see or hear anything of import, but I think it’s fair to say that Wylie and Tommy came away impressed with the habitat and thinking that ivorybill presence is at worst a possibility. Tommy took this photo of me crossing a log. He’s made of stronger stuff than I am and walked right across without hesitating.

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Photo by Tommy Michot

I devoted the next day, 12/31, to staking out the downed sweet gum that proved to have been stripped of bark by squirrels. Nothing hit the tree for the entire day; it was cold, damp, and very uncomfortable, actually considerably more difficult than walking miles through the swamps. I did think I heard a single, pretty good double knock at around 3 pm, but I don’t trust that impression, given the fact that I was alone, tired, and hopeful.

On New Year’s Day, I left Frank to stake out the downed gum and went to retrieve a trail cam so we could monitor it remotely. While crossing an area of blowdown, I knocked myself down and nearly out, trying to break off the (not so) rotted limb of a downed tree.

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Photo by Frank Wiley

I got the camera and met up with Frank. We then went to a location at the southern end of the search area that I had never visited before. Some of the habitat is very impressive, but there are many more signs of human activity (ATV tracks and empty beer cans in particular) than in some locations. We found some work on a downed sweet gum that we now think is almost certainly squirrel but did not see or hear anything else of interest.

On Saturday, the 2nd, I returned to the location I’d visited with Tom on the 28th; access is easy; it’s familiar; and it’s hard to get lost. I retrieved the card from the camera that’s trained on the downed sweet gum top I found in April. (The camera was unable to read the replacement card, so I ended up pulling it.) We’re unsure about whether the source of the scaling on this top is squirrel, as we’ve photographed them on it repeatedly over the past few months but have not documented them stripping bark. There was a little bit of fresh scaling on the tree (not enough to show up on the trail cam), and we suspect it to be Pileated Woodpecker not squirrel. Frank may replace this camera in the future.

I did not find any fresh feeding sign, but I did come across a sweet gum that had lost its top very recently, within days. I believe this to be a tree on which I photographed recent scaling last spring, and some of the fallen limbs had clearly been stripped before they fell. I found indications that a woodpecker or woodpeckers had worked on this limb at some point, as discussed in the previous post.

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Perhaps the most significant event of the day occurred at around 11 am, when I heard an extended series of kent-like calls. At the time, I estimated the calling lasted for about 5 minutes, but I suspect it was closer to 15. These seemed to be coming from 200-300 years away, across a couple of challenging sloughs. There was really no way to try and follow them, especially alone. I did manage to record some of the calls on my DSLR (with no external mic). To my ears, they sounded pretty good, similar to the ones I recorded in March 2013, although they were all single notes, with no descending pairs. Unlike the 2013 calls (which were recorded on a better device at what seemed to be closer range), these came from a single, stationary source, not two moving ones. They were repeated considerably more frequently, and the pitch is slightly higher. Like the 2013 calls, they’re more clarinet than horn-like and don’t resemble the Singer Tract recordings in that regard.

In the attached audio clip (which may have lost some quality being transferred from .m4v to .m4a), the calls come at approximately, 4, 9, 17, 20, 25, 31, 39, 1:20, 1:27, 1:53, 2:07, and 2:17. I got the recorder running fairly late in the incident, and calls in the first minute of the clip are about as numerous as they were in the preceding minutes. They tapered off dramatically before ending at 2:17.

A variety of other birds are vocalizing throughout, including Blue Jays. I think the duration of the possible kents is shorter than the Blue Jay calls, but Blue Jay can’t be ruled out; I’m nowhere near as confident about these as I am about some others I’ve heard and/or recorded, including the 2o13 calls, but am posting them anyway. At around 3:41, Blue Jays start making an unusual call that we hear very frequently in this part of the search area. I do some playbacks of the Singer Tract recordings at around the same time, but there’s no evident response.

Per Frank, the dominant frequency of the calls is 1800 hz, with another bar at 2700. Since the calls are distant and the recording is poor, this might suggest a base frequency of around 900. The structure is more consistent with Blue Jay than known ivorybill. On the other hand, the duration is between Blue Jay and the ivorybills on the Singer Tract recordings. Allowing for attenuation by distance, this makes Blue Jay less likely.

Later that morning I did some additional playback and got apparent responses from Blue Jays and a White-breasted Nuthatch. This is the first time I can recall hearing a WBNU vocalization immediately after an IBWO playback.

On the evening of the 2nd, Frank and I went through the card and found the two sequences of a squirrel removing bark. Seeing the images was a bit of a blow, though not a total surprise; Wylie Barrow had raised this possibility a day or two before. He was the first person ever to make this suggestion; removing bark from hardwoods seems to be a fairly unusual and poorly understood behavior in squirrels; most of the information online suggests that it’s done on standing live trees when food is scarce, not on fallen ones when other food is abundant.

I shared the news with several biologists, and a couple of them pointed out that not all of the work we’ve found fits the squirrel paradigm. In fact, I think most of what we’ve ascribed to ivorybills is inconsistent with squirrel and am in the process of trying to identify some diagnostics. Unfortunately, since we know squirrels are doing at least some of the work on downed trees, an avenue that seemed very promising for camera trap deployment now seems far less so.

I returned home on the 3rd, and to my relief, the trip back was uneventful save for the usual post-holiday chaos at LaGuardia.

I plan to do a series of follow-up posts exploring scaling in more depth within the next week or two. I also hope to be able to provide some stills from the sequences we obtained.

 


More on Scaling and Squirrels, Part 1

This is will be the first in a series of 3-4 posts. The subject is multifaceted and subtle. Nuances can be hard to convey in words and accompanying illustrations; it’s easier to do in talks, with bark chips in hand to provide a more visceral sense of what’s being described. Still, it seems important to make the effort.

I realize now while my initial approach to evaluating feeding sign was rigorous, I grew somewhat lackadasical and overconfident. I also got distracted by the abundant scaling on downed sweet gums we started finding a year or so ago. I’m now confident that squirrels did much of this scaling, but the same does not apply to most of the other work we’ve found over the years.

Even before we discovered that squirrels were scaling bark on downed sweet gums (and quite possibly on standing trees as well), I was contemplating a post that broke down the bark scaling we’re finding into several categories. I was aware of having gotten away from the criteria I had laid out in the past and was feeling a desire to be more specific. That seems like a good place to begin, before delving too deeply into the nuances of distinguishing between squirrel and putative ivorybill work.

The following are the different types of interesting feeding sign we’re finding. Bear in mind that this pertains only to hardwoods that appear to be alive or recently dead and are known or suspected to have tight bark, except in cases where work appears to be old but still has characteristics that suggest it was done when bark was tight. The types of sign are ranked in the order of what I think is the likelihood that most or all of it is being left by Ivory-billed Woodpeckers, although the gap among categories 1-4 is small. (Frank would reverse categories 1 and 2.)

  1. Scaling on standing boles, low enough on the trunk to be examined up close. This includes both standing trees and ones with tops broken off. The sapwood of trees in this category has multiple large exit tunnels. The most prevalent species in this category is bitternut hickory, which has very thick, dense, tight bark, but we’ve also found it on sweet gums and oaks. This scaling is extensive and has a distinctive pattern that’s immediately recognizable in the field, an almost jagged appearance, although the actual edges are curved. The tree on the homepage is one example, and the image below illustrates how even when the scaling is not recent, this distinctive appearance remains. Bark chips are easiest to find for this type of work.

    Old scaling on hickory, 2015

    Old scaling on hickory, 2015. Note the exit tunnels and the absence of other woodpecker work, save for a small dig near the top of the scaled area.

  2. Scaling on standing boles, low enough on the trunk to be examined up close. Few or no large exit tunnels but signs of insect infestation under the bark. Superficial bill marks may be evident in the remaining cambium or on the surface of the sapwood. Tree species in this category include sweetgums and oaks. Chips are similarly easy to find.IMG_0144Lateral strike marks in the cambium
  3. Scaling that has the appearance of the work in category 1 but that cannot be examined up close. No possibility of examining bark chips.Hickory3
  4. Scaling higher on boles and lower branches of standing trees where exit tunnels may be visible, but close examination is not possible. In some cases, these trees are seen at a distance, across water bodies, so there’s no opportunity to look for chips. As is the case in categories 1 and 2, older scaling may go untouched by woodpeckers for extended periods. The first example below is recent; the second is probably more than two years old.
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    Top of scaled hickory.

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    Older scaling on dead top with exit tunnels.

     

  5. Scaling on higher branches of standing trees. Since these are often seen at some distance and in poor lighting conditions, it can also be more difficult to assess the freshness of the work, and the nature of infestation. Bark chips are usually much harder to find under these circumstances. Squirrels typically girdle limbs and often scale on the undersides of large, higher branches. Thus, when larger branches are at less than approximately a 70 degree angle, work on the underside may indicate a squirrel as the source, while the presence of extensive scaling limited to the upper side may be strongly suggestive of or diagnostic for woodpecker.BigSGLimb
  6. Scaling on downed trees or limbs that are at least in part more than 4’ from the ground.Detail of scaling on downed sweet gum.
  7. Scaling on downed trees and limbs that are mostly or all horizontal and less than 4’ from the ground.
    Work now suspected to squirrel on downed sweet gum.

    Work now suspected to be squirrel on downed sweet gum.

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    Suspected Pileated Woodpecker work on same downed sweet gum

There’s an additional category that is somewhat different from the others. This involves work we’ve found on freshly dead, small sweet gums (>1’ dbh) with evidence of ambrosia beetle infestation. These trees have been stripped of bark, with some accompanying signs of excavation, ranging from targeted digging that resembles the work of Magellanic Woodpeckers (as on the left branch below) to the appearance of having been attacked with a hatchet. We think this work has strong potential for ivorybills, since we’ve found only three examples of it, in close proximity, and in an area with an abundance of other suggestive sign.HackedUpGum

It’s important to point out that when I use the word “scaling”, I am referring only to the clean removal of bark with little or no damage to underlying sapwood. While I have been quite adamant about this as a characteristic, some elaboration is probably in order, as my statements were made in reaction to woodpecker work that was often described as “scaling” in the early search years but was really bark removal in conjunction with excavation, something that’s typical of Pileated Woodpeckers. There still seems to be a good deal of misunderstanding on this subject, and the distinction is not always easy to communicate.

On close examination of some scaled areas, especially in category 1 but also in others, there are signs of targeted digging (but not deep or extensive excavation). This can range from a very slight expansion of an exit tunnel, apparently by probing with the tip of the bill, to what may be a harder strike or two, to a somewhat deeper but still targeted dig into the sapwood. Since many other species of woodpecker are capable of doing such targeted digging, I only consider this aspect when it’s in association with extensive, contiguous removal of bark. This will be explored in more depth in the next post in the series.

In category 1, known ivorybill prey species have been found under the bark or on the scaled surface of two trees. When exit tunnels are found on these trees in this category, they are consistent with infestation by large Cerambycid beetle larvae. I hypothesize that these trees are being scaled when the gregarious larvae have dug their exit tunnels but have not yet sealed their pupation chambers. This would be the stage at which they are most nutritious and most easily accessible for a species of woodpecker adapted to bark scaling, but the opportunity exists only within a very narrow time frame.

For several trees in categories 1 and 2, camera deployments of 2-4 months duration produced no return visits or evidence of what was doing the scaling; in a couple of cases Pileated Woodpeckers were photographed on the target trees for fairly protracted periods. In one, the pileated removed a few small pieces of bark, and in the other it appeared to do a little pecking and gleaning but did not remove any bark. We have revisited several of the other trees over periods ranging from months to two and a half years. One tree in category 2 (no tunnels) had a return visit approximately four months after the first one, when the bark was still tight. Several others, both with and without tunnels and including one first found in June of 2013 and re-examined during my last trip, had no obvious new scaling and little or no excavation of any kind, despite being in a more advanced state of decay

It’s also important to note that we have reason to believe that at least some of the work in all categories is being done by woodpeckers. For example, on the downed sweet gum shown above to illustrate category 7, found in November, there is obvious woodpecker work (likely Pileated) on the bole and apparent squirrel work on the upper limbs. Similarly we suspect woodpeckers did the scaling on the larger downed sweet gum (category 5) – mostly scaled higher but with some work within 4’ of the ground. I found this tree in May 2014, approximately 50 yards from the site of where we captured the squirrel stripping bark; while I do not recall looking for or examining bark chips, the edges of the scaled areas appear chiseled rather than gnawed, and the scaling on some of the higher limbs is on the upper side only.

The next post on this topic will examined the targeted expansion of exit tunnels and will revisit the similarities between what we’re finding and the work of other Campephilus woodpeckers. The following one will focus on bark chips and distinguishing between signs of gnawing and signs of scaling.


Squirrels Stripping Bark

I thought it was important to post the following advance of writing a comprehensive trip report.

On arriving in the search area last week, I found fresh scaling on a downed, recently dead sweet gum. The tree was relatively small, with a DBH of under two feet, and was alongside one of the roads that pass through our search area. There was fresh work on it on subsequent days. I staked it out on Thursday and saw nothing. We placed one of our game cams on it on Friday and retrieved it late Saturday. The trail cam photos showed a squirrel removing the bark fairly extensively. These images are currently in the game cam’s proprietary format, and we’ll post them in the near future.

As is the case with many of these blowdowns, there was also work in the tops that looked very consistent with Tanner’s descriptions of ivorybill scaling, although only on the upper sides of the limbs and branches. What this tells us is that we have to think squirrels are likely responsible for scaling on downed sweet gums and that all possible sign on downed wood should be looked at with a jaundiced eye. It also means that my previous foraging preference analysis has to be revised; we’ve taken that page private at least for the time being.

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Scaled area on bole of downed sweet gum. A squirrel expanded this considerably, working from left to right, toward the base.

I did not collect any chips that are unquestionably the work of a squirrel, but I did gather several that I presume to be. They measure:

9″x2.5″

7″x2.25″

5.75″x2″

7.5″x1.75″

4″x1.75″

and thus are all considerably longer than they are wide, stripped with the grain rather than scaled. The edges that go across the grain have a ragged appearance, and since the tree was not mature, the bark is thin and brittle compared to the bark of the mature downed top discussed below.

It’s odd that we only started finding this type of work in abundance in the past year; it doesn’t exactly match the diagnostic criteria I’d articulated earlier, but it comes close in some respects. It has been an unfortunate distraction, since the work on downed trees is much easier to find and photograph than work on the boles or upper branches of standing ones.

There was a little bit of fresh work on the downed sweet gum top found in April, but it was not extensive enough even to show up in the game cam images. There were a few chips on the ground, more like strips than chips, actually, 6′ to 8′ inches long and no more than an inch across at the largest. We’ve had numerous images of squirrels on that top but none showing them scaling bark for a period of more than two months. We got numerous images of squirrels again this time, and also a pair of Pileateds, with a Downy or Hairy (we didn’t examine the frames very closely) literally trailing the PIWOs up the trunk. In any event, there was no way to tell what did the little bit of scaling, or what did the scaling on the upper part of the downed top or the left fork, which had been almost entirely stripped before we got the camera on it. I lean toward this little bit of new  work was done by the Pileateds, but either way the chips don’t have the characteristics I associate with suspected ivorybill chips.

I had been planning to do a post refining and being more explicit about the different types of work I’d been ascribing to ivorybills. I still plan to go ahead with this project but will have to do so informed by this new information. I expect to write something later this month, after I’ve posted the trip report.

While squirrels cannot be ruled out for some of the work we’re finding, it seems unlikely that squirrels are doing all of it, especially on the boles of dense-barked, mature trees (like the hickory on the homepage and most of the others shown here) that have numerous cerambycid exit tunnels and on those that are not quite so freshly dead (and therefore don’t offer as much nutritional value). We monitored the tree on the homepage for several months and had no evidence of squirrels removing bark.

Some preliminary thoughts on what I think remains likely ivorybill work:

The chips shown in the bark chip gallery are mostly as large as or larger than an adult man’s hands. Chip size, shape, and density are probably factors that need to be looked at very closely, and perhaps the contrast between a very ragged, gnawed appearance and a cleaner one with apparent bill strikes is another key aspect.

This smashed sapling was clearly not worked on by squirrels, and the little patches of targeted digging on the small limb are highly reminiscent of Magellanic sign I’ve seen in several photographs:

If you zoom in on the image below, you can see that a woodpecker was involved because the tunnels have been expanded slightly and there’s one Magelllanic-looking dig on the smaller limb. This one also has some superficial scratches that could be from a bill:

This work on a dead oak from the old search area remains interesting, because the bark chips were huge (one as big as my forearm) and due to the apparent lateral bill strikes that were evident when additional bark as stripped several months later:

This little, dead gum (not oak, I think), because there are apparent bill strikes in the cambium and other obvious signs of lateral blows.

When it comes to high branch scaling, squirrels can do extensive damage, as in this example on a sugar maple. At the same time, some of the high branch work we’re finding shows clear signs of insect infestation and woodpecker involvement, as in this downed sweet gum limb I found on Saturday. The scaling took place before it fell.

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In next example, although the scaling has a little bit of the layered appearance we’ve suggested is more characteristic of Pileateds, it’s clear that woodpeckers are involved, since there are a few places where what we presume to be insect tunnels have been expanded.

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There’s also this one, which I initially thought could be due to natural sloughing, but how would sloughed bark fall at an upwards angle?swgumbole

While I was initially disappointed by this new data point, not only because it compels me not only to reexamine certain aspects of my hypothesis but also because it eliminates the types of targets we’ve thought most promising in terms of obtaining clear trail cam photos, I recognize that this is part of the process. It’s an opportunity to refine the hypothesis and a reminder to observe carefully. Ultimately, I think there’s more room for confusion between squirrel work and what I take to be IBWO work. We can’t help but wonder whether Tanner himself might have been fooled in some instances.