Strips, Flakes, Chips, Chunks, and Slabs: Squirrels, Pileated Woodpeckers, and Ivorybills, Part 4Posted: January 26, 2016
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.
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).
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.
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:
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.
The following are measurements of some fairly typical suspected Pileated strips from a sweet gum:
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.
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).
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.)
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.
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.
The 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.)