Pileated Woodpecker Scaling on the Limb of a Downed Sweet Gum – Part 2Posted: February 16, 2017
Thanks again to all who sent condolences, and appreciations of Frank Wiley and our work. Your sympathy and support have comforted and encouraged me during this difficult time.
Part 1 is here. This post supplements the analysis at: Feeding Sign: Some Possible Ivorybill Diagnostics. I’ll be reiterating ideas that are familiar to longtime readers; I have posted many of the photographs before; but there’s some additional research and some new perspectives informed by the Pileated scaling sequences obtained in December and January.
I am now firmly convinced that the work we’ve found on a small number of hickories over the past several years cannot have been done by Pileated Woodpeckers. I have believed this to be the case for some time, but the recent sequences showing how Pileateds scale sweet gum bark provide strong, direct evidence in support of that conviction.
As noted in Part 1, sweet gum bark is in the mid-range for tightness among hardwood species. Hickory bark in general, and bitternut hickory bark in particular, is at the highest end of the range in terms of adhesion. Hickories belong to the genus Carya, which is divided into two types, “true” and “pecan” hickories. Bitternuts are in the pecan group, “which are not equal to true hickories in strength, hardness, and toughness.” This inequality is relative, and the differences are modest. In addition, the timber industry identifies bitternuts and a true hickory species, mockernuts, as “tight barked” hickories. True hickory bark adheres so tightly that its removal poses problems for the pulp lumber industry, and I suspect that for the purposes of the linked study, bitternuts are treated as true hickories. In any case, it is safe to say that hickories are the tightest barked hardwood species in our search area, and I have observed that hickory bark can remain tight for years after death, given the right conditions.
Now let’s examine the physical evidence we’ve found with regard to both sweet gums and hickories.
These are three of the largest chips found under the medium-sized limb of the downed sweet gum. There was one larger chip that broke on handling, as well as quite a few smaller ones. This is known Pileated Woodpecker work.
It is perhaps more accurate to describe these as strips. They’re approximately .25″ thick and 2″ across at the widest points.
Now let’s look at some presumed Pileated Woodpecker work from another sweet gum that appears to have been longer dead. This work is from somewhat larger limbs and a nearby hanging broken limb. I can see indications, patchiness and layered appearance, that would lead me to suspect Pileated, just based on the field impression. The chips are even more revealing, even though some of them are larger than what I would have expected.
Here’s an image of the chips found on the ground. There’s been a lot of scaling on this tree, and some older chips (that could be consistent with ivorybill) can be seen in the photograph. Note the variability in size.
Here are some of the fresh chips I collected, shown with my 13″ MacBook Air for scale.
Again, some of these chips are slightly larger than I would have hypothesized for Pileated Woodpecker, but the appearance, which suggests that a considerable amount of pecking was required before the bark was removed, would have led me to assume Pileated. I’m confident this is not squirrel work either, based on the exit tunnels and the way they’ve been pecked at (most readily visible at the far right). Note also that these chips were so brittle that the larger ones broke in transit. This work was done on larger limbs, and the bark is approximately .375″ thick.
By contrast, the hickory scaling is on boles, where bark is tighter and thicker; the surface area involved is typically much greater; and there is no sign of the layered appearance, which I presume to be a consequence of pecking rather than chiseling/prying. In those instances in which we’ve found fresh work, most or all of it appears to have been done within a very short timeframe. The example below, the homepage tree, was still alive, with the scaled areas wet with sap when found.
We found this tree in the spring of 2013 and monitored it regularly for over a year. There were no return visits by whatever did the scaling, and the only other woodpecker work involved the removal small patches of bark by a Hairy Woodpecker (captured on a trail cam). This particular tree had been partially uprooted and was in a lower, wetter area than many of the other hickories that have been worked on in this manner. By the spring of 2016, it had fallen and Pileated Woodpeckers were feeding on the rotting log.
I’ll repost the known PIWO scaling, done over approximately 30 minutes in two visits, five weeks apart, for comparison. Even if the same species of tree were involved I’d have suspected two different sources for the scaling.
As I see it, our Pileated sequences show that it would have required hours for a PIWO to have scaled so extensively on the hickory bole and suggest that they could not have done so as cleanly. The chips (>.375″ thick on a relatively young tree, not at all brittle, and no hint of pecking or removal in layers) and the remaining adhering bark should have a very different appearance if Pileateds were responsible, especially given the substantial differences between sweet gum and hickory bark adhesion and hardness. The work we’ve found on hickories involves both live and recently dead examples. Again, I’ll repost an image of the hickory chips from this tree for reference.
As discussed previously, the hickory scaling also has a distinctive appearance that strongly resembles presumed Ivory-billed Woodpecker scaling on one of the Singer Tract nest trees, a maple.
I think it may be possible to distinguish Pileated and Ivory-billed Woodpecker work on sweet gum branches, based on very close examination of the scaling and the bark chips (when possible). The effort to do so is complicated by the fact that both Pileated Woodpeckers and squirrels can and do strip bark in similar ways. Extensive, mostly contiguous, and clean appearing scaling on larger limbs may be suggestive for ivorybill, as in the example below and as Tanner suggests, but even if ivorybills are doing some of this work, identifying it requires making some fine distinctions.
By contrast, I think the work on hickory boles in our search area is diagnostic for ivorybill. Our focus going forward will be on trying to anticipate and document whatever is scaling bark from the hickories in this distinctive manner. Given the nature of hickory bark, I suspect I will have reached a dead end if it turns out I’m wrong about this.
One final note, identifying potential target trees is a very long shot. We found no scaled hickories of this type in 2015-2016. I have been looking for candidates on the last two trips and have found two wounded trees, both within 50 yards of hickories that have been scaled in recent years.
We’ll be targeting these and will be looking for two more when I return in March.