Updated – Emerald Ash Borers and Blonding: A Large Body of Bark Scaling Evidence Tends to Rule Out Pileated Woodpecker as The Source of Scaling on HickoriesPosted: July 11, 2018
A couple of initial housekeeping notes: I still plan to do a second, more conceptual post on ivorybill evidence, one on historic range, and possibly another on non-IBWO trail cam imagery. Look for those over the course of the summer. I thought this subject should take precedence and have changed plans accordingly. The photographs (other than my own), which I’m including in the largest possible sizes, are courtesy of bugwood.org (under a Creative Commons License) and Patowmack the trickster.
Thanks to John Kearvell for inspiring me to pursue this subject.
The emerald ash borer or EAB (Agrilus planipennis) is an invasive Buprestid beetle. The first known North American outbreak was near Detroit, Michigan in 2002. Since that time, the species has spread to 33 states and three Canadian provinces.
Bark scaling, especially by Pileated Woodpeckers (Dryocopus pileatus), is one reliable indicator of EAB infestation, and Pileated Woodpecker populations appear to increase as a result of outbreaks. Thus, there is now a large body of data on bark scaling that was not previously available for comparison with suspected Ivory-billed Woodpecker (Campephilus principalis) work.
All of the numerous examples of white or green ash (Fraxinus americana or pennsylvanica) scaling by Pileated Woodpeckers (and presumably smaller woodpecker species as well) found online show “blonding” or removal of bark in layers. This may be due to anatomical limitations that preclude Pileated Woodpeckers from removing thick, tight bark in large pieces. Suspected Ivory-billed Woodpecker work on hickories – which have harder, tougher, tighter bark than ash – shows no trace of blonding or gradual removal. I think this excludes Pileated Woodpecker as the source of the hickory scaling.
Introduction: The Emerald Ash Borer
EABs are believed to have arrived in North America in packing materials. The first outbreak began near Detroit in 2002, and the species has spread rapidly since then, decimating native ashes wherever it goes. All indications are that this invasive insect will have an impact akin to that of Dutch elm disease or chestnut blight, concerted quarantine efforts notwithstanding. Because EABs were a recent arrival and had not been well-studied during the first decade of the 2000s, their relevance to the issue of bark scaling does not appear to have been recognized by the formal searches that were conducted during that period.
While the invasion’s impact has already been devastating, EAB larvae are attractive to woodpeckers, especially Pileated Woodpeckers (Koenig and Liebhold, 2017), and bark scaling is one of the most obvious symptoms of infestation. (This attractiveness may have future implications for any surviving ivorybills as the EAB expands its range.)
Unlike many bole dwelling Cerambycidae, such as Hesperandra polita, which spend the bulk of their lifecycle in the heartwood and do minimal damage to the cambium, EAB larvae live, feed, and pupate just beneath the bark, eventually destroying the cambium. This causes the bark to fracture and sometimes to slough off by itself. In the very dramatic example shown below, I suspect that woodpeckers were involved in most, if not all, of the bark removal but only reached the sapwood well after the bark had started to loosen, fracture, and perhaps fall off on its own. Nevertheless, there are still signs of layered removal on the edges of the scaled/sloughed area.
When I started researching this subject, I was unaware that the term blonding had been applied to woodpecker work in pursuit of EABs, but it has become a widely-used (and apt) descriptive. It refers to the appearance of ash trees or parts thereof, after woodpeckers have started removing the outer bark in pursuit of EAB larvae and pupae. The process of reaching the sapwood appears to be a slow one, and after examining hundreds of images showing of bark scaling on ash trees, I have been unable to find a single example that was devoid of blonding, even when very extensive work was involved.
Patowmack the Trickster’s photo is the most extensive example of apparent Pileated Woodpecker scaling on an EAB infested tree that I’ve been able to find. The tree appears to be fairly long dead – based on the extent of the superficial excavation (tunnels are no longer distinct), the apparent fracture in the trunk at the center of the frame, and on the apparent separation of the bark from the sapwood that’s most distinct on the lower right edge of the scaled surface. While the extent of this work is impressive, I’d suspect PIWO even in potential ivorybill habitat – based on the appearance of the surface, the state of decay and seeming looseness of the bark, and the blonding, which is most evident at the top and at the lower left.
While smaller woodpeckers are responsible for some ash blonding, Pileated Woodpeckers are likely the primary source, especially when the work is as extensive as in the examples shown above. Images of Pileated Woodpeckers on blonded surfaces are considerably easier to find than ones involving other species. This brief video catches a PIWO in the act, on an extensively blonded tree, and points to the difficulty PIWOs face when scaling tight, thick bark.
Blonding on Other Tree Species
I have found blonding or its equivalent on a number of other tree species, so it is not exclusively related to any characteristics of ash bark. Rather, I think it is a function of Pileated Woodpecker anatomy. I have seen this on limbs, including sweet gum (Liquidambar styraciflua) limbs, in our search area and have described it as a “layered” appearance.
It may be possible for Pileated Woodpeckers to remove tight bark from small to medium branches without leaving traces of blonding, especially if the bark is weakened or it comes from a species (like sweet gum) that is relatively soft and thin. Removing thick bark from mature boles is something else again, and I suspect that even when bark has loosened considerably, traces of blonding will often be visible when the work is done by Pileated Woodpeckers.
I have found one extreme example of suspected, extensive PIWO blonding on a bole in Louisiana. I think the tree involved is a sweet gum, but if it is an ash, it would be from a location well outside the range of the EAB today, let alone in 2011 when the tree was found. While blonding is easily visible on the trunk, it can also be recognized by examining bark chips.
I have seen the equivalent of blonding on loblolly pines (Pinus taeda) in the southeast and on softwoods in Westchester County, New York. The bark of most conifers is weaker and less tightly adhering than that of most hardwoods, and it typically becomes easy to scale far more rapidly. This is why I long since abandoned the idea that softwood scaling might be suggestive of ivorybill, unless it involves extensive work on multiple large trees.
I have also found it on live and dead hardwoods in Westchester County, NY. The first pair of images below, which I’ve posted previously, shows fresh, known Pileated Woodpecker work on a Norway maple (Acer platanoides) in my yard. (I saw the bird.) The second pair is from a local park. The snag, which I believe is a large sassafras (Sassafras albidum), appeared to be fairly long dead.
Ash Bark v. Hickory Bark
Ash bark resembles that of bitternut and pignut hickories (Carya cordifromis and Carya glabra), so much so that an arborist mistook the pignut that grows outside my office window for an ash and advised me to monitor it for EABs. Testing bark hardness with a fingernail is one way to avoid confusion. Ash bark feels corky, whereas hickory bark is extremely hard. Last year, I wrote an in-depth post on the characteristics of hickory bark and the reasons it is exceptionally difficult to remove. I won’t recapitulate it here, except to say that hickory bark is considerably harder and stronger than that of virtually any other genus. It is also tighter when trees are dormant or dead, as these reposted tables suggest.
The values shown are for shagbark hickory (Carya ovata), which is slightly stronger, tougher and tighter than bitternut or pignut. While white and green ash bark is considerably stronger and tougher than sweet gum and white ash bark is harder to remove from dead trees, neither species comes close to hickory in any category, except bark tightness when sap is flowing.
I suspect that the extreme strength and toughness of bitternut and pignut hickory bark renders it impervious to blonding. Certain pignuts may be a partial exception, as the outermost bark layer on that species is sometimes slightly subject to flaking. I removed the outer layer of bark from the pignut hickory mentioned above to illustrate; the inner layer is very hard and tight.
Our observations thus far suggest that Pileated Woodpeckers can excavate through hickory bark, leaving behind small pieces, and can remove narrow strips of hickory bark from already scaled areas.
We have found nothing to indicate that Pileateds can go straight from outer bark to sapwood and remove the hand-sized chunks we’ve found under the scaled hickories in the search area.
All of this strongly supports the hypothesis that Pileated Woodpeckers are incapable of scaling hickories in the manner that I believe to be characteristic of Ivory-billed Woodpecker. I’d further argue that the absence of blonding on boles of any hardwood species may be suggestive of ivorybill, provided the bark is thick (over ~.5″) and tight. This is not to suggest that ivorybill work never shows traces of blonding. Though the image quality is poor, Tanner’s Plate 8 may show it.
Something similar to blonding is visible in examples of scaling by other Campephilus species. Thus, an absence of blonding on scaled hickory boles may be a basis for rejecting Pileated altogether and may be suggestive of ivorybill when other tree species are involved.
On a recent visit to a park in Orange County, New York, I found many EAB infested, blonded ash trees. I only had my iPhone with me, but I took some close ups and one shot of the chips on the ground. I also collected some chips and photographed them at home. One of these chips was particularly interesting; while it include some of the outer bark, most of it was from an intermediate layer, further illustrating how the bark is flaked off and that multiple events of stripping are involved before the cambium is exposed.
I returned to the main Project Coyote search area where I spent December 27-January 1. I was joined by two new team members – Erik Hendrickson, an excellent birder and retired National Park Service engineer who had an ivorybill sighting in Arkansas back in 2005, and Jay Tischendorf, a veterinarian with a long and adventure-filled background as a field biologist. Erik lives in Colorado, so he may not be able to visit often, but Jay is much closer. I hope that both of them will be able to return and bring their considerable skills to the effort.
Stephen Pagans, who has been with Project Coyote since 2012, was in the area for the duration. Steve is a retired forester, avid birder with a great ear, and an outstanding photographer. This portrait of a feral hog (more on hogs later), which I think is award-worthy, is just one example of his work.
Tom Foti made it down from Arkansas for a day. Spending time in the woods with Tom, whose knowledge of bottomland forests is second to none, is always an education. On this trip, Tom pointed out that I’d been mistaken about the hickories in the search area. I believed that they were all bitternut hickories (Carya cordiformis), except for a very few shagbarks (Carya ovata), but it turns out that many, perhaps the majority, are in fact pignut hickories (Carya glabra). One of these, shown below, has a DBH of 42″ and may be a state champion. Tom also identified a nutmeg hickory (Carya myristicaeformis), an uncommon species that may not have been previously recorded in the parish.
Having such great companions for the week caused me to look back at the past year, with its terrible low points – the losses of Frank and Bill Pulliam – and high points, particularly the March recordings, which I think are among the strongest evidence of ivorybill persistence obtained to date, and to appreciate my friends, collaborators, and outside advisors. Although I’ve been the public face of Project Coyote for years (Frank wanted it that way), this has always been a team effort, although the composition of the group has shifted over time. While it would be cumbersome to name everyone involved and some frequent advisers prefer to remain anonymous, there are several, in addition to those mentioned above, whom I’d like to acknowledge publicly.
On more than one occasion over the years, Bob Ford has lifted my spirits when they most needed lifting. When I talked to Bob shortly before Frank’s death, I was despondent. I knew Frank’s prognosis was not good and was having doubts about carrying on. Bob helped me see a way forward, reminding me that the search area is important, ivorybills or no ivorybills, and that I’d done meaningful work related to its ecology in general.
Matt Courtman, who had some involvement early on and had known Frank for several years, reached out shortly after Frank died, giving me much needed moral and intellectual support and breathing new life into Project Coyote. In one of those odd coincidences, Matt’s New York relatives knew and did business with my father decades ago.
Philip Vanbergen, the youngest among us, had the presence of mind to turn on his recording device on March 11 and capture a couple of calls, setting the stage for his and Matt’s return on the 15th when the much longer recordings were made. Phil has also been responsible for our trail cams since 2016. His energy, enthusiasm, and interest in the natural history of the area are invaluable.
Peggy Shrum’s ideas, background studying raptors in the Peruvian rainforest (a considerably more challenging environment), and familiarity with tropical Campephilus double knocks are great assets. Peggy has made the long trip from South Carolina to participate several times, and it’s always a pleasure to have her along.
Tommy Michot and Wylie Barrow from Lafayette have also been great sources of support. Though Tommy is a retired biologist with a Ph.D, I admire his youthful enthusiasm, open-mindedness, enjoyment of the woods, and his sense of humor. To top it off, he’s also an accomplished traditional Cajun musician from an illustrious musical family. Wylie and Tommy have known each other for years, and while Wylie has seldom been able to make it into the field, his careful, scientific approach and probing questions help keep me on track. While I skipped it on this most recent trip, the lunches I have with Wylie and Tommy (and sometimes Phil) in Lafayette on the way home invariably help me absorb and evaluate whatever I’ve observed or experienced while searching.
Professor Fredrik Bryntesson has been a great online friend and supporter. He has shared details from his research into some arcane aspects of ivorybill history, some of which have found their way onto the blog. I hope we get to meet in person and that he will be able to visit our search area sometime soon.
Finally, Patricia Johnson, my wife – Patricia comes along from time to time, holds down the house when she stays at home. Her moral and morale support sustain me.
Though 2017 was difficult, I’m grateful to be surrounded by such great collaborators. I’m hoping for more highs and fewer lows in the year ahead . . . Without further ado, here’s the trip report. As with the previous one, I’ve opted not to do a day-by-day log. There’s not all that much to report.
The weather this trip ranged from cloudy, dreary, and damp to bitterly cold; there was little sunshine, except on January 1st, and avian activity was generally low throughout. Woodpeckers, except for Red-headeds, were mostly quieter and less active than usual. Nevertheless, on at least one day, we saw or heard all seven species (ivorybill excluded) that are found in the area at this time of year.
Birds may not have been very active, but the hogs certainly were. We saw upwards of 15-20 on a couple of days, and signs of their rooting were everywhere. Their numbers seem to have increased considerably since 2012, despite the presence of at least a few dedicated hunters in the area. We ran across these newborn hogs and assumed their mother had been shot. Their cute appearance belies their destructive potential should they survive.
We did not have any possible ivorybill encounters and found little recent bark scaling, except on two or three sweet gums, some extensive work on a pine, and a small patch on a cypress. Some commentary below the images.
Phil solved the problem with the trail cams, and we now have three deployed on hickories – two that have lost their tops and one that is in obvious decline. We’ll deploy the fourth in the spring when it will be easier to locate unhealthy trees. Given what we’ve observed and the life cycle of the beetles involved, I think scaling on hickories is most likely to take place between mid to late spring and fall.
Fresh scaling on the bole and branches of a recently uprooted sweet gum. Some of the bark chips were large and consistent with what I would expect for Ivory-billed Woodpecker.
With regard to the sweet gum scaling, it is far and away the most abundant form of this work we’ve found, and this has been true year after year. It is considerably more common in the Project Coyote search area than in other places I’ve visited or than in the Pascagoula, based on the Carlisles’ efforts there. It also matches the work described by Tanner as being typical of ivorybill, but as discussed in my post entitled Bark: An Exegesis, sweet gum bark is relatively easy to scale, making it more difficult to exclude Pileated Woodpecker. As an aside, I’m puzzled by the fact that we found a good deal of scaling on oaks in 2012-2013 and have seen virtually none since then.
While I’ve written previously that I think pine has no potential for being a diagnostic because it is easily scaled, the example above impressed me for its extensiveness and the fact that the presence of needles suggests the tree died very recently. Lighting conditions in the field were so poor that it was impossible to see that scattered patches of bark remained. This only became apparent when I brightened the photographs. Even so, the extensiveness so soon after death remains impressive.
I’ve included the beaver-killed cypress scaling here not because I think it’s likely ivorybill work; it could be, but the bark was loose, and the scaled area, while contiguous, covered only a modest percentage of the bole. What may be significant is the presence of insect work of a kind that is suggestive of suitable ivorybill prey. Tanner thought that cypress-tupelo swamps were poor habitats for the ivorybill, presumably because both are long-lived and relatively insect-resistant species and perhaps because he rarely ran across large scale deadenings of those species. The example shown here leads me to wonder about this assumption, particularly in places where beavers are present or other disturbances occur; fire, to which water tupelos are apparently vulnerable, for example. While Allen and Kellogg reported that Florida ivorybills nested in cypress and fed nearby on fire damaged pines, I think it’s possible that food sources would be sufficient in cypress-tupelo swamps under certain conditions. This relates, at least indirectly, to issues that have been addressed in the “Bits and Pieces” series. Stay tuned for the final installment.