Is There a Way to Recognize Ivory-billed Woodpecker Excavation?Posted: December 26, 2014
As most readers know, I have been very focused on feeding sign, and specifically on bark scaling, for several years and believe I have identified a diagnostic type of work that is beyond the physical capacity of any other woodpecker species. I have been far less focused on excavation because I was convinced that there was no way to distinguish between Pileated and Ivory-billed Woodpecker digging.
In fact, Frank Wiley and I have had a long-running joke about Plate 11 in Tanner and have always wondered why he included it. Based on some feeding sign we’ve found recently, another look at some sign found in May, and a look at online imagery of both Campephilus and Pileated excavations, I suspect that certain types of excavation are suggestive if not diagnostic.
Tanner wrote, “When Ivory-bills dig, they chisel into the sap and heartwood for borers like other woodpeckers, digging slightly conical holes that are usually circular in cross section (Plate 11).”
When I returned from Louisiana in November, I was struck by certain similarities between this excavation:
which I discussed in the most recent trip report, and Plate 11, especially the hole at the upper right and the third hole from the bottom in the plate. I was also impressed by the bill marks at the edges of these holes and by their depth. I then started looking at images from Bill Benish’s Flickr Campephilus group photos and was struck by the similarities, for example:
I then went back to a photograph I took in May of some excavation that struck me as being unusual at the time, although I couldn’t have specifically explained why.
The appearance of some of the holes is strikingly similar to the Pale-billed Woodpecker excavation shown here.
The work in the upper part of the image that’s partially cut off looks more consistent with typical Pileated excavation.
While I’ve not examined digging with nearly the attentiveness that I’ve devoted to scaling, These workings do not look like typical PIWO excavation, examples of which can be found:
Magellanic Woodpeckers, which are more PIWO-like behaviorally and anatomically, appear to excavate in a way that’s more similar in appearance to typical PIWO work, but even Magellanic excavation often seems to have a more jagged and more rounded look than does PIWO.
I wonder if the apparent differences might have to do with preferred food sources – termites and ants for pileateds and beetle larvae for ivorybill. General deep digging is an effective feeding strategy for the former; while more targeted excavation would be more efficient for the latter. Note that the PIWO work in the first image above seems to be targeted (and was likely focused on larvae) but has a much sloppier appearance.
Today, I found another tree with this type of work, not far from the area that we’ve just started to explore and think is very promising. Below are two views of the work. One potentially significant element is that the larger holes appear asymmetrical (Tanner notwithstanding) and more skewed in orientation than typical Pileated Woodpecker foraging trenches, which would be consistent with their being dug with more lateral blows.
While I’m not prepared to suggest that there’s a diagnostic when it comes to this type of feeding sign (and my comments about the excavation from last May are considerably more speculative) , I am starting to think it may be and that there may be a gestalt that is at least suggestive of ivorybill to the experienced and careful observer.
Edited to add: to reiterate, this is an evolving hypothesis, subject to revision or abandonment. I will need to start looking closely at work outside of suspected ivorybill areas and at the work of other Dryocopus woodpeckers.