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.
I made a brief visit to our search area from November 14-16. Because I was alone, I mostly avoided the more difficult and remote locations and focused on more accessible areas where possible encounters have taken place. This includes our current camera traps. The weather was a problem – steady moderate rain from 7:00-10:30 am on the 15th and early morning drizzle, moderate winds, and cloudy skies on the 16th, which was also the opening day of duck season. On that day, I ventured farther into the swamp and encountered one duck hunter in an area that appears to get very little human traffic. There was frequent gunfire throughout the morning and into the afternoon; however, even on this day when people were hunting for deer and ducks, I saw only four trucks parked along the parish roads, met two people on the road (one of them having just rescued two hunters who had gotten lost.) This was roughly the same level of traffic as we encountered on the opening day of squirrel season in October. Compared to other places I’ve visited in Louisiana, this is a fairly low level of human pressure, although between the gunfire and the weather, avian activity was suppressed on the 16th. Even the crows were less vocal than usual.
On the morning of the 14th, temperatures were in the mid-20s at sunrise. I visited the camera traps and found what may have been fairly fresh bark chips at the base of one; however, I couldn’t identify any areas of fresh scaling on the tree. Frank Wiley will be servicing the cameras and changing the cards in the near future. Time will tell whether anything was captured this time around. At 9:15, near one of the camera traps, I heard three kent-like calls from the ENE. They sounded very clarinet-like in tone, more so than some of the other calls we’ve recorded. The calls were very close together temporally, and I wrote that the cadence was “not quite what I’d expect.” At 12:55, I was in a different location and heard two more intriguing calls from the SSW (also SSW of where I was at 9:15). A Blue Jay was calling roughly simultaneously from a different direction. I consider both of these incidents ‘weak possibles’ because I was alone and because the calls were so few in number.
On the 15th, I spent most of the morning in the field despite the rain, giving up at 9:30 am. The skies cleared at around 11, and I spent part of the afternoon exploring some habitat to the east of our hot zone. One of our group members has made several visits to this section, but I had only spent one morning there. Because it was unfamiliar territory, I chose to walk the bank of the bayou that bisects it. The understory along the bayou is dense and predominantly comprised of holly, which made for tough walking (and also made it difficult to look for and photograph feeding sign.) I was only able to go about ¼ mile in an hour at which point I turned back. Although I covered very little ground I did find an abundance of feeding sign, including a recently dead snag that had been scaled in the manner that I think is diagnostic, and multiple examples of the scaling on higher branches that is consistent with what Tanner described. The high branch scaling appears to be older, but the work on the snag seemed recent, with fresh bark chips on the ground, so it may be an active feeding site. I’ve included some images to illustrate.
Due in part to weather conditions (which made looking for feeding sign a challenge) and gunfire I did not see or hear anything significant on the 16th, although I went deeper into the swamp following a familiar route. About 2.5 miles in, I came very close to stepping on a large cottonmouth as I stepped over a downed tree. Its mouth was wide open, and it was ready to strike when I spotted it. Just a reminder of how dangerous it can be to wander around alone in the swamp.