Feeding Sign: Some Possible Ivorybill Diagnostics
This page expands on a recent blog post. I’ve added some examples of other types of work that we think are suggestive for ivorybill, in addition to the first category of work that we think is diagnostic.
Over the years, I have written a great deal about bark scaling and the types of work I think are diagnostic for or suggestive of Ivory-billed Woodpecker; however, I don’t feel that I’ve been effective enough at conveying the nuances of what I look for in situ. I’m going to try a somewhat different approach using images that have been posted previously. I will be focusing on the category of bark scaling that I think is most compelling for Ivory-billed Woodpecker and have added images of three additional types of work. I hope that the tiled mosaic layout will make it easier to get my points across. You can scroll over each image to read the caption (not all are captioned) and click on any one in the mosaic to scroll through the embiggened photos.
The only work we consider is on live or recently dead hardwoods – meaning twigs and small branches are attached, and the is wood hard or apparently hard. This is the decay class that Tanner described as “the kind that ivorybills habitually feed upon” but that Pileateds use rarely if at all (p.51).
The scaling I find most compelling for ivorybill is on hickories, mostly or all bitternut hickories (Carya cordiformis). This work represents a relatively small subset of the suspected ivorybill feeding sign we’ve found, as would be expected given that under 10% of trees in the area are hickories. It is not the type of foraging sign that Tanner emphasized, and I’m not suggesting that scaling on boles is the ivorybill’s predominant foraging strategy. This work has a distinctive appearance, one that differs dramatically from presumed Pileated Woodpecker foraging sign on the same species.
The above images show presumed Pileated Woodpecker work on a recently dead bitternut hickory found in February 2016. It seems reasonable to infer that this is Pileated work because of its extensiveness and the abundance of fresh chips at the base of the snag, suggesting the work was recent and was done by a large woodpecker. Some readers might be inclined to think of this as “scaling”, when in fact it is shallow excavation. The small size of the chips and the fact that some of the chips are sapwood, not bark, support this idea. Contrast the roughened appearance of the sapwood with the clean bark removal in the images below. Also contrast the extensiveness; while the work shown above involves fairly large areas, it pales in comparison to the very extensive scaling we associate with ivorybills.
As I see it, squirrels can also be ruled out for this work due to the involvement of the sapwood, apparent bill marks, and the presence of insect tunnels.
Edited to add: On further reflection, squirrel seems possible for this work; I regret not having taken more and better photographs.
I think that all of the images immediately below show Ivory-billed Woodpecker work, all of it on hickories and most of it fresh. The similarity in the scaling’s general appearance from tree to tree should be self-evident. This type of scaling can be found from within approximately one foot off the ground to the upper parts of boles. Large Cerambycid exit tunnels are visible in the sapwood. Bark chips, when found, were large, and the only hints of excavation involved targeted digging to expand the exit tunnels. It’s worth noting that the Hairy Woodpecker in the trail cam photo below spent several minutes removing a quarter-sized piece of bark. The Pileated Woodpecker also spent several minutes on the tree; it pecked and gleaned and looked around but did no excavating or scaling. More discussion below the images.
Bitternut hickory wood is “hard and durable” and the bark is hard and “much tighter than on most other hickories.” The bark is sometimes described as being thin, but this appears to apply to young trees only. On mature boles, it can be .5″ thick or more.
Due to these qualities, the decay process for hickory snags is often more gradual than for other species, especially in higher and dryer areas. This means that the wood can stay hard and the bark remain tight for as long as three years; such is the case with the tree shown in the penultimate image above. This has enabled me to do periodic checks on some of the snags, and in most instances, they have shown little or no indication of further woodpecker work for extended periods, until the wood starts to soften and excavation becomes easier. Whatever is doing this work seems to be hitting the trees once or twice without returning or, less frequently, to be making visits several months apart. I think this suggests a thinly distributed, wide-ranging species as the culprit, and in my experience, Pileated Woodpeckers tend to return to feeding trees on a regular basis.
In my view, this very specific type of work is diagnostic for ivorybill and is beyond the physical capacity of the Pileated Woodpecker.
I’d suggest that similar appearing work on boles and large, lower branches of other tree species should be considered strongly suggestive. Here are several examples – on sweet gum, oak, and honey locust – from both search areas.
When it comes to the high branch work that Tanner emphasized (as well as work high on smaller DBH trees), it is more difficult to rule out Pileated Woodpecker and squirrel, although if bark chips can be found they may provide some clues.
As discussed in several 2016 posts, this is the type of foraging that Tanner found to be the predominant one during breeding season and immediately after fledging young, at least for the John’s Bayou family group. Thus, for work higher on trees, where bark is thinner and tightness cannot be assessed, abundance is likely a key indicator. From this perspective, it may be significant that our friends the Carlisles who are searching in the Pascagoula area have found only two sweet gums with work that I consider to be intriguing and consistent with what’s described in the literature, this between spring 2014 and November 2016. By contrast, I found over 50 such trees in our area in the 2015-2016 season alone. Whether or not there are ivorybills in the Pascagoula, the difference between the Carlisles’ observations and ours is dramatic and suggests that something unusual is going on in the Project Coyote search area.
In addition, in 2014-2015, I found feeding sign on three very freshly dead sweet gum saplings that had been killed by an invasive species of ambrosia beetle. I have never seen this work anywhere else, including in adjacent upland areas and a nearby bottomland location, where ambrosia beetle killed sweet gums were present. This represents another category that we think is suggestive.
Edited to Add: Similar looking work has been determined to have been done by Pileated Woodpeckers. I no longer consider this pursuit of ambrosia beetles to be suggestive.