More Squirrels and No Scaling on a Mature Sweetgum

I have reviewed the entire late August-late October card and some of the June-August card for what we’ve designated as deployment 5 – a three-years dead Sweetgum stub discussed last summer. Based on approximately six months of data from this deployment, I think squirrels can be excluded as the source of extensive bark removal from mature, thick-barked hardwood boles, just as the data suggest that Pileated Woodpecker can be excluded as the source of scaling on hickories.

The only potential sources of the extensive bark removal under discussion are gray or fox squirrel, Pileated Woodpecker, and Ivory-billed Woodpecker. Pileated Woodpeckers appear to be unable to remove large quantities of bark from hickories in large pieces, and squirrels appear to be unable to do so on the weaker, thinner-barked sweetgums. Based on trail cam captures obtained thus far, Ivory-billed Woodpecker is the likeliest source for the extensive bark-scaling on hickories that we’ve found infrequently in our search area and that I’ve hypothesized is diagnostic for that species.

There were no woodpecker hits on this target tree, but there are multiple sequences involving squirrels. There was minimal little bark removal, and only from previously scaled areas. In fact, I have only detected one visible change to the bark. A small quantity was removed on June 9, between 11:44:13 and 11:44:33. This is shown in the details below.

Squirrels were active on this scaled patch over the course of the deployment, but whatever removed the small strip of bark on the lower right did so during that 20-second interval and was not captured on the trail camera. I think a woodpecker of some sort is probable, since a squirrel would likely have been visible on the trunk in preceding or subsequent frames.

More importantly, squirrels were captured on or around the scaled areas on multiple occasions, and the captures shed light the way they interact with bark on standing boles and what may limit their capacity to remove it.

This deployment ran from August 19-October 21. Squirrels were detected on 17 days and on or near the scaled surfaces on at least 6 of those days. As previously documented, squirrels displayed interest in the edges of the scaling and frequently appeared to be gnawing; however, they removed little or no bark. We now have numerous captures of squirrels on target boles, both scaled and unscaled, and no captures showing them removing bark in quantity or in anything other than small strips.

Squirrels are clearly capable of rapidly and efficiently removing bark from limbs, downed trees, and thinner barked boles. However, I think there are physical limits – body structure and incisor length – on their capacity to remove thick bark from standing boles.

The following images and time lapse clips show what squirrels do when confronted with thicker bark and suggest that when hanging onto a standing trunk, they lack the leverage to remove bark quickly and leave large pieces behind. This should apparent in the selection of stills and video clips shown below as well as in the sequences posted previously. (A brief discussion of squirrels on hickories follows the images.)

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Up to now, I have not been differentiating among squirrel hits on targeted trees, squirrel hits on or near scaled surfaces, and squirrel hits in other parts of the frame. Suffice it to say there many, far more than woodpecker hits on both sweet gums and hickories. Squirrels frequently show an interest in the scaled surfaces and also in other damaged areas (like the fracture in the hickory bark shown below). To date we have no examples of squirrels removing any bark from hickories, regardless of condition. It stands to reason that the limits of their capacity on hickories would far exceed what limits their capacity on sweet gums.

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Trip Report: October 17-22, 2018

I’ve gone through some additional cards and have some more data on squirrels from the deployment that had squirrel captures earlier this spring. As with the results for Pileated Woodpeckers foraging on hickories, I think this tends to exclude squirrels as the source of extensive scaling on standing mature boles. That will be the subject of the next post, which should be up within a week. In the interim, here’s the October trip report I’ve been promising.

We had no possible encounters and found little suggestive feeding sign this time around.

I spent the first two days with Matt Courtman (and his brother on the second day) in the vicinity of last November’s Saucier sighting. The first day was rainy enough to depress avian activity but not quite enough to keep us indoors. The ground was wet but mostly not unbearably muddy.

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The second day, we found a scaled sugarberry (Celtis laevigata). Tanner called this species hackberry, which is the common name, but it’s not to be confused with the common hackberry (Celtis occidentalis), which is found farther north. Despite the appearance, the tree was either barely alive or very recently dead, since leaves were still visible on the upper branches.

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Sugarberry bark is thin, and it can fracture and break off in large chunks. Pileated Woodpecker is a possibility for this type of scaling, but it is interesting nonetheless, and it strongly resembles ivorybill work on a sugarberry (mislabeled as a “gum”) photographed by Allen and Kellogg in the Singer Tract.

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Bark scaling on sugarberry. Hand-colored photo by Arthur A. Allen.Courtesy of the Division of Rare and Manuscript Collections, Cornell University Library

There were also horizontal bill marks on the surface of the wood. These were interesting and perhaps suggestive; these superficial scratches are the only horizontal markings on sapwood that I think may be suggestive of ivorybill.

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There is so much potential habitat in this area that I’m unsure how to go about searching it, given our small team and limited time and resources.

I spent the balance of my time in our main search area. Tommy Michot and our new team member (I hope to include some of his photographs in a future post) joined me for part of the trip. Because we now have 8 functioning trail cams in the field, much of my time is devoted to servicing the cameras and changing cards.

On the last day, Matt, Lauren (his wife), and I explored a very narrow corridor of near old-growth forest that stretches for several miles to the east of the main search area. We also spoke to someone who had ivorybill sightings, though not recent ones, in the area discussed in this post.

We found more fresh beaver sign than I’m used to. The tree shown is an ash, uncommon in our search area.

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It was a very snaky trip. I had a few near misses with cottonmouths. A coral snake was a major highlight, spotted and avoided on the road by the new Coyote. I was even able to capture it briefly on video before it buried itself.

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We saw turtles too.

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And all the rain meant fungi were plentiful (including a meal’s worth of chanterelles, not shown but brought home and enjoyed).

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There was plenty of woodpecker activity, though it was sporadic, and there was not much drumming. It’s always tough to get good pictures with leaves on the trees, but this Red-headed Woodpecker was cooperative.

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In all my years of searching, I had never found the remains of a Pileated Woodpecker until the trip before this one. It’s a little unnerving for this to happen back to back. I also found Red-shouldered Hawk remains (though not in the same vicinity). I worry that these birds may have been shot, though there’s no evidence for it. The remains, feathers and a few bones, were on top of a log, suggesting that a raccoon was the last creature involved.

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One of our trail cams was hit by a falling limb, and was aiming skyward when found. It appears to be functioning and has been re-aimed at the target tree (where there was an intriguing capture in the summer of 2017).

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We didn’t find much interesting scaling, although some of the work we found was on oaks, which is rare.

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I don’t know the tree species, and Pileated Woodpecker is a possible source, but the work below is unusual. Edith Kuhn Whitehead once told Frank that cambium shredding, possibly like that shown, is suggestive of ivorybill; however, I only heard this second-hand and am not clear about what she meant.

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The sunrise on my last field day was spectacular.

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Stay tuned for squirrels . . .

 


Final Installment: Trail Cam Deployment and Pileated Woodpecker Hits April-October 2018.

I’ve completed reviewing the cards from the deployment discussed in three previous posts. As it turned out, the most dramatic and informative sequence was captured on July 29; it was the last sequence found in the course of the review.

To recapitulate: the tree is a hickory, and hickory bark is uniquely tough, tight, and hard to remove; when first found in early 2017, the tree had already been extensively scaled, probably during the spring and summer of 2016; additional and extensive scaling took place between early 2017 and early 2018; at the time the trail cam was first deployed in April 2018, I’d estimate that over 30% of the entire surface area of the tree had been stripped of bark.

This type of very extensive scaling on hickories has a distinctive appearance, and I hypothesize that it is diagnostic for Ivory-billed Woodpecker. I further hypothesize that it is beyond the physical capacity of Pileated Woodpeckers to do this type of work. We have not yet documented whatever is doing the initial scaling (which is the main objective of these deployments), but data collected thus far on Pileated Woodpecker foraging on hickories tend to exclude this species as the source of the initial work.

Minimal additional bark removal took place between April and October 2018, and all Pileated Woodpecker visits to the targeted part of the tree were captured by the trail cam, except for any that may have occurred between August 12 and August 21, when the camera malfunctioned. The images below are from the beginning and end of the deployment, and they reveal just how little bark was removed over a nearly six month period, when Pileated Woodpeckers visited the tree at least 23 times.

 

 

 

 

The breakdown of those visits may be related to beetle abundance near the interface of bark and sapwood; this could be relevant to peak ivorybill foraging times as well, although there were no possible ivorybill captures during this deployment.

Pileated Woodpeckers (alone and in pairs) visited the tree 10 times between late April and June – on May 1, May 3, May 8, May 12, May 21, May 25, May 28, May 30, June 1, and June 4.  There were nine visits between June 17 and July 3, (with two sets of of captures on June 17 and July 3rd). Hits dropped off dramatically after July 3rd. There were none between July 4 and July 25 and one each on July 26 and 28. The final hits were on September 24 and a very brief one on October 5.

The duration of these visits ranged from approximately one minute to over 20 minutes. At just under 15 minutes, with two birds present, the July 29th clip is one of the longer ones. Immediately below are the captures from July 26 and July 29 and a version of the July 29 capture at 1/10 speed, which makes it easier to see what the birds are doing while on the trunk. The relevant part of the clip ends at just after the one minute mark. If you have the capacity to download the captures and step through them frame by frame, that will also be helpful. Some additional discussion after the videos.

 

 

 

 

 

 

 

 

 

 

 

 

This capture shows the most extensive single incident of bark removal by a Pileated Woodpecker over the course of the deployment. It’s also the only incident in which bark is removed from an area that is not an edge. The area in question is on the upper right.

I think this illustrates the Pileated Woodpecker’s very limited capacity for bark removal on hickories. It takes the bird several minutes to remove approximately 8″x2″ of bark (crudely estimated, based on the size of the woodpecker). This is roughly equal to, and possibly less than, the area of many of the individual chips found under the homepage tree. In addition, it appears that the PIWO removed the bark by excavating through it, not by stripping it.

It’s also worth pointing out that the snag and remaining bark are farther along in the decay process, and hence the bark is likely easier to remove, than when the first two rounds of scaling took place.

This is congruent with what I’ve hypothesized; Pileated Woodpeckers are very well adapted for excavating, and they are capable of digging through even tough, dense hickory bark; however, they appear to be excavating but not to be capable of removing it by scaling in large chunks.

We will continue to collect data, which may end up contradicting the findings thus far, all of which suggest that some other animal is responsible for the initial, very extensive scaling. The main purpose of this deployment was to document what woodpecker activity on a tree that had already been scaled; I expected that this would involve Pileated Woodpeckers, not ivorybills. It will take considerable luck to predict which trees are likely to be scaled and capture whatever is doing the initial bark removal; that’s the primary focus of this effort. There are a lot of hickories in the woods, and we’ve only found a handful of impressively scaled ones over the years.