Feeding Sign, Foraging Preferences, and Prey Species: Some Observations and Speculation

Frank and a visiting ornithologist spent this past weekend in our search area. I’m eager to read and will be posting Frank’s report before long. For now, suffice it to say they set up three trail cams, one on the snag where we captured the image discussed here and here and one on this downed sweet gum top found in April:Big Limb

It most likely fell on April 19th. When I found it a couple of days later, it had fresh green leaves attached and no sign of insect infestation. Since then it has been partially scaled. This is an important data point, as we know the scaling took place within five and a half months of death, and Tanner documented the IBWO’s preference for freshly dead wood. We hope there will be a return visit soon.

They also placed a camera on an even more recently fallen water oak, something that started me thinking about possible patterns in the feeding sign we’re finding.

I’ve counted the examples of feeding sign from our current search area I’ve posted on the blog (which is by no means all the suggestive work we’ve found but is generally the most impressive), and the results for sweet gums are interesting, especially in light of Tanner’s observations suggesting an IBWO preference for sweet gums. Our results also suggest a preference for hickory. (Hickories were scarce in the Singer Tract, and apparently the species present in our area were not present there.) In both cases, the frequency with which we’re finding scaling seems to exceed the relative abundance of either type of tree, although we have not made formal counts. This sign was found between the spring of 2012 and the Spring of 2015, except for the downed top pictured above, which was scaled a little later.

The tally includes a couple of examples of work that falls short of what we consider to be diagnostic for IBWO. It also includes the small sweet gum snag that looks like it was attacked with a hatchet.

Edited November 2021 to add: We now have reason to think this is likely Pileated Woodpecker work.

HackedGum2

While there seemed to be a preference for sweet gums prior to the 2014-2015 season, the preference was considerably more pronounced this year when the abundance of fresh scaling on sweet gums in a relatively small area was astonishing. Here’s the multi-year breakdown:

Sweet gum:                       25

Hickory:                             10

Presumed sweet gum:        6 (One example possibly PIWO)

Oak species:                       3

Willow oak:                          2

Unknown:                            1

Maple:                                  1 (Possibly PIWO)

Ivorybills fed on sweet gums in 42.6% of Tanner’s observations, scaling in 40 instances and digging in 3. Sweet gums made up 20.8% of the forest composition in Tanner’s study area. Next on Tanner’s list of preferred foraging trees were Nuttall’s oaks. By contrast, Pileateds “appeared to have no preference for any species of tree.” Tanner observed PIWOs feeding on sweet gums on fourteen occasions; nine involved digging and five involved scaling. He further noted, “What scaling Pileateds were observed to do was mostly on loose bark and was never as extensive or cleanly done as the work of the Ivory-bills.”

On a more speculative note, I think I’ve been able to identify one species of beetle that’s infesting the sweet gums, including the small one shown above. They’re an invasive, the granulate (formerly Asian) ambrosia beetle Xylosandrus crassiuculus (or another closely related invasive). Ambrosia beetles are tiny, but they are gregarious, with adult females creating chambers and tending broods of larvae in the sapwood. They can kill small trees but also infest larger ones. They have a relatively short life-cycle, and one source suggests they can produce 3 or 4 broods a season in the deep south. It’s worth repeating that I’ve seen signs of ambrosia beetle infestation elsewhere in Louisiana (near our old search area and in upland hardwood forest adjacent to our current one) but did not find work suggestive of ivorybills in either place.

We’ve found known IBWO prey species in our search area, on trees that we suspect were fed on by ivorybills. We also suspect that, contrary to Tanner, they may feed on darkling beetles. Could they also be feeding on an invasive species? We can see no reason to suspect otherwise and will continue our investigations with this in mind. I plan to return to Louisiana Thanksgiving week.


Sweet Gums to Sweet Gums and More

In this post, I compared scaling on sweet gums in our search area with images of scaling on sweet gums taken by Martjan Lammertink in Congaree National Park; he has graciously granted me permission to post those images and some others here.

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Pileated Woodpecker Scaling on Pine – Photo by N. Banfield/Cornell Lab of Ornithology

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High Branch Scaling on Sweet Gum, Steinhagen, Texas – Photo by M. Lammertink/Cornell Lab of Ornithology

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Pileated Woodpecker Scaling on Sweet Gum, Congaree National Park, Photo by M. Lammertink/Cornell Lab of Ornithology

The focus of the original post was on the direct comparison between known Pileated Woodpecker scaling on sweet gums and the work we are finding in our search area. The differences are quite dramatic. In this post, I will simply include a number of examples of suspected ivorybill work from both our old and new search areas without too much discussion. The differences should be self-evident, even without reference to bark chips. I have come to believe that much if not all of the high branch scaling that Tanner presented as being typical and (by implication at least) diagnostic is not necessarily inconsistent with PIWO work. Thus, in the absence of other indicators, the Steinhagen photos are potentially interesting but not highly suggestive. Note that in all three images of PIWO work on boles, there is clear evidence that the bark has been removed in layers. This is true even on the pine, where signs of this layered work are visible on the left, just above the bird. I now suspect the absence or near absence of layering on extensively scaled, tight barked hardwoods may be the single most important component in the gestalt and may even be diagnostic in itself.

Even when the scaling is quite extensive, the signs of layering are likely to be a giveaway, as in this example from public land near our old search area. The bark chips around the base of this tree were all small and gave further indication that the work had been done in layers.

Presumed Pileated Woodpecker Scaling on Snag, East-Central Louisiana, 2011

Heavily Scaled Snag, East Central Louisiana 2011, Presumed Pileated Work

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Detail Showing Superficiality of Bark Removal – East-Central Louisiana, 2011

Pileated Scaling on Snag - East Central Louisiana 2011

Detail Showing Bark Removal in Layers – East-Central Louisiana 2011

Most of the images below have been discussed in other posts. The scaling is on oaks, hickories, and sweet gums and the differences in appearance should be self-evident.

Hickory4

Scaling on a Hickory Snag, Louisiana, October 2013

 

Hickory3Top

Hickory3

Scaling on a Hickory – Top to Bottom – Louisiana, June 2014

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Scaling on a Dying Hickory, Louisiana, May 2013

 

Oak1

Oak Scaling, Louisiana, October 2013

 

 

SP5140 scaled hickory (2)

SP5143 scaled hickory (2)

Spscaled hickory (2)

Hickory Scaling, Louisiana 2013 – Photos by Steve Pagans

HairyWPwork

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Hickory Scaling with eyed click beetle and Hairy Woodpecker work. We suspect that there may be a correlation between IBWO and HAWO foraging strategies.


Photo by Steve Pagans

Sweet Gum Scaling, Louisiana, January 2014, photo by Steve Pagans

ScalingNewArea

Hickory Scaling, Louisiana, June 2013

Heavily scaled young oak with suspected IBWO work extending from the base to well up on the trunk. Large bark chips are visible around the base of the tree

Heavily scaled young oak or sweet gum with suspected IBWO work extending from the base to well up on the trunk. Large bark chips are visible around the base of the tree

Extensive Scaling High on a Living Oak, Louisiana, March 2012

Extensive Scaling High on a Living Oak, Louisiana 2012

Detail of extensive scaling on oak

Detail of Extensive Scaling on Oak

Extensive Scaling on Live Willow Oak, March 2012

Extensive Scaling on Live Willow Oak, Louisiana 2012

Scaling on freshly dead oak, East-Central Louisiana, January 2010

Scaling on freshly dead oak, East-Central Louisiana, January 2010. Tree was extensively scaled including lower on the bole. Some bark chips were the size of my forearm

Sweet Gum Scaling, East-Central Louisiana, 2009

Sweet Gum Scaling, East-Central Louisiana, 2009