Insights, Ants, and Old Growth: a Nuanced View of the Ivorybill’s Decline and Possible Survival

I’ve just finished reading Tanner’s dissertation and have gained some new insights into topics that have been discussed in a number of earlier posts.

Conventional wisdom, following Tanner, holds that the Ivory-billed Woodpecker’s decline and possible extinction were caused by habitat loss, specifically the logging of old growth forests during the 19th and early 20th centuries. Birdlife International’s fact sheet on the species suggests “that large contiguous tracts of mature woodland would be required to support a viable population”, referencing Jackson 2002. Snyder et al. have proposed an alternative hypothesis that “human depredation was the primary factor.”  (p.9).

Tanner’s model depends on the idea that food supply was the limiting factor on ivorybill populations, because the species is highly specialized, and that old growth conditions were optimal or essential. While Tanner was aware that ivorybills bred successfully in an area that was predominantly second growth, at Mack’s Bayou, he glossed over this fact in the monograph, and became more dogmatic about old growth as a requirement in later years.

Snyder and some others have contended that the ivorybill is a generalist. According to Snyder, “the data available on diet and foraging methods simply do not provide compelling evidence for strong feeding specialization.” Snyder goes on to suggest that “[i]ts apparent skill in exploiting recently dead timber, coupled with its ability to feed in a variety of other ways, may even have given it some significant foraging advantages over the pileated woodpecker, a species apparently much less capable of bark stripping. Indeed, the pileated woodpecker, like other Dryocopus woodpeckers, may well be more of a food specialist than any of the Campephilus woodpeckers.” (p. 37).

As I see it, there are elements of truth in both models, but neither is complete. In addition, I think that each model relies on at least one flawed premise.

The old growth/virgin forest component of Tanner’s model fails to account for the facts that the Singer Tract population was dwindling even before logging began in earnest and that birds appear to have remained in the Tract until well after it had been extensively logged. Tanner suggested another possibility, “perhaps the greatest factor reducing the rate of ivorybill reproduction is the failure of some birds to nest. One reason for their not breeding is immaturity, for it is probable that ivorybills do not nest until they are two years old. Another possibility is that the quantity of food available to the woodpeckers may determine whether they will nest or not.” (p. 83).

Tanner struggled to account for the fact that the ivorybill population at Singer was dwindling by the mid-1930s, even though overall habitat quality had, if anything, improved relative to what it had been a few decades earlier. He attributed the higher relative abundance in previous years to tree mortality due to fires that took place in 1917 and 1924. Tanner also recognized the probable importance of fire in the pre-contact era, although he seems to have been unaware of the ways pre-contact Native Americans used fire, both for agriculture and habitat management. (The impacts of Native American fire use were almost surely different from what occurred in the 20th century Singer Tract).

Neither Tanner (whose study predates the emergence of the discipline) nor Snyder, take environmental history sufficiently into account. There had been major ‘changes in the land’ long before large scale logging began in the southeast and before the reports of local abundance on which Snyder relies. These changes include: the post-contact collapse of Native American civilizations, the introduction of European plant and animal species, the clearing of log jams on major and secondary North American rivers, habitat fragmentation due to the plantation economy, and the near extirpation of the beaver.

All of these elements likely contributed to a major decline in ivorybill populations. Ivory-billed woodpeckers likely concentrated locally in response to major disturbances, regardless of whether forests were old-growth or advanced second-growth, and this type of specialization caused birds to congregate, making it easier for collectors to kill them in large numbers in short periods of time. Snyder likely misinterpreted this collection of large numbers of Ivory-bills in short periods of time as reflecting a greater regional abundance. In contrast, and more consistent with Tanner, this ecological response to disturbed areas led, in some places, to the collectors extirpating regional populations.

In the latter part of the 19th century, hunting probably sped the collapse of the remaining population, but Snyder’s claim that available data on diet and foraging methods do not provide compelling evidence of specialization fails to account for the anatomical and other evidence that suggests otherwise. It also fails to account for the Pileated Woodpecker’s far more extensive range and ability to thrive in a wider variety of habitats, including badly fragmented and degraded ones. I made some of the case for specialization in a series of recent posts, but there’s more to add, especially with regard to ants.

In one of those posts, I hypothesized that the inability to exploit ants as a food resource was a key component, perhaps the primary component, in explaining the decline of the ivorybill. A commenter asked whether there’s evidence to support the idea that ivorybills and other Campephilus woodpeckers don’t feed on ants and also whether there’s evidence to support the idea that Campephilus woodpeckers don’t regurgitate.

Adult Campephilus woodpeckers rarely feed on ants but do not feed them to their young. They make frequent trips to the nest with food items stored in the bill or at the back of the bill. (M. Lammertink, pers. comm.) Dryocopus woodpeckers and those in closely related genera (the “tribe” Malarpicini) feed their young by regurgitating, while other woodpeckers do not. (Manegold and Topfer, 2012). I think the capacity of Pileated Woodpeckers to consume ants in large quantities and to feed them to their young is a significant distinguishing factor and that Tanner was correct in suggesting that food supply was a major limiting factor on Ivory-billed Woodpecker populations.

Ants comprise up to 33% of the world’s terrestrial animal biomass. In Finland, they comprise as much as 10%. In tropical forests, the percentage is much higher, exceeding vertebrate biomass by 400%. Tanner’s comparative analysis of available ivorybill and pileated food did not include ants, so Tanner’s comparative estimate of available insect prey – suggesting that pileateds in the Singer Tract had access to approximately four times what ivorybills did – was in fact extremely low.

Tanner’s dissertation concludes with a discussion of Audubon’s ivorybill dissection, something that was omitted from the monograph. While I had a passing familiarity with the Audubon material, I had not looked at it carefully. Nor had I compared his ivorybill and pileated dissections.

Tanner wrote: “The proventriculus is both muscular and glandular. Audubon’s drawings and text indicate that the proventriculus of a Pileated is much larger in proportion to the stomach than is the case in the Ivory-bill.” Audubon described the ivorybill proventriculus as being only minimally wider than the esophagus. By contrast, the pileated proventriculus as “an immense sac, resembling a crop, 2 1/4 inches in length and 1 and 5 twelfths in width,” or nearly three times as wide as the esophagus.

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Audubon’s drawing of Ivory-billed Woodpecker digestive tract showing slightly widened proventriculus.

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Audubon’s drawing of Pileated Woodpecker digestive tract showing large, sac-like proventriculus.

The proventriculus and stomach of one of Audubon’s specimens contained “a vast mass of ants and other insects”. According to Bent, Beal found one pileated stomach that contained 2,600 ants. (Others contained fewer, 153 and 469, according to Sutton.) Thus, it’s clear that even if ivorybills sometimes ate ants, they lacked the capacity to consume them in large quantities, let alone feed them to their young.

This supports Tanner’s view that specialization was a limiting factor on ivorybill populations. I’ve previously suggested that this might apply only to breeding season, but it seems reasonable to infer that it’s a factor year-round, based on the differences in proventricular structure.

All of that said, I’d argue that this specialization should not necessarily be read to include dependence on large tracts of mature, contiguous forest. The data from the Singer Tract suggest that even under these ‘optimal’ conditions, breeding was limited. And the fact that the Mack’s Bayou birds bred successfully in an area of second growth suggests that birds could thrive under ‘suboptimal’ conditions. The extent to which survival might be possible in fragmented habitat is less clear, but Snyder (citing Jackson) refers to the Mississippi population of six pairs in a 19.2 square mile forest that Tanner missed; the tract is less than 1/6 the area of the Singer Tract and is smaller than many contemporary wildlife management areas.

The tract, known as Allen Gray Estate, was west of Skene, Mississippi in Bolivar County; some or all of it is now part of Dahomey National Wildlife Refuge; the US Fish and Wildlife Service Habitat Management Plan for the refuge (2013) states that the forested portion of the refuge comprises 8100 acres and provides this historical information, “Dahomey NWR is located on the grounds of the old Dahomey Plantation founded in 1833 by F.G. Ellis and named after the homeland of his slaves. Much of the land west of the refuge was probably cleared for cultivation around this time. The land went through several owners and was purchased by Allen Gray in 1936. The portion that became the refuge was known as the “Allen Gray Woods”. This was the only significant portion of the plantation still forested.”  This 8100 acre figure is 25% lower than the figure reported by Jackson and Snyder.

While I have been unable to find a detailed logging history of Bolivar County, it is in the heart of the Mississippi Delta, which was known for its plantations. Between 1900 and 1940, Bolivar County was more densely populated than Madison Parish: 39.1 people per square mile as opposed to 18.9 in Madison Parish in 1900, 78.92 as opposed to 22.78 in 1930, and 74.57 as opposed to 28.33 in 1940. Based on population density and the number of towns, it seems self-evident that the habitat in Bolivar County was considerably more fragmented than was the Singer Tract.

Thus, there is good reason to question Tanner’s old growth model as well as the idea that large contiguous tracts of mature forest are required. Similarly, there’s good reason to question Snyder’s argument that hunting rather than specialization was the primary cause of the ivorybill’s collapse.

Efforts to reintroduce the beaver in the southeast began in the 1930s, and the population has been growing ever since. Beavers injure trees by partially or fully girdling them and by altering hydrology, which weakens or kills trees at the edges of the ponds they create. Beaver damage renders trees more vulnerable to infestation by ivorybill prey species, something we’ve observed repeatedly in our search area. In Tanner’s day and in the late 19th century, the beaver was barely a part of the southeastern ecosystem, but by the 1950s, beavers again were playing a role in altering southern forests, whether mature or successional.

If the ivorybill was able to survive the logging of the last large tracts of old growth forest, as I think it was, the reintroduction of the beaver may have been central to its persistence. If this hypothesis is valid, there is considerably more potential habitat today than there was in Tanner’s era; much of this potential habitat has been overlooked or dismissed in organized search efforts; and the dismissals of post-Tanner reports based on his habitat model rely, at least in part, on a false premise.

 

 

 


Scaling Data 2012-2016

To expand on some of the data included toward the end of the March trip report (which is worth reading in in conjunction with this post), I thought it would be informative to provide a season by season and sector by sector breakdown of the scaling I and others involved with Project Coyote have found since the spring of 2012. To do so, I’ve gone through my notes and photographs and have done my best to reconstruct the data collected. While not complete (I’m quite sure a good deal more scaling was found in Sector 3 during 2013-2014, for example), I think this breakdown is a fairly accurate reflection of what we’ve found over the years.

As discussed in previous posts, I think extensive scaling on hickory boles is the most compelling for Ivory-billed Woodpecker. Bark on this species is thick, dense, and usually remains very tight for a long time. Extensive scaling on sweet gum boles and oaks (upper boles and large branches) is second among work that I’ve found. Work on small boles, and higher and smaller branches is somewhat less compelling and is more significant for its abundance. Some of the high branch scaling and work on smaller boled sweet gums may well have been done by Pileated Woodpeckers (and possibly by Hairy Woodpeckers), but the abundance, the presence of large bark chips in many cases, the way it appears in clusters, and the fact that Pileateds scale infrequently suggest a different source for much of it.

I have excluded all work where squirrels are suspected but have counted one tree, a hickory found this year, on which the work could well have been that of a Hairy Woodpecker. Hairies do forage for Cerambycid beetles just under the bark, but they’re only capable of removing tight bark in small pieces; their work on hickories is perhaps more accurately described as excavation through the bark.

The trail cam images toward the end of this post are the best we have (out of many thousands of hours of coverage) showing how these species forage on suspected ivorybill feeding trees.

All trees were live or recently dead (twigs and sometimes leaves attached). All scaling was on live or recently dead wood.
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Totals

Sweet Gum (Liquidambar styracifula)

Sector 1:         46

Sector 2:         8

Sector 3:         51

                        105         (84.68%)        

~15% had scaling on boles (a few of these were large trees). The majority of work was on crowns, including larger branches. Fallen trees were included when woodpecker involvement was evident and bark was tight.

Bitternut Hickory (Carya cordiformis)

Sector 1:            3

Sector 2:            4

Sector 3:            7

                           14         (11.29%)

All trees were standing; scaling was on boles and was very extensive (the tree shown on the homepage is one example) with one exception from this year . Insect tunnels were visible in all examples. An additional hickory with a modest amount of high branch scaling was found in Sector 1 this year but was not counted for this analysis.

Oak (Quercus) spp.

Sector 1:         1

Sector 2:         4

Sector 3:         0

                         5         (4.03%)

All oaks had scaling on large branches; one also had some on the bole. All oaks in Sector 2 were found in a single cluster.

We have some information on forest composition in Sector 3, and it appears that sweet gums make up approximately 19%, oaks upwards of 35%, and hickories somewhere under 10%. Sectors 1 and 2 may differ and be more varied in overall composition.

The overwhelming preference for sweet gums relative to their abundance stands out. The scaled oaks are a mix of species, one Nuttall’s, one willow, the others unidentified.

In Sector 3, I am treating the compact stretch from the location of Frank Wiley’s sighting last spring/downed sweet gum top where we had the camera trap to just south of our current deployment as a cluster. The estimate of 23 trees being found in this area is conservative. I have only found one instance of recent scaling north of the location of the downed limb/Frank’s 2015 sighting. The main cluster has been in the same vicinity this year and last, with additional work scattered around farther south. Two of the hickories are within 30 yards of each other, approximately half a mile from the cluster, and one was on the edge of the concentration.

It also may be significant to note that we found a cluster of old but intriguing cavities in the same vicinity as the Sector 3 concentration in 2013-2014. Most of these seem to have fallen. The difficulty we’re having finding active, suggestive cavities is vexing, and may be the most compelling reason to be skeptical about the presence of ivorybills in the area. At the same time, finding Pileated cavities is difficult, even in defended home ranges.

I’m treating Sector 1 as a single concentration; the vast majority of the work is on a natural levee where sweet gums are abundant. The entire area is considerably larger than the other clusters, but given the abundance and ease with which we’ve found sign there over the last five seasons, I think it constitutes one area of concentration.

In Sector 2, there was a small cluster in the area where I recorded putative kent calls in 2013, with work found in 2012 (spring and fall) and 2013. Because the area is small with open sight lines, I can be confident there has been no recent work there since late in 2013 (I last passed through it with Tom Foti back in March of this year.)

The sweet gum work Tom and I found on that day was perhaps half a mile north of this cluster, within 100 yards of the hickory on the homepage. The other hickories found in the 2013 and 2014 seasons were not far away, no more than 500 yards apart as the crow flies.

There’s obviously some bias here, since there’s a relationship between finding feeding sign in a given area and spending time there. Nevertheless, I have little doubt that the putative ivorybill work tends to be clustered. I also have little doubt about the strong preference for sweet gums, since I’m not looking at tree species when I look for scaling. The degree to which sweet gums are favored has only become clear over the last year or so.

Frank pointed out this data does not reflect most of the scaling that likely exists in relatively close proximity to the Sector 3 cluster but cannot be quantified because it is in an area we have intermittently visited due to  inaccessibility. Only two or three examples are from this area, which has been visited a handful of times.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Old Material, New Light: More from the Archives Part 1

I’m planning to do a few more posts drawing on material I’ve found in Kroch Library’s Rare and Manuscript Collection at Cornell. There may be an intervening post or two on  other topics.

While Tanner’s monograph is well-known, the reports he wrote for the Audubon Society at the end of each season are not publicly available, except in the archives. The contents of these reports call some conventional wisdom about the species into question.

First and perhaps least important, it seems to be commonly believed that the John’s Bayou birds were the only remaining ivorybills in the Singer Tract when Tanner visited in December 1941. They were indeed the only birds he saw, as noted in his report (the first document below); however, he found feeding sign in the Mack’s Bayou area and suggested that at least two more birds remained, one at Mack’s Bayou and another in Greenlea Bend. As I read the report, Tanner referenced Bick’s observation in August ’41 (discussed here), and the context suggests that he related it to the John’s Bayou family. Other interpretations are possible, including that this was another family group that was passing through the area, which would mean that the remaining 1941 population was even larger.

In Ghost Birds, Steven Lyn Bales provides a full accounting of Tanner’s population estimates, but earlier books by Hoose and Jackson gloss over the likely presence of the other birds. Hoose (p. 120) wrote that James and Nancy Tanner “maybe heard a third” at Mack’s Bayou. (The source of this information is not identified.) Jackson (p. 132) has Nancy Tanner seeing a male and a female in December 1941. Both Bales and Hoose are clear that she saw the pair in 1940; per Bales, the actual date was December 21.

While there’s no way of knowing whether the birds Bick saw were the John’s Bayou family, I suspect that they were. I also think it’s reasonable to infer, as Tanner did, that this group bred successfully in 1941 (possibly an important point given the disturbance to the habitat). If Bick’s birds were the ones from John’s Bayou, it seems the male disappeared sometime between mid-August and December. Given the consistent presence of this family group in the vicinity for nearly a decade, there’s perhaps a hint of wishful thinking in Tanner’s suggestion that the male “might have moved away” due to the logging.

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The next interesting tidbits come from a 1938 interim report that Tanner sent to the Audubon Society, under the terms of his fellowship (the document below and accompanying map). The report includes a reference to a non-breeding pair in the Mack’s Bayou area. This pair does not show up in Tanner’s published counts, either in the monograph or in his dissertation. It seems possible that Tanner concluded the pair that was seen around Mack’s Bayou and the pair with two young that Kuhn found later were one and the same, erring on the side of caution in his final population estimates.

What stands out in both of these documents is the difficulty Tanner and Kuhn faced when trying to find ivorybills other than the John’s Bayou family. This is a topic I’ve touched on in several other posts because of the common belief, fostered by Tanner in later years and advanced by many 21st-century “skeptics”, that ivorybills should be easy to find.

During his brief, two week visit in 1941, Tanner couldn’t get to Greenlea Bend at all and didn’t find the Mack’s Bayou bird, although he found evidence that it was still there. The 1938 report illustrates how hard it was to find ivorybills even more explicitly. Kuhn and Tanner were unable to locate a pair that had been seen by others in a fairly circumscribed area, although it’s possible that Kuhn happened on this pair and the young of the year on June 15th.

Beyond that, it took Tanner and Kuhn “two or three weeks” to find an ivorybill in an area where there was “an abundance of feeding sign”, and Kuhn only found the bird in question by following it to the feeding sign from a known roost. It seems that, while ivorybills may sometimes have been “noisy and conspicuous”, they were for the most part quite the opposite.

Materials are courtesy of the Division of Rare and Manuscript Collections, Cornell University Library.

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Two More Rare Ivory-billed Woodpecker Images

These two photographs, taken by Tanner in 1938 and published in his dissertation, have not been otherwise widely disseminated or (to the best of my knowledge) reprinted elsewhere. Each is interesting in its own right, and not just because they add to the small body of indisputable ivorybill imagery; the first shows the behavior of a near-fledgling (Sonny Boy) in the nest and the second for the position of the male’s crest, which is more recurved than in most or all other stills. Another series of rare images is here. Images are Courtesy of the Division of Rare and Manuscript Collections, Cornell University Library. Screen Shot 2016-05-03 at 1.39.32 PMScreen Shot 2016-05-03 at 1.40.39 PM


Scaling and Squirrels, Part 3, A Closer Look at Surfaces and Edges

The first two installments in this series, which was inspired by the discovery that squirrels are doing some of the bark scaling in our search area, are here and here. This installment will consider the appearance of the scaling itself, and the next will focus on pieces of bark; “chips” no longer feels sufficient to describe the spectrum of what we’ve found, and using more specific terminology may shed more light on what we think is diagnostic and why.

I’ll begin with the work we are now presuming to have been done by squirrels. In retrospect, it’s easy for me to understand why I was fooled by this bark stripping. I was not seriously considering mammals as a source due in part to the extent of some of the work involved; I never saw incisor marks on the wood, something that’s often described as being an important indicator; similarly, I have been unable to find these marks in the photographs I’ve taken of stripping that we now presume to have been done by squirrels.

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Tanner’s Plate 8, “Ivory-bill feeding sign on slender limb. Courtesy of the Division of Rare and Manuscript Collections, Cornell University Library

In addition, I was somewhat misled by Plate 8 and the description of what Kuhn thought was diagnostic that his daughter shared with us. (Scroll down in this post to see where my thinking went astray.) It’s my current view that Plate 8 could conceivably be squirrel work. Tanner doesn’t state that he actually observed an ivorybill doing the scaling.

Between 1937 and 1939, Tanner observed actual scaling a total of 73 times, but it’s not clear how many instances he might have photographed. In hindsight, the scaling in Plate 8 is not particularly impressive; the scaled patch is relatively small; the bark is thin and the hanging pieces may be an indication of removal by gnawing rather than bill strikes. Adhering bits of shredded bark and cambium are evident in some of the work we believe to be squirrel, including on the tree where we captured a squirrel stripping bark (albeit much smaller ones in that case).

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Small bits of bark and cambium adhering to downed sweet gum limb after presumed scaling by squirrels.

In fact, I think one of the keys to recognizing that squirrels are likely responsible for removing bark is a ragged, shredded, or chewed up appearance to the bark and cambium, as in the examples below.

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The information we got from Mrs. Edith notwithstanding, I am going to examine the edges of scaled areas more carefully and be sure they are for the most part cleanly incised. This is one of the main criteria for ascribing the work to ivorybills (although by no means all Campephilus scaling falls into this category, and some can have ragged edges). As I’ll be discussing in the next post, I think that bark chip characteristics provide an even better diagnostic.

Now let’s turn to targeted digging and the similarities between what we’re finding and the work of other Campephilus woodpeckers. In some of my previous posts on bark scaling I’ve mentioned “little or no damage to the underlying wood”. “Little” is the operative word here. In most if not all of the examples of scaling associated with large Cerambycid exit tunnels that we’ve been able to examine up close, there are also indications of targeted digging, and we have seen similar targeted digging on some of the higher branch work we’ve found. Targeted digging involves the expansion of individual exit tunnels in varying degrees. This can range from what appears to be little more than probing with the bill to deeper and wider excavations, but this excavation is incidental to the scaling, whereas in Pileated Woodpeckers, scaling on tight barked-trees is typically incidental to excavation.

A magnificent series of photographs by Luiz Vassoler posted to the Flickr Campephilus group, showing a Crimson-crested Woodpecker scaling and doing targeted digging, is illustrative (scroll through to your right for the whole series). This is not to suggest that other woodpeckers can’t or don’t dig for larvae in a targeted way, only it’s more suggestive evidence for the presence of Ivory-billed Woodpecker in our search area, given the context and what’s known about the foraging behavior of  its congeners.

I’ll keep commentary to a minimum and post some examples from our area (the seven photos immediately below) and then links to work done by other Campephilus woodpeckers.

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Pale-billed (on palm):There’s no scaling here, but the exit tunnels have been expanded vertically, and the expansions resemble some of the rectangular ones above.

Pale-billed (at nest): Very targeted digging and slight expansion of some exit tunnels.

Pale-billed: On a scaled surface, some tunnels expanded.

Robust: I’m including this almost as much for how well it shows Campephilus foot structure and the rotation of the fourth toe and hallux.

Cream-backed: Somewhat more aggressive expansion of tunnels on longer dead wood.

Red-necked: Targeted digging to the right of the bird.

Crimson-crested: Elongated dig into exit tunnel.

Crimson-crested: another great shot of the Campephilus foot. Targeted dig at bottom of scaled area.

Crimson-crested: Video showing targeted digging on an unscaled area.

Magellanic: are the most Dryocopus-like in the genus in terms of foraging behavior. Note their smaller bills and relatively shorter necks. They seem to spend a lot more time feeding near the ground and excavating large foraging pits than the other species, but they too do a considerable amount of targeted digging.

Magellanic: The appearance of the scaling here is strikingly similar to what we think is diagnostic for ivorybill. The tunnel at bottom right has been expanded, likely with the tip of the bill. It looks as though there is more targeted digging above and to the left.

The two images below, showing targeted excavations on small limbs, associated with extensive scaling on young, freshly ambrosia beetle-killed sweet gums, bear a striking similarity to work by Crimson-crested  (the long furrows in particular) and Magellanic Woodpeckers.

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One final and more speculative observation that might be of interest to other searchers. I had dismissed this work on a live maple as likely pileated because it is generalized digging, not scaling. After going through so many images of Campephilus foraging sign, I’m a little more intrigued by it, as I see similarities to sign like this and this. Like some of the work on ambrosia beetle-killed sweet gums, this almost looks like a hatchet had been taken to the tree; the wood was not at all punky; and red maple at 950 on the Janka hardness scale, while not nearly as hard as bitternut hickory (1500), is harder than sweet gum (850). While I’m not proposing this as a diagnostic, it may be more interesting than I initially thought.

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Unusual excavation on live maple

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Scaling and Squirrels: Part 2, Digging Deeper

Part 1 of this series is here, and the event that led to my writing it is discussed here.  I now expect to write 2-3 additional posts on this topic and may create a new page that summarizes the whole series. I’ve hidden the Bark Scaling Gallery page to be reworked later or incorporated into the summary.

This post will reiterate, revise, and expand upon earlier ones dealing with bark scaling and woodpecker anatomy. The next one will focus on certain characteristics of the scaling we think is being done by Ivory-billed Woodpeckers, on finer details that characterize it (based in part on comparison with work done by congeners), and on how to differentiate it from bark removal done by squirrels. The following entry will deal with bark chips in more depth, and from a slightly different angle than previous posts on that subject.

I had originally intended to address the next post’s planned content in this one, but as I started writing, I realized the long but necessary introduction would bury the lede. It soon became clear that I’d have to divide the post in two with this one for background.

The first important point is that woodpecker taxonomy is in a state of dramatic change, so much so that the American Ornithological Union is being advised to place Downy and Hairy Woodpeckers in separate genera and that their current genus, Picoides, should be divided into four. Notwithstanding the taxonomic upheaval, there’s no question that Campephilus woodpeckers and Dryocopus woodpeckers are only distantly related, that their similarities are the product of convergent evolution, and that these similarities are far more superficial – involving size and coloration – than structural or behavioral. Formerly, some incorrect taxonomic assumptions led to the lumping of Campephilus and Dryocopus into the “tribe” Camphelini, an idea that’s discussed and dismissed in the first paper linked to above. This has been one factor in perpetuating some fairly common and persistent misconceptions – that the two species are closely related, that they occupy or occupied the same ecological niche and might be competitors, and that hybridization might be possible (something I hear surprisingly often).

The following differences are relevant to this discussion:

  1. Bill size and shape. These are dramatically divergent as any comparison shot of specimens makes clear. It’s also worth noting that the three North American Campephili are closely related to each other. DNA analysis suggests the three are distinct species and the Cuban ivorybill may be more closely related to the Imperial Woodpecker than the mainland US species. This study suggested that divergence among the three took place between .08 and 1.6 million years ago. The southern members of the genus are more remote cousins, having diverged approximately 3.9 million years ago. At one time, the southern species were considered a distinct genus, and they have smaller bills, both objectively and relative to body size. Magellanic Woodpeckers have the smallest bills relative to body size in the genus, and their foraging behavior is more Dryocopus-like than their congeners’. DSC00866
  2. Neck length. The much longer neck of the ivorybill allows for a broader range of motion.
  3. Foot and leg structure. Campephilus woodpeckers have a unique variation on what have been called pamprodactylous feet. (Wikipedia and David Sibley both miss the vast difference between Campephilus foot structure and that of most other woodpeckers.) In this genus, the hallux (first) and fourth toe (the rear toes) are both on the outer edge of the foot; the toes can be rolled forward for climbing and backward for perching in a manner that looks more zygodactylous. (The preceding links to images of Sonny Boy, the juvenile ivorybill, and Kuhn are great illustrations.) The fourth toe is highly elongated, the longest toe on the foot, and the hallux, (in the ivorybill, the outermost toe) is relatively longer than in any climbing woodpecker species. The second and third (innermost toes) are angled inward. This is shown quite clearly in a number of the images from the Singer Tract, including Plate 13 in Tanner.

    Enlargement of image used for Tanner's Plate 13 showing foot structure. Courtesy of the Division of Rare and Manuscript Collections, Cornell University Library

    Detail of Tanner’s Plate 13 showing foot structure. Courtesy of the Division of Rare and Manuscript Collections, Cornell University Library

  4. Dryocopus woodpecker feet are closer to being truly zygodactylous – two in front, two behind, with limited mobility and the hallux as the inner rear toe, although the fourth toe can be rolled outward to some extent; this provides less stability when making lateral blows.
    12491939_1681161968798531_3133799821856829215_o

    Pileated Woodpecker foot showing zygodactylous structure and slight outward rotation of fourth toe. Photo courtesy of Carrie Griffis, who posted it on the Woodpeckers of the World Facebook group and kindly granted permission to include it here.

    In addition, Campephilus woodpeckers typically climb and forage with their legs both farther apart and higher relative to their bodies than Dryocopus. This enables them to keep their lower bodies closer to the trunk and move their upper bodies more freely, providing more stability for making powerful, lateral blows.

    4. Tail structure: the ivorybill’s tail feathers are long, thin, barb-like, and stiffer than the pileated’s. The tail serves as an anchor and also helps allow for a broader range of motion.

    Tailfeathers

    Middle Tail Feathers: Flicker, Ivory-billed, and Hairy Woodpecker

    PIWO_tail_adult

    Pileated Woodpecker Tail Feathers. Note how the longest one resembles that of a Flicker more than that of an ivorybill.

    DSC00960

    5. There other structural differences, including wing shape, but these are the main ones that point to how Ivory-billed Woodpeckers have evolved in a way that makes bark scaling their most efficient foraging modality, whereas Pileateds are far better suited to digging, using a perpendicular motion.

Much of the foregoing is based on Walter Bock’s  analysis of woodpecker adaptations for climbing, which was also discussed in depth here. I’ve tried to explain Bock’s key points in straightforward and less technical terms. A longer quote from Bock appears at the end of this post.*

In addition to these structural differences, Pileated Woodpeckers (and to the best of my knowledge all their congeners) regurgitate when feeding young. Campephilus woodpeckers carry food to the nest and appear to be highly dependent on beetle larvae when caring for their nestlings. This means that Pileated Woodpeckers have to ability to take advantage of multiple food sources during nesting season, while Ivory-bills have a more limited range of options. While I don’t think this supports Tanner’s theory of old-growth dependence, it does point to a higher degree of specialization that would impact numbers, range, and suitability of habitat.

At the same time, the anatomical differences and degree of specialization convince me that certain types of feeding sign are beyond the physical capacity of a Pileated Woodpecker and are likely diagnostic for Ivory-billed Woodpecker.

There is a dearth of clear images showing Ivory-billed Woodpecker feeding sign. There are a handful of photographs, most of them very poor. The majority were taken in the Singer Tract and some showing work on pines were taken in Florida by Allen and Kellogg.  Few of them depict the high branch work that Tanner described as being characteristic, and when they do, there’s virtually nothing that can be discerned from them. It is also not entirely clear that Tanner’s attribution of feeding sign to ivorybills was always based on direct observation, which makes us wonder whether some of the work might actually have been done by squirrels. Regardless, this makes it difficult to draw inferences from the existing body of imagery.

That said and with awareness of the perils in extrapolating, one lesser known image from the Singer Tract is worth comparing with the work on boles that’s been discussed in multiple posts.

RMC2006_0563

detail

“The Blind at Elm Rock”, Ivory-billed Woodpecker nest tree and detail showing scaling and excavation on trunk. Courtesy of the Division of Rare and Manuscript Collections, Cornell University Library

This is a view of the 1935 nest tree, which was a red maple. It’s taken at a different angle than the more familiar shots, so it shows some large areas of scaling on the bole that the others do not. While I can do no more than infer that this was done by ivorybills, it’s clearly old, and there’s an abundance of excavation in the underlying wood; nevertheless, the edges and contours of the scaling are strikingly similar to the work we’ve found on boles, especially the area at the lower right, just above the intervening foliage.

This is the jagged appearance I described in the previous post; the similarities are most evident in the picture below and on the home page. ScalingNewArea

Because there are so few informative images of ivorybill feeding sign, the best available option is to look at the work of other Campephilus woodpeckers. Even though they are not as closely related as the Cuban ivorybill or the imperial, their morphology and foraging behaviors are similar; even the work of the smaller-billed but oft-photographed magellanic can provide some clues. I’ll examine this and some probable identifying features of squirrel scaling in the next post, which will take a close look at scaled patches on trees.

*”. . . in most woodpeckers, as, for example, the pileated woodpecker, the legs are held more or less beneath the body,the joints are doubled up,and the tarsus is held away from the tree trunk. This position of the legs is disadvantageous for the bird, because the body is held away from the tree trunk and the muscles of the leg are working at a mechanical disadvantage; the analogy is to the mountain climber who is standing on a narrow ledge with hand holds only beneath his chest. In the ivory-billed woodpecker, the legs are directed away from the center of the body, and the tarsus is pressed against the tree trunk. This method allows the body to be held close to the tree, with the joints of the leg extended. Hence the leg muscles have a mechanical advantage, because they are at the beginning of their contraction cycle and are acting along the length of the segments of the leg. When the body is held close to the trunk, it not only decreases the outward component of gravity but allows the tail feathers to be applied to the supporting surface for a greater distance from their tips. If the bird is climbing on smaller limbs, the feet can encircle the limb and thus obtain better support. However, no matter what size the limb is, the disposition of the legs and the spreading of the toes of the ivory-billed woodpecker furnish direct and powerful resistance to both the lateral and backward motions of the woodpecker when it is at work and, with the tail, furnish a tripodal base of great strength against the pull of gravity.”


More on Scaling and Squirrels, Part 1

This is will be the first in a series of 3-4 posts. The subject is multifaceted and subtle. Nuances can be hard to convey in words and accompanying illustrations; it’s easier to do in talks, with bark chips in hand to provide a more visceral sense of what’s being described. Still, it seems important to make the effort.

I realize now while my initial approach to evaluating feeding sign was rigorous, I grew somewhat lackadasical and overconfident. I also got distracted by the abundant scaling on downed sweet gums we started finding a year or so ago. I’m now confident that squirrels did much of this scaling, but the same does not apply to most of the other work we’ve found over the years.

Even before we discovered that squirrels were scaling bark on downed sweet gums (and quite possibly on standing trees as well), I was contemplating a post that broke down the bark scaling we’re finding into several categories. I was aware of having gotten away from the criteria I had laid out in the past and was feeling a desire to be more specific. That seems like a good place to begin, before delving too deeply into the nuances of distinguishing between squirrel and putative ivorybill work.

The following are the different types of interesting feeding sign we’re finding. Bear in mind that this pertains only to hardwoods that appear to be alive or recently dead and are known or suspected to have tight bark, except in cases where work appears to be old but still has characteristics that suggest it was done when bark was tight. The types of sign are ranked in the order of what I think is the likelihood that most or all of it is being left by Ivory-billed Woodpeckers, although the gap among categories 1-4 is small. (Frank would reverse categories 1 and 2.)

  1. Scaling on standing boles, low enough on the trunk to be examined up close. This includes both standing trees and ones with tops broken off. The sapwood of trees in this category has multiple large exit tunnels. The most prevalent species in this category is bitternut hickory, which has very thick, dense, tight bark, but we’ve also found it on sweet gums and oaks. This scaling is extensive and has a distinctive pattern that’s immediately recognizable in the field, an almost jagged appearance, although the actual edges are curved. The tree on the homepage is one example, and the image below illustrates how even when the scaling is not recent, this distinctive appearance remains. Bark chips are easiest to find for this type of work.

    Old scaling on hickory, 2015

    Old scaling on hickory, 2015. Note the exit tunnels and the absence of other woodpecker work, save for a small dig near the top of the scaled area.

  2. Scaling on standing boles, low enough on the trunk to be examined up close. Few or no large exit tunnels but signs of insect infestation under the bark. Superficial bill marks may be evident in the remaining cambium or on the surface of the sapwood. Tree species in this category include sweetgums and oaks. Chips are similarly easy to find.IMG_0144Lateral strike marks in the cambium
  3. Scaling that has the appearance of the work in category 1 but that cannot be examined up close. No possibility of examining bark chips.Hickory3
  4. Scaling higher on boles and lower branches of standing trees where exit tunnels may be visible, but close examination is not possible. In some cases, these trees are seen at a distance, across water bodies, so there’s no opportunity to look for chips. As is the case in categories 1 and 2, older scaling may go untouched by woodpeckers for extended periods. The first example below is recent; the second is probably more than two years old.
    Hickory3Top

    Top of scaled hickory.

    IMGP0376

    Older scaling on dead top with exit tunnels.

     

  5. Scaling on higher branches of standing trees. Since these are often seen at some distance and in poor lighting conditions, it can also be more difficult to assess the freshness of the work, and the nature of infestation. Bark chips are usually much harder to find under these circumstances. Squirrels typically girdle limbs and often scale on the undersides of large, higher branches. Thus, when larger branches are at less than approximately a 70 degree angle, work on the underside may indicate a squirrel as the source, while the presence of extensive scaling limited to the upper side may be strongly suggestive of or diagnostic for woodpecker.BigSGLimb
  6. Scaling on downed trees or limbs that are at least in part more than 4’ from the ground.Detail of scaling on downed sweet gum.
  7. Scaling on downed trees and limbs that are mostly or all horizontal and less than 4’ from the ground.
    Work now suspected to squirrel on downed sweet gum.

    Work now suspected to be squirrel on downed sweet gum.

    IMGP0936

    Suspected Pileated Woodpecker work on same downed sweet gum

There’s an additional category that is somewhat different from the others. This involves work we’ve found on freshly dead, small sweet gums (>1’ dbh) with evidence of ambrosia beetle infestation. These trees have been stripped of bark, with some accompanying signs of excavation, ranging from targeted digging that resembles the work of Magellanic Woodpeckers (as on the left branch below) to the appearance of having been attacked with a hatchet. We think this work has strong potential for ivorybills, since we’ve found only three examples of it, in close proximity, and in an area with an abundance of other suggestive sign.HackedUpGum

It’s important to point out that when I use the word “scaling”, I am referring only to the clean removal of bark with little or no damage to underlying sapwood. While I have been quite adamant about this as a characteristic, some elaboration is probably in order, as my statements were made in reaction to woodpecker work that was often described as “scaling” in the early search years but was really bark removal in conjunction with excavation, something that’s typical of Pileated Woodpeckers. There still seems to be a good deal of misunderstanding on this subject, and the distinction is not always easy to communicate.

On close examination of some scaled areas, especially in category 1 but also in others, there are signs of targeted digging (but not deep or extensive excavation). This can range from a very slight expansion of an exit tunnel, apparently by probing with the tip of the bill, to what may be a harder strike or two, to a somewhat deeper but still targeted dig into the sapwood. Since many other species of woodpecker are capable of doing such targeted digging, I only consider this aspect when it’s in association with extensive, contiguous removal of bark. This will be explored in more depth in the next post in the series.

In category 1, known ivorybill prey species have been found under the bark or on the scaled surface of two trees. When exit tunnels are found on these trees in this category, they are consistent with infestation by large Cerambycid beetle larvae. I hypothesize that these trees are being scaled when the gregarious larvae have dug their exit tunnels but have not yet sealed their pupation chambers. This would be the stage at which they are most nutritious and most easily accessible for a species of woodpecker adapted to bark scaling, but the opportunity exists only within a very narrow time frame.

For several trees in categories 1 and 2, camera deployments of 2-4 months duration produced no return visits or evidence of what was doing the scaling; in a couple of cases Pileated Woodpeckers were photographed on the target trees for fairly protracted periods. In one, the pileated removed a few small pieces of bark, and in the other it appeared to do a little pecking and gleaning but did not remove any bark. We have revisited several of the other trees over periods ranging from months to two and a half years. One tree in category 2 (no tunnels) had a return visit approximately four months after the first one, when the bark was still tight. Several others, both with and without tunnels and including one first found in June of 2013 and re-examined during my last trip, had no obvious new scaling and little or no excavation of any kind, despite being in a more advanced state of decay

It’s also important to note that we have reason to believe that at least some of the work in all categories is being done by woodpeckers. For example, on the downed sweet gum shown above to illustrate category 7, found in November, there is obvious woodpecker work (likely Pileated) on the bole and apparent squirrel work on the upper limbs. Similarly we suspect woodpeckers did the scaling on the larger downed sweet gum (category 5) – mostly scaled higher but with some work within 4’ of the ground. I found this tree in May 2014, approximately 50 yards from the site of where we captured the squirrel stripping bark; while I do not recall looking for or examining bark chips, the edges of the scaled areas appear chiseled rather than gnawed, and the scaling on some of the higher limbs is on the upper side only.

The next post on this topic will examined the targeted expansion of exit tunnels and will revisit the similarities between what we’re finding and the work of other Campephilus woodpeckers. The following one will focus on bark chips and distinguishing between signs of gnawing and signs of scaling.


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.


George and Nancy Lamb’s 1957 Cuban Ivorybill Study

I have been re-reading George Lamb’s 1957 report on the Cuban Ivory-billed Woodpecker. A number of items struck me as potentially significant for North American searchers, some for how they diverge from Tanner and others for their level of detail. Since this report is likely unfamiliar to many, I thought I’d do a quick post listing some of the more interesting observations

Lamb references a number of local sightings of “groups” of ivorybills, with one report to John Dennis that involved six birds. Notwithstanding, Lamb estimated the population density in Cuba to be much thinner than in the Singer Tract, at one pair per 12-25 square miles. He also pointed out that “ . . . the Cuban Ivory-bills are living for the most part in a cut-over pine forest where only small and deformed trees remain.”

The Cuban ivorybills fed on pines and hardwoods more or less equally, although most of the feeding sign was found on pines, due to the difficulty of searching for sign in the denser hardwood habitat. Roosts and nests were found exclusively in pines (one unused cavity was found in a hardwood), which is interesting in light of the fact that hardwoods were also available. Cavities were found at heights ranging from under 20 feet to nearly 60 feet. Cavities were higher in mature forest; Lamb suggested but did not conclude that the preference was for higher cavities and that the lower ones reflected an adaptation to cut-over conditions.

Lamb describes a female scaling bark: “At this point she was only about 25 feet away while she was feeding around the base of a small pine. She began ‘barking’ this tree about 30 inches from the ground and slowly worked up to the top.” Dennis too had observed birds scaling small pines. They found more scaling than excavation.

This apparent preference for pines, including small ones, may be significant, particularly since the hardwood areas were “relatively untouched”.

An estimated 17 birds were killed by humans over a ten year period, a huge number for such a small population. And it seems an open question whether the thinner population density noted by the Lambs was due to habitat quality, hunting pressure, or a combination of the two.

Regarding flight style: “. . .the flight of the Cuban Ivory-billed Woodpecker was always level and purposeful. They are strong fliers, capable of covering considerable distance in little time, as indeed they must to live successfully in cut-over woodlands. Although the Ivory-bill did not seem to undulate in its flight, the wing beats were not steady, having an almost imperceptible 2-3-2-3 rhythm.”

There’s no mention of double knocks, but calls are discussed. Lamb describes the sound as like the “note of a penny tin trumpet . . . short and usually repeated in a series of single-double-single beats, or it may begin with a double call: that is a high nasal “pent, pent-pent, pent”, or just “pent-pent”. On several occasions the female Ivory-bill most frequently observed made a few long and very loud calls, soon after leaving here roost tree in the early morning. The notes were of greater duration than normal and were repeated in a series of sixteen to twenty-two kients.”

Food for thought . . .


Additional Thoughts on Behavior and Rapid Evolution

I’d like to address an interesting post from “Sidewinder” on the Ivory-billed Woodpecker Researchers’ Forum on the rapid evolution question. His key points:

“Cyberthrush and others have suggested that natural selection has favored high levels of wariness and human avoidance in the IBWO. This position assumes that the change has a genetic rather than experiential (learned) basis. I have questioned this possibility based on the simple fact that behavior is usually one of the fastest traits to evolve. I have no problem with intense human predation on the IBWO resulting in increased vigilance among the surviving remnant, but if the IBWO persists, human predation has been absent now for dozens of generations. While many studies demonstrate that predation pressure can select for increased wariness in animals, what about the inverse? Can multiple generations of relaxed selection over a relatively short term (<100 years) result in relaxed vigilance?”

He concludes that the evidence is mixed and that the, “ . . . findings do not really support or refute Cyberthrush’s hypothesis. Clearly, we need more study–particularly of birds–to learn whether avoidance of humans might persist for many generations after selective pressure (predation) no longer exists to maintain vigilance. In the meanwhile, let’s acknowledge the highly tentative nature of this hypothesis.”

I hadn’t considered relaxed vigilance as a possibility, and it’s an interesting idea. With regard to the general evolved vigilance hypothesis, it’s certainly possible; I just don’t see it as being necessary to explain the difficulty of detection. I think normal wariness, difficult habitat, and extremely low densities suffice.

The hypothesis that the IBWO would dramatically change its foraging behavior, which is to a large degree morphologically determined, is considerably more extreme than the idea that the species became more wary. I have taken issue with the notion (or simplistic reading of Tanner), that the species is (or was) an extreme specialist, but its anatomy and historic range point to some degree of specialization – considerably more than exists in the PIWO.

I suspect that Tanner significantly overstated matters when writing about the canopy and high branch work, but even Tanner made it clear that IBWOs foraged at all levels. Some of the known prey species primarily feed and develop in the boles and in some cases quite near the ground (H. polita, for example). I suspect the high branch foraging Tanner observed was for larvae that he dismissed as being unsuitable because they feed on longer dead wood – Tenebrionidae in particular, although there’s no evidence from stomach contents to support this idea. The larvae we found under bark of this downed sweet gum have been id’d as belonging to that genus, and the tree was not very long dead.

One of the Singer Tract (in a pin oak stub, Mack’s Bayou) was in a clearing.

Mack's Bayou Ivorybill nest tree. Courtesy of the Division of Rare and Manuscript Collections, Cornell University Library

Mack’s Bayou nest tree. Courtesy of the Division of Rare and Manuscript Collections, Cornell University Library

John Dennis’s photos of Cuban IBWOs at a nest also appear to be from a very open area (and even if the Cuban IBWO is a different species, it’s a very close relative, and the hunting pressure there was almost certainly equal, if not more intense.) These seem odd nest locations for a bird that has rapidly evolved to hide in the canopy.

It’s also pretty clear to me that the John’s Bayou birds learned to tolerate human presence, while other IBWOs in the Singer Tract did not. As I’ve pointed out in several posts, Tanner and Kuhn (to a lesser extent) had a difficult time finding ivorybills in other parts of the Tract. This also suggests a behavioral rather than a genetic basis for the wariness or at the very least a substantial behavioral component.