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 2

In late December 2014, I wrote what I’ve described as a speculative post titled, “Is There a Way to Recognize Ivory-billed Woodpecker Excavation? In that post, I relied on Tanner’s Plate 11,

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Tanner’s Plate 11, “Dead hackberry, fed upon frequently by Ivory-bills”. Courtesy of the Division of Rare and Manuscript Collections, Cornell University Library

a brief description from the monograph: “When Ivory-bills dig, they chisel into the sap and heartwood for borers like other woodpeckers, digging slightly conical holes that are usually circular in cross section (Plate 11)”, and online imagery showing the work of other Campephilus woodpeckers. Material found during my recent visits to Kroch library at Cornell lends some support to the ideas contained in that post, and so does T. Gilbert Pearson’s photograph of a tree that had been fed on by ivorybills. Holt:Pearson Tree

The archival material includes additional images of ivorybill excavation and a considerably more detailed description by Tanner in a document prepared for the Cuban search in the 1980s. The passage includes somewhat more detail on bark scaling than is found elsewhere, but more importantly it describes ivorybill excavations as “hard to distinguish from similar digging by the Red-bellied Woodpecker”.

IMG_1107

Courtesy of the Division of Rare and Manuscript Collections, Cornell University Library

This description may seem counterintuitive to some. Despite my own writing to the effect that ivorybill morphology may lead the species to dig less efficiently than pileateds and my references to targeted digging, I still had an underlying assumption that the size of the bird would correlate with the size of the dig and that ivorybill excavation would often resemble the familiar large furrows dug by PIWOs. While a couple of the holes in Plate 11 and in Pearson’s photograph may well involve the merging of more than one dig, it appears that ivorybill excavations are usually more targeted and that large furrows are not typical.

Also of interest for multiple reasons, including the observation of birds scaling very small limbs and of one feeding 5′ from the ground, are Tanner’s field notes from April 3rd, 1937.

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Courtesy of the Division of Rare and Manuscript Collections, Cornell University Library

I’ll let the remaining images of known and suspected ivorybill excavations speak for themselves and will conclude with a few from our search area that seem consistent with known ivorybill work. While I’m nowhere near as confident about this material as I am about scaling, I suspect that finding excavations that are consistent with what ivorybills are known to have done in conjunction with scaling is suggestive.

I hope this material will be useful for other searchers. All images from the Singer Tract below are courtesy of the Division of Rare and Manuscript Collections, Cornell University Library. Most of these images were published in Tanner’s dissertation but have not been widely disseminated.

IMG_1112

OakNest copy

Ash Roost

'35 Nest Tree copy

1935 Nest Tree, Red Maple

RMC2006_0563

 

detail

1935 Nest Tree and Detail from a Different Perspective

And now some examples from our search area that resemble the existing images of known ivorybill excavation. This is not something I’ve focused on, so I’ve probably missed other examples.

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IMG_0854IMGP1579IMGP1476

IMGP1452

Image at bottom is a detail of the sweet gum snag above. I suspect that more than one species of woodpecker is involved.

There will be one or two more installments in this series, but the next post is likely to be a trip report, probably the last for this season.


Digging Deeper into Tanner: Part 1 of 3 – Tree Size

Although it is thematically quite different, this series of posts is rooted in my recent reexamination of my feeding sign hypothesis that culminates here. It was also inspired by my recent and much closer look at Tanner and the Singer Tract, new insights gleaned from old material, and the input of others that shaped the previous post. My original plan was to make this entry the last in the previous series, but since it has grown to over 5,000 words and addresses different issues, I decided to break it in three and will post the next two installments soon.

I’ve been engaged in an extended dialog with a biologist who is familiar with all the Ivory-billed Woodpecker literature and knows Tanner’s writings specifically. Our back and forth is the primary reason for the long interval between the previous post and this one. This person provided some very important insights that will be included in these posts. At the same time, we have a few points of disagreement. In the interests of transparency and allowing readers to draw their own conclusions, these points of disagreement will be disclosed in the text.

Ivory-billed Woodpecker foraging behavior and diet and what separates this species from Pileated Woodpecker and other North American woodpeckers are issues that have been hotly contested for years. In my view, ivorybills could (and presumably do) forage on any species of tree in any decay condition. However, Campephilus anatomy is specialized, and the only quantitative, observational data that exist on what this species does while feeding young (Tanner 1942) suggest some specialization was in fact occurring at least at the Singer Tract from 1937 to 1939. The problem is that many of the prey items (specifically identified in Tanner and emphasized by others since Tanner’s study), even during breeding, do not seem to match up well with the foraging substrates documented by Tanner as most used by ivory-bills feeding young.

In my view, there are some discrepancies between what Tanner observed and reported and the physical evidence he collected during his study related to ivorybill feeding. I also think there may be discrepancies between Tanner’s observations and those of others from the Singer Tract. At least one thing is clear, Tanner’s observations and the photographic record differ markedly from some of his later recollections. In addition, the monograph itself is sometimes ambiguous, as is evidenced by the disagreements mentioned above. It should become clear that the ambiguity and occasional lack of clarity in Tanner’s monograph have led many, myself and my collaborator included, into misinterpretations. We hope that this series of posts will shed more light and clear up some of the ambiguities.

As most readers already know, Tanner’s observations were restricted to one (and the same) family group each of the three breeding seasons during his study. While a sample size of essentially one family group would normally be a serious constraint for comparing with other information, it is important to point out this information represents the only detailed information we have on prey, foraging behavior, and breeding success for ivory-bills, keeping in mind this family successfully fledged young each of these three years. So the data and information Tanner reported on is directly relevant for understanding what was important for successfully fledging young under the conditions found at the Singer Tract during the late 1930s, but as Tanner himself pointed out in his monograph “…the conclusions drawn from them will not necessarily apply to the species as it once was nor to individuals living in other areas.”

Regarding the observations of others on the Singer Tract, I’ll begin with what may have been the last sighting of the John’s Bayou male. In August 1941, George Bick saw three ivorybills feeding in an ash flat near Sharkey Road, quite likely between the bridges over John’s and Methiglum Bayous, south and west of the John’s Bayou home range as delineated by Tanner. This is the only area along Sharkey Road that Tanner listed as “Ash Flat” on his 1941 map.

According to Bick, “I immediately stopped the car and noticed two Ivory-billed Woodpeckers perched in two small ash trees about eight inches in diameter, having recently killed tops. Only one of the birds was carefully observed. A bright, white bill, flaming red crest, and large white wing patch were all clearly noted as the bird remained at the tree. The second bird in a similar ash tree was observed less carefully . . . [A third bird] flew from a dying water-oak tree ten inches in diameter which had only a few curled brown leaves. A stripped spot about six by eight inches and about seventy feet from the ground was present on the trunk of this tree. This is thought to be a spot where the birds had been feeding and to represent the characteristic Ivory-bill ‘sign.’ In the immediate area were many ash trees with dead tops. Much of the bark was stripped in patches of varying size. This may possibly be old Ivory-bill feeding grounds.”

Logging had taken a significant toll in the Singer Tract by the time of Bick’s sighting. It’s thus possible that the birds were foraging in a suboptimal area due to logging pressure. Nonetheless, it’s still worth pointing out that Bick’s observations were in habitat and on tree species where Tanner observed virtually no foraging activity during his study (which ended two years prior, in 1939; he had no feeding observations on water oaks and only one on an ash). It’s also worth pointing out that Bick made specific reference to sweet gums (what he called “red gums”) as being abundant elsewhere but absent from this location.

My collaborator suggested that Bick’s inference that this ash flat was an “old Ivory-bill feeding ground[s]” is questionable. He suggested that changes in hydrology due to logging may have led to an ash die-off. He also noted that this was Bick’s only observation during his six month stay in the Tract, indicating that he was either not looking hard for ivorybills and/or that ivorybills were not using the ash flat on a regular basis. He added another caveat: it is important to remember that Bick’s observation was in August, well after the breeding season when even Tanner assumed foraging behavior for Ivory-billed Woodpecker likely expanded to different habitats and tree species than used during the time they were feeding young at John’s Bayou.

It’s interesting to note that the last known roost, where Don Eckelberry and young Billy and Bobby Fought famously said goodnight to a lone female ivorybill in April 1944, was apparently located in the ash flat where Bick saw his birds (W. Barrow pers. comm.). Just a few months earlier, in December-January 1943-’44, Richard Pough found a lone female roosting in the heart of the John’s Bayou range, about a mile north and east. According to Pough, who was convinced she was the last ivorybill in the Tract, this bird only crossed the Bayou once “for a brief visit to some trees a few hundred feet west of it . . . confining its activities to an area of hardly more than one quarter of a square mile, within which there were an unusually large number of dying trees.”

In our most recent conversation, my contributor and I touched on the question of whether Bick’s birds (and presumably the one seen by Eckelberry and the Foughts) were from the John’s Bayou family group. Either way, it’s a potentially interesting wrinkle. If the birds did come from John’s Bayou, this points to a heavier use of the ash flat for a period of years than is suggested by the limited information about the family group after 1939. All other observations – Pough, Peterson, Tanner, and Baker – were in the heart of the John’s Bayou home range, and at least one of those birds was reliably present there until shortly before Eckelberry and the Foughts said goodnight. On the other hand, if Bick’s birds were a different family group, it suggests that more ivorybills were in the Singer Tract in 1941 than is commonly assumed. (It’s worth repeating that Peterson wrote that one ivorybill was seen in December 1946, and the last letter to Tanner directly related to the Singer Tract birds says that game warden Gus Willett saw a pair in November 1948 and mentions other reports from around that time.)

To return to the Bick report: all of the trees seem to be in the smallest of Tanner’s size classes, 3-12″ in diameter. This class comprised 75.1% of the forest but was the source of only 12.7% of Tanner’s feeding observations. Tanner believed that ivorybills prefer larger trees because they “have more dead and dying wood” but his own data on this are ambiguous, and what he characterized as large seems problematic. The assumption about older trees having more dead and dying wood may have been true around John’s Bayou during Tanner’s study, but this is by no means always the case – the pine forests of Florida, for example, where Allen and Kellogg found abundant feeding sign on young dead pines, which are more vulnerable to fire than mature trees. And as pointed out in the previous post, even in the Singer Tract, the Mack’s Bayou home range was mostly second growth, so forest composition there must have been quite different.

There are a couple of ways to interpret this data. It’s true that 87% of the feeding was “on trees that are over a foot in diameter”, but this is somewhat misleading. 13-24″ diameter trees are the second smallest size class. They hardly qualify as large and approaching senescence, yet they account for 49% of Tanner’s feeding observations. It’s also true that, relative to abundance, the Singer Tract ivorybills showed a strong preference for trees in the 25-36″ class, but the abundance/observation ratios for 13-24″ trees and over 36″ trees are nearly equal, with a slight preference for the smaller size class not the largest. Thus, I think it’s equally accurate to characterize the data as showing that over 60% of observed ivorybill foraging was on smaller trees, under 24″ diameter at breast height and to reiterate that the most often used feeding trees were in the second largest size category, not the largest. (Tanner pp. 43-45).

On the other hand, there’s a good argument that the data show Ivory-billed Woodpeckers foraged on trees in the 13-24” class at 2.6 times the availability, in the 25-36” class at 6.7 times the availability, and in the 36” plus class 2.57 times the availability; there were very few trees in this size class, most of them sweet gums and a few Nuttall’s oaks (Tanner pp. 43-45). Contrast this with the 3-12” class, when the trees were 5.9 times more available than used.

A few additional points should be added to the mix. The numbers discussed above are aggregates, and size preferences were not at all evenly distributed among tree species. Fully 20% of Tanner’s total observations involved sweet gums in the 13-24” class, the most fed upon type. On sweet gums, frequency and abundance ratios are similar for the 13-24” and 25”-36” classes (the latter is the second most fed upon type, comprising around 18% of Tanner’s total observations). For Nuttall’s oak, 13-24” and 25-36” trees were approximately equal in abundance, but Tanner observed considerably more frequent feeding on the larger class.

My collaborator argues that it is more important is to recognize that when combining the data on sweet gums and Nuttall’s oaks, they collectively comprised 31.4% of the total forest and 79.3% of the foraging observations. Trees within the 25-36” class made up 31% and trees within the 13-24” class made up 29% of all foraging observations. Almost all of the trees in the 25”-36” class (5.2%) were in fact sweet gum or Nuttall’s oak, but for trees in the 13-24” class (18.3%) only about 5% (or about a third) were of these two species. This further highlights what Tanner described as heaviest use on sweet gum and Nuttall’s oak for the John’s Bayou family group over all other available trees, and a disproportionately high use of the second largest size class relative to abundance. However, this documented use pattern was not to the total exclusion of other tree species or even the smallest size class available.

This last was a point of contention. I took issue with aggregating sweet gums and Nuttall’s oaks, since they grow and mature at different rates. In addition, I think it’s important to highlight the fact that 13-24″ sweet gums were the single most fed upon type both in terms of frequency of observations and ratio of observations to abundance (albeit it by a small margin). As I see it, this undercuts the misinterpretation of Tanner that ivorybills are ‘large tree specialists’, a misinterpretation I think Tanner invited when he wrote, “The reason for Ivory-bills feeding on the bigger trees is that large, old trees have more dead and dying wood. Young trees grow rapidly and are resistant to the attacks of insects and disease.” As trees ‘mature’ their growth slows and becomes less vigorous, decay begins, insects attack them, and woodpeckers come after the insects.” (p. 43).

In light of this misconception, I also think it’s important to reiterate that in the aggregate, the over 36″ size did not show anything near the disproportionately high use of the 25-36″class. In fact, the rate was very slightly higher on the 13-24″ trees.

Regardless of how one interprets this very limited data set, the idea that Ivory-billed Woodpeckers required ‘large trees’ for foraging has become a truism. The reality is considerably more complex.

The next installment will focus primarily on decay class, and the final one will look at prey species. Stay tuned.


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.


Trip Report, Part One: March 31-April 5, 2015

As always, my time in our search area was very productive – inspiring new insights and ideas and producing suggestive but inconclusive evidence that Ivory-billed Woodpeckers are present in this location and have been for years. The weather was considerably more cooperative this trip than on the two or three preceding ones, although temperatures edged toward the uncomfortable – mid 80s and humid from Tuesday-Friday – and rain limited field time on Saturday and Sunday. I was alone from Tuesday-Thursday, and Frank Wiley joined me from Friday-Sunday. Later this week, I’ll post a day-to-day log that includes more about possible encounters and some additional images,

For reasons that should become clear, we are starting to think there may be a home range in an area of over four square miles (and possibly considerably more than that), much of which we have not yet explored, and some of which is very difficult to reach – a two mile walk from the nearest road and bisected by deep sloughs and streams. We have some reason to suspect that this range has been used for a number of years. This is in very mature bottomland forest, logged between 1905 and 1915, and it includes the stand of sweet gums where we found a cavity cluster last year.

Also on this trip, we did more experimenting with playbacks; I actually began the experiment shortly before I left for Louisiana, with a Pileated Woodpecker in my yard outside New York City. She responded with considerable agitation to my playback of Pileated calls and drums – calling and flying over at very close range while looking directly at me. She did not react at all to playback of ivorybill calls and pounding from the Singer Tract (the iBird Pro selections). Several species in our search area seem to react to ivorybill playbacks. Pileated, Red-bellied, and Red-headed Woodpeckers frequently react with drumming and scolding. In one instance, a calling Pileated Woodpecker went silent and flew away immediately after a playback. Barred Owls will often call immediately after, as will American Crows. In one case, a pair of crows came in to within 80 feet, apparently to investigate; in another, a Red-shouldered Hawk did the same.

There were three instances of possible ivorybill interaction with or response to playback. Two of them were very weak possibles, meriting only this passing mention. The third was a little more interesting and will be discussed in the day-by-day account. We will continue the experiment, both in Louisiana and New York (to see if and how various species react). We’ve recently been informed, by “Motiheal” from ibwo.net, that a Red-headed Woodpecker in Virginia approached in response to the playback of five kents.

One of the reasons we’re optimistic about having pinpointed a home range is the abundance of feeding sign in the area. In addition to the work sign from this area discussed in previous posts, there’s an abundance of older work, like this scaling on a hickory snag. OldHickory3 oldhickory2

Extensive scaling on an older hickory snag. Work goes from near the base to near the top. Atypically, some of the work at the base appears to be more recent than the rest.

Extensive scaling on an older hickory snag. Work goes from near the base to near the top. Atypically, some of the work at the base appears to be more recent than the rest. While the work is not fresh, and the bark has started to loosen, it is still within the decay stage described by Tanner as being preferred by ivorybills, as shown by the presence of twigs.

According to Tanner (p. 47), “Trees and limbs almost two years dead have lost almost all twigs, some small branches, and bark is loosened on some small branches.” Of course, the decay process is not as linear as Tanner’s description implies, and scaling of bark itself hastens the loosening of whatever remains. Thus, on scaled branches and boles, bark is likely to have loosened considerably unless the work is very fresh. Still, the presence of leaves and/or twigs is a strong indicator of recent death, perhaps even more so on blowdown, for which the decay process is likely hastened by proximity to the ground. In terms of more recent work, I found two sweet gums with sign on large high limbs, perhaps the most dramatic scaling that closely matches Tanner’s description we’ve found to date. Not only is it very extensive; the scaled limbs are quite recently dead. While it’s not possible to test the tightness of the bark, the presence of leaves in the case of the more recent scaling and twigs with buds in the case of the somewhat older work suggest that the limbs died within a six months to, at most, two years. SweetGum1 SweetGum2 It has been suggested that ivorybills are largely birds of the canopy that seldom if ever feed near the ground and that this behavior might account for the difficulty in obtaining clear photographs. Despite the fact that Allen and Kellogg observed a female bird feeding on the ground like a Flicker, and Tanner himself reported observations of foraging close to the ground, the idea that the species is limited to the canopy has become a kind of conventional wisdom. As I’ve discussed in previous posts, I don’t accept this notion and much of the feeding sign we’ve found has been low on standing trees and snags and on blowdown or slash. In the last trip report, I discussed feeding sign found on recently downed sweet gums (just outside of what we believe to be the hot zone, although possibly within it if it is larger than we currently suspect). On this trip, I found over two dozen examples of extensive bark scaling on downed sweet gum tops and limbs. IMG_0888 DSC00076 DSC00070 DSC00074 This work was so commonplace that photographing additional examples seemed redundant. In all cases, the blowdowns were recent and involved very freshly dead wood. At least some leaves were still attached, making it likely that these limbs and tops had fallen in the last six months to one year. In the hot zone, I found only two sweet gum tops or large limbs that had not been scaled. Most of the scaling was recent to very fresh, probably one or two days old in one instance (unfortunately, it had rained the night before, so any scat had been washed away.) I do not believe that all of this is the work of ivorybills. Nonetheless, I suspect that much of it is, due to its abundance and extensiveness and in light of Tanner’s study and the preference he found in the Singer Tract ivorybills for recently dead and dying sweet gums (this even though I believe Tanner overstated this preference and did not sufficiently account for specific conditions in the Singer Tract).

I did not find this type of work in brief visits to areas outside the hot zone, where it was ubiquitous; nor have I seen anything quite like it elsewhere. I did not see anything like it on other species of downed trees; the only partial exception was some scaling on longer dead parts of a live downed hickory. As an aside, it’s worth mentioning that the species of hickory in our area were not present in the Singer Tract, although their congeners, pecans and water hickory were. Unlike Tanner, we’re finding scaling on hickories that likely exceeds their relative abundance. We’re also finding considerably less scaling on various oak species.

In addition to the work on freshly downed sweet gums, I found two standing, recently dead young sweet gums that had been worked on in unusual ways. Both showed signs of infestation by insects that bored into the heartwood. Both had been very heavily scaled, one with minimal excavation only around the insect tunnels. The other had been hacked up in a way that, in the words of several people, looked as if someone had taken a hatchet to it; the wood was hard and not at all punky. Whatever did this work chopped through a small branch to the point where it broke off and almost severed the top of the tree as well.

SmashedSaplingLongShot SmashedSGSapling IMGP0564

Close-up of 2" diameter limb that apparently broke off while being fed upon

Close-up of 2″ diameter limb that apparently broke off while being fed upon

In his report on Cuban ivorybills, George Lamb described something similar:

Soon after we observed a female ivory-bill . . . feeding on the dead branch of a Hilacho tree (Torrubia obtusata) in a small stand of hardwoods. Suddenly the branch broke off while she was still perched on it . . . The Hilacho limb previously mentioned as breaking while being fed on, represents a type of feeding which was neither scaling nor digging. The limb was vertical and had probably originally been about three inches in diameter. Possibly it had once been scaled, but when recovered showed evidence of feeding to the extent that hardly anything was left. The wood was very punky and hand been chipped away from the perimeter to of the limb all along it’s 2 1/2 foot length. The chips, some of which we gathered, were long and splintery appearing, and were riddled with beetle larvae “tunnels”. 

Our broken branch is approximately 2″ in diameter, while the top appears to be more than 3″. Unlike the Hilacho tree, the wood on this sweet gum was hard, not punky.

While I suspect that some of the work on these trees, the very targeted work on the limbs (small rectangular scaling/digging), may have been done by Hairy Woodpeckers, the bulk of it is extremely unusual, inconsistent with any Pileated Woodpecker work I’ve ever seen and with Tanner’s description of that species’ foraging preference for longer dead wood; the type of prey is consistent with what would be expected for ivorybills. While the work on ‘hatcheted’ sapling doesn’t meet the diagnostic criteria we’ve developed over the years, we think it highly likely that this is Ivory-billed Woodpecker work. The scaling on the other small sapling is generally consistent with our criteria, although it has some very limited excavation, clearly aimed at expanding existing tunnels, rather than digging into the wood in the manner typical of Pileated Woodpeckers. Top of Snag LittleSapling ExitTunnelExpanded IMG_0876_2 Again, from the Lamb report: At one point she was only about 25 feet away while she was feeding around the base of a small pine. She began working “barking” this tree around 30 inches from the ground and slowly worked her way up to the top.

Stay tuned for the second installment, which will also include details of a sighting Frank Wiley had on Friday, April 3.


Trip Report Feb. 20-24, 2015: Still More Smoke

Note: this is a very image-heavy post, and most of them appear ‘below the fold’.

Although we faced significant challenges during this trip, it was nonetheless a very productive one. I was joined by John Henry, the photographer who was with me when I recorded kent-like calls in March 2013. Work obligations kept Frank Wiley out of the field, except on February 24th. A flight delay and 1:20 am arrival at my hotel in New Orleans on the morning of the 20th limited my field time to a couple of hours on that day. I had planned to get in a final half day on the 25th, but wintry precipitation prevented it. Weather conditions were a challenge throughout – skies were consistently cloudy and dark; there was occasional rain; and temperatures fluctuated from the 70s on Friday and Saturday to near or below freezing on Monday and Tuesday.

On the afternoon of the 20th, John Henry and I went to the eastern sector, the most easily accessible part of our search area. This is the vicinity where a visiting biologist, Frank, and I heard double knocks during my last visit, and where we have found a significant amount of feeding sign since 2012. I found some fairly impressive, extensive, and recent bark scaling high on the trunk of a fairly distant tree. I was unable to examine it up close, but from a distance it appeared to be consistent with what I think is likely, if not diagnostic, ivorybill work.

Scaling2:20

On a non-ivorybill related note, the feral hog population seems to be increasing in our area, and they do enormous damage to the habitat, probably not in way that impacts the ivorybills we believe to be present, but their impact on forest ecology is likely severe. While they are hunted by some in the area, and don’t seem to be nearly as abundant as they are in Congaree National Park, for example, they are still a severe problem.

Hogs

 

Edited to add: This poor photograph of large, relatively slow moving terrestrial mammals, the best of several taken at less than 100 yards, illustrates just how difficult it is to obtain good pictures in this environment.

On the 21st, John Henry and I went into the habitat on through the northwest corner. This is an area of fairly recent blowdown, several deep, meandering sloughs, and dense blackberry thickets, making it incredibly difficult to explore. On more than one occasion, we had to retrace our steps and find a different route. I estimate that we were able to cover a quarter mile per hour. Traversing this area is hard on body, boots, and clothing, and it’s very difficult to pay attention to anything except the next step. We finally reached the site of the target tree featured in Frank’s Pros and Cons of Trail Cams and where I recorded a possible DK in response or reaction to an ADK. We decided to do a double knock series. Following Frank’s lead, I did a little pounding on the log before doing any DKs. Then I did a DK (I wasn’t recording, as I was using an external microphone mounted on my camera and figured I’d turn it on when I finished the series). Within approximately 10 seconds, there were 3 extremely loud single knocks that came from east-southeast of us. I’d estimate they were spaced about a half second apart and were no more than a couple of hundred yards away. Nothing else happened in response to the series. Although they didn’t have the resonance of typical woodpecker drumming, they didn’t sound like branches breaking, gunshots, or industrial sounds. There were no hunters in the immediate vicinity, no vehicles parked along the access road on our way in and out of the area, and we heard nothing remotely similar during the rest of the day.

On the 22nd, Frank and I made a pilgrimage to meet J.J. Kuhn’s daughter (known to us as Mrs. Edith) who had honored us with an invitation. We spent a delightful afternoon with her and her daughter, son, and son-in-law. They regaled us with many stories about Kuhn’s life, before, during, and after his time with Tanner. As readers know, we see Kuhn as the true master at finding ivorybills. Mrs. Edith is writing a biography of her father, so we’ll leave it to her to tell the story. During our absence, John Henry visited the northern sector and reported hearing a double knock late in the afternoon. He also spoke to two local hunters who claimed to have seen ivorybills. The elder of the two men said he hadn’t seen any recently but had seen a pair 15 years ago in the area that’s discussed in the first and last paragraphs of my previous trip report. This is the third local person to have claimed a sighting in that general vicinity.

The other person’s claim was of a sighting at the south end of what I refer to as the northern sector, so John and I decided to explore that area (which had not been visited) on the 23rd. As is so often the case, travel was complicated by deep, meandering sloughs, although it was nowhere near as difficult as what we encountered on the 21st. We did not have any possible auditory or visual encounters, but I did find one very impressive looking cavity (although not a fresh one) and a downed sweet gum with very extensive and fairly recent bark scaling.

cavity2:23:13

 

Anotherlimb2:21

HangingBark2:21

John next to the main trunk to provide a sense of scale.

John next to the main trunk to provide a sense of scale.

FullViewMainTrunk

This type of work is similar to work found last year. and while it doesn’t exactly meet the criteria I’ve laid out previously for what’s diagnostic, I strongly suspect that it is Ivory-billed Woodpecker work, beyond the physical capacity of a PIWO. The bark was tight and difficult to impossible to remove without an implement.

Frank joined us on the 24th, and we entered the eastern sector farther north. The hike in at this location is long and difficult, but our efforts were rewarded, and we gained quite a few new insights. Once we were well into the bottomland area, we experimented with doing some playbacks. Frank played some Pileated Woodpecker calls and drums, which stirred up a good deal of activity. One Pileated flew in silently, and several others called with the rapid, “cackle” call and drummed in the distance. He then switched over to playing the Singer Tract recordings, and two more Pileateds flew in to the trees just overhead. They drummed and did the “wok” call, apparently in direct response to the recording. It is at least intriguing that playback of ivorybill calls would produce such a response from Pileateds.

We packed up and headed deeper into the habitat and found a sweet gum with three large, oval shaped cavities.

The lower cavity is the most obvious; the other two are near the top, partially obscured by branches.

The lower cavity is the most obvious; the other two are near the top, partially obscured by branches.

About a hundred yards away, I came across another downed sweet gum with extensive and suggestive scaling and large bark chips underneath; one of the chips, shown below, appears to have strike marks that are suggestive of IBWO, similar to the ones discussed in this post. I failed to get clear photographs showing the extent of the work on this downed tree, partly due to angle and lighting and partly due to the events discussed below.

2:24:barkchip

Large bark chip with apparent bill strike.

Large bark chip with apparent bill strikes.

Detail of downed scaled sweet gum.

Detail of downed scaled sweet gum.

This limb, which was somewhat punky, had been fully stripped of bark, apparently after it fell. Also note the scaling in the background.

This limb, which was somewhat punky, had been fully stripped of bark, apparently after it fell. Also note the scaling in the background.

There was a nearby hickory snag that had been heavily scaled in the manner that I think is diagnostic, although not recently.

Old2:24:15

John had moved some distance away while Frank and I examined the tree, and I started taking pictures. As we were doing so, we heard two distinct double knocks in close succession, roughly from the south. This was at approximately 11:15 AM. We remained in place for 30-45 minutes at which time we played back the Singer Tract recordings. John had moved closer to us. Within 30 seconds to a minute of the playback, Frank and I heard a kent-like call. We disagreed about the direction. Frank had it from the Northwest, and I thought it was from the West. Between 30 seconds and one minute later, a large black bird flew in from the west at about 85 yards. My view was fully obstructed, but Frank saw it for several seconds before it took off, at which point John saw it but could not distinguish any field marks.

We proceeded through some very impressive habitat and found some additional scaling in the vicinity, some on a hanging limb and some more on a downed sweet gum. I have now found five downed sweet gums with this type of extensive work in the past year and nothing similar on other species (I did find similar but much less extensive scaling on a downed persimmon, an uncommon species in our area.) This may be significant

Suspendedscaling

2:24:15scalingnorth

The quantity of suggestive and recent bark scaling I found on this trip relative to time spent was remarkably high, as was the possible encounter rate.

I hope to return the search area in about a month and may do one or two posts on other subjects before then. Stay tuned.


Cavities and Context

As many readers of this blog are aware, I’ve been actively searching for ivorybills since 2007 and have been obsessed with foraging sign and cavities since my first days in the field. Over the years, I’ve looked at bark scaling and cavities both in and out of suspected ivorybill territory and have developed and refined a hypothesis about what constitutes diagnostic ivorybill foraging sign. I have come to believe that no such diagnostic category exists for nest or roost cavities, although size, shape, and other contextual elements can support a suspicion that a given cavity is an ivorybill nest or roost.

The cavity cluster we found in May 2014 has characteristics that are encouraging – size, shape, tree species, bark scaling in the vicinity – and one of the cavities resembles a known Ivory-billed Woodpecker nest. This is more than ample reason to survey the surrounding area very carefully (and I’m eager to get back out there), but whereas I feel personally confident that the dramatically scaled hardwoods in our search area were fed on by IBWOs, the mere presence of intriguing cavities is nowhere near as compelling for me.

Similarly, while I suspect that Frank Wiley found a recent nest and at least a couple of roost holes in our old search area, this view is informed more by the associated conditions than by the qualities of the cavities themselves. The suspected nest was in a tree that was heavily scaled and excavated in a way that was strikingly similar to a nest tree found in the Singer Tract, and this is more important than the size and shape of the cavity itself. The two suspected roost holes were in close proximity to one another, and were certainly large enough, but were dramatically different in appearance. There are several facts that are more significant than size or shape. We had a camera trap that covered both trees for a period of several months, and no Pileated Woodpeckers were photographed using the trees in question; the only image we obtained was suggestive of ivorybill but inconclusive (no images of either species were obtained from the suspected former nest tree, even though there were active PIWO roost cavities within 20 or 30 yards); in addition, we found an abundance of feeding sign in the area and had multiple auditory encounters and possible sightings within a few hundred yards of the suspected roosts between August 2009 and April 2010.

oldareacavity2

cavity 2 reportWillow Cavities, East-Central Louisiana 2009. Photos by Frank Wiley.

In examining the images of the suspected roosts and comparing them with other images of woodpecker cavities, I came across a photograph of a Crimson-crested Woodpecker (Campephilus melaneoleucos) near a cavity and was struck by the fact that it was almost identical in appearance to one of our suspected roost holes. I did some further research and found an image of a Pileated Woodpecker nest that was quite similar, if not quite as close a match.

All of this leads me to think that, while it’s important to look for suggestive cavities, this should not be the top priority. I’d encourage other searchers to focus on feeding sign, habitat characteristics, and local reports above all. The limited available information suggests that feeding sign is what led Allen and Kellogg to the Singer Tract birds and that it’s what Kuhn and Tanner looked for. Pileateds will use big cavities (and I’ve even seen White-breasted Nuthatches nesting in holes that look perfect for ivory bills). While finding a nesting or roosting ground will be central to documenting the ivorybill if it persists, cavities alone will not point the way.


Known Ivory-billed Woodpecker Prey

Late last June, I collected several beetles and larvae from a suspected feeding tree in our search area. An entomologist has identified one of the adult specimens as Hesperandra (or Parandra) polita. All the adults were the same species, and we presume that the larvae were as well, although we were not able to preserve them for identification. Parandra polita is one of the few species specifically identified from the stomach contents of Ivory-billed Woodpecker specimens.

According to the Birds of North America species account:

“Most of the animal material (45% of the total sample, USFWS files fide Tanner 1942a) was composed of cerambycid beetles. Two species of cerambycids were identified as Parandra polita and Stenodontus dasystomus . P. polita is a long-horned beetle that has been described as “rather rare” in the s. U.S., but common in Mexico and Central America (Doane et al. 1936), thus potentially providing a specific dietary link between Ivory-billed and Imperial woodpeckers. These beetles feed on the heartwood of old and weakened hardwoods.”

It’s intriguing to have found a known Ivory-billed prey species on a suspected feeding tree.

Edited to add: We may in fact have found two prey species on suspected feeding trees; the other was an adult eyed click beetle (Alaus oculatus); Tanner found a click beetle larva fragment in a Singer Tract nest.

H.Polita