Bits and Pieces Part 3: Internalized Beliefs, How They Got That Way, and What the Record Really ShowsPosted: October 9, 2017
Most of us with an interest in the ivorybill have internalized a set of beliefs about what constitutes “suitable” habitat. To a large extent these beliefs treat the Singer Tract as a model – a vast tract of “virgin” bottomland forest dominated by oaks and sweetgums, with abundant, moss-draped cypress for atmosphere (although ivorybills seem to have avoided cypress in the Tract). The habitat description in Stephen A. Shunk’s excellent Peterson Reference Guide to Woodpeckers of North America clearly expresses some of these beliefs, which have influenced the overwhelming majority of modern search efforts and which are embedded in the minds of most searchers (myself included) to the point of being a default:
Virgin bottomland forest almost always below 100 ft. (30 m) elevation. May also have occurred in uplands but by 1900 restricted to areas downstream of pine-bald cypress interface. Requires large tracts of contiguous forest with very large-diameter trees and adequate dead and dying trees to provide forage and nest sites.
The Guide, which draws on an 1891 article by Hasbrouck for the 100 foot elevation, goes on to list three different habitat types described by Tanner – sweet gum-oak dominated forests in the southeast (with species of oak varying depending on location) outside of Florida; river swamps in Florida dominated by cypress, black gum, and green ash; and creek swamps in Florida characterized by cypress, red maple, laurel oak, black gum and cabbage palmetto, with feeding in adjacent pine woods.
This is not to criticize the Guide or its author – I recommend the book highly and the overall treatment of the ivorybill is thorough and evenhanded. The quote is intended to point out the pervasiveness of these ideas about habitat requirements, ideas that Tanner reinforced, especially in later years. They’re so pervasive in part because the myth of the “virgin forest” has shaped ivorybill lore since well before Hasbrouck and has influenced almost all habitat assessments since Tanner.
The virgin forest myth is a topic for another day; the central point is that ivorybills have been found in more diverse habitat types than most have believed. It’s worth bearing in mind that Tanner himself asserted that ” . . . at present the only suitable habitat for ivorybills is in tracts or areas of virgin timber”, a narrow, almost lawyerly, and largely conjectural conclusion – one not entirely supported by fact. Ivorybills bred in at least one Singer Tract area (Mack’s Bayou) that was predominantly regrowth, and as has been discussed in previous posts, Tanner became more dogmatic and blinkered about habitat requirements in later years, dismissing the John Dennis Texas recording because a Pine Warbler was captured on the tape.
As should become clear, Ivory-billed Woodpeckers were found in a variety of different habitats and did not always require extensive tracts of contiguous forest. Large diameter trees, their importance, and what Tanner meant by “large” are discussed in another post, but even if one accepts that large trees were preferred in the Singer Tract, much of the feeding sign Allen and Kellogg documented in Florida was on small, fire-killed pines.
My plan for this post was to focus on Ivory-billed Woodpecker records from outside the historic range as delineated by Tanner in his oft-reprinted 1942 map and adaptations thereof.
The purpose behind this original plan was in part to show that the historic range of the ivorybill was considerably more extensive than is commonly believed, but more importantly to show that ivorybills inhabited more varied habitats than is commonly believed. As time went on, my focus has shifted even more toward the question of habitat diversity, though the fact remains that the historic range was considerably more extensive than the Tanner map, or the one drawn by Hasbrouck in the 1890s, might lead one to expect.
In recent Facebook comments, several ornithologists have suggested that without physical evidence, no record should be accepted. As I see it, this standard is, to some extent, a kind of ahistorical overkill, since it has never been applied in the past. Post-1939 Singer Tract observations don’t meet it, so the last record date is pushed back by several years, which can impact statistical analyses. At the same time, the parsimonious approach is not entirely meritless, since it eliminates false positives. The problem is that there’s no purely objective standard for evaluation of historic (and pre-contact) records, even when it comes to specimens. In many cases, location information for specimens is non-existent or ambiguous; for example, one specimen in Cornell’s collection (1896) is listed as coming from the “Florida Keys”; “Key” in this context more likely refers to an island of forest surrounded by the Everglades than to the islands offshore.
Thus, in this post and the next, I’ll be looking at many reports from within the recognized historic range, as well as some from beyond those boundaries. I will be focusing on reports accompanied by physical evidence or published accounts stating that physical evidence was obtained but will include or mention a few additional ones that seem particularly credible based on the source or amount of detail.
The more surprising of these reports are unsupported by physical evidence. These come from the Eastern Shore of Maryland, Swedesboro, New Jersey, and Pennsylvania. Most date to the 18th-century, a time when ivorybills were reported to have fed on trees girdled for clearing. The most interesting of these come from Peter Kalm, a Swedish naturalist and student of Linnaeus. They have been discussed in several articles by Benjamin Leese, who has also written about early records from Ohio, Indiana, and Kentucky (for which the case is stronger). Most of these papers do not seem to be available online.
Just under 200 of the 418 specimens (including Cuban ivorybills) listed by Hahn provide no location information or merely identify the state, or country in the case of Cuba, where the collection took place. There are multiple cases in which specimens were reportedly collected but have not been found, and in several cases, there’s no way to correlate the claim of collection with an actual specimen. In one instance, not catalogued by Hahn, a pair of ivorybill specimens was mislabeled as Pileated Woodpecker until the error was corrected in the 1960s.
When it comes to pre-Columbian sites, there’s no way to be certain whether material collected from graves and middens involves trade goods or locally killed animals, although tarsometatarsi are likely local, especially east of the Mississippi, where there’s little evidence to suggest that woodpeckers had ceremonial value. Leese addresses this subject in a paper on Native American uses of ivorybill parts. I have included records involving tarsometatarsi and one from a West Virginia midden that involves parts of two lower mandibles.
I’ve created a google map showing the locations of the records from habitat types that don’t fit the ‘large tracts of contiguous bottomland forest’ paradigm. I’ve provided some details for each location. The map draws on Appendix E or the US Fish and Wildlife Service’s Recovery Plan, Tanner, and Jackson. I’ll discuss the records from coastal areas, south Florida, the upper Mississippi and locations east of the river in the next post. I’ll conclude this one with a look at the records from the western edge of the range, since they relate to the Nebraska report and why I thought it might be credible; the Nebraska location is actually somewhat east of the records from the southern plains.
One record that I find compelling does not include a specimen; it’s from the 1820 Long Expedition, the first scientific exploration of the American West.
The ivorybill’s call is described, and Pileated Woodpecker is distinguished and described as common in the area. These facts lend credibility to the report, as does the fact that Thomas Say was the expedition’s naturalist. While Say is best known as an entomologist, the expedition produced the first descriptions of a number of bird species, and an entire genus of flycatchers was named in his honor.
The location of this record is approximately south of Tulsa on the Canadian River, near the 96th Meridian. This is farther west than the location of the erroneous southeastern Nebraska report and well into the eastern Great Plains. It is also well beyond the range of the bald cypress. The relatively narrow floodplain would have been dominated by cottonwoods and willows, as it is to this day. This image, from ca. 1920s shows “Standing Rock” a geological feature now flooded that was discovered by the expedition a day after the ivorybill encounter. It should add a visceral sense of the area’s appearance to supplement the description above.
Even if one opts to reject this record for lack of physical evidence, there are several others from approximately the same longitude that do involve specimens, and some are from the 20th century.
The Recovery Plan suggests that there are two records from west of Tulsa, a specimen was “probably” collected by Woodhouse along the Cimarron River, Pawnee County in 1849. Per Jackson, the specimen was sent to the Philadelphia Academy of Natural Sciences, which has four specimens without location information in its collection. The second is from House Creek in Pawnee County, also Woodhouse 1849, and also reportedly sent to the Philadelphia Academy but not found there.
There are several Plains records from Texas. A specimen currently in the Dallas Museum was collected on Bois d’Arc Island, just southeast of Dallas, elevation 400′, in 1900. There were multiple reports from the area through 1910, and an additional bird may have been collected in 1918. A bird was reportedly “caught in a trap” in nearby Kaufman County in 1927 and examined by an R.E. Huck but not preserved. An additional Texas record, from farther south but west of the 96th Meridian, comes from New Braunfels County, south of Austin and east of San Antonio. There were multiple reports ca. 1900, with a collection reported but no specimen preserved.
Although only one record from the eastern Plains can be attached with certainty to a currently existing museum specimen, there’s proof that Ivory-billed Woodpeckers were found in this region as recently as 1900 and considerable circumstantial evidence for their presence along riparian corridors on the plains of Texas, and possibly Oklahoma, into the 20th-century. The habitat involved is markedly different from what so many have believed ivorybills require. I’m not suggesting that ivorybills persist at the western edges of their historic range, but as will be discussed in the final installment of this series, I think their ability to exploit these relatively narrow, willow and cottonwood dominated floodplains can help explain how the species could have persisted into the 21st century.
Stay tuned for Part 4.
I had been planning to do a post with various ivorybill related tidbits in anticipation of the search season, which begins next month. That will be coming in a week or so, but I want to say a little more about Bill Pulliam first (beyond his Luneau video analyses, which I think should be dispositive). This decision was inspired in part by one of our advisors who pointed similarities between what Bill observed in Tennessee and what we’re seeing in Louisiana. While the physical characteristics of our old search area seem to have more in common with Moss Island, Tennessee than where we’re currently focused, Bill’s perspectives are relevant to both.
Edited to add: Moss Island is a small wildlife management area encompassing 3400 acres. I’m not sure what percentage is mature bottomland hardwood forest, but there are a variety of other habitat types. Compared to our search areas it is relatively isolated and distant from other large tracts of forest.
As an aside, Cyberthrush also has a post honoring Bill with a link to an eBird tribute.
With comments included, Bill’s series of posts on Moss Island runs to nearly 54,000 words. There’s no telling how long this series will remain readily accessible online, and indeed some of the images and sound files are no longer available. The entire series is worth reading and saving if you’re seriously interested in the ivorybill. It starts here.
On re-reading the posts for the first time in eight years, I’m struck by how much Bill influenced me without my recognizing it and/or how much the evolution of my understanding between 2009 and today is congruent with the ideas he expressed just as I was getting more deeply involved in searching.
Like Bill, I suspect that the near extirpation and revival of the beaver may be central to the ivorybill’s decline and survival (more about this in my next post). Like Bill, I think that Tanner’s model failed to account for environmental changes that had taken place in the preceding centuries. Like Bill, I think that if the ivorybill survived, it had to have adapted in ways that are inconsistent with Tanner’s a priori assumption that the species is old-growth dependent.
Bill was tough-minded and opinionated. There were times when I thought he considered me a somewhat annoying amateur. While we hadn’t communicated about it in recent years, he took a dim view of my efforts to make sense of feeding sign in the early days. Most of our correspondence took place in the 2000s, while he was still actively blogging about the ivorybill. After that, I sought his input sparingly.
My last exchange of emails with him pertained to the March recordings. Without quoting him directly, I think it’s fair to say he thought the calls were likely or more than likely Ivory-billed Woodpecker. He also thought it unlikely that birds were resident in our search area, based on the pattern of potential encounters, the paucity of strong sightings, and lack of conclusive evidence. I’m not sure I agree; I wish there had been a chance to explore this topic in more depth and that he’d been able to see our search area for himself. Nonetheless, his perspective has led me to consider that other nearby forested areas deserve more attention than we’ve given them to date.
I’ll conclude with three paragraphs from his final post in the Moss Island series. It’s as true today as it was in November 2009 (though I suspect nesting may take place in fragmented second growth, as in our old search area). I hope it inspires you to read the rest. More from me soon.
How does this relate to Moss Island? By Cornell standards, our habitat is unsuitable. Hence, our encounters are largely dismissed out of hand. By doing so, the Cornell approach has painted themselves into a rather nasty corner. The logic is simple. To all appearances, we have Campephilus-like double knocks that are at least as good as what has been heard in the “core habitat” such as Big Woods and Congaree. If one claims that in “core habitat” these represent evidence for the possible presence of Ivorybills, but in “marginal” or “unsuitable” habitat they provide no evidence for the possible presence of Ivorybills, one has committed a logical no-no of the first magnitude. If the same sounds come from places where you have concluded that Ivorybills are not going to be, then you should conclude that these sounds have no relevance to Ivorybills anywhere. Conversely, if you feel these sounds are evidence of the possible presence of Ivorybills in South Carolina or Arkansas, then you must also accept that they would be evidence of the same in Tennessee, Illinois, Mississippi, Florida, Louisiana, and Texas. You can’t have it both ways.
Anyone who seriously considers that Ivorybills might still persist, and that double knocks and other soft evidence have a relevance to indicating their possible presence, should accept that the evidence in total suggests their habitat requirements might be broader than has been assumed by Cornell et al. I’m not suggesting they will nest in fragmented second growth, or even use it as a full-time habitat; but there are ample indications that if these sort of encounters mean anything anywhere then the birds indeed are using fragmented “marginal” habitats for at least parts of their life history. These habitats are hugely more extensive than the “core” habitats, hence this possibility raises all sorts of further hypothetical possibilities for the natural history, survival, and conservation of the species, all of them positive. In the alternative philosophy to Cornell’s, you search where you have learned of rumors, whispers, or credible declarations that something of interest might have been seen or heard there. This of course requires a lot of judgement, and eventually everyone will draw the line somewhere; I’d not put much stock in reports from western Kansas, for example — although good double knocks in Nebraska or Vermont would settle a lot about what they might mean in Arkansas! But until and unless we actually find some reproducible birds and determine what their 21st Century habitat use patterns really are, minds should be kept open.
You will not get anyone involved in the Tennessee project to state that we have established the presence of an Ivory-billed Woodpecker anywhere in Tennessee as a statistical or scientific certainty. None of us has put an Ivorybill on his or her life list. However, if you asked us off the record for our own personal unscientific feelings, I think you would hear several confessions that indeed, some of us do strongly suspect that there has been at least one of these critters tormenting and taunting us in the delta woods for the last several years. Which means we also think that all that follows from this about habitat, behavior, distribution, etc. should be given serious consideration. Interconnected mosaics of fragmented second growth bottomland forest should be included within the spectrum of possible habitats for the species. You will not get anyone involved in the Tennessee project to state that we have established the presence of an Ivory-billed Woodpecker anywhere in Tennessee as a statistical or scientific certainty. None of us has put an Ivorybill on his or her life list. However, if you asked us off the record for our own personal unscientific feelings, I think you would hear several confessions that indeed, some of us do strongly suspect that there has been at least one of these critters tormenting and taunting us in the delta woods for the last several years. Which means we also think that all that follows from this about habitat, behavior, distribution, etc. should be given serious consideration. Interconnected mosaics of fragmented second growth bottomland forest should be included within the spectrum of possible habitats for the species.
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.
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.
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.
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.
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.
I flew into Houston on February 4 and arrived at the search area on the morning of the 5th. Frank’s work schedule had precluded him from returning to the search area during my absence, and he was unable to get time off to join me this trip.
Tommy Michot visited on the February 5th; we went to the northern sector, and passed the downed sweet gum top (actually a limb) found in April of last year. Project Coyote had a camera trained on it for some time but took it down due to equipment failure. The main stem, which reaches from the ground to about 20 feet up, had been scaled extensively, down to the base, over the course of the last month. Some of the work had been done no more than a few days prior to my arrival based on the condition of bark chips found at the base.
We have a camera back on this top but have low expectations, since so much bark has been removed that it makes a much easier target for other species of woodpecker. While I don’t believe in the “curse of the ivorybill”, individuals and small groups of self-funded searchers face enormous obstacles and are dependent on equipment that’s often unreliable.
Tommy and I measured a number of the largest trees in the area, and the biggest oaks and sweet gums are around 4’ DBH, with many more in the 3’ range. Here are some of the highlights: two Nuttall oaks: 137 cm/53.94”, 119 cm/46.85″; swamp chestnut oak 110 cm/43.31” four sweet gums: 124 cm/48.82”, 123 cm/48.43”, 110 cm/43.31″, 109 cm/42.91”.
While ours was not a random sample, this table from a 1986 paper by Tanner (on data collected in the Singer Tract in 1938), is interesting for the sake of comparison.
In his 1944 report on the Singer Tract, Richard Pough described sweet gums in the 5’-6’ DBH range as being characteristic of old growth conditions, and such trees were not uncommon in the 19th century. Impressionistically, at least, most of the ~4’ DBH sweet gums in our area are moribund and are likely to have lost their tops. I know of only one gum that appears to be in the 5′ DBH category. As of 2009, the national champion sweet gum had a DBH of 5’4.6″. The tree below could be close to that.
Many, perhaps most, gums have at least some beaver damage. This may be contributing to the earlier mortality, both by stressing the trees directly and by creating the opportunity for beetles to infest them. I have long suspected that the decline of the beaver could have contributed to the IBWO’s disappearance, since beavers directly damage trees by gnawing and also stress or kill them by altering hydrology.
Beavers were extirpated from much of Louisiana by the early 19th century. As of 1931, populations were restricted to the Amite and Comite rivers in the southeastern corner of the state; they were reintroduced in other areas in 1938 and had established themselves in 21 parishes as of 1951. (Wylie Barrow, pers. comm.) Range expansion continued into the 1990s and after. They’re now considered a pest animal and appear to be found in all parishes. A recent paper suggests that the introduction of beavers into Magellanic Woodpecker habitat may have benefitted that species.
I was on my own on February 6th, and I went and staked out the downed top for the better part of the morning. Nothing landed on it except for a Red-bellied Woodpecker that pecked and gleaned but did not scale bark or do any excavating. At approximately 9:30, I did a very aggressive series of ADKs. I heard a couple of loud single knocks that seemed to come from no more than a couple of hundred yards away and also a possible double knock. These came during a period when I was standing, moving around, and doing the ADKs, so I did not hear them very well. In addition, there were a few distant gunshots within about 15 minutes after the series, so I’m not very confident about what I heard. (These were the only shots heard all day.) I found some scaling the next day a couple of hundred yards away (discussed below). This gives me some reason to think the SKs were a reaction, not shots. Still I’d place these in the weak possible category.
One highlight of the day was watching a pair of Red-shouldered Hawks in the act of mating.
I returned to the same area on the 7th, with two cameras to deploy. One is aimed at a large sweet gum stub, about 20’ tall and well over 3’ DBH that I found last trip. The top had broken off shortly before my arrival. While it’s not discussed in Tanner, T. Gilbert Pearson, who was the first modern ornithologist to observe the Singer Tract IBWOs, described this type of “stump” as one of the species’ preferred feeding sites. This is a tree on which I found high branch scaling last year, before the top broke off. I expect this to be a long-term deployment.
I also redeployed a camera on the downed top, although we’re not very hopeful about that location, since the scaling is so extensive and the bark has been loosened in many of the remaining unscaled areas.
I walked south for a couple of hundred yards and found very fresh, large bark chips at the foot of a live sweet gum (there were two large gums ~3’ dbh about 10’ apart). There was extensive scaling on live or recently dead high branches of one or both of these trees. Because there had been a major rainstorm and accompanying minor flooding a week before and the chips were mud free, I can be sure the scaling took place after the rain, and since Tommy and I had spent considerable time in the area examining some other nearby scaling two days before, I strongly suspect this work was done on the 6th. I can’t help but wonder whether the possible single knocks came from whatever was doing the scaling; that would be consistent with my immediate impression when I heard them, both in terms of distance and direction. Nonetheless, my confidence level about the SKs is low given the gunfire.
I don’t think the scaling and bark chips are consistent with squirrel; the chips are large and thick and do not show signs of having been chewed off; the ones collected weighed over five pounds.
There was a little excavation and exit tunnel expansion (visible in the first image above) associated with the scaling; and it has the generally clean edges and lack of layered, flaked off appearance around the edges or on the chips. The leaves and gumballs are attached on most of the limbs, indicating that they’re alive or very, very recently dead, so the bark is almost certainly tight. This is about as good as it gets when up-close examination is not an option
I met Tom Foti, who came in from Arkansas, on the morning of the 8th. Winds were high, with gusts approaching 50 mph. We decided it would be unsafe to venture into the woods, so we drove around the edges of the search area looking at the surrounding upland forest, much of which is impressive and mature. Tom is very enthusiastic about the area, ivorybills or not, and we’re hopeful that steps will be taken to protect and manage it appropriately. The car ride was a running lesson on southern forest ecosystems, and as I told Tom, I’ll count myself lucky if I retain 10% of what I learned.
The next morning, the winds had dropped enough to make it safe to head for the swamps, and Tom and I visited the southern sector, an area where we haven’t spent much time lately. As mentioned in some previous posts, there has been a significant uptick in four-wheeler activity in the area, and it’s heartbreaking to see the destruction these callous individuals are causing. Fortunately, the damage is almost entirely limited to the periphery, and the deeper parts of the bottom are unscathed. The habitat types here are somewhat different, and the logging date is more recent, but it remains very impressive. We walked a long way and went to places I had never been, including a lower-lying flat with tree species I haven’t noticed elsewhere – shagbark hickory, bitter pecan, and overcup oak.
We saw no recent feeding sign in any of these areas, except for some older work on a small sweet gum that I described as being about a grade B-.
We then looped back along a different track, passing the spot where I recorded calls in March of 2013 and where we’d had a concentration of feeding sign in 2012 and 2013. We found nothing until we reached a location farther north that is within 100-200 yards of the tree shown on the homepage. Tom spotted a group of trees with bark scaling, some on boles and some on branches. Once again, this was not “grade A” work, but the concentration makes it more interesting than if it were one isolated example. We did not find any chips at the base of the snag that had been scaled on the bole, and the high branch work is not as extensive some.
It’s worth pointing out that on many days, I’ll walk for hours and see nothing and then find either a dramatic example of scaling or a small cluster of it. Tom and I had probably walked 3.5 miles or more before finding this little cluster.
I was on my own again on the 9th, and I opted to go on a death march to retrieve a trail cam from a tree deep in the swamp and proceed north from there. The tree is a large blown down sweetgum discussed and shown here. There was some fresh scaling on it that I suspect was done by a Pileated Woodpecker. There are nearly six weeks of images to go through, so it will take some time before we find out if there were any captures.
As on the previous day, I walked for a couple of hours without seeing or hearing anything suggestive until I got to a part of the area we haven’t visited since last year, perhaps a quarter mile south of the southernmost point Tommy and I had reached earlier in the week. I found old sign, some of which was fresh last winter and some of which was older. I then found some fresh work on two trees in close proximity to one another. Some of the scaling was on a downed tree but was clearly done by a woodpecker, with chips and other characteristics that I consider to be suggestive. Since the chips were caked with mud, the scaling was a little over a week old. The other work was on one high branch, but conditions made it impossible to look for chips.
On the return hike, I found what I’m quite sure is Pileated Woodpecker work on a recently dead or dying hickory. Since we’ve found a number of hickories that we suspect have been scaled by Ivory-billed Woodpeckers, this was an unusual opportunity to do a direct comparison. In my view the work on hickories is the most compelling for ivorybill due to the density and tightness of the bark and the hardness of the wood. There are pronounced differences in the presumed Pileated and suspected ivorybill work on this species.
The work on the homepage is suspected ivorybill. It is extensive, with huge contiguous areas, perhaps 20% of the entire surface, completely stripped, with evidence of bill strikes targeted at exit tunnels. The Pileated work is spotty by comparison. The bark chunks scaled from the tree on the homepage were large, dense, and thick, and there were no pieces of sapwood among them. By contrast, the suspected Pileated work involves very small pieces of bark that appear to have been removed by digging rather than scaling; there were also a few pieces of punky wood among the chips.
The next morning, I drove to the Wetlands and Aquatic Research Center (formerly the National Wetlands Research Center) in Lafayette and met with Wylie Barrow, Heather Baldwin, Tommy Michot, and Philip and Eric Vanbergen. (Two young enthusiasts who will be helping us out.) Frank joined us briefly, and then Wylie, Tommy, the Vanbergens, and I went out to lunch. It was an exciting and thought-provoking day, and the Research Center is an incredible facility. Wylie and Heather shared their comprehensive and in-depth analysis of conditions in the Singer Tract in Tanner’s day. They’ve amassed an array of materials encompassing land records, Civil War era maps, and stereographic aerial photographs. Their research far surpasses my own speculative effort. It covers the finest details – roads, improved and unimproved, snag densities, tree mortality, conditions around roost and nest sites, as well as conditions in other locations where ivorybills were seen. Tom Foti has done complementary research on hydrology, soils, and vegetation.
Their presentation convinced me that I’ve been too hard on Tanner in some respects. There was a little more old growth in the Singer Tract than I had inferred from the Pough report and some of the historical documents. Nonetheless, the characterization of the Tract as a whole as “virgin” forest is somewhat misleading, since over a quarter of it was second growth, and some of it fairly young. Heather and Wylie have graciously given me permission to summarize some of their findings.
When Tanner began his study, 72% of the Singer Tract was old growth. (Tanner estimated it at over 80%.) Logging in 1938 reduced that percentage to 67%. The ridges, which Tanner deemed to be the best ivorybill habitat, were actually the least likely areas to be old growth. (Tom Foti’s analysis also points to a preference for higher, drier locations.) The regrowth percentages for each landform in Tanner’s day are as follows:
Low ridge (23%)
Total on ridges (32%)
Low flat (4%)
Cypress brake (4.5%)
For the most part, the second growth forests were not particularly old, as has been suggested in previous posts. According to Heather, most of these areas only started to regrow in the 1880s and 1890s, “due to consecutive depressions and low cotton prices”. Thus, parts of the Singer Tract were relatively young second growth, and this included one of the ivorybill home ranges and one that Tanner deemed to be “best” – Mack’s Bayou.
The nature of the habitat in the Mack’s Bayou area is immediately apparent from the 1938 aerial photos, which suggest forest conditions that are present in many parts of Louisiana today. Nevertheless, Ivory-billed Woodpeckers nested there in 1934 and 1935, at minimum, and did so successfully at least once. This fact alone refutes the idea that Ivory-billed Woodpeckers are old growth dependent. Heather informs me that there was an abundance of dead and dying trees on the eastern side of the Mack’s Bayou range, due to a fire caused by logging activities. In any event, the home range Tanner delineated in this primarily second growth area is no larger than the home range he delineated around John’s Bayou, which had more mature forest. In fact, the area he designated as “best” for ivorybills around Mack’s Bayou was slightly smaller than its older equivalent near John’s Bayou.
Tanner knew that a significant portion of the Mack’s Bayou home range was not old growth, since his 1941 map shows “old fields” in the heart of it. He seems to have been unaware of the resurgence of cotton growing during the 1870s and 1880s, so he may have overestimated the age of the forest on that basis. I can’t help but wonder if he glossed over the conditions in the Mack’s Bayou range in part for the sake of protecting the Singer Tract and (as Heather suggested) in part based on what he deemed to be best for the birds from a conservation standpoint, an approach that later ossified into a categorical set of beliefs about old-growth dependence.
As I and others have been arguing for years, extensive forest cover, sufficient dead and dying wood, and enough large trees for roosting and nesting are probably the main requirements, even if old growth or near-old growth conditions are optimal.
I plan to return to the search area in late March and have another post or two in mind in the interim.