In retrospect, I realize that I could have stated my hypothesis about historic range more explicitly in the Bits ‘n’ Pieces series, here, here, here, here, here, and here. My treatment of this subject draws on and expands upon Tanner, Jerome Jackson’s extensive review of the historical record, the work of Benjamin Leese, and Appendix E in the U.S. Fish and Wildlife Service’s Ivory-billed Woodpecker Recovery Plan, supplemented by my own research and review of the source material.
I got somewhat too focused on specimen records and even more so on habitat types. The version of the map I created for the series reflects that focus, by including barrier islands, for example. The subjects of range and habit are of course intertwined, but I’ll state the hypothesis with respect to range upfront and follow it with a more detailed discussion:
The Ivory-billed Woodpecker’s range was considerably more extensive and than is recognized by the general public and than has been represented in much of the literature, both popular and scientific. All published range maps of which I’m aware, including Hasbrouck’s (1891), Tanner’s (1942), Jackson’s revised and redrawn version of Tanner (2004), and online, poorly reflect the historic range, especially east of the Mississippi.
This has implications in terms of habitat requirements and adaptability as well.
I suggest that the northern limit of the ivorybill’s range was just above 40 degrees North and that the western limit was approximately 98 degrees West. There are no archaeological or other records from over 2000′, so I’d exclude higher elevations in the Appalachians and Ozarks. I think the previous maps are accurate to the extent that they show the range as extending farther west in the Red and Arkansas River basins than in the Missouri.
To express it somewhat differently, I think ivorybills could be found as far north as the lower Delaware River on the Eastern Seaboard and that they could be found in riparian corridors into the lower reaches of the Appalachians from there south.
In Florida, I think it’s conceivable that the range extended to the Upper Keys. In the southwest, I’d draw the line near Port Lavaca, Texas to west of Tulsa, Oklahoma. Except for an archaeological find in northeastern Nebraska that almost certainly involved trade items, the northernmost specimen record from west of the Mississippi is from Forest Park, MO (more on that below).
The story seems to have been somewhat different in the Ohio River watershed, where both archaeological evidence and sight records suggest that birds were present far upstream from the Mississippi confluence and along tributaries well north of the river itself.
I’ve created another map showing both the limits of my hypothesized range and selected reports from what could be considered the edges of that range. A screen cap is below. Click on this link for annotations. Although some of the records are pre-Columbian (the earliest estimated as dating to 0-200 CE/AD), I suspect this was the approximate range until the mid to late-18th century.
Thus my hypothesized range is considerably more extensive than the conventional one (shown immediately below). On the Eastern Seaboard, it extends much farther north and also farther inland. It is far greater within the Mississippi watershed, extending to north of Columbus, Ohio, and encompassing all but the higher elevations in the Appalachians (based on the archaeological site at 2000′ near Lebanon, VA), reaching farther north and west in Arkansas and Missouri.
It was also somewhat more extensive in Texas and Oklahoma, reaching farther into the plains and a little farther south than the maps suggest. Outside of coastal areas, the presence was probably limited to riparian corridors, with those in the western part of the range (at least) being narrow.
While what I’m suggesting may seem heretical to some, it’s well-supported by the archaeological record, accounts from early explorers and naturalists, and collection records or reports thereof, albeit to a lesser extent. I covered many of the records that led to my formulating this hypothesis in previous posts; I won’t recapitulate all of them here, but one passage is worth revisiting. Two notes on technical terminology: middens are most easily defined as “dumps for old domestic waste“, and tarsometatarsi are the lower leg bones found in birds (and some dinosuar fossils).
If our knowledge of the Ivory-billed Woodpecker were based on the archaeological record alone, we’d think of it as an upland species. Further, we might very well assume that it ranged from the hills of Georgia, to the Alleghenies in Virginia, to central Ohio and west-central Illinois.
The remains found in Native American middens were unlikely to have been trade goods; ivorybill parts seem to have been a valuable commodity for ceremonial use west of the Mississippi but not east of it, and in several cases, the remains found were tarsometatarsi, which would be consistent with use as food:
There is strong physical evidence of ritual value for woodpecker scalps and bills from the upper Midwest and Plains . . . Remains of the Ivory-billed Woodpecker can be found in sacred bundles, on pipe stems, on amulets, and with burials among the Native Americans of the region. The evidence comes from the western Great Lakes and the Plains; no evidence of a particular use of Ivory-billed Woodpeckers has yet been uncovered from the eastern area of the Great Lakes (Ohio, Indiana, and Michigan).
(Leese, 2006.) Leese also points out (in several of his publications) that there’s no evidence that ivorybill parts other than scalps and bills had any trade value.
In an unpublished 1989 update to his monograph (housed in the archives at Cornell), Tanner accepted additional reports, including archaeological finds from Scioto County, Ohio (15th or 16th-century) and Madison County, Illinois (Cahokia Mounds, approximately 15th-century), as well as a collection record from Forest Park, Missouri and an 18th century record from Lincoln County, Kentucky. Since that time, additional archaeological records from Georgia, Virginia, West Virginia, and Ohio have turned up.
Thus, the case for ivorybill presence both in the lower reaches of the Appalachians and well up the Ohio River (and its tributaries) is compelling, and any suggestion that items found in Native American middens might be trade goods is pure speculation with no evidence to support it.
In a paper titled, “Putative Records of the Ivory Billed Woodpecker in Pennsylvania and the Mid-Atlantic” (2016 Pennsylvania Birds, 20(2):71-72), Leese suggested that eastern Pennsylvania and Southern New Jersey might be the northern limit on the Atlantic Coast. I agree and might even go a step further and argue that the available evidence strongly supports that view. The discussion below relies heavily on material Leese discovered, though I disagree with Leese’s conclusion that a more extensive range and more varied habitats support Snyder’s argument that hunting was the “main cause of the species’ extinction”.
This idea that ivorybills ranged so far north on the East Coast will probably be the hardest for many to swallow. Bear in mind, however, that Audubon described the ivorybill as an accidental in Maryland. Audubon’s discussion of range is odd; he didn’t mention Florida, and there’s nothing to support the idea that the western part of the range extended to the foothills of the Rockies. But he would have been far better informed about the Eastern Seaboard.
In any event, his description dates to the 1820s, by which time the range was likely shrinking. As discussed previously in the series, I suspect that the extirpation of the beaver played a major role in the ivorybill’s decline outside of Florida. Beavers were probably extirpated in New Jersey by 1820 (Van Gelder 1984). It’s reasonable to infer a similar date for eastern Pennsylvania.
To expand on this beyond the previous posts in the series, Peter Kalm, a prominent European naturalist and student of Linnaeus, listed the ivorybill as present in the Delaware Valley and distinguished it from the Pileated, which he described as “a Black Woodpecker with a red head” and “frequent in the Pennsylvanian forests”.
It’s not clear whether Tanner was aware of Kalm’s 1749 record, which was described in The Auk in 1903. The author of that paper suggested that this record should be taken “cum grano salis,” primarily because there have been no other records from the state. Or have there?
While it is ambiguous, Leese discovered a letter from Alexander Wilson, written during the early years of his career, when he was living on William Bartram’s property near Philadelphia; it is strongly suggestive of ivorybill, describing a large and “most extraordinary Blackheaded Woodpecker”. This was at a time when Wilson seemed to be in the process of learning his birds, and he did not mention it in later correspondence, which leaves room for doubt.
While Wilson’s description is not very detailed, I find it suggestive. And as noted previously, I think the only basis for rejecting Kalm’s account (and he seems to have otherwise been meticulous) is what we think we know about the ivorybill, a knowledge base derived from observations dating to between 60 and 190 years later. While there’s no way to prove it, I think Kalm’s listing should be treated as credible; it would be if a more common species were involved. Leese mentioned a couple of additional 18th century reports from Pennsylvania (included on the map) but found them questionable.
I’m not aware of anyone else having made this observation, but I think it’s a very important one. In the 1740s, the ivorybill had not yet acquired the mystique that would accompany it from the mid-1800s to the present, a mystique that was popularized if not invented by Audubon. This lends greater credibility to earlier reports such as Kalm’s. I think the same principle supports Jefferson’s listing of the ivorybill as resident in Virginia (which may have been based on his own observations) a couple of decades after Kalm and a few decades before Audubon.
To return briefly to Wilson and another report from an unexpected location, Jackson (2004) references a specimen collected by Wilson from somewhere between Winchester, Virginia and Martinsburg in what is now West Virginia (presumably in the Potomac watershed). I have not located the primary source for this reference, which may be in the archives of the Philadelphia Academy of Natural Sciences, but here’s Jackson’s:
The Putnam County, WV find is also interesting, as it suggests a bird that may have been collected for trade rather than being acquired through it.
I want to touch briefly on two additional records, both involving specimens. The facts related to these records point to how even specimen evidence is not free from ambiguity. For one thing, specimen tags often reflect shipment rather than collection locations. In addition, labels could have been changed and replaced at any point in the chain of custody between hunter and museum.
The first specimen is housed at Cornell (and I have seen it myself). It was collected in 1898 from the “Florida keys”. In Appendix E of the Ivory-billed Woodpecker Recovery Plan, it is suggested that this might actually refer to one of the forested “keys” in the Everglades rather than to one of the offshore islands. However, given the ivorybill’s use of barrier islands on the Atlantic Coast and the 10,000 Islands in Florida, it does not seem farfetched that the specimen could have been collected somewhere in the Upper Keys proper.
From my current perspective, based on the Recovery Plan’s information about habitat on the southwest Florida coast, both possibilities seem plausible and neither is particularly surprising. However, neither location would ever have had many characteristics in common with stereotypical ivorybill habitat – vast, contiguous bottomland hardwood forests. (Although he sometimes seemed to embrace this stereotype later in life, Tanner recognized that ivorybills lived in varied habitats, as have others who have studied the subject in depth.)
The other specimen, labeled as being from Forest Park, Saint Louis, Missouri, escaped Tanner’s notice initially but was included in his 1989 update. It is housed at the Colorado Museum of Natural History in Denver and was collected in 1886. Matt Courtman pointed out that by 1886, Forest Park was hardly an isolated spot; it attracted “hundreds of thousands” of visitors a year,was located on the outskirts of a city with a population of 400,000, had been at least partially landscaped, and was accessible by streetcar.
So not only did this collection come from well north of what’s commonly accepted as the historic range; it may have come from a managed parkland on the outskirts of a major city, hardly stereotypical ivorybill habitat. The location and date are surprising, so it’s possible that the specimen was collected somewhere else (though not in a different region) and that Forest Park was the shipping location.
This may be so, but an 1886 collection from anywhere near Saint Louis is a paradigm-buster, regardless of the exact location, as this 1884 map suggests. Forest Park, to the southeast of Florisant and Ferguson, which are indicated by the red circle on the map, is not shown.
Tanner’s original map showed the ivorybill as never having ranged farther north than the Missouri bootheel (the southeastern corner of the state) and as having been extirpated from all but the southernmost tip of that region by 1880. The last specimen collected in Missouri dates to 1895, from just north of the bootheel “eight miles southwest of Morley.” (Widdman, 1908). Tanner seems to have been unaware of this record, which is mentioned in Jackson, who could not locate the specimen itself.
Tanner received at least one report (1937) from Dallas County, Missouri, which is northwest of Springfield, in the upper (southern) reaches of the Missouri River basin and well outside the generally accepted historic range. The source was a local Audubon Society officer, and the letter is archived at Cornell. There appears to have been no follow-up. According to the Recovery Plan, reports from this general area continued until 1949.
Though his map of the range ca. 1890 suggests a northernmost limit in Mississippi and Louisiana, Hasbrouck (citing Cooke, Bird Migration in the Mississippi Valley) mentioned 1884 records from near Kansas City and undated claims of former breeding near Fayette, along the river in central Missouri; Tanner considered these questionable or accidental. I agree that they’re somewhat questionable but not that they could have been accidental, since both purportedly involved breeding.
Reading Cooke reveals that both were second-hand accounts. The Kansas City report includes no details except that birds were observed “during the past few winters”, and “it probably still breeds in that vicinity”. For Fayette, the source was identified as a local farmer and egg collector by the name of Lientz, but the former breeding claim is devoid of any details, including the informant’s name.
Thus, the possibility of mistake or miscommunication exists in both instances, as in the seemingly credible report from eastern Nebraska discussed in Part 2; however, Jackson also references Harris’s Birds of the Kansas City Region (1919), which lists a “Judge Guinot” and others” for the Kansas City area records, in the “deep woods of the Missouri bottoms”. No date is given, but it seems possible if not likely that Guinot (1855-1935) was Cooke’s source
While I think the historic range probably extended as far as Kansas City, the case seems a little weaker to me than it does for the eastern seaboard and Ohio Valley – given the paucity or absence of archaeological evidence or early reports from the Missouri River watershed, a key route for explorers, traders, and early settlers. For example, Featherstonhaugh, who crossed the Missouri River basin near the confluence with the Mississippi in the 1830s, described the northern limit as being considerably farther south, in the Arkansas-White River watershed. But perhaps there’s more to uncover about the ivorybill’s history along the Missouri.
As with anything ivorybill related, it’s probably best to be comfortable with not knowing and even to revel in the uncertainty.
Regular readers are no doubt familiar with some of the images shown below. The “neck bird”, which was photographed in our old search area in August 2009, has been discussed in a number of posts. I think it likely shows a female Ivory-billed Woodpecker, something that became clearer once I satisfied myself that what appeared to be red in the crest (in the wrong place for either Pileated or ivorybill) was likely an artifact and that the crest appears to be all black, as shown in the enhanced image below. The original captures (the first taken a minute before the neck bird appears and the second showing the neck bird) are immediately below that for those who haven’t seen them.
Years after the capture and probably after the first post about this image in 2014, I noticed that an object suggestive of a light colored bill was visible in both frames, apparently protruding from the lower cavity in the snag to the right of center. While I have shared this information privately with a number of people and did a vague Facebook post about it a couple of years ago, I’ve hesitated to blog about it or discuss it in detail. That changed after I showed it to Jay and Erik before we parted company on my last trip to Louisiana. When Erik suggested that the object might be a vine or some other intervening vegetation, I decided to go back through my files. I discovered that Frank had sent me several additional captures from the same deployment. I examined these frames and found that the apparent bill was absent from all of them.
Below are details from frames 1095 and 1096 showing the apparent bill, which changes position slightly from one frame to the next. The time lapse interval between images was 1 minute. Again, the cavity in question is the lower one (below the fork) in the snag to the right of and behind the one on which the neckbird is seen in 1096. These snags are black willows (Salix nigra), and the neck bird snag (with the large cavity apparently being used by a squirrel) fell between November 2009 and January 2010. I’m also posting the close-ups in tiled mosaic format so they can be viewed side-by-side.
For this round of image processing, I used Let’s Enhance, which enabled me to retain a large format for cropped and zoomed versions.
Next are two details from images captured a few days later. The possible bill is nowhere to be seen. The same is true for the other captures from this deployment. Thus intervening vegetation and artifact can be ruled out.
To summarize, the following two photos show what appears to be a bill in the cavity:
2009-08-11 7:48 am (image 1095.jpg)
2009-08-11 7:49 am (image 1096.jpg – the neck bird photo)
The following photos show a cavity with no apparent bill:
2009-08-14 6:19 am
2009-08-14 6:20 am
2009-08-14 6:21 am
2009-08-14 4:06 pm
2009-08-14 4:07 pm
2009-08-15 6:20 am
If this is a bill, it appears to be large and light colored, consistent with Ivory-billed Woodpecker. Both Erik and I noticed that, in frame 1095, a topmost part of the white dorsal stripe also may be visible. When Jay first saw the photos, he was reminded of the Neal Wright photos from Texas. Some images from the Singer Tract also come to mind.
Thus, this apparent bill resembles those of known ivorybills in cavities – in size, shape, orientation, and contrast. It is present only in frames 1095 and 1096 (the latter of which shows another possible ivorybill); it changes position over the course of a minute, from one frame to the next. There is no way to be sure images 1095 and 1096 show an Ivory-billed Woodpecker in a roost hole, but these facts, especially taken together, suggest that they may.
When I look back at what transpired in the old search area between August 2009 and November 2010, when the adjoining parcel was logged, it’s extraordinary. I may revisit those events in a future post or two.
For now, I’ll close by tying this into the Bits and Pieces series. The old search area is not one that would be deemed suitable under most habitat models. The images above were captured in a stand of black willows at the edge of a bean field. The other trail cam capture, where I had a sighting, was also within perhaps 30 yards of that field. When I look back at my assessment of the habitat from the time, I think I somewhat naively overstated its quality; however, there was a good deal of dead and dying timber, and it was in close proximity to several much larger habitat patches. If we did indeed capture ivorybills with our trail cams, their presence in this area may point to how the species has been able to adapt to more fragmented habitats.
Thanks to Erik Hendrickson for his input on this post and his help in making it clearer.
If you’ve been following this series (Part 1, Part 2, Part 3, Part 4, Part 5) you know it has focused primarily on preconceptions about ivorybill range and habitat types and how the actual record paints a very different picture from what many of us think we know about the Ivory-billed Woodpecker. As I noted in the most recent installment, if our knowledge of the Ivory-billed Woodpecker were based on the archaeological record alone, we’d think of it as an upland species. Further, we might very well assume that it ranged from the hills of Georgia, to the Alleghenies in Virginia, to central Ohio and west-central Illinois.*
While it may border on heretical to say so, I think there’s a plausible argument that the ivorybill’s range prior to around 1800 extended as far north as the mid-Atlantic states (New Jersey and Pennsylvania on the Eastern Seaboard) and as far north as central Ohio west of the Appalachians. I’m inclined to think this is likely based on a number of accounts including: Peter Kalm (a student of Linnaeus who reported the species was present in New Jersey and Pennsylvania in the 18th-century), Jefferson (1780s) and Nuttall (1840s) who included Virginia in the range, and Gerard Hopkins a Quaker from Maryland traveling to Indiana to meet with the Miami and Potowatami Nations. Hopkins described a female ivorybill at Piqua, Ohio (north of Dayton, elevation 873′) in 1804 (Leese, 2010.)
In addition, there’s the specimen that Wilson reportedly collected near Winchester, Virginia ca. 1810 (Jackson) and the central Kentucky specimen reportedly collected in the 1780s (Jackson, accepted by Tanner in 1989). As I see it, the tendency to treat these records as suspect is based, at least in part, on post-Civil War or post-Audubon “knowledge” about the ivorybill and its habitat, rather than anything intrinsically implausible about the claims themselves.
At minimum, one of the Ohio archaeological finds dates to the 15th or 16th century, so there’s strong reason to think that the ivorybill’s range extended that far north at the time of contact. North American Native populations began to decline after Columbus’s arrival, and De Soto’s expedition, 1539-1542, led to the collapse of the Mississippian culture. (De Soto also introduced the hogs that plague the southern forests to this day.) As a consequence, countless acres of formerly agricultural lands throughout the eastern United States were reforested and remained so into the 18th and 19th centuries. There’s little reason to think that the ivorybill’s range would have contracted at a time when the total acreage of potential habitat was increasing.
I’m reminded that tree girdling may have been an important factor. The only counterargument to the foregoing suggestion about the increase in total acreage after De Soto is that Native American agricultural activity declined drastically during that period, so that while habitat acreage increased, habitat quality may not have. Tree girdling and intentional burning likely played an important role in creating good conditions for ivorybills and could conceivably have led to range expansion during the Mississippian period and again temporarily during the first couple of hundred years of European settlement.
Ivory-billed Woodpecker use of girdled trees was noted by several early observers – notably Audubon, Gosse, and Scott (in Florida, later). While researching this aspect, I came across an interesting account from 1840s Central Louisiana, apparently just south of Alexandria (the citizens of that city are described as “chiefly gamblers or cunning speculators, a nest of incarnate devils, who live by cheating the latest comers, and, whenever possible, each other.”) I’m not aware of this account having found its way into ivorybill literature:
From Echoes from the Backwoods; or, Scenes of Transatlantic Life, Captain R.G.A. Levinge (1849).
With this as background, I’d like to propose an alternative explanation (or more accurately an alternative group of explanations) for the ivorybil’s decline. If you think, as I do, that the ivorybill has persisted, this may help explain how the species survived and may even provide some hope for its future, even in this era of mass, anthropogenic extinction.
When it comes to the decline and possible extinction, there has been a tendency to look for one or two causes. The IUCN Species Account gives the following reasons:
Logging and clearance for agriculture are responsible for the dramatic decline in numbers and range. These factors are likely to threaten any remaining population. Hunting has also been implicated in the rapid population decline, and it has been proposed that this was the primary cause of its decline, with habitat destruction playing a secondary role, but this theory is contentious (Snyder 2007, Hill 2008, M. Lammertink in litt. 2012).
Tanner emphasized the importance of logging during the post-Civil War era, although several of his data points seem to suggest that ivorybills were disappearing prior to the most active logging dates. He also stated that the ivorybill’s disappearance “coincided at least roughly with a time of active or rapidly increasing logging.” Elsewhere in the monograph, he focused on food supply, and I suspect that this, rather than logging per se was a more important factor in the ivorybill’s decline.
That’s not to say logging was unimportant; it clearly played a major role. To expand briefly on the point Bill Pulliam raised: by the late 19th century, the more adaptable Pileated Woodpecker, had been extirpated in many parts of its range, and many expected it to ‘go the way of the ivorybill’. That didn’t happen, and PIWOs returned to or became more common in many areas (my own included) as farming gave way to suburban development and forested acreage increased as a result. I’d suggest that for the ivorybill, habitat degradation, rather than habitat loss, was what initiated the decline, with extensive logging and then hunting accelerating an already existing trend.
That is to say, a number of additional anthropogenic factors likely played a role in the ivorybill’s decline and dwindling range, especially outside of Florida, where hunting and collecting likely had much greater impacts than elsewhere. Hasbrouck, writing in the 1890s, contrasted the lack of collecting in Louisiana, Arkansas, Missouri, and Tennessee with what was transpiring in Florida at the time. And it’s important to remember that Florida, which retained ‘frontier’ characteristics far longer than other parts of the eastern United States, was ground zero for the killing and collecting of birds – for commercial and ostensibly ornithological purposes. Ivorybills appear to have been more common in Florida than elsewhere by the second half of the 19th century, but it also seems probable that they were far more heavily persecuted there than anywhere else.
I’m hypothesizing that the shrinking distribution was correlated with settlement patterns in the northeastern part of that range and that by the middle of the 19th-century, east of the Mississippi, it had dwindled to the now familiar outlines, such as those shown on the IUCN range map.
The situation west of the Mississippi is somewhat more ambiguous. A specimen was collected at Forest Park, Missouri (near Saint Louis) in 1886, and there are records from west of the map in Texas dating to the early 20th century. Nevertheless, the general trend toward a shrinking range, which was frequently described in the 19th century literature, is clear.
European settlement brought about numerous changes in the land even before wholesale clearing of forests began.
As mentioned briefly in the discussion of tree girdling, Native Americans used fire for agricultural and wildlife management purposes, something that was likely beneficial for ivorybills. As Native Americans were exterminated, pushed out of their original homelands, or confined to small reservations, and as European settlers tried to control or eliminate fires, a significant factor contributing to tree mortality was likely reduced, dramatically.
Fulton’s invention of a commercially viable steamboat in 1807 revolutionized commerce, drastically accelerating the clearing of log jams from many watersheds in eastern North America. It’s fair to say that “widespread removal of instream wood for steamboat routes, timber rafts, and flood control was equally significant in decreasing floodplain sedimentation and river complexity, and in causing a fundamental, extensive, and intensive change in forested river corridors throughout the United States.” (Wohl, 2014.) As with changes in fire regimes, this clearing of log jams likely led to a decline in the number of stressed and dying trees along the riparian corridors that seem to have been so important for the ivorybill.
Perhaps equally if not more important in my view is the extirpation of the beaver. It is almost impossible to overstate the role of the beaver in shaping ecosystems throughout North America, a subject that’s addressed in engaging detail in Frances Backhouse’s Once They Were Hats. Beavers help create conditions that are good for woodpeckers by stressing and killing trees, through foraging and by changing hydrology. I’ve never tried to quantify it, but many, perhaps most, medium to large sized sweet gums in our search area show signs of beaver damage, and many others have been killed or severely weakened by beaver-caused flooding.
While beavers are not native to peninsular Florida, the ivorybill’s dwindling range elsewhere roughly tracks their decline; with extirpation starting in the northeast, moving West, and then South. (Southern beaver pelts were less valuable.) By 1900, beavers had disappeared from most of the southeastern US, and in Tanner’s day, a very small population persisted in the Florida Parishes of eastern Louisiana. Reintroductions began in the 1950s, and beavers are now considered a pest animal in Louisiana. It’s worth pointing out that the introduced beaver population in Tierra del Fuego appears to be benefitting the native Magellanic Woodpecker (Soto et al. 2012).
The resurgence of the beaver throughout the southeastern US is almost certainly producing substantially improved habitat conditions in many places. While the old growth forests may be virtually gone, it’s not inconceivable that ivorybill food sources are considerably more abundant now than they were in Tanner’s day, and if the species survived, conditions may actually be more favorable than they were in the 1930s and ’40s. It’s also worth pointing out that the southeastern United States is one of the few places in the world where forest cover has increased substantially in the 21st century.
It should be clear to readers of this series that the Ivory-billed Woodpecker inhabited a larger range and was able to exist in more varied habitats than most publications on the species suggest. This has implications for searchers and for what is deemed to be suitable habitat. For example, the trail cam images from the old Project Coyote search area were obtained near the edge of a bean field, and the putative ivorybill roost holes were in willows (more on that in my next post). Since ivorybills in the western part of their range seem to have lived in willow and cottonwood dominated riparian corridors, fast growing, short-lived willows might have played an important role in the species’ survival in other areas too, although willow-dominated habitat would be dismissed as unsuitable under conventional standards of habitat appropriateness.
It seems to me that even a slightly higher degree of adaptability would increase both the chances of survival and the likelihood that surviving populations might be overlooked due to preconceptions about habitat “suitability” ; this was doubtless one of the factors that led officials to dismiss the landowner in our old search area. Now that beavers are again abundant in the southeast, habitat that might otherwise have been deemed “unsuitable” may now be able to support ivorybills, even if the forest itself is not very old. While I don’t envision a recovery along the lines of what’s happened to the Pileated since my youth (when seeing my first one was a thrill as much for its scarcity as its beauty), I think it’s possible that ivorybill numbers have been increasing gradually and modestly over the past few decades. There was, of course, fairly intensive searching from around 2000-2010 (though it’s mostly over now), but it may be that the more numerous sightings from this period and afterwards are due to more than just the increased effort.
*The remains found in Native American middens were unlikely to have been trade goods; ivorybill parts seem to have been a valuable commodity for ceremonial use west of the Mississippi but not east of it, and in several cases, the remains found were tarsometatarsi, which would be consistent with use as food:
There is strong physical evidence of ritual value for woodpecker scalps and bills from the upper Midwest and Plains . . . Remains of the Ivory-billed Woodpecker can be found in sacred bundles, on pipe stems, on amulets, and with burials among the Native Americans of the region. The evidence comes from the western Great Lakes and the Plains; no
evidence of a particular use of Ivory-billed Woodpeckers has yet been un-
covered from the eastern area of the Great Lakes (Ohio, Indiana, and Michigan).
(Leese, 2006.) Leese also points out (in several of his publications) that there’s no evidence that ivorybill parts other than scalps and bills had any trade value.
A number of these midden records were accepted by Tanner in his unpublished 1989 update.
Bottom line upfront: In pre-contact and early colonial times and into the 19th century, Ivory-billed Woodpeckers inhabited a more varied and expansive range than most people realize. The range probably reached from the southern tip of Florida to central Ohio, with the 40th parallel as the approximate northern limit, westward to St. Louis and perhaps along the Missouri River. As discussed in the previous post, the western limit of the range appears to have been somewhere around the 96 or 97th Meridian, in the southwest, and probably somewhat farther east at the northwestern edge, if unproven historic reports from the Kansas City area are valid. Outside of coastal areas, distribution appears to have followed riparian corridors to its outer limits, and there are no records from elevations of over ~1000′.
This is a new avenue of exploration for me, and I’m not personally familiar with many of the areas involved. I need to do additional research on areas within Tanner’s range map, along the coasts and in Florida, to be sure my characterizations are accurate. I’m leaving some of these locations on the master map for now (but removing them from the graphic below which includes extralimital and edge of range records). The master map is thus subject to change, so view it with the caveat that the notations may be incomplete or inaccurate. This post will address locations that are outside the confines of Tanner’s 1942 range map, although he accepted some of these records in 1989.
As in the previous post, my analysis relies on records accompanied by reported physical evidence (even if that evidence has been lost) and to Native American sites where remains found are deemed unlikely to have been trade items. I relied on the US Fish and Wildlife Service’s Recovery Plan, Appendix E, Tanner, Jackson, and a few additional sources.
Before undertaking a whirlwind tour of the locations involved, I thought I should return to the mythology discussed in the previous post. I chose my words poorly in describing that mythology: “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).”
In fairness to Tanner, he didn’t characterize cypress as being abundant in the Tract. (It was not.) And his overall view was that cypress-tupelo swamps were not good ivorybill habitat. Audubon, with his romantic, indeed gothic, language is the father of the cypress myth.
I wish, kind reader, it were in my power to present to your mind’s eye the favourite resort of the Ivory-billed Woodpecker. Would that I could describe the extent of those deep morasses, overshadowed by millions of gigantic dark cypresses, spreading their sturdy moss-covered branches, as if to admonish intruding man to pause and reflect on the many difficulties which he must encounter, should he persist in venturing farther into their almost inaccessible recesses, extending for miles before him, where he should be interrupted by huge projecting branches, here and there the massy trunk of a fallen and decaying tree, and thousands of creeping and twining plants of numberless species! Would that I could represent to you the dangerous nature of the ground, its oozing, spongy, and miry disposition, although covered with a beautiful but treacherous carpeting, composed of the richest mosses, flags, and water-lilies, no sooner receiving the pressure of the foot than it yields and endangers the very life of the adventurer, whilst here and there, as he approaches an opening, that proves merely a lake of black muddy water, his ear is assailed by the dismal croaking of innumerable frogs, the hissing of serpents, or the bellowing of alligators! Would that I could give you an idea of the sultry pestiferous atmosphere that nearly suffocates the intruder during the meridian heat of our dogdays, in those gloomy and horrible swamps! But the attempt to picture these scenes would be vain. Nothing short of ocular demonstration can impress any adequate idea of them.
Hasbrouck (1891) perpetuated the emphasis on cypress and very low-lying locations:
Hasbrouck’s explanation of the Missouri extralimital records is odd. The locations given are well outside bald cypress range.
That aside, the myth discussed in the previous post is a composite. The emphasis on cypress originates with Audubon and Hasbrouck, and the emphasis on large tracts, old growth, oaks, sweetgums, and tree size is largely drawn from Tanner.
Here are the extralimital records:
Reedy River, South Carolina: Nest with eggs reportedly collected in 1896 and later lost. The location is in the Piedmont, south of Greenville, at an elevation of approximately 900′. The Reedy flows into the Salad, which flows into the Congaree. This report is listed in the Recovery Plan because it was accepted by Sprunt as “definitive” but is considered highly questionable.
Etowah Mounds, Georgia: Pre-contact site, elevation approximately 700′. Presumably not trade goods “but requires further discussion” per the Recovery Plan. The Etowah River is at the northern end of the Alabama River watershed.
Between Martinsburg, West Virginia and Winchester, Virginia: Specimen reportedly collected by Wilson ca. 1810. Elevation at Winchester is 725′ and at Martinsburg is 453′. This would appear to be in the Potomac watershed.
Moundsville, West Virginia: Two lower mandibles found in a pre-contact (early Common Era, 0-200) midden. Potentially trade goods. Elevation 696′. The location is on the Ohio River.
Philo, Ohio: Near the Muskingum River. Tarsometatarsus found in pre-contact midden, dates from ca. 1100-1500. Elevation 735′.
Sciotto County, Ohio: Same as above. Elevation of the site is 1050′, but the nearby Sciotto River is lower. The site is about 10 miles from the Ohio, and the elevation at the confluence is 533′.
Ross County, Ohio: Same as above. Also on the Sciotto River but farther upstream. Elevation 863′
Near Troy, Ohio: Near the Miami River, March 1804 sight record by Gerard Hopkins, a Quaker envoy to the Miami and Pottwatomi. The report includes a description, “. . . resembling the red headed woodcock of Maryland, except that its head is black and its bill ivory. ” (Leese 2001). Omitted from the map because it doesn’t involve a specimen, but included here because it adds weight to the archaeological records.
Franklin County, Indiana: Report of a specimen, 1869, now lost. Elevation at least 490′. Probably along the Whitewater River, an Ohio tributary. There are a number of early reports from Indiana, but no other reported specimens and no archaeological records. In light of Audubon’s collection at Henderson, KY (just across the Ohio River) as well as the Ohio records, it seems likely that ivorybills were present in parts of Indiana into the 19th century.
Henderson, Kentucky: Female specimen collected by Audubon in July 1810 and used as a model for his first painting of the species. Elevation 400′. This record does not appear in the Recovery Plan or Jackson, and it seems to have been overlooked by researchers. Audubon’s own notation describes the location as “Red Banks”, on the Ohio River at the northernmost limit of the cypress-tupelo association, well upstream from the confluence with the Mississippi. Article by R. Haven Wiley in Kentucky Warbler, May 1970.
Stanford, Kentucky: Pair reported, with one specimen collected by a Colonel Fleming, 1790. Record accepted by Tanner in 1989. Elevation 942′. The Dix River, which flows into the Kentucky and thence the Ohio, is nearby.
Cahokia Mounds, Illinois: East of the confluence of the Mississippi and the Missouri, 1500s or earlier, tarsometatarsus. Elevation 490′.
Forest Park, Missouri or Vicinity: West of the confluence of the Mississippi and Missouri. Specimen collected 1896 and in the collection of the Colorado Museum of Natural History. Elevation approximately 500′.
I find it interesting that Ohio is the state with the most pre-contact records involving likely food items – 3 out of a total of 4-6.
With regard to Missouri and the Missouri River watershed, Hasbrouck accepted reports from Fayette and Kansas City, and given the overall picture, this does not seem implausible. In addition, there were persistent reports from the vicinity of Lake of the Ozarks, in the Missouri River watershed, until the end of the 1940s; Tanner received information about Missouri reports from local Audubon society officers but apparently disregarded it. There’s no way to assess the validity of these old, anecdotal claims and no evidence to support them, but given this perspective on the historic range, they may be somewhat less far-fetched than it seems at first glance.
I’m heading for Louisiana soon. More after I return – a trip report and probably two additional installments.
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.
At an IBWO Recovery Team meeting during 2007, a report was shared by Dr. Nathan Schiff and his colleagues at the USDA Forest Service’s Southern Hardwoods Laboratory that more formally described many of the paradoxes that have been discussed in this series of posts. It provides more information on what is known today about the ecology of the wood boring species documented as having been fed upon by Ivory-billed Woodpeckers. Schiff and his colleagues point out that the larvae Tanner collected from a John’s Bayou nest cavity and those described from stomach contents don’t prefer sweetgums, don’t live in high branches, and spend the bulk of their lives in the heartwood, often in the lower parts of trees.
While it’s not mentioned in the Schiff et al. paper, Mallodon dasytomus or what Tanner called Stenodontes (by far the largest single food source in his sample of remains from the nest cavity described above) is commonly known as the “hardwood stump borer”, and Neandra brunnea, a close relative of another known prey species, Parandra (or Hesperandra polita), is called the “pole borer”. These beetles have a life cycle of 3-4 years.
The authors point to direct evidence that of the six species of insect identified in Tanner’s monograph, none would use wood consistent with the high branch/sweet gum focused foraging model. In addition to Mallodon, and P. polita, these species are: Neoclytus caprea (banded ash borer), Dynastes tityus (Eastern Hercules beetle), Alaus ocualtus (eyed click beetle) or a close relative, and an unidentified Scolytid or bark beetle (not found by Tanner.) We have found both P. polita and A. oculatus adults on suspected feeding trees.
Scolytids are tiny. Neoclytus begins its one year life cycle in early spring; the larvae start feeding under the bark and then burrow into the sapwood, where they pupate and spend the winter before emerging as adults. The species prefers ash but may also occur in hickory, oak, and elm. It is found in downed logs, as well as standing trunks and limbs of stressed to dead trees. Dynastes tityus or Hercules beetle larvae live and feed in the “rotting heartwood of logs and stumps.” Alaus larvae are predatory on Cerambycid larvae and live in decaying stumps and logs; eggs are laid in the ground. In addition, the authors point out that at least some of the larvae Tanner found under bark on higher branches (p. 42) require wood that’s in an advanced state of decay, when bark would be loose.
The insect larvae identified for Tanner (Mallodon, Alaus, Neoclytus, and Dynastes) came from remains he found in nest debris. I think this suggests he may have failed to observe or have unduly downplayed one or more foraging behaviors related to obtaining food for nestlings – excavation of very decayed stumps and logs and extensive scaling on boles in particular – since these are lower dwelling species and two of the four inhabit wood that’s in an advanced state of decay. My anonymous correspondent disagrees with my reading of Tanner but makes a very interesting observation that sheds important new light on the data.
Schiff et al. point to an apparent contradiction; none of the food items found in the nest reflect the preference for high branch foraging that Tanner described. The importance of large Cerambycid larvae (especially Mallodon or Stenodontes dasytomus) in the feeding of young ivorybills at Singer Tract remains unclear. Tanner’s observations indicate that most foraging events involved a substrate (recently dead or dying branches) that doesn’t support these large wood-boring larvae. Tanner reported that Mallodon and other large larvae that were “frequently carried in the bills of adult Ivory-bills”. Some fragments of larvae that were found in the remains of at least one nest cavity had to have come from boles or large, lower branches and were likely to have been obtained from longer dead wood, at least in some cases.
It appears that attention today on the Cerambycid larvae “paradox” may have been founded in part on a misreading of Tanner. The Cerambycid and other large larvae found in the three stomachs reported above were from birds collected in August and November, well after the breeding season. Because Mallodon is so large, was the most abundant prey species found in the nest, was identified in one of the stomachs, and was quite likely the species found by Wilson and others, many have interpreted Tanner as saying that it was the primary prey species. It was undoubtedly an important and calorically rich one, but Tanner’s observations suggest that smaller larvae played a more important role, at least in the case of the John’s Bayou birds.
While he frequently saw adult ivorybills carrying large larvae in their beaks, he observed the birds carrying large numbers of “small” larvae even more frequently. He noted the apparent conflict between his observations and what was found in the nest debris and resolved it by hypothesizing that the smaller insect parts probably remained “imbedded in the feces” and were “removed when the adults cleaned the nest” (pp.40-41). Thus, while there is direct evidence that large wood borer larvae were part of the ivorybill prey base, Tanner’s overall interpretation was that smaller larvae were more important during the breeding season. (pp. 40-41, 51-52).
Tanner admitted that he did not fully understand why ivorybills did not forage more frequently on substrates supporting larger larvae when they were fully capable of doing so. He speculated that the smaller larval woodborers when abundant “are very abundant” for short periods of time, beneath the bark of recently dead or dying wood. In sum, Tanner concluded “The Ivory-bill’s insect food supply is smaller, more variable and erratic, and more unevenly distributed than that of the Pileated.”
To reiterate, Tanner stated specifically that while most of his observations involved scaling of high branches, presumably for smaller larvae, he also observed scaling on boles where larger larvae dwell. Tanner suggested that foraging on trunks took place when trees were “longer dead” and that ivorybills “move downward with the progression of shallow borers” (p. 41) The balance of his observations (27.8%, a not inconsequential number) involved digging for “deeper-living” larvae that spend most of their lives in the heartwood, between the ground and the large lower branches.
In their unpublished manuscript, Schiff et al. concluded that: the “. . . Ivory-billed Woodpecker is an opportunistic feeder with catholic tastes that eats beetle larvae where it can find them and that it probably digs for them with its powerful bill. ” This conclusion was intended to challenge Tanner’s finding that food supply imposed a limitation on ivorybill nesting success, but a close reading of Tanner suggests this conclusion actually is not at variance. It is clear now that Ivory-billed Woodpeckers could and did forage by digging into older boles like Pileateds, though less frequently. It is also clear that they scaled bark at all levels. The new revelation for many of those interested in ivorybills today is that this species showed a preference for stripping bark in pursuit of large numbers of smaller larvae in recently dead and dying trees and carried these smaller larvae en masse to their young.
I think the foregoing observations make a lot of sense. As discussed, perhaps ad nauseaum, I have some doubts about what I take to be Tanner’s conclusions about decay class. I have questions about the way he characterized his data on tree size and wish he had quantified scaling on branches relative to scaling on boles. I also question his suggestion that scaling on boles was done on longer dead trees (and the rationale that trees die from the top down) because it doesn’t account for the fact that the larger bole dwelling Cerambycids can attack injured live trees and hasten or bring about mortality, as was the case with the suspected feeding tree shown on the homepage. I have little doubt about his observations at the nest. For one thing, the number of is considerably greater, 159 as opposed to 101.
There is some reason to think Tanner was at least partly correct with respect to variability and scarcity of this food supply, especially in the higher branches. As noted in the previous post, Tanner found no Cerambycid larvae at all in a random sampling of cutover plots near Horseshoe Lake. The location of these surveys was likely between the Bayou Despair and Greenlea Bend home ranges and not far from where two young birds were seen in 1932. Ivorybills were disappearing from these two home ranges, as well as from the nearby Little Bear Lake range, and the three ranges only produced one successful nest (Greenlea Bend, 1937) between 1934 and 1939. (p. 39), and it seems possible that scarcity of this food supply was a contributing factor.
Tanner specifically looked for insect larvae “from several situations similar to places where ivorybills fed”. This was presumably not a random sample. While details about these “situations” were not provided, they included: under bark of dead sweet gum and willow oak limbs (presumably downed), under the bark of a Nuttall’s oak (condition and part of tree unspecified but presumably a downed limb or limbs based on the species found), and the trunk of a dead hackberry. As might be expected, he found Mallodon, P. brunnea, and A. oculatus in the hackberry bole.
He found Urographis (now Graphisurus) fasciatus and Leptostylus sp. in both species of oak and in the sweet gum. These are small Cerambycids (adults up to 15 mm). He found small Cerambycids, Aegomorphus decipiens (now modestus) under sweet gum bark and Xylotrechus colonus under the willow oak bark. In addition, he found Pyrochroidae (torch beetle) larvae, possibly Dendroides canadensis, in sweet gum and Nuttall’s oak and unidentified Elaterids and Buprestids in the Nuttall’s oak.
Questions remain. Some of these larvae, the Elaterids and Pyrochroids in particular, are found under loose bark in decayed wood, suggesting that at least some of the infestation took place after the limbs Tanner examined had fallen. Aegomorphus also feeds in “soft, decaying hardwoods.” Graphisurus fasciatus is a common species that prefers trunks and large branches. Xylotrechus colonus, prefers “recently killed trees” and is described as “one of the commonest eastern Cerambycids”. At the same time, Tanner’s very limited random sample suggested that high branches had considerably less available substrate and food than other tree parts. This may suggest that sporadic, localized outbreaks of larval infestation in high branches are crucial for breeding.
There are a couple of added twists to this story. To restate and expand on the foundation of my hypothesis about diagnostic feeding sign: Campephilus anatomy, and especially that of the northern triad (Imperial, Cuban ivorybill, and U.S. ivorybill), is highly specialized. Members of this genus are built to scale bark with greater speed and efficiency than any other woodpecker species, but they are also certainly capable of digging. When they dig, they may be powerful, but I suspect their morphology makes excavation a less efficient foraging strategy.
In contrast to Pileated Woodpeckers, which have evolved to make perpendicular blows, ivorybills have pamprodactylous feet (an evolutionary adaptation that rivals the opposable thumb in terms of how radically it differs from other picids), longer necks, longer, stiffer tails, and larger, broader bills. All these adaptations enable them to deliver strong lateral blows but probably impact their ability to excavate. This may explain why many of the foraging pits shown in the Pearson photograph and in Plate 11 are skewed and why ivorybill nest cavities are asymmetrical. It might also explain why ivorybills dig relatively infrequently during breeding season and instead undertake long daily circuits to strip bark and gather larvae, both large and small, for their young.
Ivory-billed Woodpeckers don’t eat ants or termites and don’t regurgitate. They must obtain live, and when possible large, beetle larvae or large quantities of smaller ones. It’s beyond dispute that they do this most often by scaling bark and finding these insects at or near the exposed wood. Based on the presence of Neoclytus in the nest, it’s reasonable to infer that some prey species are taken early in the life cycle, before they burrow into the heartwood, while others simply live under bark. In addition, several species (Mallodon and H. polita at least) may be exposed when bark is stripped from the bole and their larvae are digging exit tunnels but have not yet sealed their pupation chambers. This is the time when the larvae are largest and most nutritious. This is the substrate in which Tanner found the highest concentration of food, and ivorybills are uniquely adapted for exploiting this opportunity. I believe we have seen evidence of this behavior on some hickories, sweet gums, and oaks in our search area.
One or both of these foraging strategies may be keystones. Fluctuations in the availability of these particular food sources might have a significant impact on nesting success.
Whether or not I’m exactly right about all this, I think there are several important points that deserve to be reiterated.
- The Singer Tract ivorybills “usually” or frequently fed on high, freshly dead sweet gum and Nuttall oak branches; what they were feeding on remains unclear; however, there is no doubt about the importance of the prey collected (whatever it was) at the treetops for raising young. Specifically, on April 23, 1939, Tanner observed both adults feeding “Baby Bunting” from prey captured from the top of a dead pecan (hickory), and also the long flights these three, along with “Sonny Boy” (the previous year’s young, still with adults), made from one foraging tree to another. There is also no reason to doubt that prey from treetops made up a substantial part of what was fed to the young before fledging.
- Ivory-billed Woodpeckers in the Singer Tract could and did feed at all levels and on wood in all stages of decay, but during breeding season, at least, they took most advantage of more recently dead and dying trees.
- Despite the habitat and tree species preferences documented by Tanner during the 1930s, the last few ivorybills could and did feed in areas and on tree species that Tanner did not document as being heavily used during his study. This was mostly in the 1940s, after massive cutting was under way. Subsequent interpreters of Tanner have inferred that these tree species and areas were unimportant or unsuitable, and some of Tanner’s later statements may have abetted this misunderstanding. The takeaway is that ivorybills will feed on a variety of tree species, provided the trees are stressed and infested with wood boring larvae that can be quickly collected by scaling bark.
- Prey species were most heavily concentrated in what Tanner called “hard but partly punky” stumps. Though it’s not explicitly stated, this class is likely to include the boles and large lower branches of standing trees, including Cerambycid infested trees that have not yet succumbed.
- Despite popular perceptions, large trees are not a requirement. Notwithstanding our disagreement about how to characterize foraging frequencies and size class explored at length in the first post in this series, my collaborator and I agree that insect abundance, not tree size per se, is the most significant factor. The foraging behavior documented by Allen and Kellogg and the nesting successes in mostly second growth but fire damaged forest (Mack’s Bayou) earlier in the 1930s support this interpretation.
I hope this series of posts will prove useful to other searches and that it provides greater clarity about ivorybill foraging behavior.
Addendum, March 26: A biologist wrote to point out that I may have been regurgitating conventional wisdom on the subject of Campephilus regurgitation. Some of the literature states that they do feed their young in this manner, and there is language in Tanner to suggest this may be so for ivorybills (pp. 74-75). “Often it seemed to be jerking as if working food from the back of its mouth.” As I read Tanner, the number of larvae that may have been regurgitated seems small, a single grub in at least one instance. The passage in Allen and Kellogg (mentioned in the comments) involved termites, and it is highly speculative. And I recall reading that ivorybills were hunted for food specifically because they didn’t taste of formic acid, unlike pileateds.
At present, I don’t think this information calls for a major revision of the hypotheses presented here, but I plan to do some additional research and may have more to say on these subjects in future. I’ll be completing a week in the field today and expect to post a trip report before too long. As a preview, I’ve found an unprecedented quantity of recent high branch and upper bole scaling this week, all of it on sweet gums.