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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

 

 

 


Old Singer Tract Images Compared with Two More Recent Ones (from Elsewhere)

1967 slides taken by Neal Wright of a putative Ivory-billed Woodpecker in Texas are viewable on Vireo (search Ivory-billed Woodpecker), but high resolution scans have not been widely circulated as far as I know. These images were not made public until after the the Arkansas “rediscovery”, more than three decades after they were obtained. Wright’s story is mentioned in Jackson (2004) “Reynard saw the photo and said that it was fuzzy but definitely of a Campephilus woodpecker.” It’s clear from the context that Jackson had not seen the images at the time of writing.

When I first encountered the Wright slides, I was skeptical, but after seeing some lesser-known Singer Tract photographs as well as other images of Campephilus woodpeckers in cavities, my opinion started to shift. After finding additional ivorybill photographs in the Cornell archives and in Tanner’s dissertation, I thought it would be worth posting some of those images along with one of Wright’s slides for the sake of comparison.

Of course, it’s up to readers to draw their own conclusions, but I think a few things are worthy of note. First, the Wright slides were taken long before the internet, at a time when the only readily available image of an ivorybill in a nest cavity was Tanner’s Plate 1, which is quite similar to Fig. 43b (below). The posture of Wright’s bird is much closer to the ones shown in the then virtually unknown and/or unpublished images, especially those from the 1938 nest. The placement of the cavity is also strikingly similar, just below a major fork. It seems highly unlikely that Wright would have been aware of obscure Singer Tract photographs.

While the image quality is too poor to be certain, there appears to be excavation similar to work found on some Singer Tract nest and roost trees to the right of the nest cavity in Wright’s slide. Again, this is a fine detail that would likely have been unknown to Wright and that would have been difficult to fabricate.

These are very poor quality images; the malar stripe seems a little too extensive, although this could easily be a function of angle and lighting. As with the Fielding Lewis photographs, which were taken several years later, I have to wonder why anyone intent on committing a hoax wouldn’t do a better job. And in the case of the Wright pictures, it would make more sense if the template for such a hoax would have been Plate 1 in Tanner, rather than photos that were unknown to all but a handful of people, most of them at a northeastern university.

Finally, I think the fact that the images were turned over to an ornithologist (George Reynard, scroll down for his obituary) but were kept confidential for so long also tends to support the idea that they’re authentic. Neal Wright may have had an agenda – a desire to protect the area where he took the picture – but the images were not used to serve that purpose.

Edited to add: This fascinating article on a recent, non-ivorybill related hoax suggests that it’s not uncommon for hoaxes to be paradoxically uneven in quality, and that hoaxers’ motives can be murky and bizarre. Nonetheless, I think that other factors point to authenticity for both the Wright and Lewis photos.

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© N. Wright/VIREO USA – Nest with adult protruding, slide mount dated 5/70 (apparently the duplication date). Poorly defined bird is apparently peering out of a cavity in the upper left of the trunk, below the fork.

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Ivorybills at Nest, John’s Bayou 1938, female’s head protruding from cavity

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Ivorybills at Nest, John’s Bayou, 1935, male’s head protruding from cavity

 

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Images from the Singer Tract and James T. Tanner’s Dissertation Courtesy of Courtesy of the Division of Rare and Manuscript Collections, Cornell University Library

 

Another item I found in Tanner’s dissertation merits comparison with one of Project Coyote’s camera trap photos, since the tree species involved are the same. Plate 7 in Tanner shows ivorybill feeding sign on honey locusts, but the reproduction in the monograph is very dark. The figure from the dissertation is much brighter, making it clearer what Tanner was attempting to show. I think the similarity to the work on our target tree, where I had a sighting a week prior to the capture, is striking.

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Courtesy of the Rare and Manuscript Division, Cornell University Libraries

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Trail cam photo with scaled tree in the foreground and suspected female Ivory-billed Woodpecker in red box, Nov. 2009

To enlarge the trail cam photo, click here.


Scaling Data 2012-2016

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

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

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

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

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

Sweet Gum (Liquidambar styracifula)

Sector 1:         46

Sector 2:         8

Sector 3:         51

                        105         (84.68%)        

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

Bitternut Hickory (Carya cordiformis)

Sector 1:            3

Sector 2:            4

Sector 3:            7

                           14         (11.29%)

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

Oak (Quercus) spp.

Sector 1:         1

Sector 2:         4

Sector 3:         0

                         5         (4.03%)

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

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

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

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

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

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

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

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

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

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

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Digging Deeper into Tanner, Part 3 of 3 – Prey Species

Part 1 is here. Part 2 is here.

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.

  1. 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.
  2. 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.
  3. 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.
  4. 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.
  5. 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.


More on Scaling and Squirrels, Part 1

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

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

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

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

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

    Old scaling on hickory, 2015

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

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

    Top of scaled hickory.

    IMGP0376

    Older scaling on dead top with exit tunnels.

     

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

    Work now suspected to be squirrel on downed sweet gum.

    IMGP0936

    Suspected Pileated Woodpecker work on same downed sweet gum

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

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

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

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

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

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

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


Trip Report: April 22-26, 2015

This was a difficult trip on multiple levels. Weather and road conditions prevented me from spending much time in our core search area, and a bad chest cold kept me out of the field almost entirely on the 26th. On that day, all I could manage was a morning, roadside stakeout of an intriguing cavity, in a pine snag a few miles from the core of the search area. (Frank will be posting a write up of that event and his perspective on it in the near future.) To our chagrin, the new game cam, which we had aimed at the spot where Frank had the sighting earlier this month, shut down about an hour after we left it. We suspect this was due to was some kind of card programming error on our part that Frank will try to address. That said, the image quality is far superior to our old cameras, and once we’ve worked out the bugs, we expect that the percentage of unidentifiable blobs will plummet.

Despite the challenges, the trip was still a productive one for a number of reasons. We were able to develop some strategies for reaching the more inaccessible areas when I return in June (provided water levels subside), and I was able to get some new insights into the feeding sign found on the last couple of trips and to make comparisons with other locations, even though I found no fresh work during my limited time in the core area.

On the 22nd, I drove to the trailhead; the access road was in poor condition due to the quantity of rain over the past month, and I nearly got stuck in a couple of spots. While a truck or 4-wheel drive vehicle would not have encountered any problems, I was mindful of the possibility of getting stranded in my small rental car, a very unappealing prospect. Heavy thunderstorms were predicted for the afternoon. I spent the morning in the area where Frank had his sighting and where there’s a concentration of scaling but did not see or hear anything suggestive, despite doing some playbacks and double knocks. What may be significant in future is that I found a large, live sweet gum limb that had blown down very recently. The base was embedded in the ground and the top was perhaps 20’ high. This presents us with an opportunity to monitor a potential feeding site for an extended period (once we’ve resolved the camera issues). At present, there are no signs of insect infestation in this blowdown, and we’re discussing the optimal time to begin the monitoring.

Big Limb

Biglimbbase

Cell phone access is spotty at best, so I was unable to monitor the local radar; shortly before noon, the skies darkened, and the air felt threatening. I decided it would be best to get out of the woods rather than risk getting stuck, retrieving the trail cam on my way out. As it happened, the rain didn’t start until much later in the day.

The forecast for the 23rd was even more ominous, with severe thunderstorms predicted for the area beginning late in the morning. Based on the forecast, I opted to visit some public land near our original search area for the first time since 2012. Some of the intriguing recordings from 2010 were obtained there, and I found some suggestive bark scaling in 2012.

This area has a great deal more standing water than where we’re currently focused, and the bugs were awful, gnats in particular. The diversity of the habitat makes it a great birding spot; it’s a fairly long walk into the mature hardwood areas, and I covered about eight miles round trip. The habitat is pretty impressive, and much of it is very inaccessible and unvisited (few people go off the ATV trails.) The forest is impressive –  very mature second growth. The soil type is not the same as in our current search area, so the understory composition and secondary tree species are somewhat different, but as in much of our search area, oaks and sweet gums predominate. Many of the sweet gums are in the 3’ DBH range, and oaks of between 4’-5’ DBH are not unusual.

5 foot DBH Oak

I did not see or hear anything suggestive, but I found several downed sweet gum limbs that appeared to be infested with the same larvae as the ones in our core search area (more on this below.) None of these limbs had been scaled.

infestation

Beetle galleries in small limb found near old search area. Identification is discussed below.

UnscaledLimb

Infested, unscaled sweet gum limb from near the old search area.

Bigunscaled

Base of large, unscaled infested sweet gum limb from near the old search area

I got back to my car shortly before noon, anticipating bad weather and headed back toward Frank’s. Once again, the forecasts were less than reliable. I stopped for lunch, and a squall blew through the area, but the skies brightened. I went to Frank’s, checked the radar, and decided to return to the most easily accessible part of our current search area. This is a location where there have been sightings, auditory encounters, and where we’ve found concentrations of scaling in the past but that does not seem to be very active at present. It is a couple of miles from the concentration in a straight line and considerably more distant if mature bottomland corridors are followed. I found a little higher branch work there in February of this year; we heard double knocks in late December 2014, and found this heavily scaled sweet gum in May of last year. I found the same signs of infestation on downed sweet gum limbs in this area but only minimal scaling from no more recently than last fall. This work could have been done before the branch fell.

OldScalingdowned

On the 24th, I decided that the best option would be to look for ways to get into the less accessible parts of our search area by walking an old logging road that traverses nearby uplands. The composition of the forest traversed by the old road is mostly hardwood, but it is nowhere near as impressive as the bottomland forest. In many places it is abutted by pine plantations, which play a major role in limiting access to the core area, since the younger plantations are virtually impenetrable. I covered about 5 miles round trip, and made several attempts to find ways into the bottomlands, both by going cross country and by following old logging roads. Only the last of these attempts succeeded, although I didn’t go far because the weather was getting ominous, and I’m not keen on exploring new and inaccessible territory unaccompanied. The near total absence of flagging tape in this area points to how few people go off trail here, and even those who do seldom go into the lower lying areas (I found a deer stand at the edge of an impenetrable pine plantation.) As in the other non-core areas, I found signs of insect infestation in sweet gum limbs but no scaling.

The next day (4/25) Frank joined me, and we took his truck to the main access point. We hiked in following a somewhat different cross country route that took us into a perviously unvisited part of the area. Despite a favorable forecast, we got caught in a thunderstorm that lasted for approximately half an hour. We managed to stay almost completely dry during the storm itself but got drenched as we moved through the woods in its aftermath. The understory is often quite dense and above head height, which tends to force one to follow the beaten track. Because we’d entered the bottom at a different location, we were forced to fight our way through this dense understory. With full leaf out, looking for feeding sign, let alone ivorybills, is far more difficult. The photo below was taken with my pocket point-and-shoot, on full automatic, through an opening; it should provide a sense of just how hard it is to see anything in much of the search area once leaves are out.

ViewfromthegroundMy cough grew worse as the day went on, and we left the woods at around 3 pm, without having seen or heard anything suggestive, other than some older scaling on a large limb that had fallen into the crotch of a tree within 30 yards of the spot where Frank had his sighting, likely during the same storm that brought down the live branch.

LimbinCrotch

Based on the appearance of the insect tunnels and frass found both in and outside of our core search area, I believe the sweet gum limbs and tops we’re finding are infested with ambrosia beetles (though not always exclusively). There are a number of different species, both domestic and invasive, that feed on sweet gums. While ambrosia beetles are tiny, the females tend to significant numbers of larvae within a chamber.

Close-up of 2

Close-up of 2″ diameter limb with suspected ambrosia beetle galleries that apparently broke off while being fed upon

Suspected ambrosia beetle galleries in trunk of smashed sweet gum. Same tree as above.

Suspected ambrosia beetle galleries in trunk of smashed sweet gum. Same tree as above.

This would make them an attractive food source for a large woodpecker, including an adult ivorybill (though not to feed to a nestling, since Campephilus woodpeckers do not regurgitate). Most ambrosia beetles require live or very freshly dead wood as a substrate for the fungus on which they actually feed.

The foregoing leads to a few observations and the beginnings of a hypothesis. First, we did not find any fresh scaling on this trip, and the work found on the last was recent but mostly not fresh, probably less so than what I found in February. We thus suspect that the bulk of the scaling was done during the time frame when ivorybills would be courting, nesting, and brooding (this may also be related to the beetle’s life cycle, since in some species adults are most active in March.) We also cannot help but reiterate that evidence of recent woodpecker bark scaling on ambrosia beetle infested wood is abundant – found on well over 90% of downed medium to large sweet gum limbs and on the two young recently dead trees – in a very concentrated area where we suspect ivorybills are present. Recent woodpecker sign is absent on ambrosia beetle infested limbs in several nearby locations with similar forest composition and woodpecker populations (in one of these, where indications of ivorybills have been noted in the past, there was a very limited amount of older work.)

This may shed light on Tanner’s observations regarding high branch scaling on recently dead or dying wood (high branches are not preferred by the larger Cerambycids). This is exactly the substrate required by ambrosia beetles, some species of which are associated with sweet gums. While the larval chambers are not immediately beneath the bark, they are shallow enough, especially on smaller limbs, to be accessed with a blow or two and don’t require extensive digging. There is of course no way to prove this is so (nor are we suggesting that ambrosia beetles might be the sole prey species), but it makes intuitive sense to us and seems to resolve some apparent contradictions between what’s known about prey species and the way Tanner interpreted what he observed.


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

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

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

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

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

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

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

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

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

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

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

SmashedSaplingLongShot SmashedSGSapling IMGP0564

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

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

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

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

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

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

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


Known Ivory-billed Woodpecker Prey

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

According to the Birds of North America species account:

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

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

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

H.Polita