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Cavities and Context

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

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

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

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

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

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

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How The Ivory-billed Woodpecker Might Have Survived

I have been corresponding with Christopher Carlisle, a Mississippi birder who has recently started searching for ivorybills in the Pascagoula watershed. These exchanges, along with a post on IBWO.net about the Choctawhatchee, led me to start thinking, in a somewhat more methodical fashion, about habitat conditions and how the ivorybill might have survived and to consider the significant differences between the old Project Coyote search area and the new one.

I suspect there may have been three behaviors, probably operating separately and together, that made survival possible and detection and documentation difficult. These behaviors are consistent with the historical record, which suggests the species was considerably more adaptable than the simplified reading of Tanner that treats “virgin” or old growth timber as essential. Tanner’s own views on this issue became considerably more dogmatic over time, but even his early surveys of possible habitat in the southeast were influenced by this belief, which I’d suggest was more cultural than scientific, since Tanner was a product of an era in which frontier mythology profoundly influenced American thinking. Tanner’s description of the Singer Tract and especially his ivorybills are reminiscent of Edward S. Curtis’s Native Americans, magnificent, worthy of honor, but ultimately doomed and incapable of adapting.

The reality about Native Americans was considerably more complex of course, and the same goes for the Singer Tract. It was by no means a vast tract of virgin forest in the 1930s; much of it had been under cultivation prior to the Civil War, less than a century prior to Tanner’s seasons there. In pre-Columbian times, the southeast had a significant indigenous population, with perhaps as many as 5.2 million people in the Mississippi Valley alone. Thus, much of what was deemed to be “virgin” forest in the 20th-century was quite likely agricultural land in the pre-Columbian era. As I see it, Tanner’s preconceptions about what constituted “suitable habitat” led him to be somewhat cavalier, even in the early days – dismissing areas based on very brief visits, most often due to lack of “virgin” forest. As a result of this prejudice, Tanner may have underestimated the IBWO population.

This is not to negate the argument that IBWOs are more specialized than PIWOs; their morphology clearly places them in a different ecological niche, and their considerably more limited historic range also points to a higher degree of specialization. The fact that IBWOs do not regurgitate may place limits on behavior and home range during breeding season. The specialization, however, has far more to do with foraging behavior than with habitat requirements.

The IBWO.net post suggested (and implied some direct knowledge) that Geoff Hill and the Auburn team focused too heavily on the main channel of the Choctawhatchee. A person calling himself “Ranger Mike” wrote:

“During the last expedition by Auburn here on the Choctawhatchee River Basin I noticed two things that in my amateur opinion could have been better-First every time I saw researchers, or others who hunted and fished the area saw them, they were far to close to the main river. I am well aware of how hard it is access the flood plain areas, but the birds will likely be closer to the banks in the floodplains where there are very large old growth long leaf interspersed with the large cypress and gum that has been missed by logging due to its inaccessibility. This transition zone will be good habitat, and in my very significant time in these in both work and hunting/fishing has produced some interesting sightings and sign, with nothing of interest in the more frequently traveled areas. Second, I don’t think much time was spent on East Island. Its a very remote and promising area, but I think it was avoided because it would have required traversing by foot instead of floating around in kayaks or canoes.”

While I have not verified this account with anyone on the Auburn team, the general observation makes sense and is consistent in some respects with what Tanner observed in the Singer Tract. Nesting habitat was primarily located along tributary streams, not the Tensas River itself.

Edited to add: I have never been to the Choctawhatchee, and so have no first-hand knowledge with which to assess Ranger Mike’s comment. My intention was not to criticize Dr. Hill or the search efforts but to highlight a possible survival scenario. Since posting, I’ve heard from a couple of people with more knowledge of the area; one emailer stated that East Island is “way overlooked”, so if anyone’s interested in revisiting the Choctawhatchee, that might be a place to start.

The two Project Coyote search areas are quite different in character and forest composition. The current search area is secluded, very mature and surrounded by a good deal of contiguous lower quality habitat. It is part of a major watershed but is somewhat distant from the main river system, in the floodplain of a tributary. The old search area was on a small parcel of private land, about 3/5 of a mile distant from a medium-sized WMA, with bean fields in between. There are a number of larger WMAs in the surrounding area. The habitat in this area is mostly if not all of lower quality than in the new area and is discontinuous. Frank Wiley described it as “pearls on a string”. Assuming that ivorybills are or were present in both areas, it seems likely that the differences in habitat require different behaviors, and this may in turn point to how the species managed to persist post-Singer Tract. The following may be the behaviors that made survival possible.

Survival Strategy 1. Seek seclusion in remnant stands of mature forest and areas that were selectively logged, with substantial tracts of contiguous lower quality habitat associated; core habitats provide sufficient food supply during breeding season, and surrounding areas, pine plantations, younger upland hardwood forests and the like, might provide additional food sources the rest of the year. Examples of this type of area may include the Choctawhatchee, possibly other Florida rivers, the Carolinas, and the Pearl.

Survival Strategy 2. Expand home range substantially to forage in degraded habitat, using forested corridors to move around whenever possible but traversing open fields when necessary. This would entail having roosts and possibly nest sites near field edges in some instances, as appeared to be the case in the old Project Coyote search area, near Patterson, LA , a few other Louisiana locations, and possibly Wattensaw WMA in Arkansas. This idea is in part inspired by the November ’48 report to Tanner from Gus Willett, Singer Tract warden, saying that he saw a pair of ivorybills at “North Lake #1” and that the “birds are moving over a much larger area than formerly.” This is the last letter to Tanner pertaining to the Singer Tract, and it points to the likelihood that the widely circulated story of Don Eckelberry’s encounter with the last female IBWO is just another facet of the mythology that surrounds the species.

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Suspected recent nest cavity found by Frank Wiley near the edge of a bean field, East-Central Louisiana, 2009.

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Black and white image of tree in which suspected nest cavity was found. Compare with the appearance of this nest tree from the Singer Tract.

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Close up of suspected roost cavity in a willow at the edge of a bean field. This cavity was in the tree where we obtained a Reconyx image of a possible ivorybill, discussed here.

Survival Strategy 3. The IBWO can function as a “disaster species”, as Dennis and others have argued, having a high degree of mobility when necessary. “Disaster” in this context could be a slow motion sort of disaster as in the Singer Tract, where sweet gums were undergoing a die-off, so this could include elements of either 1 or 2.

Strategy 1 would help explain some of the difficulty finding, relocating, and documenting the species, since these are remote and inaccessible locations and sightings would most often take place outside of core habitats. Strategy 2 might also help explain why detection is so difficult. These areas are sparsely populated, birds would only be in the open briefly, and would not stay in one place for long, except during nesting season. And as Frank Wiley pointed out, the main human activity during nesting season is turkey hunting, and David Kullivan notwithstanding, turkey hunters are unlikely to see ivorybills, in part because of where they’re focused and in part because their methods would be likely to be disruptive and cause any birds in the vicinity to flee.