Some Thoughts on The Ivorybill’s Decline

Jamie Hill, who has worked with the Cornell and Auburn teams, recently posted a Facebook link to a very interesting article from the September 2014 issue of Smithsonian. Ivory-billed Woodpecker aside, the piece is well worth reading, but for the purposes of this blog, the article got me thinking about reasons for the ivorybill’s decline and the possible role of the longleaf pine. These ideas are not entirely new or original with me; Lester Short went even further, suggesting that pine might have been the ivorybill’s primary habitat; Jerome Jackson devoted several pages of In Search of the Ivory-billed Woodpecker to pines, and Fangsheath of the ivorybill researchers forum has hinted at this too.

I was struck by just how congruent the historic range of the ivorybill is with the range of the longleaf pine (Pinus pilastrus). The overlap is not exact, and the pre-Columbian range of the ivorybill extended as far north as Ohio. Nonetheless, conditions in the Singer Tract were objectively quite different from what they were in many other parts of the historic range.

A recent blog post on the Tallahassee Democrat site reiterates the conventional wisdom about the species and the reasons for its decline. Author Budd Titlow writes: “Before the Civil War, when much of the southeastern U.S. was covered with vast tracts of primeval hardwood swampland, ivory-billed woodpeckers ranged from North Carolina south to Florida, west to Arkansas and Texas, and north into Oklahoma and Missouri. Then, after the Civil War, extensive logging of these old-growth swamps wiped out most of the ivory-billed’s habitat in one fell swoop.”

While there’s some truth to this history, it’s also a stereotype that’s based in large part on an imperfect reading of Tanner’s monograph and even more on Tanner’s dedication to protecting the Tract as the last remaining extensive old-growth stand in the southeast (although the Tract contained considerably less old growth than Tanner believed). Tanner’s efforts were admirable; the loss of countless acres of magnificent old-growth swamp forest was devastating environmentally and is unquestionably something to be mourned, but it seems unlikely that the destruction of these forests was the primary cause for the ivorybill’s decline.

The species was known to be disappearing by 1890 or even earlier, and Chester Reed’s 1906 Bird Guide to Land Birds East of the Rockies stated that the birds were restricted to isolated parts of Florida and possibly to “Indian Country” (Oklahoma). In The Travails of Two Woodpeckers, Noel Snyder, who attributes the decline primarily to hunting, points out that intensive logging of bottomland hardwoods began between 1890 and 1900. Logging of pine forests began considerably earlier, and these forests were severely fragmented, even before the Civil War. Snyder reads the early record (I think selectively) as indicating that ivorybills strongly preferred bottomland hardwoods and seldom used pines, in contrast to the Cuban ivorybill and the Imperial.

Jackson takes a different view, citing multiple references to the use of pines for feeding and nesting. Where Snyder reads Alexander Wilson’s early account as reflecting a preference for “swamps and bottomlands”, Jackson reads him as describing the preferred Carolina habitat as “a mosaic of baldcypress swamp and pine uplands, similar to the habitat in Florida”. Jackson goes on to suggest that, “It appears . . . that ivory-billed woodpeckers will inhabit both hardwood forests of river bottoms and pine forests of higher elevations, particularly old growth forests supporting healthy populations of beetles. They seemed to do best at the interface of these forest types, taking advantage of the resources of each.” (Emphasis added).

This meshes well with what Allen and Kellogg observed in Florida in 1924; the birds nested and roosted in cypress and were observed and photographed foraging in open pine forest. The Lambs’ limited observations in Cuba suggest something similar, a preference for roosting in pines but an equal division between pines and hardwoods for foraging.

Thus, it seems possible that the Singer Tract was actually suboptimal habitat for the ivorybill, since it contained no pine and little cypress. I’m also led to suspect that habitat fragmentation, rather than habitat loss may have been central to the decline of the ivorybill, with hunting as one of several other contributing factors. This fragmentation actually began well before the Civil War, but it accelerated with the post-war destruction of the longleaf pine forests, followed by the logging of the bottomlands. I’m personally convinced that the species beat the odds and survived, using one or both of the strategies discussed in this post. I wonder whether some of the modern search efforts have focused excessively on the bottomland hardwood model and not enough on areas where there’s an interface between forest types.

7 thoughts on “Some Thoughts on The Ivorybill’s Decline

  1. This makes sense, given the correlation you point out between the species’ historic range and that of the longleaf pine forest. It would bode well for the continued survival of the species, especially given the relatively short period of maturation for pine forests, as well as their extent. Unfortunately for searchers, this would necessarily multiply the size and scope of their efforts on a nearly impossible scale. The DeSoto National Forest alone encompasses over 800 square miles of mostly pine forest in south Mississippi, terrain which poses its own unique challenges to bipedal creatures. Careful consideration would have to be given to the areas merging mature upland pines and creek and river bottoms, the (I suppose) “slope forest” where as has been suggested the ivorybill could take advantage of the roosting and feeding benefits of both types of habitat. Those areas certainly do seem to offer the greatest variety of tree species; and magnolias, the berries of which (if I remember correctly) are a food source, are most often found there.

  2. If I was knocking my head against wood for food, I’d prefer softwood too!

  3. Hi Chris . . . It struck me during the night that one approach might be to look for areas that have mature bottomland forest (even just narrow corridors) and are within perhaps 3 miles of a Red-cockaded Woodpecker colony. I pulled the 3 miles out of thin air, but you get the idea . . .

  4. Ever since I started reading about IBWO:s I have thought about the fact that they seemed to often lay 3-5 eggs but only 1-2 young would hatch and often some eggs would be infertile. What if this was sign of IBWO:s suffering the effect of lost habitat already in the early 1900s? What if as you say the habitat then was not optimal and IBWO:s in optimal habitat would actually be able to have 5 fertile eggs and a good year even raise 5 young? What if the ivory-bills were suffering either effects of less optimal habitat and perhaps even inbreeding due to the discussed fragmentation and therefore had less fertility?

    The thing with inbreeding is that it can strengthen good genes as well as bad genes and the low fertility combined with less of their optimal food source(s) might have meant that the young that did survive was better suited for a new habitat than their parents. These birds live a long time and to replace themselves they would not really need to raise that many young to adulthood to keep the population alive so maybe this gradual change slowly changed the ivory-bill to be more adaptable. If the big catastrophe happened already when they lost the pineforests then perhaps the loss of other types of forest might not have been as significant.

    I am just an amateur so go easy on me if you think I am dead wrong but I have friends who have saved varieties of domestic chicken here in Sweden which were often kept without taking in any new animals for hundreds of years. These animals are often very hardy and strong because they have basically been bred beyond the point where inbreeding has a negative effect. The strong and hardy animals were the ones which would raised all or most of their young to adulthood while the weaker birds raised no or few young until the point where the animals were quite similar genetically but healthy. Such a population would be sensitive to fast changes in the environment but might be very good at surviving in their own niche. If the ivory bills that survived where those that were more adaptable though that might not be so problematic.

  5. I’ve have thought about some aspects of this previously and have now taken a quick look at some readily available literature. It appears that woodpeckers that rely on wood boring beetles lay smaller clutches generally than other species – this may be relevant to the success of the Pileated compared to the IBWO and is reflected in Tanner who reported that Pileated clutches averaged 3.6 eggs per set, while ivorybills averaged 2.9. My personal view is that ivorybills are/were considerably more adaptable than the simplistic reading of Tanner (old growth hardwood dependent) suggests. That said, there are severe limits on adaptability as it relates to breeding – relatively large trees are needed for nesting and roosting; beetle larvae are a crucial food source for nestlings; adults do not regurgitate when feeding young.

    I suspect that habitat fragmentation would increase the distance adults need to travel from the nest to obtain food, thus making young more vulnerable to predation. Tanner only found a minimal difference between PIWO and IBWO in young out of nest per brood 2.14 (for PIWO) versus 2.11 for IBWO , but his sample was very small.

    There’s just not very much to go on . . .

  6. Clearly the pileated is a much more adaptable species than the ivorybill is or was, I believe there really is no comparison between the two, because while they may not exactly be extremely abundant, pileateds can be found fairly commonly today even in suburban areas with sufficient tree cover. (I saw one a number of years back in the Coconut Grove area of Miami, fluttering about the branches of a live oak tree.) I don’t think the ivorybill was ever commonly found so close to, or within, urban areas.

  7. I’m not sure if or how I gave the impression that IBWOs are/were anywhere near as adaptable as PIWOs. That was certainly not my intention; the higher level of specialization is evident in their morphology, as is discussed in multiple posts. I’m just arguing against the misguided idea that this specialization is equivalent to dependence on old growth bottomland hardwood habitat. The record doesn’t support this notion; Tanner didn’t believe it when he wrote his monograph, though his later statements reinforced others’ misreading of his work. Pileateds have always had a more extensive range and have thrived in more varied habitats. That said, they have become far more common in many areas (such as New York City’s northern suburbs) since I first saw one in the 1970s, and if I remember correctly, the idea that they might vanish too was widely held earlier in the 20th century.

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