-- Commentary --

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The previous referenced paper concerns itself primarily with the question of with what probability should IBWOs have been detected by now (given the effort put forth) if they persisted in the White River or Bayou De View regions of Arkansas. And skeptics will actually find much to latch onto in the analysis done, as the authors acknowledge at one point: "...given this search effort, if more than a very few Ivory-billed Woodpeckers were present in the search area during the surveys, their presence should have been detected."

There does however remain the significant possibility of just 1-2 IBWOs inhabiting the areas surveyed and going undetected (and of course Cornell's initial claims for the Big Woods were simply for the presence of at least a single bird).

The authors note that for the searches to be even "moderately effective" the Ivory-bill would need to have a "large" home range (exceeding 5000 hectares -- to increase the chance of encounter with an observer), and then go on to say the following :

"Home-range size is unknown for Ivory-billed Woodpeckers. During his studies, Tanner (1942) followed birds and found that, during the nesting season, individuals often traveled >2.0 km from the nest, with one record of a bird traveling 4.0 km from its nest in the course of daily activities. Based on anecdotal information, winter ranges (when current Ivory-billed Woodpecker surveys are done) were much larger than nesting-season ranges (Tanner 1942). From this, if winter home ranges are equivalent to a circle with a 4.0 km radius, home range size would be 50 km2 (5000 ha), which would produce posterior probabilities of extinction slightly under 80% in both BDV [Bayou de View] and WR [White River]. From this analysis, we conclude that much greater search efforts will be required to obtain a level of 90% or greater for posterior probabilities of extinction."

I think the 'home range' argument is a bit tenuous (and could almost be argued in an opposite way), but not worth niggling over here.

and later, this:

"The search effort required to have a high degree of certainty that a species occurs (or does not occur) in an area becomes extremely large for populations of 10 or fewer individuals. Our analysis of the search effort for Ivory-billed Woodpeckers in the White River and Bayou de View, assuming a uniform distribution of birds if they are present, suggest that if birds were present the actual number of individuals was very low (N<2). With this assumption it is unlikely that birds were still present in the intensively searched area but not seen during surveys. However, below, we present distributions other than the uniform, which suggest higher probabilities that the Ivory-billed Woodpeckers may still persist in White River and Bayou de View."

and finally toward the end, this:

"The Ivory-billed Woodpecker surveys we considered included only ~12% of the forested habitat in the overall search area in Arkansas, so our analysis does not enable us to assess the likelihood that Ivory-billed Woodpeckers are extinct in the wider search area, much less across the currently presumably suitable habitat within the species’ historic range. Based on a statistical assessment using time series of historic sightings, Roberts (2006) argued that a declaration of extinction is premature for this species."

Just a couple of points I'll make about the study: As noted above, the paper's analysis ONLY covers work completed in Arkansas, and regardless of the outcome there, essentially argues for the need of similarly intense efforts carried out in other prospective areas of the Southeast before conclusions about IBWO persistence be drawn with any assurance. Also, this analysis operates on the assumption of no "valid detections" occurring during the period of study... an assumption that may be drawn for empirical reasons, but which may be totally false, as there were in fact both sightings claims and possible auditory encounters over that time period. Obviously, just 1 or 2 "valid detections" hugely alters the resultant statistics.

The take-home message here is what we've already known for a long time: that it is exceedingly difficult to demonstrate with great confidence the extinction of a species being repeatedly reported in vast habitat. Some folks, unfortunately, continue to think it easy.
The upside for conservation, should the Ivory-billed Woodpecker ever be conclusively documented, is massive --- the "charisma" of the species alone would send tremendous ripples through the conservation establishment, but beyond that, the vast habitat tracts to be saved would have impact on many other species as well... possibly more impact than carried by saving any other currently endangered North American bird. One ought not risk dismissing such an upside prematurely. As the authors note early in their article, "Rediscovery of “extinct” species occurs often enough to give one pause about making premature pronouncements." Indeed it does, indeed it does...


But enough academic rambling, now for your sheer viewing entertainment... some BennyHillified hummingbirds!
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