.comment-link {margin-left:.6em;}

IVORY-BILLS  LiVE???!  ...

=> THE blog devoted to news and commentary on the most iconic bird in American ornithology, the Ivory-billed Woodpecker (IBWO)... and... sometimes other schtuff.
-------------------------------------------------------------------------------------------------------------------



Google
 
Web ivorybills.blogspot.com

"....The truth is out there."

-- Dr. Jerome Jackson, 2002 (... & Agent Fox Mulder)

“There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy.”

-- Hamlet

"All truth passes through 3 stages: First it is ridiculed. Second, it is violently opposed. Third, it is accepted as self-evident."

-- Arthur Schopenhauer






Sunday, January 04, 2009

 

-- Commentary --


--------------------------------------------------------------------------------------------

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!
------------------------------------------------------------------------------------------

Comments:
The conclusions regarding the probabilities of having found IBs in Arkansas, based on varying population numbers, are presumably based on the assumption of well-conceived and well-executed search techniques. As a searcher in Arkansas in February, 2007, I would question this assumption.

Most of my searching was done in the southern part of the White River NWR, a very remote area that required a long ride in a van each morning from our lodging in St. Charles, Arkansas, to the search area. I was dropped off by the van not earlier than 7:30 and sometimes after 8 each morning. I would then begin my walk to a destination search area--often a mile or more off the gravel access road. Moving slowly through the woods and often wading sloughs of varying depths, I would typically reach my "main" area at 10 a.m. or later. (The best woods were often not in close proximity to roads or ATV trails.) This unfortunately was after the documented (in Tanner) main period of a.m. IB activity. Likewise, to get out by dark, I would have to start walking out of the woods in the late afternoon, thereby missing at least part of the evening activity period. My principal point, of course, is that much of my search time was ineffectual by virtue of being concentrated in the middle part of the day.

The only solution to this would have been to camp out in or near the search area so as to achieve a start at (or before) daybreak and to allow a later end to each day's efforts. This would have produced serious logistical and management problems for the search managers.

My point here is not to criticize Cornell but to point out that the probabilities of discovery as contained in the article are probably too high considering the search procedures used.
 
I haven't read the paper closely, but aren't they using detection probabilities derived from Pileated Woodpecker surveys? Of course, these could be adjusted for time of day.
 
There was a great deal of critical 'back chatter' about the protocol that searchers were 'forced' to follow especially for the '07-08 search (...in fact frankly I've not heard anyone say they think it was sound), and I presume it is not being followed this season (it wasn't followed 100% last season).

Detection data for PIWO are casually mentioned in the article, but it's not clear to me that those are the main basis for any of the assumptions being made???

BTW, if anyone is avoiding reading the article because of the heavy math early on, I think the text and tables at the end are clear enough that one can grasp the arguments put forth without a statistics background.
 
As an additional probability issue, there is the question of how many detections are needed to produce good physical evidence (ie., a photo) of an IB. In White River NWR, we saw and heard Pileateds every day. In discussing this with my fellow searchers, I found that they on average thought they were detecting 5 or 6 Pileateds per day. I posed this question: in how many of these detections do you believe you could have obtained a good photograph of the bird? The answer: maybe one per day, or 15 to 20%. So the probability of evidence must be layered onto the probability of detection and this, coupled with the search methodology, makes the odds very long indeed against a good photo being obtained.
 
makes the odds very long indeed against a good photo being obtained.

I think we all can agree on that.

Amazing how they never return to their A-holes or feeding sites when the automatic cameras are up.
 
Why are these people not hideously embarrassed to be publishing such material?
 
"Why are these people not hideously embarrassed to be publishing such material?"

Perhaps because seeing is believing. Some of these folks have experienced something you obviously have not.
 
It's astounding that Cornell searchers weren't camping (or weren't camping very often) and were therefore wasting prime search time. Too bad if it would have caused logistical problems for the search managers. No one said the search was going to be easy. This is but one of many ways in which the search has been mishandled, in my view.

In any event, it's clear that nothing like a thorough search has taken place, even in Arkansas, which has gotten more attention than anywhere else.

5-6 Pileated "detections" per day in that area seems like a very low number, even with the abbreviated search days. But even if you were to double (or triple) that number, the point about how hard it is to get a good photo is well-taken.
 
"Perhaps because seeing is believing. Some of these folks have experienced something you obviously have not."

Like the blob on the tree that they identified as an Ivory-bill that turned out to be a branch stub, remember?
 
"blob on the tree...turned out to be a branch stub"

Nothing like a distraction from the Luneau video. Folks need to judge for themselves of course, but the branch stub theory is bogus, though it was based on a sloppy mistake using an incorrect still image for the Science paper. The actual image of the "six-pixel" bird in question from reviewing the Luneau video in motion remains unexplained as anything other than an object exhibiting characteristics remininscent and expected from an otherwise presumably extinct species of large woodpecker (or an abnormally plumaged, but more common, species of woodpecker) that twenty or so seconds later flushed from a different but nearby tree.

The real story and object in question that does not change in shape or color pattern as the boat moves by it (unlike any known image artifact), but is gone when a large woodpecker is flushed from a nearby tree (i.e., not a branch stub unless they too can fly) can be reviewed for anyone still remotely interested at the following link:

http://www.birds.cornell.edu/ivory/evidence/segments/perched
 
You could have stopped after sloppy and incorrect.

The point is that there have been any number of mistakes. The six-pixel bird is, any way you want to spin it, another example of something believers see and know is an Ivory-bill yet when an image is captured it's unidentifiable to the rest of us.
 
The more obvious point is that some look for any opportunity to heap ridicule on those who are open-minded to the bird's possible existence. The "evidence" is hardly the issue here.
 
The evidence IS the issue. If there was sufficient evidence there would be no debate. If the Luneau video was clear and had been followed up by good independent sightings and more video and photos the skeptics would rightfully be those "ridiculed."

In the Cornell link they actually explain they used the wrong image of the perched bird in their paper. In other words, their evidence was so thin and their image was so profoundly poor that even they couldn't tell their "IBWO" from an artifact.

As long as people present such trash as evidence there will be justifiable ridicule.
 
Post a Comment

Links to this post:

Create a Link



<< Home

This page is powered by Blogger. Isn't yours?

Older Posts ...Home