Here is a recent (and very technical) paper that addresses the accuracy of species distribution models relative to species rarity. Although the conclusions are derived from amphibian and reptile data, they should be generalizable, as the models are also applied to flora and other fauna.
Franklin, J., K. E. Wejnert, S. A. Hathaway, C. J. Rochester, and R. N. Fisher. 2008. Effect of species rarity on the accuracy of species distribution models for reptiles and amphibians in southern California. Diversity and Distributions 15:167–177.
ABSTRACT
AIM. Several studies have found that more accurate predictive models of species’ occurrences can be developed for rarer species; however, one recent study found the relationship between range size and model performance to be an artefact of sample prevalence, that is, the proportion of presence versus absence observations in the data used to train the model. We examined the effect of model type, species rarity class, species’ survey frequency, detectability and manipulated sample prevalence on the accuracy of distribution models developed for 30 reptile and amphibian species. LOCATION. Coastal southern California, USA. METHODS. Classification trees, generalized additive models and generalized linear models were developed using species presence and absence data from 420 locations. Model performance was measured using sensitivity, specificity and the area under the curve (AUC) of the receiver-operating characteristic (ROC) plot based on twofold cross-validation, or on bootstrapping. Predictors included climate, terrain, soil and vegetation variables. Species were assigned to rarity classes by experts. The data were sampled to generate subsets with varying ratios of presences and absences to test for the effect of sample prevalence. Join count statistics were used to characterize spatial dependence in the prediction errors. RESULTS. Species in classes with higher rarity were more accurately predicted than common species, and this effect was independent of sample prevalence. Although positive spatial autocorrelation remained in the prediction errors, it was weaker than was observed in the species occurrence data. The differences in accuracy among model types were slight. MAIN CONCLUSIONS. Using a variety of modelling methods, more accurate species distribution models were developed for rarer than for more common species. This was presumably because it is difficult to discriminate suitable from unsuitable habitat for habitat generalists, and not as an artefact of the effect of sample prevalence on model estimation.
Click here for a summary of the paper and here for the abstract and e-mail address to request a PDF reprint from the author.
The journal Endangered Species Research is hosting a forum for exchanging views on the theme “The IUCN Red List of Threatened Species: Assessing its Utility and Value.” The Editors invited a range of authors to submit "As I / We See It" articles, hoping the exchange of opinions and information will help identify problems and possible solutions, and move toward strengthening the Red List and its output. More details including a number of the papers are here. Related to this is a recent paper in Conservation Biology, available here, which describes in detail the criteria currently used for assigning endangerment categories to plants and animals. I know that some here have questions about the IUCN categories. One can query the Red List data here. The IBWO, by the way, is listed as critically endangered.
I spent Friday and Saturday at Cornell reading James Tanner's papers. There's a lot to go through, and I didn't get to all his field notes; the handwriting is very compact and not always easy to read.
It was thrilling to examine the original glass slides from which the famous photos were made. Seeing the images in color gives them an added layer of nuance.
A few things that struck me:
Tanner corresponded with some of his local informants until early 1949. They told him a pair was present in the Singer Tract until at least November or December of 1948, several years later than is commonly believed. There's no further correspondence after the letter that mentions these sightings.
The image of the Singer Tract as a primeval forest that saw little human activity is perhaps exaggerated, for example a test oil well was drilled in the late '30s (?) not far from John's Bayou.
Tanner initially relied on Kuhn to find birds. In later years, he relocated birds by returning to known roost areas and holes.
I don't think the Birdwatcher's Digest article is available online, but it contains a rather shocking story in which Tanner climbed a ladder to a nest hole (after an IBWO nestling had fledged), discovered three eggs in the nest, picked one up and promptly dropped it. Fortunately, the egg turned out to belong to a Wood Duck, which had occupied the cavity after the Ivory-bills left.
Tanner was quite adamant in his belief in extinction, even as he worked to save bottomland forests in areas like the Congaree. He was far more respectful toward George Lowrey, with whom he corresponded about the Fielding Lewis photos, pointing out that the feet are not visible, than he was toward John Dennis. When informed (years after he had trashed the Dennis reports) that an independent analysis of the Dennis recording was consistent with an IBWO, he could only reply that it was "a mystery," without acknowledging the possibility that he had been mistaken. I came away with the impression that he had very fixed ideas about suitable habitat, a prejudice that's displayed as early as the late '30s; his dismissal of areas like the White River NWR is perhaps even more cavalier in his notes than it is in the monograph.
These are only a few quick impressions. Going through the materials is hard work, but it was a very worthwhile trip. I may go back and spend a couple of days with the field notes when time allows.
On edit: I should add that Tanner's note-taking was meticulous and thorough, and his tone was always civil. I think he got locked into some unduly narrow ideas about IBWO ecology early on, and in later years was blinded by these prejudices, and perhaps by an unconscious desire to maintain his status as the world's leading (indeed only) authority. He did a lot of good work both in the field and for conservation, and he deserves a lot of credit for both, my critiques notwithstanding.
The more I learn about Ivorybills, the more I realize that there are many in Ivorybill circles who still do not think outside the box. Many seem to think the Ivorybill was a static, unchanging, unadaptable bird with zero ability for flexibility. I have heard it said several times by different people that after the Singer tract was logged, the birds simply died because they had nowhere to go. I personally do not believe this. I believe these birds are still with us, but very different birds behaviorally than the birds of Tanners day. Many other species that were suspected as being unadaptable have adapted and in some cases flourished.
In the area I grew up in, wild turkeys and deer were believed by many to be the unadaptable emblems of true wilderness. Many believed they could only occur in some of the most remote wild tangles available. I rarely saw live deer (and never turkeys or roadkill deer) in the early 1980s. Both these species seem to be everywhere now, with both turkeys and deer sometimes invading residential areas.
These are just common examples, but they have certainly proved far more adaptable any many people would have ever admitted.
A few others that have proven quite adaptable are Pileated, cougars, black bears, otters, beaver, eagles, osprey.........................
I was thinking about Tanner's notes the other day. Did you have to make any special arrangements, or are the Tanner materials available for public reading?
A few others that have proven quite adaptable are Pileated, cougars, black bears, otters, beaver, eagles, osprey.........................
Don't forget the now-ubiquitous coyote.
I don't know just how married Tanner was to the habitat inflexibility argument. I know he allowed the bird lived a very different lifestyle in Peninsular Florida than in the Singer Tract. Tanner also cited as credible IBWO reports from some very different habitat types, such as the Everglades, Big Cypress, the mangrove forests of South Florida, and the Sea Islands of South Carolina. I do not think it was so much a matter of lack of adaptability as a matter of habitat availability. He certainly seemed to think the bird needed older forests to survive in the long term (including reproduction). I think he determined that food availability in very young forests was too low for long term survival. I tend to agree on that point, but do not necessarily think that the dichotomy between uncut and cut-over forests is the same today as in Tanner's day.
In Tanner's day everything was either old growth remnants, agricultural fields, or very early regrowth. There was not much in the way of 80 to 100 year old forests around. Now there is less old growth, but much more age diversity in forests. I don't think IBWOs could survive in managed loblolly pine stands as the PIWO can (at low densities, anyway). I am relatively sure the IBWO would starve among the rice fields of Arkansas or the cane fields of Louisiana. I do, however, think that a mosaic of forest ages with at least some trees large enough for nesting might sustain the IBWO over time (including enough reproduction to sustain the species). I think such a mosaic did not seem a realistic possibility in 1940. It certainly seemed like all the older forest would soon be gone and the birds would be left in a sea of agricultural fields and 1 to 25 year old forests. I think maybe Tanner concluded that the bird could not have made it through the bottleneck of the 1940s. Since he had concluded that the bird had perished, I think maybe he considered the debate over. Having spent more time with the bird than anyone else, I imagine it was rather a sore point with him.
I think the IBWO might survive in an area of generally young forests, finding enough food to keep from starving. I would not be surprised if Tanner would agree with that statement. I do not think the bird could reproduce under those conditions, except under remarkable circumstances where nesting sites are available and something like a storm, flood, or fire causes enough tree death to provide a temporary abundance of food. I don't know if such serendipitous breeding would be enough to maintain the species. However, if you allow that a few remnants of old growth survive today and a few more (I suspect quite a few more) made it into the 1970s, it is quite possible that there was just enough suitable habitat to hold the birds over until regrowth created some older forests with enough tree death and large enough trees to allow not just survival, but regular reproduction. I suppose Tanner just figured that those surviving bits of old forests were not enough.
I agree: Tanner recognized that the birds are not quite the specialists they are widely believed to be. He certainly noted the differences among the populations in Florida, South Carolina, and Louisiana. At the same time, it's pretty clear he viewed the Singer tract as quintessential Ivory-bill territory and measured everything against it, so there is a bit of a disconnect.
In addition, he discounted areas (the Big Woods, for example, parts of which are and have been on par with the Singer tract all along) on what seems to me a rather arbitrary basis. He missed the Congaree altogether when he did his initial survey. He dismissed places like the Pearl, which had a pretty decent report from the mid-'30s, that had been logged in the 19th century and would have had the chance to regrow considerably by the time he was doing his study. He also was not open to the possibility that birds could survive and reproduce in small remnants of optimal habitat, surrounded by second growth.
This tendency to dismiss areas based on cursory observations persisted; he and Paul Sykes (mostly Sykes actually) did examine the Neches River quite thoroughly, found no sign and no suitable habitat and determined (rightly in my opinion) that the cavities Dennis referenced were PIWO cavities, but the thoroughness of that effort was not typical, and given the subsequent validation of the Dennis recording, I'm forced to wonder how blinded by their biases he and Sykes may have been. I see this tendency to jump to conclusions as Tanner's biggest weakness.
Quote:
Originally Posted by gdebusk
Don't forget the now-ubiquitous coyote.
I don't know just how married Tanner was to the habitat inflexibility argument. I know he allowed the bird lived a very different lifestyle in Peninsular Florida than in the Singer Tract. Tanner also cited as credible IBWO reports from some very different habitat types, such as the Everglades, Big Cypress, the mangrove forests of South Florida, and the Sea Islands of South Carolina. I do not think it was so much a matter of lack of adaptability as a matter of habitat availability. He certainly seemed to think the bird needed older forests to survive in the long term (including reproduction). I think he determined that food availability in very young forests was too low for long term survival. I tend to agree on that point, but do not necessarily think that the dichotomy between uncut and cut-over forests is the same today as in Tanner's day.
In Tanner's day everything was either old growth remnants, agricultural fields, or very early regrowth. There was not much in the way of 80 to 100 year old forests around. Now there is less old growth, but much more age diversity in forests. I don't think IBWOs could survive in managed loblolly pine stands as the PIWO can (at low densities, anyway). I am relatively sure the IBWO would starve among the rice fields of Arkansas or the cane fields of Louisiana. I do, however, think that a mosaic of forest ages with at least some trees large enough for nesting might sustain the IBWO over time (including enough reproduction to sustain the species). I think such a mosaic did not seem a realistic possibility in 1940. It certainly seemed like all the older forest would soon be gone and the birds would be left in a sea of agricultural fields and 1 to 25 year old forests. I think maybe Tanner concluded that the bird could not have made it through the bottleneck of the 1940s. Since he had concluded that the bird had perished, I think maybe he considered the debate over. Having spent more time with the bird than anyone else, I imagine it was rather a sore point with him.
I think the IBWO might survive in an area of generally young forests, finding enough food to keep from starving. I would not be surprised if Tanner would agree with that statement. I do not think the bird could reproduce under those conditions, except under remarkable circumstances where nesting sites are available and something like a storm, flood, or fire causes enough tree death to provide a temporary abundance of food. I don't know if such serendipitous breeding would be enough to maintain the species. However, if you allow that a few remnants of old growth survive today and a few more (I suspect quite a few more) made it into the 1970s, it is quite possible that there was just enough suitable habitat to hold the birds over until regrowth created some older forests with enough tree death and large enough trees to allow not just survival, but regular reproduction. I suppose Tanner just figured that those surviving bits of old forests were not enough.
I think Tanner was willing to acknowledge that ivory-bills used habitats rather different from those in the Singer Tract, particularly in peninsular Florida. But what colored his thinking perhaps even more than habitat specialization was his notion that the bird, along with certain other species, required "wilderness." He unequivocally described the Singer Tract as the "last wilderness" of the Mississippi Valley, and his belief that the species persisted in Florida, despite the fact that he never saw an ivory-bill there, was clearly influenced by the "wilderness" conditions there. He referred to the Big Cypress, where he estimated as many ivory-bills persisted as in the Singer Tract, as "one of the largest primitive areas in southern states." Conversely, areas that he judging lacking in "wilderness" character he dismissed as ivory-bill refugia; the Big Thicket he described as "greatly over-rated as a wilderness area."
It is clear from the writings of Tanner and others that it was not only the ivory-bill that was thought doomed by the loss of southern wilderness. The black bear, the red wolf, and the cougar were all widely thought to be on the verge of extirpation in the South by the 1930's, and sure to vanish from the region by the mid 20th century. In a way this is not surprising given the relentless and haphazard shooting of every kind of wild animal in the early 1900's - and all of these species did decline to very low levels. The Singer Tract, in Tanner's writings and others, was clearly seen as a last refuge for species that were believed extirpated elsewhere in the region. All have in fact survived (although the red wolf has been genetically swamped by the coyote).
Excellent point. I hadn't thought of it in those terms, but it makes sense. Tanner was very much a product of his time, and he probably bought into the "closing of the frontier" mythology that persisted well into the 20th century. It's the same mindset that shaped the mistaken 19th century belief that Native Americans would inevitably die off as "civilization" advanced.
On edit: your point is reinforced by his notes on potential habitat he visited. In more than one instance, he cited the relative scarcity of game animals as a reason for deeming the habitat unsuitable.
Quote:
Originally Posted by fangsheath
I think Tanner was willing to acknowledge that ivory-bills used habitats rather different from those in the Singer Tract, particularly in peninsular Florida. But what colored his thinking perhaps even more than habitat specialization was his notion that the bird, along with certain other species, required "wilderness." He unequivocally described the Singer Tract as the "last wilderness" of the Mississippi Valley, and his belief that the species persisted Florida, despite the fact that he never saw an ivory-bill there, was clearly influenced by the "wilderness" conditions there. He referred to the Big Cypress, where he estimated as many ivory-bills persisted as in the Singer Tract, as "one of the largest primitive areas in southern states." Conversely, areas that he judging lacking in "wilderness" character he dismissed as ivory-bill refugia; the Big Thicket he described as "greatly over-rated as a wilderness area."
It is clear from the writings of Tanner and others that it was not only the ivory-bill that was thought doomed by the loss of southern wilderness. The black bear, the red wolf, and the cougar were all widely thought to be on the verge of extirpation in the South by the 1930's, and sure to vanish from the region by the mid 20th century. In a way this is not surprising given the relentless and haphazard shooting of every kind of wild animal in the early 1900's - and all of these species did decline to very low levels. The Singer Tract, in Tanner's writings and others, was clearly seen as a last refuge for species that were believed extirpated elsewhere in the region. All have in fact survived (although the red wolf has been genetically swamped by the coyote).
It certainly looks interesting, but $30 is a lot of money for a civil servant who's pay keeps getting cut. Maybe I can convince my local library to buy a copy . . .
It certainly looks interesting, but $30 is a lot of money for a civil servant who's pay keeps getting cut. Maybe I can convince my local library to buy a copy . . .
thanks for bringing this to our attention (hadn't heard of it before) -- I'm partial to anything Noel Snyder has a hand in (his work on the Carolina Parakeet and C. Condor also interesting); even if the volume only compiles info that is already available elsewhere, may be worth it to some folks to have both species covered in a single book (I agree the cost is a hindrance).
Noel's wife Helen use to participate in this forum -- any chance she's out there and could fill us in a bit more on the contents of the work?
Noel Snyder and his wife have made some excellent contributions to bird conservation. I like the two-part titles of his books (The Carolina Parakeet: Glimpses of a Vanished Bird; The California Condor: A Saga of Natural History and Conservation; Raptors of North America: Natural History and Conservation; The Parrots of Luquillo: Natural History and Conservation of the Puerto Rican Parrot; and Parrots: Status Survey and Conservation Action Plan 2000-2004), which brought a smile to my face as I read them (again) at the Amazon link. He appears to have colonitis. ;-)
It certainly looks interesting, but $30 is a lot of money for a civil servant who's pay keeps getting cut. Maybe I can convince my local library to buy a copy . . .
I recently acquired this book, much of it continues the theme of Snyder's 2007 monograph, that food specialization and dependence on old-growth forest are far from demonstrated for the ivory-bill (or the imperial), while human depredations, not merely "scientific" collecting may be far more significant than much of the literature would suggest. It also contains a fairly thorough history of observations on the imperial woodpecker, including 2 sightings (one a male, the other a female) by Mexican biologist Alberto Gonzalez in the late 1970's.
Of particular interest to me are 2 letters from Arthur Wayne to Frank Chapman in 1905. Among other things, Wayne is adamant that the ivory-bill is still a common bird in parts of Florida at this time (although not so in other parts). This was 11 years after he had finished collecting ivory-bills, and he stated that "I know that I left more than 100 birds in a radius of 20 square miles." I welcome the publication of such original material and hope that Cornell will see fit to publish Tanner's journal at some point, a veritable treasure trove of information
Of particular interest to me are 2 letters from Arthur Wayne to Frank Chapman in 1905. Among other things, Wayne is adamant that the ivory-bill is still a common bird in parts of Florida at this time (although not so in other parts). This was 11 years after he had finished collecting ivory-bills, and he stated that "I know that I left more than 100 birds in a radius of 20 square miles."
Fang, in what location of Florida was Wayne speaking of a remaining population, and did he or Snyder offer a reason for its eventual loss? Collecting by someone else? Habitat loss?
Wayne cited 3 areas as having good numbers of ivory-bills during this time:
(1) The area near the Florida "volcano," which has never been precisely located to my knowledge but was near the Wakulla/Jefferson County line southeast of Tallahassee.
(2) Suwannee Hammock, Levy County.
(3) San Pedro Bay "must contain innumerable ivory-bills today" according to Wayne.
Wayne also advises Chapman to go to Brushy Hammock and Pumpkin Swamp, off the Suwannee. He says that he has been offered "large sums of money" to go to Florida and get ivory-bills but has refused.
In his 23 Aug letter Wayne says something quite interesting that to my knowledge he does not mention in his published papers: "The ivory-bill is a bird of the inland swamps, not the river swamps...." By inland swamp he seems to mean any of the hardwood- or cypress-dominated forests of what we now call the Gulf Hammock region, not associated with major rivers. This seems to include hammocks, bays, and cypress domes, which interdigitate with pine flatwoods in this region. In his 1893 paper he stated that the birds were to be found in large tracts of heavy timber "destroyed" by fire. This suggests to me that occasional fires burning from the pyrogenic pine forests and into fire-tender swamp forests/hammocks yielded patches of high tree mortality, attracting ivory-bills. The preference of the birds for hardwood and cypress forests away from major rivers in this area may also explain why Brewster saw so few of these birds along the Suwannee.
Snyder argues that human "predation," not primarily specimen collecting, may have been the primary cause of decline in both the ivory-bill and imperial. This includes killing for food, for sport, and simply out of curiosity. He adds that habitat destruction may well have exacerbated this, but clearly believes that the carrying capacity of many forests is/was far higher than Tanner supposed.
Based on his recent book I would have to say yes, but not much. Snyder et al. express hope that both species have survived, and in fact argue that recent searches have perhaps focused too much on mature forests, whereas better success might be achieved by looking for areas that have been free of shooting pressures. They appear to place their greatest hopes on Cuba but are clearly not optimistic.
Anyone remember which issue of LIFE magazine ran John Dennis article on his Texas efforts? I believe the year was 1972, but I don't remember the specific issue?
Also, anyone read John Kilgo's book Deep Enough for Ivorybills? Not specifically about the birds, but relevant to the Pee Dee area of SC, and I believe he heard a kent in LA.
I was not aware that there was an article in Life. Dennis did publish an article in Audubon magazine and another in Avicultural Magazine. These were in 1967 and 1979, respectively.
Dennis, J.V. 1967. The ivory-bill flies still. Audubon 69(6):38-44.
Dennis, J.V. 1979. The ivory-billed woodpecker (Campephilis principalis). Avicultural Magazine 85:75-84.
Anyone remember which issue of LIFE magazine ran John Dennis article on his Texas efforts? I believe the year was 1972, but I don't remember the specific issue?
Bobby Harrison read about the ivory-billed woodpecker in an April 7,
1972 issue of Life magazine... google indicates a
Don Moser article with mention of John Dennis??
edit add: more info on Life Magazine April 7, 1972 ibwo article at:http://www.2neatmagazines.com/life/1972.html
-
-
(April pic of unique swamp trail marker - in Dagmar - east of Hickson lake)
Last edited by duck stamp : 06-09-2009 at 10:51 AM.
Reason: add info
My wife got me a copy of this issue for Christmas, and the article is a worth a read, not only for how well it shows that the more things change, the more they stay the same, but also for its portrait of Dennis, some other tidbits about sightings during that time period, and for its assertion that IBWOs are extreme specialists, eating "only grubs infesting recently dead trees of certain species."
It can be had for under $10 on ebay.
Quote:
Originally Posted by duck stamp
Bobby Harrison read about the ivory-billed woodpecker in an April 7,
1972 issue of Life magazine... google indicates a
Don Moser article with mention of John Dennis??
edit add: more info on Life Magazine April 7, 1972 ibwo article at:http://www.2neatmagazines.com/life/1972.html
-
-
(April pic of unique swamp trail marker - in Dagmar - east of Hickson lake)
There is a forthcoming paper available at "Early View" of the journal, Conservation Biology. Here's the citation and an excerpt of the Abstract:
Rout, T. M. , Heinze, D., and McCarthy, M. A. 2010. Optimal allocation of conservation resources to species that may be extinct. Conservation Biology (in press).
Statements of extinction will always be uncertain...Two errors can be made...Extinction can be declared prematurely, with a resulting loss of protection and management intervention. Alternatively, limited conservation resources can be wasted...Optimal decisions depend on the cost of continued intervention, the probability the species is extant, and the estimated value of management (the benefit of management times the value of the species). We illustrated our approach with three examples: the Dodo...the Ivory-billed Woodpecker...and the mountain pygmy-possum...The dodo was extremely unlikely to be extant, so managing and monitoring for it today would not be cost-effective unless the value of management was extremely high. The probability the Ivory-billed woodpecker is extant depended on whether recent controversial sightings were accepted. Without the recent controversial sightings, it was optimal to declare extinction of the species in 1965 at the latest. Accepting the recent controversial sightings, it was optimal to continue monitoring and managing until 2032 at the latest. The mountain pygmy-possum is currently extant, with a rapidly declining sighting rate. It was optimal to conduct as many as 66 surveys without sighting before declaring the species extinct...If the value of management is high enough, continued intervention can be cost-effective even if the species is likely to be extinct.
To summarize my take on the Ivory-billed Woodpecker portion of the study, the authors relied on a 2010 paper by Roberts et al., which divided sightings into three categories: 1) those with physical, noncontroversial evidence; 2) those with sufficient documentation to satisfy independent experts; and 3) controversial sightings accompanied by substantial debate and lack of verifying evidence. Sightings from the first two categories gave a most recent sighting of 1944, whereas inclusion of controversial sightings gave 2006 as the most recent sighting. Using a constant sighting rate, they applied a formula to calculate the probability that the IBWO is extant and used another equation to find the optimal solution for a range of relative management values (including the proposed USFW 5-year budget of US$27.8 million over 5 years). When they used only the first two categories of sightings, the probability of the bird being extant in 2009 was a sobering 0.000000000000178 (ouch!), reflecting the large number of years without an accepted sighting. When they used the controversial sightings, the likelihood of being extant in 2009 was 0.93. When they considered only the generally accepted sighting records, the maximum amount of time to manage and monitor the Ivory-billed Woodpecker (at a cost of US$5.56 million/year) was 21 years after the final sighting in 1944, with extinction declared in 1965. When they included the recent controversial sightings, the maximum amount of time to manage and monitor the species was 26 years after the most recent sighting in 2006, with the species declared extinct in 2032 if no further sightings occur.
I'll look for the Roberts et al. paper...
Last edited by Sidewinder : 03-21-2010 at 07:28 AM.
Roberts, D. L., C. S. Elphick, and J. M. Reed. 2010. Identifying anomalous reports of putatively extinct species and why it matters. Conservation Biology 24:189–196.
As species become very rare and approach extinction, purported sightings can stir controversy, especially when scarce management resources are at stake. We used quantitative methods to identify reports that do not fit prior sighting patterns. We also examined the effects of including records that meet different evidentiary standards on quantitative extinction assessments for four charismatic bird species that might be extinct: Eskimo Curlew (Numenius borealis), Ivory-billed Woodpecker (Campephilus principalis), Nukupu`u (Hemignathus lucidus), and O`ahu `Alauahio (Paroreomyza maculata). For all four species the probability of there being a valid sighting today, given the past pattern of verified sightings, was estimated to be very low. The estimates of extinction dates and the chance of new sightings, however, differed considerably depending on the criteria used for data inclusion. When a historical sighting record lacked long periods without sightings, the likelihood of new sightings declined quickly with time since the last confirmed sighting. For species with this type of historical record, therefore, new reports should meet an especially high burden of proof to be acceptable. Such quantitative models could be incorporated into the International Union for Conservation of Nature’s Red List criteria to set evidentiary standards required for unconfirmed sightings of “possibly extinct” species and to standardize extinction assessments across species.
Here are the Ivory-billed Woodpecker sighting data they used:
Data were from Tanner (1942), Hahn (1963), Jackson (2002, 2004), Fitzpatrick et al. (2005), Hill (2006), and Floyd (2007).
Some conclusions (from copy-and-paste): For the Ivory-billed Woodpecker, the prior sighting record suggests that even by the time of the first controversial sighting, the species was relatively unlikely to remain extant (ca. 21% chance), regardless of the level of evidence (physical or independent expert opinion) used...the effect on the predicted extinction date will depend on the details of the sighting record. Including controversial sightings will, by definition, move expected extinction dates forward in time. An ever-increasing burden of proof should be required with increasing time since the last verified sighting. The burden of proof also should be greater when there is a pattern of frequent sightings prior to the last accepted record and lower when long periods between sightings are common in the historical record.
That's pretty much it!
Last edited by Sidewinder : 03-21-2010 at 07:30 AM.
The crux of the problem is the reliance on "expert opinion" as a criterion for "non-controversial" sightings, which leads to a rather vicious circularity. Why don't the 7 sightings by highly experienced birders in Arkansas in 2004 qualify as verified by "independent expert opinion"? What exactly makes them "inferior" to the above second-hand sighting reports prior to 1945? What is being suggested, as far as I can tell, is that we rely on the opinions of a few experts such as Tanner and Jackson as to whether a given sighting is valid, then we use the last sighting accepted by them as the cutoff for extrapolating the species likely survival.
Linear Mode
