Schroedinger's Woodpecker
Barring dramatic new information, the Ivory-billed Woodpecker situation has once again settled in to stalemate. Various summaries and such will be coming out in the near future, but they will be unlikely to reveal anything major that is not already known. I've got a few big-picture summary points I want to make as well. To begin, I want to review the order-of-magnitude probability issues I have gone over several times in the past.
A fundamental split in opinion can be summarized as follows:
Opinion A. If there were any out there, surely they'd have been adequately documented by now.
Opinion B. Finding a few birds in a large area is extremely difficult, and they could remain undocumented for a very long time even with many people looking.
Biologists are generally a bit math-phobic; ask anyone who has taught undergraduate genetics about the blank stares and panicky fidgeting that fill the classroom as soon as you get to population genetics and write the first equation on the board. People in general are also quite poor at comprehending the very small and the very large. Because of these two factors, most bird people have been arguing Opinions A and B based on not much more than hunch, intuition, and common sense. Those who work in other sciences, in contrast, are much more inclined to try to work with actual numbers when dealing with these matters of the huge and tiny. The order-of-magnitude approximation is a time-honored tool in most natural sciences. So here, once again, I'm going to apply this tool to Opinions A and B.
The question of how much effort it takes to find a bird can be summed up in a simple equation:
D = A*c
Here D is your detection rate, in terms of detections per hour, A is the actual abundance of the bird (birds per km2), and c is the coefficient of detectability. This coefficient is dependent on the species, time of year, habitat, etc., and your criteria for a "detection" (e.g. heard, seen, captured in a mist net, etc.). For a general and reasonable approximation, for a typical forest bird, if there's one per km2 an experienced observer moving about through this square kilometer will detect it by sound or sight about once every 10 hours. This means that c has a value of 0.1 if you are dealing with hours and square kilometers. In spite of all the arguments that ivorybills should be either less conspicuous or more conspicuous than average, I'll use this nice round order-of-magnitude number.
Now we need estimates for A, abundance expressed as Ivorybills/km2, under various scenarios. Estimates for the total extent of bottomland hardwoods vary, but a value used by The Nature Conservancy of 20,000 km2 is typical. Using this number, if there is only one ivorybill out there, its abundance in this habitat is 0.00005 bird/km2. This one individual Ivorybill would be "detected" (more on what this means later) about once for every 200,000 hours of birder effort spent in bottomland hardwoods. If there are 100 Ivorybills scattered in this region, this rate becomes once per 2000 hours of effort.
To address the Opinions A vs. B question, we need an estimate for total observer effort within this region. Here I am just going to make up order of magnitude numbers based on my own experiences as an active birder who has lived in or near the historical range of the Ivorybill for most of my life. I'm going to guess that within this region there are roughly 1000 birders who are competent, reliable, and experienced enough to be able to produce an Ivorybill report that could be granted credibility. This is on the order of 100-200 per state. I'm going to guess that each of these observers spends about 1000 hours per year afield; as this is 20 hours per week it is likely a rather generous estimate. Working with orders of magnitude, this gives us 1,000,000 hours of birding time per year in the region.
How much of this time is spent in closed canopy coastal plain bottomland forests? A quite small fraction, actually. The forested bottomlands are not a magnet for birders; in fact they are a bit of a repellant. After getting their Swainson's Warbler for the year, most birders have little additional need for this habitat. That 20,000 km2 of bottomlands is about 2% of the land area within the region; most of it is inaccessible, all of it is frequently to occasionally flooded, and rich in biting insects much of the year. Hence, it seems reasonable to guess than only about 1% of this general birding effort is within this habitat, or 10,000 hours per year.
Now to combine these two ballpark numbers:
-- Individual Ivorybill within 20,000 km2 of bottomlands detected every 200,000 hours
-- Birders spend 10,000 hours per year in this habitat
It's simple to figure that a lone Ivorybill would be "detected" once every 20 years.
But what does "detected" mean? In the context used so far, for a typical woodland bird, it means heard or seen well enough to "count" an individual of a species that is expected to be within the area. In the case of forest birds, this means "heard" about 90% of the time; sometimes heard faintly, distantly, and/or only once. Only about 10% of these detections will be visual; one might estimate that only about 10% of those visual detections would be "good" ones that would allow for a detailed description or the opportunity for a diagnostic photograph.
If we use this more nuanced definition of "detection," we find that once every 20 years or so, this lone Ivorybill will be heard, and not necessarily well. It would be seen about once every 200 years; most of these sightings would be "lousy." To expect a good sighting and a shot for a photo or video, you would be waiting about 2000 years.
This all scales up linearly of course. If we have 100 Ivorybills spread within this area, we still predict only one (probably lousy) sighting every 2 years, and a good sighting or photo every 20 years.
The gist of this is that small populations of mobile forest animals (say less than 100 individuals) spread over very large areas are almost impossible to detect with the typical birder effort. The scenario for 10 birds is indistinguishable from no birds at all, given the reality of honest mistakes and the possibilities of fraud.
There are two extensions to this ballpark analysis I'm going to run through. The first is the matter that all of these 20,000 km2 might not be suitable habitat, which conceivably narrows the search range. The second is the matter of intensive targeted searches within smaller areas.
I'll start with the "suitable habitat" question. True, in all likelihood only an unknown fraction of all bottomland forest is actually suitable Ivorybill habitat. It is likely, though, that the "suitable habitat" is less accessible, and hence disproportionately less often visited by birders, than the more accessible, "marginal" habitats. Hence, the numbers get even worse if you try to account for this, not better -- one quarter the area with one tenth the effort, for instance.
Now for the target search scenario. Here people identify an area within which they think there is an especially high probability of finding the bird, and focus effort there. This is of course the usual method that birders and ornithologists use to find rare birds. Here a species-specific complication comes in to play. The overall consensus of historical accounts for the Ivorybill indicated that it was a highly mobile bird with a surprisingly large (and entirely forested) home range. It was generally not described as remaining within any small area for very long. Even nesting pairs were difficult to nail down. A general estimate for the size of this home range would reasonably be 10 mi2, or 25 km2, an area slightly more than 3 miles on a side and approximately the size of a typical breeding bird atlas block. Those who have atlassing experience might think, "surely if I had an ivorybill within one of my atlas blocks I would have found it!" Or, if you are an Ivorybill searcher, you might think that if you did get within the home range of a bird, you'd have a good chance of nailing that sucker. Think again.
A single observer within a 25 km2 home range that contains one bird would expect encounters with the following frequency:
Auditory every 250 hrs
Visual every 2500 hrs
Good sighting or photo op every 25,000 hrs
Note that 25,000 hours is 10 hours a day, every day, for 6.8 years. Under the same circumstances, you'd expect some visual contact every 250 days (about 8 months) and an "I heard something suspicious" encounter every 25 days. Any wonder, then, that Tanner only found his birds with the help of a man who effectively lived in the forest full-time?
What about the Cornell scenario? They had about 10 people in the field, all day, for about 4 months each year. That's about 12,000 hours per field season. What is the expectation there, if all this effort was within the home range of this hypothetical Ivorybill, and all of it was good field time, not preoccupied with other tasks (like servicing field equipment, etc.)? That works out to 48 audio detections, 5 sightings, and a half of a photo. For Cornell's initial secret search, these numbers are somewhat high on the audio, low on the sightings, and about right on the photo (I think the Luneau video can be counted as half a photo...). Considering that I am working in orders of magnitude, it's a pretty good approximation. For comparison, look at our Moss Island searches, where we put in about about 2000 hours of effort. The prediction is for 8 audios, 0.8 sightings, and 0.08 photos. Again, this is a pretty fair agreement. The audio rate was about right, we had three uncertain glimpses (does this total to 0.8 sightings?) and were absolutely skunked on the photo front.
Even if you are in the right place, documenting a thinly spread forest bird is daunting. It's nearly impossible for a single observer; and challenging for a group of 10 observers. If you look at the total birding community over the entire historical range of this bird, it would be hard to distinguish even as many as 10-100 residual birds from the background noise of honest misidentifications and weird occurrences, with photo ops coming only a few times a century, if even that much. Some will doubtless try to turn this inside out and say "See, that proves the bird is extinct and all these reports are bogus!" which is certainly a bit of backwards logic. What it actually demonstrates is that those of Opinion A who say "If they were out there, we'd surely have found them by now" are in fact mistaken. Between 10 and 100 surviving birds is far from extinct, yet even this many birds would easily avoid "firm confirmation" of their existence for decade after decade. Thinly spread forest creatures, with very large areas within which they might be scattered, are destined to remain phantoms. Their existence will always be extremely challenging to confirm; their extinction will be essentially impossible to establish. Like it or not, this is the way of things.
What one does about this is a matter of policy, resource allocation, etc. That's a different matter. But anyone who declares that the species is "extinct" or "probably extinct" based on existing information is just voicing a personal belief. From a scientific perspective, this is not knowable. Sibley and Kaufmann were in error in concluding that the extinction of this species (and two others) was certain enough that it did not need to be included in "comprehensive" North American field guides. Of course, the same is true of those who declare that the species is definitely extant. Even if the Arkansas video were undeniably an ivorybill, and even if those double knocks I heard at Moss Island in 2009 were absolutely accepted as being the real deal, well, those two spots are only about 100 miles apart, and it's been over a year since then. Conceivably, it might have all been the same bird, it might have been the last bird, and it might be dead now. Far fetched, but not impossible. The only way this will ever be resolved is if the population manages to rebound in at least one area to a point that firm sightings and good photos can be obtained regularly. I think everyone will agree that this would be a great day; I think most would also agree that this day is not likely coming any time soon.
Schroedinger's Woodpecker is still locked up tight in that box.
posted by Bill Pulliam @ 10:19 AM
25 comments
25 Comments:
you're speaking to the choir here in my case Bill, but nonetheless I'll play devil's advocate and say where the skeptics won't buy into your argument (at least one point), which is in your "target search scenario":
your initial case only calculates the figures for a single searcher finding a single bird within a given home range, but what about a half-dozen+ searchers involved and a PAIR of IBWOs who for part of the year are flying around with 2-3 juveniles in tow. The averages or expectations go up significantly, not necessarily for a crystal-clear photo or video, but for some sort of encounters (and if there are more searchers or more IBWO pairs, well higher averages yet). You then use Cornell's experience as a case-in-point, but continue to use straight-out "averages" as the working numbers. Their 7+ sightings (not to mention auditory encounters) in the first year would very much skew what the expectations going forward would be; i.e. if you had two areas (call them A & B) of exactly equal size and habitat quality, and you send in exactly the same number of searchers for the same amount of time, BUT area A has had one IBWO sighting say 50 yrs. ago, and area B had 7 or more sightings last year... well, obviously straight-out computed "averages" mean little as far what the "expectations" would be. (In short, "hot zones" can't be calculated with the same math as more 'run-of-the-mill' zones.)
Further, it is likely (or at least possible) during much of the search season that IBWOs are not randomly flying about large expanses, but going out at early morning and returning at dusk, along established flight paths to the same roost or nest holes day after day after day. Have no humans been stationed anywhere along those flight paths in the last 6 yrs.???
(hey, I'm just putting all this out there before one of the skeptics does...)
Therefore, one "good" sighting per year suggests 2000 birds. A single good sighting per year average in the past ten years is very reasonable (not counting multiple sightings in the same area in the same year).
It doesn't matter whether the spatial distribution is uniform, random, or whatever. So long as you don't know what the distribution and movement patterns are, they might as well be random to you. Clumping (e.g. pairs or family groups) actually makes detections happen less often; it just means when you do have a detection it's more likely to be more than one individual. Predictable flight paths also make the initial detection more difficult, not easier. If a bird moves about widely within a 10 square mile home range, then you can spend your time anywhere within that range and have about the same chance of encountering the bird. But if it prefers particular areas over others, you will need to spread your effort much more extensively through the area (including the places that are hard to get to) before you have a chance of finding the critter. Think of it this way: If you have 10 squares, and the bird moves randomly between all the squares, you can just sit in any one of them and your odds of encountering it are the same. So there's no need to traipse all over the swamp. But if it is much more likely to spend time in some squares than in others, you need to keep moving. Otherwise, if you just pick one spot and wait, and you picked a spot it does not go to, you can sit forever and never encounter it. The uniformly spread randomly moving bird is the EASIEST to find if you don't already know where to look. Clumping and repeated movement patterns make it harder to find initially, but then easier to relocate.
Besides, talking abut family groups and roosting patterns is getting ahead of yourself when you have yet to conclusively document any single place and time where even one individual occurred one time.
Obviously, if a species exists at low enough density over a large area, it can become extremely difficult to find.
However, the argument cuts another way as well. As a species decreases in density, but has a wide range, it will become exceedingly difficult for dispersing birds to find mates. An inevitable consequence of this is that the reproduction rate will fall below the replacement level, the density will decrease, it will be even harder for the remaining individuals to find mates, and the population will decline to zero (extinction). Such a hypothetical "low-density, broadly dispersed" population is not stable, and will only exist for a brief period of time.
I believe this is thought to have happened fairly recently with the Bachman's Warbler. The population declined, a few widely dispersed, unmated males were seen and heard on territory, and then no more could be found. The same thing probably happened with the Eskimo Curlew.
I think the process started with the Ivory-billed Woodpecker in the 1880's with widespread settlement, persecution and forest clearance in southern swamp and pine forests. There were scattered populations reported for a few decades, but then they too died out. That interpretation seems consistent with the verifiable data.
Cotinis -- it's a hypothesis, and a reasonable one. Three reasons why it is just a hypothesis however, not an inevitability:
Some species do persist at very low density, especially if they are mobile enough. These birds have all day, every day to find each other and are always within the correct habitat; one would think their own encounter rate with each other would be much higher than our own.
This hypothetical small population of birds does not have to be uniformly spread within 20,000 square kilometers; they just have to be in places we do not know about. They could much more dense in some areas than others. As I went through, even if they are as abundant as one per 10 square miles in some places, that would still be pretty hard to track down even if you did stumble across one of these places.
There was a recent study published (I forget the citation off the top of my head but is was widely references online) whose models predicted that subpopulations of as few as 5 birds could persist indefinitely. Spread these 5 birds in 50 square miles (e.g. one river swamp 20 miles long and 2.5 miles wide) and you'd still have a hell of a time documenting their presence there even if you knew which swamp to survey.
It remains that people do not really intuitively grasp how friggin huge 20,000 square km is and how proportionately teeny the detection abilities of individual humans are within this enormous context.
I quite agree, to repeat your own language, that this interpretation "seems consistent with the verifiable data," at least until the 1950's. But I submit that this is a far cry from suggesting, as others have, that it is the only reasonable interpretation, and I disagree with your assertion that a terminal population crash is an "inevitable" consequence of low density per se. Many North American animals, with no more mobility than ivory-bills, experienced devastating population declines due to relentless persecution a century ago. The La. black bear for example. How is that such animals managed to find each other in the mid-twentieth century, when La. forests were at their most devastated and many people shot bears on sight? And incidentally, LDWF was so despondent that there were no more La. black bears, they imported some from Minnesota in the 1960's. I could cite other examples, but low density in this context must be examined in the context of mobility. The ivory-billed woodpecker is DESIGNED FOR DISTANCE. This obvious fact seems to be routinely overlooked.
I just hope you took the cat out of the box prior to putting the woodpecker in...
Well, I feel like you are cooking the numbers to justify your conclusion--that the IBWO persists, but cannot be detected by practical means due to its "low density". This is not science, because you are starting from your conclusion, and then figuring out how low the density has to be to make it possible. One can always make this sort of argument, but it is not very useful, because it can never be refuted. I've been hearing that the IBWO is "still around, just a bit farther back in the woods" for forty years.
I think you need to examine your assumption that the biology of the IBWO allowed it to persist at such extraordinarily low densities. As CT pointed out, birds cluster during the breeding season, and the local density becomes quite high. Also, birds don't wander far for the several months while they are defending territories and raising young. They are also much more "detectable" while leading noisy fledglings around. Again, with fledglings flying weakly, the adults cannot wander very far.
Look--here is an analogy. I have a fair amount of experience with the Red-cockaded Woodpecker, which does occur at low densities (overall) in southern pinelands, many of which are rather difficult of access. Their call is soft, but I have heard it almost a quarter of a mile away through woods, likewise with the drumming. When male birds are doing their territorial thing, they are "detectable" over a large distance. I've also found them during the non-breeding season because they call to each other and fly from tree-to-tree as they forage. Any woodpecker has to fly from tree-to-tree occasionally, and if you are walking through the woods quietly, you will see them. Their habitat is not all that accessible, and there are lots of ticks in it, typically, and a few mosquitoes. However birders across the south find them all the time. I can find them whenever I want in the breeding season, and I have also just run into them while driving around looking for other birds. This all despite the low density--just an estimated 12,000 groups (40,000 birds?) spread over millions of square miles of southern pinelands. According to your figures, my sightings of these birds are a statistical long shot. (I've taken photos too, and it did not take me thousands of hours of effort.)
How does the fact that Eskimo Curlews and Bachman's Warblers are migratory impact the calculus? I've been less optimistic about those species; their movements should be more predictable, with a better chance that they could be seen in certain known places.
It's ironic that habitat management efforts for the Bachman's Warbler are apparently ongoing, and it doesn't seem to have caused much (or any) outcry.
http://www.wlf.louisiana.gov/experience/threatened/bachmanwarbler.cfm
cotinis --
Did I use my argument to conclude that Ivorybills are not extinct? No, I believe I used it to conclude that it is really hard to determine this. I would suggest that you are pushing the arguments to achieve a certainty that you desire but which science cannot support. What you call my "conclusion" was in fact my "hypothesis" and I ran the rough numbers to see if the hypothesis was reasonable. If you feel starting with a hypothesis is unscientific then you have a pretty large hole in your understanding of science.
Let's talk about cooking the numbers:
"Millions of square miles of pinelands [which is a gross exaggeration]" the vast majority of which are entirely unsuitable as Red-cockaded habitat, as you know. Their habitat requirements are well known and are very narrowly defined by the obligate presence of at least one of a very small number of pine species within a narrowly restricted age and physiognomic structure. Plus, these birds are sedentary -- once you have found them, you can relocate them very easily. Their home ranges are tiny - 125 acres (0.5 km2) per pair. And the population you are talking about is at least 1000 times larger than what any realistic person optimistically would hypothesize for residual Ivorybills. There are well-known local areas where this bird is almost common. I lived in Georgetown County SC for several years, please don't try to tell me I don't know what I am talking about with this species. The nest trees can also be spotted from a hundred yards away with little difficulty, and the birds almost always remain fairly close to these trees.
So, let's run the numbers here on your bird. The habitat is not "millions of square miles." The entire U.S. including Alaska has an area of less than 4 million square miles. Obviously you just pulled this number out of thin air; at least I actually looked up the area of bottomland hardwoods (I smell numbers stew...). The total area of the southern pine region is closer to 400,000 square miles or about 1,000,000 square kilometers. I'll be super generous here and give you 10% of this area as potential Red-cockaded Habitat, even though I know this is too high by probably a factor of 10. So we've got 40,000 birds in 100,000 square km, or 0.4 bird/km2 I'l be even more generous here, and downgrade this to 0.1 family group per km2 to make them harder to find. Even with all these allowances, this means you would only need to put in 100 hours of random searching before you heard a bird, and 1000 hours before you saw one. And this is just random searching in pine stands, without any a priori knowledge of where the birds actually are. Plug in my same estimates for birder effort in the region, and you have birders stumbling across Red-cockadeds, even if they did not previously know where to look, hundreds or thousands of times each year.
The people you disagree with might or might not be arguing from a priori conclusions; you definitely seem to be doing so, however.
Mark --
I don't really think that being migratory affects the big picture that much. Site fidelity only becomes useful after you find the bird the first time. Until then it's a crap shoot.
I think the prospects are probably worst for the Eskimo Curlews, just because of habitat issues. Shorebirds and shorebird habitat receive disproportionately large amounts of attention from birders, which would make a rare shorebird harder to hide. Still, I can't really say off the top of my head how the numbers might pan out. For Bachman's Warbler I think the situation is pretty comparable to the Ivorybill. The big difference would be that once a singing male was found he should be easy to relocate. But until that happens it's all pretty equivalent.
FYI...For some reason Mark, the link that you posted, that should directly reference the LDWF aquisition and "set-aside" of some 300 acres of habitat for the Bachman's Warbler has been taken down. I do remember the article, though. I seem to remember the location was somewhere near Waterproof, LA.
Maybe someone could do the math and let us know what the potential population is if the claimed sightings over the last ten years are good records?
This could be quite large indeed and when extrapolated over the suitable range available, the figure could be quite astonishing. (I am presuming that birds also occur in unsearched areas where they are not being detected, and possibly in some lightly searched areas due to the super elusive nature of the bird that allows it to seemingly escape 'easy' detection).
I can't believe that birds are only occuring in the areas they have been detected recently - they must surely be in other suitable unsearched areas at similar density.
So, bear with me as I've made a few assumptions, if the reports are good, what possible total are we looking at?
Hoatzin --
If you take the reports from several places as valid, I still think we're only in the 10-100 range globally. As I'm only working in orders of magnitude I won't hazard a guess more precise than that. I do think if we were over 100 then the encounter rate would start to get high enough that we would get "concrete" evidence.
That 100 number may seem like a whole lot, but as it's over the entire range that's still not many birds in any one State and no real "hot spots" of high local abundance. Other notable endangered species that have been brought back from double digits have been in populations that were clumped in one or two small locales where they were easy to find it was possible to directly manage them.
The relative inability to turn IBWO-putative auditory detections into sightings is something often cited by skeptics as evidence the bird isn't really there. There is a logical problem, however, in assuming a sound should be trackable to its source. Something is making Campephilus Double Knocks in southern bottomlands.
The hypothesis that these Double-Knockers are Pileateds is a weak one to me, because A) we are talking about a characteristic Double Knock, not hitting a tree twice in succession B) the Double Knocks in question are not interspersed with normal Pileated calls and C) nobody has reported hearing Campephilus-like Double Knocks within Pileated range but outside of potential Ivory-bill range.
Let's ignore these problems, however. If the sounds should be readily trackable and Double Knocks are coming from Pileateds, shouldn't we be able to track them down and observe them actually making the sound? Some of the Ivory-bill sightings have come after tracking down Double Knocks - surely someone could have found a Pileated and observed it making the Double Knock if it were the source.
Lacking a credible alternative source for Double Knock sounds, you'd think scientifically-minded skeptics would hold off on the pronouncements of the Ivory-bill's demise. There's nothing wrong with science not having the answers yet.
Emu --
The double knock thing is a real frustration; I've written a lot about it earlier in this blog of course. The fact that no one has been able to spot the source, whatever it is, is very annoying. Sightings that happen within a few minutes of the sound are not definitive, of course. Part of the Pileated problem is that you are ALWAYS near a Pileated in these environments. They tend to be packed in at many pairs per square km, so you are hardly ever more than a few hundred meters from one.
I have personally met people who, combined, have had good sightings of ~10% of the 100 remaining birds in the U.S. And that was just in some scattered spots in LA and AR. What are the odds on that?
Coyle --
Of course I'm only dealing with sightings by experienced, careful, psychologically stable bird people. It's hard enough to figure out what to make of this small pool of sightings without throwing in the general hunting and fishing public, the treasure hunters, the emotionally unstable, etc. The good sightings I know of by people fitting the former description don't require more than a few birds in a few places at best.
100 seems to be extremely low considering the number of reports, the amount of suitable unsearched habitat and the (now) extremely secretive nature of the species.
But as you say Bill, if the population were that high, surely there would be some better (concrete) evidence? This is a sticking point for me - the numbers being encountered in the vast tracts of forest must indicate a reasonably large population, or have searchers been 'unbelievably' lucky?
Well, I stand corrected, in part, on the areas. Perhaps half a million square miles of RCW range, but thousands of square miles of habitat. I think the same argument goes for potential IBWO habitat--old growth Baldcypress swamp or whatever--a much smaller proportion of the entire Southeast. (Lester Short's hypothesis: Longleaf Pine was important for the IBWO, just as for the RCW. Food for thought.)
I think the "clumpiness" argument is completely valid. If any IBWO are present, and breeding, an initial "detection", of which there are allegedly plenty, should lead in many cases to finding more birds, nests, etc. For the RCW it happens all the time, for the IBWO it has not in the past 60 years. To me, that is telling.
Likewise, the IBWO was supposed to have distinctive sign (bark stripping, nest holes), and this, if valid, should lead searchers to get good sightings, but it has not. (With the RCW, the distinctive nest cavities, likewise, lead one to look for the birds.)
I'd like to address the "IBWO is nomadic" hypothesis, too. Like most birds, I'm sure young dispersed, often colonizing new habitat, but that is not nomadism. The population in the Singer Tract was followed for decades. That does not sound nomadic to me. This is mentioned in Allen's paper.
Really, I'd like to know where all this is going. Is the conclusion, as always, that more searching is needed? It's been going on for sixty years, really, 100, since the bird really declined in the late nineteenth century.
Cotinis -- I'm not going to keep belaboring the differences in life history etc. between Ivorybills and Red-cockadeds. My goal here is not anything exhaustive or precise; as I said from the get-go its a back-of-the-envelope order-of-magnitude estimation. And as such I think your counter-example actually reenforced it. The same simple model that predicted that a very small residual population of Ivorybills would be exceedingly difficult to detect even with extensive surveys predicted that Red-cockadeds should be found all the time. Which they are.
Where is it going? Why do you ask me this? I have no influence over what agencies and NGOs do with their time, cash, and other resources. Nor do I stand to benefit or suffer personally to any great extent from whatever decisions those groups make. If you ask the IRS I think my total net income for all my Ivorybill searching has been about $200 spread over three years. I'm just one individual birder and the owner of one Little Red Blog. If those are your concerns you'd be better spending your time lobbying people who actually have some say in those matters.
It seems odd, though, that you would think that the conclusion that might be derived from a model that indicates that phantom-level Ivorybills would be damn near undetectable is that we should keep searching just like we have been. Remember the story about the potato farmers? If not, google back in my blog and you will find it. I've always been a proponent of not just planting more potatoes.
I will have another post at some point about what I think the birding community as a whole might voluntarily do about this bird in particular and about their pervasive disregard for bottomland forest habitats in general. All conservationists agree that bottomland corridors are critically important habitats for birds and other wildlife; yet typical rank-and-file birders pay them scant attention. More on this in a future post (which will also likely be my final post on the Ivorybill unless some game-changing info comes to light).
The inability of searchers over the last 6 years to locate an active nest or roost, despite putative double-knocks and kent calls being recorded in search areas in early morning and late in the day, is a real toughie in my opinion. I merely consider that it is less of a challenge than explaining away the many clear observations of ivory-bills by highly experienced birders over the same period, among other things. There is nothing unscientific or idiotic about concluding that the bird is either extinct or extant from the available information.
I suggest that you read Tanner more carefully. I'm not sure where you get that the Singer Tract birds were "followed" for decades. Spencer brought the attention of the ornithological community to the area in 1932. Allen first visited in 1935, and the area was logged primarily from 1940 to 1945. By 1939 Tanner and Kuhn could find only 1 breeding pair in the tract, despite the fact that most of it remained unlogged. Tanner's own conclusion was that most of the birds had left. I truly don't understand why you would dismiss things like:
(1) The ivory-bill is built for distance. Is this in question? Why should a non-migratory woodpecker have such an unusual wing morphology?
(2) Tanner stated that "Considering all of the evidence, I believe that ivory-bills were not sedentary birds." p.35
(3) The Singer Tract was over 100 square miles. Tanner cited 2 examples in which ivory-bills apparently moved into areas with high tree mortality and left after a few years (p. 46).
(3) Richard Pough, who was sent to the Singer Tract to evaluate it for the Audubon Society in 1943-33, stated that, "I suspect that the ivory-bill never has been a sedentary species. It seems to me entirely possible that no forest, virgin or otherwise, has a large enough, concentrated enough and continuous enough food supply for them to be permanent breeding residents."
Regardless of our opinions about the status of the ivory-bill, I would like to think that reasonable people would agree that the conclusion of a nomadic or semi-nomadic bird is far from an outlandish one.
From Allen and Kellogg, 1937 (PDF), some emphasis added:
This [range] does not give one very important fact in the distribution, namely, that the birds are non-migratory and moreover they are probably sedentary. It is our belief that most individuals spend their entire lives within a few miles of the place where they are hatched and develop little Ivorybill communities. These, when left to themselves may develop such local abundance as reported by early observers and give a wrong impression of the general status of the species. On the other hand, one not knowing the exact whereabouts of one of these communities might search for days [note: days, not decades] in suitable forest cover within a few miles of the right spot without discovering the birds. The birds which we discovered in Florida were within a mile of the place where a hunter reported having seen three and shot one three years before. The birds discovered in Louisiana in 1935 were apparently close to the spot where Beyer (1900) reported collecting seven specimens nearly forty years previously; the place had been known to local residents for fully as long and had been reported by Pearson in 1932.
The Singer Tract population had been known to locals and ornithologists from 1900 until the last bird was seen in 1944. That is decades, and it does not sound like that population was nomadic. Though Tanner thought they left, I think he was being optimistic--it is quite likely they died there, with surrounding habitat degraded. Who knows? ( Allen documented a Florida population that was noted for several years as well.)
Another note. It has not been six years that an IBWO nest/roost has been documented well, it has been 66.
The Tanner versus Allen and Kellogg passages have been argued back and forth at each other many times in the past. You can pick your quotes; but you also should seriously consider that the species' behavior might have varied under different conditions and in different environments. I'll just throw a third quote into the mix:
"It does not remain long in one place, and during the day ranges over an extended territory." Frank M. Chapman, Handbook of Birds of Eastern North America (first published 1895; I have the 1939 edition).
But even taking the most sedentary quote, the A&K one, my results are the same. They say that it remains within "a few miles." My scenario suggested that finding a bird even when you are within its home range is daunting and consistent with results from recent intensive searches. The home range I used was 10 square miles, which is a square 3.3 miles on a side or a circle with a radius of 1.8 miles. In other words, a bird that remains within an area only a few miles across. Nor did I assume special wariness above and beyond that of any other average woodland bird. I reiterate my main point that birders DRASTICALLY overestimate how efficient we are as bird finding machines, especially in forests.
In sum -- even if the birds generally remain within "a few miles," and even if you have managed a real bona-fide detection of a lone Ivorybill who moves around within a home range this size, you will STILL have a hell of a time relocating the bird. Your results would be expected to be very similar to what Cornell experienced in their first search year, and what we experienced at Moss Island over two years.
Dude, the site where Beyer collected birds "close to the spot" in the Singer Tract was at Big Lake in Franklin Parish, at least 20 miles away. But my point was not whether we could engage in dueling quotes, or whether the Singer Tract was continuously inhabited by ivory-bills from 1900 to 1940 (I think it was). My point was that surely in agreeing with Tanner and Pough I am not unreasonable in surmising that the species was not generally sedentary? You seem intent on arguing that your position is right and the three of us are wrong. I am merely suggesting that our inference is reasonable.
Post a Comment
<< Home