Delving into Tree-Cavity Ecology
I want to believe that the principle investigators involved in the various ongoing searches for the Ivory-billed Woodpecker are carefully reviewing the rich scientific literature on tree cavities: their formation, ecology, natural history, and use by a variety of wildlife (not just birds)--and incorporating that body of knowledge into their investigations of tree cavities, one of the pieces of “evidence” being put forth in support of the hypothesis that the Ivory-billed Woodpecker still survives.
Unfortunately, many of the reports that have appeared online suggest that this may not be the case. For example, in all of the discussions about "interesting," "large," and "potential" Ivory-bill cavities there seems to be an unstated belief that only the Ivory-billed Woodpecker could be responsible for such "large" cavities, while conveniently overlooking the reality that woodpeckers are just one of many factors (and possibly one of the least important ones) responsible for the formation of tree cavities, and that other species of wildlife commonly use cavities as large as, or larger than, those excavated by Ivory-bills.
As but one example, raccoons, a common mammal that ranges throughout the known historical range of the Ivory-bill, are said to prefer tree cavities with 5 to 10 inch openings. A study conducted at the Muscatatuck National Wildlife Refuge in south-central Indiana and published in the Journal of Mammalogy found that "Den sites of raccoons did not appear to be a limiting resource in winter because of a large number of unused cavities." I wonder how all those "large" cavities were created?
Unfortunately, many of the reports that have appeared online suggest that this may not be the case. For example, in all of the discussions about "interesting," "large," and "potential" Ivory-bill cavities there seems to be an unstated belief that only the Ivory-billed Woodpecker could be responsible for such "large" cavities, while conveniently overlooking the reality that woodpeckers are just one of many factors (and possibly one of the least important ones) responsible for the formation of tree cavities, and that other species of wildlife commonly use cavities as large as, or larger than, those excavated by Ivory-bills.
As but one example, raccoons, a common mammal that ranges throughout the known historical range of the Ivory-bill, are said to prefer tree cavities with 5 to 10 inch openings. A study conducted at the Muscatatuck National Wildlife Refuge in south-central Indiana and published in the Journal of Mammalogy found that "Den sites of raccoons did not appear to be a limiting resource in winter because of a large number of unused cavities." I wonder how all those "large" cavities were created?
posted by John L. Trapp at
2/11/2007 10:14:00 PM
16 Comments:
both Cornell and Auburn are well aware that large cavities can be caused by a number of factors and critters -- that is exactly why they can only be called 'interesting' and not in any way diagnostic.
By "interesting" they surely mean useful in some way.
A large cavity without an IBWO tied to it is USELESS. Well it's useful for one thing, stringing along gullible believers.
It's all part of the mountain of garbage the "rediscovery" is teetering upon: lousy views, video of pileateds, frame grabs of some sort of bird, sounds of something that sounds like sounds that might be IBWOs!!!
Take away the faith people have in these shaky observations and there's nothing left.
Okay, cyberthrush, I'm willing to give Cornell, Audubon, and others involved in the search for the IBWO the benefit of the doubt on this, but I still think the repeated references to "interesting" cavities on Web sites and in the media raise false expectations in the eyes of the genral public and are perhaps just a bit misleading.
John,
I agree with you 100% on this. A quick look at online photos that have been held up as examples of "interesting cavities" reveals a number that were very clearly NOT made by woodpeckers of any species. To me, better than 50% of Hill's cavity photos are non-woodpecker! Many are holes created where branches broke off. IBWO's apparently dug holes directly below broken branchess, but certainly not in them. This isn't to say that animals didn't do some of the work or that an IBWO couldn't roost in one, but these are absolutely not cavities created by IBWO's or even PIWO's. It is little things like this that continue to chip away at my hope that anyone is really seeing IBWO's.
I'm with Cyberthrush. Cornell and Auburn both know full well that even the most promising looking cavities are more likely than not to either be empty or in use by other organisms. I've visited both sites and talked extensively with everyone down there and most of them are the biggest skeptics of all. But without checking as many of these cavities as you can, you're relying almost completely on dumb luck to bring the bird into your path while you have the camera out.
Why would you give them the benefit of the doubt? On what reasoned logic could you possibly give them the benefit of the doubt?
Or are you just playing nice and humoring Cyberthrush?
How many "interesting" large-holed cavities do the various teams have to investigate without finding IBWOs in them before large holes stop being "interesting"? What is so "interesting" about the large holes if in several years of searching nobody has ever found IBWOs in them?
Anonymous asked, Why would you give them the benefit of the doubt?
The principal investigators are all accomplished scientists. I would hope that they would approcah their study, investigation, and analysis of tree cavities objectively, without preconceived notions about how they were formed or what kind of critters might be using them, and have done their homework by reading what has been published about tree cavities. If nothing elese, the IBWO searches could result in a useful survey of cavity use by wildlife, if conducted properly. But by focusing only on "interesting" and "large" cavities they have already introduced bias into whatever results they might produce.
And yes, it always helps to be diplomatic.
Oops! In my first comment (the 3rd on thei post), I accidentaly typed "Audubon" instead of "Auburn." I meant to say, "I'm willing to give Cornell, Auburn, and others . . ."
The birdchaser asked, What is so interesting about the large holes if in several years of searching nobody has ever found IBWOs in them?
The level of "interest" in these "large" holes should diminish rapidly. I sense that the focus is already shifting to trying to confirm kent calls and double-knocks.
Some excerpts on acoustical surveys from Summary and Conclusions of the
2005–06 ivory-billed Woodpecker Search in Arkansas, available here.
In January 2005 an ARU in the WRNWR recorded kent-like calls that were suggestive of IBWO vocalizations. For a more detailed analysis of these sounds, see Charif et al. 2005. However, it is also possible that these calls were produced by a Blue Jay. ...
During the ongoing review of ARU recordings, Blue Jay calls with similarities to kent calls have been identified, but again this has not yielded a recording similar to those of January 2005. Nonetheless, it still cannot be ruled out that the ARU-recorded kent calls are a rarely occurring call of Blue Jay.
...
[Discussion of double-knocks]
As noted in the results section, we believe that duck wings produce double-knock sounds with surprising frequency. In the field, we have observed Gadwalls and Mallards producing double knocks both in flight and during a short wing whir given while on the water, directly after preening. ...Yet some apparent duck-generated double knocks are surprisingly crisp and may be mistaken for woodpecker knocks, especially at a distance. Some of the sounds of unknown origin presented by Charif et al. (2005) may be duck knocks.
Because our understanding of alternate sources for sounds (especially flapping ducks) has evolved over the course of this last field season, we are presently reviewing the classification of all A and A4 double knocks to ensure that they are classified with consistent criteria. Although many of our possible double-knock recordings may eventually prove to originate from alternative sources, there remain a small number of double knocks (Table 4) that meet most or all of the above criteria and remain as possible additional evidence of IBWO in the study area. Results of theses analyses will be presented in a separate report.
END QUOTES
I'm reading this as, "yes, the kent calls are possibly Blue Jays", and "the double-knocks are possibly produced by duck wings". How does anyone else read it?
What's left as evidence of the IBWO in Arkansas?
-Brief sight records not recording pertinent field marks (white dorsal stripes, white bill)
-A video, debatable at best, showing marks quite consistent with a Pileated on some frames.
-A truly extensive search in the 2005-06 season, with 100 + stealthy observers, with cameras--no good sightings, and no photographs
What's left to make anyone believe there were IBWO in Arkansas during this century? It's a serious question!
Video: In fact, I do not find one single character in that video (by this I mean real, repeated character) that is diagnostic of a PIWO. The alleged PIWO field marks that have been pointed out are all artifacts of the digital imaging process and/or motion blur. Conversely, there are some real, repeated characteristics of the bird that are inconsistent with a PIWO. Whether these are diagnostic of an IBWO is another matter, but the statement that the video shows PIWO diagnostic features is just flat not true (in my own evaluation). If you are interested in a third take on the video other than either the Cornell or the Sibley/Nelson axes, you can read the discussions on my own blog.
Cavities: I think y'all are confusing two separate ideas here. Item #1 is the search for cavities that, regardless of how they were constructed, might be suitable for use as roost holes by an IBWO and therefore might merit monitoring if you have some a priori reason to suspect that IBWOs might be in the area. Item #2 is the search for holes that might actually show features that indicate they could have been constructed by IBWOs. Though I think much of the popular press and many of the enthusiastic upstart freelance searchers have confused these two, I don't think the ornithologists and experienced birders are confused. Most of the cavity inventory and monitoring has been in pursuit of item #1. Only a precious few holes turn up that might be suggestive of item #2, if we even really know enough abut the species' life history to evaluate this. I don't believe any of the researchers you mention are actually thinking that the presence of large cavities by itself indicates the presence of IBWOs.
I'd have to disagree with you (politely), Bill, that the alleged PIWO field marks must be artifacts, and the alleged IBWO field marks are consistent. I see dark primaries and dark trailing edges to the wings of the bird in the Luneau video. I did an analysis of the video back in December, 2005 and posted it here on Nelson's blog. (I don't know Nelson, and am not part of any axis. I've also posted on Cyberthrush's blog--I actually know him personally and have birded with him--he's an excellent birder, and a heck of a good guy.)
I did that analysis independently, and I believe it is very similar to the analysis by Sibley et al. Do you really think that is a coincidence or part of some plot? I am not an ornithologist, but I have a lot of experience in digital photography and have done quite a bit of scientific image analysis when I was a researcher. This does not make me infallible, just somewhat experienced!
The compression artifacts that cause dark edges to light areas are not actually huge in the area of the bird because the focus is off. They are strong in the foreground (the canoe paddles) because the camera was focused close--a big error on the part of the searchers--they should have manual-focused to infinity.
A lot of Cornell's conclusions were based on the size analysis, and I just feel those are based on erroneous assumptions about the posture of the bird in the first frames, and, I believe, the famous "six-pixel" bird, which may not be real. In doing image analysis, I would never base any measurements on six pixels, especially if I knew they were out-of-focus pixels.
It is an awful video, at any rate, and I think at the only safe thing to say is that it is an unidentifiable black-and-white bird that was perched on a tree and flew off. Even Cyberthrush, the unflappable cheerleader for the IBWO (even pre-Arkansas sightings) does not put much stock in the video. He puts much more stock in the sight records. I did too, until I recently looked at them again. The best one was that of Gallagher and Harrison, and it is just very iffy. I posted some comments on that one on Birdforum. I don't think they ruled out some sort of waterfowl with a strong black-and-white pattern, either a Hooded Merganser or a White-winged Scoter. (Or perhaps it was the molting Pileated Cornell documented on their web site.) The sighting was brief, and they only noted the white patch on the wing, and not the white stripes on the back, despite getting a clear view. The other sightings were made under worse conditions and have even fewer details. (Sparling, I feel, saw one of the molting Pileateds.)
Again, I must emphasize I am part of nobody's axis. I post under my own name. (Google me, I'm all over the web.) I'm a lily-livered liberal who usually votes Democratic. I'm fairly active in my local Audubon Society and Land Conservancy. I'm very worried about global warming.
I've wanted to see an IBWO since I started birding in 1964 at the age of 5. I remember the hoopla over the alleged IBWO in the Big Thicket, and it had the same result as the current flap--no verification, no breeding population ever found. I was so happy in 2005 when the news came out, but I've come to the conclusion now that it was all wishful thinking. There would have had to be a breeding population somewhere, and breeding IBWO's would be a cinch to find at the nest. It hasn't happened yet, and at this point, I think it is not going to happen.
I think Cornell published their very preliminary findings too early because they were under a lot of pressure to do so, and they were sure they would get more verification soon. If you have not done so, you should read their 2005-06 season report--it is very upbeat in tone, but very discouraging in the details.
With best wishes to all...
Patrick and Bill:
Thank you for your contributions to this discussion.
Patrick --
The thing I note in the video is that those narrow black edges appear just as often on the leading edge of the wing as on the trailing edge, hence I conclude they are meaniningless artifacts. Same thing for the black wing tip -- there's just not enough resolution on a moving blurry wing to conclude anything about the shape of the black area at the bird's wingtip, a feature both species share. My conclusion is that we can't tell much of anything about the bird's underwing other than that it has a lot of white on it. I agree that Cornell's analysis was flawed and overly generous and that they got major things very wrong. But I still don't find any PIWO marks resolved on that bird, whereas I do see very clearly a flight style (not just wingbeat rate, but total flight style, especially the way the wings are held during the downbeat) that does not match any PIWO video I have seen. Does this match IBWO? We have no way at all to know this. The four existing still frames of IBWOs in flight can't be compared given the lack of context (Upstroke? Downstroke? Powered? Gliding?). In my dream world, someone gets an indisutable video of an IBWO in flight and the comparison can then be made. Until then...? I've got no argument with someone concluding the bird's speces can't be conclusively determined; I do however have an argument with claims that the bird either shows no features that are inconsistent with a PIWO, or shows features that ID it definitively as a PIWO. You and I are actually not as far apart on that matter as it might at first appear.
I actually was impressed with the 2005-2006 report, in that it represented a major breakdown of Cornell's wall of secrecy and a far more honest presentation of the situation. Though this seems to be a very unpopular position in the birding world at present, I am not so willing as many to just throw out all the sightings, both in AR and in FL. I feel that does violence to one of the foundation pillars on which we all collectively built late 20th Century birding/field ornithology. Having spent quite a bit of time in those environments, I am perhaps also less troubled than most by the notion that a very small population of flying needles could evade detection in that enormous tangled haystack for a very long time... though not forever. If no one comes up with a photo by the end of this summer, I will be more worried; and by 2008 I'll be agreeing that whatever was in AR in 2005, there probably aren't any IBWOs left anymore. Until then I am still going with the working hypothesis that the BDV bird really was a male IBWO, unmated, untethered to the area, probably wandering widely over the months or years to make a living in fragmented and suboptimal habitat, and that there easily could be a few others like him, survivors from occasional succesful matings in patches of habitat (such as maybe hurricane scars?) that provide enough food in a small enough area for a few years to get off barely enough fledgling to keep the species limping along.
That's not all that unreasonable a hypothesis, really.
A p.s....
Interesting thing to ponder: What happens if we do get an iron-clad IBWO confirmation? We're still stuck with a species that, on the whole, we don't know how to find, living we don't really know where, doing we don't really know what. But to make matters worse, we then do know that it is out there, SOMEWHERE, and we really have to figure out how to manage the recovery of a phantom. You thought things were weird NOW...
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