"Fangsheath" on BirdForum has recently posted the following data from his own testing of Ivory-bill vs. Pileated tree gouging, coinciding more-or-less with ongoing work being done by Steve Holzman and Paul Sykes (see "Ivory-bill/Pileated Grooves" past post in left-hand side-bar). This is a new line of study which will hopefully prove helpful in the field at some point (if not already) :
"I have now completed synthetic beaks representing the largest published southern pileated and smallest published northern ivory-bill. With these and my previously fabricated beaks representing the averages for each species have have been gouging away in balsa wood. Here are the results for gouge width (n= 20 gouges for each data set). Five width measurements were taken on each gouge and averaged.Possibly some of you out there, depending on where you live, can start putting this sort of info to use immediately!
average pileated - mean = 2.93 mm, range = 2.44-3.40 mm
largest pileated - mean = 3.50 mm, range = 2.85-4.04 mm
smallest ivory-bill - mean = 4.20 mm, range = 3.74-4.64 mm
average ivory-bill - mean = 4.40 mm, range = 3.77-5.25 mm
From these studies I would expect some species overlap in gouge width on individual gouges, but this appears to be eliminated by measuring at least 10 gouges and averaging. To be safe I would recommend measuring 20 gouges. I understand that some people are searching for ivory-bills as far north as Illinois and Indiana (which I think is perfectly reasonable). The pileateds up there may be larger and gouge width correspondingly greater for that species. However, the wider gouges produced by ivory-bill beak are not merely due to its larger size, but especially the result of its distinctive flat-sided shape.
I reiterate that gouges consistently greater than 3.5 mm should be regarded as suspicious, those greater than 4.0 mm should be regarded as highly suspicious, particularly if accompanied by unusual sign such as scaling of very tight-barked trees or excavation of still-living trees."
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2 comments:
That's really interesting. I'm surprised the widths aren't more different, given the different sizes of the birds. I guess the tips of the beaks are not all that different.
Has anybody been able to look at the length of the marks? The IBWO has a longer beak than the PIWO.
I do not know of any field data on gouge length. I have noted some very long gouges that were almost certainly pileated work. There is a possibility of a difference in gouge curvature, at least on deep excavations. Pileated gouges that I have seen tend to curve downward noticeably toward the center of the tree, the suspected ivory-bill gouges I have seen less so. This is something I will be looking at.
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