Aug 24 audio information weakens Cornell's case?

Ok, I listened to the January 24 double-knocks and took a look at the sonograms. In my opinion, these double-knocks are a very poor match for the detailed IBWO double-rap description from "The Grail Bird" (see snippet far below).

For one thing, the second knock of the IBWO is supposed to be "nowhere near as hard". In the Jan 24 recordings, the second knock is actually louder than the first.

For another thing, the spacing between the knocks is supposed to be about 75 milliseconds; the Jan 24 spacing looks more like 100 milliseconds to me. You might think that an extra 25 milliseconds of spacing is no big deal, but I think it is significant. Nancy Tanner (below) said that the spacing on a real IBWO double-rap is so close that some people heard them as a single rap. I can't imagine anyone hearing these knocks (spaced at 100 milliseconds) as a single rap.

A double-rap on wood is a very simple sound. If you record one with an ARU (autonomous recording unit), I think you have only two major variables to think about--the relative loudness of the two raps (ie, which of the two raps is louder, and by how much), and the spacing between the two raps. In the Jan 24 recording, neither of those variables is a reasonable match for The Grail Bird's double-rap description.

Of course, the other "half" of the audio information is the kent-like calls. Blue Jays sometimes make kent-like calls, and the IBWO made kent-like calls. I would argue it this way: in 20,000 person-hours in the woods, the searchers must have had thousands of conclusive sightings of Blue Jays, and they had zero conclusive sightings of IBWOs. Given that information, if you hear a kent-like call, it doesn't seem prudent to assume that an IBWO was the likely source.

Overall, in my opinion, the audio information presented yesterday considerably weakens Cornell's case that the IBWO survives. It's important to consider what the ARUs recorded, but I think it's just as important to consider what the ARUs didn't record.

If strategically placed ARUs recorded 17,000 hours of audio in an area where IBWOs live, I think you should expect to capture a good number of classic, "BAM-bam" double-raps, with something like 75 milliseconds separating the raps. The fact that these raps weren't recorded leaves me feeling doubtful that any IBWOs were present (although it's still possible). In 17,000 hours of audio, I'm wondering why you wouldn't capture some Pileated Woodpecker feeding knocks that would sound similar to the recorded Jan 24 double-knocks.
==============================
Below is some background information...

From this link on Cornell's web site:
----
The recording of a distant double knock followed by a single knock on January 24, 2005, is especially intriguing. Russell Charif, who leads the acoustic research effort, first heard the recording with woodpecker expert Martjan Lammertink. “I immediately felt a thrill of excitement when I heard the recording,” Charif said. “Martjan looked at me and said something understated, like, ‘That sounds really good!’” Charif said, however, that as he listened to the sound repeatedly, his excitement was tempered as he began to wonder about slight differences in the sound compared with scientific descriptions of Ivory-billed Woodpecker display drums.

For example, those descriptions mention that the first knock is louder than the second. In the recording from Arkansas, the second knock is slightly louder. However, there are so few records of these display drums that researchers do not know to what degree they may vary depending on the geographic location and the context in which they are used. Without any recordings of known double knocks, there is no precise reference with which to compare the mysterious sounds from the Big Woods.
----

Here's a paragraph from "The Grail Bird", page 40:
---
This BAM-bam is the characteristic drum of a Campephilus woodpecker, a genus found through much of South and Central America, with the ivory-bill being the northernmost representative of the group. "The second part of the double rap is so quick," said Nancy, "it sounds like an echo of the first and is nowhere near as hard." The space between the two parts of the double rap is only about seventy-five milliseconds, which is so close that some people hear them as a single rap. But the separate parts are clear if you look at a sonogram (a visual representation of a sound showing its pitch and duration).
---
"Nancy" in the paragraph above is Nancy Tanner, who was married to the ivory-bill expert Jim Tanner. Nancy Tanner heard real Ivory-bill double-knocks in the 1940s.