A couple have people have written to say they’re having difficulty hearing the calls on the raw clips from March 2, 2013. I’m posting an amplified version of the morning first clip. The clarinet toots and rustling will be quite loud, but the calls are definitely much easier to hear.
In addition to the calls at 0:03, 0:17, 2:04, 3:36, and 3:47, another much fainter call can be heard at 3:19. This call is so soft as to be barely audible on the unamplified version. This tends to support the strong field impression that the calls came from two distinct sources.
I’ve consolidated what was formerly an independent post with this one, since the point it makes a relatively minor and pertains to a subject area in which my knowledge is very limited.
I’m not able to use Cornell’s Raven sonogram software. I created the sonogram I posted here showing the last calls in the morning of March 2, 2013 series using AudioXplorer, a free program. Frank Wiley has run the first call through Raven (see below), and the results are interesting.
As with the other calls I’ve looked looked at, the duration is under 100 ms. This is consistent with the Singer Tract recordings. If I read Frank’s sonogram correctly, the third harmonic is stronger than the second. I’m no expert and am not unbiased; the readings are very faint, but that’s my impression. If this is correct, the harmonic structure is also similar to the Singer Tract recordings. The base frequency for this call is 925 Hz., while some of the others are slightly lower, approximately 910 Hz. The Singer Tract kents range from approximately 580-790 Hz. with most clustered between 610 and 690, so there is a substantial difference in that regard.
Edited to add: In listening again to various confusion species (most of which I think can be ruled out), I’m struck by the similarity between these calls and the “kek” call of a Cooper’s Hawk. But I don’t think these calls are from Cooper’s Hawks (and I’ve had nesting Coopers’ in the woods behind my house for years); they’re somewhat less harsh and have a slightly airier quality. They’re also unaccompanied by other Cooper’s Hawk calls and aren’t persistent. (And a couple of people don’t hear the similarity that I’m hearing.) While the similarities are not discussed in the monograph, Tanner mistook the calls of a Cooper’s Hawk for an ivorybill in 1937, after the Singer Tract recordings were made (Bales p.102).
This recording includes examples of the Cooper’s Hawk call I’m describing. The base frequency appears to be just over 1000 Hz, since it’s not visible on the sonogram when the slider is set to 1000 Hz maximum.
It’s also worth noting that Kuhn and Tanner seem to have believed they could distinguish the calls of the solitary male, known as “Mack’s Bayou Pete”, from the John’s Bayou birds (Bales pp. 153-157). On one occasion, Tanner wrote that Mack’s Bayou Pete, ” . . . yipped and pecked” (Bales p. 155).