Ivory-bills were known to be noisy birds. They produced three major sounds: a loud double-rap, a "kent" call powerful enough to be heard (under good conditions) nearly a quarter-mile away, and a loud wooden wing sound. When the birds were around, observers often reported hearing two or all three of these sounds within a short time.
In Cornell's 18,000 hours of audio data from Arkansas, they recorded some kent-like calls (in an area where Blue Jays were observed making kent-like calls). They recorded some double-knocks, but the recordings are a poor match for verbal descriptions of the Ivory-bill double-rap. They don't mention recording any loud wooden wing noise, and they don't mention any double-rap ever being recorded in conjunction with a kent-call.
If Ivory-bills were present, I would expect some of the ARUs to record a combination of Ivory-bill sounds. Sometimes, I think they would record kent calls, some double-raps, and maybe some loud wing noise within a few minutes. It seems very unlikely that an Ivorybill would produce only some kent-like calls, or only a double-rap or two, while never producing the other sounds while within range of the ARU. I just don't think they could be wary enough to avoid an ARU.
Of course, Blue Jays can make kent calls, but are unlikely to produce double-raps or loud wing noise. And of course, Pileateds can produce double-raps, but not kent calls or a loud wooden wing noise.
Overall, I think Cornell's sound evidence significantly weakens an already-weak case for Ivory-bills in Arkansas.
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Note that you can hear the Ivory-bill's wooden wing sound in John Fitzpatrick's presentation here. He plays a short 1935 audio clip about 2/3 of the way through, near the end of the section on the Luneau video. This short clip, recorded at a nest hole, contains kent calls, some tapping, then the wooden sound of the Ivory-bill flying away.
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