Note that Collinson's observation on flap rate is similar to mine here:
For another thing, Cornell has a single data point for the wingbeat frequency of a fleeing Ivory-bill, and that claim may also be bogus.
The 1935 wingbeats (analyzed by Cornell here) may not be the wingbeats of a fleeing Ivory-bill. The recorded sounds may have been made by an agitated Ivory-bill fluttering near the nest hole.
Listen to the wingbeats here (WAV format). Why do the wingbeats stop abruptly? Note that the eighth wingbeat is still fairly loud, and although the recording continues, no further wingbeats are heard. If the bird was really fleeing, why don't we hear (and why doesn't the spectrogram show) wingbeats 9, 10, etc?