Picture 1

0805-1 (5.5s, mp3).
A pulse train preceded by what appears to be a broader than usual pulse. The pulse train has a frequency of about 10 hz. On closer inspection, the leading broad pulse is itself a unusually rapid fire pulse train, with a pulse frequency of about 100 hz (see picture below).

Picture 2

0.3 s region of Picture 1.
0805-1b (0.8s, mp3).
Closeup of the very fast pulse train leading the main pulse train (the 2.25s region of the previous plot). One counts at least 10 pulses in 1/10 th of a second, or faster than 100 hz. The sound frequency within each pulse is 2.25 khz * 16 = 36 khz.

Picture 3

0.35 s region of Picture 1.
Closeup of a faint sound preceding the first pulse (Picture 2). The 36 khz sound is already visible, as well as pitch bands an what appears to be quick pitch doubling transition (from 6 to 12 khz). This also indicates that many, if not most, of the fainter signals in the background may also be bats, receding or too far away.