Rich and NatureRecordists:
Klas' reply prompts me to add to this thread. In 1999 I had the pleasure
of working with Dr. Michael Garstang, a meteorologist who was interested
in recording elephant vocalizations. He pointed out something that all of
us NatureRecordists have known, but which few of us has really stopped
to realize: that surface air turbulence and winds have circadian rhythm,
being minimal at dawn and dusk, and that temperature inversions are
most apt to occur at such times. Of course, one consequence of temper-
ature inversion is that sound is "channeled" or "ducted" along the surface.
We also know that low frequencies travel further than high frequencies,
as evidenced by the spectral difference between the "crack" and "rumble"
of nearby and distant thunder, respectively. Combine this with the mini-
mized turbulence, and you have a formula to favor evolution of acoustic
communication systems which, for long distance efficacy, use low
frequencies and do so primarily at dusk and/or dawn.
Good recording,
Randy
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