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From: troach@netcom.COM (Tom Roach)
Newsgroups: sci.bio
Subject: Bat's sonar revisited
Keywords: bat sonar resolution chirp
Message-ID: <1991Jun13.210934.16333@netcom.COM>
Date: 13 Jun 91 21:09:34 GMT
Organization: Netcom - Online Communication Services  UNIX System {408 241-9760 guest}
Lines: 34

I have given some though to the interesting postings on sonar
capabilities of bats I read recently.  In at least one posting there
were claims of bats being able to distinguish "temporal" differences in
the 10 nanosecond range.  I know little about bat's sonar and just a bit
about human radar.  Still I would question any such claims.  There is no
doubt that the bat can catch insects on the wing, and there is a fairly
good presumption that it uses sound, and "chirped" sound at that, to do
this.
 
For a bat, or anything else, to be able to distinguish a 10
nanosecond differential in time of arrival of a sound wave is difficult
for me to believe.  There would have to be an incredible lack of "noise"
in the signal, given the speed of sound, for it to make useful phase
comparisons at this level.  Also even if it could resolve phase
differences this accurately, such information apparently must be
transformed into something that results in changes in wing attitude and
even more likely, the content of its "chirp", before such information
would result in actions leading to the bat catching the insect in its
mouth. I am also thinking that the speed of nerve impulses and the
physical changes in wing shape, angle or whatever are far too slow to
profit from such incredible resolution, even if it existed.  If this is
the case, then evolution would be unlikely to result in changes which
would generate such "overkill".
 
Sharks apparently use a combination of magnetic, aural, and visual
information to capture prey.  Has any work been done to see if the bat
has additional sensors, or uses multiple sensory systems in catching
insects?
 
Anybody out there with more information, or better yet, an explanation
to discount/explain anything I have said above?
 
Tom Roach