Most bats also produce so called 'social calls' for communicating among eac=
h
other. These call types are different from the echolocation calls. They are
often lower in frequency (because lower frequencies are less attenuated at
long distances as higher-pitched calls) and have a more complex structure (=
more
intense harmonics and more complex frequency modulation patterns).
See http://www.avisoft-saslab.com/sounds/pipistr3.gif for an example of bot=
h
echolocation calls and social calls of a Common pipistrelle bat (the call a=
t
t=3D0.14 is a social call).
For more example see also
http://www.avisoft-saslab.com/sounds/sounds.htm#bats
As far as I know, the information that these social calls transmit is mainl=
y
encoded in the specific pattern of the single calls and less (or not) in
the repetition rate.
The varying pulse rate and duration's of the echolocation calls is mainly
determined by the physical limitations. As long as the bat is far away from=
a
target, the sound bursts have a relatively long traveling time. Bats usuall=
y
prevent to emit a new echolocation call as long as they have not received t=
he
echoes of the previously emitted call. So they have to wait for at least th=
e
time the sound requires to travel from the bat to the target and back to th=
e
bat. Therefore they can increase the pulse rate (and decrease the duration =
of
the single pulses) while approaching an insect.
Regards,
Raimund
> Somewhere in the archives there is a recording of the echo location sound
> used by a bat in persuit of prey. The repitation rate increases as the ba=
t
> closes on the prey. The recording has been modified to bring the sound
with
> in human hearing.
>
> Do bats have other frequency calls for bat to bat communication or is the
> echo location frequency specific to the species? Perhaps the size and
shape
> of the resinator in the bat's head sets the frequency. If so, then
> communication might be by pulse rate variation.
>
> Would Graham care to comment?
>
> Stuart.
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