> Why do you think that it isn't a bat? Look at the other spectrogram I
> mentioned above or slow down the recording and listen.
Even from just the power spectrum, it's not a bat. The sharp peaks show a
constant frequency and the "band" is because the algorithm is not perfect.=
Bat navigation calls are generally of two types, frequency modulated and
constant frequency (FM and CF). Bat social calls vary with the species, but=
are often atonal at frequencies generally lower than the echolocation
frequencies.
FM calls have a rapid downward frequency sweep over a wide frequency range.=
CF calls, as with horseshoe bats, are a peep emitted at a constant frequenc=
y
with a "grunt" at the start and finish. Some bats such as pipistrelles
combine both types with a sweep ending in CF.
On a heterodyne (frequency shift) detector, flight movement with a CF call=
produces an exaggerated doppler shift which is very useful for showing
movement and which can be used to calculate flight speeds. Going back to th=
e
original question, a passing bat would not give a sharp frequency peak,
whatever the species.
See:
http://en.wikipedia.org/wiki/Bat_detector
and
http://en.wikipedia.org/wiki/Bat_species_identification
David Brinicombe
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