When discussing properties of bat calls, important parameters are
peak frequency (frequency of energy maximum)
and
characteristic frequency.

Characteristic fequency is according to sound science the same as resonant frequency but when it comes to bat calls that is no longer the case:

Call frequency – the characteristic frequency of a bat call in kHz; the ending frequency of the flattest part of a call (the body); one of the most useful call characteristics for identification.

 

The frequency of a sound at which the threshold of a single fibre of an auditory nerve is lowest and to which it is therefore most responsive. See also tuning curve. CF abbrev.

 

characteristic frequency: A frequency which can be easily identified and measured in a given emission. A carrier frequency may, for example, be designated as the characteristic frequency.