Variable resonance in constant frequency bats



Bats of the two closely related families Rhinolophidae and Hipposideridae, and also Chilonycteris rubiginosa of the family Phyllostomatidae, emit echo-location pulses with a relatively long portion of constant frequency followed by a rapid frequency sweep. The greatest amplitude occurs either during the constant frequency or at some point in the sweep with the constant frequency at a lower amplitude. Two hypotheses are advanced to account for the changes in frequency of peak amplitude: a variable vocal tract resonance or “source generated” amplitude changes, and their relative merits are considered. The importance to the animals of high amplitude frequency sweeps is discussed, considering the conditions under which they are produced and whether the echoes from such pulses can be detected.