Vespadelus pumilus     VEPU

Characteristic frequency 50 up to 58 kHz.
Curved often with prominent up-sweeping tail.
Overlaps with other species though calls with end frequency higher than 55 kHz can successfully be identified as V. pumilus.

Here is a typical high frequency bat with clear up-tails.

VpumM00306, 121230 23:56:39, Sawtell, Google Earth

VpumM00590, 121231 03:56:09, Sawtell, Google Earth