Appendix D Terrestrial and Aquatic Biodiversity - Environment ...

SZ247: Bat survey from the Western Desert Resources Towns River project area, NT
3.2 Acoustic detection
The ultrasonic echolocation calls of bats, which are produced for spatial orientation and prey
detection in flight, are useful for taxonomic identification because each species produces a
unique and distinguishable (in many cases; see Milne 2002 for examples in the Northern
Territory) signal type. Analysis of the recordings made using electronic 'bat detectors' can
reveal echolocating bat diversity at sampling sites with minimal effort as part of a
comprehensive approach to surveying bats. On the present survey, acoustic recordings
were made with AnaBat SD1 bat detectors (Titley Scientific, Brisbane), which were chosen for
their ease of use and deployment, and the efficiency of data storage; plus D500x full spectrum
recorders (Pettersson Elektronik AB, Sweden) that retain amplitude information and features
such as harmonic structure that can potentially be useful for species identification.
AnaBat detectors were waterproofed in plastic boxes, and microphones (ST1) on an
extension lead were placed in a funnel made from a plastic drink bottle to reduce the chance
of water exposure. The use of funnels reduces slightly the zone of signal detection, but was
unavoidable given the possibility of heavy rain. The D500x units were also placed in
waterproof boxes with microphones on 1 m extension leads and protected by a PVC pipe
(microphone was positioned flush with the edge of the pipe). The detectors were employed
as passive stationary data recorders, being set in position prior to dusk and collected after
dawn, and with the microphone capsule tied to trees at a height of c. 1 m. The equipment
was placed in a variety of habitats to maximise the potential to encounter all species present.
A GPS position was recorded at each recording site and associated with the serial number of
the recording unit and deployment date.
Echolocation signals from AnaBat detectors were divided by a factor of 8, and stored
automatically on a Compact Flash card, with each sequence of calls receiving a time and date
stamp. The sensitivity was set to around 7. The recording settings for the D500x were as
follows: sampling frequency 300 kHz, Pre-trigger off, Recording length 1 sec, HP filter yes,
Autorec yes, Trigger source 0, Trigger sensitivity 1 High, Input Gain 45, Trigger level 30,
Interval 0, Timer 19:00 – 06:00.
3.3 Analysis of acoustic recordings
AnaBat recordings were downloaded using CFC Read ver. 4.3s software. The output
consisted of two sets of data: 1. the individual sequence files produced during interpretation
by CFC Read software, which are organised into folders representing a single night’s
recording; and 2. the continuous representation of the AnaBat recordings in ZCA and MAP
files, which show all of the signals detected by the AnaBat microphone but which have not
been parsed into individual sequence files according to default interpretation parameters.
The signals in both parsed sequence files and the ZCA and MAP files were examined in
AnalookW ver. 3.8s software, and three parameters were measured on good quality search
phase pulses in a subset of representative call sequences: pulse duration (milliseconds),
maximum frequency (kHz) and characteristic frequency (the point at the end of the flattest
portion of a pulse before any terminal secondary frequency sweep; kHz). A fourth variable
was measured on Constant Frequency calls: the frequency with the greatest number of cycles
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