Appendix D Terrestrial and Aquatic Biodiversity - Environment ...

SZ247: Bat survey from the Western Desert Resources Towns River project area, NT
(the flattest part of the call, designated as Fpz in AnalookW software). Identifications were
made based on a comparison of pulse shapes and measurements with those in Milne (2002).
The recordings made with the D500x detectors were analysed using a hybrid automated –
manual approach, given the significant memory size of the dataset (42.6 GB from MLA –
Towns River; 26.9 GB from Rosie's Camp – Bing Bong) and the lack of a reference library set
of calls in full spectrum format from the study area. Firstly, the WAV format files were
converted to Zero Crossings files compatible with AnalookW software using the Anabat
Converter ver. 0.3 Java batch utility written by Sikken (2012) (using automatic thresholding in
50 ms chunks). Subsequently, the dataset was further reduced by employing a filter to
exclude ZCA files containing only noise (relevant settings being: Smoothness 50, Body over
2000 ms, Fc and Fmin 10 kHz minimum, Fmax 10 kHz minimum, Slope S1 -9999 to 9999,
Duration 2 ms minimum). The resulting subset of ZCA files was examined in AnalookW
software in a similar fashion to those recorded directly by AnaBat detectors. It is
acknowledged that the WAV to ZCA batch conversion software does not perform as well as
AnalookW software (K.N. Armstrong unpubl. obs.), and both programmes cannot readily
distinguish calls buried in the sound floor, however for poorer quality ZCA files the
spectrographic representation in the corresponding WAV file was examined to assist in the
identification.
The search phase echolocation calls of S. flaviventris and S. saccolaimus are very similar in
structure and characteristic frequency, but both are readily distinguishable from molossid bat
species based on their harmonic structure. In situations where calls with a characteristic
below 25 kHz had features indicative of either Saccolaimus spp., Chaerephon jobensis or
Mormopterus beccarii, the harmonic structure was examined in the WAV files, with
Emballonuridae being distinguished from Molossidae based on the presence of a
fundamental component around 10 kHz. The molossid species were distinguished from
each other based on patterns of structure in successive pulses in the same sequence.
Particular attention was paid to call sequences of Saccolaimus that contained approach and
feeding buzz calls, given some apparent differences noted in Asia by Corben (2010). In
addition to details of that presentation, an unpublished AnaBat call dataset of S. saccolaimus
from Cairns generously donated by Greg Ford was used as a basis for distinguishing the two
species, but for nearly all call sequences, no distinguishing features were recognised.
Several feeding buzzes with characteristics of S. flaviventris were noted, but none of the
buzzes with relatively high characteristic frequency and serpentine pulse shape (cf. search
phase pulses) were observed.
3.4 Identification from acoustic recordings – limitations and considerations
Several caveats and considerations are noted with regard to the identification of bat species
based on recordings of their echolocation calls, of relevance to this survey:
Two or more bat species may produce calls that are so similar that they cannot be
distinguished reliably using the available methods or reference recordings (examples in
Milne 2002).
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