Appendix D Terrestrial and Aquatic Biodiversity - Environment ...

SZ247: Bat survey from the Western Desert Resources Towns River project area, NT
A single bat species may produce more than one call type (e.g. search phase calls,
approach phase calls, clutter calls) that might suggest the presence of more than one
species. With sufficient experience of related species, it is generally possible for a bat
echolocation specialist to take this into account, and to base identifications on the
typically more diagnostic search phase calls.
Absolute abundance of each species or call type at a site cannot be estimated from bat
detector recordings because it is not possible to distinguish between relatively few bats
passing the detector but contributing many calls, and a larger number of individuals
passing the detector with each contributing relatively few calls.
Finally, it should be noted that in all acoustic surveys the 'detectability' of each species
is influenced by several factors such as bat detector model (microphone sensitivity
profile and zone of reception, mode of recording, and the type of built-in preamplification
and filter components), atmospheric conditions and characteristics of echolocation calls.
Species that produce ultra-high frequency (> 100 kHz) calls or those that produce calls
with low amplitude (e.g. long-eared bats Nyctophilus spp.) will have relatively short
detection distances, which will lead to their being under-represented or even missed
altogether in an acoustic survey. The detectability of different call types is also
influenced by atmospheric conditions, most notably relative humidity and temperature
that act together to attenuate ultrasound, the effects of which are dramatic at higher
frequencies (e.g. Armstrong and Kerry 2011). Thus, acoustic detection represents
only one component of a comprehensive survey approach for bats, and targeted effort
is required for species with lower acoustic detectability.
3.5 Trapping
Not all bat species in the Northern Territory can be identified reliably from their echolocation
calls (Milne 2002), and there are several species that must be captured in order to make an
unambiguous identification. In addition, trapping is recommended to obtain a more complete
inventory of bats in a given assemblage because of several biases in the acoustic survey
technique (e.g. Duffy et al. 2000; see also point 4 in section 3.4). Trapping was conducted
on four of the five available survey nights (31/1/2012 – 3/2/2012) using mist nets and harp
traps. This activity was conducted under a permit issued by the Northern Territory Parks and
Wildlife Commission (permit number 43654), and all procedures were approved by the Animal
Ethics Committee of The University of Adelaide (project number S-2011-195).
Mist nets were placed over pools and rivers to maximise the chance of capturing bats.
Previously Milne et al. (2005) and Milne (2006:79) had identified greater richness of bats in
riparian and adjacent areas, and it was anticipated that high flying species such as
Saccolaimus would be more likely to encounter a mist net set over water than one set in open
woodland. Three mist nets were arranged in an 'N' configuration over a small creek
(Melaleuca viridflora +/- Eucalyptus microtheca Low Open Woodland; site M01; 31/1/2012);
three nets were strung across a wide flowing river in the south-east corner of the project area
(Melaleuca viridflora Low Open Woodland; site M02; 1 – 2/2/2012); and a single net was
strung across a pool in the Towns River (Melaleuca nervosum Low Open Woodland; site M03;
3/2/2012). Vegetation habitats are defined as per the vegetation survey described in the
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