Publications

The ghost bat (Macroderma gigas) is Australia's largest echolocating bat. It is restricted to several disjunct populations in the north of the continent, including a population in the Pilbara region of Western Australia. In 2016 the ghost bat was listed as Vulnerable under Australian federal legislation, owing to declining numbers across many regional populations. The most severe threat to ghost bats in the Pilbara region is the destruction and disturbance of habitat due to mining operations, but disturbance to their roosts from other infrastructure developments and changes to and loss of foraging habitat also pose significant threats. A set of research priorities for ghost bats in the Pilbara was developed during a workshop attended by mining industry representatives, environmental consultants, scientists and government regulators. Five research priorities were identified: (1) identify and characterise critical diurnal roosts and foraging habitat; (2) improve knowledge of the distribution, movement and dispersal patterns of ghost bats in the region; (3) improve knowledge of population size, persistence and long-term trends; (4) better understand the cumulative, direct and indirect impacts of mining and other development activities; and (5) better understand the threats posed by fence entanglements, cane toads and feral cats.

The Pilbara leaf-nosed bat (Rhinonicteris aurantia 'Pilbara form') is a threatened insectivorous microbat endemic to the Pilbara region of Western Australia. It is at risk of significant population decline, particularly due to habitat loss from mining. To address its key threats, stakeholders from a range of backgrounds collectively listed and prioritised research actions in 2013. This exercise was repeated in 2022 to evaluate and update progress of the research priorities. We conducted a review of scientific and grey literature (2013–2023) to: (1) identify the work undertaken to date that addressed the research priorities identified in the 2013 stakeholder workshop; (2) identify the current knowledge gaps in Pilbara leaf-nosed bat ecology, conservation, and threatening processes; and (3) highlight how these gaps relate to the newly ranked 2022 priority list for both research and management outcomes. We found that the 2013 research priorities were largely unaddressed, with most publications and unpublished industry reports in the review period primarily reporting presence or monitoring data around areas of interest to the resources sector, with minimal focus on the species' conservation or management directly. Therefore, the knowledge gaps identified in 2013 were still largely relevant in 2022. Further targeted research is required to meet the 2022 priorities and better understand the habitat characteristics, movement ecology, disturbance buffer requirements, and cumulative impacts of mining on Pilbara leaf-nosed bat colonies. Overall, targeted research beyond traditional mining outputs, changes to regulatory procedure, and collaborative, adaptive management, are key to supporting the long-term persistence of Pilbara leaf-nosed bats.

Feral cat predation is recognised as a significant threat to Australian wildlife that has contributed to population declines and extinctions. Cat predation of bats worldwide is a growing concern, though there are few studies focusing on Australian species. This research consolidated empirical evidence of cat predation on the threatened Pilbara leaf-nosed bat (Rhinonicteris aurantia) in the Pilbara region of Western Australia. Observations in video and camera trap datasets demonstrated repeated predation of R. aurantia by several individual cats at three significant roosts. Between 2020 and 2023, the study documented 183–200 bat kills at these sites. The authors recommend feral cat predation be formally recognised as a key threat to this species. To prevent declines at key colonies that would contribute to a population reduction, ongoing monitoring and proactive control of cats at known R. aurantia roosts should be prioritised. As demonstrated herein, camera trap monitoring is a valid method for quantifying the impact of feral cats at roost sites. Because relatively few individual cats at just a few sites can have a large impact, and most of the larger roost sites of R. aurantia have been discovered, there is potential for amelioration of this threat with multiple established and emerging methods deployed concurrently.

Abstract reproduced from the open-access article under CC BY 4.0 .

Genetic tagging from scats is a minimally invasive sampling approach used to guide management decisions and evaluate conservation efforts. This study presents a novel method for individual identification in the threatened ghost bat Macroderma gigas using custom-designed SNP arrays on the MassARRAY system. Researchers identified 611 informative SNPs from DArTseq data and designed three SNP panels containing 44–50 SNPs each. SNP genotyping and molecular sexing were applied to 209 M. gigas scats collected from seven caves in the Pilbara, Western Australia. The average amplification rate was 0.90±0.01 with low SNP genotyping errors (allelic dropout 0.003±0.000), enabling clustering of scats based on one or fewer allelic mismatches. The study identified 19 unique bats (9 confirmed/likely males and 10 confirmed/likely females) from maternity and transitory roosts, with two male bats detected using roosts 9 km and 47 m apart. Targeted SNP genotyping provides a valuable tool for monitoring and tracking non-model species through minimally invasive sampling.

Abstract reproduced from the open-access article under CC BY 4.0 .

The ghost bat (Macroderma gigas) is a carnivorous species of bat endemic to northern Australia that roosts in colonies up to 1,500 individuals. The ghost bat produces a number of social vocalisations, but little is known about the species' behaviour and what role social vocalisations play in interactions between conspecifics. The aim of this study was to construct an ethogram of ghost bat behaviours and determine the associations between vocalisations. To achieve our aims, we filmed the captive ghost bat colony (one male, five females) using four trail cameras installed within the enclosure over a six-week period, coinciding with the estimated mating season. Video recordings were examined by eye, and solitary and social behaviours were catalogued into distinct behavioural units (e.g. hang-alert, chew, wing-groom, etc.) along with context and associated social vocalisations if applicable. To assess associations between vocalisation types, we combined each of the six behavioural classes (eating, grooming, mating, huddling, flying, fighting) and used generalised linear models to determine which behavioural classes significantly predicted the production of vocalisation. There was a strong association between flight behaviour and member 'Chirp-trill' vocalisation by the male of the colony, suggesting a territorial or mate attraction function. There was also a strong association between fighting and 'Squabble', 'Rasp' and 'Grumble' vocalisations, with Squabble and Rasp likely representing levels of agonistic vocalisations produced by aggressive bats during altercations. The Grumble, on the other hand, was produced by the target of the aggressor and so may function as an appeasement call. The ghost bat's ethogram with its associated social vocalisations provides a formal basis for future behavioural studies of this species and can serve as a template for such studies in other echolocating bats. Our study revealed an unexpected degree of complexity in ghost bat behaviour and highlights the need for other kind of studies in this and other species.

Conservation is particularly challenging for species that are highly sensitive to disturbance and negatively affected by monitoring procedures. Australia's ecologically and culturally significant ghost bat (Macroderma gigas) has suffered substantial population declines, in part due to disturbance and loss of roost sites. This sensitivity poses impediments to studies of the ghost bat's ecology and behaviour, which in turn inhibits evidence-based conservation and management of the species. We used full-spectrum acoustic playback, in combination with thermal video recordings and netting, as a novel method to investigate the behavioural ecology of this enigmatic bat. We tested whether ghost bats are responsive to conspecific social vocalisations and, if so, whether responses differ according to signaller and receiver characteristics. Individuals were attracted strongly to two of four vocalisation types, and responses depended on sex, thus providing the first experimental evidence that the ghost bat's complex vocal repertoire has multiple functions. Responses did not differ with geographic location, indicating that our method can be used across the species' range. We discuss how full-spectrum acoustic playback helps improve our knowledge of the behavioural ecology of this species and highlight the applicability of our methods for targeting specific conservation needs in bats.

Reliable information on population size is fundamental to the management of threatened species. For wild species, mark-recapture methods are a cornerstone of abundance estimation. Here, we show the first application of the close-kin mark-recapture (CKMR) method to a terrestrial species of high conservation value; the Christmas Island flying-fox (CIFF). The CIFF is the island's last remaining native terrestrial mammal and was recently listed as critically endangered. CKMR is a powerful tool for estimating the demographic parameters central to CIFF management and circumvents the complications arising from the species' cryptic nature, mobility, and difficult-to-survey habitat. To this end, we used genetic data from 450 CIFFs captured between 2015 and 2019 to detect kin pairs. We implemented a novel CKMR model that estimates sex-specific abundance, trend, and mortality and accommodates observations from the kin-pair distribution of male reproductive skew and mate persistence. CKMR estimated CIFF total adult female abundance to be approximately 2050 individuals (95% CI (950, 4300)). We showed that on average only 23% of the adult male population contributed to annual reproduction and strong evidence for between-year mate fidelity, an observation not previously quantified for a Pteropus species in the wild. Critically, our population estimates provide the most robust understanding of the status of this critically endangered population, informing immediate and future conservation initiatives.

Abstract reproduced from the open-access article under CC BY 4.0 .

The ghost bat (Macroderma gigas) is a colonial and highly vocal species that is impacted by human visitation of caves. The ability to document behaviours inside the roost by recording vocalisations could provide an important new tool for the management of this disturbance-prone species by removing the need for in-person confirmation of reproductive activity, and, in turn, identifying roosts of conservation importance. To assess whether vocalisations are indicators of daily and seasonal behavioural events, we aimed to determine whether total vocal activity significantly varied by time of day and time of year and, further, how the relative frequencies of occurrence of three common social vocalisations ('Chirp-trill', 'Squabble' and 'Ultrasonic Social') aligned with previously reported seasonal reproductive behaviour. We recorded sound inside the largest known maternity roost, extracted all vocal signals and classified them into types using semiautomated methods. Total vocal activity varied significantly by time of day and time of year, peaking around sunrise and sunset, and during the mating and nursing seasons. The relative frequencies of occurrence of vocalisation types varied significantly seasonally, with the Chirp-trill and Squabble produced most during the mating season and first flight periods, whereas the Ultrasonic Social peaked during parturition and weaning periods. This timing aligns with a previously suggested vocalisation function, providing further evidence that these signals are important in mating and maternity behaviours. Further, this suggests that peaks in the relative frequency of occurrence of distinct social vocalisations may act as indicators of in-roost reproductive and pup development behaviours and provides a low-disturbance, semiautomated method for using long-term acoustic recordings to study and monitor behaviour in this sensitive species.

Significant biodiversity offset funds have been allocated towards conservation research on threatened species as part of the environmental approvals process for resource development in the Pilbara region of Western Australia. One of these species is the Pilbara leaf-nosed bat (Rhinonicteris aurantia Pilbara form), which is entirely reliant on roosting in a limited number of caves and disused mines, many of which exist in the mineral-bearing strata that are the focus of mining activity. A research agenda for the Pilbara leaf-nosed bat was developed during a workshop attended by scientists, environmental consultants and mining industry representatives. Five research priorities were identified: (1) collate existing data contained within unpublished environmental surveys; (2) clarify and better characterise the number and distribution of day roosts; (3) better understand habitat requirements, particularly foraging habitat, and the movement of bats between roosts; (4) provide more robust estimates of total population and colony size, and improve understanding of social behaviour; and (5) investigate appropriate buffers in a range of mining contexts and protocols for artificial roost construction. Meta-analysis of current data, confirmation of potential day roosts, and long-term monitoring of activity patterns would rapidly increase our knowledge of the Pilbara leaf-nosed bat to enable effective conservation actions.

The ghost bat (Macroderma gigas) is endemic to Australia but is under threat, with scarce information available on the genetic health of remaining populations. Here, we develop molecular assays for microsatellite genotyping and molecular sexing of non-invasive samples as a genetic monitoring tool to identify individuals, measure genetic diversity and investigate spatial and temporal patterns of habitat use by ghost bats. We identified novel microsatellites through high-throughput sequencing on the Illumina MiSeq platform. Of 48 loci tested, six markers were added to five previously developed microsatellite loci. We developed three Y-linked (DDX3Y, Zfy and SRY) and one X-linked markers (Zfx) to enable molecular identification of sex. To assess performance, all 11 microsatellite and four sex-linked markers were amplified in three multiplex reactions in 160 M. gigas faecal samples from the Pilbara region, Western Australia. The combined markers offered a high level of individual discrimination (PIDsibs = 0.00002) and we detected 19 bats in total (11 males, 4 females and 4 sex undetermined). The number of alleles per locus ranged from 5 to 14 and the average observed and expected heterozygosity across loci were Ho = 0.735 (0.58–0.91) and uHe = 0.785 (0.59–0.89) respectively. Our molecular assays allowed identification of individuals from faecal samples at multiple time points and spatial locations and enabled us to elucidate patterns of habitat usage at the study site. This study highlights the value of our molecular assays as a potential capture-mark-recapture technique for population monitoring for this species.

Assessing risk to threatened species from anthropogenic disturbances is challenging when species identification is problematic and biology is poorly understood. The bare-rumped sheath-tailed bat has an unclear distribution across northern Australia. This study presents empirical data for detecting this species across the region, critically analyzes acoustic identification methods, and assessed presence in tall Eucalyptus tetrodonta forest on Cape York Peninsula using trapping and acoustic recordings. Capture of other Saccolaimus species exceeded previous Australian surveys, demonstrating that high-flying bats in tall forests can be effectively captured with elevated mist nets. Reference echolocation calls from the study area and other northern Australian locations enabled characterization and comparison of low-frequency-emitting echolocating bat species calls. While multivariate statistics separated most species-specific search phase calls, similarity between S. mixtus and S. saccolaimus calls prevented distinction. A multi-method approach incorporating these recommendations will improve robustness in ecological studies and clarity in environmental impact assessments.

Effective land management and biodiversity conservation policy relies on good records of native species occurrence and habitat association, but for many animal groups these data are inadequate. In the Murray–Darling Basin (MDB), the most environmentally and economically important catchment in Australia, knowledge gaps exist on the occurrence and habitat associations of insectivorous bat species. We relied on the interest and effort of citizen scientists to assist with the most intensive insectivorous bat survey ever undertaken in the MDB region of South Australia. We used an existing network of Natural Resource Management groups to connect interested citizens and build on historical observations of bat species using a fleet of 30 Anabat Swift bat detectors. The survey effort more than doubled the number of bat occurrence records for the area in two years (3000 records; cf. 2693 records between 1890 and 2018; freely available through the Atlas of Living Australia). We used multinomial logistic regression to look at the relationship between three types of environmental covariates: flight space, nearest open water source and vegetation type. There were no differences in species richness among the environmental covariates. The records have been, and will continue to be, used to inform government land management policy, more accurately predict the impact of development proposals on bat populations, and update conservation assessments for microbat species. A social survey tool also showed that participation in the project led to positive behaviours, and planned positive behaviours, for improving bat habitat on private land.

We examined a recent notion that differences in echolocation call frequency amongst geographic groups of constant frequency (CF)-emitting bats is the result of a trade-off between maximising prey detection range at lower frequencies and enhancing small-prey resolution at higher frequencies in different atmospheric (relative humidity; RH) environments. Isolated populations of the endemic Australian orange leaf-nosed bat Rhinonicteris aurantia were used as an example since geographic isolation in different environments has been a precursor to differences in their characteristic echolocation call frequencies (mean difference c. 6 kHz; means of 114.64 and 120.99 kHz). The influence of both atmospheric temperature and RH on maximum prey detection range was explored through mathematical modelling. This revealed that temperature was of similar importance to relative humidity and that under certain circumstances, each could reduce the effect of the other on ultrasound attenuation rates. The newly developed models contain significant conceptual improvements in method compared to other recent approaches, and can be applied to the situation of any other species of bat. For a given set of atmospheric conditions, the prey detection range of R. aurantia was reduced slightly when call frequency increased by 6 kHz, but an increase in RH, temperature or both reduced detection range significantly. A similar trend was also evident in prey detection volume ratios calculated for the same conditions. Spatial volume ratios were applied to assess the impact of changed atmospheric conditions and prey size on foraging ecology. Reductions in detection range associated with increases in RH and/or temperature also varied in relation to the size (cross sectional area) of insect prey. Modelling demonstrated that small (6 kHz) movements in call frequency could not compensate for the changes in prey detection range and spatial detection volumes that result from significant changes in atmospheric temperature or RH. The notion that differences in RH are the primary cause leading to adaptive evolution and speciation in CF-emitting bats by precipitating intraspecific differences in the mean call frequency of geographically isolated bat populations was not supported by the results of this case study.

Most previous studies considering intraspecific differences in bat echolocation call frequency among geographic groups have related this to morphological features not directly involved in producing the characteristics of emitted signal. We related a pattern of intraspecific differences in size of nasal chambers (estimated from radiographs of museum specimens), expecting chamber dimensions to be functionally coupled with sound source. Such a relationship is potentially informative in the context of competing hypotheses that account for call frequency differences. Allopatry has been a precursor to differences between isolated populations of Australian endemic orange leaf-nosed bat (Rhinonicteris aurantia (Gray, 1845); Pilbara isolate: 120.99 ± 1.91 kHz; compared with Kimberley region: 114.65 ± 1.98 kHz and Northern Territory: 114.62 ± 2.10 kHz). Correlations of morphological signal production or modification were either moderate (nose-leaf width) or absent (forearm length). Overall nasal chamber volume was shown to be relatively smaller in the population which had higher average call frequency. This relationship was expected given the suggested function of the nasal chamber in impedance matching. The finding is significant because the nasal chamber was the only character observed to vary in a species that was otherwise conserved morphologically, suggesting adaptation. We consider that the combination of patterns of echolocation call frequency associated with morphological features, as well as neutral DNA markers, provide adequate support for recognition of separate populations of R. aurantia for conservation.

The endemic orange leaf-nosed bat, Rhinonicteris aurantius, is a relict both in a phylogenetic and a geographic sense. Prior to this study, two colonies in disused mines and seven other records of single animals were known from the disjunct Pilbara population of Western Australia. Cave roosts were located in the region for the first time, five new roosts were found in disused mines and the species was recorded in five new localities. Cave roosts were discovered in sandstone bedding. Free-flying R. aurantius were located in a diverse range of landscapes composed of banded iron formation, Cleaverville Formation geology and granite. Mines utilised as roosts were structurally complex and in some cases breached the watertable. This study revealed that while the species is widespread throughout the region, it is restricted to certain landform units, the number of suitable roosts within landform units is limited and the population appears to be subdivided within the region. Dispersal and connectivity within the population may be dependent on the availability of roosts in intervening areas, which may be a function of the availability of groundwater to subterranean formations for the control of roost microclimate. Currently, the known breeding range is one gorge at Barlee Range Nature Reserve and one mine at Bamboo Creek.

Horn loaded loudspeakers increase the efficiency and control the spatial distribution of the sound radiated from the horn mouth. They are often used as components in cinema sound systems where the sound can be broadcast evenly onto the audience at all frequencies, improving the listening experience. The sound distribution, or beamwidth, is related to the shape of the horn and is not predicted adequately by existing analytical horn models. The aim of the work described in this thesis is to develop a method to optimise the shape of the horn to give a specified beamwidth, which is ideally frequency independent, thus giving a high quality listening experience. This thesis begins with a thorough review of the literature relevant to modelling and optimising horn loaded loudspeakers. It gives an introduction to horn loaded loudspeakers, and describes traditional modelling approaches and their limitations. The applications of alternative modelling techniques to horn loaded loudspeakers, which have been found in the literature, are critiqued as are horn optimisation techniques. To examine the validity of the plane wave radiation assumption made by a number of horn models, experiments were undertaken to measure the sound field at the mouth of two small horns. These horns are representative of the size and design required for cinema loudspeaker systems, but are axisymmetric. The sound field was measured by an automated microphone traverse with almost 3500 measurements made across the face of each horn, providing a high spatial resolution. The results of the measurements showed that at low frequencies the sound fields from both the conical and exponential horns were similar and that above a certain frequency the sound field became more complex. An analysis of the data, using a modal decomposition with cylindrical duct modes of the same diameter as the mouth of the horns, revealed that almost all of the energy in the system existed in modes with no circumferential variation, and that above a certain limiting frequency, plane waves ceased to exist at the mouth of each horn. This work showed that any numerical model developed must be capable of efficiently modelling variations in the sound field across the mouth of the horn, and that models based on plane wave approximations should not be used for modelling these experimental horns, at least above a certain critical frequency. Numerical models able to accurately and quickly calculate the far field pressure from arbitrary shapes are also investigated. Calculations of the beamwidth from the analytical solutions for a 45° vibrating spherical cap, mounted on the surface of a unit sphere, were compared with those obtained from an implementation of the direct Boundary Element Method (BEM) and a source superposition technique. The investigation found excellent agreement between these results for mesh densities of 6 elements per wavelength, the generally recommended minimum mesh density for BEM simulations. The source superposition technique was significantly faster than the direct BEM for comparable accuracy in the far field. There was also excellent agreement between analytical calculations and all of the numerical methods for a mesh density of 3 elements per wavelength. This is a significant finding as it allows a reduction in mesh density, and hence matrix size and solution time, for a given accuracy of far field solution. Alternatively, higher frequencies can be reached for a given mesh density. It was also found that the source superposition technique produced matrices that are highly diagonally dominant, and well suited to fast iterative solution techniques. The validation of the numerical methods for modelling the beamwidth of horn loaded loudspeakers was undertaken by comparing the source superposition technique to experiment, as well as with an alternative numerical method, the direct BEM. It was shown that such models are capable of modelling the sound field generated by a horn loaded loudspeaker from a specification of the horn geometry. This accuracy of the model is adequate for design purposes within the given frequency range. Both the direct BEM and the source superposition technique are capable of modelling the experimental beamwidth; however, the source superposition technique is considerably faster and hence more suitable for use in optimisation techniques. During the literature review, a type of sonar transducer called a Constant Beamwidth Transducer (CBT) was found that was able to produce an easily specified frequency independent beamwidth. These are desirable characteristics for the design of a horn. The concept used in the development of these transducers, a specified velocity profile over the surface of a sphere, is explored in this thesis in relation to horn design. A semi-analytical technique, using solutions to the Helmholtz equation in spherical coordinates and numerical integration of Legendre functions, was developed to efficiently calculate the beamwidth for an arbitrary velocity profile over the surface of a sphere. It was used to calculate the beamwidth for four different velocity profiles: a spherical cap mounted on the surface of a sphere; a CBT profile; and two smooth tailed CBT velocity profiles. The results showed that the smooth tailed CBT velocity profiles produce the smoothest beamwidth, possibly at the expense of low frequency performance. It was also found that the performance of each velocity profile is consistent with CBT theory, with the best performing profile having the highest rate of energy decay in the spherical Legendre modes. CBT theory also suggests that the performance of the CBT transducers is unaffected by the removal of the inactive part of the sphere, i.e. that part over which the velocity profile is zero. This was confirmed numerically by simulations using the source superposition technique. The numerical model developed to investigate the CBT was used to test robust optimisation techniques suitable for optimising horn loaded loudspeakers. Two different objective functions were considered, one that uses least squares to drive the velocity profile to a minimum, and the other that uses a constrained optimisation of a smoothness parameter. It was found that constrained optimisation was able to robustly find an optimal solution in an acceptable number of objective function evaluations. As the cost of evaluating the objective function for horn loaded loudspeakers is high, the potential of surrogate modelling techniques, designed to reduce the overall number of objective function evaluations, was investigated. Optimal solutions were found for two different parameterisations of the velocity profile. One parameterisation was similar to the smooth tailed CBT velocity profiles and the other, which allowed a more variable velocity profile, was defined by Bézier curves. The idea of CBT theory, that is, defining an optimal velocity profile over a spherical cap, was applied to the optimisation of horn loaded loudspeakers. A number of different horn geometry parameterisations were developed, with the aim of producing an optimal velocity profile over the mouth of the horn. The robust optimisation techniques developed previously were applied, and an optimal horn geometry calculated. It was found that a very simple geometry parameterisation could produce near constant beamwidth performance while keeping the desired design (or nominal) beamwidth, and that a more complicated parameterisation (using splines) could not keep the nominal beamwidth but provided superior constant beamwidth performance. A series of optimisations using the spline parameterisation were undertaken to map the design space, with the result being a design chart for constant beamwidth horns. The desired performance characteristics of a constant beamwidth horn such as length, mouth to throat ratio or nominal beamwidth can be specified, and the horn performance and specifications easily read from a chart. The overall aim of this thesis was to develop fast and reliable optimisation techniques for horn loaded loudspeakers to achieve a robust horn design method for cinema loudspeakers. This thesis achieved this aim for axisymmetric horn geometries by: developing fast and well validated numerical methods for calculating the beamwidth of horn loaded loudspeakers; by examining how optimal beamwidth control is achieved in CBTs, and how this can be achieved in horn loaded loudspeakers; by developing robust objective functions and optimisation techniques capable of finding an optimal beamwidth from a parameterised geometry; and by developing a design chart for constant beamwidth horns.