Informing conservation management of the bilby (Macrotis lagotis) in the Pilbara: a review of research and future directions
Amy S. Northover
A * , Martin A. Dziminski A , Fiona M. Carpenter A , Harry A. Moore A B , Kym Ottewell A , Russell Palmer A and Lesley A. Gibson A C
A
B
C
Abstract
For threatened species that occur across multi-use landscapes, a coordinated cross-tenure management approach is desirable to achieve long-term conservation outcomes. To provide a comprehensive understanding of the progress towards achieving conservation priorities for the greater bilby (Macrotis lagotis) in the Pilbara region of Western Australia (WA), and inform ongoing research and funding investment, we review a research program that has focused on the species over the past decade. Priorities were initially established at a stakeholder workshop in 2013, and research targeting key areas has greatly enhanced ecological knowledge of the bilby in the Pilbara and elsewhere in WA. Highlights include the development of a non-invasive scat DNA-based abundance monitoring technique, an improved understanding of habitat use and diet, including the importance of Acacia spp. that host root-dwelling larvae, and the threat posed by introduced predators. Proposed future research directions focus on better understanding habitat requirements and the association between key food resources and fire, evaluating genetic structure and gene flow at the landscape-scale and examining threat interactions. Management to mitigate a range of threats including introduced predators, grazing livestock/feral herbivores and fire is recommended, with consideration for an integrated approach.
Keywords: habitat use, integrated management, marsupial, matters of national environmental significance (MNES), multi-use landscape, survey techniques, threat mitigation, threatened fauna.
Introduction
Despite a commitment to reduce the rate of global biodiversity decline (Tittensor et al. 2014), anthropogenic activities continue to drive biodiversity loss at an unprecedented rate (Butchart et al. 2010; Maxwell et al. 2016; Jaureguiberry et al. 2022). While effective conservation requires the ongoing management of a range of threats to biodiversity, the expansion of protected areas has been at the forefront of conservation efforts (Watson et al. 2014). More recently, other area-based conservation initiatives, which aim to deliver conservation outcomes across land tenures by expanding management effort beyond protected areas (IUCN-WCPA Task Force on OECMs 2019), are being advocated to address global biodiversity goals (Dudley et al. 2018; Maxwell et al. 2020; Jonas et al. 2021; Kearney et al. 2022). Threatened species that occur across multi-tenure landscapes (i.e. 75% of threatened Australian taxa; Kearney et al. 2022) are likely to benefit from a coordinated management approach such as this.
The Pilbara bioregion, a vast multi-use landscape in the north-west of Western Australia (WA), has significant biodiversity and cultural values (McKenzie et al. 2009). The Pilbara is also of national economic importance with pastoral and/or mining leases covering 82% of the bioregion (Booth et al. 2021). Several threatened fauna species, including the greater bilby (Macrotis lagotis Reid, 1837), occur in the Pilbara and are classified as matters of national environmental significance (MNES) by the Australian Government (Department of the Environment 2013). Enhancing ecological knowledge to inform on-ground conservation management of Pilbara MNES fauna has been a research focus among stakeholders (e.g. Cramer et al. 2016a, 2016b, 2017, 2022; Gibson et al. 2023). There is also growing support for a more coordinated cross-tenure management approach to achieve conservation outcomes for threatened species inhabiting multi-use landscapes such as the Pilbara (Carwardine et al. 2014; Kearney et al. 2022; Gibson et al. 2023).
The greater bilby (henceforth, the bilby) is an iconic and culturally important medium-sized (800–2500 g) burrowing marsupial and the sole extant member of the Thylacomyidae family (order Peramelemorphia) (Lynch 2008; DCCEEW 2023a). Formerly occupying a variety of habitat types across mainly arid and semi-arid Australia (Southgate 1990; Woinarski et al. 2014; Silcock et al. 2023), bilby populations have declined in response to a combination of threats including the impacts of introduced non-native animals (i.e. predation and competition), habitat modification and altered fire regimes following European colonisation (Bradley et al. 2015; Woinarski et al. 2015). The bilby now occupies approximately 20% of its former range (Southgate 1990; DCCEEW 2023a), with remnant wild populations persisting in central and northern WA, the Northern Territory (NT) and an isolated area in south-western Queensland (Qld; Bradley et al. 2015). In WA, wild bilby populations occur in the Kimberley, Pilbara, central and western deserts, and rangelands regions (Cramer et al. 2017; Lohr et al. 2021). The Pilbara bioregion supports the north-western extent of the bilby’s range and represents an important stronghold for the species (Dziminski et al. 2020b).
The bilby is currently listed as ‘Vulnerable’ under the WA Biodiversity Conservation Act 2016 (Government of Western Australia 2016), the Commonwealth Environment Protection and Biodiversity Conservation Act 1999 (DCCEEW 2023b) and on the International Union for Conservation of Nature Red List of Threatened Species (Burbidge and Woinarski 2016). In the Pilbara, key threats to the bilby include inappropriate fire regimes, predation by the feral cat (Felis catus) and European red fox (Vulpes vulpes), habitat loss and fragmentation from land clearing, and degradation of habitat by introduced herbivores (Bradley et al. 2015; DCCEEW 2023a). The small and isolated nature of many bilby populations in the Pilbara enhances their vulnerability to threats (Dziminski et al. 2020a).
Until recently, the status and ecology of the bilby in the Pilbara was poorly understood, with studies limited to general and targeted survey work to search for bilby presence (Cramer et al. 2017). With growing pressure from key threats, in particular the rapid development of the mining industry over the past two decades (Department of Parks and Wildlife 2017), the then Department of Parks and Wildlife (now the Department of Biodiversity, Conservation and Attractions; DBCA) hosted a workshop in October 2013 to review current knowledge and identify research priorities to inform conservation management of the bilby in northern WA. This was a facilitated process involving scientists, environmental consultants, mining proponents, natural resource management groups and other organisations working with Traditional Owners, and State and Federal government agencies (Cramer et al. 2017). Five key areas or ‘themes’ for future research effort were identified and prioritised. Here, we summarise progress against each of these priorities and provide recommendations to guide future research and conservation management of the bilby in the Pilbara.
Research priorities – progress
Key outcomes for each research priority identified by Cramer et al. (2017) are summarised in Table 1 and described below.
| Research priority | Key outcomes | |
|---|---|---|
| Refine survey methods |
| |
| Improve understanding of habitat use |
| |
| Improve understanding of the genetic structure of bilby populations |
| |
| Improve understanding of the threat posed by introduced predators and herbivores |
| |
| Improve understanding of how fire regimes affect bilby conservation |
|
Priority 1: refine survey methods
Monitoring cryptic and trap-shy species such as the bilby poses a challenge (Dziminski et al. 2020a). Bilbies are nocturnal, with a tendency for low site fidelity and high mobility, and this is particularly true for males (Southgate et al. 2007). To verify bilby presence, surveys have typically relied on the detection of bilby sign (i.e. scats, diggings and tracks; Moseby et al. 2011). Burrows are not a reliable indicator of bilby presence unless accompanied by evidence of fresh bilby sign (Southgate et al. 2019). While remote sensor cameras can be used to confirm bilby presence, bilbies lack unique markings for individual identification. Free-standing cage traps have been used with little success, as wild bilbies are reluctant to enter traps and are not consistently lured by baits (Southgate et al. 1995).
To address the need for an efficient, cost-effective and reliable population monitoring tool, a new survey technique was developed, combining DNA extracted from georeferenced bilby scats to genotype individuals using polymorphic microsatellite markers and spatially explicit capture–recapture (SECR) analyses, to estimate bilby abundance (Carpenter and Dziminski 2017; Dziminski et al. 2020a). This non-invasive scat DNA-based monitoring technique provides a standardised approach to measuring abundance that is comparable between sites across the extent of the species’ range and has been applied to reliably quantify bilby abundance within the Pilbara (Dziminski et al. 2020a) and other WA regions (e.g. Department of Biodiversity, Conservation and Attractions 2017a, 2021; Lohr et al. 2021). Recent upgrades to the genetic methodology include the use of single nucleotide polymorphism (SNP) markers to enable automated sample genotyping (see below; Hogg et al. in review). Monitoring in the Pilbara and other sites in WA has shown that bilby populations are typically small and geographically isolated, mostly comprising fewer than 10 individuals (Department of Biodiversity, Conservation and Attractions 2017a; Dziminski et al. 2020a; Department of Biodiversity, Conservation and Attractions 2021). Based on research to date and considering the advice of Southgate et al. (2019), we provide a summary of recommended survey and monitoring techniques specific to bilbies (Table 2) and discuss in further detail below.
| Survey type | Recommended techniques | Advantages (+) and disadvantages (−) | References | |
|---|---|---|---|---|
| Bilby presence/absence | Helicopter or drone survey with ground truthing | Southgate et al. (2005), Southgate and Moseby (2008), Moseby et al. (2011), Department of Biodiversity, Conservation and Attractions (2017b) | ||
| 2-ha sign plots (foot, vehicle or ATV) | ||||
| Bilby occupancy | 2-ha sign plots (four resurveys within a season recommended) | Southgate et al. (2019) | ||
| Access on foot, ATV, vehicle or helicopter | ||||
| Bilby abundance | Scat DNA monitoring of discrete populations | Dziminski et al. (2020a) | ||
| Scat DNA survey subsampling contiguously occupied area |
To promote a standardised and comparable occupancy survey approach, best practice survey guidelines (Department of Biodiversity, Conservation and Attractions 2017b), including a mobile data app, 2-ha sign plot datasheet (Dziminski and Carpenter 2018) and a protocol for verifying bilby presence from sign (Southgate et al. 2019), have been developed. The 2-ha plot method has been the most effective on-ground technique for establishing bilby presence/absence and occupancy (see Southgate et al. 2005, 2019; Southgate and Moseby 2008; Moseby et al. 2011). This method has been broadly applied, often in partnership with Traditional Owners/Indigenous Ranger groups, across the Pilbara and other parts of arid and semi-arid Australia (e.g. Kimberley; Department of Biodiversity, Conservation and Attractions 2021). Similar methods have also been used by Martu Traditional Owners to monitor bilbies in the nearby Western Desert region (Skroblin et al. 2022). Searching 2-ha plots on foot for bilby sign, however, is labour intensive and placement of survey plots is often restricted to areas that can be accessed by vehicle (Dziminski et al. 2020a). While occupancy surveys across broad regions in the Kimberley have been completed (Department of Biodiversity, Conservation and Attractions 2017a, 2021; Moore et al. 2023b), a baseline occupancy survey of bilbies across the Pilbara region is yet to be undertaken (a recommended action in Appendix 1). Stratified sampling among key habitat types in the known range (see Dziminski et al. 2020b) is recommended to estimate regional occupancy within the Pilbara. A local scale survey on Coongan Pastoral Station (16,000 ha) recorded an occupancy of 0.05 (±0.05 SE) to 0.1 (±0.06 SE) from 16 2-ha plots surveyed on four occasions within 6 months (Dziminski et al. 2019).
On a broader scale, the use of remotely piloted aircraft (RPA; or drone) fitted with real-time video imagery to detect bilby sign has been explored (Dziminski and Carpenter 2017). Field trials in the Pilbara revealed that burrows were difficult to detect as they were often concealed by vegetation. Diggings, however, were more numerous, prominent and easier to detect (greatest detectability around midday due to less obscuration by oblique shadows), particularly when the RPA was flown at lower altitude and speed (Dziminski and Carpenter 2017). While the use of RPA allows more efficient and cost-effective targeted surveys to be conducted in remote areas of the Pilbara, battery power currently limits the distance they can traverse and ground-truthing is necessary to confirm the rate of false positive and false negative error (Dziminski and Carpenter 2017; Southgate et al. 2019). Helicopter surveys in combination with ground-truth survey plots remains an effective and efficient method of monitoring bilby presence/absence (Southgate et al. 2005), although it is costly if repeated visits are required for measures of occupancy. A remote sensing trial using light detection and ranging (LiDAR) mounted on a fixed-wing light aircraft, showed that a resolution of 30 cm was not high enough to detect bilby burrows at a site in the east of the Pilbara (M. Dziminski pers. comm.). There may be merit in trialling higher resolution LiDAR in the 5–10 cm range requiring a lower altitude with LiDAR mounted on RPA, or alternatively increase the number of passes by a fixed-wing aircraft to achieve a higher resolution. In more open habitats, such as in south-west Qld (i.e. Astrebla Downs National Park), vehicle-mounted thermal imaging cameras have been used to estimate bilby density (Augusteyn et al. 2020), however, these surveys were limited to existing tracks. According to Augusteyn et al. (2020), estimating density across the entire national park would require correlating vehicle surveys with aerial counts of burrows. The use of drone-mounted thermal imaging cameras could be trialled in the Pilbara, but obscuration by vegetation is likely to limit the use of this technique (e.g. Burke et al. 2019).
Priority 2: improve understanding of habitat use
In the north of WA, bilbies occupy a range of substrate and vegetation types including residual, fluvial and sand plain landforms with a low shrub cover of Acacia spp. over grasslands (e.g. Triodia spp.; Cramer et al. 2017). Bilby prevalence and persistence may differ between habitat types and fluctuate in response to rainfall and fire, due to their effect on habitat suitability and food availability (Southgate and Carthew 2006). In the Pilbara, it was largely unknown how substrate and landform characteristics, including resource availability, influenced habitat suitability and bilby prevalence (Cramer et al. 2017). This information is important to focus conservation and management effort and enable informed and evidence-based environmental impact assessments to be undertaken.
To better understand the distribution of bilbies in the Pilbara, Dziminski et al. (2020b) compiled bilby records (4386 in total between 1899 and 2019) to document the species’ extent of occurrence across the region. This showed bilby populations are mostly distributed across the eastern half of the Pilbara bioregion, occupying various land tenures, predominantly mining tenements and/or pastoral land. Few presence records occur within formal conservation reserves, which constitute only 6% of the bioregion (Booth et al. 2021) (Fig. 1).
Map of the Pilbara region, Western Australia, with the locations of greater bilby (Macrotis lagotis) records from the Western Australian Department of Biodiversity, Conservation and Attraction’s fauna database from 1990 to 2023.
Data obtained during 2-ha plot field surveys has revealed an association with particular substrate and vegetation types, notably Acacia stands that provide a key food resource, cossid moth larvae, from their root systems (Southgate et al. 2019). Acacia species known to host root-dwelling (Cossidae) insect larvae in the Pilbara include A. bivenosa, A. colei, A. dictyophleba, A. melleodora, A. stellaticeps and A. trachycarpa (Southgate et al. 2019). A preliminary examination of 144 scats collected from 17 populations in WA (including the Pilbara) confirmed cossid moth larvae were common in the diet of Pilbara bilbies (M. Dziminski pers. comm.). Associations with other vegetation (e.g. Senna notabilis; Southgate et al. 2019) and sand, soil, sandy clay or sandy gravel substrates suitable for burrow construction have also been identified (Dziminski and Carpenter 2016). Preliminary habitat suitability modelling identified elevation, as well as soil type and depth as key predictor variables contributing to habitat suitability for the bilby in the Pilbara (Dziminski and Carpenter 2017). Population viability analysis also indicated the area of suitable habitat required to support a self-sustaining population of bilbies without management intervention (i.e. for a potential reserve) was at least 50,000 ha (probability of extinction <0.1 over 100 years) (Dziminski et al. 2012).
Priority 3: improve understanding of the genetic structure of bilby populations
Early studies investigating the genetic structure of the national bilby meta-population suggested low to moderate levels of genetic differentiation amongst NT and Qld regional subpopulations (Southgate and Adams 1994; Moritz et al. 1997), leading Moritz et al. (1997) to suggest a conservative approach of recognising Qld and WA/NT as separate management units. Following more extensive sampling, it is now recognised that the Qld, NT and WA populations were in fact historically well-connected with the observed genetic structure reflecting contemporary fragmentation and range contraction (Smith et al. 2009), and that the bilby should be managed as one meta-population (DCCEEW 2023a). A meta-population management plan, which aims to maintain a sufficiently large, interconnected and genetically diverse meta-population, is currently under preparation (DCCEEW 2023a). Within WA, an understanding of how populations are structured genetically, including the relatedness of individuals within populations and gene flow at the landscape scale, was needed (Cramer et al. 2017). Landscape connectivity, which facilitates gene flow (Shaw et al. 2023), can be difficult to achieve for small, isolated subpopulations inhabiting fragmented and multi-tenure landscapes such as the Pilbara. This is particularly true for subpopulations occurring at the edge of their range, which are typically small (Bahn et al. 2006). The use of non-invasive molecular genetic techniques (e.g. Carpenter and Dziminski 2017) offers a different approach for assessing the genetic structure of populations and determining the need for management intervention (e.g. translocations).
To better understand bilby population dynamics within the Pilbara and across other regions of WA and Australia as a whole, the scat DNA-based molecular toolkit developed by Carpenter and Dziminski (2017) has been refined. Reduced representation sequencing data (RRS, specifically DArTseq https://www.diversityarrays.com) was used as the foundation to create an individual-based targeted SNP genotyping array for repeatable genotyping of bilby scats on the MassARRAY® (Agena BioScience) automated system (Hogg et al. in review). A suite of sex-linked markers from Brandies (2021) have also been incorporated into the bilby SNP array to allow identification of individuals, their sex and kinship patterns in a single assay (Hogg et al. in review). Individual genetic ‘capture’ records are maintained in a time-stamped, georeferenced database at DBCA (K. Ottewell pers. comm.), enabling individual movement patterns and survivorship to be examined through space and time, and associated kinship estimates to infer dispersal of individuals and their descendants. Broader analyses of the genetic relationships within and amongst regional subpopulations can be undertaken in the future as SNP genotypes accumulate from projects in the Pilbara, Kimberley and elsewhere in Australia.
A large consortium of researchers, led by the University of Sydney (Bilby Genome Project | (sydney.edu.au)), have recently provided a comprehensive assessment of the reference genome of the greater bilby (chromosome-length assembly), including an understanding of the prevalence of genes associated with semi-arid and temperate lifestyles and sequencing the genome of the lesser bilby (Macrotis leucura) (Hogg et al. in review). As part of this project, RRS data were used to examine genome-wide diversity across the national captive/fenced bilby meta-population with a small number of samples from the Pilbara (n = 6) and the Kimberley (n = 3) included to provide some insight into the contemporary genetic diversity of the wild bilby population. Samples from the Pilbara had reduced genetic diversity relative to captive and fenced bilby populations and the highest estimate of inbreeding (Hogg et al. in review), which may reflect the reduced range, low density and isolated nature of bilby populations in the Pilbara (Dziminski et al. 2020a, 2020b). However, further comparison with other wild populations and a much larger sample size is needed to place the Pilbara populations in appropriate context.
Priority 4: improve understanding of the threat posed by introduced predators and herbivores
The local extirpation of the bilby across southern Australia coincided with the arrival and spread of the European red fox (Abbott 2001). There is a negative correlation between the presence of bilbies and foxes (Southgate 1990; Southgate et al. 2007) and the risk of extirpation is greatest when foxes become well established across the landscape (DCCEEW 2023a). In the Pilbara, foxes mostly inhabit the coastal fringe and hinterland plains, with some extension inland along major drainage lines (King and Smith 1985; Department of Parks and Wildlife 2017; Turpin and Riley 2020). Feral cats also co-exist with and prey on bilbies (McRae 2004; Bradley et al. 2015). While feral cat predation can constrain or extirpate local bilby populations (Woinarski et al. 2014), bilbies have some resilience to feral cat presence (Department of Biodiversity, Conservation and Attractions 2021), although the density or activity threshold of predators below which bilbies can persist is currently unknown. There is also evidence to show wild bilbies display anti-predator responses towards cat faeces and visits by cats to their burrows (Steindler and Letnic 2021; Chen et al. 2023). In the Pilbara, feral cats are widespread and high feral cat occupancy has been recorded in non-rocky sandplain habitat where bilbies are present (Dziminski et al. 2021).
The threat posed by other predators in the Pilbara, including dingoes (Canis familiaris), is largely unknown. Dingoes are considered a naturalised predator, as the distribution of bilbies and dingoes has overlapped for thousands of years (DCCEEW 2023a), and bilbies have shown instinctive antipredator behaviour towards dingoes (Steindler et al. 2018). While further research is needed to evaluate the interaction between bilbies, dingoes and other predators, there is evidence to suggest that dingoes predate, and competitively exclude foxes and potentially feral cats from some landscapes (Southgate et al. 2007; Kennedy et al. 2012; Letnic et al. 2012), but this contention is still subject to debate (Castle et al. 2023). Dingoes have been shown to be a potential threat to bilbies elsewhere, for example, bilby remains were detected in 13–85% (mean 43%) of canid scats over a 7-year period at Astrebla Downs National Park in Qld (Augusteyn et al. 2021).
Introduced herbivores, particularly grazing livestock, compete with bilbies for resources, degrade habitat and attract predators (Bradley et al. 2015; Woinarski et al. 2015). The establishment of artificial water points facilitates predator expansion, supports higher introduced herbivore (and predator) numbers and fragments bilby populations (McRae 2004; Bradley et al. 2015). Bilbies are also less likely to inhabit areas with a history of cattle grazing (McDonald et al. 2015). In the Fitzroy River catchment in the Kimberley, a clear negative correlation between bilby and cattle occupancy was reported (Department of Biodiversity, Conservation and Attractions 2021). With almost 60% of the Pilbara leased as pastoral land (largely commercial cattle grazing), undisturbed habitat is scarce (Department of Parks and Wildlife 2017). On Coongan Pastoral Station (see details below), cattle occupancy derived from cameras was very high (>0.94), including detection at burrows (Dziminski et al. 2021). Determining the level of threat posed by introduced predators and herbivores in the Pilbara, including interactions with other threatening processes (e.g. fire), was identified to inform effective on-ground conservation strategies for bilbies (Cramer et al. 2017).
In 2018, an offset-funded collaborative project was established on Coongan Pastoral Station near Marble Bar, which aimed to evaluate the benefits of feral cat and fire management for bilby conservation in the Pilbara (Dziminski et al. 2021). Management efforts, implemented as part of this project, are focused within a 17,000 ha Bilby Land Management Area (BLMA) near the Warralong Aboriginal Community, where at least two bilby colonies were identified. A total of 30 long-term monitoring sites (20 within and 10 outside the BLMA) were established to assess changes in feral cat and bilby occupancy in response to management activities. Sites have been monitored using a combination of remote sensing cameras and 2-ha plot surveys. In addition to occupancy, the abundance of the two known bilby populations has been monitored annually using DNA extracted from georeferenced scats (Dziminski et al. 2019, 2020c; Moore et al. 2022). Baseline monitoring conducted between March 2019 and June 2022 prior to management indicated that feral cat occupancy inside and outside the BLMA area was generally high (>0.85); a single fox was also detected in 2019 (Dziminski et al. 2021). Bilby abundance was consistently low during the same period (≤8 individuals per population), although only one population could be located in 2021, and no estimates were made in 2020 due to the COVID-19 pandemic (Dziminski et al. 2020c, 2021; Moore et al. 2022).
In June 2022, Eradicat® feral cat baits were aerially deployed within the Warralong BLMA at a density of 50 baits per km2 (Moore and Gibson 2023). Post-baiting monitoring, conducted from June to November 2022, suggested that Eradicat® baiting did not significantly reduce feral cat occupancy within the BLMA (Moore and Gibson 2023). Similarly, bilby abundance at the two known colonies did not appear to change substantially in response to baiting; however, the statistical power to detect changes was limited due to the small number of individual bilbies (Moore et al. 2023a). A second round of Eradicat® baiting was conducted within the BLMA in July 2023 with results pending (H. Moore pers. comm.).
Priority 5: improve understanding of how fire regimes affect bilby conservation
Vegetation in semi-arid ecosystems, such as the Pilbara, is often characterised by fire adapted plant species which can tolerate frequent burns (Gill 1975). However, loss of Aboriginal burning practices in combination with other landscape-scale changes (e.g. herbivore grazing and weeds) has increased the risk of large contiguous fires burning vast areas of habitat (Bowman et al. 2020). As well as the direct impacts on wildlife (Jolly et al. 2022), loss of vegetation cover can reduce resource availability and increase predation pressure (Nimmo et al. 2019). In northern WA, feral cats have shown a preference for open habitat recently subject to intense fire where small-mammal density remains high (McGregor et al. 2014) and they will travel long distances to hunt (McGregor et al. 2016).
Bilbies use a variety of post-fire successional stages including recently burnt and long-unburnt vegetation (Southgate 1990). An association with recently burnt areas and vegetation with high fire age heterogeneity has been identified in the Tanami Desert, which is likely to be influenced by seed production from fire-promoted plants (Southgate et al. 2007). On the Dampier Peninsula in the Kimberley, fire frequency and the extent of long unburnt habitat are important factors in predicting the presence of bilbies (and feral cats), with bilbies favouring areas that are surrounded by a high proportion of long unburnt habitat (>3 years) and reduced fire frequency; the opposite trend was observed for cats (Moore et al. 2023b).
How fire regimes influence habitat suitability and food production, and thus the prevalence and persistence of bilbies in the Pilbara, is poorly understood, as are the interactive effects of fire on other threats such a predation and total grazing pressure (Cramer et al. 2017). A recent analysis which used a Pilbara-wide database of bilby presence records found that bilby habitat suitability declines with increasing extent of recently burnt habitat (<3 years since fire) (unpubl. data; H. Moore, L. Gibson and D. Nimmo), highlighting the need to limit large-scale wildfire in the Pilbara. Consideration should also be given to the timing of burns in relation to the biology of key food producing plants. In the Tanami desert, prescribed burning is recommended in late spring or early summer, or during late summer/early autumn following significant (>300 mm) rain, to improve Panicum australiense (formerly Yakirra australiensis) production (Southgate and Carthew 2007).
Due to their small and isolated nature, bilby populations in the Pilbara are highly susceptible to the impacts of fire (Dziminski et al. 2020a). For example, large, intense wildfires near Pardoo Station (2012, 2013 and 2014) and McPhee Creek (2015) in the eastern Pilbara likely led to the local extirpation of bilbies by removing a large amount of vegetation, which both depleted food resources and may have increased predation pressure (Dziminski and Carpenter 2017; Dziminski et al. 2020a). Similarly, lack of fire can also reduce habitat quality, with high-density, long-unburnt vegetation rendering habitat unsuitable for bilbies by limiting movement (Bradley et al. 2015). Fire management is, therefore, a critical component of managing habitat for bilbies and avoiding further loss of populations. To produce fire age heterogeneity and potentially improve habitat and resource diversity for bilbies, smaller, more frequent ground-based patch mosaic burning under prescribed conditions, in combination with strategic firebreaks, have been recommended (Southgate and Carthew 2006, 2007; Burrows 2019). Similar results can be achieved by aerial incendiary deployment under the right weather conditions (Burrows et al. 2021).
To date, fire management to protect bilby populations in the Pilbara has been limited. In 2017, controlled burning of a 27.5 ha linear strip was undertaken at Nullagine to create a fire break, with mineral earth fire breaks and grading tracks also established to protect bilby habitat (Dziminski and Carpenter 2018). A fire management plan has also been developed for the Warralong BLMA (Burrows 2019). While fire breaks were established with some burning conducted around the BLMA perimeter in 2019, logistical issues have thus far delayed the application of prescribed fire at Warralong (H. Moore pers. comm.). Replicated experimental burns could be considered to refine fire management by increasing our understanding of the impact of patch burning on local flora and identifying appropriate fire intervals for improving habitat and food availability for the bilby. This would also help to determine if burning strategies for inland deserts designed to improve habitat for bilbies (Southgate and Carthew 2007) are also applicable to the Pilbara.
Future research and management
Based on our review of existing knowledge and progress made to date, we propose a revised set of research priorities for the bilby (Appendix 1) to further improve knowledge and guide conservation management of the bilby in the Pilbara. Research priorities are ranked as high, medium or low given our current understanding. We also provide population-scale and landscape-scale management options that are most likely to benefit and facilitate the persistence of bilbies in the Pilbara (Appendix 2). Management options closely align with the proposed on-ground actions listed in the National Bilby Recovery Plan (DCCEEW 2023a) and for other wild bilby populations in northern WA that face similar threats (Dziminski and van Leeuwen 2019; Department of Biodiversity, Conservation and Attractions 2021).
Conclusions
Research undertaken over the past decade has greatly improved our understanding of the status and ecology of the bilby in the Pilbara, and elsewhere in WA. With a clear focus on improving survey and monitoring practices, a standardised population monitoring technique has been developed and implemented across WA to reliably quantify bilby abundance and provide comparative information on population trends across the species’ range. The development and optimisation of a scat DNA-based molecular toolkit that allows for the identification of individuals and their sex, and the establishment of a georeferenced and time-stamped database of bilby genetic captures, has enabled the tracking of individuals and their descendants through space and time.
Survey information to date has revealed that bilby populations in the Pilbara are geographically isolated and comprise a small number of individuals. Further research to evaluate genetic structure will help to understand population connectivity and genetic diversity across the Pilbara and place it in the context of their broader distribution. We also have an improved understanding of the resources that are important to bilbies within the Pilbara, such as Acacia spp. that provide root-dwelling (Cossidae) insect larvae, although further research is needed to evaluate spatial and temporal variation and identify other habitat attributes that influence suitability. Likewise, our understanding as to how fire and introduced herbivores influence these important food resources remains limited.
Crucial to the ongoing persistence of bilbies in the Pilbara is the management of introduced predators and fire. The impact of introduced herbivore grazing, including synergistic effects with introduced predators and fire, requires further investigation. The adaptive management and monitoring approach at Warralong, where both introduced predators and fire are being managed to benefit the local bilby population, will help to provide insight into the effectiveness of controlling multiple threats. The application and upscaling of this approach to other wild Pilbara populations, including the incorporation of introduced herbivore management, will help to inform best practice management, and assist in ensuring the persistence of the bilby across the vast Pilbara landscape.
Data availability
Data sharing is not applicable as no new data were generated or analysed during this study. All cited reports can be accessed at https://library.dbca.wa.gov.au.
Declaration of funding
This review was commissioned by the Department of Water and Environmental Regulation with funding from the Pilbara Environmental Offset Fund.
Acknowledgements
We acknowledge the Traditional Owners of the Pilbara region of Western Australia on whose lands fauna conservation work was undertaken, as well as the many ranger groups for their partnership in these projects. We thank the Mugarinya Community Association and Yandeyarra Rangers, Nullagine Community School and members of the Warralong community for their assistance with bilby monitoring, field surveys and threat management within the Pilbara. The Pilbara Bilby Research Program (PBRP) was supported through offset funding from Fortescue Metals Group, Millennium Minerals and Roy Hill. The 2013 Bilby Workshop hosted by the then Department of Parks and Wildlife (now DBCA), was undertaken in collaboration with the then Department of Environment and sponsored by Aurizon and Buru Energy. DBCA has worked in partnership with universities and other stakeholders, including environmental consultancies, CSIRO and Traditional Owners to deliver the PBRP. This review is derived from a Departmental report, which was prepared for the Department of Water and Environmental Regulation (DWER) (see Northover et al. 2023). A section of this report was also summarised in another Departmental report, also prepared for DWER (https://www.wa.gov.au/system/files/2023-08/summary-of-knowledge-for-six-faunal-species-that-are-mnes-in-the-pilbara_final-report.pdf). ‘Guidelines for surveys to detect the presence of bilbies, and assess the importance of habitat in Western Australia’ was prepared by DBCA in association with Richard Southgate (Envisage Environmental) and Mike Bamford (Bamford Consulting Ecologists). The standardised data sheet for 2-ha sign plot surveys was developed in partnership with the World Wildlife Fund and Environs Kimberley with advice from experts including Richard Southgate. Faecal samples obtained from Kanyana Wildlife Rehabilitation Centre were used to refine faecal DNA extraction methods and conduct DNA degradation trials. We would like to express our gratitude to those that have contributed to bilby recovery, either through their employment, student projects or volunteer involvement, with particular thanks to Frank Morris. We would also like to acknowledge the support of Rangelands NRM, Main Roads WA, Greening Australia and DBCA Karijini National Park Rangers for their assistance with logistics.
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Appendix 1.Suggested research priorities for the greater bilby (Macrotis lagotis) in the Pilbara, ranked high, medium or low (modified from Northover et al. 2023).
| Priority | Research topic | Objective | Outcome | |
|---|---|---|---|---|
| High | Survey and monitoring – baseline occupancy survey of the Pilbara | A baseline occupancy survey of bilbies in the Pilbara is lacking. Conduct a large-scale survey to compare bilby occupancy with other regions where this approach has been undertaken (e.g. Fitzroy River catchment) and establish a baseline to compare occupancy in the future. Selection of sites should include areas where there is a high level of uncertainty of bilby presence (Dziminski et al. 2020b). | Estimates of bilby occupancy in the Pilbara will help to inform conservation planning including environmental impact assessments. | |
| High | Survey and monitoring; understanding population dynamics – establishment of long-term monitoring | Based on the occupancy survey above, and previously monitored populations, establish long-term monitoring at selected populations, and resurvey at regular intervals, to better understand population dynamics and changes in distribution over time in response to environmental variables (e.g. temperature, rainfall and fire). Concurrent monitoring of introduced herbivores and predators, and habitat condition (e.g. food availability and shelter), would also enable the identification of potential factors influencing changes in bilby abundance and distribution. | Improved understanding of long-term population trends of the bilby in the Pilbara to identify changes in conservation status, the potential cumulative effects of developments and effectiveness of threat mitigation. | |
| High | Habitat requirements – undertake habitat suitability modelling to identify important habitat | Using both historical information and data collected from the occupancy survey above, produce a habitat suitability model to identify important bilby habitat. A landscape genetics approach could also be used to examine population connectivity (gene flow) and genetic diversity hotspots across the Pilbara (e.g. Shaw et al. 2023). | Identification of areas important for targeted conservation management to support bilbies in the Pilbara. | |
| High | Habitat requirements – association of key food resources and fire | Identify the association of root-dwelling invertebrate larvae favoured by bilbies with their host Acacia (or other) spp. and the relationship between these plant species and fire (e.g. re-seeders/re-sprouters), including interactions with other flammable vegetation (e.g. spinifex (Triodia spp.), buffel grass (Cenchrus ciliaris)). This could also include other attributes such as rainfall. | Fire management strategies that promote food resources for bilbies and maintain/promote suitable habitat. | |
| High | Threat mitigation – threat interactions and their management | Better understand how multiple interacting threats influence bilby populations (e.g. introduced predators, grazing and fire) by using established survey and monitoring protocols and a network of paired managed and unmanaged bilby populations. | Effective integrated threat management to better protect bilbies. | |
| High | Habitat requirements – influence of spatial and temporal fire attributes on bilby habitat | Using existing information on the distribution of the bilby across the Pilbara, combined with satellite-derived spatially explicit fire data, investigate the influence of multi-scale fire attributes on bilby presence. This could be further refined following the baseline occupancy survey that would also include data on introduced predator and herbivore occupancy. | Fire management strategies that promote/protect bilby habitat. | |
| Medium | Threat mitigation – resilience of bilbies to feral cat density/activity thresholds | Interrogate survey and monitoring data to determine the density/activity threshold of feral cats below which bilbies can persist to inform targeted feral cat management. | Identification of a feral cat management strategy that facilitates the persistence of bilby populations. | |
| Medium | Population dynamics – understanding population shifts | Develop and test a long-term satellite tag and attachment system to enable long-term tracking (6+ months) of individual bilbies, to better understand what triggers populations to shift location across the landscape. | Management strategies that enhance population connectivity. | |
| Validate the use of scat DNA to track individuals/descendants as a complementary approach. | ||||
| Medium | Survey and monitoring – understand genetic diversity and gene flow in the Pilbara relative to other wild populations | Continue to refine sequencing techniques based on scat DNA to understand the broader genetic structure of wild populations. For example, broader meta-population genetic analyses may benefit from the use of other methodology (e.g. DArTcap, Feutry et al. 2020; Hohwieler et al. 2022) that produce more markers than the current SNP genotyping panel to detect subtle patterns of population structure. The inclusion of putative functional genetic markers as identified in Brandies (2021), in addition to neutral genetic markers, may help to better clarify patterns of adaptation across the species range. | Accurate measurement of population genetic parameters to inform management. | |
| Medium | Threat mitigation – influence of invasive buffel grass (Cenchrus ciliaris) on habitat suitability | The interaction of introduced buffel grass, grazing and wildfire has been identified as a potential threat to bilbies by hindering or altering fire management. Research to improve knowledge on the complex interactions between buffel grass, fire and introduced herbivores will help to inform threat mitigation. | Threat mitigation strategies effective for management of buffel grass to ensure suitability of bilby habitat is maintained. | |
| Low | Survey and monitoring – continue to investigate broadscale survey techniques | Continue trialling, development and optimisation of aerial survey techniques including RPA and, if technology develops and becomes more cost-effective, reinvestigate very high-resolution LiDAR over large areas to detect burrows and diggings. | Improvement in survey extent including previously inaccessible areas of the Pilbara to better understand bilby distribution. | |
| Evaluate trade-offs between accuracy, efficiency and cost-effectiveness per area covered of new technology compared to plot and/or transect-based methods. | ||||
| Low | Habitat requirements – trial eDNA approaches to further evaluate diet using scats | Develop (or refine existing) DNA barcode libraries of potential dietary items and match DNA extracted from scats to provide a more comprehensive understanding of dietary requirements (e.g. Dawson et al. 2021). | Improved understanding of bilby diet and habitat requirements. | |
| Low | Threat mitigation – influence of climate change | Undertake a climate change vulnerability assessment (e.g. Foden and Young 2016) for the bilby that considers interactions with threats. | Improved understanding of the influence of climate change on bilby populations in the Pilbara. |
Appendix 2.Threat management options for the greater bilby (Macrotis lagotis) in the Pilbara (modified from Northover et al. 2023). Population scale actions are to be applied to an area ~10,000 ha surrounding the population.
| Threat | Population-scale actions | Landscape-scale actions | |
|---|---|---|---|
| Introduced predators | Implement localised, strategic aerial and/or ground baiting using Eradicat® in managed populations and surrounding buffer zones, in conjunction with supplementary methods such as trapping (e.g. Lohr and Algar 2020) and shooting (Commonwealth of Australia 2015). | Implement annual, strategic aerial Eradicat® baiting. The bilby has benefited from large-scale introduced predator management using baits and supplementary control methods elsewhere in WA (e.g. Matuwa; Lohr and Algar 2020; Lohr et al. 2021). | |
| Consider trialling Felixer™ feral cat grooming traps, which show potential as an effective complementary tool for targeted feral cat control (Moseby et al. 2020; Dunlop et al. 2020). | Eradicat® baiting (and wild dog baiting operations on pastoral lands) will also kill foxes. | ||
| Inappropriate fire regimes | Implement localised, ground-based patch mosaic burning in and around managed populations and establish firebreaks around managed areas (Burrows 2019) to prevent large wildfires destroying habitat and food resources (Wright and Clark 2007) and facilitating predator access (McGregor et al. 2014; McGregor et al. 2016). | Implement adaptive fire management across selected large areas of the Pilbara with suitable bilby habitat (Department of Biodiversity, Conservation and Attractions 2021). | |
| The fire management plan developed for the Warralong BLMA (Burrows 2019) can be used as a template to be applied to other bilby populations in the Pilbara. | |||
| Introduced herbivores | Opportunistic ground culling of feral herbivores and unmanaged livestock (Department of Biodiversity, Conservation and Attractions 2021). | Consider aerial culling of feral herbivores and unmanaged livestock over large areas of suitable bilby habitat (Department of Biodiversity, Conservation and Attractions 2021). | |
| Negotiate the closure of artificial water points near bilby populations (Department of Biodiversity, Conservation and Attractions 2021). | Consider fencing to exclude livestock (DBCA 2021). | ||
| Exclude introduced herbivores from bilby habitat using livestock fencing (Department of Biodiversity, Conservation and Attractions 2021). | Closure of artificial water points. | ||
| Land clearing | Avoid clearing habitat near bilby populations (Department of Biodiversity, Conservation and Attractions 2021). | To reduce the impacts of land clearing, conserve large tracts of connected suitable habitat to support wild bilby populations (Department of Biodiversity, Conservation and Attractions 2021). | |
| Create formal conservation reserves within the established range of the bilby (Department of Biodiversity, Conservation and Attractions 2021). | |||
| Threat interactions | Introduced predators and fire: Implement localised fire management (as above) and concurrent targeted ground Eradicat® baiting and trapping/shooting at managed sites and surrounding buffer zones (Department of Biodiversity, Conservation and Attractions 2021). | Implement fire management across selected large areas of the Pilbara within suitable bilby habitat, with concurrent aerial Eradicat® baiting and targeted trapping/shooting (Department of Biodiversity, Conservation and Attractions 2021). | |
| Loss of genetic diversity | Consider genetic supplementation of populations with low levels of genetic diversity. | Promote habitat integrity and connectivity to facilitate dispersal and enhance gene flow across the Pilbara. | |
| Establish and maintain a bilby meta-population that preserves genetic diversity and evolutionary potential (DCCEEW 2023a). | |||
| Mining associated infrastructure and disturbance | Avoid clearing habitat near bilby populations where possible (Department of Biodiversity, Conservation and Attractions 2021). | Consider the cumulative impacts of mining operations in areas of bilby habitat, e.g. habitat surrounding salt lakes where there is increasing development of mineral sand, rare earth and lithium mining. | |
| Consider wide culverts/underpasses under railway lines and roads in the proximity of bilby populations. | |||
| Introduce dusk to dawn speed limits and signage near bilby populations. | |||
| Weeds | Targeted management of buffel grass and habitat restoration. | ||
| Road mortality | Limit disturbance associated with the construction and upgrading of roads in areas where there are bilbies. | ||
| Introduce dusk to dawn speed limits and signage near bilby populations. | |||
| Population decline | Reintroduce free ranging bilbies, and the beneficial ecosystem services they provide, to areas where they were locally extirpated, without the need of high-cost predator exclusion fencing (e.g. replicate the success of Matuwa; Lohr et al. 2021). This would require management of introduced predators and herbivores, and fire as above. |
