The taxonomy of Bettongia penicillata has been unsettled. The species was once the most widespread of any member of the Potoroidae with records from all mainland States and the Northern Territory (Start et al. 1995). It is possible that the two subspecies represent distant ends of clines that terminated in southeastern Australia (subspecies penicillata), southwestern Australia (subspecies ogilbyi) and northern Queensland (B. tropica, originally described at a subspecies of B. penicillata). Bettongia penicillata penicillata is Extinct. Bettongia penicillata ogilbyi is extant.

A 95% decline occurred in the largest extant Woylie subpopulations (in the Upper Warren region, Western Australia) between 2002 and 2008. At a species level, woylies declined ~90% (1999–2006), from a peak of ~200,000 individuals in 1999. This led to the assessment of Critically Endangered in 2012. The decline has ceased, partly due to control of introduced predators and partly due to translocations. Currently (2024) the Woylie occurs at 19 locations, has a population size of c. 140,000, and its population size has increased over the past 11 years, having suffered a major decline over the previous 15 years. However, estimated population size in 2024 is 70% of the population size in 1999 when they reached their peak from recoveries achieved since the 1970s and population size will have reduced in 2023-2024 due to a severe drought.

The Woylie does not meet Criterion A or Criterion C as the population size is >10,000 and while it has been increasing in the past, the recent severe drought in the south-west of Western Australia (where most Woylies occur) will have caused a reduction in population size. It does not meet Criterion B as there are >10 locations and there are no extreme fluctuations; however there has been a recent decline in population size due to severe drought, and as there is a continuing decline in mean rainfall in the south-west of Western Australia due to climate change, the it is precautionarily inferred that the decline is likely to continue. A continuing decline in habitat quality is also likely. It does not meet Criterion D as the population size and AOO are larger than thresholds. Due to its history of major declines and recovery, followed by another decline and recovery, and because the status of the species is highly dependent on the continuation of intensive management needed to protect extant subpopulations from introduced predators, and because of the declining rainfall and increasing frequency of drought where most Woylies occur it is assessed as Near Threatened approaching Vulnerable B2ab(iii,v).

Formerly (prior to European colonisation of Australia in 1788) Woylies were very widespread: they occupied most of semi-arid and arid Australia, mostly south of the tropics, including the arid and semi-arid zones of Western Australia, the Northern Territory, South Australia, New South Wales and Victoria, and possibly extended north along the east coast into Queensland, the remnant of this population now being accepted as Bettongia tropica. Woylies also occurred on Saint Francis and St Peter Islands, South Australia (Robinson et al. 1996). Burbidge et al. (2009), using modern, historical and subfossil records, found that Woylies (excluding B. tropica) are known to have occurred in 28 of Australia’s 85 bioregions, but that they were extinct in all but two. Pacioni et al. (2015) estimated from ancient DNA and genetic analysis and modelling (with limitations and caveats) that the Woylie experienced more than a 99% decline in population size in <4,000 years, but especially since European settlement, being most pronounced in the last 100 years or so.

By 1970, Woylies persisted only in four subpopulations in south-western Australia: Dryandra Woodland National Park, Tutanning Nature Reserve, Greater Kingston National Park and Tone-Perup Nature Reserve. 

In 1975, the South Australian National Parks and Wildlife Service began a breeding program for the species at Para Wirra Recreation Park from animals sourced from Perth Zoo with the goal of providing stock to re-establish the species in South Australia. The first experimental releases were onto three small islands, Bird Club Island (8 ha) in 1979, Venus Bay ‘Island A’ (20 ha) in 1980, and Baird Island, Baird Bay (11 ha) in 1982. These were followed by translocations to three larger islands, St Francis Island (809 ha) in 1980, St Peter Island (3493 ha) in 1981 and Wedge Island (947 ha) in 1983 (Delroy et al. 1986, Freegard 2008, Yeatman and Groom 2012). Woylies did not survive on Bird Club or Baird Islands, probably due to Red Foxes Vulpes vulpes accessing the islands. Nor did they survive on St Francis Island (reasons unknown) (Robinson et al. 1996) but they have established on Saint Peter and Wedge Islands. These translocated Woylie subpopulations are genetically depauperate (Pacioni 2010), having been derived mostly from the small Para Wirra founder group.

There have been numerous subsequent reintroductions on the mainland, to parts of the south-west of Western Australia, the Northern Territory, South Australia, and New South Wales, although some have failed in the medium- to long-term (Priddell and Wheeler 2004, Wayne et al. 2011, Yeatman and Groom 2012). Translocations have been either to unfenced areas subject to control of introduced predators (especially the Red Fox) or to areas in which predators have been eradicated and are excluded by predator-proof fences. Areas that currently (in 2024) have extant subpopulations (mostly due to establishment of translocated animals with continued control or exclusion of predators) are listed in Table 1 in the Supplementary Material. 

A subpopulation sourced from Perup, Kingston, Dryandra, and Wedge Island, South Australia, has (2022) been established in Dhilba Guuranda-Innes National Park in South Australia, although it is too early to determine whether this subpopulation will persist. Following predator eradication on Dirk Hartog Island (620 km²) there are plans to reintroduce Woylies there in 2025.

Pacioni et al. (2011) used a molecular approach (12 microsatellite loci and mitochondrial DNA) to investigate relationships between these subpopulations and, using ancient DNA, of locally extinct subpopulations. Their study demonstrated a severe loss of genetic diversity.

Accounts by early settlers (e.g. Facey 1981) and Aboriginal people (e.g. Burbidge et al. 1988) demonstrate that Woylies were once abundant. In arid Australia Woylies declined after European settlement and survived the establishment of the feral Cat Felis catus but disappeared soon after the arrival of the Red Fox Vulpes vulpes (Burbidge et al. 1988). Abundance in the four remnant Western Australian wheatbelt subpopulations has varied, with Sampson (1971) at Tutanning and Christensen (1980) at Perup finding numbers to be relatively high during the 1960s and 1970s. However, numbers fluctuated, e.g. Kinnear et al. (2002) found Woylies to be rare at Tutanning in 1984. Trap success rates at Tutanning increased from c. 2% in 1984 to c. 28% in 1992 following the implementation of fox control (Wayne et al. 2010), but Woylies are likely to now be extirpated or, if not, no longer viable, in this location. Following the introduction of widespread fox control under ‘Western Shield’ in 1996, Woylie numbers rapidly increased at all four of the original subpopulations and translocations were conducted to several sites in the northern jarrah forest and wheatbelt in Western Australia, a total of 46 translocations in all, and to sites in eastern Australia by 2007 (Wayne et al. 2008).

From about 2000, there was a significant decline in all free-ranging (mainland, unfenced) Woylie populations, natural and reintroduced (Groom 2010). At a species level Woylies were found to have declined by c. 90% from a peak of c. 250,000 individuals in 1999 to 33,000 in 2010. The largest subpopulation, at Upper Warren, declined by 95% from an estimated peak of 215,000 in 1999 (Wayne et al. 2011). A major research program coordinated by the Western Australian Department of Biodiversity, Conservation and Attractions, investigated the reasons for the decline including predation (Wayne et al. 2011, 2013)  and disease (e.g. Botero et al. 2013). Intensive control of feral Cats and Red Foxes has seen Woylie subpopulations in the Upper Warren (Tone-Perup Nature Reserve) and Dryandra Woodland National Park remain relatively stable in recent years, though at numbers appreciably fewer than once thought to occur there.

The most recent populations estimate from the Woylie Recovery Team (2024) is 143,197 (95% confident limits 72,936 – 235,569). Most Woylies occur in the original, natural subpopulations at Upper Warren (28,700 and Perup (83,000). Other subpopulations have relatively few Woylies.

Translocations

Translocations include:

Karakamia, Western Australia (2.6km²). Woylies were reintroduced to Karakamia Wildlife Sanctuary in the early 1990s (Schmidtz and Copley 1997) and a small, established population persists to date.  Population size was estimated at 211 + 15 individuals in January 2024.

Yookamurra, South Australia (11 km²). Woylies were reintroduced to Yookamurra in the early 1990s and a small, relatively stable population of approximately 100 individuals persisted until 2018 when the population collapsed in the 2018-19 drought. Despite supplementary release of remaining animals from Scotia and above-average rainfall since the population has still not recovered, with only 12 individuals captured during annual monitoring in 2023 (Ross et al. 2023).  

Forty-two Woylies were translocated to the Wadderin Sanctuary (4.27 km²) in 2010 and 2012. Numbers peaked at c. 300 individuals (0.71 ha^-1) in 2018 before declining to c.170 individuals in 2021 (Short 2023). Population decline was attributed to food shortage due to high densities of Woylies exacerbated by dry years.

One hundred and eleven woylies were translocated to the Perup Sanctuary (4.23 km²) mainland island (i.e. fenced reserve), 2010-2022 to create an insurance population with representation of the genetic diversity extant among the indigenous populations (Perup, Kingston, Dryandra and Tutanning). Numbers peaked at c. 500 (1.2 ha^-1) in 2016 and have since declined to c. 230 in 2024. Between 2013 and 2022, 420 individuals have been sustainably harvested for translocations elsewhere. Population changes have been correlated with rainfall suggesting the population may be regulated by food resources and at long-term carrying capacity (Harrison et al. 2024.).

Dryandra Sanctuary (mainland island), Western Australia (10 km²) was established in 2015 and has increased to c. 1,300 individuals 2022-2024.  

Mt Gibson, Western Australia (78 km²). Translocations established from Karakamia, Perup and Whiteman Park stock (Smith et al. 2020); this subpopulation was released into a large mainland island (predator-free fenced area) in the Sanctuary (7,832 ha) in 2015-2018. 162 individuals were translocated and the population grew rapidly to ~2,700 in 2022, then declined during a severe drought. Population size is currently estimated as between 400 and 800 individuals.

Mallee Cliffs, New South Wales (96 km2). Translocations to the fenced feral predator-free area in 2021, with founders sourced from reintroduced populations at Scotia, New South Wales and Mt Gibson, Western Australia. A total of 70 animals were translocated. In 2024 the population was estimated at 285 individuals.

Southern Yorke Peninsula, South Australia. A total of 193 individuals were translocated across three years (2021 – 2023) to Dhilba Guuranda-Innes National Park mainland island, with founders sourced from both wild and sanctuary sites in Western Australia (Perup, Dryandra) and South Australia (Wedge Island). KTBA from trapping in 2024 = 83 individuals (735 trap nights). 

Pilliga State Conservation Area, New South Wales (56 km²). Translocations to the fenced feral predator-free area in 2022, with founders sourced from Perup and Mt Gibson, Western Australia. A total of 55 animals were translocated. In 2024 the population was estimated at 174 individuals.

Scotia Sanctuary, New South Wales (40 km²). Significant drought-driven decline was observed during the 2018-19 drought. As an emergency response, all remaining animals were translocated offsite to Yookamurra, South Australia (n = 26) and Mallee Cliffs, New South Wales (n = 16). Woylies no longer persist at Scotia.

Woylies originally inhabited a wide range of country. In the western deserts, Aboriginal people reported that they occupied sand plains and dunes with spinifex (Triodia spp.) hummock grassland (Burbidge et al. 1988). The remnant subpopulations in south-western Australia inhabit woodlands and adjacent heaths with a dense understorey of shrubs, particularly Gastrolobium spp., which contain monofluoroacetic acid, the compound present as sodium monofluoroacetate in the vertebrate pesticide ‘1080’. Diet is largely underground fungi, although it also includes tubers, bulbs and seeds. Woylies can store seed in their cheek pouches for later caching and are a major disperser of fungal spores and seeds (Murphy et al. 2005). Their digging also has a positive impact on the non-wetting property of soils (Garkaklis et al. 1998).

They are solitary animals but nest sharing (usually mother and young at heel) has been recorded (Sampson 1971, Christensen and Leftwich 1980, Start et al. 1995). They occupy home ranges that vary in size between habitats, sites and according to Woylie density. Small home ranges (less than 6 ha) are generally observed at high density occurrences (Nelson 1989 in Nelson et al. 1992, Hide 2006). Males tend to have larger home ranges than females (Sampson 1971, Leftwich 1983), although this is not always so when Woylies are at higher densities (Yeatman 2010). Woylie home ranges have been estimated at 59.1 ha in Perup Sanctuary, and 72.6 ha in Kenninup (part of Tone-Perup) – a combined average of 65.4 ha in the Upper Warren (Yeatman and Wayne 2015).

The major reason for past declines has been predation by Red Foxes and feral Cats, exacerbated in the deserts by changed fire regimes. The crash in numbers recorded between 2000 and 2010 is thought to be primarily due to feral Cats, although exotic disease may have been involved (Abbott 2006, Wayne et al. 2015). Inappropriate fire regimes and the increasing frequency and intensity of drought periods may exacerbate fox and cat predation. The majority of woylie mortalities during the period of decline in the Upper Warren were associated with cats (Wayne et al. 2011, 2013). Marlow et al. (2015) showed that feral Cats became the dominant predator of Woylies at Dryandra Woodland National Park after sustained fox control. Cat control stabilised this subpopulation (Wayne et al. 2011, 2013).

Hall et al. (1991) was the first edition of the Woylie Recovery Plan and guided work between 1991 and 1993. Nelson et al. (1992) guided work in South Australia. Start et al. (1995) was the second edition of Woylie Recovery Plan for the period 1994-2003, written with the expectation that the species could be removed from the threatened species list within a short period of time. Woylies were removed from the Commonwealth and Western Australian threatened species lists in 1996 following an assessment of status (Start et al. 1998). However, from about 2000, Woylies suffered a significant decline and they became again the subject of conservation research and management. Woylie conservation was then guided by an interim recovery plan (Freegard 2008). A revised national recovery plan was finalised in 2012 (Yeatman and Groom 2012). This recovery plan, guided by a national Recovery Team, had seven recovery actions:

·         Verify the causes of the decline and suppression of recovery and implement remedial action to address these.

·         Minimise predation by introduced foxes and cats at priority sites.

·         Maintain or improve the health, genetic diversity, relative value and viability of wild populations.

·         Maintain genetic diversity of the insurance captive populations at least at 2012 levels.

·         Maintain captive population sizes sufficient to act as source populations for future translocations.

·         Undertake targeted translocations as re-introductions (and as introductions where necessary) to achieve an enhanced conservation status for the species.

·         Inform and educate the community about, and involve the community in, recovery actions.

There has been considerable research and management of Woylies in the south-west of Western Australia over a long period of time. The Western Australian Department of Environment and Conservation (DEC, now DBCA Department of Biodiversity, Conservation and Attractions) initiated a major research program to investigate Woylie decline and that of other ‘critical weight range’ (Burbidge and McKenzie 1989) mammals in the late 1990s and early 2000s. The ‘Mesopredator release’ project and ‘Woylie conservation research project’ involved the Invasive Animals Cooperative Research Centre, DEC staff, and researchers from Murdoch University, Perth Zoo, Australian Wildlife Conservancy, South Australian Department of Environment and Heritage, Australian Wildlife Health Network, Wildlife Disease Association (Australasia), University of Adelaide, Data Analysis Australia, University of Western Australia and a number of other professionals and organisations. The major hypotheses examined were that the declines were due to fox predation, cat predation (possibly partly due to mesopredator release), epizootic disease, and/or changes to food resources. Twenty-four university student research projects have also been associated with this research.

The results (Wayne et al. 2008, 2011, 2013, 2015; Marlow et al. (2015), indicated that:   

·         the current fox-baiting regime is approximately >90% effective in removing foxes from baited reserves despite a high non-target uptake of baits by Common Brushtail Possums Trichosurus vulpecula and birds (Australian Ravens Corvus coronoides and Grey Currawongs Strepera versicolor)

·         there is a mesopredator release of feral Cats in the presence of effective fox control in at least some circumstances (Marlow et al. 2015)

·         feral Cat predation is currently the most significant cause of Woylie mortality (given effectiveness of broad-scale baiting in controlling populations of the Red Fox) and operational cat control for the south-west of Western Australia is being implemented in some localities

·         the Woylie subpopulations, in the Upper Warren at least, provide evidence that potentially pathogenic parasites may be associated with the declines and that it is possible disease is making Woylies more vulnerable to predation, but the evidence for it as a primary cause is equivocal (e.g. Smith et al. 2008, Botero et al. 2013, Thompson et al. 2013, Thompson et al. 2014, Wayne et al. 2015, Hing et al., 2016, Godfrey et al. 2018).

There have been > 70 translocations of this species (Morris et al. 2015, Short 2023) to both fenced and unfenced (but baited) sites in WA, SA and NSW, with variable success. Reintroductions of Woylies to unfenced sites (e.g. Katarapko Island on the River Murray floodplain (South Australia) (Katarapko Community Action Group 2001) and to Flinders Ranges National Park (South Australia) (Bellchambers 2000, 2001); Yathong Nature Reserve, NSW (Priddel and Wheeler 2004)) have often failed due to predation, primarily by introduced Red Foxes and feral Cats.

The Red Fox is controlled via aerial and ground baiting in >38,000 km² of conservation lands in the south-west of Western Australia. There is ongoing, long-term research and management aimed at using operational feral Cat control technology. Conservation lands in the south-west of Western Australia with Woylie subpopulations and the Whiteman Park, (managed by the WA Department of Planning, Lands and Heritage), Perup and Dryandra Sanctuaries are managed by the Western Australian Department of Biodiversity, Conservation and Attractions, along with Dirk Hartog Island (where woylies are proposed to be reintroduced in 2025). The South Australian Department of Environment and Water manages islands in South Australia and the Dhilba Guuranda-Innes National Park with Woylie subpopulations. The Australian Wildlife Conservancy manages Karakamia, Mt Gibson, Newhaven, Yookamurra and Scotia Sanctuaries, with Mallee Cliffs and Pilliga reserves in partnership with the NSW government. Wadderin Sanctuary (430 ha) is managed by a local community group with assistance from Wildlife Research and Management Ltd and the Shire of Narembeen. The Red List shows an ex situ population of 154 males, 170 females and 11 unsexed in 73 holding institutions in 22 countries, managed via the Association of Zoos & Aquariums (AZA), European Association of Zoos & Aquaria (EAZA), Japanese Association of Zoos and Aquariums (JAZA), and Zoo and Aquarium Association Australasia.

The Woylie is listed as Endangered under Australian environmental legislation.