Why Are Bilbies Endangered? Threats & Conservation

Greater bilbies are endangered primarily because introduced predators, especially red foxes and feral cats, have decimated their populations across most of Australia. Their geographic range has contracted by roughly 70%, with the species now confined to scattered pockets of arid and semi-arid land in Western Australia, the Northern Territory, and a sliver of Queensland. Predation alone does not tell the whole story, though. Livestock grazing, competition with rabbits, and changed fire patterns have degraded the landscapes bilbies depend on, compounding the damage in ways that make recovery far harder than simply removing a single threat.

A Range That Has Shrunk Dramatically

Before European colonisation, bilbies occupied a vast stretch of the Australian interior and beyond, from arid spinifex country to semi-arid woodland. The lesser bilby, a close relative, went completely extinct by the 1950s. The greater bilby has survived, but barely. Research modelling the bilby’s historical and current extent of occurrence found a 70% reduction in geographic range alongside a 46% decline in the environmental conditions the species actually uses, a measure researchers call the “realised niche.”¹ That niche decline matters because it means bilbies are not just occupying less land; they have been pushed out of entire habitat types they once thrived in. Today the species clings to the hottest, driest corners of its former range, places that happen to be less hospitable to foxes rather than especially good for bilbies.

The Fox Problem

Of all the threats bilbies face, the European red fox stands out as the single best predictor of where bilbies have disappeared. The same study that documented the 70% range collapse tested multiple explanatory variables, including rainfall change, land clearing, and cat distribution, and found that fox presence explained bilby losses more convincingly than any other factor.¹ Foxes spread across the continent in the late 1800s and early 1900s, and their wave of colonisation closely tracks the bilby’s wave of retreat.

Reintroduction programs have shown just how lethal foxes are. In a set of ten reintroduction attempts in arid South Australia, half failed outright, and predation was the main reason. Outside predator-proof reserves, bilbies released into areas where cats and foxes were present but managed with poison baiting still could not survive; mortality from cat and fox predation was simply too high.² Even dingoes contributed to post-release kills in some cases. The lesson conservationists took away is that reducing predator numbers through baiting, while helpful, is often not enough on its own.

Feral Cats and the Burrow Problem

Feral cats kill bilbies through a different hunting style than foxes, but the outcome is equally devastating. Research in arid Australia has shown that feral cats focus their hunting on conspicuous prey cues like burrows, foraging digs, and warrens. Bilby burrows, which can be up to two metres deep with distinctive spiralling entrances, essentially advertise the animal’s location. GPS tracking of cats revealed that they spent significantly more time near these kinds of prey cues, and evidence of kills was higher at those sites.³ Worse, the researchers found that resident cats learn to identify and return to prey cues within their home range, meaning the vulnerability of burrow-dwelling species like bilbies increases over time as cats become more efficient hunters.

This creates a grim paradox. Bilby burrows are central to the species’ survival and to the health of arid ecosystems, but they also function as a homing beacon for one of their deadliest predators. Cat control in the open rangelands of inland Australia is notoriously difficult because the landscape is so vast and cats are so resourceful, which is one reason fenced sanctuaries have become a cornerstone of bilby conservation.

Livestock, Rabbits, and Altered Fire Regimes

Predation gets the most attention, but the degradation of bilby habitat has been a quieter, slower-moving disaster. A comprehensive ecophysiology review attributed most of the bilby’s decline to a combination of altered fire regimes, grazing by domestic livestock and introduced rabbits, and unnaturally high predation levels.⁴ These factors reinforce each other. Cattle and sheep compact the soil and strip vegetation, which changes the structure of the ground bilbies dig through and reduces the invertebrate prey they feed on. Rabbits compete for food and further degrade the topsoil.

Fire is a particularly underappreciated factor. Before European settlement, Indigenous Australians managed the landscape with carefully timed, small-scale burns that created a mosaic of vegetation ages. Bilbies benefit from this kind of patchwork because recently burned areas produce fresh growth that attracts insects and bulbs. When that fire management collapsed, large wildfires became more common, burning through huge tracts of spinifex and leaving bilbies with less food and less cover over broader areas.

What Bilbies Do for the Landscape

Bilbies are not just passive victims of environmental change. They actively shape the ecosystems they inhabit, which means their disappearance has knock-on effects that ripple outward. When bilbies dig for food, they create small pits in the soil. Research in South Australian dunefields found that these pits acted as critical nutrient sinks: litter was almost exclusively found inside animal-created pits rather than on the surrounding surface, and over 1,300 seedlings from 46 genera germinated from litter collected in the pits while zero seedlings emerged from surrounding soil samples. The pits also had significantly higher levels of carbon and nitrogen than the soil around them.⁵

Rabbits dig too, but they are a poor substitute. A comparison of bilby, burrowing bettong, and rabbit foraging pits found that native engineers’ pits contained about 80% more seedlings per square metre than rabbit pits. Rabbit pits actually supported fewer seedlings than equivalent undisturbed soil surfaces outside the study area.⁶ The upshot is that losing bilbies does not just mean losing an animal; it means losing a process that helps arid soils capture water, trap seeds, and cycle nutrients. Replacing bilbies with rabbits makes the problem worse, not better.

Bilbies also play a role in dispersing fungi. Digging mammals spread mycorrhizal spores through the soil, and their pits create sheltered microsites where those fungi can establish.⁷ These fungal networks help plants absorb water and nutrients, so the loss of digging mammals can start a slow cascade of declining plant health, further soil degradation, and reduced habitat quality for everything else living there.

Predator-Free Fenced Reserves

Given how lethal foxes and cats are, the most successful bilby conservation efforts have involved completely removing introduced predators from an area rather than trying to suppress them. Several fenced reserves across Australia now house reintroduced bilby populations behind predator-proof barriers. Long-term monitoring at one such reserve found that all three reintroduced threatened species, bilbies included, preferred shrub vegetation but were able to use every available habitat type in the absence of introduced predators. Over time, the animals expanded their habitat use and shifted their movement patterns, suggesting a level of behavioural flexibility that bodes well for their persistence.⁸

Fenced reserves are not a perfect solution, though. They are expensive to build and maintain, vulnerable to breaches, and inherently limited in area. A population of bilbies thriving behind a fence is better than no bilbies at all, but the long-term goal has to include animals surviving in open landscapes. That tension between the safety of enclosures and the need for wild-ranging populations is one of the central dilemmas in bilby conservation.

Teaching Bilbies to Survive Cats

One of the more creative approaches to bridging the gap between safe havens and the wild involves training bilbies to recognise and avoid predators they have never encountered. Bilbies raised in predator-free enclosures are “predator-naive,” meaning they have no instinct to flee from cats or foxes because they have never been exposed to them. Early experiments tried to condition bilbies using cat scent cues. Trained animals in a predator-free setting did change their behaviour: they moved farther, used more burrows with multiple entrances, and relocated when they detected predator smells. But when those same trained bilbies were released into an area with real cats and foxes, there was no improvement in survival compared to untrained controls.⁹ Recognising a predator’s scent in a quiet enclosure is very different from surviving a real encounter at night in the desert.

A more promising approach has been to expose bilbies to actual cats rather than just their scent. Researchers introduced a controlled number of feral cats into a large fenced paddock containing bilbies and let them coexist for about two years. The bilbies that survived this exposure developed measurably warier behaviour: they spent less time moving in the open and more time in cover. When predator-exposed bilbies were later translocated into a cat-inhabited environment, they were more likely to survive to 40 days and less likely to be killed by cats than predator-naive bilbies.¹⁰ Separate research examining bilbies conditioned by living alongside cats within enclosures also found morphological and behavioural shifts that appeared to boost anti-predator ability.¹¹ This “in situ” conditioning approach is now being integrated into reintroduction planning, though scaling it up remains a challenge.

Genetic Health and Captive Breeding

Small, isolated populations face a genetic threat that is less visible than a feral cat but just as dangerous over time. Inbreeding reduces a population’s ability to fight disease and adapt to changing conditions. Genomic work on bilbies across multiple source populations found that most exhibited lower genetic diversity than expected, a signal that inbreeding is likely occurring. However, populations that had been created by mixing individuals from different source groups showed higher diversity, and this boost carried through to their offspring.¹²

Captive breeding programs have been running since the late 1990s, with at least two major programs using different strategies. One allowed semi-free-range natural mating; the other used selective pairings to minimise relatedness. Both programs maintained genetic diversity over time, especially when new individuals were periodically introduced from wild or other captive stocks.¹³ The consensus among geneticists managing the species is that connectivity between populations, moving selected individuals between reserves and breeding facilities, is now essential to long-term survival.¹⁴ Without regular mixing, each isolated pocket of bilbies drifts further into genetic trouble.

Indigenous Knowledge and On-the-Ground Monitoring

Bilbies hold deep cultural significance for many Aboriginal groups, who have observed and managed the species for thousands of years. In the Western Desert of Western Australia, Martu Traditional Owners refer to the bilby as “Mankarr” and have detailed knowledge of its behaviour, diet, and habitat preferences that predates any European scientific study by millennia. A collaborative monitoring program developed with Kanyirninpa Jukurrpa Indigenous ranger teams combined this biocultural knowledge with Western ecological methods to track bilby populations on country.¹⁵ The “two-way learning” approach acknowledges that Indigenous rangers bring expertise that scientists lack, including the ability to read tracks, identify burrow activity, and interpret landscape cues that standard survey methods miss.

Complementing this ground-level expertise, non-invasive genetic monitoring has become an increasingly practical tool. Researchers have developed techniques to extract DNA from bilby scats (droppings) and use it to identify individuals without ever trapping or handling the animals. Faecal DNA can be amplified with a 99% success rate and low error rates when pellets are collected within two weeks of being deposited, and usable DNA persists for months in the arid conditions where bilbies live.¹⁶ Combined with spatial modelling, this scat-based approach allows researchers to estimate population sizes and track individuals across time.¹⁷ For a nocturnal, burrowing animal that lives at very low densities across remote deserts, being able to monitor populations without physically catching them is a significant practical advantage.

Climate Change and the Bilby’s Body

With the bilby already pushed to the hottest parts of its former range, rising temperatures add another layer of concern. Research comparing bilby populations from different climatic regions found a strong link between local temperatures and physical traits. Bilbies in areas where summer temperatures hit 40°C had skulls roughly 14% shorter and 12.5% narrower than bilbies from cooler 25°C regions. Six different fur traits, including density and length, also declined with increasing temperature, consistent with the idea that smaller bodies and thinner coats help animals shed heat.¹⁸

Intriguingly, bilbies from the same source population that were translocated into climatically different reserves, one hot and arid, one cooler and more temperate, showed significant divergence in fur traits within about 25 years, even though body size had not yet shifted.¹⁸ That pace of change suggests bilbies have some capacity to adapt to warming conditions. Whether that plasticity will keep up with the speed of climate change across inland Australia is an open question, but it offers at least a glimmer of resilience in a species that has precious little margin for error.