The bilby is a long-snouted, desert-dwelling marsupial native to Australia, recognized by its large, rabbit-like ears and silver-gray fur. Only the greater bilby remains today; the lesser bilby became extinct in the mid-20th century. Historically, the greater bilby occupied over 70% of the Australian mainland. Today, its range is severely fragmented, and the species is classified as vulnerable, surviving only in isolated pockets of central and western Australia.
The Threat of Introduced Predators
The greatest driver of the bilby’s population decline is the introduction of non-native predatory mammals, primarily the feral cat and the red fox. Australia’s native fauna evolved without these terrestrial predators, meaning bilbies possess few effective defensive behaviors. This lack of adaptation makes them vulnerable to these new threats.
Bilbies fall into the “critical weight range” (30 grams to 5.5 kilograms), making them highly susceptible to predation by cats and foxes. Bilbies typically weigh between 1 and 2.4 kilograms. The red fox, first introduced for recreational hunting in the 1860s, has been linked to a 70% contraction in the bilby’s geographic range. Foxes are highly efficient hunters that have spread across most of the continent, thriving due to the lack of natural controls.
Feral cats pose an equally significant threat, with an estimated average population of 2.8 million across Australia. Cats kill an estimated 460 million individual native mammals each year, placing unrelenting pressure on bilby populations. Their predatory behavior is not limited to hunting for sustenance, as cats often kill native prey even when not hungry.
The widespread distribution and high reproductive rates of both cats and foxes make broad-scale control extremely challenging. The presence of other invasive species can indirectly boost predator numbers. Abundant feral rabbit populations provide a stable food source that supports a higher density of feral cats, increasing predation risk on bilbies when rabbits are less available. This combined pressure has overwhelmed the bilby’s ability to recover in the wild.
Habitat Degradation and Resource Competition
Beyond direct predation, the bilby’s decline is compounded by extensive environmental changes that degrade its habitat and limit its access to food and shelter. Habitat loss due to land clearing for agriculture and urban development has fragmented bilby populations, isolating them into smaller areas. This fragmentation restricts gene flow, making remaining populations less resilient to disease and localized environmental pressures.
The clearing of woody vegetation, especially for cattle stations in states like Queensland and New South Wales, directly destroys the bilby’s foraging grounds and shelter. Bilbies rely on their burrow systems for refuge from predators and extreme desert temperatures, but these are often compromised by introduced livestock. Trampling by cattle can cause the collapse of burrows, making them unusable and exposing the animals to heat stress and predation.
Resource competition further strains bilby survival in compromised environments. Feral rabbits are widespread and compete directly with bilbies by grazing on native grasses and plants. Livestock grazing alters the composition of native vegetation, reducing preferred food sources and promoting the growth of introduced or less palatable plant species. This combination of lost shelter, reduced food availability, and altered vegetation structure significantly lowers the bilby’s chance of survival in unfenced areas.
Strategic Conservation and Recovery Efforts
Conservation efforts focus on creating secure, predator-free havens where bilbies can breed and thrive without the threat of introduced species. Large, fenced sanctuaries, such as the 9,000-hectare Australian Wildlife Conservancy’s reserve at Mali Cliffs, provide extensive safe areas. These feral-free zones allow bilby populations to recover and fulfill their role as “ecosystem engineers” by turning over soil through digging.
Captive breeding programs provide a consistent source of bilbies for reintroduction into these secure reserves, as well as into areas where feral predators have been successfully eradicated. For instance, the Taronga Sanctuary maintains a successful breeding site that supports reintroduction efforts. In some recovery programs, bilbies are put through predator avoidance training, which exposes them to predator scents or decoys before release to improve their survival instincts in the wild.
Effective land management practices are also being integrated into recovery plans to address habitat degradation. This includes the incorporation of Indigenous fire management knowledge, which utilizes controlled burning practices to maintain healthy ecosystems and prevent catastrophic wildfires. These collaborative strategies, combining scientific research with traditional knowledge, are necessary for the long-term success of bilby recovery and potential reintroduction into larger, unfenced areas of their former range.