A release of captive-bred greater bilbies on a South Australian island has become a useful example of what threatened native mammals can do when introduced predators are removed.
Bilbies were introduced to Thistle Island in 1997. According to Australia’s 2023 greater bilby recovery plan, surveys conducted a decade later found that the population had increased and occupied the entire island.
That is an encouraging result, but it needs careful framing. Thistle Island is a protected setting, not a picture of recovery across Australia. The greater bilby remains listed as Vulnerable, its former range has contracted sharply, and there is still no robust national population estimate.
What happened on Thistle Island
Thistle Island was not part of the greater bilby’s known historical range. Captive-bred animals were introduced there because the offshore island offered something that much of mainland Australia could not: freedom from exotic predators.
The island had a history of grazing and habitat clearance. Even so, bilbies established there and reached high density, according to a 2020 study in Wildlife Research.
The researchers compared the island population with bilbies in a mainland enclosure where feral cats and European rabbits remained present. Adult survival was similar at the two sites, but the mainland population declined and produced few surviving younger animals despite adult females continuing to breed.
The researchers concluded that low recruitment on the mainland was probably linked to feral cats preying on young bilbies after they emerged from the pouch. That qualification matters. The study supports predator control as a central explanation, but it does not show that every difference between the two populations had a single cause.
Why predator-free havens make a difference
Greater bilbies evolved without foxes and cats. When those predators are removed, breeding has a better chance of producing young animals that survive long enough to join the adult population.
That is the practical value of safe havens. Islands and fenced reserves can sharply reduce predation pressure while conservation teams monitor populations, manage habitat and maintain genetic diversity.
Australia’s environment department identifies predation by feral cats and foxes among the species’ key threats. Its current greater bilby profile describes safe-haven populations as insurance against extinction in the wild and as a foundation for returning bilbies to parts of their former range.
The Thistle Island case also shows that habitat does not have to be untouched to support a new population. Removing the most damaging threat can allow an adaptable species to use a landscape with a history of disturbance.
Safe havens are not effortless, however. Fences require inspection and repair, islands need biosecurity, and populations need monitoring. Managers must also plan for genetic health, food availability, fire and changing environmental conditions.
Can bilbies recover beyond fences?
Predator-proof fences are not the only possible approach. A reintroduction at Matuwa, an Indigenous Protected Area in Western Australia, offers evidence that bilbies can persist in an open landscape when feral predators are consistently controlled.
A 2021 study of the Matuwa reintroduction reported that 144 bilbies were released between 2007 and 2010. By 2017 to 2019, the estimated area they occupied had increased by 88 per cent from the first four years after reintroduction. The researchers attributed the result to sustained, landscape-scale control of feral predators, alongside broader management of herbivores and fire.
Matuwa is important because it points towards recovery outside fully enclosed reserves. It does not remove the need for long-term work. Predator control must be maintained, populations must be monitored, and results in one landscape cannot simply be assumed elsewhere.
First Nations management is central to that wider task. The federal profile says around 70 per cent of current bilby populations occur on lands managed by First Nations peoples. Ranger-led monitoring, fire management and predator control are therefore part of the species’ national recovery, not a separate supporting activity.
Protected populations are growing, but the national picture is incomplete
Recent results from fenced sanctuaries add to the evidence that bilbies can increase when cats and foxes are excluded.
On 30 March 2026, Australian Wildlife Conservancy said its annual census estimated 5,330 bilbies across six sanctuaries and partnership sites. That was more than four times its reported 2021 figure of 1,230.
The figures come from the organisation managing the sanctuaries and should be read as its estimates, not as an independent national count. All six populations are protected within fenced safe havens. Rainfall and food conditions also helped drive growth at some sites.
The result is still significant. It shows that managed refuges can hold large and growing populations. What it does not show is that bilbies are recovering at the same rate across their remaining wild range.
A refuge is a foundation, not the finish line
The greater bilby’s range has contracted by more than 80 per cent, according to the federal environment department. Foxes, feral cats, damaging fire patterns and competition from introduced herbivores continue to affect the species.
There is no robust estimate of the total population. The department says reintroduced populations were estimated to contain about 3,000 animals in 2021, but that figure does not measure every bilby in the wild.
Thistle Island demonstrates what becomes possible when a major threat is removed. The harder conservation test is whether that success can be sustained across different safe havens and extended into open landscapes through durable predator control, appropriate fire management and close work with Traditional Owners.
The island result is therefore neither a curiosity nor a declaration of victory. It is evidence that bilbies can rebuild when they are given protection, and a reminder of how much protection the species still needs.
