Time is running out for many iconic Australian animals. Rewilding can repair their ecosystems, but each attempt faces unique and sometimes controversial challenges. John Read poses 12 current conundrums, as a conservation ecologist seeking solutions.
A pair of eyes peeks through the open door of a petpack, placed carefully under a low bush.
A safe distance away, a throng of focused onlookers interpret nervousness, inquisitiveness and maybe jetlag in those eyes.
These witnesses collectively share an even wider range of emotions.
Traditional Owners are reconnecting with their land, culture and responsibilities through this once familiar animal.
Conservation managers are reflecting on the years of research, planning, construction and red tape required to reach this milestone.
Philanthropists and politicians, integral to this conservation program, are reluctantly following the rules not to use their flashes to capture the moment of truth.
Vets and animal keepers, who nursed and housed the little animal are handing over responsibility to wildlife ecologists, now responsible for its future.
This progression of a rare animal from captivity to the wild, mirrors our human healthcare system. Different healthcare workers tend patients from ambulances, through emergency response and recovery wards, then back home.
Conservation also requires the ecological equivalent of physiotherapists, dieticians, psychiatrists and occupational therapists who are key to successful, sustained recovery.
But with no allied health textbooks to follow, ‘rewilding’ relies on duplicating successes, learning from failures and the dedicated pursuit of novel solutions.
Our aim? For once-threatened species to be integrated into dynamic, functioning ecosystems with minimal ongoing intervention.
Warru, the black-flanked rock-wallaby
“Warru kuna tjuta,” whispers Sherada, as he points to the shiny black wallaby scats known as ‘kuna’, under the flowering spearbush.
I nod, but with more elation than the reserved Indigenous ranger.
The plentiful wallaby scats on the burnt orange monolith of Wamitjara, just south of Uluru in the Anangu Pitjantjatjara Yankunytjatjara (APY) Lands of South Australia are cause for celebration.
Sherada was with me in 2006 when we confirmed the localised extinction of warru, or black-flanked rock-wallaby (Petrogale lateralis centralis) from Wamitjara. Now, six years after we had successfully reintroduced these 3–5kg marsupials, the wallaby scats under the pruned spearbush demonstrated the success of rewilding, or returning, free-living threatened species back to their former ranges.
Warru were historically an important food source and cultural icon for Sherada’s ancestors. At one cave, ancient rock and log walls barricaded warru escape routes to assist hunters spear these nimble prey. The floor of the cave was piled with warru kuna, like sheep manure under a shearing shed. But the scats were now old and grey, indicating warru were long gone from even this key habitat.
Invasive foxes and cats and episodic fires wiped out all but the largest warru colonies in the safest rocky refuges. Gradually, over more than a century, hundreds of colonies – that early naturalist Hedley Finlayson described as “swarming on every hill” – blinked out.
Fearing statewide extinction, the Warru Recovery Team was established in 2007 when we only knew of two remnant populations of what had become South Australia’s rarest mammal.
Our team set out to mirror the success of Western Australian ecologists who had bolstered rock wallaby populations in the wheatbelt by poisoning foxes. However, a decade of fox baiting did not arrest the warru decline in the APY Lands.
Baiting made the situation worse. Fox baits also killed dingoes, the main predator of euros, a kangaroo that browsed important tasty perennials out of the reach of their smaller cousins.
After we had started predator baiting, Sherada and I would typically count over 100 euros on a spotlight circumnavigation of Wamitjara but not a single warru.
With fox baiting unsuccessful, the Warru Recovery Team embarked on an emergency program of harvesting small joey warru from remaining colonies and cross-fostering them to yellow-footed rock wallaby females at Monarto Zoo.
Once weaned, these young warru were returned to a feral predator exclosure, not far from Wamitjara. The whole process, from deciding where warru could be sourced from, assigning them names and welcoming them back to country was orchestrated by a group of senior Anangu women, known as the Warru Minyma.
The Warru Minyma, including Sherada’s grandmother, also added the story of ‘stolen’ warru babies being returned to their lands into their evolving warru Tjukurpa or traditional dance story.
The number one rule of rewilding is to resolve main threats before attempting reintroductions.
We had been working on the assumption that foxes were the main threat, but the Warru Rangers helped make an important discovery.
Ranger Ethan Dagg found warru remains in the stomachs of five cats. He even shot a cat feeding on a freshly killed wallaby. That was all the evidence we needed to change tack.
1. How can introduced mid-level predators be controlled while retaining useful apex predators?
The Warru Rangers suspended their baiting and increased their hunting frequency.
Contract feral cat and fox shooters were hired, shooting hundreds of cats. Dingoes – that helped regulate euro and probably fox populations – were off limits.
Unlike in densely wooded habitats, the bright eyes of cats and foxes are visible for hundreds of metres on the rock outcrops, so easy to shoot.
Because some cats will avoid spotlights (or traps or baits), multiple control tools are required for sustainable feral cat control.
Sherada, Ethan and the other rangers also installed newly developed Felixers. These devices are designed specifically to target cats and foxes by applying toxic gel to their fur, avoiding dingoes and other wildlife.
Within a few years euro numbers declined and remnant wild warru numbers increased. With a strategy to control their main threats, we were now ready to rewild warru to new locations.
2. How can rewilding activities avoid exacerbating threats, like spreading weeds?
Minutes after Sherada and I enjoyed the rewarding sight of warru kuna once again on Wamitjara, we shared another, more troubling, observation.
A dense patch of invasive buffel grass (Cenchrus ciliaris), locally known as ‘mamu tjampi’ or devil grass, was growing through the boulder field, largely obscuring our footsteps and making walking risky.
This was the same area Brett Backhouse, regional landscapes ecologist and fellow member of the Warru Recovery Team, had unsuccessfully treated with herbicide a couple of years earlier.
This buffel patch represented a microcosm of the most serious invasive species threat not only to warru, but to conservation and culture in central Australia.
Rock figs, or ili, provide sustaining figs for warru, bowerbirds and Anangu. Normally protected from fire by bare rockfaces, these ili are now increasingly placed at risk by dense flammable buffel grass growing right up to, and through, their spreading branches.
The same holds true for groves of red gums and desert oaks being wiped out throughout central Australia by the buffel scourge.
Simply by visiting rewilding locations, and even when attempting to slow the spread of buffel with ineffective herbicides, Indigenous rangers and conservation biologists are often ironically enhancing its spread, which can only realistically be curtailed by biological control.
3. How can ‘overachievement’ of conservation programs be prevented?
The warru ‘Pintji’, or fence, is the ‘recovery ward’ for captive bred warru. The 100-hectare predator exclosure allows captive-bred warru to adapt to regional conditions and breed up prior to wild release.
The Pintji population doubles every couple of years in the absence of predators. By carefully adding genetics from distant warru colonies, we established a viable source for rewilding. By 2020 the Pintji supported nearly 100 warru, even after 70 had been removed for the Wamitjara rewilding.
The horrific 2018–19 drought coincided with the onset of COVID-19 access restrictions. This created a potentially catastrophic overabundance issue within the enclosure, when even ili were being debarked by hungry warru.
Overachievement is an often overlooked challenge of conservation programs. But starving overabundant warru destroying their habitat is just as serious as buffel replacing palatable plants or cats killing warru.
In response, the Warru Recovery Team have brainstormed a meticulous plan to keep warru populations within sustainable thresholds.
Five years after warru were rewilded at Wamitjara, 40 pouched pioneers were driven in a convoy of troopcarriers to Kulitjara, over 100km south-east of the Pintji, near the community of Mimili.
A few gung-ho male warru were killed by dingoes when they dispersed away from the rocky hills. But most survived and are breeding. They’re leaving distinctive scats in quadrats monitored by a new team of Warru Rangers.
Other Anangu communities are now nominating to receive meaningful employment and training, and reinvigorating cultural ties with their country through warru rewilding.
The Warru Recovery Team is also eager to expand. The best hope for the future of warru and other threatened species in remote deserts, is to have more colonies, supported by sustainable environmental management.
In time, Anangu may once again be able to share warru hunted sustainably from their own rewilded population and cooked over a smoky fire in the traditional way.
The greater stick-nest rat
Black and white film of Aboriginal hunters burning rats from their nests in the early 1900s reveals how recently greater stick-nest rats (Leporillus conditor) occupied saltbush country of much of southern and central Australia.
Within decades, the arrival of sheep and rabbits destroyed the refuge habitats of these industrious herbivores. Foxes and cats also preyed on this sedentary rodent, so the last remaining stick-nest rats were marooned on the tiny Franklin Islands in South Australia.
Pioneers from the Franklin Islands were successfully translocated to nearby islands that were also free of livestock, cats and foxes, but the real challenge was rewilding the placid native rodents on the mainland.
4. How can we adapt programs to our changing climate?
I vividly recall our elation when my partner Dr Katherine Moseby and I recorded the first breeding female, in saltbush shrubland in the Arid Recovery Reserve of central South Australia. But joy turned quickly to despair when a large proportion of the new population died, virtually overnight, during their first summer heatwave.
The survivors had constructed their stick nests in airconditioned old rabbit warrens, but those living in surface nests simply couldn’t tolerate temperatures their species had not experienced for decades, maybe ever.
Despite building a cat and fox free haven in prime chenopod shrubland, we were faced with the sobering reality that just like the recent demise of the Bramble Cay melomys (Melomys rubicola), the environment may no longer be suitable for some species.
5. How can we manage multispecies rewilding?
Some warren dwelling stickies did survive, even thrive, where old warrens provided refuge. But then the next challenge came.
Boodies (Bettongia lesueur), also reintroduced from island refuges, bred up well in the Reserve. So much so that they depleted the stickies’ food resources, especially in drought.
The best way of keeping boodies at sustainable levels was the introduction of predators, including woma pythons and quolls, but unfortunately for the stickies they were more susceptible to native predators than the larger marsupials.
The stickies were caught between overabundant boodies, quoll predation and extreme summer temperatures. The rewilded population dwindled to extinction after just two decades.
While this story has a sombre ending for greater stick-nest rats, we continue to try. We learn from these failures, but rewilding will continue to be a rollercoaster of emotions for conservation biologists. The more of these questions we can answer, the better our chance of protecting Australia’s unique wildlife.
The mallee emu-wren
The mallee emu-wren (Stipiturus mallee) is one of Australia’s most diminutive birds, sporting an improbably long tail resembling emu feathers.
Like threatened sandhill dunnarts and night parrots, they are dependent upon sheltering in long unburnt spiky Triodia hummocks.
Bushfires within remnant mallee patches caused their extinction within South Australia in 2014. Fires remain a serious threat, but our drying climate was also likely contributing to their decline.
In 2018 a mallee emu-wren rewilding pilot translocated Victorian birds back into Ngarkat Conservation Park in South Australia.
Luke Ireland and his team faced the major challenge of relocating 78 of these tiny cryptic animals that can’t be fitted with long-term radio-tracking devices, making monitoring difficult.
“Even banding these tiny birds to reidentify individuals was risky because their toothpick thin legs could potentially get stuck or even break when the birds scurried through dense spinifex,” Luke explains.
6. How can we monitor small, cryptic or delicate animals?
The easy option is to release any reintroduced species without monitoring. But as Luke attests, “Without monitoring we don’t know if they survive, we can’t optimise rewilding strategies, we can’t intervene if necessary and we can’t learn about their behaviour or ecology”.
Although the long term success of the rewilding will be difficult to assess, another of the emu-wren researchers, Tom Hunt, has already been able to document cooperative breeding in the wild for this species. This will influence how potential future rewilding projects are conducted.
The southern corroboree frog
The critically endangered southern corroboree frog (Pseudophryne corroboree) is just 2.5–3cm in length, but it’s an important part of its alpine ecosystem.
These striking yellow and black frogs are restricted to just the Snowy Mountains region of Kosciuszko National Park. However, these coroborree frogs would be completely extinct if not for emergency captive breeding by the Taronga Conservation Society Australia and Zoos Victoria.
7. How can we protect susceptible species from widespread disease?
Southern corroboree frogs are threatened by chytridiomycosis, a disease caused by infection with the amphibian chytrid fungus (Batrachochytrium dendrobatidis). This same pathogen has been responsible for a spate of frog extinctions globally.
The greatest challenge to rewilding corroboree frogs is the presence of another native frog, the common eastern froglet (Crinia signifera) which hosts, but is not affected by, the fungus.
Disease-free field enclosures that exclude the common eastern froglet have successfully maintained insurance populations of southern corroboree frogs. But like all threatened species recovery plans, rewilding to natural and recreated habitats is the ultimate goal. For corroboree frogs, this also means selecting areas that are not occupied by the common eastern froglet.
8. How can we keep pest herbivores from eating sensitive habitats?
Creating small wetland areas is attracting another major threat to the Kosciuszko environment; feral deer, brumbies, pigs and even cattle. These pests trample and destroy the wetland structure and fragile vegetation.
Dr David Hunter, Chair of the Corroboree Frog Recovery Team explains. “There’s no point doing all the captive breeding and reintroduction work on this iconic frog, only to have the key breeding habitat destroyed by deer and pigs.”
In addition to landscape-scale deer and pig control being undertaken by the NSW National Parks and Wildlife Service, David’s team are also focused on protecting individual breeding pools at critical locations. Exclusion fences have been used and the team plan to broadcast human voices to scare deer from other ponds.
Idnya, the chuditch
Known as western quolls or chuditch (Dasyurus geoffroii), 93 pioneering individuals changed their postcode and their name when flying to the Ikara–Flinders Ranges in South Australia. These nationally vulnerable, 1–2kg marsupial predators with distinctive white spots, became known as idnya in the Adnyamathanha dialect.
The rewilding of idnya back into South Australia after their disappearance in the early 1900s fulfilled both an important cultural and ecological void.
Idnya are voracious predators and were hoped to be able to limit the rabbit population.
Unlike the stick-nest rats that were quickly wiped out and cannot tolerate invasive predators, quolls can defend themselves against small cats and have managed to survive in mainland remnants.
9. How can we stop catastrophic predation?
There was initial reintroduction success for the chuditch, but the celebration didn’t last long.
“We then had a spate of killings in a short space of time,” reports Katherine, who coordinated the rewilding. DNA testing of saliva left on the quolls, or their collars, proved that a single cat was responsible.
“After the culprit was captured, the killing stopped until another catastrophic cat learned to hunt quolls and another killing spree ensued,” Katherine explains.
These ace hunters are not so interested in baits or traps. As such, they were the biggest challenge the pioneering quolls and their team of rewilders faced.
Katherine and her team focused on the grisly task of setting cat traps around freshly-killed idnya carcasses.
In the future they hope that a stable toxic implant for threatened animals will poison a catastrophic cat after it has eaten its first prey and before it could wipe out a population.
10. How can we manage long-distance dispersal?
The other key challenge faced by the idnya rewilding was ‘hyperdispersal’, especially of males, outside the cat management zone.
With no fences or other barriers to restrict their movement, some cavalier quolls moved 18km a night. Quolls at other release sites have moved up to 150km over time.
Even if these animals could survive in an unmanaged area with high predator numbers, they are unlikely to find a mate and contribute to the population.
Hyperdispersal is not just limited to quolls. Indeed 10–20% of individuals in more than half of all reintroductions have wanderlust.
The woma python
Woma pythons (Aspidites ramsayi) are large nonvenomous snakes that weigh up to 6kg. They formerly occupied sand dunes and sandplains throughout much of arid Australia. Now they have disappeared from, or become critically endangered, in parts of their former range.
I was keen on rewilding woma pythons to the Arid Recovery Reserve in northern South Australia to keep bourgeoning populations of reintroduced mammals in balance.
11. How can naïve translocated animals be equipped for ‘wild’ challenges?
Crawling slowly to observe a released radiotracked woma in dense canegrass, I was shocked to come face to face with a very fat, perhaps even smug, mulga snake (Pseudechis australis) with a full belly. Over the next few months this fate was repeated with other womas.
Although adult womas can eat snakes, predation of half-grown womas bred at Adelaide Zoo by mulga snakes thwarted this rewilding.
Captive bred animals are not as aware of, or skilled at avoiding, predators or even finding food or shelter sites as their wild cousins. This is a challenge we’re yet to completely resolve.
12. How can we allow wildlife, but not invasive threats, to pass through conservation fences?
At Wild Deserts in Sturt National Park, womas can become entangled in the netting fences designed to exclude rabbits, cats and foxes.
Dr Reece Pedler from Wild Deserts explains, “We have this unfortunate conundrum of needing to maintain an exclusion fence for invasive species that enables passage of native wildlife, especially rare womas”.
The Wild Deserts team is now designing and trialling a range of portals that enable womas – but not rabbits or cats – to pass through.
For this and all 12 challenges, resilient populations of once-threatened species will be our measure of success.