For the past five years the Kimberley forecast has been cloudy with a chance of cane toad sausages.

The 'wart wurst' sausage, made from toad legs and laced with nausea-inducing chemicals, are supposed to teach native wildlife not to eat the amphibian before the main invasion wave reaches them.

There were high hopes the method could halt the devastation and localised extinctions of native predators.

But with the toads only 150 kilometres from Broome, after travelling 200 kilometres in the past five years, there are doubts about whether aerial sausage bombardment has worked at a grand scale.

For at least one major conservation group in the Kimberley, the taste aversion experiment is over.

And it wants to see toad-related management expenditure in the region going into other measures.

A bad taste:

Cane toads when threatened release a milky toxin from glands on the back of their head.

The defence mechanism is supposed to encourage predators to spit them back out.

For domestic pets like dogs the bufotoxin can be a natural high but also deadly.

When it comes to several native animals that ingest, or even just get some of the poison in their mouth, the toad can be fatal.

Two of the hardest hit animals have been northern quolls and a species of goanna called the yellow-spotted monitor.

The northern quoll and the yellow-spotted monitor are vulnerable to cane toads

Northern quolls (Above right) were once found across the entire top third of the country.

By 1994, their range had been reduced by 75 per cent to six main areas — probably as a result of cattle, disease and cane toads — and populations have been under pressure ever since.

Yellow-spotted monitors declined by 83–96% when cane toads arrived.

Without the monitors, smaller animals like ta ta lizards have seen their numbers increase as they can breed without having their population kept in check.

Trying to prevent the toads from moving further west has proven impossible to date.

So management of the pest has been focused on things like mitigation.

For more than a decade some of that preventative work has been in the field of conditioned taste aversion (CTA).

Research into CTA for lizards has been focused on the use of toad carcasses to bait individual animals, with work underway on a broadscale response that could work across entire landscapes.

CTA for quolls, meanwhile, has been based around giving them sausage baits over vast environments, following successful small-scale trials in lab settings, that could see the species learn to avoid toads in the wild.

But a field-based study of the effectiveness of the sausages in a wild setting, published earlier this year, had a surprising result.

Researchers gave baits to three quoll populations in the Kimberley's Mornington Wildlife Sanctuary — run by the Australian Wildlife Conservancy (AWC) — and compared the result to four control quoll populations, that weren't given the sausage baits.

Quoll numbers in the control populations declined by 65% after the arrival of the cane toad. But the losses in the areas where baits where deployed was even higher, with populations declining by 94%.

The authors suggest the results may reflect the dose of nausea-inducing drugs in the sausages is too low, or there's an issue with the choice of quoll groups.

And they also note that the mammals were no longer toad-averse, despite training, after 120 days.

"Our result calls into question the value of this approach for conserving quoll populations, at least in its current form," the researchers said.

"More generally, our results point to the often-unexpected complexities encountered as ideas progress from captive trials to field deployment."

Toad snags not working for quolls in Artesian range:

Tom Sayers, a wildlife ecologist for the Australian Wildlife Conservancy, said another yet-to-be published small-scale trial run by the organisation at the Artesian Range found quolls did not even eat the baits.

He said the trial highlighted the uncertainty and variability of bait take-up in wild settings where there was plentiful wild prey alongside other factors.

"There's a lot of questions unanswered with CTA, in wild-trained settings particularly," Dr Sayers said.

"Despite the promise of CTA, the toad front has infiltrated the whole region now.

"And for the Kimberley it is now largely too late to implement CTA given toads are established across the landscape."

Despite a 73% decline on baseline quoll numbers in the Artesian Range in the first year after toads arrived, numbers bounced back to 39% below baseline after three years.

The Australian Wildlife Conservancy — which has a hand with partners in the management of some 4.26 million hectares of land in the Kimberley, about 10% of the region — has taken the view it is too late for further investment into CTA programs across the region.

Instead, AWC will put its resources into reducing other pressures on quolls like fire and feral management.

Dr Sayers said, as conservation practitioners, the organisation aimed to support the natural adaptive capacity of quolls to cane toads.

"There is research to suggest that there is innate or naturally learned toad aversion in quoll populations." 

"And it is therefore possible that some populations over the long-term naturally adapt to avoid consuming toads.

"Going forward in the future there is also the chance of returning quolls back to where they once occurred or bolstering populations through assisted translocations."

The WA Department of Biodiversity, Conservation and Attractions (DBCA), which manages the aerial drop of toad sausages, is yet to publish results from its operations.

Just how effective it has been in other parts of the Kimberley will not be known until the trial is finished in 2024.

A DBCA spokeswoman said results would then be considered alongside other research as to whether it was an effective way to buffer the impacts of toads on quolls.

"There are very few tools available to mitigate the impact of cane toads on northern quolls," the spokeswoman said.

"It is important to collect as much information as possible on all tools available, including CTA."

Hope persists for Kimberley reptiles:

While sausages for quolls has shown some cases of poor results, investigations into CTA for reptiles continues to show great potential.

Efforts to train lizards and fresh water crocodiles, in the parts of the Kimberley where the invasion is yet to reach, are ongoing and getting closer to a landscape-level rollout.

Goannas have not shown much of an interest in sausages and so research has been more focused on the intensive task of setting carcass baits on the ground for different species.

Macquarie University research fellow and conservation scientist Georgia Ward-Fear said big lizards like the yellow-spotted monitor could learn to avoid toads by interacting with juveniles.

"My initial field trials had trained animals surviving in the environment for years among high densities of cane toads, which is unheard of really," Dr Ward-Fear said.

"They either remembered for a really long time, or were getting constant reinforcement from smaller (less-toxic) toads."

"Since then, we've been working on ways to scale those methods up to a landscape level, with many large reptiles"

Research published last year found freshwater crocodiles would take toad carcasses hanging over water bodies and goannas would go for ones set up on the bank.

A DBCA spokeswoman said further research into CTA mitigation for crocodiles and goannas in the Kimberley was showing promising results which would be published within months.

Although toads have nearly infested the whole Kimberley, those results could have implications for the southern invasion front and a major new frontier for the toads, the Pilbara.

There is a proposal, however, that could make management practices like mitigation unnecessary.

Once-in-a-generation chance to halt invasion

Last month, two long-time toad scientists found themselves at the cane toad front line.

Curtin University population biodiversity professor Ben Phillips and Deakin University marine biology and aquaculture professor Tim Dempster have dedicated years to studying the golden-eyed creatures.

Every year they fly into the region to see how far west the toads have got.

Professor Dempster said he believed the toads would be in Broome within three wet seasons.

"This year, they were all fat, so they're in extraordinarily good condition," he said.

"Sometimes at the end of the dry season you see toads that are a bit emaciated and hanging on in these arid locations."

Once they get to the Broome, the Pilbara could be soon to follow.

The toads have not been able to spread far south in WA with the Great Sandy Desert acting as a barrier to the Pilbara.

Without standing water, toads can dry out in a matter of days and perish.

But artificial water points, such as bores, on the cattle stations located along a narrow strip between Broome and Port Hedland makes it possible toads could get through, despite the arid conditions.

From there they could cause untold damage to the many species of the region which is also the last stronghold for northern quolls.

Professor Phillips said if the toads got through to the Pilbara, that 10 to 15 animals could be added to the national threatened species list or have their threat level raised.

"Without management they will move down that corridor," he said.

"Once they've done that they'll have another 270,000 square kilometres.

"It's an area larger than Great Britain they'll be able to access, we have this amazing opportunity to stop them."

Original Story By | Peter de Kruijff