Vanilla, fake eggs and nausea: How Australian scientists are training foxes to avoid turtle nests

Researcher Ligia Pizzatto dug a small hole in the ground on the sloping banks of Ryan’s Lagoon in southeast Australia. She carefully placed an egg inside the hollow before covering it with soil, then reached for a large spray bottle and doused the area with a fine mist. The scent of vanilla filled the air, oddly sweet against the smell of damp earth and eucalyptus trees.

While looking for another spot to repeat the process, Pizzatto came across a scattering of small bones, flat and almost geometrical in shape.

“Turtle bones,” Pizzatto said. “Probably eaten by a fox.”

These bones are a small sign of a much larger crisis. Freshwater turtle species that are native to Australia’s Murray-Darling River Basin are increasingly under threat, their populations collapsing under pressure from introduced predators. Not only do foxes kill turtles that venture onto land — typically nesting females — but they also dig up their nests to eat their eggs.

Pizzatto, a biologist at La Trobe University in Victoria, is testing an innovative approach to intervene — one that doesn’t require killing a single fox.

Freshwater turtles under threat

The Murray River is the longest in Australia; its course marks the boundary between the states of Victoria and New South Wales in the country’s southeast. This river and its basin are a major biodiversity hotspot and home to three native turtle species: the Murray short-necked turtle (Emydura macquarii), the eastern long-necked turtle (Chelodina longicollis) and the broad-shelled turtle (Chelodina expansa).

While the IUCN, the global wildlife conservation authority, doesn’t currently list these species as threatened, experts say there’s a need for updated assessments. Locally, all three are under growing threat, with surveys showing population declines of up to 91% for at least one of the turtle species since the 1970s.

Foxes are “probably the main threat to turtles” in the basin, said Mike Thompson, a leading expert in turtle biology from the University of Sydney. But they are not the only threat.

Dams, locks and barrages built to control the river have significantly altered the waterway’s natural course and seasonal flow patterns. Vast volumes of water are diverted for human use every year — around 11,800 gigaliters (more than 3 trillion gallons) — enough to fill Sydney Harbour 22 times.

Combined with climate change, these shifts have led to more frequent droughts and degraded the wetlands that turtles depend on. To counteract this, the government releases some of the diverted water back to ecosystems that need it. But this is a politically contentious issue, and environmental water is often lower priority than private and industrial interests. In April 2026, hundreds of turtles died in New South Wales when state authorities halted environmental water flows following complaints from private landowners.

Turtles are also collateral victims of the roads and waterways that now cut through their habitat: They’re run over by cars, hit by boats and caught in illegal fishing nets.

Then there are red foxes (Vulpes vulpes), which pose the leading threat. They were first introduced to Australia in 1870 by settlers keen to continue the British tradition of fox hunting and have since spread across most of the continent. Many native species never evolved defenses against them, including freshwater turtles, which makes them easy prey. Foxes are killing them faster than populations can recover.

Conservationists are protecting the region’s turtle nests in various ways, from baiting and culling foxes to physically shielding nests with fences and plastic mesh. They’re also creating artificial islands — floating platforms covered in soil and anchored to the wetland floor, where turtles can nest away from the reach of foxes.

Along with providing needed water to wetlands, these techniques form part of what Thompson describes as a “multipronged approach to reversing the decline of freshwater turtles.”

While effective, each of these methods has its drawbacks. To install mesh barriers, every nest must be located and covered. Artificial islands are costly — up to $7,000 — and may leave nests exposed to predators that can swim or fly, such as birds, aquatic reptiles and water rats.

Culling, which is typically done by shooting or baiting foxes with poisoned meat, isn’t always effective or practical. Research suggests that even when fox numbers are reduced, turtles remain at risk, as surviving foxes can adapt and may hunt even more intensively. Baiting is difficult to implement in suburban areas, where risks to people and pets are higher. And while people tend to be more accepting of culling non-native species, attitudes toward lethal control remain polarized.

Pizzatto and her team are developing a non-lethal approach to protect turtle nests from foxes using a behavioral technique called “conditioned taste aversion.” By planting decoy eggs laced with a substance that causes stomach upset, they are teaching foxes to associate turtle eggs with nausea.

From his perspective as a turtle expert, Thompson sees promise in the approach. Like some other methods, it requires considerable labor, he noted, but if it works, it would “add another tool to the toolbox,” which conservationists need.

Pizzatto hopes to develop an accessible protocol that could complement existing approaches and be easily replicated by local communities.

What it looks like in the lab

At La Trobe University’s biology lab, Pizzatto put on a white coat and a pair of latex gloves. Laid out in front of her was a carton of chicken eggs, a jar of beeswax pellets, a large bottle of vanilla extract and a set of scales.

“I always feel like I’m making a cake when I do this,” she chuckled as she opened the freezer. She took out a plastic tub filled with quail eggs, which are about  the size of turtle eggs.

“These are the aversive eggs,” she said, “the ones that make foxes feel sick.”

She had prepared them earlier, perforating their white and brown speckled shells with a drill and injecting a chemical inside — a fungicide typically used by farmers, which causes foxes to vomit if they ingest it. Then she sealed each egg with a small dot of wax to keep the chemical from spilling out.

In small doses, the fungicide induces vomiting but doesn’t really harm foxes, Pizzatto said. However, it can be toxic if they consume too much. To prevent them from overdosing, she puts only a small amount in each egg and makes sure not to plant too many laced eggs within a given radius.

On that morning, Pizzatto’s first task was to prepare a small batch of “control eggs.” Though they’re not injected with fungicide, they must be manipulated in the exact same way. Their purpose is to serve as a baseline against which to measure the foxes’ consumption of aversive eggs.

Bringing the carton of chicken eggs toward her, she carefully drilled a tiny hole into each shell and inserted an empty syringe before sealing the hole with a drop of melted wax.

Then she moved on to the next task: The vanilla extract, which she combined with glycerol for a stickier consistency, and poured the mix into a spray bottle.

After eating a few spiked eggs, foxes learn to associate all eggs with nausea. It usually keeps them away from turtle eggs, at least for a while, Pizzatto said.

The vanilla extract, which Pizzato sprays around the nests, adds another layer to the association. “The idea is that the vanilla — a new smell that doesn’t naturally occur in these habitats — reinforces their memory,” Pizzatto said. “It’s like when you feel really sick after eating something; just the smell of that food can put you off.”

Eventually, she hopes that it can be used as a sort of “sensory fence” around turtle nests, keeping foxes away from nesting areas entirely.

Having finished her lab work, she loaded the eggs, vanilla spray bottle and some gardening tools into a basket and headed out to the field.

Testing the theory

Conditioned taste aversion to protect threatened prey species isn’t a new concept, but it has had mixed results. Often, the problem has been that predators could taste or smell the chemicals, Pizzatto said, and could differentiate between treated and untreated eggs.

In 2020, researchers in Spain successfully applied this method to protect endangered European rabbits (Oryctolagus cuniculus) from red foxes on the Iberian Peninsula. The breakthrough came from using a flavorless chemical to induce vomiting, in combination with a novel smell. The Spanish Institute for Game and Wildlife Research said this triggers “a survival mechanism that many animals develop to avoid the consumption of toxic or spoiled food once they have had a first bad experience.”

When Pizzatto came across this study in the journal Animal Conservation, she contacted the lead author, Jorge Tobajas, an ecologist at the University of Cordoba in Spain. With his support, she developed her project, which she called “Once Bitten, Twice Shy.”

While taste aversion has been used in Australia before — for example, to teach Northern quolls (Asyurus hallucatus) not to eat toxic cane toads (Bufo marinus) — this is the first project in the world, Pizzatto said, that has applied this method to train foxes not to eat turtle eggs.

The initial trials have been promising. Pizzatto, working with a team of students and citizen science volunteers, prepared hundreds of decoy eggs and buried them across eight nesting sites in the Murray River basin — some of them on public land, such as Ryan’s Lagoon, and others on private property.

The experiment had three phases. First, they planted only control eggs to establish a baseline rate of how many the foxes ate. Then, in the “conditioning” phase, they introduced aversive eggs. Finally, during postconditioning, the team removed the study eggs to see how long foxes stayed away from nests.

During the conditioning phase, the team found that foxes ate about 30% fewer eggs, though, results varied significantly across sites. At one site, 90% of eggs were untouched. Researchers discovered that after being sickened by the spiked eggs, foxes also avoided turtle and chicken eggs, not just the treated quail eggs.

But the challenge is how to make the foxes’ aversion to eggs stick. In this study, foxes avoided eggs for up to seven weeks after the laced eggs were removed. But in some sites, they returned to their old habits after just two weeks. The Spanish study had much longer-lasting results: The foxes stayed away for several months.

There are a few possible reasons for this, Pizzatto said. New foxes that have not been exposed to the intervention might be moving into the area. It’s also likely that Australia’s introduced foxes have adapted over the years, becoming less risk averse than their European counterparts to survive in this environment. “It almost seems like they don’t care as much about vomiting,” Pizzatto said.

Foxes may also be able to smell the difference between real turtle eggs and the decoys. Part of the purpose of the vanilla spray is to create a “sensory barrier” that sends foxes on their way before they notice differences in the eggs’ appearance or scent. But this didn’t work as planned in the trials.

In the coming months, Pizzatto plans to try out different placements for the vanilla, spraying it more widely across the nesting area rather than concentrating it on the decoy nests — so that the smell is associated with turtle nesting areas rather than advertising the location of the decoys.

She also may test whether infusing them with turtle scent — by sprinkling them with turtle pond water or crushed turtle eggs — makes it more difficult for foxes to tell fake nests apart from the real thing.

While the project currently relies on camera traps to observe fox behavior, Pizzatto also hopes to find funding to outfit foxes with GPS collars. By tracking their movements, she could gain clues about how they react to the tampered eggs.

The objective is to make the aversion last as long as possible, while keeping the intervention simple and accessible.

Working with Traditional Owners

After a couple of hours burying eggs and collecting camera traps at Ryan’s Lagoon — a wetland reserve and one of the project’s research sites — Pizzatto packed up her things and made her way to a cabin a few hundred meters from the water’s edge, the office of the Duduroa Dhargal Aboriginal Corporation, the Indigenous organization that manages the reserve.

Allan and Valda Murray were inside. They’re co-leaders of the corporation and elders of the Duduroa People, whose ancestral lands span parts of northeastern Victoria and the upper Murray River region. They’ve been managing Ryan’s Lagoon since 2022, when the land, which was previously used for grazing and left badly degraded, was moved to their care.

During a packed lunch, they caught up on Pizzatto’s research and the Murray’s progress with land restoration. Allan unrolled a large, laminated map across the table. The wetland reserve spans approximately 160 hectares (400 acres) and connects to the Murray River. “This lagoon was pretty much empty when we started,” he said. “It was just cow paddock.”

Today, the land is teeming with life — not just turtles but also birds, frogs, snakes and mammals. The organization restored it through a combination of Indigenous practices, including controlled burning to clear out weeds and reduce wildfire risk, as well as modern techniques to deal with problems that their ancestors never faced, like introduced predators.

“Turtles are a totem species for us,” said Valda, who was wearing red turtle-shaped earrings. Totem species, she explained, are sacred for First Nations Peoples, though each group has their own.

“You don’t eat your totem. You don’t kill your totem,” she said, and you care for them. “If [a turtle is] on the side of the road or something, put it off the road, but try to keep it pointed in the same direction, because it’s going some way.”

“We’re doing what we can for the turtles,” Allan said. “Of course, our main problem is foxes digging up turtle eggs. So many of them.

When Pizzatto first approached the corporation to propose a collaboration, they were immediately enthusiastic about it. If it works, her experiment could protect the turtle population that has returned to the lagoon. In the meantime, they provide her access to a carefully managed wetland where the experiment can run undisturbed.

“It’s just a matter of working together with everyone,” Allan said. “The more you work with others, the more you can achieve.”

A recipe for anywhere

Back at the university, Pizzatto sorted through turtle specimens, frozen in labeled Ziplock bags. Most were very young. They were small enough for several to fit in the palm of her hand. They were found dead by Pizzatto, her students and volunteers during fieldwork.

The project runs in collaboration with numerous community-based organizations, including Wodonga Urban Land Care, Borinya-Wangaratta Community Partnership, Wangaratta Landcare and Sustainability and local councils. For Pizzatto, the success of the project depends on engaging local people, both for access and safety.

One of her project sites is a public park where people walk their dogs. It was important to alert the community about the experiment, since the eggs could sicken pets but also sensitize them about the importance of keeping dogs on a leash in turtle nesting areas.

“If you can’t convince the community that this is important, and get them involved in doing it, then there’s no point,” she said.

The window for protecting Australia’s native animals from introduced predators is narrowing. Foxes have already contributed to the extinction of as many as 16 mammals and remain a threat to over 70 species. If perfected, the taste aversion approach could offer a non-lethal, scalable, long-term solution, not only for turtles, but potentially for any ground-nesting species whose eggs are vulnerable to predators.

Pizzatto hopes to develop a protocol that can be shared with Traditional Owners and community conservationists, for free; hence her insistence on using easily accessible materials like chicken eggs and vanilla extract.

“It’s simple enough to replicate anywhere,” Pizzatto said. “Like a cake recipe.”

Banner image: At the La Trobe University campus, Ligia Pizzatto sorts through frozen turtle specimens she has collected over the course of her fieldwork. Most are very young, found dead by Pizzatto or her team of students and volunteers. Image by Ana Norman Bermudez.

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Chessman, B. C. (2011). Declines of freshwater turtles associated with climatic drying in Australia’s Murray–Darling Basin. Wildlife Research, 38(8), 664–671. doi:10.1071/WR11108

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