Cane toads, introduced to Australia from South America in the 1930s, have wreaked havoc on native wildlife. Their poisonous nature has led to the demise of countless animals, including goannas, snakes, and critically, freshwater crocodiles. Recognizing the ecological importance of these crocodiles, scientists and Indigenous rangers have devised an innovative solution to protect them.
The method involves a clever use of conditioned taste aversion. De-poisoned cane toad carcasses are injected with a chemical that makes crocodiles sick, turning the toads into a deterrent rather than a meal. These ‘baited’ toads are then strategically placed near crocodile habitats, training them to associate the taste of the toad with unpleasant consequences.
Dr. Georgia Ward-Fear from Macquarie University, the lead researcher, explains the success of this strategy: “Our baiting completely prevented deaths in areas where cane toads were arriving and decreased deaths by 95 per cent in areas where toads had been for a couple of years.”
The importance of freshwater crocodiles in maintaining a balanced ecosystem cannot be overstated. As Paul Bin Busu, a ranger coordinator, emphasizes, “Losing freshwater crocodiles to cane toads will mean that bottom feeders in our rivers will eat all the bait such as judembah (cherrabin, a large freshwater prawn) and lardy (bony bream, an estuarine fish), leaving no fish for the barramundi and stingray to eat.”
The research team, comprised of scientists from Macquarie University, Bunuba Indigenous rangers, and the Department of Biodiversity, Conservation and Attractions (DBCA) in Western Australia, conducted the trials during the dry season, when crocodiles congregate in limited water bodies, making them particularly vulnerable to the invasive toads. Over four years, they collected hundreds of cane toads, removed their poisonous parts, and injected the carcasses with the nausea-inducing chemical. These defanged toads were then strategically placed along riverbanks in the northwest Kimberley region.
The results were overwhelmingly positive. The team observed a significant reduction in crocodile mortality rates in areas where the baited toads were deployed, compared to control sites without the treatment. “These are really exciting results that provide land managers with tools to use ahead of the invasion, but that also work behind the invasion front,” says Sara McAllister from DBCA. “Together we’ve shown that collaborations between academics, Indigenous rangers and land management agencies can be really effective for science,” she adds.
Professor Rick Shine, the senior author of the study, highlights the success of conditioned taste aversion as a crucial tool in tackling invasive species. “At a time when globalisation has massively increased the spread of invasive species, behavioural ecology can protect vulnerable ecosystems,” he concludes. This research represents a significant advancement in managing invasive species and protecting biodiversity. It underscores the potential of interdisciplinary collaborations between scientists, Indigenous communities, and conservation agencies in developing practical and effective solutions for environmental challenges.
