In the wilds of Western Australia’s Kimberley region, freshwater crocodiles face a lethal temptation—one that could easily wipe out entire populations. These crocs are not as dangerous to humans as their saltwater cousins, but they are vital to their ecosystem, and they have developed a taste for something deadly: cane toads. The problem? While cane toads might look like an easy snack, their skin is packed with toxins that can kill anything that dares to eat them.
This toxic attraction has led to a staggering loss of life among freshwater crocodiles. In some areas of northern Australia, up to 90% of the population has been wiped out. But now, scientists and rangers are fighting back with a clever trick that’s saving crocodiles by teaching them to avoid these toxic invaders.
A Deadly Temptation
Freshwater crocodiles are smaller and much less aggressive than the infamous saltwater crocs, but they play a crucial role in maintaining the balance of Australia’s river systems. Because they pose little threat to humans, they are highly protected. But their fondness for cane toads has become a severe problem. These invasive toads, first introduced to Australia in the 1930s, have spread rapidly across the northern regions, carrying deadly toxins in their skin.
A cane toad seems like an easy catch for the crocs, but one bite can be their last. The toxins are potent enough to kill a croc, and as the toads march further across the country, entire populations of freshwater crocodiles have been decimated. In some parts of northern Australia, crocodile numbers have dropped by as much as 70%—a devastating blow to both the ecosystem and the Indigenous communities that rely on these creatures.
A Clever Trick to Save Crocs
Faced with this crisis, scientists from Macquarie University teamed up with Bunuba Rangers and the Department of Biodiversity, Conservation and Attractions (DBCA) to develop a solution. And it’s brilliant: teach the crocs that cane toads aren’t worth the risk.
Between 2019 and 2022, the team worked in four gorges across the Kimberley region, preparing bait made from dead cane toads. The trick? They removed the toad’s deadly toxins and injected the carcasses with lithium chloride—a chemical that causes nausea but doesn’t do any permanent harm. The idea was simple: make the crocodiles associate the taste of cane toads with feeling sick, and they’ll be much less likely to eat one when they encounter the real thing.
At first, the crocs eagerly went for the toad baits, but after a few days, something amazing happened. They learned. By the fifth night, the crocodiles were avoiding the toad bait altogether, turning instead to the toxin-free chicken baits that had been set up for comparison.
A Remarkable Turnaround
The results of this taste-aversion experiment were nothing short of remarkable. In areas where the toad baits were deployed, crocodile deaths dropped dramatically. In one gorge system where cane toads had already been present for two years, the mortality rate among crocodiles fell by an incredible 95%. Meanwhile, in areas that weren’t part of the experiment, crocodile bodies continued to pile up as the cane toads made their deadly advance.
This breakthrough didn’t just save the crocodiles—it helped preserve an entire ecosystem. Freshwater crocs play a crucial role in river systems by keeping fish populations in check. Without them, bottom feeders like catfish could take over, throwing the balance of the river’s food chain completely out of whack.
For Indigenous Bunuba Rangers like Paul Bin Busu, the stakes were even higher. Crocodiles hold deep cultural significance for the Bunuba people, and their loss would have had devastating ripple effects on local traditions and wildlife. Saving these crocs meant more than just protecting a species—it meant preserving a way of life.
The Future of Croc Conservation
While this experiment has been a huge success, it’s still unclear whether the crocodiles will pass this learned behaviour on to future generations. If they don’t, researchers are ready to step in and repeat the process. And they’re not stopping there—this taste-aversion method could be used to protect other species around the world, like in Madagascar, where a similarly toxic toad is wreaking havoc on local wildlife.
For now, the crocs in the Kimberley have a fighting chance against the cane toad invasion. And as they continue to swim through the region’s gorges, their survival is a testament to the power of science, ingenuity, and a bit of good old-fashioned trickery.
