29 Jul Crocs vs Cane Toads: Who’s got a stronger stomach?
By K. Sullivan, UNE Discovery
Ever since their introduction to Australia in 1935, cane toads have been a scourge on native wildlife. Not only to they eat everything in their path, but they themselves are highly toxic to any predators that might try to make a meal of them. Even freshwater crocodiles, native to northern Australia were not immune to the cane toad’s poison. In regions where cane toad populations have established themselves, researchers reported crocodile population declines of up to 70%, largely as a result of ingesting cane toads.
However, some scientists have found a way to stave off future crocodile deaths: teach them to avoid cane toads altogether. Lead by Dr Ward-Fear of Macquarie University, and aided by Bunuba Rangers and the Department of Biodiversity, Conservation and Attractions (DBCA), the research team identified an area in north Western Australia that cane toads were just beginning to invade. From 2019-2022, they then set out over 2,000 cane toad carcasses. The toxins naturally found in the cane toad’s body were replaced with lithium chloride— enough to make any hungry croc sick, but not enough to kill it. According to Paul Bin Busu, “”It was hard work, from collecting around 600-900 cane toads, cutting out the poison, to cleaning them, making sure they don’t have any poison inside their guts.” Once the traps were set, the research team monitored them closely for the next five days.
Image: A freshwater crocodile closely inspecting a baited cane toad carcass. Credit: DBCA
The crocodiles’ response was astonishing. At first, they readily helped themselves to the drugged snacks. However, by the third day the crocodiles were carefully inspecting the bait before taking it, and by the fifth day they avoided the cane toads entirely. Even more promising, as the wave of cane toads has swept over the region, the crocodile population held steady. “We saw no mortalities in those gorge systems, which was really exciting,” Dr. Ward-Fear said. Freshwater crocodiles hold great cultural and ecological significance in the Danggu and Bandilngan gorge systems, where the research was carried out, and their continued survival is a cause for great celebration.
However, these crocs aren’t out of the woods yet. It is unclear whether future generations of crocodiles will learn to avoid cane toads from their parents, and so the population must be monitored closely for signs of decline. A representative from DBCA, Sara McAllister, said that “”If we do start to see mortalities again, we can think about doing another baiting round, but we haven’t had any deaths since and that was two years ago.” So far, so good!