The cane toad in Australia is a text book example of a feral species. As an introduced species, it has no natural predators and out-competes native animals for food and habitat. Things are made worse by the fact that cane toads are highly poisonous - so poisonous that they can kill animals as large as crocodiles.
One species imperilled by the cane toad is the Northern Quoll. The northern quoll has been almost driven to extinction in many parts of northern Australia because they attack the toad and are subsequently poisoned. The poison kills the quolls too quickly for them to learn not to do it again.
In a recent study Conditioned taste aversion enhances the survival of an endangered predator imperilled by a toxic invader in the Journal of Applied Ecology, Stephanie O'Donnell, Jonathan Webb and Richard Shine from the University of Sydney tested whether quolls could be taught to avoid eating cane toads through "conditioned taste aversion" (CTA).
I spoke to Dr Webb about their study and how quolls can possibly be saved from extinction by CTA. To listen to this show, tune in here (or press play below):
Working with the Territory Wildlife Park, the researchers took a group of quolls and taught half (the "toad-smart" group) to associate eating a cane toad with feeling sick by feeding them a small dead cane toad laced with thiabendazole. The cane toad was too small to kill the quolls with its poison, however the tiabendazole made them feel sick. The second half of the quoll group ("toad-naive") were not fed the cane toad.
The next part of the experiment was to feed the quolls a small, live cane toad in plastic container to see whether or not they attacked it. It was found that the toad-smart group was less likely to attack the toad in the plastic container. See the video below to catch this behaviour in action. It was also found that the toad-smart group survived up to five times longer in the wild than "toad-naive" quolls. The researchers also found that male quolls were far more likely than female quolls to attack cane toads. Dr Webb thinks that aerially deployed 'toad baits' ahead of the cane toad invasion front could educate quolls to avoid attacking cane toads before the toads invade.
Cane toads were introduced to Australia from Hawaii in June 1935 to control the native Cane Beetle. They bred immediately in captivity, and by August 1935 more than 102 young toads were released in northern Queensland. Toads now number over 200 million and have steadily expanded through Queensland, reaching the border with New South Wales in 1978 and the Northern Territory in 1984. It is estimated that cane toads migrate at an average of 40 kilometres per year.
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The video below (from YouTube) shows the toad-smart quoll leaving the cane toad alone - then knocking over the camera.